Ntpc Summer Training Report

SUMMER TRAINING REPORT 15th June to 25th July

Submitted By:Shivani Chhabra 7225 ECE-2(5th sem)

ABOUT THE COMPANY CORPORATE VISION : “A world class integrated power major, powering India's growth with increasing global presence.”

CORE VALUES : B- Business ethics C-Customer focus O-Organisational & professional pride M-Mutual respect & trust I-Innovation & speed T-Total quality for excellence NTPC Limited is the largest thermal power generating company of India, public sector company. It was incorporated in the year 1975 to accelerate power development in the country as a wholly owned company of the Government of India. At present, Government of India holds 89.5% of the total equity shares of the company and the balance 10.5% is held by FIIs, Domestic Banks, Public and others. Within a span of 31 years, NTPC has emerged as a truly national power company, with power generating facilities in all the major regions of the country.

NTPC LimiteD

Type

Public

Founded 1975 Headquart ers Key people

Delhi, India R S Sharma, Chairman & Managing Director

Industry Electricity generation Products Electricity Revenue Net income

▲INR 416.37 billion (2008) or USD 18.15 billion ▲INR 70.47 billion (2008) or USD 1.89 billion

Employees 23867 (2006) Website

http://www.ntpc.co.in

EVOLUTION OF NTPC 1975

NTPC was set up in 1975 with 100% ownership by the Government of India. In the last 30 years, NTPC has grown into the largest power utility in India.

1997

In 1997, Government of India granted NTPC status of “Navratna’ being one of the nine jewels of India, enhancing the powers to the Board of Directors.

2004

2005

NTPC became a listed company with majority Government ownership of 89.5%. NTPC becomes third largest by Market Capitalisation of listed companies

The company rechristened as NTPC Limited in line with its changing business portfolio and transform itself from a thermal power utility to an integrated power utility.

NTPC is the largest power utility in India, accounting for about 20% of India’s installed capacity.

THERMAL POWER PLANT A thermal power station consists of all the equipments and a subsystem required to produce electricity by using a steam generating boiler fired with fossil fuels or befouls to drive an electric generator. Some prefer to use the term ENERGY CENTER because such facilities convert form of energy like nuclear energy, gravitational potential energy or heat energy (derived from the combustion of fuel) into electrical energy. Typical diagram of a coal power thermal power station1. Cooling water pump 2. Three phase transmission line 3. Step up transformer 4. Electrical generator 5. Low pressure steam 6. Boiler feed water pump 7. Surface condenser 8. Intermediate pressure steam turbine 9. Steam control valve 10.High pressure steam turbine 11.Deaerator feed water heater 12.Coal conveyer 13.Coal hopper 14.Coal pulverizer 15.Boiler steam drum 16.Boiler ash hopper 17.Super heater 18.Force draught (draft) fan 19.Reheater 20.Combustion air intake 21.Economiser 22.Airpreheater 23.Precipitator 24.Induced draught(draft) fan 25.Fuel gas stack The description of some of the components above is as follows: 1. Cooling towersCooling towers are eveporative coolers used for cooling water. Cooling tower use evaporation of water to reject heat from processes such as cooling the circulaing water used in oil refineries, chemical plants, power plants, etc. The tower vary in size from small roof – top units to very large hyperboloid structures that can be upto 200 meters tall and 100 meters in diameter, or rectangular structure that can be over 40

