Thermal-Power-Plant.pdf

Thermal Power Plant

In a thermal power plant, steam is produced and used to spin a turbine that operates a generator. Shown here is a diagram of a conventional thermal power plant, which uses coal, oil, or natural gas as fuel to boil water to produce the steam. The electricity generated at the plant is sent to consumers through high-voltage power lines.

1 Chimney.

2 ID Fan.

3 ESP.

4 FD Fan.

5 PA Fan.

6 SCAPH.

7 Air Pre Heater.

8 Economiser.

9 Feed Water Line.

10 Primary SH(LTSH).

11 Final SH.

12 Platent SH.

13 Extended Steam Wall.

14 Reheater.

15 Super Heated Steam.

16 Cold Reheat Line.

17 Hot Reheat Line.

18 Boiler Drum.

19 Down Commer.

20 BR Header.

21 Furnace.

22 Burner.

23 Wind Box.

24 Hot PA Header.

25 Cold PA Header.

26 Coal Mill.

27 Coal Crusher.

28 Seal Air Fan.

29 RC Burner.

30 PC Pipes.

33 IP Turbine.

34 LP Turbine.

35 Condenser.

31 Water Platent. 32 HP Turbine. 36 Ejactor.

37 Condensate Pump.

38 Gland Steam Cooler 1,2.

39 LP Heaters.

40 Deareator.

41 Boiler Feed Pump.

42 HP Heaters.

43 Makeup Pump.

44 Circulating Water Pump.

45 Water Treatement Plant.

46 Control Structure.

47 Generator.

48 Hydrogen Plant.

49 Main Transformer. 50 Aux. Transformer.

51 Air Circuit Breaker.

52 Cooling Towers.

53 CT Pump.

Steam Turbine Introduction to the Steam Turbine De Laval, Parsons and Curtis developed the concept for the steam turbine in the 1880s. Modern steam turbines use essentially the same concept but many detailed improvements have been made in the intervening years mainly to improve turbine efficiency. Steam turbines are used in all of our major coal fired power stations to drive the generators or alternators, which produce electricity. The turbines themselves are driven by steam generated in 'Boilers' or 'Steam Generators' as they are sometimes called. Energy in the steam after it leaves the boiler is converted into rotational energy as it passes through the turbine. The turbine normally consists of several stages with each stage consisting of a stationary blade (or nozzle) and a rotating blade. Stationary blades convert the potential energy of the steam (temperature and pressure) into kinetic energy (velocity) and direct the flow onto the rotating blades. The rotating blades convert the kinetic energy into forces, caused by pressure drop, which results in the rotation of the turbine shaft. The turbine shaft is connected to a generator, which produces the electrical energy. The rotational speed is 3000 rpm for Australian (50 Hz) systems and 3600 for American (60 Hz) systems.

Steam

Turbines

In a typical larger power stations, the steam turbines are split into three separate stages, the first being the High Pressure (HP), the second the Intermediate Pressure (IP) and the third the Low Pressure (LP) stage, where high, intermediate and low describe the pressure of the steam. After the steam has passed through the HP stage, it is returned to the boiler to be re-heated to its original temperature although the pressure remains greatly reduced. The reheated steam then passes through the IP stage and finally to the LP stage of the turbine. A distinction is made between "impulse" and "reaction" turbine designs based on the relative pressure drop across the stage. There are two measures for pressure drop, the pressure ratio and the percent reaction. Pressure ratio is the pressure at the stage exit divided by the pressure at the stage entrance. Reaction is the percentage isentropic enthalpy drop across the rotating blade or bucket compared to the total stage enthalpy drop. Some manufacturers utilise percent pressure drop across stage to define reaction. Steam turbines can be configured in many different ways. Several IP or LP stages can be incorporated into the one steam turbine. A single shaft or several shafts coupled together may be used. Either way, the principles are the same for all steam turbines. The configuration is decided by the use to which the steam turbine is put, co-generation or pure electricity production. For co-generation, the steam pressure is highest when used as process steam and at a lower pressure when used for the secondary function of electricity production. A typical power station steam turbine and its View of the internals of a typical power station steam turbine.

Nozzles

and

external

equipment;

and

Blades

Steam enthalpy is converted into rotational energy as it passes through a turbine stage. A turbine stage consists of a stationary blade (or nozzle) and a rotating blade (or bucket). Stationary blades convert the potential energy of the steam (temperature and pressure) into kinetic energy (velocity) and direct the flow onto the rotating blades. The rotating blades convert

the kinetic energy into impulse and reaction forces caused by pressure drop, which results in the rotation of the turbine shaft or rotor. Steam turbines are machines which must be designed, manufactured and maintained to high tolerances so that the design power output and availability is obtained. They are subject to a number of damage mechanisms, with two of the most important being: Erosion due to moisture. The presence of water droplets in the last stages of a turbine causes erosion to the blades. This has led to the imposition of an allowable limit of about 12% wetness in the exhaust steam; and Solid particle erosion. The entrainment of erosive materials from the boiler in the steam causes wear to the turbine blades. Cogeneration cycles In cogeneration cycles, steam is typically generated at a higher temperature and pressure than required for a particular industrial process. The steam is expanded through a turbine to produce electricity and the resulting extractions at the discharge are at the temperature and pressure required by the process. Turbines can be condensing or non-condensing design typically with large mass flows and comparably low output. Traditionally, pressures were 6.21 MPa and below with temperatures 441º C or lower, although the trend towards higher levels of each continues. There are now a considerable number of co-generation steam turbines with initial steam pressures in the 8.63 to 10 MPa range and steam temperatures of 482 to 510º C.

Bearings

and

Two types of bearings are used to support and locate the rotors of steam turbines:

Lubrication

Journal bearings are used to support the weight of the turbine rotors. A journal bearing consists of two half-cylinders that enclose the shaft and are internally lined with Babbitt, a metal alloy usually consisting of tin, copper and antimony; and Thrust bearings axially locate the turbine rotors. A thrust bearing is made up of a series of Babbitt lined pads that run against a locating disk attached to the turbine rotor. High-pressure oil is injected into the bearings to provide lubrication. The oil is carefully filtered to remove solid particles. Specially designed centrifuges remove any water from the oil. Shaft

Seals

The shaft seal on a turbine rotor consist of a series of ridges and groves around the rotor and its housing which present a long, tortuous path for any steam leaking through the seal. The seal therefore does not prevent the steam from leaking, merely reduces the leakage to a minimum. The leaking steam is collected and returned to a low-pressure part of the steam circuit. Turning

gear

Large steam turbines are equipped with "turning gear" to slowly rotate the turbines after they have been shut down and while they are cooling. This evens out the temperature distribution around the turbines and prevents bowing of the rotors. Vibration The balancing of the large rotating steam turbines is a critical component in ensuring the reliable operation of the plant. Most large steam turbines have sensors installed to measure the movement of the shafts in their bearings. This condition monitoring can identify many potential problems and allows the repair of the turbine to be planned before the problems become serious. Reference Web site Back

:

http://www.energy.qld.gov.au/electricity/infosite/index.htm

Transformers

Introduction For transmission and distribution networks to transfer large amounts of alternating current electricity over long distances with minimum losses and least cost, different voltage levels are required in the various parts of the networks. For example, the transfer of electricity efficiently over a long transmission line requires the use of high voltages. At the receiving end where the electricity is used, the high voltage has to be reduced to the levels required by the consumer. Transformers enable these changes in voltage to be carried out easily, cheaply and efficiently. A transformer used to increase the voltage is called a "step up" transformer, while that used to decrease the voltage is called a "step down" transformer. Theory

of

the

Transformer

The operation of a transformer is based on two principles: 1. A voltage is induced in a conductor when the conductor passes through a magnetic field. The same effect is produced if the conductor is stationary but the magnetic field in which it is located varies; and 2. A current passing through a conductor will develop a magnetic field around the conductor. Note: In this discussion on transformers, the term magnetic "flux" will usually be used instead of magnetic "field". A magnetic field is the space or region surrounding a magnet or a current carrying conductor, in which magnetic effects can be detected. The strength of the magnetic field is generally expressed in terms of magnetic flux density (magnetic flux per square meter). Magnetic flux refers to the magnetic lines of force.

A transformer consists of two coils electrically separate but linked by a common magnetic circuit of low reluctance formed by a laminated soft iron core. If one coil (the primary coil) is connected to an AC supply, an alternating magnetic flux is set up in the iron core. This alternating magnetic flux passes through the secondary coil and induces and alternating voltage in the secondary coil. The magnitude of the secondary voltage is directly proportional to the ratio of the number of turns in the secondary and primary windings and to the primary voltage.

Construction

of

a

Large

Transformer

The iron core, which forms a complete magnetic circuit, is made up of laminated strips of special steel having low hysteresis loss and high electrical resistivity. The lamination of the core reduces the eddy-current loss. For the average transformer used in a power station, the conductor used for the windings consists of paper insulated copper bar or wire. In assembling the transformer, great care is taken to ensure windings are well insulated both from the iron core and from each other. The basic construction of a core type transformer consist of the iron core, then a cylinder of insulation, followed by the low voltage winding, then a further insulating cylinder and then the high voltage winding. Clamps are used to hold the assembly in place. These basic components are shown on the attached diagram and are also shown in the attached part cross-section of a very large transformer. The assembled transformer has its winding and iron core assembly usually contained in a tank and immersed in transformer oil. The oil is used for further insulating purposes plus the removal of heat from the windings. The assembly of the windings on the core allows gaps to enhance the oil circulation around the windings. The tank is constructed with fins or tubes to allow better circulation of the oil and to provide a greater surface area for contact with the cooling air. Very large transformers have banks of fans to provide greater air-cooling and are operated in conjunction with temperature sensors. Some transformers also have forced oil circulation using a pumping system and an oil cooling circuit. In installations where the use of transformer oil needs to be avoided, the cooling medium used can be gas (nitrogen is often used). Small transformers are often solely air-cooled. Large transformers that are of open construction so that cooling is provided by direct contact with the surrounding air are being developed for indoor use.

Most distribution type transformers have a tap changer, which is a selector switch that allows the voltage ratio of the transformer to be changed by increasing or decreasing the turns of the winding. The different coils of the transformer winding are brought out and connected to the selector switch to allow the additional turns to be brought into or taken out of circuit. In some distribution transformers, the tap changer switch is an off load manual switch, while in others, the tap changer is an on-load automatic switch. In a generator transformer, the tap changer is a very sophisticated device that is automatically operated on load by the system control. Devices on a transformer normally protect against overload, earth fault, pressure and temperature. For these protection systems, current and voltage transformers are built into the transformers. In large transformers, current transformers are provided in conjunction with the insulated terminals. Testing Manufacture To ensure that the manufacturing process is proceeding as per the design program, a number of tests will be required. The most important of these are: 1. Core plate checks - Incoming core plate is checked for thickness and quality of insulation covering; 2. Core frame insulation resistance - This is checked by megger and by application of a 2 kV RMS or 3 kV DC test voltage on completion or erection of the core and again following replacement of the top yoke after fitting of the windings; 3. Core loss measurement - This is carried out by application of a few temporary turns of cable before the windings are fitted and the core excited to normal flux density; and 4. Tank tests - The first tank of any new design is checked for stiffness and vacuum withstand capability. Tanks are also checked for leak tightness by filling with a fluid of lower viscosity than transformer oil and pressurising for a period of time. Prior to final testing, the assembled core and windings are heated to between 850°C and 1200°C for a length of time. The time taken can be as long as weeks for very large transformers or a few days for medium sized transformers. The transformer windings will be considered dry when plotted values of power factor drop to a minimum value and the insulation resistance increases rapidly. It is then best to immerse the transformer winding in the transformer oil while the windings are hot because they tend to absorb the oil. Before the final tests are carried out the transformer, is left to stand for several days to let any remaining air bubbles become absorbed by the oil. Final

Testing

The final works test on a transformer fall into three categories: Tests to prove that the transformer has been built correctly - These include ratio; polarity; resistance and tap change operation tests; Tests to prove guarantees - These are losses; impedance; temperature rise and noise levels tests; and Tests to prove that the transformer will be satisfactory in service for at least thirty years - The test in this category include dielectric or overload and load current runs. For the first transformer of a new design, impulse tests including chopped waves to simulate lightning strikes and withstand capability are usually required. Transformer

Losses

Losses in a transformer are known as 'Iron losses' and Copper Losses'. Iron

Losses

Iron losses are due to hysteresis and eddy-current loss produced by the alternating magnetic flux in the iron core. The iron losses are almost independent of the load and thus are considered to be constant at all loads. In order to determine the iron loss, one winding of the transformer (whichever is the most convenient) is open circuited. A voltage is applied to the other winding and the power (watts) in this circuit is measured. This power represents the iron losses. Copper losses under these circumstances are negligible.

Copper

Losses

Copper losses are the heat losses in the windings due to the electrical resistance of the windings. The copper losses are proportional to the square of the current and therefore to the kVA output. These losses can be calculated from the design data but can also be measured by a test. This test is known as the short circuit test for copper losses. The short circuit test is carried out by short circuiting one winding, thus causing the transformer to behave like a coil having a leakage impedance equal to that of both windings. A low voltage is applied to the open winding sufficient to circulate full load current through the open winding due to transformer action in the short-circuited winding. Under these conditions, the flux set up in the core is so small that iron losses can usually be neglected and the wattmeter would give the total copper loss.

Maintenance Large transformers are usually very reliable and efficient. To ensure their continued reliable and efficient operation, the maintenance of the average oil filled type transformer requires a check on the following: 1. Oil quality; 2. The condition of the tank in regard to leaks and cleanliness; 3. A check on the insulating terminals for condition of insulation (breaks or cracks and cleanliness) and oil leaks; 4. Condition of the pressure and temperature elements, and indicators; 5. A check on the connections and the current and voltage transformers where fitted; 6. A check on the breather and the condition of its silica gel; 7. A check on the tap changer; 8. A check on the explosion vent (if fitted); 9. A check on the condition of the connecting cables and connections in the terminal boxes; and 10.

A

check

on

the

insulation

of

the

transformer

windings.

If considered necessary, the internals may have to be removed from the tank and a check made on the condition of the windings and their bracing. This is usually only necessary if the transformer has been subjected to unusual circumstances, such as an external fault, or if the transformer has registered high temperatures or excessive noise. If the oil does not meet its quality standards, it will have to be changed or filtered. Maintenance procedures may require the oil to be filtered on a regular basis.

Reference Web

site

:

http://www.energy.qld.gov.au/electricity/infosite/index.htm

Back

Power

Grids

Electrical power is a little bit like the air you breathe: You don't really think about it until it is missing. Power is just "there," meeting your every need, constantly. It is only during a power failure, when you walk into a dark room and instinctively hit the useless light switch, that you realize how important power is in your daily life. You use it for heating, cooling, cooking, refrigeration, light, sound, computation, entertainment... Without it, life can get somewhat cumbersome. Power travels from the power plant to your house through an amazing system called the power distribution grid

The grid is quite public -- if you live in a suburban or rural area, chances are it is right out in the open for all to see. It is so public, in fact, that you probably don't even notice it anymore. Your brain likely ignores all of the power lines because it has seen them so often. We will look at all of the equipment that brings electrical power to your home. The next time you look at the power grid, you will be able to really see it and understand what is going on! Power

Plant

Electrical power starts at the power plant. In almost all cases, the power plant consists of a spinning electrical generator. Something has to spin that generator -- it might be a water wheel in a hydroelectric dam, a large diesel engine or a gas turbine. But in most cases, the thing spinning the generator is a steam turbine. The steam might be created by burning coal, oil or natural gas. No matter what it is that spins the generator, commercial electrical generators of any size generate what is called 3-phase AC power. To understand 3-phase AC power, it is helpful to understand single-phase power first. Single-phase power is what you have in your house. You generally talk about household electrical service as single-phase, 120-volt AC service. If you use an oscilloscope and look at the power found at a normal wall-plate outlet in your house, what you will find is that the power at the wall plate looks like a sine wave, and that wave oscillates between -170 volts and 170 volts (the peaks are indeed at 170 volts; it is the effective (rms) voltage that is 120 volts). The rate of oscillation for the sine wave is 60 cycles per second. Oscillating power like this is generally referred to as AC, or alternating current. The alternative to AC is DC, or direct current. Batteries produce DC: A steady stream of electrons flows in one direction only, from the negative to the positive terminal of the battery. AC has at least three advantages over DC in a power distribution grid: Large electrical generators happen to generate AC naturally, so conversion to DC would involve an extra step. Transformers must have alternating current to operate, and we will see that the power distribution grid depends on transformers.

It is easy to convert AC to DC but expensive to convert DC to AC, so if you were going to pick one or the other AC would be the better choice. The power plant, therefore, produces AC. However, it produces three different phases of power simultaneously, and the three phases are offset 120 degrees from each other. There are four wires coming out of every power plant: the three phases plus a neutral or ground common to all three. If you were to look at the three phases on a graph, they would look like this relative to ground: There is nothing magical about 3-phase power. It is simply three single phases synchronized and offset by 120 degrees. Why three phases? Why not one or two or four? In 1-phase and 2-phase power, there are 120 moments per second when a sine wave is crossing zero volts. In 3-phase power, at any given moment one of the three phases is nearing a peak. High-power 3-phase motors (used in industrial applications) and things like 3-phase welding equipment therefore have even power output. Four phases would not significantly improve things but would add a fourth wire, so 3phase is the natural settling point. And what about this "ground," as mentioned above? The power company essentially uses the earth as one of the wires in the power system. The earth is a pretty good conductor and it is huge, so it makes a good return path for electrons. (Car manufacturers do something similar; they use the metal body of the car as one of the wires in the car's electrical system and attach the negative pole of the battery to the car's body.) "Ground" in the power distribution grid is literally "the ground" that's all around you when you are walking outside. It is the dirt, rocks, groundwater, etc., of the earth. The 3-phase power leaves the generator and enters a transmission substation at the power plant. This substation uses large transformers to convert the generator's voltage (which is at the thousands of volts level) up to extremely high voltages for long-distance transmission on the transmission grid.

You can see at the back several three-wire towers leaving the substation. Typical voltages for long distance transmission are in the range of 155,000 to 765,000 volts in order to reduce line losses. A typical maximum transmission distance is about 300 miles (483 km). High-voltage transmission lines are quite obvious when you see them. They are normally made of huge steel towers like this:

All power towers like this have three wires for the three phases. Many towers, like the ones shown above, have extra wires running along the tops of the towers. These are ground wires and are there primarily in an attempt to attract lightning. The Distribution Grid For power to be useful in a home or business, it comes off the transmission grid and is steppeddown to the distribution grid. This may happen in several phases. The place where the conversion from "transmission" to "distribution" occurs is in a power substation. A power substation typically does two or three things: 1. It has transformers that step transmission voltages (in the tens or hundreds of thousands of volts range) down to distribution voltages (typically less than 10,000 volts). 2. It has a "bus" that can split the distribution power off in multiple directions. 3. It often has circuit breakers and switches so that the substation can be disconnected from the transmission grid or separate distribution lines can be disconnected from the substation when necessary.

A typical small substation

The transmission lines entering the substation and passing through the switch tower

The switch tower and the main transformer Now

the

distribution

bus

comes

Distribution

into

the

picture. Bus

The power goes from the transformer to the distribution bus:

this case, the bus distributes power to two separate sets of distribution lines at two different voltages. The smaller transformers attached to the bus are stepping the power down to standard line voltage (usually 7,200 volts) for one set of lines, while power leaves in the other

direction at the higher voltage of the main transformer. The power leaves this substation in two sets of three wires, each headed down the road in a different direction

The next time you are driving down the road, you can look at the power lines in a completely different light. In the typical scene pictured on the right, the three wires at the top of the poles are the three wires for the 3-phase power. The fourth wire lower on the poles is the ground wire. In some cases there will be additional wires, typically phone or cable TV lines riding on the same poles. As mentioned above, this particular substation produces two different voltages. The wires at the higher voltage need to be stepped down again, which will often happen at another substation or in small transformers somewhere down the line. For example, you will often see a large green box (perhaps 6 feet/1.8 meters on a side) near the entrance to a subdivision. It is performing the step-down function for the subdivision. Regulator

Bank

You will also find regulator banks located along the line, either underground or in the air. They regulate the voltage on the line to prevent undervoltage and overvoltage conditions.

A typical regulator bank Up toward the top are three switches that allow this regulator bank to be disconnected for maintenance when necessary:

At this point, we have typical line voltage at something like 7,200 volts running through the neighborhood on three wires (with a fourth ground wire lower on the pole):

Taps A house needs only one of the three phases, so typically you will see three wires running down a main road, and taps for one or two of the phases running off on side streets. Pictured below is a 3-phase to 2-phase tap, with the two phases running off to the right:

Here is a 2-phase to 1-phase tap, with the single phase running out to the right:

At

the

House

And finally we are down to the wire that brings power to your house! Past a typical house runs a set of poles with one phase of power (at 7,200 volts) and a ground wire (although sometimes there will be two or three phases on the pole, depending on where the house is located in the distribution grid). At each house, there is a transformer drum attached to the pole, like this:

In many suburban neighborhoods, the distribution lines are underground and there are green transformer boxes at every house or two. Here is some detail on what is going on at the pole:

The transformer's job is to reduce the 7,200 volts down to the 240 volts that makes up normal household electrical service. Let's look at this pole one more time, from the bottom, to see what is going on:

There are two things to notice in this picture: 1. There is a bare wire running down the pole. This is a grounding wire. Every utility pole on the planet has one. If you ever watch the power company install a new pole, you will see that the end of that bare wire is stapled in a coil to the base of the pole and therefore is in direct contact with the earth, running 6 to 10 feet (1.8 to 3 m) underground. It is a good, solid ground connection. If you examine a pole carefully, you will see that the ground wire running between poles (and often the guy wires) are attached to this direct connection to ground. 2. There are two wires running out of the transformer and three wires running to the house. The two from the transformer are insulated, and the third one is bare. The bare wire is the ground wire. The two insulated wires each carry 120 volts, but they are 180 degrees out of phase so the difference between them is 240 volts. This arrangement allows a homeowner to use both 120-volt and 240-volt appliances. The transformer is wired in this sort of configuration:

The 240 volts enters your house through a typical watt-hour meter like this one:

The meter lets the power company charge you for putting up all of these wires. Fuses

and

Circuit

Breakers

Fuses and circuit breakers are safety devices. Let's say that you did not have fuses or circuit breakers in your house and something "went wrong." What could possibly go wrong? Here are some examples: 1. A fan motor burns out a bearing, seizes, overheats and melts, causing a direct connection between power and ground. 2.

A

wire

comes

loose

in

a

lamp

and

directly

connects

power

to

ground.

3. A mouse chews through the insulation in a wire and directly connects power to ground. 4. Someone accidentally vacuums up a lamp wire with the vacuum cleaner, cutting it in the process and directly connecting power to ground. 5. A person is hanging a picture in the living room and the nail used for said picture happens to puncture a power line in the wall, directly connecting power to ground.

When a 120-volt power line connects directly to ground, its goal in life is to pump as much electricity as possible through the connection. Either the device or the wire in the wall will burst into flames in such a situation. (The wire in the wall will get hot like the element in an electric oven gets hot, which is to say very hot!). A fuse is a simple device designed to overheat and burn out extremely rapidly in such a situation. In a fuse, a thin piece of foil or wire quickly vaporizes when an overload of current runs through it. This kills the power to the wire immediately, protecting it from overheating. Fuses must be replaced each time they burn out. A circuit breaker uses the heat from an overload to trip a switch, and circuit breakers are therefore resettable.

The power then enters the home through a typical circuit breaker panel like the one above. Inside the circuit breaker panel you can see the two primary wires from the transformer entering the main circuit breaker at the top. The main breaker lets you cut power to the entire panel when necessary. Within this overall setup, all of the wires for the different outlets and lights in the house each have a separate circuit breaker or fuse:

If the circuit breaker is on, then power flows through the wire in the wall and makes its way eventually to its final destination, the outlet.

