24747759-Thermal-Power-Station-Report

Thermal Power Station

phase-II

THERMAL POWER STATION Very Brief Account of Visit to Thermal Power Station

ENGR. SYED MUHAMMAD MUNAVVAR HUSSAIN

Engr. Syed Muhammad Munavvar Hussain

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Thermal Power Station

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Thermal power station A thermal power station is a power plant in which the prime mover is steam driven. Water is heated, turns into steam and spins a steam turbine which either drives an electrical generator or does some other work, like ship propulsion. After it passes through the turbine, the steam is condensed in a condenser and recycled to where it was heated; this is known as a Rankine cycle. The greatest variation in the design of thermal power stations is due to the different fuel sources. Some prefer to use the term energy center because such facilities convert forms of heat energy into electrical energy. T.P.S. Muzaffar Garh:  Installed Capacity This Power Station is a vital and major thermal power generating installation connected with National grid system in Pakistan. This Power Station was constructed in different Phases having total capacity of 1370 MW. It consists of:  Three Russian units of 210 MW each  Two Chinese units of 200 MW each  One Chinese unit of 320 MW  Fuel Dual fuel combustion provision (Gas & Furnace Oil) has been made for all the machines. Furnace oil is transported through Railway Wagons and tank Lorries.

Unit No

Installed Capacity

Rated Capacity

Make

Commg. Date

Fuel Type

ST-1

210 MW

200 MW

USSR

Sep. 1993

P. Gas, F. Oil

ST-2

210 MW

200 MW

USSR

Mar. 1994

P. Gas, F. Oil

ST-3

210 MW

200 MW

USSR

Feb. 1995

P. Gas, F. Oil

ST-4

320 MW

300 MW

China

Dec. 1996

P. Gas, F. Oil

ST-5

210 MW

200 MW

China

Dec. 1995

P. Gas, F. Oil

ST-6

210 MW

200 MW

China

Dec. 1995

P. Gas, F. Oil

Total

1370MW

1300MW

Table 1.1 brief views of TPS units

Engr. Syed Muhammad Munavvar Hussain

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Thermal Power Station

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Amid sand dunes of area known as Rakh Khanpur, at a distance of 6 km. from Muzaffargarh City, is located Thermal Power Complex. A few years back nobody perceived that such a desert would yield green trees, more than 1,500 families would be residing here and a Power Station will turn into a huge Power Complex. Now, with the day and night efforts of foreign as well as Pakistani engineers, technicians and workers, the complex has grown to the realities with three sky-high chimneys, being highest concrete structure in Pakistan and visible from the bridge of River Chenab, which is flowing to the east of the site at distance of 8 kms. In September, 1987 contract of supply and erection of a 3x210 MW capacity Thermal Power Station was signed with M/s. TECHNOPROMEXPORT of ex-USSR, Moscow, and 1,134 acres of government land was acquired. Initially, about 230 acres land for the Power Station and 164 acres for residential colony was leveled and subsequently construction was started. Later on contracts with Chinese firm, M/s. CMEC, were signed for three units in two stages - Two Units each of 210 MW and one unit of 320 MW. In this way a power complex emerged which is going to be the biggest of all Thermal Stations in Pakistan with the possibility of construction of two more units. Presently, the total generation capability of three phases is envisaged as 1,370 MW. Phase - 1 (Units 1, 2 & 3): This phase consists of three steam units each capable of generating 210 MW electricity. The supplier started delivery of equipment to site in January, 1989, and after pre-assembly of equipment at Site, erection started in July, 1990. Unit No. 1 was commissioned in September, 1993 and Unit No. 2 in March, 1994. Main Building: It contains the turbine hall having a span of 45 meters and dearator bay, 12 meters wide. The steam turbines which drive generators are of three stages condensing type arranged transversely to the axis of turbine hall. The operational platform is at elevation 12.6 meters and a maintenance bay at ground floor near Unit No. 1. The power plant is designed on the block principle: boiler-turbine-generator-unit transformer. The fuel gas exhaust section of two units is connected with a 200 meter high stack, outer section of which is a 195-meter high concrete shell. Combined Auxiliary Building: The building is connected with the main building and it houses water treatment plant to produce 100 t/h demineralized water for the replenishment of station losses, hydrogen plant to provide hydrogen for cooling of generators rotors, maintenance shops, laboratories and central control room. Fuel & Oil Facilities: Fuel oil facilities are constructed for decanting, oil storage, preparation and supply of fuel to boiler nozzles. It also includes HSD storage as well as oil facilities for reception, storage, purification and centralized delivery of turbine oil and insulating oil to power plant. Hydraulic Structures: The cooling water used in condensers is re-circulated in closed cycle with inducted draft cooling towers. The water is being cooled for each unit in two cooling towers each consisting of eight fans. Two cooling towers carry 27,500 Cu m/h circulating water for condensers of one unit.