meters tall and 80 meters long. Smaller towers are normally factory built while larger ones are constructed on site. The primary use of large, industrial cooling tower system is to remove the heat absorbed in the circulating water system used in power plants, petroleum refineries, petrochemical and chemical plants, natural gas processing plants and other industrial facilities. The absorbed heat is rejected to the atmosphere by the evaporation of some of the cooling water in mechanical forced – draft or induced draft towers or in natural draft hyperbolic shaped cooling towers as seen at most nuclear power plants. 2. Three phase transmission lineThree phase electric power is a common method of electric power transmission. It is a type of polyphase system mainly used for power motors and many other devices. In a three phase system, three circuits reach their instantaneous peak values at different times. Taking one conductor as reference, the other two conductor are delayed in time by one-third and two-third of cycle of the electrical current. This delay between phases has the effect of giving constant power over each cycle of the current and also makes it impossible to produce a rotating magnetic field in an electric motor. At the power station, an electric generator converts mechanical power into a set of electric currents one from each electromagnetic coil or winding of the generator. The currents are sinusoidal functions of time, all at the same frequency but offset in time to give different phases. In a three phase system, the phases are spaced equally giving a phase separation of one-third of one cycle. Generators output at a voltage that ranges from hundreds of volts to 30,000 volts. At the power station. Transformers step-up this voltage for suitable transmission. After numerous further conversions in the transmission and distribution network, the power is finally transformed to standard mains voltage i.e. the household voltage. The power may already have been split into single phase at this point or it may be still three phase. Where the step-down is three phase. The output of the transformer is usually star connected with the standard mains voltage being the phase neutral voltage. 3. Electrical generatorAn electrical generator is a device that coverts mechanical energy to electrical energy, using electromagnetic induction whereas electrical energy is converted to mechanical energy with the help of electric motor. The source of mechanical energy may be a reciprocating turbine steam engine. Turbines are made in variety of sizes ranging from small 1 hp(0.75 kW) used as mechanical drives for pumps, compressors and other shaft driven equipment to 2,000,000 hp(1,500,000 kW) turbines used to generate electricity.

4. Boiler Feed PumpA Boiler Feed Pump is a specific type of pump used to pump water into steam boiler. The water may be freshly supplied or retuning condensation of steam produced by the boiler. These pumps are normally high pressure units that use suction from a condensate return system and can be of centrifugal pump type or positive displacement type. Construction and Operation feed water pumps range in size upto many horsepower and the electric motor is usually separated from the pump body by some form of mechanical coupling. Large industrial condensate pumps may also serve as the feed water pump. In either case, to force water into the boiler, the pump must generate sufficient pressure to overcome the steam pressure developed by the boiler. This is usually accomplished through the use of centrifugal pump. Feed water pumps usually run intermittently and are controlled by a float switch or other similar level-sensing device energizing the pump when it detect a lowered liquid level in the boiler substantially increased. Some pumps contain a two stage switch. As liquid lowers to the trigger point of the first stage, the pump is activated. If the liquid continues to drop (perhaps because the pump has failed, its supply has been cut-off or exhausted, or its discharge is blocked),the second stage will be triggered. This stage may switch off the boiler equipment (preventing the boiler from running dry and overheating), trigger an alarm or both. 5. Control valvesControl Valves are the valves used within industrial plants and elsewhere to control operating conditions such as temperature, pressure, flow and liquid level by fully or partially opening or closing in response to signals received from controllers that compares a “set point” to a “process variable” whose value is provided by sensors that monitor changes in such conditions. The opening or closing of control valves is done by means of electrical, hydraulic or pneumatic systems. 6. DeaeratorA Deaerator is a device for air removal and used to remove dissolved gases from boiler feed water to make it non-corrosive. A deaerator typically includes a vertical domed deaeration section as the deaeration feed water tank. A steam generating boiler requires that the circulating steam, condensate and feed water should be devoid of dissolved gases, particularly corrosive ones and dissolved or suspended solids. The gases will give rise to corrosion of the metal. The solids will deposit on heating surfaces giving rise to localized heating and tube ruptures due to overheating. Deaerator level and pressure must be controlled by adjusting control valves-the level by regulating condensate flow and pressure by regulating steam flow.