What an unbelievable story! It took all of that equipment to get power from the power plant to the light in your bedroom. The next time you drive down the road and look at the power lines, or the next time you flip on a light, you'll hopefully have a much better understanding of what is going on. The power distribution grid is truly an incredible system. Reference Web http://people.howstuffworks.com

site

:

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Power Stations Power

Stations

This section provides a brief description of the major types of power stations and their suitability for particular operational duties. Where possible, examples of actual power stations. 1. Steam Turbine 2. Hydro Electric 3. Tidal Fuel Cells 4. MHD 5. Open Cycle Gas Turbines 6. Pumped Storage Wave 7. Photovoltaic 8. Nuclear 9. Combined Cycle Gas 10. Reciprocating 11. Wind 12. Solar Thermal 13. Combinations Power

Station

Turbines

Operations

Modern coal fired power stations with generating units of approximately 200 MW or over, are generally used to generate continuous power for up to 24 hours a day. The abundance of cheap fuel makes these units the most economical generators to run, but due to their inability to change their output quickly, and follow demand, they are not suitable for use as a provider of 'peak demand' power. This is known as providing 'Base Load' power. Smaller coal fired units are more likely to provide intermediate power, or power to 'top up' the base load providers to meet normal variations in daily power demand. These are normally run

as a 2-shift station (2 x 8-hour shifts) which runs at high load during the morning and evening peak demand periods. At times of very high or very low temperatures, demand for heating or air conditioning power becomes higher than normal. This presents an opportunity for the 'peaking' units to come 'online'. These units, usually gas or oil fired turbines, can respond rapidly to changes in demand. The cost of running these units is much higher than for the coal fired units, and so they are only used when absolutely necessary, and when the spot price of electricity is high enough for them to be run at a profit. In the past, a conventional cycling unit (either an oil or a natural gas fired peaking unit) was described as one designed for rapid rates of load increase and a significantly large number of start-up and shutdown cycles compared to base load operation. There is a growing number of small 'renewable energy' stations, fuelled by the wind, sun, landfill gas, bagasse, water, tide and waves. The power generated by these stations is generally used to supply energy to local users, or connected to the grid as 'green power'.

Steam turbine Steam turbine Steam turbine Steam turbine Hydro-electricity

using

using gas using using

coal as or oil as biomass as geothermal

fuel fuel fuel energy

Thermal-Electric Power Plants in India (100 MW and Greater ) Location Power Plant

Owner

Fuel

Total Capacity (MW)

City

State

Maharashtra SEB

Durgapur

Maharashtra

Coal

2,340

Neyveli Lignite Corp. Ltd.

Neyveli

Tamil Nadu

Coal

2,280

Conventional Thermal Power Plants Chandrapur Neyveli Vindhyachal

NTPC

Sidhi

Madhya Pradesh

Coal

2,260

Korba STPS

NTPC

Bilaspur

Chattisgarh

Coal

2,100

Ramagundam

NTPC

Karimnagar Dist.

Andhra Pradesh

Coal

2,100

Singrauli

NTPC

Sonebhadra Dist.

Uttar Pradesh

Coal

2,050

Talcher

NTPC

Angul

Orissa

Coal

1,970

Anpara

UPRVUNL

Mirzapur Dist.

Uttar Pradesh

Coal

1,630

Farakka

NTPC

Murshidabad

West Bengal

Coal

1,630

UPRVUNL

Obra Dist.

Uttar Pradesh

Coal

1,550

Obra Tuticorin

Tamil Nadu SEB

Tuticorin

Tamil Nadu

Coal

1,550

Raichur

KPCL

Raichur Dist.

Karnataka

Coal

1,470

Wanakbori

Gujarat SEB

Sevalia

Gujarat

Coal

1,470

West Bengal Power Development Corp.

Medinipurt Dist.

West Bengal

Coal

1,260

Punjab SEB

Ropar

Punjab

Coal

1,260

Vijayawada

Andhra Pradesh Power Generation Corp.

Krishna

Andhra Pradesh

Coal

1,260

Kothagudem

Andhra Pradesh Power Generation Corp.

Paloncha

Andhra Pradesh

Coal

1,180

Tata Power Co. Ltd.

Mumbai

Maharashtra

Coal; Natural Gas

1,150

Kolaghat Ropar

Trombay (coal-fired section) Satpura

Madhya Pradesh SEB

Betual Dist.

Madhya Pradesh

Coal

1,143

Koradi

Maharashtra SEB

Koradi

Maharashtra

Coal

1,100

Rihand

NTPC

Sonebhadra Dist.

Uttar Pradesh

Coal

1,000

Simhadri

NTPC

Paravade

Andhra Pradesh

Coal

1,000

Suratgarh

Rajasthan RV Utpadan Nigam

Suratgarh

Rajasthan

Coal

1,000

Maharashtra SEB

Nasik

Maharashtra

Coal

910

Gujarat SEB

Gandhi Nagar

Gujarat

Coal

870

Punjab SEB

Bhatinda

Punjab

Coal

860

Haryana Power Generation Corp. Ltd.

Panipat

Haryana

Coal

860

Nasik Gandhi Nagar Guru Hargobind Tau Devi Lal Kota

Rajasthan RV Utpadan Nigam

Kota

Rajasthan

Coal

850

Ukai

Gujarat SEB

Ukai Dam

Gujarat

Coal

850

NTPC

Dadri

Uttar Pradesh

Coal

840

Dadri (coal-fired section) Kahalgaon

NTPC

Kahalgaon

Bihar

Coal

840

Khaperkheda

Maharashtra SEB

Khaperkheda

Maharashtra

Coal

840

Korba West

Chattisgarh SEB

Bilaspur

Chattisgarh

Coal

840

Mettur

Tamil Nadu SEB

Mettur

Tamil Nadu

Coal

840

Sanjay Gandhi

Madhya Pradesh SEB

Umaria Dist.

Madhya Pradesh

Coal

840

Unchahar

NTPC

Rai Bareilli

Uttar Pradesh

Coal

840

Bokaro

DVC

Bokaro

Jharkhand

Coal

805

Patratu

Jharkhand SEB

Patratu

Jharkhand

Coal

770

Chandrapura

DVC

Chandrapura

Jharkhand

Coal

750

Angul Smelter

National Aluminum Corp. Ltd.

Angul

Orissa

Coal

720

NTPC

New Delhi

Delhi Territory

Coal

720

Badarpur Parli Bakreshwar Mejia North Chennai Renusagar * Dhuvaran

Maharashtra SEB

Parli Vaijnath

Maharashtra

Coal

690

West Bengal Power Development Corp.

Birbhum Dist.

West Bengal

Coal

630

DVC

Durlavpur

West Bengal

Coal

630

Tamil Nadu SEB

Chennai

Tamil Nadu

Coal

630

Hindalco Industries Ltd.

Renukoot

Uttar Pradesh

Coal

619

Gujarat SEB

Anand

Gujarat

Coal

534

Bandel

West Bengal SEB

Hooghly

West Bengal

Coal

530

Budge Budge

CESC Ltd.

Calcutta

West Bengal

Coal

500

Dahanu

BSES Ltd.

Thane Dist.

Maharashtra

Coal

500

Bhusawal

Maharashtra SEB

Jalgaon

Maharashtra

Coal

483

Santaldih

West Bengal SEB

Santaldih

West Bengal

Coal

480

Ennore

Tamil Nadu SEB

Ennore

Tamil Nadu

Coal

450

Sabarmati Harduaganj Tanda

Ahmedabad Electric Co. Ltd.

Sabarmati

Gujarat

Coal

450

UPRVUNL

Harduaganj

Uttar Pradesh

Coal

440

NTPC

Faizabad

Uttar Pradesh

Coal

440

OPGC; AES

Barhanpalli

Orissa

Coal

420

Andhra Pradesh Power Generation Corp.

Cuddapah Dist.

Andhra Prdesh

Coal

420

Tenughat

Jharkhand SEB

Bokaro Dist.

Jharkhand

Coal

420

Durgapur

West Bengal SEB

Burdwan

West Bengal

Coal

405

Korba East

Chattisgarh SEB

Bilaspur

Chattisgarh

Coal

400

DVC

Waria

West Bengal

Coal

350

Ib Valley Rayalaseema

Durgapur DVC Barauni Amarkantak Bokaro Works * Panki NTPC BALCO Rourkela Works *

Bihar SEB

Hazaribagh Dist.

Bihar

Coal

310

Madhya Pradesh SEB

Shahdal

Madhya Pradesh

Coal

300

Steel Authority of India Ltd.

Bokaro

Jharkhand

Coal

287

UPRVUNL

Panki

Uttar Pradesh

Coal

279

NTPC

Korba

Madhya Pradesh

Coal

270

Steel Authority of India Ltd.

Rourkela

Orissa

Coal

269 260

Torangallu Works *

Jindal Tractebel Power Co. Ltd.

Torangallu

Karnataka

Blast Furnace Gas; Coal

Neyveli Zero

CMS India Ltd.

Neyveli

Tamil Nadu

Coal

250

Gujarat Industrial Power Corp. Ltd. (GIPCL)

Surat

Gujarat

Coal

250

Indraprastha

Indraprastha Power Generating Co. Ltd.

New Delhi

Delhi Territory

Coal

248

Bongaigaon

Assam SEB

Salakati Dist.

Assam

Coal

240

Sikka

Gujarat SEB

Sikka

Gujarat

Coal

240

CESC Ltd.

Titagarh

West Bengal

Coal

240

Surat

Titagarh Jamshedpur Works *

Tata Iron & Steel Co.

Jamshedpur

Bihar

Coal

238

Vizag Steel Works *

Rashtriya Ispat Nigam Ltd.

Visakhapatnam

Andhra Pradesh

Coal

236

CESC Ltd.

Calcutta

West Bengal

Coal

225

Cossipore Muzaffarpur

Bihar SEB

Kanti

Bihar

Coal

220

Paricha

UPRVUNL

Jhansi

Uttar Pradesh

Coal

220

Kutch Faridabad Mulajore Durgapur Works * Rajghat Southern Raigarh Works * Choudwar

Gujarat SEB

Kutch

Gujarat

Coal

210

Faradibad Power Systems Ltd.

Faridabad

Haryana

Coal

165

CESC Ltd.

Shyamnagar

West Bengal

Coal

150

Steel Authority of India Ltd.

Durgapur

West Bengal

Coal

140

Delhi Transco Ltd.

New Delhi

Delhi Territory

Coal

135

CESC Ltd.

Calcutta

West Bengal

Coal

135

Jindal Steel & Power Ltd.

Raigarh

Madhya Pradesh

Coal

112

Indian Charge Chrome Ltd. (ICCL)

Choudwar

Orissa

Coal

108

Nagda Works *

Melodeon Exports

Nagda

Madhya Pradesh

Coal

106

CMS India Ltd.

Chennai

Tamil Nadu

Oil

200

Scintilla Power Co.

Bangalore

Karnataka

Oil

158

Diesel Engine Power Plants Chennai Vasavi Whitefield Ind. Park Yelahanka

Karnataka SEB

Bangalore

Karnataka

Oil

132

Kozhikode

Kerala SEB

Kozhikode

Kerala

Oil

128

Brahmapuram

Kerala SEB

Kochi

Kerala

Oil

110

Samayanallur

Balaji Power Corp. Ltd.

Samayanallur

Tamil Nadu

Oil

106

Samalpatti

Samalpatti Power Corp.

Samilpatti

Tamil Nadu

Oil

105

Gas Turbine Combined Cycle Power Plants Uran Dahbol Dadri (gas-fired section) Kawas Paguthan

Maharashtra SEB

Ransai Dam

Maharashtra

Natural Gas

912

Dahbol Power Co. Ltd.

Ratanagiri Dist.

Maharashtra

Naphtha

826

NTPC

Dadri

Uttar Pradesh

Natural Gas

817

NTPC

Surat

Gujarat

Naphtha

656

Gujarat Pagathuan Energy Corp.

Paguthan

Gujurat

Natural Gas

655

Auriaya

NTPC

Etawah

Uttar Pradesh

Natural Gas

652

Gandhar

NTPC

Bharuch

Gujarat

Natural Gas

618

Essar Power Ltd.

Hazira

Gujarat

Natural Gas

516

Faridabad NTPC

NTPC

Faridabad

Haryana

Natural Gas

430

Anta

NTPC

Baran

Rajasthan

Natural Gas

413

LANCO Kondapalli Power Private Ltd.

Kondapalli

Andhra Pradesh

Natural Gas

368

NTPC

Aleppey Dist.

Kerala

Natural Gas

349

PPN Power Generating Co.

Pillaiperumalnallur

Tamil Nadu

Natural Gas; Naphtha

330

Pragati Power Corp. Ltd.

New Delhi

Delhi Territory

Natural Gas

330

NEEPCO

Dibrugarh Dist.

Assam

Natural Gas

291

Indraprastha Power Generation Co. Ltd.

New Delhi

Delhi Territory

Natural Gas

282

Andhra Pradesh Gas Power Corp. Ltd.

Vijjeswaran

Andhra Pradesh

Natural Gas

272

BSES Ltd.

Peddapuram

Andhra Pradesh

Naphtha

220

Spectrum Power Generation Ltd.

Kakinda

Andhra Pradesh

Natural Gas

210

Hazira Essar

Kondapalli Kayamkulam Pillaiperumalnallur Pragati Kathalguri Indraprastha GT Vijjeswaran Peddapuram Godavari Tanir Bavi Barge

Tanir Bavi Power Co. Pvt. Ltd.

Mangalore

Karnataka

Oil

208

Jegurupadu

GVK Industries Ltd.

Jegurupadu

Andhra Pradesh

Natural Gas

205

Trombay (gas-fired section)

Tata Power Co. Ltd.

Mumbai

Maharashtra

Natural Gas

180

Kochi-Kerala

BSES Ltd.

Kochi

Kerala

Naphtha

173

Hazira GSEG

Gujarat State Energy Generation Ltd. (GSEG)

Surat Dist.

Gujarat

Natural Gas

159

Baroda GIPCL

Gujarat Industrial Power Corp. Ltd. (GIPCL)

Baroda

Gujarat

Natural Gas

108

Utran

Gujarat SEB

Utran

Gujarat

Natural Gas

135

Lakwa

Assam SEB

Lakwa

Assam

Natural Gas

120

Kovilkalappal

Tamil Nadu SEB

NagaiquaidE. Milloth Dist.

Tamil Nadu

Oil

108

Perungulam

Tamil Nadu SEB

Perungulam

Tamil Nadu

Natural Gas

105

Vatwa

Ahmenabad Electric Co. Ltd.

Vatwa

Gujarat

Natural Gas

100

Conventional Gas Turbine Power Plants Baroda GIPCL *

Gujarat Industrial Power Corp. Ltd. (GIPCL)

Baroda

Gujarat

Natural Gas

216

Pampore

Jammu & Kashmir SEB

Pampore

Jammu & Kashmir

Oil

175

Hazira RIL *

Reliance Industries Ltd.

Hazira

Gujarat

Natural Gas

165

South Bassein

ONGC

Bassein

Maharashtra

Oil

152

Jamnagar RIL *

Reliance Industries Ltd.

Jamnagar

Gujarat

Naphtha

132

GMR Group

Chennai

Tamil Nadu

Naphtha

124

Haldia Petrochemicals Ltd.

Haldia

West Bengal

Natural Gas

104

Indian Farmers Fertilizer Cooperative

Anola

Uttar Pradesh

Natural Gas

100

City

State

Basin Bridge Haldia Chemicals * Anola

Power Plant

Owner

Fuel

Location

India's Hydroelectric Power Plants (100 MW and Greater) Location Power Plant Koyna I-IV

Owner Maharashtra SEB

River(s)

State

Total Capacity (MW)

Koyna

Maharashtra

1,920

Sharavathi

KPCL

Sharavathi

Karnataka

1,035

Dehar

BBMB

Beas; Satluj

Rajasthan

990

Kalinadi Nagjhari

KPCL

Kalinadi

Karnataka

840

Nagarjuna Sagar

Andhra Pradesh Power Generation Corp.

Krishna

Andhra Pradesh

810

Kerala SEB

Idduki

Kerala

780

Andhra Pradesh Power Generation Corp.

Krishna

Andhra Pradesh

770

BBMB

Satluj

Rajasthan

710

Idduki Srisailam Right Bank Bhakra Right Bank Salal Ranjit Sagar Upper Indravati Kundah

NHPC

Chenab

Jammu & Kashmir

690

Punjab SEB

Ranjit

Punjab

600

OHPC

Indravati

Orissa

600

Tamil Nadu SEB

Kundah

Tamil Nadu

555

Bhakra Left Bank

BBMB

Satluj

Rajasthan

540

Chamera I

NHPC

Ravi

Himachal Pradesh

540

Uri I

NHPC

Jhelum

Jammu & Kashmir

480

Lower Sileru

Andhra Pradesh Power Generation Corp.

Godavari

Andhra Pradesh

460

Srisailam Left Bank

Andhra Pradesh Power Generation Corp.

Krishna

Andhra Pradesh

450

Ranganadi I

NEEPCO

Ranganadi; Dikrong

Arunachal Pradesh

405

Kadampari

Tamil Nadu SEB

Cauvery

Tamil Nadu

400

Koteshwar

THDC

Bhagirathi

Uttar Pradesh

400

Balimela

OHPC

Machkund

Orissa

360

Pong

BBMB

Beas

Himachal Pradesh

360

Total Capacity (MWe)

Upper Kolab Bansagar Hirakud Ukai Rihand

OHPC

Kolab

Orissa

320

Madhya Pradesh SEB

Sone

Madhya Pradesh

315

OHPC

Mahanadi

Orissa

308

Gujarat SEB

Tapti

Gujarat

305

UPJVNL

Rihand

Uttar Pradesh

300

Kerala SEB

Anathodu; Pamba

Kerala

300

Rengali

OHPC

Brahmani

Orissa

250

Chibro

UJVNL

Yamuna

Uttaranchal

240

Sabarigiri

Kadana

Gujarat SEB

Mahi

Gujarat

240

Andhra Pradesh Power Generation Corp.

Godavari

Andhra Pradesh

240

Karnataka Power Corp. Ltd.

Varahi

Karnataka

230

Punjab SEB

Beas

Punjab

207

NEEPCO

Umrong

Assam

200

Tamil Nadu SEB

Cauvery

Tamil Nadu

200

Ramganga

UJVNL

Ramganga

Uttaranchal

198

Baira Siul

NHPC

Siul

Himachal Pradesh

180

Upper Sileru Varahi Mukerian Kopili Mettur Tunnel

Gerusuppa

KPCL

Sharvathi

Karnataka

180

Kerala SEB

Periyar

Kerala

180

Rajasthan State Electricity Corp. Ltd.

Chambal

Rajasthan

172

Madhya Pradesh SEB

Narmada

Madhya Pradesh

160

Bhira PSS *

Tata Electric Co.

n/a

Maharashtra

150

Kadra

Karnataka Power Corp. Ltd.

Bethi; Kalinadi

Karnataka

150

Chilla

UJVNL

Ganga

Uttaranchal

144

Rajasthan State Electricity Corp. Ltd.

Mahi

Rajasthan

140

Tamil Nadu SEB

Periyar

Tamil Nadu

140

Punjab SEB

n/a

Punjab

134

Lower Periyar Rana Pratap Sagar Pench

Mahi Bajaj Sagar Periyar Anandpur Sahib Bhira

Tata Electric Co.

n/a

Maharashtra

132

Subernrekha

Bihar SEB

Subernrekha

Jharkhand

130

Upper Sindh

Jammu & Kashmir SEB

Sindh

Jammu & Kashmir

127

Kerala SEB

Kuttiadi

Kerala

125

n/a

n/a

Chattisgarh

120

Jog

KPCL

Sharvathi

Karnataka

120

Khodri

UJVNL

Tons

Uttaranchal

120

Kuttiadi Hasdeobango

Kodasalli

KPCL

Kalinadi

Karnataka

120

Lower Mettur

Tamil Nadu SEB

Cauvery

Tamil Nadu

120

Sanjay Bhaba

Himachal Pradesh SEB

Bhaba Khad

Himachal Pradesh

120

NHPC

Sarda

Uttaranchal

120

Madhya Pradesh SEB

Chambal

Madhya Pradesh

115

Andhra Pradesh Power Generation Corp.

Machkund

Andhra Pradesh

115

Meghalaya SEB

Umiam

Meghalaya

114

Punjab SEB

Uhl

Punjab

110

Tanakpur Gandhi Sagar Machkund Umiam Shanan (Uhl I)

Loktak I

NHPC

Leimatak

Manipur

105

Lower Jhelum

Jammu & Kashmir SEB

Jhelum

Jammu & Kashmir

105

Kalinadi Supa

KPCL

Kalinadi

Karnataka

100

Tamil Nadu SEB

Kodayar

Tamil Nadu

100

Kodayar

River(s) Power Plant

Owner

State Location

Total Capacity (MW)

India's Largest Windpower Facilities (10 MW and Greater) Location Power Plant

Owner

City

State

Total Capacity (MWe)

Vankusawade Wind Park

Suzlon Energy Ltd.

Satara Dist.

Maharashtra

259

Cape Comorim

Aban Lloyd Chiles Offshore Ltd.

Cape Comorim

Tamil Nadu

33

Kayathar Subhash

Subhash Ltd.

Kayathar

Tamil Nadu

30

Ramakkalmedu

Subhash Ltd.

Ramakkalmedu

Kerala

25

Muppandal Wind Farm

Muppandal

Tamil Nadu

22

Tamil Nadu

21

Muppandal Wind Gujdimangalam Puthlur RCI

Gujdimangalam Wind Farm Gujdimangalam Wescare (India) Ltd.

Puthlur

Andhra Pradesh

20

Lamda Danida

Danida India Ltd.

Lamda

Gujarat

15

Chennai Mohan

Mohan Breweries & Distilleries Ltd.

Chennai

Tamil Nadu

15

Jamgudrani MP

MP Windfarms Ltd.

Dewas

Madhya Pradesh

14

Jogmatti BSES

BSES Ltd.

Chitradurga Dist.

Karnataka

14

Newam Power Company Ltd.

Perungudi

Tamil Nadu

12

Kethanur Wind Farm

Kethanur Wind Farm

Kethanur

Tamil Nadu

11

Hyderabad APSRTC

Andhra Pradesh State Rapid Transit Corp.

Hyderabad

Andhra Pradesh

10

Muppandal Madras

Madras Cements Ltd.

Muppandal

Tamil Nadu

10

Poolavadi Chettinad

Chettinad Cement Corp. Ltd.