Engr. Syed Muhammad Munavvar Hussain

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Thermal Power Station

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Startup Boiler: One startup boiler using diesel oil as fuel with steam output of 50 t/h is provided to meet steam requirement for initial start of unit as well as a backup of power plant auxiliaries. A separate stack of 30-meter high has been constructed for it. Electrical Part: The electricity generated at 15.75 KV is brought out from Unit transformer at 220 KV and fed to the National Grid via a switchyard. Power Plant auxiliaries are fed at 6.6 KV. Phase-II (Units 5 & 6): It consists of two units of 210 MW each having equipment similar to Phase-I. Turbines are placed longitudinally in main building. Outdoor boilers exhaust of two units is connected to one stack Overview: There are many different types of power plants including thermal power plants and hydel power plants. Thermal power plants use fuel such as Gas, HSD, Furnace Oil or nuclear fuel to produce heat energy that is converted to electrical energy through a series of intermediate processes. Hydel power plants convert the potential energy of water to electrical power as it flows from higher to lower elevations. The "traditional" thermal power plant is the Rankine cycle plant, named after the man who invented the cycle. A power plant cycle is a series of processes in which a fluid, generally water/steam, is used to convert heat energy to mechanical energy. The Rankine cycle in its simplest form consists of a boiler, a turbine, a condenser, and a boiler feed pump. Early plants had thermal efficiencies of approximately 25% to 30%. Only 25% to 30% of the heat energy in the fuel burned in these plants was converted to electrical energy. The rest was lost in various ways. The Rankine cycle has been refined considerably over the years and made more efficient by the addition of components like Economizer, Feed water heaters, Super heaters and Reheaters. The efficiency of the Rankine cycle has also been improved by increasing the pressure and temperature of the cycle. The laws of thermodynamics and considerations such as material limitations have prevented any significant improvement since then. Power plants commonly use heat rate to measure efficiency.

Fuel Energy

Boiler

Heat Energy

Engr. Syed Muhammad Munavvar Hussain

Turbine

Mechanical Energy

Generator

Electrical Energy

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Thermal Power Station

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Boiler The boiler is the main part of any thermal power plant. It converts the fuel energy into steam energy. The fuel may be furnace oil, diesel oil, natural gas or coal. The boilers may be fired from the multiple fuels. The type of boiler used in the TPS phase-II is “water tube type”. Water Tube Boilers: In watertube boilers, boiler water passes through the tubes while the exhaust gases remain in the shell side, passing over the tube surfaces. Since tubes can typically withstand higher internal pressure than the large chamber shell in a firetube, watertube boilers are used where high steam pressures (as high as 3,000 psi) are required. Watertube boilers are also capable of high efficiencies and can generate saturated or superheated steam. The ability of watertube boilers to generate superheated steam makes these boilers particularly attractive in applications that require dry, high-pressure, high-energy steam, including steam turbine power generation. Parameter of Boiler: Rated evaporating amount Reheat steam amount Main steam pressure Temperature Outlet pressure of Reheat System Outlet Temperature of Reheat System Inlet pressure of Reheat System Inlet Temperature of Reheat System Feed water Temperature Boiler Efficiency (burn oil) Boiler Efficiency (burn gas) Exit gas Temperature (burn oil) Exit gas Temperature (burn gas) Consumption of crude oil Consumption of natural gas Main Parts of Boiler: The boilers consist of the following main parts:  Forced Draft Fan (FDF)  Air Preheater (RAH)  Burners  Furnace  Up Rise Tubes  Down Comer Tubes  Water Tubes  Super Heaters  Gas Recirculation Fan (GRCF)  Re-Heater  Induced Draft Fan (IDF) Engr. Syed Muhammad Munavvar Hussain

680 t/h 575.8 t/h 140 kg/cm2 g 541 C 23.8 kg/cm2 g 541 C 25.8 kg/cm2 g 310 C 251 C 90.26 % 85 % 153 C 136 C 48.2 t/h 59650 Nm 2 /h

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 Chimney  Boiler Drum  Economizer Forced Draft Fan (FDF): The forced draft fan (FDF) sucks the air from the atmosphere which is used in the furnace for burning. The air from the atmosphere is passed through the filter to remove the dust and other particles from the air. The air from the FDF is then feeded to the regenerative air heaters. The motor of the FDF has following specification; Type KK 800 11- 8 Rated Voltage 6.6KV Rated Current 114 /121.3A Rated Speed 747rpm Output 1000KW Connection of Stator /Rotor Y Insulation Class F Permissible Rise 80K Ambient Temperature 40C No. Of Phase 3 Rated Frequency 50Hz Power Factor 0.81 Degree Of Protection IP54 Moment Of Inertia 310Kg.m2 Weight 12020K/13250Kg Induced Draft Fan (IDF): ID fan sucks the flue gases from boiler and exhaust through chimney. The motor of the IDF has following specification; Type YKK 800 11- 6 Rated Power 2000kw Rated Voltage 6.6KV Rated Current 20 A Rated Speed 991rpm Connection of Stator Winding 2Y Insulation Class F Permissible Rise 80k Ambient Temperature 40C No. Of Phase 3 Rated Frequency 50Hz Degree of Protection IP54 Moment Of Inertia 410Kg.m2 Weight 15970Kg

Engr. Syed Muhammad Munavvar Hussain

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Thermal Power Station

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Gas Recirculation Fan (GRCF): The motor of the GRCF has following specification; Type KK 400 11- 4 Rated Power 315KW Rated Voltage 6600V Rated Current 34 A Rated Speed 1491rpm Connection of Stator Winding Y Insulation Class F Permissible Rise 70k Ambient Temperature 50C No. Of Phase 3 Rated Frequency 50Hz Degree of Protection IP54 Moment Of Inertia 11.7Kg.m2 Weight 3200Kg Cooling Towers: Cooling towers are heat removal devices used to transfer process waste heat to the atmosphere. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or rely solely on air to cool the working fluid to near the dry-bulb air temperature. Common applications include cooling the circulating water used in oil refineries, chemical plants, power stations. Cooling Water Pump: The motor of the CWP has following specification; Type Y1600-16/2150 Out Put Power 1600KW Stator Voltage 6.6KV Speed 372rpm Frequency 50Hz Stator Rated Current 182A Stator Connection 2Y Ambient Temperature 50C Insulation Class B Weight 17500Kg CW Pump: Type is single stage double suction centrifugal pump Type 1400S25-1 Capacity 16000m3/H Speed 370rpm Power 1600KW Weight 35000kg Head 25m NP SHR 8.5m