Most deaerators guarantee that if operated properly, oxygen in deaerated water will not exceed 7ppb by weight. 7. Feed Water HeaterA feed water heater is a power plant component used to pre heat water delivered to a steam generating boiler. Feed water heater improves the efficiency of the system. This reduces plant operating costs and also helps to avoid thermal shock to boiler metal when the feed water is introduced back into the steam cycle. Feed water heaters allow the feed water to be brought upto the saturation temperature very gradually. This minimizes the inevitable irreversibility associated with heat transfer to the working fluid(water). A belt conveyer consists of two pulleys, with a continuous loop of material- the conveyer belt that rotates around them. The pulleys are powered, moving the belt and the material on the belt forward. Conveyer belts are extensively used to transport industrial and agricultural material, such as grain, coal, ores, etc. 8. PulverizerA pulverizer is a device for grinding coal for combustion in a furnace in a fossil fuel power plant. 9. Boiler Steam DrumSteam Drums are a regular feature of water tube boilers. It is reservoir of water/steam at the top end of the water tubes in the water-tube boiler. They store the steam generated in the water tubes and act as a phase separator for the steam/water mixture. The difference in densities between hot and cold water helps in the accumulation of the “hotter”-water/and saturated –steam into steam drum. Made from high-grade steel (probably stainless) and its working involves temperatures 390’C and pressure well above 350psi (2.4MPa). The separated steam is drawn out from the top section of the drum. Saturated steam is drawn off the top of the drum. The steam will reenter the furnace in through a super heater, while the saturated water at the bottom of steam drum flows down to the mud- drum /feed water drum by down comer tubes accessories include a safety valve, water level indicator and fuse plug. A steam drum is used in the company of a mud-drum/feed water drum which is located at a lower level. So that it acts as a sump for the sludge or sediments which have a tendency to the bottom. 10. Super HeaterA Super heater is a device in a steam engine that heats the steam generated by the boiler again increasing its thermal energy and decreasing the likelihood that it will condense inside the engine. Super heaters increase the efficiency of the steam engine, and were widely

adopted. Steam which has been superheated is logically known as superheated steam; non-superheated steam is called saturated steam or wet steam; Super heaters were applied to steam locomotives in quantity from the early 20th century, to most steam vehicles, and so stationary steam engines including power stations. 11. Economizers-

Economizer, or in the UK economizer, are mechanical devices intended to reduce energy consumption, or to perform another useful function like preheating a fluid. The term economizer is used for other purposes as well. Boiler, power plant, and heating, ventilating and air conditioning. In boilers, economizer are heat exchange devices that heat fluids , usually water, up to but not normally beyond the boiling point of the fluid. Economizers are so named because they can make use of the enthalpy and improving the boiler’s efficiency. They are a device fitted to a boiler which saves energy by using the exhaust gases from the boiler to preheat the cold water used the fill it (the feed water). Modern day boilers, such as those in cold fired power stations, are still fitted with economizer which is decedents of Green’s original design. In this context they are turbines before it is pumped to the boilers. A common application of economizer is steam power plants is to capture the waste hit from boiler stack gases (flue gas) and transfer thus it to the boiler feed water thus lowering the needed energy input , in turn reducing the firing rates to accomplish the rated boiler output . Economizer lower stack temperatures which may cause condensation of acidic combustion gases and serious equipment corrosion damage if care is not taken in their design and material selection. 12. Air Preheater-

Air preheater is a general term to describe any device designed to heat air before another process (for example, combustion in a boiler). The purpose of the air preheater is to recover the heat from the boiler flue gas which increases the thermal efficiency of the boiler by reducing the useful heat lost in the fuel gas. As a consequence, the flue gases are also sent to the flue gas stack (or chimney) at a lower temperature allowing simplified design of the ducting and the flue gas stack. It also allows control over the temperature of gases leaving the stack. 13. Precipitator-

An Electrostatic precipitator (ESP) or electrostatic air cleaner is a particulate device that removes particles from a flowing gas (such As air) using the force of an induced electrostatic charge. Electrostatic precipitators are highly efficient filtration devices, and can easily remove fine particulate matter such as dust and smoke from the air steam. ESP’s continue to be excellent devices for control of many industrial particulate emissions, including smoke from electricity-

generating utilities (coal and oil fired), salt cake collection from black liquor boilers in pump mills, and catalyst collection from fluidized bed catalytic crackers from several hundred thousand ACFM in the largest coal-fired boiler application. The original parallel plate-Weighted wire design (described above) has evolved as more efficient ( and robust) discharge electrode designs were developed, today focusing on rigid discharge electrodes to which many sharpened spikes are attached , maximizing corona production. Transformer –rectifier systems apply voltages of 50-100 Kilovolts at relatively high current densities. Modern controls minimize sparking and prevent arcing, avoiding damage to the components. Automatic rapping systems and hopper evacuation systems remove the collected particulate matter while on line allowing ESP’s to stay in operation for years at a time. 14. Fuel gas stack-