Poolavadi

Tamil Nadu

10

Perungudi Newam

Reference Web

site

http://fossil.energy.gov/international/indiover.html http://www.energy.qld.gov.au/electricity/infosite/index.htm

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Sources of Energy Non RenewablePrimary Energy Source Coal The major use of coal in electricity generation is as a fuel burnt in the furnace of a large steam

:

generator. The high pressure and temperature steam is then supplied to a turbo-generator which produces the electricity. The overall process is simple but there is a large amount of associated plant and equipment used to optimise the cycle efficiency and minimise environmental pollution. Fuel Oil The term fuel oil covers a wide range of petroleum products from heavy oil which requires preheating for burning and handling through to a light petroleum fraction similar to kerosene. It is a product of an oil refinery after crude oil has been processed. Fuel oil contains no (or very little) ash and this makes the furnace design much easier compared to a design for coal fired plant. The combustion of the oil can be completed in a smaller volume resulting in smaller furnace size and lower cost. Heavy fuel oil (also known as residual or bunker C) is difficult to use since it has a very high viscosity and must be heated to about 40°C for pumping purposes. It is usually burnt in the furnace of a steam generator which supplies steam to a turbo-generator. Distillate Distillate is a lighter fraction of fuel oil having a low viscosity and which may be pumped at ambient temperature. Distillate is used to generate electricity by being burnt in a gas turbine or a reciprocating engine, the output of which drives a generator. Jet

Fuel

Jet fuel (also known as kerosene) is the lightest fraction of fuel oil having the lowest viscosity and which may be pumped at ambient temperature. Jet fuel is usually burnt in the combustion chamber of a gas turbine (aero-derivative type) which then drives a generator. Gas Gas is an important energy resource, which plays an increasingly significant role as a fuel source for electricity generation, industrial processes, business and residential consumers. The term "gas" usually encompasses: Two types of related, naturally occurring gases (natural gas and coal seam methane), both of which contain mainly methane (CH4). LPG (liquefied petroleum gas) is one of the petroleum products produced in the oil refining process. Renewable Primary Energy Sources Solar Solar systems are powered by energy from the sun. Solar radiation reaching the earth's surface is called insolation and has two components - direct normal insolation (DNI) is that part of the radiation coming directly from the sun (usually 80%) and diffusion insolation is that part that has

been scattered by the atmosphere or is reflected off the ground or other surfaces. Systems in which the solar radiation is concentrated use only direct normal insolation. Insolation is typically given as a power density in kW/m2 and average daily insolation as an energy density in kWh/m2-day. For much of the earth's area, the instantaneous insolation on a surface oriented towards the sun at noon on a very clear day is typically in the range of 0.9 kW/m2 to 1.1 kW / m2. The insolation may be reduced by clouds, atmospheric haze or by the angle of the sun to the surface. It quickly increases in the early morning and just as quickly falls away in the late afternoon and varies throughout the day. The best information on insolation resource for a particular location is measured data at that location. Direct normal insolation is measured with a pyroheliometer, a device that tracks the sun. Electricity generation using solar energy is by means of two quite different methods - solar photovoltaic and solar thermal. Solar photovoltaic systems convert solar radiant energy directly to electricity through the use of solar cells which are typically solid-state semiconductor devices, usually containing silicon. Sunlight striking the solar cell produces an electric current which may be transmitted to the external load. A vast amount of research effort has been expended in recent years in developing solar cells which are cheaper to produce, are more efficient and which can produce more energy than is used in their manufacture. Solar thermal technologies convert radiant energy from the sun to thermal energy. All of these technologies include a collector which redirects and concentrates the insolation on to a receiver. In the receiver, the solar energy is absorbed, heating a fluid that powers a heat engine to generate electricity. There are several different arrangements of solar thermal systems incorporating different shapes of collectors and varying mechanisms of heat transfer. Many demonstration plants have been or are currently being performance tested within Australia and throughout the world. Wind Wind energy systems convert the wind's kinetic energy into mechanical or electrical energy. The energy flow rate per unit area is proportional to the wind velocity cubed - this means that a doubling of the velocity results in an eight times increase in available power. Hence the economics of a wind power system are extremely sensitive to the wind velocity resource. The wind velocity at a particular location varies with the height above ground level and the nature of the terrain. The actual amount of energy that can be extracted from the wind is less than the theoretical amount of energy available with the theoretical limit being about 60%. A typical efficiency for a wind turbine is about 40%; that is, about 40% of the power available in the area swept by the wind turbine blades is converted to electricity. On a global scale, winds result from temperature gradients between the equator and the poles and between the land and seas. On a smaller scale, thermal winds can be generated by local thermal effects. Local factors such as high altitude, unobstructed terrain and natural wind tunnelling features cause some areas to have inherently higher wind speeds. At present, areas with a mean wind speed greater than 6 metres per second are considered suitable for wind energy projects but it is anticipated that improvements in technology will permit areas with lower wind speed to be developed.

Electricity generation using wind as the energy source uses a wind turbine consisting of a large rotor, a gearbox and a generator. Wind turbine technology has developed significantly is the last 25 years and one of the latest turbines has done away with the gearbox since this was a major cause of failure in some early machines. The tendency is to construct wind farms consisting of a number of interconnected turbines in a cluster to achieve an economy of scale. The wind farm must be carefully located so as to prevent objections from residents on the grounds of visual or noise pollution. Care must also be taken in the site selection so as to avoid bird kills, particularly to threatened and/or migratory species. Water Water energy systems use the energy contained in the water resource. The energy may be in the form of the potential energy stored in an upper water reservoir which can be released as the water falls to a lower reservoir. It may also be potential energy resulting from the changes in the level of ocean water during tidal cycles. Another form of water energy resource is associated with the kinetic and potential energy of ocean waves. The kinetic energy of waves is associated with the velocity of the water mass; the potential energy is associated with the displacement of water above or below the mean sea level. The greatest resource for wave power typically occurs between 40 degrees and 60 degrees latitude in each hemisphere. The west coasts of the United States, Europe, New Zealand and Japan are considered suitable for wave energy extraction. A hydro-electric plant is used to generate electricity from the potential energy stored in the water. As the water is released from the upper to the lower reservoir it passes through a water turbine which drives a generator. There are numerous hydro-electric schemes throughout the world, with some having a capacity of thousands of megawatts. A tidal energy conversion plant typically consists of a tidal basin created by a dam, a turbogenerator and a sluice gate in the dam to allow the tidal flow to enter or leave the tidal basin. Tidal energy using conventional hydro-electric technology has been demonstrated on a large scale. There are a number of different devices used to generate electricity from ocean waves. One arrangement uses a water oscillation chamber incorporating a Wells turbine. The rise and fall of waves in the chamber cause air in the chamber to pass backwards and forwards through a Wells turbine, thereby generating electricity. The Wells turbine spins in the same direction irrespective of the direction of the air passing through it. Biomass Biomass is regenerative organic material used for energy production. Sources for biomass fuel include agricultural and forestry residues and municipal and animal wastes. Bagasse (the waste from the crushing of sugar cane) has been used for many years in the sugar industry as boiler fuel for the generation of steam and electricity for use in the sugar mill during the crushing season. Its use, together with other agricultural/forest wastes, is now being promoted in facilities that operate all year and which, in the non-crush season, generate electricity for sale back to a retailer. Such schemes depend on Government subsidy and/or generous buy back prices for their viability. S Biomass has a number of advantages over traditional fossil fuels with its primary advantage being that it is renewable. The growth and combustion cycle of biomass does not increase the

atmospheric carbon dioxide level (however, cultivation and harvest of biomass requires the use of fuels that may increase the carbon dioxide level). It is usually a low cost fuel since many biomass sources are agricultural or industrial residues that, if not used for energy production, would result in disposal costs. Electricity production from biomass generally uses direct combustion of the biomass in a steam generator which supplies a turbo-generator. Allowance must be made in the design of the materials handling system and the steam generator for the specific properties of the biomass to enable satisfactory plant operation. For example, bagasse, which is the fibrous residue from sugar cane milling, is a light-weight material with a high ash content and demands special consideration in the design stage. An alternative method is to process the biomass in a gasifier with the gaseous output being burnt in a combined cycle gas turbine plant. Reference Web

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Fuel-Coal Coal is created as the result of a natural chemical process in which vegetation is transformed by time, pressure and temperature. The time involved is very long to accommodate the organic chemical reaction which proceeds at a slow rate. Pressure is also important because coal of high rank is generally found in regions that have been under high pressure. The temperature at which the reaction takes place need not be high, for time brings about a relatively great change even at the low temperatures prevailing in the earth's crust. There is no satisfactory definition of coal. It is a mixture of organic chemical and mineral materials - the organic chemical materials produce heat when burned and the mineral matter remains. An analysis, known as the 'proximate analysis', is used to rank coal and it determines four constituents in the coal: 1. water, called moisture; 2. mineral impurity, called ash, left when the coal is completely burned; 3. volatile matter, consisting of gases driven out when coal is heated to certain temperatures; 4. fixed carbon, the coke-like residue that burns at higher temperatures after volatile matter has been driven off. Coals are grouped according to rank and are known as anthracite, bituminous, subbituminous and lignite. The coal rank increases as the amount of fixed carbon in the coal increases and ranges from anthracite (highest rank) to lignite (lowest rank). Anthracite Hard and very brittle, anthracite is dense and shiny black. It has a high percentage of fixed carbon and a low percentage of volatile matter. The amount of volatile matter in the coal influences the ease with which the coal can be burnt, with coals with a high amount of volatile matter being the easiest. This means that anthracite is difficult to burn and special consideration

must be made in the design of the combustion system to ensure that stable combustion is achieved. Bituminous By far the largest group, bituminous coals derive their name from the fact that on being heated they are often reduced to a cohesive, binding, sticky mass. Their carbon content is less than that that of anthracites, but they have more volatile matter and burn easily. Subbituminous These coals have high moisture content, as much as 15 to 30 percent, and are free-burning. Lignite Lignites are brown and of a laminar structure in which the remnants of woody fibres may be quite apparent. They have high volatile content and are free burning but they have high moisture content (up to 65%) and low heating value so they are not economical to transport long distances. It is very important that the properties of the coal and ash are well known when designing a coal fired power station since they can strongly influence the capital cost and availability of the plant. In particular, coal properties influence the coal handling and boiler plants while ash properties influence the boiler, ash and dust handling and flue gas cleaning plants. Extensive testing of the coal and ash is required prior to the design of a plant for a new coal field. This consists of laboratory and perhaps small scale tests but usually not full scale due to the expense. The design of a plant for a new coal field is a difficult exercise since much of the design is reliant on empirical data from past experience on other similar coals. Sometimes this results in an inappropriate design due to an unusual coal/ash property which is not discovered until the plant is operational. Plant modifications (if feasible) are then required which usually require an extensive plant outage resulting in lost revenue as well as capital expense. Use

of

Coal

in

Electricity

Generation

The major use of coal in electricity generation is as a fuel burnt in the furnace of a large steam generator. The high pressure and temperature steam is then supplied to a turbo-generator which produces the electricity. The overall process is simple but there is a large amount of associated plant and equipment used to optimise the cycle efficiency and minimise environmental pollution. The high usage of coal for electricity generation reflects the ready availability of low cost coal which has enabled Australia to be one of the lowest cost producers of electricity in the world. A more thermally efficient way to use coal is in an Integrated Gasification Combined Cycle (IGCC) plant. This is new technology and is not yet commercial, with only a few demonstration plants in the world. In an IGCC plant, coal is gasified and the gas burnt in combined cycle gas turbines. The coal may be gasified in a chemical reactor vessel that is integrated with the gas turbine plant. However, recent pulverised coal plants have been designed to operate at very high steam pressure and temperature with a much improved efficiency approaching that of IGCC without the complexity.

Another method of coal gasification is to partially combust it while the coal is still underground. This is known as Underground Coal Gasification (UCG) and is an idea which has been around for over 100 years but has not been adopted commercially in any Western economy. It has been used for about 40 years in Uzbekistan where the gas was burnt in a conventional steam generator. The idea has been researched and trialed in many countries with the latest trials being conducted in Australia by CS Energy and Linc Energy. The proposal is to produce a low cost gas which is burnt in a combined cycle gas turbine. The idea has some inherent practical difficulties concerning the monitoring of a partial combustion process underground together with the possibility of pollution of underground aquifers by the products of combustion. Reference Web

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Electricity and power definitions Auxiliary power/energy All electricity consumed internally within the boundary of a power station or cogeneration plant to run the plant. Aeroderivative gas turbine Aeroderivative gas turbines originate from the aviation industry. They are lightweight. They have higher thermal efficiency and capital cost than industrial gas turbines and their maintenance costs can also be higher. Exhaust gas temperatures are generally lower than industrial gas turbines. Performance decreases dramatically at high ambient temperatures. Auxiliary Fuel fired

boiler

used

to

raise

the

site

boiler steam

and/or

hot

water

requirements.

Availability (%) Availability is an indicator of the maximum amount of electrical energy that a unit is able to generate during a period, after making allowances for outages due to all causes (Total installed capacity (MW) * period hours MWh losses due to all outages during the period) * 100 divided by: Total installed capacity (MW) * period hours Back pressure steam turbine A simple non-condensing steam turbine. High-pressure steam is expanded through the backpressure steam turbine to generate electricity, and is exhausted at the required steam conditions for use in a process or for direct heating. Base load Operating regime in which the generator operates at its full capacity (or close to it) at all times. Biomass Is material produced by photosynthesis or is an organic by-product of a waste stream suited as a feedstock for electrical and/or thermal energy or the manufacture of fuels and substitutes for petrochemicals and other energy intensive products. Includes a wide variety of renewable organic materials (eg sugar cane pulp, food processing waste, animal manures and sewerage,

and organic municipal solid waste). Energy conversion paths include combustion and gasification for heat and power (cogeneration), pyrolysis for liquid and gaseous fuels and chemicals, and anaerobic digestion and fermentation. Biomass fuels tend to be renewable. Boiler blowdown Stream of water which is bled from the boiler drum or steam supply system to control the concentration of total solids and other contaminants in the boiler water. Boiler drum Generally the steam drum of a boiler where the steam generated is separated from the circulating boiler water. Bottoming cycle Heat is recovered from an industrial process (eg a furnace) and then used to generate steam through a boiler, which is then used to generate electricity. Lower pressure steam can also be used for process. Capacity The rated continuous load carrying ability expressed in megawatts, of generation equipment; sometimes referred to as maximum continuous rating (MCR). Capacity factor (%) Total energy produced for a specified period relative to the total possible amount of energy that could have been produced for the same period. Total period energy generated (MWh) * 100 divided by: Total installed capacity (MW) *period hours Centralised Generation Electricity production based on large-scale power stations which are usually remote from electricity consumers, and which require long-distance, high-voltage transmission networks. Circuit Breakers A type of switch used to control the flow of power in an electrical circuit. Special forms of these are used in switchyards and substations for the control of power between power (transmission and distribution) lines. Clean-as-new New

unit,

no

degradation.

Cogeneration Involves the generation of two products from a single fuel. e.g. useful combined heat and power. It is typically, two to three times more efficient than major conventional, predominantly coal-fired, centralised power stations. Production efficiency is achieved by harnessing heat that would otherwise be wasted. The heat and power can also be converted into many applications such as cooling. Condensate Steam which

has

been

condensed

for

return

to

the

boiler.

Creep The plastic (i.e. inelastic) movement of a metal or other solid. Temperature and stress on the material directly influence the rate of creep. The composition of the material also has a bearing on its rate of creep. Consideration of the material's creep properties is particularly impotant in the selection of materials for components subject to high temperature and high stresses, such as those in

boilers,

turbines

and

superheaters.

Deaerator Used to preheat feedwater before entering the waste heat boiler, and to drive off noncondensable and potentially corrosive dissolved gases. Requires steam to provide the energy for heating. Not relevant to hot water case. Deep Connection Transmission assets and services provided by the Transmission Network Operator which are: initially for one participant, but where the assets may eventually become part of the shared network; and immediately part of the shared network, but are assets which would not need to exist if not for connection to one participant. Charges and risks associated with Deep Connection services may eventually be shared with other participants, when arrangements change. DegradationDemand Deterioration in power output and/or heat rate of an engine or turbine under operating conditions due to, for example, inlet air contaminants, fuel contaminants and thermal stress. Continuous process occurring between overhauls. Demand Demand is usually taken to mean the electricity requirements of the end consumer. However, in the NEM, the term "demand" includes consumption and losses in the distribution and transmission networks and in the power stations as well as end user consumption. Extreme care should therefore be taken in the use of published "demand" values. The demand requirements are usually in two forms: Instantaneous Demand - the size of the demand at any instance in time and is measured in MW. It is important in determining the generating capacity required to on-line, particularly at peak usage times. It also is important in determining if the transmission and distribution systems can cope with the flow of electricity during peak demand times; and Period Demand - the amount of electrical energy used by the end use consumers over a period of time (measured in MWh or GWh). This measure is used to estimate how hard the power stations need to operate during that period, the amount of fuel consumed in the generation of that energy and the potential income for electricity retailers and generators. Demineralised water Pure water produced by removing mineral salts, usually by an ion exchange process. Distributed Generation Is power generation generally located close to where it is consumed, for example, supplying electricity on-site or over-the-fence. Distributed generators can also export electricity into the local grid. Also referred to as decentralised, embedded or localised. Includes cogeneration and other types of generation such as fuel cells and photovoltaic. This can be as small as a 3 kWe micro-cogeneration plant, or as large as a 450 MW industrial on-site system. Distribution Electrical cabling system which transfers power, usually over long distances, to the consumers. Distribution systems are usually operated at medium to low voltages (eg 110kV, 66kV, 33kV, 11kV, 6.6kV & 415V). Dump condenser Excess steam from the waste heat boiler bypasses the steam turbine and goes directly to the

condenser.

Used

to

balance

site

load

with

steam

generated.

Dump stack & damper Used to control flow and temperature of exhaust gas to bypass the waste heat boiler. Can also be used to isolate equipment in the exhaust gas stream when the equipment is out of service or requires maintenance. Used to balance steam generated with site load. DUOS Distribution use of system charge. In the National Electricity Code, the charge for using the electricity network on or below 66 kV voltage level. Economiser A counterflow heat exchanger for recovering energy from the exhaust gas. It increases the temperature of the water entering the boiler drum using otherwise wasted exhaust heat and hence increasing steam-raising ability. Economisers are assumed on WHBs in this analysis. Efficiency Thermodynamically, the ratio of useful energy output to energy input into a process. Has many specific definitions and care needs to be taken that the meaning is clear. See also Heat Rate. Efficiency (Generated)% Total energy generated (kWh) * 3600 * 100 divided by: Quantity fuel (kg) * higher heating value of fuel consumed (kJ/kg) Efficiency (gen) is related to Heat Rate (gen) by: Efficiency (gen) (%) = 3600 * 100 . Heat Rate (gen) (kJ/kWh) Efficiency (Sent Out)% (Total energy generated (kWh) - total auxiliary energy (kWh) * 3600 * 100 divided by / Quantity fuel (kg) * higher heating value of fuel consumed (kJ/kg) Efficiency Efficiency

(s/o) (s/o) (%)

is =

related 3600 *

to 100

/

Heat Heat

Rate Rate

(s/o) by: (s/o) (kJ/kWh)

Electrical efficiency (Cogen) NFT) [Cogen gross elec output] + [imported electricity] - [parasitic electricity] dividede by: [Fuel to cogen unit] + [fuel used for imported electricity] Embedded Generation Smaller-scale generators that are connected to electricity distribution networks. By nature of where they connect to the grid, they are distributed generators. Are in contrast to large-scale coal-fired generators that are connected to very high voltage electricity transmission networks. Enthalpy Measure Entropy A measure Feedwater Total flow

of

the of

supplied

heat

unavailable to

the

content energy

boiler,

of

in sum

a of

a

substance.

thermodynamic condensate

and

system. makeup.

Forced outage rate (%) Forced outages require the removal of a generating unit from service for repairs that have not been planned.

Energy Total

lost due installed

to

forced capacity

outages (MW)

(MWh)

* *

100 divide by: period hours

Fossil Fuel Derived from hydrocarbon and includes coal, natural gas, coal seam methane, oil and liquid petroleum gas. Gas turbine An engine operating on what is known as the Brayton cycle with continuous steady flow compression of air, constant pressure combustion and expansion of the compressed heated gases through an expansion turbine. Working fluid is usually air, fuels can be gaseous or premium liquid fuels such as distillate. Generated Electrical

energy

Energy by

generated

the

(MWh) plant.

power

Greenhouse Gases (GHG) Those gaseous constituents of the atmosphere, both natural and anthropogenic, that absorb and re-emit infrared radiation. Greenhouse Intensity (GI) Measure of Greenhouse efficiency as the emission rate of greenhouse gases from fuel burning expressed in kg CO2 (equiv.) per MWh sent out. For cogeneration, this is discounted for steam/heat production. Heat rate A form of expressing efficiency of an engine or turbine. The fuel heating value consumed per unit of useful output (usually electrical output). Common unit is kJ/kWh. To convert to efficiency divide by 3600 and invert. Heat Rate (Generated) (kJ/kWh) Quantity fuel (kg) * higher heating value of fuel consumed (kJ/kg) divided Total energy generated (kWh)

by:

Heat Rate (gen) is related to Efficiency (gen) by: Heat

Rate

(gen)

(kJ/kWh)

=

3600

*

100

divided

by:/

Efficiency

(gen)

(%)

Heat Rate (Sent Out) (kJ/kWh) Quantity fuel (kg) * higher heating value of fuel consumed (kJ/kg) divided by:/ Total energy generated (kWh) - Total auxiliary energy (kWh) Heat Rate (s/o) is related to Efficiency (s/o) by Heat

Rate

(s/o)

(kJ/kWh)

=

3600

*

100

./

Efficiency

(s/o)

(%)

Heat Recovery Steam Generator A boiler that uses waste heat (such as gas turbine or reciprocating engine exhaust gas) to produce steam or hot water. Higher Heating Value (HHV) The amount of heat recovered when the products of complete combustion of a unit quantity of a fuel are cooled to the initial temperature of the air and fuel (kJ/kg).

For Natural Gas, the relationship between Higher Heating Value (HHV) and Lower Heating Value (LHV) is (approximately): HHV

=

1.1

*

LHV

Industrial gas turbine Heavier, more robust, and cheaper than aeroderivative gas turbines. Generally have lower thermal efficiency and higher exhaust gas temperatures than aeroderivative gas turbines. Isentropic Constant entropy, or effectively zero loss. Used in the context of steam turbine ability to convert steam energy into mechanical energy, as opposed to leaving the turbine as exhaust steam energy at the exhaust steam pressure. ISO conditions Ambient conditions stated in the ISO Standard 2314 = 15°C, 0 metres ASL, (i.e. at average sea level) and 60% Relative Humidity (RH). Load factor (%) (Also called Output Factor) - total energy produced for a specified period relative to the total possible amount of energy that could have been produced for the operating hours during the same period. It can be thought of as the load (% MCR) that would have produced the same total energy over the same operating hours. Total Total

energy generated during installed capacity

the (MW)

period *

(MWH) operating

*

100 hours

Lower Heating Value (LHV) The amount of heat recovered when the products of complete combustion of a unit quantity of a fuel are cooled to just above the dew point of the water vapour it contains (kJ/kg). For Natural Gas, the relationship between Lower Heating Value (LHV) and Higher Heating Value (HHV) is (approximately): LHV = HHV/1.1

Makeup Treated raw water, which is added to the system to replace steam and water lost to site requirements, blowdown, evaporation, sampling or venting. Network Losses Amount of energy lost when electricity flows in the power lines of a transmission and/or distribution network. The electrical resistance of the power lines is the main contributor to these losses. Operating Hours Total number of hours during which a unit generates electricity over a period of time. Parasitics The plant's

internal

power

consumption

and

losses.

Peaking Operating regime in which the generator operates at its full capacity (or close to it) only for short periods at times of high demand. The plant is shut down for the remainder of the time.

Planned outage rate (%) Planned outages are due to overhaul (or other) work which is planned well in advance, usually by more than one year. Energy Total

lost due installed

to planned outages capacity (MW) *

(MWh) period

*

100 hours

Pool Price Price of electricity available for supply in the National Electricity Market. Each generator provides prices at which it is willing to supply designated levels of MW. The grouping of these prices within the NEM is known as the pool. Process Steam

used

within

an

industrial

plant,

usually

for

steam heating.