Engr. Syed Muhammad Munavvar Hussain

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Thermal Power Station

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Air Preheater: An air preheater or air heater is a general term to describe any device designed to heat air before another process (for example, combustion in a boiler) with the primary objective of increasing the thermal efficiency of the process. They may be used alone or to replace a recuperative heat system or to replace a steam coil. 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 flue 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. Economizers: Flue gases from large boilers are typically 450 - 650°F. Stack Economizers recover some of this heat for pre-heating water. The water is most often used for boiler make-up water or some other need that coincides with boiler operation. Stack Economizers should be considered as an efficiency measure when large amounts of make-up water are used (i.e. not all condensate is returned to the boiler or large amounts of live steam are used in the process so there is no condensate to return) or there is a simultaneous need for large quantities of hot water for some other use. The savings potential is based on the existing stack temperature, the volume of makeup water needed, and the hours of operation. Economizers are available in a wide range of sizes, from small coil-like units to very large waste heat recovery boilers. The savings potential is a function of how much heat can be recovered, which is a function of how much cold water needs to be heated. A generally accepted "rule of thumb" is that about 5% of boiler input capacity can be recovered with a properly sized economizer. A higher percentage can be recovered with a Flue Gas Condenser, assuming there is enough cold water to condense all of the flue gas that is available. Therefore, for 'ball parking' purposes, start by comparing boiler input capacity with the need to heat water. An economizer that recovers 5% of boiler input should easily have a 2 year payback in a year-round application. Boiler Protection:             

Fuel protection Gas pressure protection Diesel oil protection Furnace oil protection FD fan trip ID fan trip Regenerative air pre heater trip Drum level high Drum low level Reheat steam pressure drop Furnace pressure low Furnace flame out Natural gas pressure high

Engr. Syed Muhammad Munavvar Hussain

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Thermal Power Station

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Steam Cycle:

Boiler Drum

HP Cylinder

Re- Heater

Economizer

LP Cylinder

Circulating Water

Condenser

STEAM CYCLE

HP Heaters

Feed Water Pumps

IP Cylinder

Feed Water Tank

De-aerator

Engr. Syed Muhammad Munavvar Hussain

Condensate Pump

LP Heaters

Ejector

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Thermal Power Station

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Steam Turbine Turbine is used to convert the heat energy into mechanical energy. Turbine used in tps Muzaffar Garh is impulse-reaction steam turbine. The load requirement is controlled by the steam flow through a governing valve. Maximum steam flow at full load is 670 tons/hour. When the load at the generator is suddenly decreased then the rpm (frequency) of the generator is increased and to decrease the frequency we lower down the steam flow which decreases the speed and maintains the frequency. If load is suddenly increased rotor speed becomes slower, to increase the speed, steam flow is increased. Steam turbine has three parts. 1. HP turbine 2. IP turbine 3. LP turbine. HP (High Pressure) Turbine: First of all steam from boiler comes into the HP turbine. Steam in the HP turbine is called live steam or main steam. Rotor blades diameter of this part of turbine is smallest of the other parts of the turbine. Inlet steam temperature of the HP turbine is 540 C and pressure is 130 kg/cm2. Outlet steam temperature of the HP turbine is 290 C and pressure is 15 kg/cm2. HP turbine has total of 12 stages including one is governing stage. IP (Intermediate Pressure) Turbine: Steam comes into the IP turbine from HP turbine via reheaters. The steam pressure in this section of the turbine is 14 kg/cm2 and temperature is 540 C. This part has total of 10 pressure stages. . LP (Low Pressure) Turbine: The outgoing steam of the IP turbine entered into the LP turbine. Steam from the LP turbine goes into the condenser. Specification of the steam turbine: Maximum load Live steam pressure Live steam temperature Rated speed HP cycle Exhaust steam temperature HP cycle Exhaust steam pressure Reheat steam temperature Reheat steam pressure Engr. Syed Muhammad Munavvar Hussain

210 MW 132 kg/cm-2 538 C 3000 rpm 310 C 24 kg/cm2 538 C 14 kg/cm2 10

Thermal Power Station

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Turbine Protection:        

Lube oil pressure (low and high) Vacuum drop Live steam temperature drop Axial shift displacement Gas cooling pump tripping HP heater level high All FW pump trip high vibration tipping Trip unit by switch/emergency

Engr. Syed Muhammad Munavvar Hussain

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Thermal Power Station

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Furnace Safeguard Supervisory System (FSSS) The FSSS station consists of the following parts;  De-kending area  Fuel oil tanks  First Lift pump  Main Heaters  Second Lift pump  Diesel pumps  Recirculation pumps  Recirculation heaters  Filters  control Room De-kending Area: The furnace oil that is used as a fuel in the burners of the boiler furnace to produce the steam is transported to the TPS through two ways;  Oil Tankers  train For unloading of the fuel from oil tankers and train there is separate unloading or dekending station for each. The unloaded fuel oil is initially stored in the underground reservoir; from there it is filled in the main storage tanks. 02 pumps are used to fill the main storage tanks from the oil tankers de-kending area. One of them is active (on load) and other is standby. Fuel Oil Tanks: From the de-kending area the furnace oil is filled in the storage tanks. From there it is supplied to the burners of the boiler furnace after proper heating. Usually one storage tank is called service tank, from there furnace oil is supplied to the units. The furnace oil is filled in the other tanks first and then filled in the service tanks through recirculation pumps (RCP). The oil in the tanks is kept heated at the temperature 75 C to 80 C. There are total 06 storage tanks for furnace oil each having a volume of 20,000 cubic meters hence each can store 2, 00,00,000 liters. There are 2 diesel oil storage tanks each having capacity of 1000 ton. First Lift Pump: First lift pump takes the furnace oil from the service tank and supplied to the main heaters. There are total 04 first lift pumps which are operated according to the unit load conditions. The specification of fist lift pump motor is as under; 3 phase 50 Hz Induction Motor Connection: Star