A Fuel gas stack is a type of chimney, a vertical pipe, channel or similar structure through which combustion product gases called fuel gases are exhausted to the outside air. Fuel gases are produced when coal, oil, natural gas, wood or any other large combustion device. Fuel gas is usually composed of carbon dioxide (CO2) and water vapor as well as nitrogen and excess oxygen remaining from the intake combustion air. It also contains a small percentage of pollutants such as particulates matter, carbon mono oxide, nitrogen oxides and sulfur oxides. The flue gas stacks are often quite tall, up to 400 meters (1300 feet) or more, so as to disperse the exhaust pollutants over a greater aria and thereby reduce the concentration of the pollutants to the levels required by governmental environmental policies and regulations.

ELECTRICITY GENERATION PROCESS (A BASIC OVERVIEW) At NTPC (Badarpur) the man two paths are the flue gas or air cycle and steam or condensate paths. CAPITAL OVERHAUL NTPC has been in news due to extensive load sheds in many areas in delhi and the main cause behind these load sheds was the capital overhaul of one of 210 MW units. Unit IV was under an extensive check , which has caused shut down of the plant and the plant, was dismantled completely to change the old parts and cleaning up the whole unit. But capital overhaul has no meaning because such a deep checking of the plant happens once in five to seven years. HOW ELECTRICITY IS GENERATED?

Thermal power station burns fuel and uses the resultant heat to raise steam which drives the TURBO GENERATOR. The fuel may be ‘fossil’(coal,oil,natural gas) or it may be fissionable, whichever fuel is used, the objective is same to convert the mechanical energy into electricity by rotating a magnet inside a set of winding. COAL TO STAEM Its other raw materials are air and water. The coal brought to the station by trains or by other means, travels handling plant by conveyer belts, travels from pulverizing mills, which grind it as fine as the face powder of size upto 20 microns. The finely produced coal mixed with preheated air is then blown into the boiler by a fan called primary air fan where it burns more like a gas than as a solid, in the conventional domestic or industrial grate, with additional amount of air, called secondary air supply, by forced draft fan. As coal is ground so finally the resultant ash is also a fine powder. Some of it binds together to form pumps, which falls into ash pits at the bottom of the furnace. The waterquenched ash from the bottom is conveyed to pits for subsequent disposal or sale. Most of ash, still in fine partical form is carried out of boilers to the precipitator as dust, where electrodes charged with high voltage electricity trap it. The dust is then conveyed to water to disposal area or to bunker for sale while the clean flue gases are passed on through IP fans to be discharged through chimneys. The heat released from the coal has been absorbed by the many kilometers tubing which line the boiler walls. Inside the tubes the boiler feed water, which is transformed by heat into staemat high temperature and pressure.. The steam superheated in further tubes (superheaters) passes to turbine where it is discharged through the nozzle on the turbine blades. Just as the energy of wind turns the sail of the windmill, the energy of steam striking the blade makes the turbine rotate. Coupled to the end of the turbine is the rotor of the generator. The rotor is housed inside the stator having heavy coils of the bars in which electricity is produced through the movement of magnetic field created by the rotor. Electricity passes from stator windings to step-up transformer which increases its voltage so that it can be transmited efficiently over lines of grid. The staem which has given up its heat energy is cahnged back into water in a condenser so that it is ready for re-use. The condenser contains many kilometers of tubing through which cold water is constantly pumped. The staem passing around the tubes looses heat.Thus it is rapidly changed back into water. But, the two lots of water, that is, the boiler feed and cooling water must never mix. Cooling water is drawn from river- bed, but the boiler feed water must be absolutely pure, far purer than the water we drink (de-mineralized water), otherwise it may damage the boiler tubes.

TABLES OF CYCLES  COAL CYCLE

 CONDENSATE CYCLE

 FEED WATER CYCLE

 STEAM CYCLE

CONTROL AND INSTRUMENTATION

This division basically calibrates various instruments and takes care of any faults occur in any of the auxiliaries in the plant.