Pulveriser A machine that grinds coal into a fine powder for injection into the furnace of a pulverised coal fired boiler. Reciprocating engine An engine characterised by the movement of the pistons in the cylinders back and forth in a straight line driving a crankshaft to convert the work into rotary shaft work. Typical vehicle engine. Renewable Generation Produces no net greenhouse emissions. Includes power generated from non-hydrocarbon, natural resources such as biomass, hydro, wind, solar (photovoltaic) and tidal. It also includes power generated using waste products. Tend to be distributed and connected to local distribution networks. Reserve Plant Margin Reserve Plant Margin is a well used (but generally misunderstood) simplistic measure which, in theory, is meant to give an indication of the ability of the electricity system's generation plant to cope with the estimated peak (instantaneous) demands on the system. It is measured by: 1. Summing the supply capacities of all the power stations able to operate at any time during a particular interval of time(usually the three winter months or the three summer months); 2. Dividing by the total power station sent out supply required to meet the maximum peak (instantaneous) demand estimated for that interval of time; 3. Taking away 1. A value of (say) 0.3 means that there is a 30% "excess" in sent out supply capacity available to meet the maximum peak demand (i.e. the Reserve Plant Margin - 30%). Note: The reserve plant margin calculation may not take into account: The generating capacity kept in reserve for system stability reasons; The unavailability of power stations due to scheduled and unscheduled outages; The short term overload capabilities of some of the power stations; The energy limits of the northern hydros and some peaking plants, such as Wivenhoe pumped storage hydro power station; The ability of demand side management techniques (such as hot water switching and short

term reduction in industrial loads) to reduce peak loads; The interconnectors being able to supply some of the required capacity; or The load limits on the interconnectors and inter-zonal transmission lines. For these, and other, reasons, the reserve plant is compared to a "guesstimated" optimum value that is supposed to take some account of these factors. Historically, values between about 20% to 25% have been used in Queensland. A reserve plant margin less than this meant that there was a risk of not having sufficient plant to meet the demand peaks, while more than this indicated an over-capacity in generating plant to meet the peak demands and that some plant would be under-utilised. The main problem with using the reserve plant measure is that most people are not be aware of the way in which it is calculated and so would assume that there was always a large excess in generating capacity and that all peak loads would be met. With the advent of the NEM, the importance of the Reserve Plant Margin measure has, thankfully, declined in importance, usefulness and usage. Retrofit Any improvement activity on an existing power plant that generally involves fitting new equipment to an existing plant. Sent Out Energy Electrical energy leaving the power plant. This is the generated energy minus the auxiliary energy used in the plant. Energy

generated

(MWh)

minus

auxiliary

energy

(MWh).

Shallow Connection Transmission assets and services provided for one participant where the assets will never be part of the shared network. Steam turbine An engine in which a vaned wheel is made to revolve by the impingement of steam. Converts steam energy to mechanical energy. Substation Similar to a "switchyard" but is usually associated with lower voltage distribution lines. Most of the equipment is enclosed within a building. Superheater A heat exchanger part of a boiler for increasing the temperature of saturated steam to superheated steam. Generally steam admitted into a steam turbine must be superheated (that is, above the saturation temperature at that pressure). Supplementary fired Additional gas firing into a waste heat boiler when the unfired exhaust gas is not sufficiently hot for raising the site steam requirements (temperature or steam mass flow). Can generally be done on gas turbine exhausts because sufficient oxygen remains in the exhaust. Not generally done on reciprocating engine exhausts due to lower excess oxygen in exhaust. Supply Supply has many meanings depending on the point of view of the organisation providing the data. The main definitions can be described by working back from the electricity end user to the power station:

Supply from the distribution system - this is equal to the end user consumption; Supply from the transmission system - this is equal to the end user demand plus the demand from any large user being supplied directly from the transmission system plus the losses in the distribution system; Supply sent out from the power stations - this is equal to the supply from the transmission system plus transmission system losses; and Supply generated - this is the electricity generated by the power stations and is equal to the supply sent out from the power stations plus losses within the power stations that are associated with the generation of the electricity. Note: For each of these, the "instantaneous" and "period" values of the electricity supply are required. Switchyard Fenced area containing electrical equipment used to control the transfer of power from one set of power lines to another set of power lines. It is usually associated with high voltage transmission lines, but is also used in association with lower voltage distribution lines. Thermal efficiency (Cogen) [Cogen gross elec output] + [imported electricity] + [site steam] [fuel to cogen unit] + [fuel used for imported electricity] + [fuel to aux boiler] Where

[site

steam]

includes

hot

water

as

(overall) divided by:

applicable.

Topping cycle High-pressure steam is raised in an auxiliary boiler and expanded through a backpressure steam turbine to the required site steam conditions. Total Sum

of

the

installed capacity of each

unit

capacity making up the

power

plant.

Transmission Electrical cabling system which transfers large amounts of power, usually over long distances. Transmission systems are usually operated at extra high voltages (eg 132kV, 275kV & 330kV). TUOS Transmission use of system charge. In the National Electricity Code, the charge for using the electricity network above 66 kV voltage level Turnkey Installation to the point of readiness for operation, generally a single design and construct contract. Some owner's costs, such as owner's engineering, spares, owner's start up labour and fuel, may be excluded and need to be considered in the indirect costs or elsewhere. Waste Waste products used in power generation include cane residue (bagasse) in the sugar industry; sludge gas from sewerage treatment plants; and methane from landfill sites. Waste heat boiler A boiler that uses waste heat (such as gas turbine or reciprocating engine exhaust gas) to produce steam or hot water. Reference Web Back

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Electricity and motors Electricity The word "electricity" can be used to mean an electrical charge that does not move (static electricity) or an electric charge that moves (current electricity) or a form of energy (electrical energy). All of these depend on what is happening to the electrons in a material. All materials are made up of atoms. Every atom consists of a nucleus containing a number of positively charged protons around which an equal number of negatively charged electrons move. The nucleus also contains neutrons, which do not have any electrical charge. The number of electrons in each atom of the material largely determines a material's physical, chemical and electrical properties. The atoms in some materials have "free" electrons that are loosely bound to their nuclei. A free electron can easily be induced to leave its atom and move about in random directions in the spaces between the atoms. When wandering electron encounters an atom, the electron could attach itself to the atom and could force another electron to leave that atom. Electricity passes easily through these materials which are called conductors. In other materials, most of the electrons are firmly bound to the nucleus and hence there are few "free" electrons. Electricity does not easily pass through these materials which are called nonconductors or insulators. Electric

Current

Normally, the free electrons in a conductor are moving in random directions. If an appropriate electrical force (called an electromotive force or EMF) is applied to the conductor, the free electrons can be induced to move (drift) generally in one direction. This movement of electrons is called current electricity and an electric current is said to flow. The rate at which the electrons appear to drift through the conductor is called the drift velocity. The number of electrons per second appearing to move past any point of the conductor gives a measure of the electric current. Increasing the magnitude of the EMF applied to the conductor will increase the drift velocity of the electrons in the conductor. This increase in drift velocity

would manifest itself as an increase in the electric current passing through the conductor. The source of EMF can be a battery or a generator or a photoelectric cell. For an electric current to flow through a conductor, the EMF source must apply an electric charge to one end of the conductor and an opposite electric charge to the other end. A simple example of this is the electric current flowing in a metal wire (the conductor) connected between the "negative" terminal and the "positive" terminal of a battery (the EMF source). All materials offer some resistance to the flow of electrons and hence work has to be done in forcing the electrons through the material. Materials with low resistance are the "conductors", the "insulators" having high resistance. The degree of resistance ranges from almost zero (for special materials called "super conductors") to very high (for the materials used to insulate powerlines). When an electric current flows through a conductor, two effects are produced: the electrical energy used to overcome the electrical resistance in the conductor is converted to thermal energy which increases the temperature of the conductor. Examples:heaters, stoves and electric kettles use the heating effects (conversion of electrical energy to thermal (heat) energy); and incandescent light bulbs emit light because their elements are raised to a high temperature (electrical to thermal energy conversion). a magnetic field forms around the conductor. for example: When a current carrying conductor is placed in a magnetic field, the interaction between its magnetic field and the other magnetic field exerts a force on the conductor. In an electric motor, this interaction forces the shaft to rotate (conversion of electrical energy to mechanical energy). Most of the ways in which electricity is used can be traced back to these two effects. Electrical

energy

can

therefore

be

easily

converted

to

other

forms

of

energy.

Conversely, most of the electricity in a large electricity supply system is generated by the use of magnetic fields in machines called, appropriately enough, "generators" (which can be thought of as being electrical motors driven backwards). Other forms of energy are used to produce the mechanical energy used to rotate the shafts of the generators. There are other ways in which electricity can be generated, but they all involve the conversion of a source of energy into electrical energy. Electrical energy can therefore be easily produced by the conversion of other forms of energy. A law of physics formulated by Isaac Newton notes that 'Energy cannot be created or destroyed but can be transferred from one form into another'. The usefulness of electricity therefore lies in its unique ability to be a convenient and easily controlled means to transport energy from one location to another location and to convert energy from one form into another form. The

Familiar

Forms

of

Electricity

Ever walked on a carpet and been "zapped" when you touch a metal object. That is an example of static electricity. Static electricity is used to a lesser extent than current electricity in our every day lives. The ENERGEX web site has a good explanation of this form of electricity. A more useful form of electricity is "current" electricity in which the electric current "flows" in one direction only - Direct Current (DC). The batteries in our torches, toys, portable radios and cars

are the most common sources of DC low voltage, low power electricity. Higher voltage, higher power DC systems are used for particular applications, such as energy storage systems associated with renewable energy systems that are not connected to an electricity supply network. High voltage, high power DC powerlines have been used successfully in special applications such as interconnectors between transmission systems and undersea power cables. Large DC electric motors are common in certain applications, such as electric locomotives where high starting torque and variable speed are required. The most useful type of "current" electricity is the type in which the direction of flow of the electrical current changes direction many times in each second - Alternating Current (AC). AC electricity powers the appliances in our homes, turns the electric motors of industry and energises our electric lights. The current in an AC system does not instantaneously change direction. Rather, it gradually (in relative terms) increases in magnitude until it reaches a maximum in one direction, then gradually reduces to zero, gradually increases to a maximum in the other direction, then reduces to zero - and the whole cycle starts all over again. The number of complete cycles carried out in a second is called the frequency of the AC electricity supply. In Australia, the AC frequency is 50 cycles per second, with 60 cycles per second used in America. If DC and AC electricity can both be used successfully, why is AC the dominant form of current electricity? The answers lie in the consideration of: economics - in general, AC electrical equipment is smaller and cheaper to manufacture than DC equipment of similar duty; and voltage changes - changes in voltages can be easily carried out in an AC system, but voltage changes in DC systems are complicated and require significant equipment. This ability to change voltage is particularly important in transmission and distribution systems where line losses are reduced if the voltage is increased. The voltages used in a large electrical supply system and the importance of having various voltages in the system are discussed in the Transmission and Distribution section.

Phases There is one further major characteristic of an AC electricity supply that requires explanation phases. A DC circuit has two wires through which the current in the circuit flows from a source of electricity through a load and back to the source. A single-phase AC circuit also has two wires connected to the source of electricity. However, unlike the DC circuit in which the direction of the electric current does not change, the direction of the current changes many times per second in the AC circuit. The 240 volt electricity supplied to our homes is single phase AC electricity and has two wires - an "active" and a "neutral". The distribution line supplying your home may be single phase and have only two wires strung between the poles (we will use the overhead power lines as examples because they can be easily seen). However, the distribution line may be made up of 4 lines. What are the others? The other lines carry the currents from two other electrical circuits, making a total of three circuits or phases. The reason why there are only 4 lines is because the 3 phases have a common neutral line (i.e. 3 active lines and 1 common neutral line).

But why 3 phases? Why not 2 or 4? Because the magnitude and direction of the electricity flowing in each of the phases is slightly displaced in time from the electricity flowing in the other phases, the current flowing in the common neutral will be the sum of the neutral currents from the 3 phases. The resultant current in the common neutral is smaller in a 3 phase system than in systems with other numbers of phases. This ability to use a common neutral of relatively small capacity has large economic advantages and is the main reason why 3 phases are used. 3 phase electricity has another advantage. We mentioned above that, in Australia, the voltage between the active and neutral in the single phase, low voltage supply to our homes is 240 volts and that this phase is only one of the phases in the 3 phase system. The voltage between the phases of this 3 phase system is 415 volts (in Australia). A 415 volt, 3 phase supply is able to deliver more energy than a 240 volt, single phase supply. 3 phase supplies are normally restricted to large electrical loads, such as large electric motors. As we travel back up the electrical network, the voltage increases and the neutral disappears! Why? The answer can be found in the consideration of why a neutral is used. A single phase supply must have a neutral, whereas a 3 phase supply does not require a neutral. More complicated reasons deal with fixing the voltage of the single phase supply relative to the earth (because domestic appliances have their metal enclosures connected to earth) and for fault protection purposes. 3 phase, medium voltage, distribution systems and high voltage transmission systems therefore use one wire for each phase and no neutral. The above discussions focussed on active and neutral conductors (wires) as being the means to convey the electricity. One type of system uses the earth as the return path, with only the active being conveyed by a wire conductor. This type of single-phase supply system is called the Single Wire Earth Return (SWER) system and is use to supply small loads which are located far from the main distribution networks.

Electrical

Safety

No section on electricity is complete without a short warning on the dangerous aspects of electricity. The following discussion is brief. Electricity

and

the

Human

Body

Water makes up most of the human body, thus making the body an electrical conductor. If a person touches an electrically energised object (such as a bare wire or faulty equipment) and the person is touching the ground, electricity will pass through the person to ground. Depending on the voltage of the electricity, the frequency of the AC supply, the magnitude of the current flowing through the body and the amount of time the current is flowing, the result can range from a slight tingle to a harmful and potentially fatal shock. The critical path of electricity through the human body is through the chest cavity. A current flowing from one hand to the other, or from a hand to the opposite foot, or from the head to either foot will pass through the chest cavity and could paralyse the respiratory or heart muscles (thus initiating ventricular fibrillation) and/or burning of vital organs. Electricity passing through any area of the body can result in burns caused by the current flowing in tissues and can be at the skin surface or in deeper layers or both. Electrical

Protection

Any piece of approved electrical equipment is designed for operation at a particular voltage and is insulated to protect its operator from coming into contact with its electrically live parts. Portable hand held electric appliances, such as electric drills, are unlikely to cause an electric

shock because they are usually double insulated, with the outside of the item made from a suitable insulating material. Protection against faulty equipment or circuits causing shocks to people in a domestic dwelling can be provided in two ways. 1. by having the circuits wired in accordance with the Multiple Earthed Neutral system, in conjunction with suitably rated circuit breakers or fuses. The circuit breakers or fuses are rated to operate just below the current limit of the wiring. When there is a fault to earth on an appliance, and the appliance is connected to the earthing circuit, the current in the circuit will greatly exceed that of the circuit breaker or fuse and cause them to operate. This disconnects the appliance from the supply. The disadvantage of the system is that, if the appliance does not have an earth connection or if the earthing circuit is faulty, the protection will not operate; or 2. for an electrical component to function, the electrical supply must have an active and a return path. The current through the circuit will be identical through both the active and neutral conductors. A protective device has been developed to sense any imbalance of current through the active and neutral conductors. This device does not provide protection unless the electricity has a path to earth, which could, in the worst case, be through a person. If this happened, the device's short detection and operating times would normally prevent severe injury to the person. This device is identified by various names, including Earth Leakage Circuit Breaker (ELCB), Residual Current Device (RCD) and Safety Switch. Some install

simple safety

ways

switches

on

to the

Avoid household

Electrical power

and

Accidents lighting

circuits;

have a qualified electrician regularly check the household's electrical systems, extension leads and appliances, particularly electric blankets and those appliances with metal cases; make sure that a light has been switched off before changing the bulb - and do not use your finger to clean the connection; protect power points from the probing of children; replace

worn

electrical

leads,

particularly

those

on

electric

irons;

NEVER touch a fallen powerline unless given specific assurances of its safety by a person qualified to do so; and think "safety" when doing anything associated with electricity. If

an

Electrical

Accident

Occurs

Do not touch the victim unless you are sure that the victim is not still in contact with the electrical hazard or that the electricity has been switched off. If you are unsure of how do this, get qualified help without delay. If the victim has been removed from the electrical hazard, first aid can be applied. Again if you are unsure of how do this, get qualified help without delay.

Theory of Electric Motors An electric generator converts mechanical energy to electrical energy in the presence of a magnetic field. An electric motor converts electrical energy to mechanical energy in the presence of a magnetic field.

An electric motor operates on the principle of electrodynamics that states that when a current carrying conductor is placed in a magnetic field, the conductor experiences a force, when the conductor is inclined to the magnetic field. When a current carrying loop is placed in a magnetic field so that it makes an angle with the magnetic field, the forces acting on the loop will rotate it, thus producing mechanical energy. The magnetic field can be produced by a magnet or by a current carrying coil wound on soft iron pole pieces. Electric motor use the latter method to produce a magnetic field. Motors can operate on direct current (DC) or alternating current (AC). In general, DC motors and small single phase AC motors (up to about 2.5 kW) are used for specific purposes. Larger three phase AC motors are the electric motors most used, particularly in industrial applications. The principal types of three phase motors are the induction motor and the synchronous motor.

DC

Motors

DC motors have two main parts: a) A Yoke which supports poles and field windings and provides a path for the magnetic flux; and b) An Armature with commutator and brushgear. DC motors are classified on the type of connections to the field windings: a) Separately excited motor - The field winding in a separately excited motor is energised from an independent source of electricity and so not affected by the load or voltage drop in the armature. Its speed remains practically constant over the entire load range; b) Shunt motor. The speed of a shunt motor drops slightly as the load increases. However, a shunt motor is considered a constant speed motor for all practical purposes. The starting torque of a shunt motor is 100-150 % of the full load torque; c) Series motor - The field in a series motor is connected in series with the armature winding. The speed of a series motor is high at light loads and falls off rapidly with increasing load. It cannot be run on light or no load because it may overspeed. For this reason, a series motor is used with a directly coupled load. The starting torque is of the order of 300-500% of the full load torque. The series motor finds extensive application in traction and in other jobs where high starting and accelerating torque is required and the motor is never required to run on light load; and d) Compound motor - A compound motor has a series as well as shunt field and its speedtorque characteristic is determined by the relative strengths of the two fields. The field windings are designed to give practically constant speed at all loads. The starting torque about 250-300% of full load torque. Compound motors are used where high starting torque and fine speed control are desired, such as cranes, rolling mills, and excavators.

DC

motors

possess

the

following

advantages:

High starting torque; Speed control over a wide range, both below and above the normal speed; and Quick starting, stopping, reversing and accelerating. The

disadvantages

of

DC

motors

are:

High capital cost of the motor and the control gear; Increased operating and maintenance costs because of commutators and brushgear.

and

AC

Motors

3

Phase

Induction

The most commonly used motor in industrial applications is the three-phase induction motor. Principle

of

operation

of

a

three

phase

induction

motor

The principle of operation for all three-phase motors is the rotating magnetic field. There are three factors that cause the magnetic field to rotate. 1. The voltages of the three-phase system are 120° out of phase with each other; 2. 3.

The The

three

voltages

arrangement

of

the

change stator

polarity windings

at around

regular the

intervals;

inside

of

the

and motor.

The speed at which the magnetic field rotates is known as the synchronous speed. The synchronous speed of a three-phase motor is determined by two factors. 1. 2.

The The

number

of

frequency

stator

poles;

of

the

and AC.

The field set up by the stator windings cuts the copper bars of the rotor. The voltage induced in the squirrel cage winding produces current in the rotor bars. As a result, a field is created in the rotor core. The attraction between the stator field and the rotor field causes the rotor to follow the stator field. The rotor always turns at a speed slightly less than that of the stator field. In this way, the stator field cuts the rotor bars and induces the required rotor voltage and current in the rotor field. The torque produced by an induction motor results from the interaction between the stator flux and the rotor flux. In the case of wound rotor induction motor, the voltage and current are induced by the rotating field similar to that in the squirrel cage induction motor. The induced current set up form a closed path from the rotor windings through the slip rings and brushes to a star connected speed controller. At the start up, all of the resistance of the star connected speed controller is inserted in the rotor circuit. This additional resistance causes an excellent starting torque and a large percent slip. Characteristics

of

Induction

Some of the important characteristics of induction motors are:

Motors

i) For the same slip, the torque varies as the square of the terminal voltage; ii) The slip is proportional to the load, and since the slip varies over a small range only, the speed of an induction motor is more or less constant with load; iii) The torque varies directly with the slip; iv) The slip varies inversely as the square of the terminal voltage; and v) The efficiency of an induction motor is inversely proportional to slip. A motor with a lower value of slip will be more efficient than a motor with a higher slip because of the increased losses in the rotor of the latter. The efficiency of three phase induction motors varies with type, size and load. It ranges from 85% to 99% in the case of squirrel cage motors above 5 HP. It is about 75% for smaller motors. The efficiency is less in the case of slip-ring motors, slow speed motors and motors running at part load. The

advantages

Simple Rugged Reliable Low Easy Simple High

of

an

1. 2.

induction

motor

are

as

follows:

design; construction; operation; initial operation control gear

for

Construction Broadly

AC

and starting and efficiency.

of

there

are

two

Squirrel-cage Wound-rotor

Induction types

of

induction or

cost; maintenance; speed control;

slip-ring

three-phase

and Motors

induction

motor;

and

induction

motor.

motors:

Each of these two types of three phase induction motors consist of: The Stator; and The Rotor. Stator: The squirrel-cage and the wound-rotor induction motors have nearly the same stator construction and winding arrangement.The stator is a three-phase winding placed in the slots of a laminated steel core and formed of three single-phase windings spaced 120 electrical degrees apart. The three single-phase windings are connected in star or delta formation. The three line leads from the three windings are brought out to a terminal box mounted on the frame of the motor. The laminations of the steel core are insulated by varnish or oxide coating, and are slotted in their inner periphery. Squirrel

cage

rotor:

The rotor is constructed of laminated steel sheets assembled around a shaft. The rotor winding consists of copper or aluminium bars. The copper bars are soldered to two copper end rings. In the case of rotors with aluminium windings, the bars and end rings are all die cast in position without soldering at the ends. The aluminium conductor rotors are therefore more rugged. The slots of the rotor are not always parallel to the slots on the stator. Skewed rotors are twisted (skewed). Skew effectively reduces noise, eliminates the magnetic locking of the rotor and increases starting torque. In very small motors, the rotor is sometimes made up of solid steel without any winding. Such motors operate by virtue of the eddy currents established in the rotor.

The speed performance of a squirrel cage motor is measured in terms of slip. Slip is usually expressed as the percentage by which the speed of the rotor falls behind the speed of the rotating synchronous speed of the stator field. Wound-rotor (or slip-ring motor): The cylindrical core of the rotor is made up of steel laminations, slotted to hold the formed coils of the three single-phase windings. These windings are placed 120 electrical degrees apart. The insulated coils of the rotor winding are grouped to form the same number of poles as in the stator windings. The three single-phase rotor windings are connected in star. The three leads from these windings terminate at three slip rings mounted on the rotor shaft. Carbon brushes press against these slip rings and are held securely by adjustable springs mounted in the brush holders. The brush holders are fixed rigidly. Leads from the carbon brushes are connected to an external speed controller. The Its

advantages susceptibility

High

starting

to torque

of speed of

200

a control -

slip-ring by

250%

motor

regulating of

full

rotor load

are:

resistance; torque;

and

Relatively low starting current (250 to 350% of the full load current) compared to a squirrel-cage motor, which may have a starting current in the order of 600% of its full load current. Power

Factor

of

Induction

Motors

The power factor of an induction motor depends on its type, size, rotational speed and load. Slip-ring motors have lower power factors than squirrel cage motors of the same size. A motor running at high speed and near full load has a better power factor than when it operates at part load and low speed. The power factor at no load is approximately 0.15 lagging. The no load current consists mainly of magnetising current. This current produces the magnetomotive force (mmf) required to send the stator flux across the air gap and through the magnetic circuit. The in-phase component of the no load current is low. Hence the power factor at no load is low. As the load on the motor incr4eases, the in-phase current component supplied to the motor increases and hence the power factor increases. In practice, the power factor of the inductive motor at the rated load is between 0.85 and 0.90 lagging. Induction

Motor

Losses

and

Efficiency

The losses in an induction motor consist of stray losses and the copper losses. The stray power losses include mechanical friction losses, windage losses and iron losses. These losses are nearly constant at all loads and are often called fixed losses. The copper losses consist of the I2R losses in the windings of the motor. An increase in load increases the current in the motor windings and hence the I2R losses. At light loads, the percent efficiency is low because the fixed losses form a large part of the input power. As the load increases, the fixed losses become a smaller part of the input power. Thus, the efficiency increases with load. However, as the rated capacity of the motor is exceeded, the copper losses become excessive and the efficiency decreases.