Engr. Syed Muhammad Munavvar Hussain

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Thermal Power Station Power: Power factor: Efficiency: Voltage Speed Current

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55KW 0.9 90% 230/400V 2950rpm 177/102A

Main Heaters: There are 04 main heaters each is connected to the respective first lift pump. The main heaters heat the furnace oil through the steam which comes from the boiler. Steam is use to heat the oil in the recirculation heaters. The seam flows through the pipes which heats the oil outside the tube. The temperature and pressure of the steam in the main heaters is Temp 270 C Pressure 11 to 13 kg/cm2 Second Lift Pump: Second lift pumps take the furnace oil from the main heaters and supplied to boilers of the units. There are total 04 second lift pumps which are operated according to the unit load conditions. The temperature of the oil that is supplied to the boiler is 105 C to 120 C. The specification of second lift pump motor is as under; 3 phase 50 Hz Induction Motor Power: 250KW Voltage 6.6kV Speed 2950rpm Current 252A

Fuel Oil Cycle:

Engr. Syed Muhammad Munavvar Hussain

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Thermal Power Station

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Exhaust (Chimney)

ID Fan

FUEL OIL CYCLE Air Pre Heater

Furnace Oil Tanks

Oil Heaters

Gate & Quick Closing Valves

Burners (Boiler Furnace)

Flue Gases

The Generator The generator is a device which converts the mechanical energy into electrical energy. Working Principle: The working principle of generator is based on the Faraday’s law of electromagnetic induction, which states that “The emf is always produced in the conductor which is placed in the magnetic field when there is a relative motion between conductor and the magnetic field”. If the output electrical energy is AC, it is called AC generator or alternator. If the output electrical energy is DC, it is called DC generator. In fact there is no difference between alternator and DC generator except the way the output is obtained from the generator. In alternator the AC supply is produced in the armature and supply is obtained through slip rings where as in the DC generator the generated AC supply is obtained from the armature through split rings or commutator which converts the AC into DC. The following three things are necessary for the generation of electrical energy;  Magnetic field  Conductor  Relative motion between conductor and Magnetic field

Engr. Syed Muhammad Munavvar Hussain

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Thermal Power Station

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In the small generator the magnetic field is being produced in the stator and the emf is produced in the rotor through Faraday’s law of electromagnetic induction. The electromagnetic are used in the generator to produce the magnetic field. In the large generator the magnetic field is produced by the electromagnetic in the rotor and the emf is produced in the stator. The output is taken from the stator because if the output is taken from the rotor, the rotor must have high insulation due to the high voltage induction and it must have heavy insulation which may increase the size of the rotor, and require more power for the prime mover to rotate this heavy rotor. Synchronous Generator: The generators used in the TPS are synchronous generator. Synchronous generators are by definition synchronous, meaning that the electrical frequency produced is locked in or synchronized with the mechanical rate of rotation of the generator. A DC current is applied to the rotor winding, which then produces a rotor magnetic field. The rotor is then turned by a prime mover (e.g. Steam, water etc.) producing a rotating magnetic field. This rotating magnetic field induces a 3-phase set of voltages within the stator windings of the generator. “Field windings” applies to the windings that produce the main magnetic field in a machine, and “armature windings” applies to the windings where the main voltage is induced. For synchronous machines, the field windings are on the rotor, so the terms “rotor windings” and “field windings” are used interchangeably. Generally a synchronous generator must have at least 2 components: a) Rotor Windings or Field Windings  Salient Pole  Non Salient Pole b) Stator Windings or Armature Windings The rotor of a synchronous generator is a large electromagnet and the magnetic poles on the rotor can either be salient or non salient construction. Non-salient pole rotors are normally used for rotors with 2 or 4 poles rotor, while salient pole rotors are used for 4 or more poles rotor.

Engr. Syed Muhammad Munavvar Hussain

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Thermal Power Station

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A dc current must be supplied to the field circuit on the rotor. Since the rotor is rotating, a special arrangement is required to get the dc power to its field windings. The common ways are:  Supply the dc power from an external dc source to the rotor by means of slip rings and brushes.  Supply the dc power from a special dc power source mounted directly on the shaft of the synchronous generator.  Slip rings are metal rings completely encircling the shaft of a machine but insulated from it. One end of the dc rotor winding is tied to each of the 2 slip rings on the shaft of the synchronous machine, and a stationary brush rides on each slip ring. A “brush” is a block of graphite like carbon compound that conducts electricity freely but has very low friction; hence it doesn’t wear down the slip ring. If the positive end of a dc voltage source is connected to one brush and the negative end is connected to the other, then the same dc voltage will be applied to the field winding at all times regardless of the angular position or speed of the rotor. Some problems with slip rings and brushes:  They increase the amount of maintenance required on the machine, since the brushes must be checked for wear regularly.  Brush voltage drop can be the cause of significant power losses on machines with larger field currents. Small synchronous machines – use slip rings and brushes. Larger machines – brushless exciters are used to supply the dc field current. A brushless exciter is a small ac generator with its field circuit mounted on the stator and its armature circuit mounted on the rotor shaft. The 3-phase output of the exciter generator is Engr. Syed Muhammad Munavvar Hussain

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Thermal Power Station

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rectified to direct current by a 3-phase rectifier circuit also mounted on the shaft of the generator, and is then fed to the main dc field circuit. By controlling the small dc field current of the exciter generator (located on the stator), we can adjust the field current on the main machine without slip rings and brushes. Since no mechanical contacts occur between the rotor and stator, a brushless exciter requires less maintenance.