This department is the brain of the plant because from the relays to transmitters followed by the electronic computation chipsets and recorders and lastly the controlling circuitry, all fall under this. Instrumentation can be well defined as a technology of using instruments to measure and control the physical and chemical properties of a material. Control and instrumentation has following labs: 1. Manometry lab 2. Protection and interlocks lab 3. Automation lab 4. Electronics lab 5. Water treatment plant 6. Furnaces Safety Supervisory System Lab

1. Manometry lab •

Transmitters- Transmitter is used for pressure measurements of gases and liquids, its working principle is that the input pressure is converted into electrostatic capacitance and from there it is conditioned and amplified. It gives an output of 420 ma DC. It can be mounted on a pipe or a wall. For liquid or steam measurement transmitters is mounted below main process piping and for gas measurement transmitter is placed above pipe.

•

Manometer- It’s a tube which is bent, in U shape. It is filled with a liquid. This device corresponds to a difference in pressure across the two limbs.

•

Bourden Pressure Gauge- It’s an oval section tube. Its one end is fixed. It is provided with a pointer to indicate the pressure on a calibrated scale. It is of two types : (a) Spiral type : for low pressure measurement and (b) Helical type : for high pressure measurement

2. Protection and Interlock Lab •

Interlocking- It is basically interconnecting two or more equipments so that if one equipments fails other one can perform the tasks. This type of interdependence is also created so that equipments connected together are started and shut down in the specific sequence to avoid damage. For protection of equipments tripping are

provided for all the equipments. Tripping can be considered as the series of instructions connected through OR GATE. When The main equipments of this lab are relay and circuit breakers. Some of the instrument uses for protection are: 1. RELAY It is a protective device. It can detect wrong condition in electrical circuits by constantly measuring the electrical quantities flowing under normal and faulty conditions. Some of the electrical quantities are voltage, current, phase angle and velocity. 2. FUSES It is a short piece of metal inserted in the circuit, which melts when heavy current flows through it and thus breaks the circuit. Usually silver is used as a fuse material because: a) The coefficient of expansion of silver is very small. As a result no critical fatigue occurs and thus the continuous full capacity normal current ratings are assured for the long time. b) The conductivity of the silver is unimpaired by the surges of the current that produces temperatures just near the melting point. c) Silver fusible elements can be raised from normal operating temperature to vaporization quicker than any other material because of its comparatively low specific heat. •

Miniature Circuit Breaker- They are used with combination of the control circuits to. a) Enable the staring of plant and distributors. b) Protect the circuit in case of a fault. In consists of current carrying contacts, one movable and other fixed. When a fault occurs the contacts separate and are is stuck between them. There are three types of -MANUAL TRIP - THERMAL TRIP - SHORT CIRCUIT TRIP.

•

Protection and Interlock System- 1. HIGH TENSION CONTROL CIRCUIT For high tension system the control system are excited by separate D.C supply. For starting the circuit conditions should be in series with the starting coil of the equipment to energize it. Because if even a single condition is not true then system will not start. 2. LOW TENSION CONTROL CIRCUIT For low tension system the control circuits are directly excited from the 0.415 KV A.C supply. The same circuit achieves both excitation and tripping. Hence the tripping coil is provided for emergency tripping if the interconnection fails.

3.

Automation Lab

This lab deals in automating the existing equipment and feeding routes. Earlier,

the old technology dealt with only (DAS) Data Acquisition System and came to be known as primary systems. The modern technology or the secondary systems are coupled with (MIS) Management Information System. But this lab universally applies the pressure measuring instruments as the controlling force. However, the relays are also provided but they are used only for protection and interlocks.

Pyrometry Lab

4. •

Liquid in glass thermometer - Mercury in the glass thermometer boils at 340 degree Celsius which limits the range of temperature that can be measured. It is L shaped thermometer which is designed to reach all inaccessible places.

•

Ultra violet censor- This device is used in furnace and it measures the intensity of ultra violet rays there and according to the wave generated which directly indicates the temperature in the furnace.

•

Thermocouples - This device is based on SEEBACK and PELTIER effect. It comprises of two junctions at different temperature. Then the emf is induced in the circuit due to the flow of electrons. This is an important part in the plant.