AC 3 Phase Synchronous Motors A synchronous motor consists of a DC field winding on its rotor, a three-phase winding on its

stator and a means to bring it to speed (usually a squirrel cage winding placed in the salient poles on the rotor). A synchronous motor is started as an induction motor or by a separate induction motor. When the motor comes up to speed, the DC excitation is supplied to the field winding and the motor pulls into synchronism. No voltage is generated in the auxiliary rotor winding during synchronous operation. The DC excitation is provided by an exciter driven either from the motor's shaft or by a separate motor. To reduce maintenance, brushless synchronous motors are now being manufactured. An alternator mounted on the motor shaft replaces the exciter. The AC from the alternator is converted to DC by bridge connected silicon diodes and then supplied directly to the field winding. This arrangement eliminates the exciter, commutator and the field slip rings. The ability of a synchronous motor to operate at leading power factor makes it suitable to be used for power factor improvement. When a synchronous motor is used exclusively for power factor improvement and not for driving any mechanical load, it is called a synchronous condenser.

AC

Single

Phase

Motors

Single phase motors are usually used in domestic appliances because they are suitable for low power ratings. The magnetic effect of a single phase winding results in a pulsating magnetic field which may not be able to start the rotor turning if the rotor is in certain positions. In order to make a single phase motor self-starting, a second (starting) winding is installed in the stator slots at 90 degrees, or half a pole pitch, from the main winding. As the motor is only supplied by a single phase source of electricity, further variations are required to provide a phase difference for starting purposes. This is done by either: placing a non-inductive resistance in series with the starting winding. This does not produce an exact 90 degree phase difference, but is enough to start the motor; or connecting a condenser in series with the starting winding. This will provide a 90 degree phase difference. It is usual to fit the single phase motor with a centrifugal switch which will take the starting winding out of service as soon as the motor comes up to speed. If a condenser is provided, the starting winding and condenser are left in the circuit. The torque of the induction motor is dependent on the magnetic field strength (flux per pole), the rotor current and the rotor power factor. On starting with the rotor at standstill, the rotor frequency will be less than the stator or supply frequency. As a laminated iron frame surrounds the rotor conductors, there is considerable inductance inherent in the rotor circuit. Due to this large inductance, the reactance of the rotor is much higher than the resistance when the motor starts, subjecting the rotor current to a low power factor. The starting torque of the induction motor is therefore low. As the motor comes up to speed, the inductive effect decreases and the power factor improves. The resistance is constant and the torque improves to a maximum at approximately 80% nominal speed. Starting torque can be improved by adding resistance to the rotor circuit. Maximum torque is reached when the value of rotor reactance reaches the value of rotor resistance. Above this speed, the power factor decreases and the torque rapidly reduces to

become zero at synchronous speed. The induction motor will therefore never reach synchronous speed due to its inherent induction and loss factors.

Maintenance

of

Electric

Motors

Under normal operation, motors should be checked on a regular basis. The environment in which the motors are operating and the importance of the motors' continued operation should dictate the regularity of the checks to be made. If the environment is hostile (e.g. wet, dirty and hot), the checks should be at least on a daily basis. Visual

checks

should

include:

Cleanliness of the surroundings, ensuring that cooling vanes are clear of extraneous matter; Signs The The

of motor motor

Protection

grease frame is

or

and not

against

oil

leakage

from

bearing

plates

(if

accessible)

showing

signs

of

abnormal

the

weather,

sun,

dust,

heat,

the are

bearings;

not

unduly

hot;

vibration

or

noise;

etc

in

place;

is

There is no evident damage to incoming cables and or terminal boxes; and Air intakes and filters (if applicable) are not clogged. It is normal to carry out maintenance on motors when the item being driven is to be serviced. The maintenance on a motor can include the following: Disassemble

the

motor

in

a

workshop;

Clean the windings and the rotor. This may involve as little as dusting the parts down with a clean dry cloth. It can be as much as washing the parts including the windings thoroughly with a spray using water and a solvent. Under these circumstances, the stator and rotor will have to be placed in an oven or at least heated to thoroughly dry the insulation. After this process, the windings are given an appropriate insulation test; The insulation needs to be checked to ensure there has been no movement, no cracking or signs of deterioration. In some cases the insulation may need to be sprayed with an insulating varnish or even re-dipped; The

slot

wedges

should

be

checked

for

tightness

and

or

cracking;

Checks are to be made for any signs of abrasion on the rotor or the iron core of the stator; The

condition

of

the

fan

and

fan

cover

is

to

be

checked;

An insulation check is to be made on the stator prior to assembly and a further test given when the motor is being reinstalled; The condition of any internal connections is to be made and the connections into the terminal boxes. This includes the connections to any heaters, RTDs or thermocouples; The motor frame/housing is to be checked for any damage. This applies particularly to the feet of the motor;

The coupling of the motor is to be checked for wear and any sign of looseness during operation; Bearings must be checked for wear and deterioration. If there is any sign of deterioration, the bearings must be changed, ensuring that the correct type is used, and, on reassembly, the correct recommended grease or oil is used; Where possible, the motor should be given a no load run in the workshop prior to reinstallation in the field; On reinstallation in the field, it is normal to further check the state of the coupling or other drive mechanism associated with the motor; Terminations are checked and made in accordance with maintenance instructions for tightness and phasing; Care is taken to ensure rotation direction is correct prior to final connection to the driven equipment; and The cables being connected to the motor are checked for condition and to ensure they are connected in the correct sequence on the motor terminals. Electric

Motor

Standards

and

Tests

When purchasing an electric motor, the specification will list a number of Engineering Standards that the motor will have to meet. These will determine the details of the motor type, size, speed, winding insulation, cooling system and required temperature rise limits, mounting and the tests that the motor must be subjected to during manufacture. Other items will detail the starting characteristics, the vibration and noise levels, the inbuilt thermal protection devices required, use of anti-condensation heaters, requirement for special lubrication systems and bearings, use of porous plugs and type of painting. The protection required during transport and lifting facilities can also be specified. Generally the larger electric motors would be expected to comply with at least the following Australian Engineering Standards or their equivalent: -AS -AS -IEC -AS

1359 parts 1081 34-6: 1939 -

4; 50; 60; 69 & AS 1469 1991 Methods Protection Degree

Rotating Electrical Machines; Noise Levels; of Cooling; and Ratings of Enclosures.

The performance tests required during manufacture are specified to be in accordance with AS 1359 part 60 or its equivalent. It is normal to require that the first motor of a design be subjected to a more stringent set of tests than subsequent motors of the same design. This series of tests are called 'Type Tests'. The tests normally required for type tests are as follows: 1. Resistance of windings; 2. No-load losses and current; 3. Locked rotor test (see description below); 4. Temperature rise (see description below); 5. Power factor; 6. Efficiency; 7. Momentary overload; 8. Medium voltage insulation (as per AS 1359 Pt. 60); 9. Vibration (as per the requirements of AS 1359 Pt. 50 or equivalent); 10. Noise (as per AS 1081 with the level as described in AS 1469); and

11.

Determination

of

run-up

speed/torque

characteristic.

If the proposed manufacturer has previously produced this type of motor and has carried out the required type tests, less stringent test may be allowed. These less stringent tests are known as 'duplicate' tests and include the following: 1.

Resistance

2. 3.

No-load Locked

4. 5.

Medium

of losses

rotor

windings; and

(see

current;

description

voltage

below);

insulation;

Vibration.

Test Certificates are required for all tests and should show the results and description of all tests. Locked Rotor Tests are performed with the rotor locked to establish starting torques and starting currents. Starting torque can be evaluated using a torque arm which locks the rotor. The voltage is slowly increased until full load current circulates in the stator winding. It is preferable to carry out this test at 100% rated voltage but if this is not possible (due to the potential of damaging the motor and/or the limitations of the test facilities), the voltage can be raised in equal increments up to 50% rated voltage. A curve is then drawn through the plotted values and extrapolated to the 100% rated voltage value. Temperature Tests are conducted in two parts: 1. A no-load test which provides full voltage iron loss for the motor - the motor is uncoupled and run at full voltage until thermal equilibrium is reached; and 2. A full load test at full copper loss - the motor is coupled to a load as close to full load as the test facility will allow, the voltage reduced until full load current is reached and the motor run until thermal equilibrium is reached. A record of all readings, including temperature, voltage and current, are to be supplied as part of the test results. Note that, if anti-condensation heaters are fitted, then these are to be energised while the test is in progress. To satisfy the specified requirements, the motor temperature rise should not exceed that specified. The Insulation Class on the windings, the maximum Temperature Rise under full load conditions and the maximum ambient temperature are usually specified together. For example, the specification could require a motor whose windings are to have insulation of 'F' Class and a maximum temperature rise of 800° C when operating at an ambient temperature of 400° C. Terminals are usually described to suit the cabling requirement of size and direction of location of the cables on the side or top of the motor. Photographs STATOR OF 6.6 kV, 5.65 mw, 3 PHASE INDUCTION MOTOR

DIAGRAM

OF

A

LARGE

SQIRREL

CAGE

INDUCTION

MOTOR

This motor is similar to that in the above photo. Note the air cooler mounted on the top of the motor assembly.

Reference Web

site

Back

Electrical Cables

:

http://www.energy.qld.gov.au/electricity/infosite/index.htm

The electrical conductors strung between the poles and towers of overhead powerlines are usually bare wires without an insulation covering. An electrical cable is generally defined as being an insulated electrical conductor. This information sheet does not discuss uninsulated wires and focuses only on insulated cables. This information sheet is not meant to provide the reader with an in-depth knowledge of cable sizing, selection or methods of installation. It is meant to provide: 1. A general appreciation of the factors that should be generally considered when confronted with cabling information; and 2. A general understanding on what is involved in sizing and installing electrical cables. Theory The sole function of an electric cabling system is the transfer of electric power. The load to be supplied can vary from a small indicating lamp to a large generator transformer. Any cabling system must meet the following requirements: Safety 1. The cable must be able to withstand the voltage to which it will normally be subjected; 2. A cabling system must be installed in such a manner that it presents no danger to any person likely to come in contact with the cables; 3. The cables must not develop a hazard by induction, or through other means, in other equipment; and 4. The type of insulation must suit the type of installation and the environment. The temperature rating of the cable must be suited to ambient conditions. Also if the cable is to be installed where it is subject to direct sunlight, resistance to UV becomes a factor. If the cable is to be installed in an area where it is subject to flammable dust or liquid, additional factors must be considered. Conductor

sizing

The cables must be able to conduct power in a manner that will allow the connected device to operate to its full capacity. The cable must be able to conduct the full load current without causing any significant voltage drop at the terminals of the load connection. In considering this factor, the starting current requirements of the connected device has also to be taken into consideration and the cable must be able to withstand a fault on the system to which it is connected. Installation 1.

The

requirements installation

of

cables

Wiring

Rules;

2. The cable support must protect the cable from any reasonable chance of damage; and 3. The cable also must be protected from the detrimental effects of the environment in which the cable is installed. Cable

Construction

Conductors Copper and aluminium are the materials most used for conductors. Aluminium conductors of cross-sectional area less than 16 mm2 have proved difficult to terminate due to its tendency to 'cold flow'. Therefore below 16 mm2 , aluminium cables are not generally used Copper is a better conductor than aluminium. To achieve the same current flow as a copper conductor, an aluminium conductor would need to have 1.6 times the cross sectional area. Because of the equivalent aluminium conductor requiring a larger cross sectional area than that of copper the size of the cable is larger. This will result in greater space required to terminate an aluminium conductor than a copper conductor of equivalent current carrying capacity. The termination of an aluminium conductor requires great care to avoid problems due to the formation of aluminium oxide on the metal surface, which will interfere with the conductivity of the termination. Normally aluminium conductors cost less than copper conductors. Aluminium conductors have approximately half the specific gravity as copper conductors. The decision on which conductor to be used in the cable will require the above factors to be considered. The sizing of the conductors will require consideration of the information in the various standard specifications and the Wiring Rules. In most cases the main factors to be considered are: 1. Current required by the load being supplied. This includes the rated full load and the starting current (if applicable); 2.

Possible

short

circuit

withstand

currents;

3. Type of protection being provided for the circuit to which the cable is to be connected; 4. How the cable is to be installed (e.g. underground direct buried, underground in conduit, above ground, in cable ladders, etc.); and 5. The maximum ambient temperatures expected to be encountered by the cable. Insulation The type of insulation is influenced by a number of factors such as: 1.

The

maximum

operating

voltage

of

the

cable;

and

2. The temperature the cable has to withstand. This influences the quality and type of the insulation, coverings, sheathings, insulating sleeves on connections and sealing compounds used on the cable. The current carrying capacity for Mineral Insulated Metal Sheathed (MIMS) cables are based on an operating temperature of 100° C for the external surface of either bare metal sheathed or served cables. Higher continuous operating temperatures are permissible for bare metal sheathed cables, dependant upon factors such as:

1. 2.

The The

suitability location

of

of

the

cable

the

cable

away

terminations from

the

and

mountings;

combustible

materials;

3. The location of the cable away from areas where there is a reasonable chance of persons touching the exposed surface; and 4.

Other

environmental

and

external

influences.

The minimum temperature of use of MIMS cables will be dependent on the cable seal used and manufacturer's recommendations should be followed. Current carrying capacities determined in accordance with the AS/NZS 3008.1 series, do not take into account the effect of temperature rise on the terminals of electrical equipment. This can result in the temperature limits of the insulation of cables in the vicinity of the terminals exceeding the limits otherwise specified. In such cases reference should be made to warnings given in the electrical equipment Standards. For power cables, the colour coding of the cable cores is designated in the standards and the Wiring Rules. The cable cores (the conductors) are encased in an outer sheath to provide additional protection and insulation. Typical combinations of outer sheathing and protection are: 1. On 415 volt cables, the outer covering is a PVC sheath and the insulation described as PVCPVC; 2. Mechanical protection can be provided by placing steel or aluminium wire along the length of the cable between a plastic bedding material wrapped around the insulated cores and the outer sheath; 3. Higher voltage cables are generally subject to greater electrical stresses than 415 volt cables. This is due to them normally being connected to loads of higher fault ratings through circuit breakers rather than fuses. The circuit breakers do not restrict the fault current as much as fuses thereby placing the high voltage cable under greater stress. To assist in overcoming electrical stresses the high voltage cable is manufactured with conductor and core screens. The conductor core screen normally consists of an extruded layer of semi-conducting support tape, which prevents the extruded material being 'lost' between the conductor strands. The insulation screen may be either an extruded layer of semi-conducting material or a semi-conducting varnish applied direct to the insulation surface, with a semiconducting tape applied over it as protection against mechanical damage from the metallic screen. Where extruded screens are used, these should be 'cold strippable' to ease the process of terminating. A helically applied copper tape screen is provided over the semi-conducting insulation screen to carry both leakage and fault currents. A PVC inner sheath is provided over the copper tape to provide a bedding for the armour wires. This inner sheath also provides a secondary moisture barrier to prevent water reaching the primary insulation in the event of the outer sheath being damaged. The cable construction is completed by applying a layer of aluminium armour wires, these being non-ferrous to avoid eddy current heating. Finally an outer PVC sheath is applied. For 11 kV cables, the choice of insulation is usually between paper and polymeric. Paper insulated cables have lead or alloy sheaths and in consequence are heavier and more difficult

to terminate and install than plastic insulated cables. Plastic insulated cables can be made more fire retardant than paper insulated cables and are therefore preferred for power station applications. The preferred insulation for 11kV cables used in power stations is of the thermosetting type, i.e. XLPE or EPR. These give a conductor continuous operating temperature of 900C and a short circuit temperature of 2500C. Thermosetting materials give significant benefits since short circuit requirements and resultant temperature effects often dictate the size of 11 kV cables. Typical construction diagrams of several types of cables can be viewed at the bottom of this page: 1.

11

2.

3.3

3. 3.3 kV multi-core cable.

kV kV

single single

core core

cable; cable;

and

Installation The requirements for the installation of cables are generally those required to meet the Wiring Rules AS/NZS 3000. There are a number of precautions that must be considered for the longterm reliability of the cables: 1. Adequate support of the cables - Insufficient support of the cables can place strain on the cables causing premature electrical and or mechanical failure; 2. Selection of cables that are unsuitable for the ambient temperatures. As noted above, it is crucial that cables are selected of the right type and construction to suit the surrounding temperatures or they will fail under short circuit conditions, or the insulation will rapidly

deteriorate; 3. Change of original installed conditions can cause cable problems. For example, cables originally installed as open wiring and then covered with heat absorbent material can become overheated if operating at maximum rating and could cause a fire; 4. Bending radiuses should not be less than 15 times the cable diameter. This is particularly important for larger diameter cables and cables of medium voltage and above. Tables are available which recommend radii Vs cable diameter and type; 5. The withstand capability of cable fixing methods needs consideration. For example, if three single-phase cables are installed in trefoil, care must be taken to ensure to ensure that the clamps used are of sufficient mechanical strength to withstand the effects of a cable fault; 6. Where cables are installed in a location where they can be subject to mechanical damage, they must be given suitable mechanical protection; When terminating cables, correct terminating accessories must be used. If terminating lugs are used they must be: -Of the correct material to suit the conductor. This is particularly important if the conductor is aluminium; -The lugs must be of the correct size and type for the terminating procedure used and the cable size; -The terminating of the lugs must be carried out with tools of the correct type and size to suit the lug and cable size; -The terminal to which each cable core is to be fixed must be of a size suited to the size of the cable; -There should be sufficient space in the terminal box to maintain safe electrical clearances and allow the terminations to be carried out without undue bending of the cables; -Segregation of cables should be maintained to prevent undue heating and induction. This is most important in respect to the separation of power and control or communication cables. Bunching of cables in cable ladders or if passing through openings can result in cables becoming overheated and failing; and -Cables should be designated with cable numbers and the cores identified with wire numbers. This is important in assisting trouble shooting and reconnection at a later date. Maintenance Cable maintenance consists primarily of: 1. Checking its insulation resistance between phases and to earth; Checking the cable insulation for physical deterioration or damage, if possible this is done along the length of cables and its support system; 2. Checking of the terminations for signs of overheating and damage, and suitable tightness of the connections; and 3.

Checking

cable

installations

for

change

in

original

installation

conditions.

4. Care should be taken to ensure that mechanical protection is in place and in good condition where deemed necessary. Cable

Size

and

Type

Designation

When designating the required cable size and type, it is usual to nominate the cable's cross sectional area, the operating voltage and the insulation required. Examples of cable descriptions are given below: * 100 metres; 3.5 core + E copper; 16 mm2; 0.6/1.0 kV; This indicates that 100 metres of cable are required. The cable has 5 cores: Three 1.

cores One

2.

of

reduced One

cross diameter core

sectional core for

area for the

the

equal neutral earth

to

PVC-PVC.

16

mm2;

connection;

and

connection.

3. All these cores are of copper. The cable is to be suitable for voltages up to 1.0 kV. The insulation structure is to be PVC on the cores and a sheath of PVC as the outside cover. * 1000 metres; 12 core + E; 4 mm2; 0.6/1.0 kV; PVC/PVC - cores white with black numbers 1 to 12 with outer sheath black. This describes a control cable of 1000 metres in length, with 12 cores of copper conductor each of 4mm2 cross sectional area, insulated in white PVC and suitable for a voltage up to 1.0kV. Each core to be numbered in black inscription in order to provide ready core identification. The outer sheath is to be black in colour. An earth core is also required Reference Web

site

:

http://www.energy.qld.gov.au/electricity/infosite/index.htm

Back

Condenser and cooling system The condensers and cooling systems involved in condensing the exhaust steam from a steam turbine and transferring the waste heat away from the power station. The environmental effects of these systems will also be briefly discussed.

Condensers The function of the condenser is to condense exhaust steam from the steam turbine by rejecting the heat of vaporisation to the cooling water passing through the condenser. The temperature of the condensate determines the pressure in the steam/condensate side of the condenser. This pressure is called the turbine backpressure and is usually a vacuum. Decreasing the condensate temperature will result in a lowering of the turbine backpressure. Note: Within limits, decreasing the turbine backpressure will increase the thermal efficiency of the turbine. The condenser also has the following secondary functions: The condensate is collected in the condenser hot well, from which the condensate pumps take their suction; Provide

short-term

storage

of

condensate;

Provide a low-pressure collection point for condensate drains from other systems in the plant; and Provide

for

de-aeration

of

the

collected

condensate.

A typical power plant condenser has the following functional arrangement.

Large power plant condensers are usually 'shell and tube' heat exchangers. These types of condensers are also classified: As single pressure or multi-pressure, depending on whether the cooling water flow path creates one or more turbine backpressures; By the number of shells (which is dependent on the number of low-pressure turbine casings); and As either single pass or two-pass, depending on the number of parallel water flow paths through each shell.

Other

types

of

condensers

are:

Plate types consisting of a series of parallel plates that provide paths for the steam and the cooling water. Plate condensers are used mainly for smaller power plants; and Direct contact types where the cooling water is sprayed directly into the steam. This type of condenser is used in applications where the cooling water is the same quality as the steam condensate. Systems that have dry cooling (described in a following section) sometime use direct contact condensers. The parts of shell and tube condensers and plate condensers involved in the transfer of heat from the steam and condensate to the cooling water should have the following properties: Be resistant to corrosion from both the steam/condensate and the cooling water; Have a minimal resistance to the flow of heat from the steam/condensate through the material into the cooling water; and Provide mechanisms to remove organic and inorganic deposits on the heat transfer surfaces in contact with the cooling water. Types

of

Cooling

Systems

Some power stations have an open cycle (once through) cooling water system where water is taken from a body of water, such as a river, lake or ocean, pumped through the plant condenser and discharged back to the source. Inland plants away from large water bodies prefer to use closed cycle wet cooling system with wet cooling towers. Plants in remote dry areas without economic water supplies use closed cycle dry cooling systems that do not require water for cooling. Hybrid cooling systems are used in particular circumstances. The type of cooling system used is therefore heavily influenced by the location of the plant and on the availability of water suitable for cooling purposes. The selection process is also influenced by the cooling system's environmental impacts (refer to a following section for a brief discussion on this topic). Open

Cycle

Cooling

Systems

Open cycle (once through) cooling systems may be used for plants sited beside large water bodies such as the sea, lakes or large rivers that have the ability to dissipate the waste heat from the steam cycle. In the open system, water pumped from intakes on one side of the power plant passes through the condensers and is discharged at a point remote from the intake (to prevent recycling of the warm water discharge).

Open systems typically have high flow rates and relatively low temperature rises to limit the rise in temperature in the receiving waters. A typical 350 MW unit would have a flow of some 15000 to 20000 L/s. Lake cooling systems are a variant on a true open system as the temperature of the lake is increased from the circulation of the warm water. Environmental requirements have become more stringent on the allowable rise in temperature of the receiving waters, so that closed systems are now more commonly used in Australia. Open

Cycle

with

Helper

Cooling

Tower

In this system, cooling towers are installed on the discharge from open systems in order to remove part of the waste heat, so that the load on the receiving waters is contained within pre set limits. Systems with helper cooling towers are common in Germany and France where cooling supplies are drawn from the large rivers. The helper towers are used in the warmer summer periods to limit the temperature of the discharged cooling water, usually to less than 30º C.