The Speed of Rotation of a Synchronous Generator: Synchronous generators are by definition synchronous, meaning that the electrical frequency produced is locked in or synchronized with the mechanical rate of rotation of the generator. A synchronous generator’s rotor consists of an electromagnet to which direct current is supplied. The rotor’s magnetic field point in the direction the rotor is turned. Hence, the rate of rotation of the magnetic field in the machine is related to the stator electrical frequency by:

Excitation of Generator: Excitation of synchronous generator is done via DC supply which is given to the field winding of the generator to produce the magnetic field. The generator can be classified, with respect to the excitation, as under; Separately Excited Generator: The generator in which the DC supply is given to the field winding of the generator through the external source is called separately excited generator. Self Excited Generator:

Engr. Syed Muhammad Munavvar Hussain

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Thermal Power Station

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The generator in which the DC supply is given to the field winding of the generator through its own generated supply is called self excited generator. Synchronous Generator in TPS: The main generators used in the TPS phase-I are separately excited generators. For this purpose another synchronous generator is installed on the same shaft of the turbine and main generator which is called “Exciter”. The exciter is a self excited synchronous generator. In the initial startup the DC supply is given to the field winding (rotor) of the exciter by the DC batteries for 4 seconds. After that the DC batteries are cut off and the DC supply is given to the field of the exciter by its own generated supply after the rectification. The AC supply generated by the exciter is also given to the field winding (rotor) for its excitation after the rectification. The AC produced by the exciter is sent to the rectifier room where it is converted to the controlled DC supply by thyristers. The firing angles of the thyristers are controlled by the AVR (automatic voltage regulator) and hence the excitation of the generator is controlled. Exciter generator: Excitor generator of the excitor provides independent power supply(3-phase, 50 Hz) to the excitation system. The exciter generator is installed on the same shaft with the turbo generator. The exciter is excited by two water cooling thyristor converters. The thyrister converters are connected in parallel and operate in turn: one is in operation while other is in automatic stand-by duty. The ac and dc circuits of the thyristers includes several knife switches for removal either of the converters from service for repair. Initial excitation of the exciter generator is carried out by a short term connection of the storage batteries through a contactor and rectification bridge.

Main Generator Parameters Pilot Exciter: Type Rated Voltage Rated Current Rated Speed Rated Power Factor Phase Rated Frequency Armature Connection Specification Mfg. Date Rated Capacity

Tfy-46-500 93/161V 286/165A 3000rpm 0.875 3 500Hz ∆/Y OEA.513.039 1993-3-1 46KVA

Alternating Excitor:

Engr. Syed Muhammad Munavvar Hussain

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Thermal Power Station Type Rated Voltage Rated Current Rated Speed Rated Power Factor Phase Rated Frequency Armature Connection Specification Mfg. Date Rated Capacity

phase-II Tl-1165-4 431V 1562A 3000rpm 0.91 3 100Hz Y OEA.513.039 1993-8-24 1165KVA

Turbine Generator Water Hydrogen Cooled Type Rated Capacity Rated Output Rated Voltage Rated Current Rated Speed Rated Frequency Phase Connection Of Stator Winding Insulation Class Power Factor Excitation Voltage Excitation Current Max.Inlet Water Temp. For Stator Winding Max.Inlet Cooling Hydrogen Water Flow For Stator Winding Rate H2 Pressure Specification Mfg. Date

QFSN-210-2 246MVA 210MW 15.75KV 9056A 3000rpm 50Hz 3 2-Y F 0.85 289V 18.67A 50C 50C 35m2/h 0.3MPa OEA.512.137 1993-2

Cooling System of Turbo Generator: The first question arises here is that why we need cooling of the generator? As the current flow in the stator and rotor of the generator is very high so it increases the temperature of the stator and rotor winding. As a result the resistance of the stator and rotor windings increases which increase the power losses and may cause the insulation breakdown. Two types of cooling is used in the turbo generator of TPS phase-II 1. Stator cooling 2. Rotor cooling Stator cooling:

Engr. Syed Muhammad Munavvar Hussain

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Thermal Power Station

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The stator of the turbo generator is cooled by the distillated or demineralized (demi) water. For this purpose a special plant is installed which prepares the demi water for the stator cooling. This demi water is also used for the cooling system of the thyrister converters. The water is passed though the hollow conductors of the stator winding for its cooling. The demi water is necessary for the cooling of the stator winding because raw water is not a pure insulator which may cause the flow of leakage current when passed through stator winding. The demineralized water plant removes the impurities and minerals of the raw water and make it good insulator whose Resistivity is taken at a minimum level of 200 kΩ.cm. The demi water that passes through the stator winding absorbs the heat of the stator winding making it cool and becomes hot itself. The demi water then passes through heat exchangers (coolers) where its temperature is decreased by the circulating water coming from the cooling towers. This demi water is also passed through the mechanical and magnetic filters before passing through stator winding and thyrister converters. The stator and thyristers cooling circle is shown in figure below; Water parameters in Heat Exchangers Rated temp.of cold water at inlet Min: temp of cold water No. of gas heat exchangers Rated water flow in on heat exchangers

32 C 15 C 02 150 m3/h

Rotor Cooling: The rotor cooling is done by the Hydrogen gas. Hydrogen gas is used for the following purposes: 1. Its heat exchange capability is much better than other gases 2. It is very lighter than other gases so do not overload the rotor. 3. Its preparation is very easy and cheap. Hydrogen gas is filled in the generator and maintained at a pressure of 4kg/cm2. It takes all the heat of the rotor and cools the rotor winding and gets warmed itself. For the cooling of the gas there are four gas coolers inside the generator on each corner. Circulating water of the cooling tower is used in the gas cooler for the hydrogen cooling. Hydrogen gas is explosive if it is combined with oxygen under pressure so to avoid any leakage of gas and entrance of air inside the generator the rotor assembly is sealed by the seal oil whose pressure is at least 0.7kg/cm2 more than hydrogen gas inside the generator. When the generator is turned off for a long time for maintenance purpose hydrogen is released from the generator in the air using special method. Method involves that firstly fill the generator with CO2 which release the hydrogen in the air and then in the end air is filled in the generator and CO2 is released in the air. This method is adopted because if hydrogen is released using air instead of CO2 then it can cause explosion due to oxygen in the air which will meet hydrogen under pressure in the generator. After maintenance hydrogen gas is refilled in the generator using the reverse process as described above.