•

RTD(Resistance temperature detector) - It performs the function of thermocouple basically but the difference is of a resistance. In this due to the change in the resistance the temperature difference is measured. In this lab, also the measuring devices can be calibrated in the oil bath or just boiling water (for low range devices) and in small furnace (for high range devices).

5.

Furnace Safety and Supervisory System Lab

This lab has the responsibility of starting fire in the furnace to enable the burning of coal. For first stage coal burners are in the front and rear of the furnace and for the second and third stage corner firing is employed. Unburnt coal is removed using forced draft or induced draft fan. The temperature inside the boiler is 1100 degree Celsius and its height is 18 to 40 m. It is made up of mild steel. An ultra violet sensor is employed in furnace to measure the intensity of ultra violet rays inside the furnace and according to it a signal in the same order of same mV is generated which directly indicates the temperature of the furnace. For firing the furnace a 10 KV spark plug is operated for ten seconds over a spray of diesel fuel and pre-heater air along each of the feeder-mills. The furnace has six

feeder mills each separated by warm air pipes fed from forced draft fans. In first stage indirect firing is employed that is feeder mills are not fed directly from coal but are fed from three feeders but are fed from pulverized coalbunkers. The furnace can operate on the minimum feed from three feeders but under not circumstances should any one be left out under operation, to prevent creation of pressure different with in the furnace, which threatens to blast it.

6.

Electronics Lab

This lab undertakes the calibration and testing of various cards. It houses various types of analytical instruments like oscilloscopes, integrated circuits, cards auto analyzers etc.Various processes undertaken in this lab are: 1. Transmitter converts mV to mA. 2. Auto analyzer purifies the sample before it is sent to electrodes. It extracts the magnetic portion.

AUTOMATION AND CONTROL SYSTEM AUTOMATION: THE DEFINITION

The word automation is widely used today in relation to various types of applications, such as office automation, plant or process automation. This subsection presents the application of a control system for the automation of a process / plant, such as a power station. In this last application, the automation actively controls the plant during the three main phases of operation: plant start-up, power generation in stable or put During plant start-up and shut-down, sequence controllers as well as long range modulating controllers in or out of operation every piece of the plant, at the correct time and in coordinated modes, taking into account safety as well as overstressing limits. During stable generation of power, the modulating portion of the automation system keeps the actual generated power value within the limits of the desired load demand.

During major load changes, the automation system automatically redefines new set points and switches ON or OFF process pieces, to automatically bring the individual processes in an optimally coordinated way to the new desired load demand. This load transfer is executed according to pre- programmed adaptively controlled load gradients and in a safe way.

AUTOMATION: THE BENEFITS The main benefits of plant automation are to increase overall plant availability and efficiency. The increase of these two factors is achieved through a series of features summarized as follows:

 Optimisation of house load consumption during plant start- up, shut-down and

operation, via: • •

•

Faster plant start-up through elimination of control errors creating delays. Faster sequence of control actions compared to manual ones. Figures 1 shows the sequence of a rapid restart using automation for a typical coal-fired station. Even a well- trained operator crew would probably not be able to bring the plant to full load in the same time without considerable risks. Co-ordination of house load to the generated power output.

 Ensure and maintain plant operation, even in case of disturbances in the

control system, via: • •

Coordinated ON / OFF and modulating control switchover capability from a sub process to a redundant one. Prevent sub-process and process tripping chain reaction following a process component trip.

 Reduce plant / process shutdown time for repair and maintenance as well as

repair costs, via: •

•

Protection of individual process components against overstress (in a stable or unstable plant operation). Bringing processes in a safe stage of operation, where process components are protected against overstress

PROCESS STRUCTURE

Analysis of processes in Power Stations and Industry advocates the advisability of dividing the complex overall process into individual sub-processes having distinctly defined functions. This division of the process in clearly defined groups, termed as FUNCTIONAL GROUPS, results in a hierarchical process structure. While the hierarchical structure is governed in the horizontal direction by the number of drives (motorised valves, fans, dampers, pumps, etc.) in other words the size of the process; in the vertical direction, there is a distinction made between three fundamental levels, these being the:  Drive Level  Function Group Level  Unit Level.