Closed

Cycle

Wet

Cooling

Systems

In closed cycle wet cooling systems, the waste energy that is rejected by the turbine is transferred to the cooling water system via the condenser. The waste heat in the cooling water is then discharged to the atmosphere by the cooling tower. In the cooling tower, heat is removed from the falling water and transferred to the rising air by the evaporative cooling process. The falling water is broken up into droplets or films by the extended surfaces of the tower 'fill'. This 'fill' in the later Queensland towers is manufactured from plastic. Some of the warm water, typically 1 to 1.5% of the cooling water flow, is transferred to the rising air, and this is visible in the plume of water vapour above towers in times of high humidity. The evaporation rates of the Queensland 350 MW cooling systems are typically 1.8 litres of water per kWh of power generated.

The major components of a closed cycle wet cooling water system are: Cooling towers - two types are commonly used, concrete natural draught towers and mechanical draught towers; and Pumps and pipes. Natural

Draught

Towers

Concrete natural draught towers have a large concrete shell. The heat exchange 'fill' is in a layer above the cold air inlet at the base of the shell as shown in the tower sectional view. The warm air rises up through the shell by the 'chimney effect', creating the natural draught to provide airflow and operate the tower. These towers therefore do not require fans and have low operating costs. The cooling towers have two basic configurations for the directions of the flow of air in relation to the falling water through the tower fill: The counter-flow tower where the air travels vertically up through the fill (a diagram of this type of tower is shown below); and

The

cross-flow

tower

where

the

air

travels

horizontally

through

the

fill.

Natural draught towers are only economic in large sizes, which justifies the cost of the large concrete shell. Natural draught towers are the most common towers for large generating units in Europe, South Africa and Eastern USA. They are not used in the drier areas of Western USA, as their performance is better suited to cooler and more humid areas. This performance limitation also limits their use in Australia.

Mechanical

Draught

Cooling

Towers

In mechanical draught cooling towers, large axial flow fans provide the airflow. While fans have the disadvantage of requiring auxiliary power, typically 1.5 to 2.0 MW for a 420 MW unit, fans have the advantage of being able to provide lower water temperatures than natural draught towers, particularly on hot dry days.

Mechanical draught towers are used exclusively in central and western USA as their climate can vary from freezing to hot with low humidity, and the mechanical towers can provide a more controlled performance over this wide range of conditions. The most common materials used in large mechanical draught cooling towers are timber for the framing and plastic for the cladding and internals. Pumps

and

Pipes

in

a

Cooling

Water

System

Circulating water pumps supply cooling water at the required flow rate and pressure to the power plant condenser and the plant auxiliary cooling water heat exchangers. These pumps are required to operate economically and reliably over the life of the plant. The three types of pumps commonly used for circulating water service are 'vertical wet pit', 'horizontal dry pit' and 'vertical dry pit'. For once through systems, vertical wet pit pumps are in common usage. For re-circulating cooling systems, vertical wet pit and horizontal dry pit are used about equally, with occasional use of vertical dry pit pumps. Circulating water piping carries the cooling water from the circulating water pumps to the condenser and returns the water to the cooling tower or discharge structure. The large flow rates associated with circulating water systems typically require the use of large diameter piping in the range 900 mm to 2400 mm diameter. The design of the pipework must consider the environment internal to the pipe as well as the external environment. Pipe materials used include steel, fibre reinforced plastic and reinforced concrete. The large water requirement generally makes it uneconomical to use high quality water sources. The source of water for the plant generally depends on the plant's location. Coastal sites generally use seawater or brackish water as the circulating water source, either by pumping directly from the sea or extracting the water from the local bores. Water from many sources can contain high concentrations of corrosive contaminants. Any pipe materials considered must include measures to protect the pipe for the service life of the plant. For example, carbon steel pipes in seawater service require either an internal coating, or a cathodic protection system, or both. Concrete pipes may require a dense concrete mix to withstand chloride attack. These protective measures significantly increase the capital cost of an installation such that it can be as economical to install fibre reinforced plastic pipe to obtain the same service life. As existing water sources become strained and new water sources more scarce and expensive to develop, the quality of circulating water in future power plants is expected to decline further. This will increase the trend towards corrosion resistant piping materials. Closed

Cycle

Dry

Cooling

Systems

Dry cooling systems are used where there is insufficient water, or where the water is too expensive to be used in an evaporative system. Dry cooling systems are the least used systems as they have a much higher capital cost, higher operating temperatures, and lower efficiency than wet cooling systems. In the dry cooling system, heat transfer is by air to finned tubes. The minimum temperature that can be theoretically provided is that of the dry air, which can be regularly over 30º C and up to 40º C on typical summer afternoons in Queensland. Compare this to wet cooling towers, which cool towards the wet bulb temperature, which is typically 20º C on summer afternoons. The steam condensing pressures and temperatures of a dry cooled unit are significantly higher than a wet cooled unit, due to the low transfer rates of dry cooling and operation at the dry bulb temperature.

There are two basic types of dry cooling systems: 1. The direct dry cooling system; and 2. The indirect dry cooling system. Variations on the full dry and full wet systems are hybrid systems, which may be wet with some dry or dry with part wet. Direct

Dry

Cooling

System

In the direct dry system, the turbine exhaust steam is piped directly to the air-cooled, finned tube, condenser. The finned tubes are usually arranged in the form of an 'A' frame or delta over a forced draught fan to reduce the land area. The steam trunk main has a large diameter and is as short as possible to reduce pressure losses, so that the cooling banks are usually as close as possible to the turbine. The direct system is the most commonly used as it has the lowest capital cost, but significantly higher operating costs. The power required to operate the fans of this system is several times that required for wet towers, being typically 4 to 5 MW for a 420 MW unit.

Indirect

Dry

Cooling

System

Indirect dry cooling systems have a condenser and turbine exhaust system as for wet systems, with the circulating water being passed through finned tubes in a natural draught cooling tower. The water pipework allows the towers to be sited away from the station. A variation on this type of indirect system is the system that uses a direct contact condenser in place of the traditional tube type condenser. In the spray condenser, the water from the cooling cycle mixes with the boiler water. The maintenance of the water quality to suit all circuits is critical to the successful operation of the system.

Hybrid

Systems

There are two common hybrid systems, which have been developed to overcome some of the disadvantages of the full wet and full dry systems. Wet

with

Part

Dry

One of the problems with wet towers is that in cold and humid climates the towers plume, can create fog. In the part dry or plume abatement tower, a dry section above the wet zone provides some dry cooling to the exhaust plume to remove the condensing water vapour. These towers

are common in Germany and England where environmental problems with mechanical towers have arisen. Dry

with

Part

Wet

Problems with full dry towers are centred on loss of performance in hot weather. With the part wet towers, there is provision for water sprays to evaporatively cool the finned tubes for short periods of extreme temperature.

Environmental

Effects

of

Cooling

Systems

All the heat transferred from the exhaust steam to the cooling system eventually finds its way into the earth's atmosphere. In the once-through cooling water system, heat is removed from the steam turbine and transferred to the source body of water. The heat is then gradually transferred to the atmosphere by evaporation, convection and radiation. However, this waste heat transfer process may negatively affect the body of water buy increasing the temperature of the water. In a re-circulating cooling system, the cooling water carries waste heat removed from the steam turbine exhaust to the cooling tower, which rejects the heat directly to the atmosphere. Because of this direct path to the atmosphere, surrounding water bodies typically do not suffer adverse thermal effects. Some water is discharged from the cooling water system to maintain the concentration of chemicals in the cooling water below licensed limits. This water is often discharged to surrounding watercourses. In dry cooling systems, the waste heat is transferred directly to the atmosphere.

Types of energy storage General Electrical energy cannot be stored directly. Electrical energy can be indirectly stored by converting the electrical energy to some other form of energy ("storage" energy). When a supply of electrical energy is required, the storage energy is reconverted back to electrical energy. Large quantities of "storage" energy are difficult to store and reconvert

Energy storage technologies allow generation facilities to be more evenly utilised. Additional electrical energy generated during off-peak hours (i.e. when there is spare generating capacity and the cost of electricity is lower) can be converted and stored, then reconverted for use during peak hours (when electricity can be sold at a premium). In this type of application, energy storage concepts are economical when the costs of the energy storage system's construction, operation and maintenance are offset by the differential between peaking and base-load energy costs. Energy storage systems could also be justified if they are more economic than new generating capacity that would be used only during times of peak load. If economically competitive, storage systems may also be useful in combination with intermittent energy sources, a common trait of many renewable energy sources. The most common example of this is a system that utilises the excess electricity from a photovoltaic array to charge a battery during daylight hours, then draws off the battery during the night. Furthermore, storage systems may produce additional system advantages, such as spinning reserve, and area frequency and voltage control.The most widely used energy storage systems are pumped hydroelectric storage systems, batteries and compressed air storage systems. An energy storage system under development is based on regenerative fuel cell technology. Other developmental storage technologies include superconducting magnets and flywheels, but these will not be discussed here. Pumped Hydro-electric Storage In the pumped hydroelectric storage concept, such as that employed at Wivenhoe power station in Queensland, electrical energy from the electricity supply network is used to pump water from a lower level water storage to a higher level water storage. The electrical energy is therefore stored as the gravitational potential energy of the water in the upper storage. When required, the water in the upper storage is released and flows through a turbine on its way back to the lower storage. The potential energy in the water is reconverted into electrical energy again by the turbine / generator. Because of losses and inefficiencies in the elements of this system, the storage efficiency could be as low as 70%. Note: Storage efficiency = Electrical Energy Output / Total Electrical Energy Input

Battery

Storage

A battery storage system comprises the battery, dc/ac converter, charger, transformer, ac switchgear and a building to house these components. Battery energy storage systems have several advantages in addition to their load levelling capability. Because battery systems can be added to in small increments, they offer a means of matching load growth. Battery storage systems also have dynamic source benefits because they provide spinning reserve, area frequency and voltage control, and increased system reliability. Because of their small sizes and because battery storage systems are environmentally compatible in virtually any area, they can be located near the loads, with a consequential reduction in system losses. A disadvantage of battery storage systems is the high initial cost. Also, batteries using existing technologies require replacement every 8 to 10 years. Currently, the only battery available for large energy storage applications is the lead-acid battery, which uses lead electrodes and a sulphuric acid electrolyte. Advanced batteries such as the sodium-sulphur and the zinc-bromine battery are being developed for this application. Typical round trip (ac to ac) efficiencies are around 72%, made up of battery round trip (dc to ac) efficiencies of about 78% and power conditioning system efficiencies of about 94%. Examples

of

large

battery

installations

in

operation

are:

17 MW, 14.4 MWh in Germany; 21 MW, 14 MWh in Puerto Rico; and 10 MW, 40 MWh in USA. Note: A 17 MW, 14.4 MWh system would be able to produce 17 MW of instantaneous electrical power and provide a total of 14.4 MWh of electrical energy before requiring a recharge. Compressed

Air

Energy

Storage

Compressed Air Energy Storage (CAES) is a technology in which energy is stored in the form of compressed air in an underground cavern. Air is compressed during off-peak periods, stored in a cavern, and then used on demand during peak periods to generate power with a turbogenerator system. A

typical

CAES

unit

consists

of

five

basic

1. 2. 3. 4. 5.

Compressor

after-cooler);

Turbine

combustors);

train (compressor, inter-coolers and Motor Generator; expander train (including expanders and Recuperator; and Underground

components:

cavern

Electricity from the grid powers an electric motor, which drives an air compressor. The heat generated by the compression process is extracted by inter-stage cooling and after cooling and stored. Most of the electric energy from the grid is therefore stored as the pressure potential energy of the compressed air in the cavern, with the small amount extracted by the compressor coolers is stored as heat energy. When air is extracted from the cavern, it is first preheated in the recuperator. The recuperator reuses the energy extracted by the compressor coolers. The heated air is then mixed with small quantities of oil or gas, which is burned in the combustor. The hot gas from the combustor is expanded in the turbine to generate electricity. The combustor and turbine components are identical to those used in a conventional gas

turbine. However, instead of having to utilise some of its output to compress its air needed for combustion, all the power of the turbine can be used to generate electricity (its combustion air has already been compressed and stored). Less fuel is therefore required to generate the same quantity of electricity, resulting in a high thermal efficiency of the energy recovery stage. However, the overall cycle efficiency would be the ratio of the electrical energy generated to the total energy input (electrical energy from the grid + fuel energy). An important performance parameter for a CAES system is the charging ratio, which is defined as the ratio of the electrical energy required to charge the system versus the electrical energy generated during discharge (the number of kWh input in charging to produce 1 kWh output). A low charging ratio results in low off-peak electrical energy requirements during the charging cycle. Fast start-up is an advantage of CAES. A CAES plant can provide a start-up time of about 9 minutes for an emergency start, and about 12 minutes under normal conditions. By comparison, conventional combustion turbine peaking plants typically require 20 to 30 minutes for a normal start-up. A significant contributor to the cost of a CAES system is the construction of the underground cavern. Three types of geological formations used for compressed air storage are salt dome, aquifer and rock caverns. Two of these are illustrated below.

In addition to the geological formation classifications, there are two classes of cavern design concepts, constant volume (also called un-compensated) and constant pressure (also called compensated). In a constant volume cavern, the air pressure is allowed to drop as air is withdrawn from storage. In a constant pressure cavern, water from a surface reservoir displaces the compressed air to maintain a constant pressure in the cavern. The first commercial scale CAES plant in the world is the 290MW Huntorf, Germany, plant operated by Nordwest Deutsche Kraftwerke (NDK) since 1978. The Huntorf plant runs on a daily cycle in which it charges the air storage for 8 hours and provides generation for 2 hours. The plant has reported high availability of 86% and a starting reliability of 98%. The Huntorf plant has a salt cavern. The Alabama Electric Co-operative, Inc, in McIntosh, Alabama built the second commercial scale CAES plant. This plant has the maximum existing CAES cavern capacity of around 1.8

million cubic metres. It began operation in 1991 and provides 110 MW of power generation. The cavern for the McIntosh plant was mined from a salt dome by dissolving salt with fresh water. The cavern which is 70m in diameter, 305m tall and 460m below grade, supplies compressed air supporting generation of 100MW for 26 hours. The CAES plant has a full load nett plant heat rate of 4819 kJ/kWh (74.7 % thermal efficiency) with a charging ratio of 1.3. In addition to the NDK and the McIntosh CAES facilities, a 35MW CAES unit is under construction in Japan. Israel also has a 100MW CAES unit under construction, which uses an aquifer cavern for storage. The

Regenerative

Fuel

Cell

Energy

Storage

System

There are several methods to used chemical energy as the form of energy storage. One of the most commercially advanced of these is the regenerative fuel cell technology. The regenerative fuel cell, (sometimes known as redox flow cell technology) converts electrical energy into chemical potential energy by 'charging' two liquid electrolyte solutions. This chemical energy is converted back to electrical energy on discharge. Regenerative fuel cell systems store or release electrical energy by means of a reversible electrochemical reaction between two salt solutions (the electrolytes). The reaction occurs within an electrochemical cell. The cell has two compartments, one for each electrolyte, physically separated by an ion-exchange membrane. In contrast to most types of battery system, the electrolytes flow into and out of the cell through separate manifolds and are transformed electrochemically inside the cell. A commercial application of this system is the Regenesys™ system. This system has a high speed of response, supplies real and reactive power and is therefore suited to many different applications on a power system. The first Regenesys™ system is expected to be operational in 2002 at Little Barford. It will be used in conjunction with an adjacent combined cycle gas turbine power station to meet power requirements. The plant is designed to store 120 MWh of energy and discharge it at a nominal power rating of 15 MW.

Electricity

Generation

The electricity production process involves, in simple terms, the conversion of energy from a (primary) energy source to electrical energy.

There are many sources of energy that may be used and many types of energy conversion processes. It is important to distinguish between the primary energy source and the energy conversion processes because some primary energy sources can be used in several types of energy conversion processes. Conversely, some energy conversion processes can be used to convert several different sources of primary energy. Energy

Conversion

Processes

This section will look in particular at the energy conversion processes. These processes can be grouped in several ways, but the following grouping is used here: Conversion

of

Rotational

Energy

in

a

rotating

generator;

A rotating generator is the most common means of generating electricity. The various methods used to develop the rotational energy are discussed. Electricity Generation By Conversion of Rotational Energy Turbines - Steam Turbines , Hot Gas Turbines , Water Turbines , Wind Reciprocating Engines This section provides brief discussions on how rotational energy can be produced, with emphasis on turbines & reciprocating engines. The

Generator

Before turbines are discussed, it is pertinent to give some mention to the item of equipment fundamental to the conversion of rotating energy into electrical energy and is the final link in the energy conversion process which commenced with the energy source - the generator. The

major

generator

components

are

the

stator,

rotor

and

frame.

The stator, as the name implies, is the stationary portion of a generator and consists of a core and windings. The stator winding provides the generator output voltage and current and which is connected to the electric power system. The rotor of the generator is connected to the turbine, either directly or through a gearbox. It carries the rotating electric field into which direct current is introduced to produce the electromagnetic field and which is used to convert mechanical energy to electrical energy in the stator. The amount of direct current required is produced by an excitation system. The generator frame supports the weight of the stator and rotor and acts as a containment vessel for the coolant gas, which is usually hydrogen for large machines. Rotational

Energy

Rotational energy is the kinetic energy possessed by a spinning shaft. The shaft is made to spin by fluid energy imparted to components attached to it. In the case of a turbine, the components are blades which are driven by a fluid which may be air, water, gas or steam. In the case of a reciprocating engine, the components are pistons and connecting rods driven by internal combustion forces.

Turbines The main component of any turbine is the rotor. This is mechanically connected to the rotor of the generator which produces the electrical power output from the generator stator. All turbine rotors may be considered to be generically similar in that they all consist of a shaft with blades attached. The actual detailed design of the rotor is, however, quite different depending upon the properties of the fluid which drives it. The turbine rotors for steam, hot gas, water and wind turbines are very different with respect to size, blade shape and materials. For example, the rotor of a steam turbine has many blades and is much smaller in diameter than the rotor of a wind turbine which may only have three blades made from a quite different material. The operating duty is quite different also and depends upon the ease of starting and stopping the turbine, the time involved in reaching full load and the life consumed each start. Reciprocating Reciprocating

Engines engines

and

their

use

in

electricity

generation.

Conversion of Chemical Energy in a Fuel Cell or Battery; A battery converts chemical energy into electrical energy through an electrochemical process involving stored materials. Fuel Cells are devices that convert a fuel to electricity also by electrochemical means. Conversion of Electromagnetic Radiation (Solar Energy) in a Photo Voltaic cell (which produces an electrical potential when exposed to light) or by heating a working fluid in an electricity generating cycle; Conversion of Kinetic Energy by the MagnetoHydroDynamic (MHD) process in which the flow of a conducting plasma through a static magnetic field produces an electrical current.

Types of energy storage General Electrical energy cannot be stored directly. Electrical energy can be indirectly stored by converting the electrical energy to some other form of energy ("storage" energy). When a supply of electrical energy is required, the storage energy is reconverted back to electrical energy. Large quantities of "storage" energy are difficult to store and reconvert Energy storage technologies allow generation facilities to be more evenly utilised. Additional electrical energy generated during off-peak hours (i.e. when there is spare generating capacity and the cost of electricity is lower) can be converted and stored, then reconverted for use during peak hours (when electricity can be sold at a premium). In this type of application, energy storage concepts are economical when the costs of the energy storage system's construction, operation and maintenance are offset by the differential between peaking and base-load energy costs. Energy storage systems could also be justified if they are more economic than new generating capacity that would be used only during times of peak load. If economically competitive, storage systems may also be useful in combination with intermittent energy sources, a common trait of many renewable energy sources. The most common example of this is a system that utilises the excess electricity from a photovoltaic array to charge a battery during daylight hours, then draws off the battery during the night. Furthermore, storage systems may produce additional system advantages, such as spinning reserve, and area frequency and voltage control.The most widely used energy storage systems are pumped hydroelectric storage systems, batteries and compressed air storage systems. An energy storage system under development is based on regenerative fuel cell technology. Other developmental storage technologies include superconducting magnets and flywheels, but these will not be discussed here. Pumped Hydro-electric Storage In the pumped hydroelectric storage concept, such as that employed at Wivenhoe power station in Queensland, electrical energy from the electricity supply network is used to pump water from a lower level water storage to a higher level water storage. The electrical energy is therefore stored as the gravitational potential energy of the water in the upper storage. When required, the water in the upper storage is released and flows through a turbine on its way back to the lower storage. The potential energy in the water is reconverted into electrical energy again by the turbine / generator. Because of losses and inefficiencies in the elements of this system, the storage efficiency could be as low as 70%. Note: Storage efficiency = Electrical Energy Output / Total Electrical Energy Input

Battery

Storage

A battery storage system comprises the battery, dc/ac converter, charger, transformer, ac switchgear and a building to house these components. Battery energy storage systems have several advantages in addition to their load levelling capability. Because battery systems can be added to in small increments, they offer a means of matching load growth. Battery storage systems also have dynamic source benefits because they provide spinning reserve, area frequency and voltage control, and increased system reliability. Because of their small sizes and because battery storage systems are environmentally compatible in virtually any area, they can be located near the loads, with a consequential reduction in system losses. A disadvantage of battery storage systems is the high initial cost. Also, batteries using existing technologies require replacement every 8 to 10 years. Currently, the only battery available for large energy storage applications is the lead-acid battery, which uses lead electrodes and a sulphuric acid electrolyte. Advanced batteries such as the sodium-sulphur and the zinc-bromine battery are being developed for this application. Typical round trip (ac to ac) efficiencies are around 72%, made up of battery round trip (dc to ac) efficiencies of about 78% and power conditioning system efficiencies of about 94%. Examples

of

large

battery

installations

in

operation

are:

17 MW, 14.4 MWh in Germany; 21 MW, 14 MWh in Puerto Rico; and 10 MW, 40 MWh in USA. Note: A 17 MW, 14.4 MWh system would be able to produce 17 MW of instantaneous electrical power and provide a total of 14.4 MWh of electrical energy before requiring a recharge. Compressed

Air

Energy

Storage

Compressed Air Energy Storage (CAES) is a technology in which energy is stored in the form of compressed air in an underground cavern. Air is compressed during off-peak periods, stored in a cavern, and then used on demand during peak periods to generate power with a turbogenerator system.

A

typical

CAES

unit

consists

of

five

basic

1. 2. 3. 4. 5.

Compressor

after-cooler);

Turbine

combustors);

train (compressor, inter-coolers and Motor Generator; expander train (including expanders and Recuperator; and Underground

components:

cavern

Electricity from the grid powers an electric motor, which drives an air compressor. The heat generated by the compression process is extracted by inter-stage cooling and after cooling and stored. Most of the electric energy from the grid is therefore stored as the pressure potential energy of the compressed air in the cavern, with the small amount extracted by the compressor coolers is stored as heat energy. When air is extracted from the cavern, it is first preheated in the recuperator. The recuperator reuses the energy extracted by the compressor coolers. The heated air is then mixed with small quantities of oil or gas, which is burned in the combustor. The hot gas from the combustor is expanded in the turbine to generate electricity. The combustor and turbine components are identical to those used in a conventional gas turbine. However, instead of having to utilise some of its output to compress its air needed for combustion, all the power of the turbine can be used to generate electricity (its combustion air has already been compressed and stored). Less fuel is therefore required to generate the same quantity of electricity, resulting in a high thermal efficiency of the energy recovery stage. However, the overall cycle efficiency would be the ratio of the electrical energy generated to the total energy input (electrical energy from the grid + fuel energy). An important performance parameter for a CAES system is the charging ratio, which is defined as the ratio of the electrical energy required to charge the system versus the electrical energy generated during discharge (the number of kWh input in charging to produce 1 kWh output). A low charging ratio results in low off-peak electrical energy requirements during the charging cycle. Fast start-up is an advantage of CAES. A CAES plant can provide a start-up time of about 9 minutes for an emergency start, and about 12 minutes under normal conditions. By comparison, conventional combustion turbine peaking plants typically require 20 to 30 minutes for a normal start-up. A significant contributor to the cost of a CAES system is the construction of the underground cavern. Three types of geological formations used for compressed air storage are salt dome, aquifer and rock caverns. Two of these are illustrated below.