Engr. Syed Muhammad Munavvar Hussain

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Thermal Power Station Water parameters in gas cooler Rated temp.of cold water at inlet Min: temp:of cold water Max: water pressure No. of gas coolers Rated water flow in on gas cooler

phase-II

32 C 15 C 3 kg/cm2 04 76.5 m3/h

Protections of Generator: The following protection are installed for the protection of the generator in TPS phase-I; 1.

Longitudinal differential current protection This system is intended to protect against multi phase short circuit in generator stator winding and at its leads including against double earth fault, one of which being in the generator. 2.

Lateral differential current protection This system is intended to protect against turn-to-turn short circuit of one phase in the generator stator winding. 3.

Earth fault protection of stator winding This system is intended to reveal and disconnect one phase earth fault of generator stator winding. 4. Differential protection of the unit This system is intended to backup longitudinal differential protection of generator. 5.

Negative sequence current protection This system is intended to prevent damage of generator incase of overloading by negative sequence current caused by asymmetric load or external asymmetric short circuit and abnormal operating condition of power grid. 6.

Over current protection against overloading of generator This system is intended for signaling at symmetric overloading of generator stator.

7.

External symmetrical short circuit protection This system is intended to protect the generator against external symmetric short circuit.

8.

Protection against asynchronous mode, when excitation loss This system is intended to protect against asynchronous mode. One of the elements of resistance block relay for protection of the unit against external symmetrical short circuit is used. 9.

Protection of generator rotor against overloading This system is intended to protect against overloading under emergency condition as well as incase of failure of generator excitation system which cause long term flow of current of abnormal value along the rotor winding.

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10. Earth fault protection in one point of excitation circuit This system is intended to protect the generator incase of earth fault at one point of excitation circuit. 11. Protection against voltage increase at generator at idle operation This system is intended to prevent inadmissible increase in voltage at turbo generator and transformer of unit during idle operation of the unit incase of failure of excitation system. 12. Zero sequence current protection This system is intended to backup protection operating at one phase short circuit in the 220KV network. It is also used to backup unit protections when short circuit at the 220KV side of the unit. 13. Differential protection of the exciter This system is intended to protect against all kind of short circuit in the exciter winding and on its leads. 14. Over current protection of exciter against external short circuit This system is intended to protect against over current in the external system of the exciter.

Transformer Generally following type of transformers are used in our power house.  Main transformer  Stand by transformer  Auxiliary transformer Parts of Transformer: Main transformer consists of following parts: Engr. Syed Muhammad Munavvar Hussain

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1. Power fans 2. Condenser type bushing 3. Oil conservator 4. Bucholz relay 5. Winding temperature controller 6. Thermostat and thermometer 7. Current transformers 8. Tap changer 9. Earthing tower 10. Fire protection cooling system 11. Automatic voltage regulator Power Fans: The natural cooling of the transformer can be increased by the addition of power fans placed at the base or along the side of radiators, whether they are fitted directly to the tank or groups in outside gangs. The fans are of helical type and are of capable of generating an air flow. The motor designed for an absorbed power .25 ÷1 HP is closed, self cooling, with cage rotor and mounted on bearing. Normally the fans are controlled automatically through a thermostat. In addition to make manual operation possible as well, a preselector is often built into the system, allowing operation by means of push buttons on the protection and control cover. When forced cooling is provided the power fans unit is split into two units each controlled through it’s own switch by same thermal relay. Condenser type Bushing: The bushing is packaged in cases, generally in the vertical position. Packing is providing to protect the bushing from blows and moisture during transients. Moreover, the part of each bushing normally immersed in oil is protected from moisture by a cup shaped metal or plastic covering directly fitted to the bushing flange. On spare bushing, not used for transformer testing, a water proof film may be found for some construction type on the surface of resin paper. Before using the bushing, this film should be removed with a blunt tool, for not to damage the surface underneath. The bushing should be stored in dry place, always in the vertical position, even for short period. Atmoseal Type air-cell oil conservator: For air cell conservator the contact between oil and outside air is prevented. Moreover the pressure on the oil surface remains constant and equal to the atmosphere pressure. When transformer is running, it requires a very small maintenance limited to routine inspection. In conservator an oil resistant, flexible, rubber oil-cell is arranged in communication with the outside through a drier that prevents condensation in the cell. The air cell gets bigger or smaller so as to compensate oil volume variations and to keep pressure an oil surface at the atmospheric valve. The working condition of the Buchholz relays, installed on the tank to conservator pipe, is not out all affected by the air cell.