To the Drive Level, the lowest level, belong the individual process equipment and associated electrical drives. The Function Group is that part of the process that fulfils a particular defined task e.g., Induced Draft Control, Feed Water Control, Blooming Mill Control, etc. Thus at the time of planning it is necessary to identify each function group in a clear manner by assigning it to a particular process activity. Each function group contains a combination of its associated individual equipment drives. The drive levels are subordinate to this level. The function groups are combined to obtain the overall process control function at the Unit Level. The above three levels are defined with regard to the process and not from the control point of view.

CONTROL SYSTEM STRUCTURE

The primary requirement to be fulfilled by any control system architecture is that it be capable of being organized and implemented on true process-oriented lines. In other words, the control system structure should map on to the hierarchy process structure. BHEL’s PROCONTROL P®, a microprocessor based intelligent remote multiplexing system, meets this requirement completely.

SYSTEM OVERVIEW The control and automation system used here is a micro based intelligent multiplexing system This system, designed on a modular basis, allows to tighten the scope of control hardware to the particular control strategy and operating requirements of the process Regardless of the type and extent of process to control provides system uniformity and integrity for:  Signal conditioning and transmission  Modulating controls

CONTROL AND MONITORING MECHANISMS There are basically two types of Problems faced in a Power Plant 

Metallurgical



Mechanical

Mechanical Problemcan be related to Turbines that is the max speed permissible for a turbine is 3000 rpm , so speed should be monitored and maintained at that level Metallurgical Problem can be view as the max Inlet Temperature for Turbile is 1060 oC so temperature should be below the limit.

Monitoring of all the parameters is necessary for the safety of both:



Employees



Machines

So the Parameters to be monitored are :



Speed



Temperature



Current



Voltage



Pressure



Eccentricity



Flow of Gases



Vaccum Pressure



Valves



Level



Vibration

PRESSURE MONITORING Pressure can be monitored by three types of basic mechanisms



Switches



Gauges



Transmitter type

For gauges we use Bourden tubes : The Bourdon Tube is a non liquid pressure measurement device. It is widely used in applications where inexpensive static pressure measurements are needed. A typical Bourdon tube contains a curved tube that is open to external pressure input on one end and is coupled mechanically to an indicating needle on the other end, as shown schematically below.

Typical Bourdon Tube Pressure Gages For Switches pressure swithes are used and they can be used for digital means of monitoring as swith being ON is referred as high and being OFF is as low. All the monitored data is converted to either Current or Voltage parameter. The Plant standard for current and voltage are as under •

Voltage : 0 – 10 Volts range

•

Current : 4 – 20 milliAmperes

We use 4mA as the lower value so as to check for disturbances and wire breaks. Accuracy of such systems is very high . ACCURACY : + - 0.1 % The whole system used is SCADA baseD. Programmable Logic Circuits ( PLCs) are used in the process as they are the heardt of Instrumentation .

Pressure

AN D

HL switch

Electricity

Start Level low Pressure in line Level HighLL switch High level pump Stop Pressure

Electricity

Electricity BASIC PRESSURE CONTROL MECHANISM

TEMPERATURE MONITORING We can use Thernocouples or RTDs for temperature monitoring Normally RTDs are used for low temperatures. Thermocoupkle selection depends upon two factors:



Temperature Range



Accuracy Required

Normally used Thermocouple is K Type Thermocouple: Chromel (Nickel-Chromium Alloy) / Alumel (Nickel-Aluminium Alloy)

OR

This is the most commonly used general purpose thermocouple. It is inexpensive and, owing to its popularity, available in a wide variety of probes. They are available in the −200 °C to +1200 °C range. Sensitivity is approximately 41 µV/°C. RTDs are also used but not in protection systems due to vibrational errors. We pass a constant curre t through the RTD. So that if R changes then the Voltage also changes RTDs used in Industries are Pt100 and Pt1000 Pt100 : 0 0C – 100 Ω ( 1 Ω = 2.5 0C ) Pt1000 : 0 0C - 1000Ω Pt1000 is used for higher accuracy The gauges used for Temperature measurements are mercury filled Temperature gauges. For Analog medium thermocouples are used And for Digital medium Switches are used which are basically mercury switches.