In addition to the geological formation classifications, there are two classes of cavern design concepts, constant volume (also called un-compensated) and constant pressure (also called compensated). In a constant volume cavern, the air pressure is allowed to drop as air is withdrawn from storage. In a constant pressure cavern, water from a surface reservoir displaces the compressed air to maintain a constant pressure in the cavern. The first commercial scale CAES plant in the world is the 290MW Huntorf, Germany, plant operated by Nordwest Deutsche Kraftwerke (NDK) since 1978. The Huntorf plant runs on a daily cycle in which it charges the air storage for 8 hours and provides generation for 2 hours. The plant has reported high availability of 86% and a starting reliability of 98%. The Huntorf plant has a salt cavern. The Alabama Electric Co-operative, Inc, in McIntosh, Alabama built the second commercial scale CAES plant. This plant has the maximum existing CAES cavern capacity of around 1.8 million cubic metres. It began operation in 1991 and provides 110 MW of power generation. The cavern for the McIntosh plant was mined from a salt dome by dissolving salt with fresh water. The cavern which is 70m in diameter, 305m tall and 460m below grade, supplies compressed air supporting generation of 100MW for 26 hours. The CAES plant has a full load nett plant heat rate of 4819 kJ/kWh (74.7 % thermal efficiency) with a charging ratio of 1.3. In addition to the NDK and the McIntosh CAES facilities, a 35MW CAES unit is under construction in Japan. Israel also has a 100MW CAES unit under construction, which uses an aquifer cavern for storage. The

Regenerative

Fuel

Cell

Energy

Storage

System

There are several methods to used chemical energy as the form of energy storage. One of the most commercially advanced of these is the regenerative fuel cell technology. The regenerative fuel cell, (sometimes known as redox flow cell technology) converts electrical energy into chemical potential energy by 'charging' two liquid electrolyte solutions. This chemical energy is converted back to electrical energy on discharge. Regenerative fuel cell systems store or release electrical energy by means of a reversible electrochemical reaction between two salt solutions (the electrolytes). The reaction occurs within an electrochemical cell. The cell has two compartments, one for each electrolyte, physically separated by an ion-exchange membrane. In contrast to most types of battery

system, the electrolytes flow into and out of the cell through separate manifolds and are transformed electrochemically inside the cell. A commercial application of this system is the Regenesys™ system. This system has a high speed of response, supplies real and reactive power and is therefore suited to many different applications on a power system. The first Regenesys™ system is expected to be operational in 2002 at Little Barford. It will be used in conjunction with an adjacent combined cycle gas turbine power station to meet power requirements. The plant is designed to store 120 MWh of energy and discharge it at a nominal power rating of 15 MW.

Electricity

Generation

The electricity production process involves, in simple terms, the conversion of energy from a (primary) energy source to electrical energy.

There are many sources of energy that may be used and many types of energy conversion processes. It is important to distinguish between the primary energy source and the energy conversion processes because some primary energy sources can be used in several types of energy conversion processes. Conversely, some energy conversion processes can be used to convert several different sources of primary energy. Energy

Conversion

Processes

This section will look in particular at the energy conversion processes. These processes can be grouped in several ways, but the following grouping is used here: Conversion

of

Rotational

Energy

in

a

rotating

generator;

A rotating generator is the most common means of generating electricity. The various methods

used

to

develop

the

rotational

energy

are

discussed.

Electricity Generation By Conversion of Rotational Energy Turbines - Steam Turbines , Hot Gas Turbines , Water Turbines , Wind Reciprocating Engines This section provides brief discussions on how rotational energy can be produced, with emphasis on turbines & reciprocating engines. The

Generator

Before turbines are discussed, it is pertinent to give some mention to the item of equipment fundamental to the conversion of rotating energy into electrical energy and is the final link in the energy conversion process which commenced with the energy source - the generator. The

major

generator

components

are

the

stator,

rotor

and

frame.

The stator, as the name implies, is the stationary portion of a generator and consists of a core and windings. The stator winding provides the generator output voltage and current and which is connected to the electric power system. The rotor of the generator is connected to the turbine, either directly or through a gearbox. It carries the rotating electric field into which direct current is introduced to produce the electromagnetic field and which is used to convert mechanical energy to electrical energy in the stator. The amount of direct current required is produced by an excitation system. The generator frame supports the weight of the stator and rotor and acts as a containment vessel for the coolant gas, which is usually hydrogen for large machines. Rotational

Energy

Rotational energy is the kinetic energy possessed by a spinning shaft. The shaft is made to spin by fluid energy imparted to components attached to it. In the case of a turbine, the components are blades which are driven by a fluid which may be air, water, gas or steam. In the case of a reciprocating engine, the components are pistons and connecting rods driven by internal combustion forces. Turbines The main component of any turbine is the rotor. This is mechanically connected to the rotor of the generator which produces the electrical power output from the generator stator. All turbine rotors may be considered to be generically similar in that they all consist of a shaft with blades attached. The actual detailed design of the rotor is, however, quite different depending upon the properties of the fluid which drives it. The turbine rotors for steam, hot gas, water and wind turbines are very different with respect to size, blade shape and materials. For example, the rotor of a steam turbine has many blades and is much smaller in diameter than the rotor of a wind turbine which may only have three blades made from a quite different material. The operating duty is quite different also and depends upon the ease of starting and stopping the turbine, the time involved in reaching full load and the life consumed each start. Reciprocating

Engines

Reciprocating Conversion

engines of

Chemical

and

their

Energy

use in

a

in Fuel

electricity Cell

or

generation. Battery;

A battery converts chemical energy into electrical energy through an electrochemical process involving stored materials. Fuel Cells are devices that convert a fuel to electricity also by electrochemical means. Conversion of Electromagnetic Radiation (Solar Energy) in a Photo Voltaic cell (which produces an electrical potential when exposed to light) or by heating a working fluid in an electricity generating cycle; Conversion of Kinetic Energy by the MagnetoHydroDynamic (MHD) process in which the flow of a conducting plasma through a static magnetic field produces an electrical current. Reference Web

site

http://www.energy.qld.gov.au/electricity/infosite/index.htm

Back

FAQ on electricity 1. Question Can you please explain the terms Volts, Watts and Kilowatt Hours?

:

Answer: The correct use and meaning of many electrical terms have, in many cases, become unclear through general use. These explanations attempt to show the correct usage of these terms. Electrical Terminology – VOLTS, WATTS & KILOWATT HOURS These are the electrical terms most frequently used, both at work and at home. For example you may (or may not) know: 1.

that

the

electricity

supplied

to

your

home

is

at

240

volts;

2. that transmission lines (the ones using large steel towers) operate at “high voltage”; 3. that you use light bulbs of different wattage (e.g. 75 watt or 60 watt) in your home; 4. that when you purchase a new electrical heater, one of your considerations is its wattage (e.g. 1,000 watts); and 5. that when you pay your quarterly electricity account, you are paying for the kilowatt-hours of electricity you have used in your home during that quarter. Electrical voltage can be thought of a measure of the electrical “pressure” applied to the electrical system to force the electricity to flow through the wires. A commonly used analogy is the water supply to your home where the water pressure forces the water through the pipes. Voltage is measured in volts (V). For convenience, higher voltages are identified in kilovolts (kV) where 1 kV = 1,000 V. In the “high voltage” parts of the electrical supply network, voltages of 11 kV, 33 kV, 66 kV, 110 kV and 275 kV are common. In the “low voltage” part of the electricity supply network, your home is supplied with 240 V electricity and, if you have a large air conditioner, with 415 V electricity. (More correctly, these should be called a 240 V single phase supply and a 415 V 3-phase supply. We will talk about “phases” in a later discussion.) Electrical wattage is a harder concept to visualise because it is, essentially, a measure of how fast electricity is being used – more correctly the “rate of use of electrical energy”. For example, a 2,000 W electrical heater would use electrical energy twice as fast as a 1,000 W heater. For convenience, the term kilowatt (kW) is often used instead of 1,000 watts. The wattage of the new 1,000 W electrical heater mentioned above therefore could be identified as 1 kW. At the other end of the electricity supply system, power stations are producing electricity to match the rate electricity is consumed by the end users (plus losses). The “rate at which electrical energy can be produced” determines the wattage of a power station. Usually, power stations are rated in terms of kilowatts (kW) or megawatts (MW) where 1 MW = 1,000 kW. Electrical energy is commonly measured in terms of kilowatt-hours (kWh) here 1 kWh = 1,000 watt-hours. As a simple example, the 1 kW electrical heater mentioned above would use 1 kWh of electrical energy during each hour it is switched on (i.e. electrical energy used in 1 hour = 1 kW x 1 hour = 1 kWh). Large amounts of electrical energy are measured in terms of megawatthours (MWh) where 1 MWh = 1,000 kWh, or gigawatt-hours (GWh) where 1 GWh = 1,000 MWh. Note: The “rate of use of electrical energy” (kW) in your home is continually varying. The meter in the switchboard of your home is designed to overcome this variability in its recording of your consumption of electrical energy (kWh). Your quarterly electricity account uses data from this

meter to identify the amount of electrical energy (kWh) you have used (and for which you have to pay) during the quarter.

2. Question: What is meant by the terms AC, DC and frequency? Answer: Electricity is said to flow when electrons in a suitable material (a “conductor”) are induced to move in a particular direction when a suitable force (an “electromotive force” or EMF) is applied to the material. This flow of electricity is called an electrical current and is measured in terms of amperes (usually shortened to amps). The EMF is measured in terms of volts. Direct Current (DC) electricity is the easiest to visualise because here the electrons (the electrical current) always move in the same direction. A battery is the EMF source most commonly used to produce small amounts of direct electrical current. For example, the common torch uses a battery as the EMF source. Electrical current flows from one side (e.g. the positive side) of the battery, through the element in the torch bulb (in the process heating the element to produce light) and completes the circuit back to the other side (e.g. the negative side) of the battery. Alternating Current (AC) electricity can be thought of as electricity that flows in one direction for a short period of time, then reverses its direction of flow for a short period of time, then reverses flow again, and again, and again…. Why does it do this? It’s because the EMF source is not constant and changes its polarity (positive and negative sides) in a regular manner. The rate at which the electrical current changes direction through a full cycle (flows in one direction, changes direction and flows in the opposite direction then changes back to the original direction) is called its “frequency”. In Australia and most of the rest of the world, AC electricity has a frequency of 50 cycles per second. America uses 60 cycles per second AC electricity. NOTE: An expansion of the above answer can be found in the Office of Energy’s new “Electricity Information” web site by clicking on the “What and How of Electricity” icon in the home page of the Office of Energy web site.

3. Question: Can you please tell me what is meant by Voltage, Current and Resistance? Answer: Voltage can be thought of as being the electrical "pressure" in an electrical circuit. It is important to understand that when the term voltage is used, it really means the voltage difference between two parts of an electrical circuit. For example, a 9 volt battery is a shorthand way of saying that the voltage across the terminals of the battery is 9 volts. When we talk about the 240 volt supply to our homes, we really mean that the voltage between the active and neutral wires is 240 volts and, because the neutral wire is kept at the voltage of the earth, the voltage between the active wire and earth is also 240 volts. Let us now consider a simple DC (direct current) circuit, for example a torch. This circuit consists of a battery, a switch and a light bulb connected by wires to form a loop from one terminal of the battery to the other terminal. When the switch is closed, an electrical current flows, the light bulb glows and produces light. What is happening in the light bulb? The simple answer is that the current flowing through the filament of the bulb heats the filament to a high enough temperature that it glows. But why does the filament heat up? This is where the term "resistance" come into the picture.

Put simply, every item inhibits the free flow of electrical current through it. The degree to which the current is inhibited is termed the "resistance" of the item. The resistance of an item results from the electrical properties of the material(s) that make up the item and the geometry (length, height and width) of the material(s) in the item. When a voltage (ie voltage difference) (V) is applied across an item that has a resistance (R), a current (I) will flow. The relationship between them is V = I x I x R. Note that, if the voltage (V) remains constant, then increasing the resistance (R) will decrease the current (I) and, conversely, decreasing the resistance (R) will increase the current (I). The V = I x I x R relationship applies to any part of the circuit. In our torch, there will be resistance in the following items and therefore an associated voltage drop (Note: for simplicity, we will call the metal connector pieces in the torch "wires"): between one battery terminal and the wire connected to along the wire; between the wire and the switch; through one part of the switch; across the contact surfaces of the switch; through the other part of the switch; between the switch and the next wire; and so on. It is important to realise that:

it;

the total voltage drop from one battery terminal through the circuit to the other battery terminal is made up of the sum of all these voltage drops; the current through all the items is the same; and the total resistance in the circuit is made up of the sum of all the resistances of the items. You are probably wondering why we've gone to such detail? Well, it is to highlight the large number of items, each with their own voltage drop, in this simple circuit. Now think about the enormously more complex electricity supply network and try to work out the huge number of items (each with their own voltage drop remember) involved in the supply of electricity to our homes! We think that the operators of the network do a pretty good job of keeping the voltages in every part of the network within the set limits. There is one further concept that is associated with voltage, current and resistance, and that is the loss of electrical energy when current flows through an item. The magnitude of this energy loss is given by the equation Energy Loss = I2R. This energy is absorbed by the item and the temperature of the item increases. This is why the filament in our torch bulb heats up when current passes through it! We can draw another conclusion from our torch example - the total energy loss in the circuit is made up of the sum of all the energy losses from each of the items.

4. Question: Could you please explain 'Earthing', and how safety switches work? Answer: The power points in your home have three sockets. Some of your appliances have three pin plugs while other appliances have only two pin plugs. Why? The answer lies in the concept of "earthing".

The top two sockets in a power point are connected to the active and neutral wires. The bottom socket is connected to a separate wire which is "earthed" (connected to the earth). The need for a separate earth wire can be explained by considering your toaster. A toaster usually has a metal enclosure. Because metals are electrical conductors (ie allow electricity to pass through them), this metal enclosure is "earthed" so that, if the active wire came in contact with the metal enclosure, the electricity would pass to earth. An appliance that requires its enclosure to be earthed must therefore have a three pin plug (active, neutral and earth). An increasing number of appliances are enclosed in materials that prevent the flow of electricity through them (ie they are electrical insulators). Because these insulated enclosures do not need to be earthed, the appliances may have plugs with only two pins (active and neutral). If, for any reason, the active wire comes in contact with the earth wire, the electrical current (flow of electricity) passing through the active wire to earth through the earth wire could be large enough to activate the overload protection device in the active wire's circuit. A circuit is the term used to describe an active wire that can be isolated from within your home's switchboard. For example, your electric hot water system and your electric stove usually have their own circuits. Your power points may all be connected to the one "power" circuit or they could be divided into two or more separate power circuits. Your lights could also be supplied from one or more "lighting" circuits. Each circuit in your home should be protected against overload by a device that senses the current passing through the active wire of the circuit and isolates the circuit when the current is too high. The overload protection device could be a fuse (a special type of wire that melts if the current passing through it is more that its rated current). More usually now, the overload protection device could be a type of switch that operates on current overload. We saw above that the overload protection device in a circuit could operate if the active wire contacted the earth wire. A current overload could also occur if the active wire came into direct contact with the neutral wire. Lets now look at what happens when you become part of an electric circuit. If you contact an active wire and you are electrically connected to the earth, current will pass through you to earth. If your connection to earth is poor (eg you are standing on a carpet or a wood chair), you may be lucky enough to escape with only a mild shock. If not, the size and duration of the electric current passing through you to ground may have more drastic consequences! A current could also flow through you if you contact both the active and neutral wires. In both these cases, the current passing through you may be high enough to activate the circuit's overload protection device and turn off the supply to that circuit - but by the time that happened, it may have been too late so save you. What is needed is a device that would sense that something is wrong and switch off the supply of electricity before you are injured. One such device is the "safety switch". This device is also called an "earth leakage circuit breaker" because of the way it operates. To understand how it operates, we need to realise that, in a normal circuit, the current flowing in the active wire of the circuit is exactly the same as the current in the neutral wire of the circuit. If a fault occurs in the circuit and some current flows to earth, the current in the neutral wire would be less than the current in the active wire. A safety switch senses this imbalance in currents and isolates the circuit if the imbalance becomes greater than a preset value. Because safety switches can sense and react to this type of situation much quicker (and at a smaller current) than a normal overload protection device, severe electrical shocks and electrocutions are prevented.

However, it must be realised that safety switches cannot protect you if you come in contact with both the active and neutral wires because in this case current does not flow to earth and there is no imbalance in the active and neutral currents.

5. Question: What is meant by the term 'Phases'? Answer: Alternating Current (AC) electricity changes its direction of flow in a regular, cyclic manner. Because electrical current flows in response to an applied voltage, the voltage of the AC supply must also have been changing polarity from positive to negative and back again at the same frequency as the alternating current. The distribution line supplying your home may be single phase and have only two wires strung between the poles (we will use the overhead power lines as examples because they can be easily seen). However, the distribution line may be made up of 4 lines. What are the others? The other lines carry the currents from two other electrical circuits, making a total of three circuits. Because these circuits are electrically linked (see below), they are called phases. The reason why there are only 4 lines is because the 3 phases have a common neutral line (i.e. 3 active lines and 1 common neutral line). In this “low voltage” part of the distribution system, the voltage between the active and neutral wires is 240 volts (in Australia). The neutral wire is kept at the same electrical potential as the earth, so that the voltage between the active and earth is also 240 volts. The voltage between the phases in the low voltage distribution system is 415 volts (in Australia). A 415 volt 3-phase supply is able to deliver more energy than a 240 volt single phase supply. A 3-phase supply to a home would normally be required only for large electrical loads, such as a large air conditioner, this can be identified by the larger than normal plugs. 3 phase supplies are common in industrial areas and shopping centres. As we travel back up the electrical network, the voltage increases and the neutral disappears! Why? The explanation can be found in the Office of Energy’s new “Electricity Information” web site by clicking on the “What and How of Electricity” icon in the home page of the Office of Energy web site and going to the “Introduction” section. This section also contains additional information on phases and on a type of electricity supply system that uses a single wire - the Single Wire Earth Return (SWER) system.

Reference Web

site

:

http://www.energy.qld.gov.au/electricity/infosite/index.htm

Flue gas cleaning This information sheet explores the options available to reduce the concentrations of pollutants in the flue gas being discharged from a thermal power station. Except if explicitly mentioned otherwise, discussions in this section will be directed to coal fired power stations. These pollutants usually have some form of discharge licence limits imposed on their concentrations. These licence limits are usually: 1. Concentration limits at the point of discharge which have been set regardless of the amount of the pollutant or the location of the point of discharge; and/or

2. Concentration limits at one or more points away from the point of discharge. Equipment can be installed to clean the flue gas so that it complies with the discharge point concentration limits. This equipment is discussed below. Compliance with concentration limits away from the point of discharge usually is brought about by economic and performance optimisations of several factors: 1. The height of the chimneys - height is usually an advantage, but more costly; 2. The buoyancy of the flue gas leaving the chimneys - hotter gas has more buoyancy (i.e. has a lower density), but may reduce the thermal efficiency of the generating plant; 3. The discharge velocity of the gas from the chimneys - higher velocities are an advantage, but may require additional fan power; and 4. The location of the chimneys in relation to each other, the power station's buildings and cooling towers, buildings outside of the power station boundaries and weather conditions, particularly the strength and direction of the wind. These factors will not be discussed further in this information sheet, except where they (mainly buoyancy and discharge velocity) are influenced by the flue gas cleaning equipment. The equipment to clean the flue gas can be divided into several groups: 1. Equipment to remove solid particles (generally called "particulates") - the two main types of equipment for this duty are electrostatic precipitators and fabric filters; 2. Equipment to remove gaseous impurities such as oxides of sulphur and oxides of nitrogen; and 3. Equipment to remove other gases for which there are not licence limits but which could have economic implications, such as carbon dioxide if carbon taxes or carbon trading are implemented. Reference Web site : http://www.energy.qld.gov.au/electricity/infosite/index.htm Back

Geothermal Power Plants This unique system taps the natural supplies of heat energy that have accumulated inside the earth. Thus, geothermal power is generally considered to be "earth friendly".

Design & Construction Features HIGHLY

EFFICIENT

AND

STRONG

STEAM

PATH

The steam path is designed on the basis of massive results of tests and studies and by means of the most advanced computer techniques so that the maximum stage efficiency can be obtained. The impulse type design, in which the diaphragm type nozzles are combined with strong cross section blades, is strong enough against foreign matter. STABLE

AND

LOW-FATT

ROTOR

Because the turbine rotor operates in erosive geothermal steam, it is made of highly corrosionresistant Cr- Mo-V steel. This rotor is a low-FATT type, which has been used for many high and intermediate-pressure united rotors in fossil fuel powered steam turbines. EFFECTIVE

SEPARATION

OF

MOISTURE

AND

DUST

Moisture and dust in the steam path are satisfactorily shaked off by centrifugal force toward the outside wall. The wall is covered with a stainless steel impingement shield to prevent erosion. SIMPLE

SINGLE-SHEEL

CONSTRUCTION

Simple single-shell construction without an internal casing considerably simplifies maintenance. Furthermore, careful consideration is given to minute details including the dust-and-drain prevention and disposal structures, corrosion-resisting protector, and the inspection manhole. HIGHLY

RELIABLE

LONG

BLADE

SERIES

12Cr steel blades backed up by close calculation and ample experience are adopted. Special care is given to determine blade width and blade tip shroud band construction.

Geothermal Turbine Sectional View 110MW

Geothermal

Steam

Turbine

The geothermal steam turbine is, so to speak, a thermal turbine in which mother nature plays the role of a boiler. However, since geothermal steam contains up to several percent of gaseous impurities, geothermal steam turbines require much more technical consideration than do standard thermal steam turbines. Issues involved include such phenomena as corrosion of turbine component parts and the accumulation of and erosion by solid substances in the steam paths. Left: 110MW Geothermal Turbine

Above: 110MW geothermal turbine under shop assembly Since the steam does not contain hot water and its maximum superheating degree is 9°C, no flashing was required. Consequently, direct condensing system utilizing natural steam spurting out from production wells was employed for the power plant. Superheating steam is changed into wet steam from the turbine second stage and is expanded up to 102 mmHg absolute, 52°C. When contacting and mixed with sprayed cooling water in the condenser, which is directly connected to the turbine, the wet steam becomes condensed water at 49°C. This condensed water is pumped to the cooling tower by a condensate pump and is cooled to 27°C. Cooled water is used as condenser cooling water, oil cooling water, etc. This cooling water is delivered to the condenser by utilizing potential energy between the cooling tower and the condenser rather than by pumping, and also by vacuum conditions in the condenser interior. Since the

condensed water is recycled in this system, no water replenishment is required from the exterior. Overflowing condensed water is fed back to the underground through injection wells. Noncondensed gases contained in the steam are continuously ejected from the condenser by using steam ejectors. Steam flowing through the ejectors amounts to approximately 34 tons per hour, about 4% of the total steam. Since 4,000kW power is consumed for driving the condensate pump and the cooling fans and other pumps, the net power output at high tension side of step-up transformer is 106,000kW.