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Buchholz type gas accumulation relay: This relay is provided for transformer protection when electrical breakdown occurs between the live parts, or in the event of fault to ground, short circuits between turns, phase interruptions, burning of core, oil leakage in the tank or in the oil cooling system. This relay will operate on the occurrence of gas formation or on sudden variations of oil level resulting from abnormal transformer conditions by actuating an alarm signal and if the fault is serious or persistent, by putting the transformer out of service. The Buchholz relay is installed directly on the oil pipe connecting the tank to the conservator and is normally flooded with oil, in which its inner armature is permanently immersed with the actuating device. The upper contact for signaling purpose is closed by operation of pertaining float, when due to an inflow of gas to the relay or the other reason, the oil level contained in the upper part of the relay is lowered. The lower contact which controls the tripping circuit is operated by the corresponding float when the oil level reaches the lower part of the relay. Whenever the Buchholz relay operates the alarm and the tripping circuit, it is necessary to open the gas drawing cock and to make sure that gas is released. Winding temperature controller A thermal image device is used to detect the “Hot Spot” temperature in the winding of a power transformer. A coil is immersed in the hottest oil layer of the transformer, transmits through the capillary tube, the temperature variation to the temperature indicator. A heater coil is placed around the thermometer bulb and is supplied by the secondary of main current transformer. The current in the heater is proportional to that is flowing in the winding. The heater is designed to obtain a temperature rise and a thermal inertia equal to those of transformer winding. It should be noted that the temperature values read on the indicator are “Hot Spot” values, i.e. maximum local winding temperature. Therefore, when the transformer operates at full load, the reading may exceed the temperature limit by the standards for the average winding temperature. Temperature indicator: The indicator is sealed in the tank; it is a potentiometer for remote indication and is mounted at man’s height at the tank of the transformer. The thermometer bulb located in the probe, is connected through the capillary tube to the actuating bellows of the instruments. A second capillary tube runs parallel to the preceding one and is connected to the compensating bellows to cancel the influence of the ambient temperature. The system is filled with a special stable and non corrosive liquid. The instrument dial is graduated from 0 to 150 C over an arc of 270. The index 7 is actuated through a sector gear, the latter is also operates the lever , moving the slider of potentiometer if required and the lever which controls the fixed differential switch and the variable differential switch. The device is fitted with a maximum index that can be reset to zero. The switches and the potentiometer are connected to terminal boards and the potentiometer has fine and zero adjustments. Thermostat and thermometer This device is used for the temperature control and consists of a bulb at the top part of the transformer tank and connected through the capillary tube to a dial indicator. Besides indicating the temperature, this instrument closed a circuit connected to an alarm device and subsequently a second circuit directly connected to the main breaker and capable to cause the detachment of the

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transformer from the line. The measurement system can be of liquid thermometer type. The scale is not linear but approximately logarithmic expandable with the temperature Main Transformer: The specification of main transformer is; Type Phase Frequency Rated Power Rated Voltage Type Of Cooling Insulation Class Connection Symbol Current No-load Noise Level Impedance Voltage No Load Losses Load Losses Temp. Rise

SFP7-250000/235TA 3 50HZ 250000KVA 235± 3/5*2.5% /15.75 KVA OFAF A YN.D1 0.25% 90db 13.9% 170.2 KW 675.9KW 60K

WEIGHT Active Part Oil Bell Tank Total

158t 55.6t 17.9t 261.83t

Stand By Transformer: Type Phase Frequency Rated Power Rated Voltage Type of Cooling Installation Connection Symbol Noise Level No Load Current

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SFP7-250000/235TA 3 50Hz 2500/25000/8400KVA 230± 8*1.25% /6.9 /3.984KVA OFAF Outdoor YN yno d1 90db 0.33%

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No-load Losses Load Losses Temp. Rise

34KW 113.8KW 60K

WEIGHT Active Part Oil Bell Tank Total Quantity Of Cooler Spare Cooler Temperature Classification

35.1t 34.54t 10t 98.64t 4 1 A

NOTE: This transformer can be operated with out coolers for 20 minutes. Auxiliary Transformer: Type Phase Frequency Rated Power Rated Voltage Rated Current Type Of Cooling Insulation Class Connection Symbol Noise Level Impedance Voltage No Load Current No-load Losses Load Losses

S27-2500/15TA 3 50HZ 25000KVA 15.75± 7*2% /6.9 KVA 916.4/2092A ONAN A D.yn11 69db 12.2% 0.336% 22.5 KW 109.4 KW

Limit for Temperature Rise: Winding Top Oil Insulation Level

60K 50K LI150AC55/LI60AC25

WEIGHT Active Part Oil Total

27500kg 19500kg 58580kg

Transformer Protections:

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Differential current protection of unit t/f Gas protection of unit transformer Gas protection of on-load tap changer section Remote protection at 6kv side Current different of working and standby power supply 6kv section Over current protection against over-loading of 6kv winding Arc protection at 6kv side/winding MT Buchholz MT cooling fan stop Relief value

SWITCH YARD Mainly there are different but most important things for the protection, measurement, metering and for the other purposes     

Circuit Breaker Isolator Insulator Insulator strings Bus Bar

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Current transformer (C.T.) Potential transformer (P.T.) Conductor Control Switch Relays Power Line communication box

Circuit Breaker: This is the basic and the most important part of the switchyard. Isolators are used for it’s protection because the minimum cost of the circuit breaker which has been installed in KAPCO is of 10 million rupees. So, we are required to provide protection to it to avoid the burning and the familiar of the breaker. Objective: This is installed to protect or making some disconnection or connection part, So that there can be a bridge between the two parts. This is an automatic device which opens and closes by sensing the characteristics defined by the designer. Suppose if we want to work on the transmission line going to any other region, then we make open the connections of the circuit breaker. On the other hand, if any fault occurs on any side of the breaker, then current transformer which is certainly installed with a breaker senses the abnormal current and sends information to the central control room and also performs some action to protect the system from any accident. Any of the line is no longer in contact with the generator, all lines are coming out from the bus bar and there is a circuit breaker in between the line and the bus bar. So, by chance, if occurs a fault in transmission line then we can easily recover it by opening the breaker. Similarly the line from the step-up transformer to the bus bar is also protected by a circuit breaker. So, this circuit breaker is a kind of connection and disconnection between the generator, bus bar and the transmission line. So, by this way, the transmission line or substation or bus bar itself and also generator are protected from any kind of small or big accidents.