FLOW MEASUREMENT Flow measurement does not signify much and is measured just for metering purposes and for monitoring the processes

ROTAMETERS: A Rotameter is a device that measures the flow rate of liquid or gas in a closed tube. It is occasionally misspelled as 'rotometer'. It belongs to a class of meters called variable area meters, which measure flow rate by allowing the cross sectional area the fluid travels through to vary, causing some measurable effect.

A rotameter consists of a tapered tube, typically made of glass, with a float inside that is pushed up by flow and pulled down by gravity. At a higher flow rate more area (between the float and the tube) is needed to accommodate the flow, so the float rises. Floats are made in many different shapes, with spheres and spherical ellipses being the most common. The float is shaped so that it rotates axially as the fluid passes. This allows you to tell if the float is stuck since it will only rotate if it is not. For Digital measurements Flap system is used. For Analog measurements we can use the following methods : 

Flowmeters



Venurimeters / Orifice meters



Turbines



Massflow meters ( oil level )



Ultrasonic Flow meters



Magnetic Flowmeter ( water level )

Selection of flow meter depends upon the purpose , accuracy and liquid to be measured so different types of meters used. Turbine type are the simplest of all. They work on the principle that on each rotation of the turbine a pulse is generated and that pulse is counted to get the flow rate.

VENTURIMETERS :

Referring to the diagram, using Bernoulli's equation in the special case of incompressible fluids (such as the approximation of a water jet), the theoretical pressure drop at the constriction would be given by (ρ/2)(v22 - v12). And we know that rate of flow is given by:

Flow = k √ (D.P) Where DP is Differential Presure or the Pressure Drop.

CONTROL VALVES A valve is a device that regulates the flow of substances (either gases, fluidized solids, slurries, or liquids) by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but usually are discussed separately. Valves are used in a variety of applications including industrial, military, commercial, residential, transportation. Plumbing valves are the most obvious in everyday life, but many more are used.

Some valves are driven by pressure only, they are mainly used for safety purposes in steam engines and domestic heating or cooking appliances. Others are used in a controlled way, like in Otto cycle engines driven by a camshaft, where they play a major role in engine cycle control. Many valves are controlled manually with a handle attached to the valve stem. If the handle is turned a quarter of a full turn (90°) between operating positions, the valve is called a quarter-turn valve. Butterfly valves, ball valves, and plug valves are often quarter-turn valves. Valves can also be controlled by devices called actuators attached to the stem. They can be electromechanical actuators such as an electric motor or solenoid, pneumatic actuators which are controlled by air pressure, or hydraulic actuators which are controlled by the pressure of a liquid such as oil or water. So there are basically three types of valves that are used in power industries besides the handle valves. They are : •

Pneumatic Valves – they are air or gas controlled which is compressed to turn or move them

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Hydraulic valves – they utilize oil in place of Air as oil has better compression

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Motorised valves – these valves are controlled by electric motors

FURNACE SAFEGUARD SUPERVISORY SYSTEM FSSS is also called as Burner Management System (BMS). It is a microprocessor based programmable logic controller of proven design incorporating all protection facilities required for such system. Main objective of FSSS is to ensure safety of the boiler. The 95 MW boilers are indirect type boilers. Fire takes place in front and in rear side. That’s why its called front and rear type boiler. The 210 MW boilers are direct type boilers (which means that HSD is in direct contact with coal) firing takes place from the corner. Thus it is also known as corner type boiler. IGNITER SYSTEM

Igniter system is an automatic system, it takes the charge from 110kv and this spark is brought in front of the oil guns, which spray aerated HSD on the coal for coal combustion. There is a 5 minute delay cycle before igniting, this is to evacuate or burn the HSD. This method is known as PURGING. PRESSURE SWITCH Pressure switches are the devices that make or break a circuit. When pressure is applied , the switch under the switch gets pressed which is attached to a relay that makes or break the circuit. Time delay can also be included in sensing the pressure with the help of pressure valves. Examples of pressure valves: 1. Manual valves (tap) 2. Motorized valves (actuator) – works on motor action 3. Pneumatic valve (actuator) _ works due to pressure of compressed air 4. Hydraulic valve