Geothermal power plant unit capacity has been increasing in recent years , supported by technological innovation and driven by the economics of larger installations. At the same time, demand for small sized geothermal power plant has also expanded. Small sized geothermal power plant is generally used for the following purposes: • • • • •

An experimental unit as a pilot plant for a larger size installation Meet the needs of electricity demand in limited area Power source during construction Auxiliary or emergency power source for main geothermal generating plant Simplification steam transmission lines as a well-head unit, because geothermal wells are scattered in geothermal field

Toshiba has a developed a standardised series of portable small size geothermal turbine and generator sets, suitable toa range of applications. This portable type turbine and generator set is supported by our extensive experience with geothermal units. Special consideration is given to easy transportation, easy operation including start and stop, maintainability, high efficiency and high reliability. The Toshiba portable type turbine and generator set is completely assembled on a common base then shipped to the site. Consequently, installation and adjustment work at site can be minimised. Toshiba is always working to satisfy customer needs in the geothermal power generation field, based on our high engineering capability and extensive experience. Frame

Type-TPO

Type-TPB

Type-TPC

Turbine type

Back pressure/

Back pressure

Condensing

condensing Type

Single stage curtis with reduction gear

Multistage rateau with reduction gear

Multistage rateau with reduction gear

Power range

500-2000kW

2000-9000kW

2000-9000kW

Steam condition throttle press

3-10 kg/cm2 g

3-10 kg/cm2 g

3-10 kg/cm2 g

Speed

50Hz 6200/1500RPM 60Hz 7400/1800RPM

50Hz 6000/1500RPM 60Hz 6000/1800RPM

60Hz 5000/1800RPM 50Hz 5000/1500RPM

No of stage

1 stage

Max. 6 stages

Max. 6 stages

Oil cooler

Water or air

Water or air

Water or air

Application

Power source for construction and start for blackout

Power generation and power Power generation and power for auxiliaries for auxiliaries

High

efficiency

and

high

reliability

Toshiba portable steam turbines are of impulse type, multistage nozzles and blades and low steam consumption. The impulse design features sturdy and simple construction. This construction minimized damages from foreign materials and less susceptible to deterioration of performance due to increased leakage caused by packing rules. The nozzle diaphragm consists of web with an inner and an outer ring of sufficient strength, and the nozzle partitions are rugged and efficient cross section. The blades also have a rugged and efficient cross section, and are strongly fixed to a solid type rotor wheel. Portable Turbine Generator Main

Flow

Diagram

Typical main flow diagram of the portable turbine generator with low level type condenser and water cooled oil cooler is as follows.

(Click to Enlarge)

Toshiba's portable turbine generator's versatility is suited to a wide range of applications, operation patterns and site conditions. For example, oil cooler can be selected from two typesair cooled oil cooler and water cooled oil cooler-depending on site suitability. Mechanical Outline Outline

Weight

Dimen sion

T Y P E · T P C

Turbine: 17.0 Reduction Gear: 2.5 Generator: 13.3 Others: 12.5 Total: 45.3

2.7W 7.3L 2.6H (m)

(ton)

T Y P E · T P B

Turbine: 15.0 Reduction Gear: 2.5 Generator: 13.0 Others: 12.3 Total: 42.8

2.7W 7.0L 3.3H (m)

(ton)

Easy

transportation

and

construction

Toshiba's portable turbine generator unit's compactness ensures simplicity of construction and ease of handling. The equipment can thus be installed and relocated at various sites and operated successfully. in addition, since the turbine, generator and their necessary auxiliary equipmentare all skid mounted in Toshiba's workshopso transportation to site is quite simple. No

power

source

for

start

Toshiba portable turbine generator can be started without any auxiliary power source except a battery for instrumentation. The unit has a steam turbine driven oil pump and mechanicalhydraulic control system. Therefore the unit can be installed without need for any electric network in the area. Reference Web http://www.atals.com/newtic/geo_home.htm Back

site

:

GAS

TURBINE

Introduction

to

Gas

Turbines

Gas turbines have been used for electricity generation for many years. In the past, their use has been generally limited to generating electricity in periods of peak electricity demand. Gas turbines are ideal for this application as they can be started and stopped quickly enabling them to be brought into service as required to meet energy demand peaks. However, their previously small unit sizes and their low thermal efficiency restricted the opportunities for their wider use for electricity generation. There are two basic types of gas turbines - aeroderivative and industrial. As their name suggests, aeroderivative units are aircraft jet engines modified to drive electrical generators. These units have a maximum output of 40 MW. Aeroderivative units can produce full power within three minutes after start up. They are not suitable for base load operation. Industrial gas turbines range in sizes up to more than 260 MW. Depending on size, start up can take from 10 to 40 minutes to produce full output. Over the last ten years there have been major improvements to the sizes and efficiencies of these gas turbines such that they are now considered an attractive option for base-load electricity generation. Industrial gas turbines have a lower capital cost per kilowatt installed than aeroderivative units and, because of their more robust construction, are suitable for base load operation. How

does

a

Gas

Turbine

Work?

Gas turbines use the hot gas produced by burning a fuel to drive a turbine. They are also called combustion turbines or combustion gas turbines. The main components of a gas turbine are an air compressor, several combustors (also called burners) and a turbine. The air compressor compresses the inlet air (raises its pressure). Fuel is mixed with the high pressure air in burners and burnt in special chambers called combustors. The hot pressurised gas coming out of the combustors is at very high temperature (up to 1350° C). This gas then passes through a turbine, giving the turbine energy to spin and do work, such as turn a generator to produce electricity. As the turbine is connected to its compressor, the compressor uses some (about 60%) of the turbine's energy. Because some of its heat and pressure energy has been transferred to the turbine, the gas is cooler and at a lower pressure when it leaves the turbine. It is then either discharged up a chimney (often called a stack) or is directed to a special type of boiler, called a Heat Recovery Steam Generator (HRSG), where most of the remaining heat energy in the gas is used to produce steam.

The attached cross section of a typical large gas turbine and photo of a similar large gas turbine with its top half casing removed, show these major components. Air

Compressor

The air compressors used in gas turbines are made up of several rows of blades (similar to the blades on a household fan). Each row of blades compress and push the air onto the next row of blades. As the air becomes more and more compressed, the sizes of the blades become smaller from row to row. The row of largest blades can be seen at the left end of the compressor in the photo above, with the smallest blades to the right (the direction of air flow is from left to right). Note: A row of blades fixed to the outer casing of the compressor is also located after each row of moving blades. Filters are used to remove impurities from the inlet air. However, as they can never completely eliminate all impurities, "washing" of the compressor blades must be carried out whenever blade fouling becomes too severe. This washing can be carried out on line (with the gas turbine operating) or when the compressor is stopped. Demineralised water and detergent are commonly used for washing. Erosion of the blades can be caused by hard particles in the air entering the compressor. Inspections for fouling and erosion are usually carried out at defined intervals of operating time. This type of air compressor can change its capacity (mass of air sucked through the air compressor) only by changing its speed of rotation. However, when the gas turbine is used to generate electricity, the speed of rotation of the generator, gas turbine and air compressor must remain constant (3000 rpm in Australia). The mass of air being compressed therefore remains constant regardless of the amount of air required for combustion of the fuel at partial loads. The energy used to compress this excess air accounts for most of the reduction in efficiency of a gas turbine at partial loads. Fuel Gas

turbines

can

operate

on

a

variety

of

gaseous

or

liquid

fuels,

including:

Liquid or gaseous fossil fuel such as crude oil, heavy fuel oil, natural gas, methane, distillate and "jet fuel" (a type of kerosene used in aircraft jet engines); Gas produced by gasification processes using, for example, coal, municipal waste and biomass; and Gas produced as a by-product of an industrial process such as oil refining.

When natural gas is used, power output and thermal efficiency of the gas turbines are higher than when using most liquid fuels. The fuel must be free of chemical impurities and solids as these either stick to the blades of the turbine or damage the components in the turbine that operate at high temperature. The fuels used in gas turbines power generation plants are often relatively more expensive and in smaller quantities than those required by power generation plants using other fuels (such as coal). Inlet

Air

The air coming into the compressor of a gas turbine must be cleaned of impurities (such as dust and smoke) which could erode or stick to the blades of the compressor or turbine, reducing the power and efficiency of the gas turbine. Dry filters or water baths are usually used to carry out this cleaning. The power and efficiency ratings of a gas turbine are usually based on the inlet air being at ISO conditions of 15° C and 65% relative humidity. If the inlet air is hotter and drier than ISO conditions, the power of the gas turbine decreases. This effect can be reduced by cooling the air (by equipment similar to air conditioners) or, more usually, by passing the air through an evaporative cooler (the air evaporates droplets of water, thus cooling the air). The inlet air is usually passed through silencers before it enters the compressor. Burners

and

Combustors

The compressed air and fuel is mixed and metered in special equipment called burners. The burners are attached to chambers called combustors. The fuel & air mixture is ignited close to the exit tip of the burners, then allowed to fully burn in the combustors. The temperature of the gas in the combustors and entering the turbine can reach up to 1350° C. Special heat resistant materials (such as ceramics) are used to line the inside walls of the combustors. The area between the combustors and the turbine are also lined. Water or steam can be injected into the combustors to reduce the concentration of NOx (oxides of nitrogen) in the exhaust gas (by reducing the temperature of the flame). Special burners (usually called "dry low NOx burners") are used to reduce the concentration of NOx in the exhaust gas to less than 25 ppm at full load, without the use of water or steam injection. These dry low NOx burners usually cannot operate effectively below about 60% load. At this point, another type of burner takes over and allows the fuel to be burnt stably down to low loads. These "low load" burners produce significantly higher concentrations of NOx (over 100 ppm). Some burners incorporate both types of burner into the one arrangement (called "hybrid" burners). Note: the values of NOx concentrations and loads depend on the design of the equipment and on the fuel used. When a gas turbine starts, the combustor quickly heats up. When the gas turbine shuts down, the combustor cools. This rapid heating and cooling produces stresses in the combustor and can cause cracking, particularly in the heat resistant lining material. The combustors must be inspected for cracks after a certain number of starts. Turbine The turbine (also called the "power" turbine) consists of several rows of blades (the "moving" blades) that are fastened to the rotating shaft of the turbine. A row of "fixed" blades is located after each row of the "moving" blades. These fixed blades are attached to the casing of the turbine and do not rotate. As the hot gas from the combustors passes through the moving and fixed blades of the turbine,

energy is transferred from the hot gas to the turbine, causing it to rotate. This energy transfer reduces the pressure of the gas and causes the gas to become cooler as it passes through the turbine. The blades of the turbine become larger from row to row to accommodate the expansion of the gas as its pressure reduces. The smallest row of blades can be seen at the left end of the turbine in the photo of the gas turbine with its top half casing removed, with the largest blades to the right (the direction of gas flow is from left to right). The moving blades in the turbine are subjected to extreme temperature (from the hot gas exiting the combustors) and stress (from the combination of their rotation and the pressure of the hot gas). The efficiency of the gas turbine improves if the hot gas temperature rises. New materials and techniques used to manufacture the turbine blades have resulted in a significant increase in operating temperatures. Currently, turbine blades are made from exotic alloys that retain their strength at the high temperatures experienced in the turbine. Ceramic blades offer the possibility of still higher operating temperatures. However, materials to withstand the higher temperatures are usually more expensive than those that can withstand lower temperatures. The materials for the turbine blades (and other components of the turbine) are therefore selected to give a balance between hot gas temperature (and efficiency) and material selection (and cost). Research into better (and cheaper) materials for these high temperature, high stress duties is ongoing. Turbine blades can be manufactured with passages inside the blades that allow air to pass through the blades to keep them cool. The compressor section of the gas turbine provides this cooling air. This allows the blades to operate in combustion temperatures that would otherwise be too hot for the material of the blades. At these high operating temperatures, hard particles and chemical impurities in the air and fuel (even at extremely low levels) can damage the blades of the turbine, thus reducing their effectiveness. The ability of the gas turbine to do work and the efficiency of the gas turbine are consequently reduced. Some of this reduction can be regained by maintenance of the gas turbine. The type and cleanliness of the air and fuel used therefore has a major impact on the amount of maintenance performed on the gas turbine. Various coatings for turbine blades have been developed as another way to minimise this high temperature damage to the blades. The hot components of the turbine, particularly the blades, are also subject to "creep" failure. Metals at high temperature & high stress gradually change their metallurgical properties and plastically deform ("creeps"). This deformation could result in the moving parts touching the fixed parts with possible catastrophic results. The turbine components most subject to conditions causing creep are regularly inspected and tested. Exhaust

Gases

The temperature of the exhaust gas from the gas turbine is typically in the range of 500°C to 640°C, depending on the design of the gas turbine and the fuel used. The heat energy in this gas can be extracted in a Heat Recovery Steam Generator (HRSG) to produce steam that can be used to produce electricity (Combined Cycle generating plant) or used for process heating. If the exhaust gas is not passed to a HRSG, it is ducted through a silencer and then discharged up a stack. The exhaust gas is usually visually clear and free of particles. Refer to "emissions" for information on the chemical compositions of the exhaust gas. Emissions The main chemical emissions from a gas turbine are dependent on the type of fuel used.

However,

some

generalisations

can

be

made.

NOx (oxides of nitrogen) can be controlled either by injecting water or steam into the combustors or by using special dry low NOx burners. Further details of these are given in the "burners and combustors" section above. SOx (oxides of sulphur) are usually not a problem as most fuels used in gas turbines have low sulphur contents. The concentration of CO2 (carbon dioxide) in the exhaust gas is dependent on the carbon content of the fuel used. The amount of CO2 produced per unit of electrical energy is also highly dependent on the thermal efficiency of the gas turbine. Power

Output

Gas turbine output power values are usually given for ISO conditions of 15° C, 60% relative humidity and an atmospheric pressure equivalent to average sea level conditions. Variations in these conditions during the operation of the gas turbine will result in changes to the power output of the gas turbine as indicated below. In general, the power output from the gas turbine is influenced by: 1. The energy used by the air compressor - if less energy is used to compress the air, more energy is available at the output shaft; 2. The temperature of the hot gas leaving the combustors - increased temperature generally results in increased power output; 3. The temperature of the exhaust gas - reduced temperature generally results in increased power output; 4. The mass flow through the gas turbine - in general, higher mass flows result in higher power output; 5. The drop in pressure across the inlet air filters, silencers and ducts - a decrease in pressure loss increases power output; 6. The drop in pressure across the exhaust gas silencers, ducts and stack - a decrease in pressure loss increases power output; 7. Increasing the pressure of the air entering or leaving the compressor - an increase in pressure increases power output. Various methods that have been used to achieve an increase in power output include: 1. Using the exhaust gas to heat the air from the compressor (mainly used in cold weather conditions); 2. Divide the compressor into two parts and cool the air between the two parts; 3. Divide the turbine into two parts and reheat the gas between the two parts by passing the gas through additional burners and combustors located between the two parts; 4. Cooling the inlet air mainly used in hot weather conditions; 5. Reducing the humidity of the inlet air; 6. Increasing the pressure of the air at the discharge of the air compressor; 7. Inject steam or water into the combustors or turbine; 8. Wash or otherwise clean the fouling from the blades of the air compressor and turbine at regular intervals; and 9. Combinations of the above methods. However, all these methods increase costs and some decrease the thermal efficiency of the gas turbine. The methods used are therefore a compromise between cost, power and efficiency for each application. Thermal

Efficiency

The thermal efficiency of a gas turbine is the proportion of the energy in the fuel that is converted to mechanical energy in the output shaft. Gas turbine efficiency values are usually given for ISO conditions of 15° C (dry bulb), 60% relative humidity and an atmospheric pressure equivalent to average sea level conditions. Variations in temperatures and relative humidities during the operation of the gas turbine will result in changes to the thermal efficiency of the gas turbine as indicated below. In general, thermal efficiency is influenced by: 1. The energy used by the air compressor - if less energy is used to compress the air, more energy is available at the output shaft; 2. The temperature of the hot gas leaving the combustors - increased temperature generally results in increased efficiency; 3. The temperature of the exhaust gas - reduced temperature generally results in increased efficiency; 4. The mass flow through the gas turbine - in general, higher mass flows result in higher efficiencies; 5. The drop in pressure across the inlet air filters, silencers and ducts - a decrease in pressure loss increases efficiency; 6. The drop in pressure across the exhaust gas silencers, ducts and stack - a decrease in pressure loss increases efficiency. Various methods have been used to achieve the above goals: 1. Using the exhaust gas to heat the air from the compressor (mainly used in cold weather conditions); 2. Divide the compressor into two parts and cool the air between the two parts; 3. Divide the turbine into two parts and reheat the gas between the two parts by passing the gas through additional burners and combustors located between the two parts; 4. Cooling the inlet air mainly used in hot weather conditions; 5. Reducing the humidity of the inlet air; 6. Increasing the pressure of the air at the discharge of the air compressor; 7. Inject steam into the combustors or turbine; 8. Wash or otherwise clean the fouling from the blades of the air compressor and turbine at regular intervals; and 9. Combinations of the above methods. However, all these methods increase costs and some decrease the amount of power able to be output by the gas turbine. The methods used are therefore a compromise between cost, power and efficiency for each application. Reliability The reliability of a gas turbine depends mainly on the design of its components and the selection of materials used in critical components. Operational factors such as the cleanliness of the fuel and inlet air, the way the gas turbine is operated and the quality of the maintenance practices also have an effect of reliability. New models of gas turbines often have significant changes to critical components in an effort to improve power output, increase thermal efficiency and reduce costs. However, the use of unproven designs and technologies can result in unforseen failures. The manufacturers analyse these failures and improve the component. The reliabilities of the models improve as these types of failures are designed out.

Noise Gas turbines are very compact and occupy small ground area. Statutory limits on noise levels at site boundaries can be achieved either by increasing the distance from the boundary to the plant or by installing noise abatement equipment on the machines. Silencers are usually fitted in the inlet air and exhaust gas ducts.

The inlet air (blue) enters the compressor at the left. The exhaust gas (red) leaves the turbine at the right. The burners and combustors are located between the compressor and turbine.

The photo shows what such a gas turbine looks like when its top half casing has been removed for inspection or maintenance. The air compressor is on the left and the turbine is on the right. The section that would hold the burners and combustors is between the compressor and the turbine. Note the large bolts that are used to hold the two halves of the casing together.

The photo shows, for a large gas turbine, the cross-section of a typical burner/combustor combination, the arrangement of these combustors and the area between the combustors and the turbine. The heat resistant ceramic tiles used in these hot areas can be clearly seen.

The combustion (gas) turbines being installed in many of today's natural-gas-fueled power plants are complex machines, but they basically involve three main sections: The compressor which draws air into the engine, pressurizes it, and feeds it to the combustion chamber literally at speeds of hundreds of miles per hour. The combustion system, typically made up of a ring of fuel injectors that inject a steady stream of fuel (e.g., natural gas) into the combustion chamber where it mixes with the air. The mixture is burned at temperatures of more than 2000 degrees. The combustion produces a high temperature, high pressure gas stream that enters and expands through the turbine section. The turbine is an intricate array of alternate stationary and rotating aerofoil-section blades. As hot combustion gas expands through the turbine, it spins the rotating blades. The rotating blades perform a dual function: they drive the compressor to draw more pressurized air into the combustion section, and they spin a generator to produce electricity. Land based gas turbines are of two types: (1) heavy frame engines and (2) aeroderivative engines. Heavy frame engines are characterized by lower compression ratios (typically below 15) and tend to be physically large. Aeroderivative engines are derived from jet engines, as the name implies, and operate at very high compression ratios (typically in excess of 30). Aeroderivative engines tend to be very compact. One key to a turbine's fuel-to-energy efficiency is the temperature at which it operates. Higher temperatures generally mean higher efficiencies which, in turn, can lead to more economical operation. Gas flowing through a typical power plant turbine can be as hot as 2300 degrees F, but some of the critical metals in the turbine can withstand temperatures only as hot as 1500 to 1700 degrees F. Therefore air from the compressor is used for cooling key turbine components; however, the requirement for cooling the turbine limits the ultimate thermal efficiency. One of the major breakthroughs achieved in the Department of Energy's advanced turbine program was to break through previous limitations on turbine temperatures using a combination of innovative cooling technologies and advanced materials. The advanced turbines that

emerged from the Department's research program were able to boost turbine inlet temperatures to as high as 2600 degrees F - nearly 300 degrees hotter than in previous turbines. Another way to boost efficiency is to install a recuperator or aste heat boiler onto the turbine's exhaust. A recuperator captures waste heat in the turbine exhaust system to preheat the compressor discharge air before it enters the combustion chamber. A waste heat boiler generates steam by capturing heat from the turbine exhaust. These boilers are also known as heat recovery steam generators (HRSG). High-pressure steam from these boilers can be used to generate additional electric power with steam turbines, a configuration called a combined cycle. A simple cycle gas turbine can achieve energy conversion efficiencies ranging between 20 and 35 percent. With the higher temperatures achieved in the Energy Department's turbine program, future gas turbine combined cycle plants are likely to achieve efficiencies of 60 percent or more. When waste heat is captured from these systems for heating or industrial purposes, the overall energy cycle efficiency could approach 80 percent. Turbine

Successes

-

"

Breakthrough"

Gas

Turbines

For years, gas turbine manufacturers faced a barrier that, for all practical purposes, capped power generating efficiencies for turbine-based power generating systems. The barrier was heat. Above 2300 degrees F, the scorching heat of combustion gases caused metals in the turbine blades and in other internal components to begin degrading. Since higher temperatures are the key to higher efficiencies, this effectively limited the generating efficiency at which a turbine power plant could convert fuel into electricity. The Department of Energy's Fossil Energy took on the challenge of turbine temperatures in 1992, and nine years later, two of its private sector partners produced "breakthrough" turbine systems that pushed firing temperatures to 2,600 degrees F and permitted combined cycle efficiencies that surpassed the 60 percent mark - the "four-minute mile" of turbine technology. Moreover, the advanced turbines achieved the higher firing temperatures while actually reducing the amount of nitrogen oxides formed to less than 10 parts per million (NOx is a product of high temperature combustion). Among the innovations that emerged from the Department's Advanced Turbine Systems program were single-crystal turbine blades and thermal barrier coatings that could withstand the high inlet temperatures, along with new firing techniques to stabilize combustion and minimize nitrogen oxide formation.

The

GE

H-System

Turbine

On February 18, 2000, GE Power Systems unveiled the first gas turbine slated for the U.S. market that would break through the temperature barrier and push efficiencies to unprecedented levels. Using advanced materials and revolutionary new steam-cooling technology, the new turbine is capable of operating at 2600 degrees F. The H System was the first turbine to surpass the 60 percent efficiency threshold, nearly five percentage points better than the prior best available system, in an industry where improvements are typically measured in tenths of a percent. Using an innovative dry low-NOx combustion system, the turbine achieved nitrogen oxide emission levels of 9 parts-per-million, half the average of the turbines in commercial use. The unit announced in February 2000 was slated to be one of two 60-hertz turbines that would have powered the 800-megawatt Heritage Station being built in Scriba, New York. The power plant, however, was not built when the anticipated demand for electric power in the region failed to materialize. A 50-hertz version, specially designed for the European power grid, was shipped to Baglan Bay Power Station near Cardiff, South Wales, in December 2000 and began test operations in November 2002.

Siemens

Westinghouse

W501G

Advanced

Gas

Turbine

In May 2001, the Energy Department's other advanced turbine development partner, Siemens Westinghouse, announced that its advanced W501G turbine had gone into commercial operation at the 360-megawatt, combined cycle Millennium power plant in Charlton, Massachusetts. In addition, the City of Lakeland, Florida's McIntosh Unit 5, a 249-megawatt simple cycle plant, also went into operation using the advanced turbine at about the same time. The Siemens Westinghouse engine has demonstrated a net efficiency of approximately 58 percent in combined cycle application. Reference Web site http://www.energy.qld.gov.au/electricity/infosite/index.htm http://www.fossil.energy.gov Back

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