The Necessary Capabilities of Breaker: 1. It should be capable of extinguishing the arc without undue delay. 2. It should withstand the transient voltage that appears across the contacts immediately after the current flow ceases. So it should provide sufficient dielectric strength immediately after the rupture of current. Components of the circuit breaker: Auxiliary switch This is only for the purpose of the taking information about the working of the C.B. e.g. it consists of PLC’s which take information that whether the breaker is open or close. The information about the opening and the closing of the breaker is taken by such a way that there are Engr. Syed Muhammad Munavvar Hussain

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some normally open and normally closed contacts in auxiliary switch. So, if the breaker is closed then information from the normally closed contacts is sent to C.C.R. (Central Control Room) and a light is made ON there showing that Breaker is in closed condition. Similarly is the breaker is open, then Normally open contacts are closed and in the similar fashion described above, light is made ON in C.C.R. showing that breaker is in open condition. Mechanical switching: This process is done with help of the oil pressure. A certain oil pressure is obtained and then according to the information supplied by the manufacturer, opening and closing of the breaker is done at some pressure defined, i.e. if pressure goes less than 273 bars than breaker is opened and then does not close itself until it is done manually. Inside protection: As because of the opening and closing of contacts by some other reasons, arcs are produced inside the breaker which is dangerous for the life and the characteristics of the breaker. So, these arcs must be quenched. There are many methods for quenching these arcs, e.g. • Air quenching • Gas quenching • Vacuum quenching Now days, most commonly used methods for quenching the arch is the use of the SF 6 gas which is very much efficient for doing this task. Types of Circuit Breakers: They can be classified with respect to two criteria 1. arc quenching media 2. construction With respect to arc quenching media , we have most used types listed below • The oil circuit breakers • The air circuit breakers • The SF6 circuit breakers • The vacuum type

Oil Type: In the oil type circuit breaker, the arc is produced in the oil thus oil decomposes and replaced by the surrounding oil thus provides both cooling and give proper dielectric strength. Such an arrangement can work for breaking duty not exceeding 150MVA. Addition can be done to increase the rating by providing pressure pot and externally generated pressure to extinguish the arc by pushing it and also by dividing it into sections by means of insulators .By these means, a rating of 7500MVA at 132 kV is possible. Also low oil content breaker can be used to decrease the size and increase the life and performance of oil.

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Air Type: Axial, radial or cross blast is used in these breakers to extinguish arc and also insulators can be added to increase the dielectric strength. Vacuum Type: In this type, the vacuum is created at the contact position. When the contacts open, the resistance becomes very high since no ionization in the medium occurs. only source of electrons is the harmonic emission through the surfaces. So no chance of re-striking arc after it is once extinguished. Current transformers: Current transformers are used in power transformers as a source of energy for operation of relays, to measure the equipment of a thermal image plant, a line drop compensator and protection system etc. The current transformers normally incorporated in power transformers may be of bushing type with primary winding. The primary is formed by connection which goes from the winding of each individual phase of the transformer to the corresponding insulator and which crosses the transformer centrally. If the transformer ratio is very low and the accuracy is high, it is advisable to use the type with the primary winding. As far as possible, these current transformers are arranged on the machine in an easily accessible position.

Chemical section The chemical section consists of the following sections;    

Hydrogen plant Demineralization plant Oil testing lab Water testing lab

Hydrogen Plant:

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Hydrogen plant prepares the hydrogen gas which is used for the cooling of the rotor of the turbo generator. The hydrogen gas is used for the cooling of the rotor of the turbo generator because it has better heat transfer characteristics, cheap and easy preparation and also it is very light and hence do not over load the rotor. The hydrogen is prepared by electrolyses of the water. For this DC supply is given to the electrolyzer. This Dc supply is produced after step down of the 6.6 kV supply to 400 V and then by 3-pahe rectifier. Raw water is used for the preparation of the hydrogen as it supports fast electrolyses action then de-mineralized water. Potassium Hydro oxide (KOH) is used as a catalyst. The oxygen and hydrogen are prepared in the ratio of 1:2. A generalized layout of the hydrogen plant is shown in the figure below;

DC Power Supply (330A)

Alkaline Solution

Electrolyzer

Air Compressor

Rotor (Generator)

Storage Tanks

Separating Columns

Dryer

Purifier

Gas Scrubber (Gas Washer)

Generation of HYDROGEN

DC Power Supply: The 3-phase 6.6 kV supply is stepped down to 400 V through step down transformers. For this purpose 02 transformers are installed in the section which has a specification as follow; Rated Power: Rated Voltage: Rated Current:

96 kVA 415 V 133.6 A

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Each transformer follows a 3-phase thyrister rectifier converting the 3-phase AC into DC supply which is given to the electrolyzers. The thyrister converters can provide the 60 V, 1250 A DC supply to the electrolyzers. . Electrolyzer: The process of electrolyses of the water takes place in the electrolyses. The process in which DC current is passed through the water resulting the separation of the cation and anion is known as electrolyses. The electrolyzer has 25 cells each takes 2.2 V, a total of 55 V DC and a maximum current of 1000 A. The separated hydrogen and oxygen then leaves the electrolyzer on its own ways. Separating Column: The hydrogen leaving the perforated flash box (PFB) enters the separating column which removes the small parts of alkali from it Gas Scrubber: Gas scrubber is also called gas washer. It removes the impurities from the hydrogen such as dust particles etc. Dryer: The dryer dry the hydrogen coming out from the gas scrubber. As gas scrubber do the washing of the hydrogen gas so it has to be dried. Receiver Tanks: The receiver tanks store the prepared hydrogen gas. For this purpose 06 receiver tanks are used. The pressure inside the tanks is kept 10kg/cm2. 03 tanks are for oxygen and 03 are for carbon dioxide storage.

Demineralization plant “The water which is free of all the impurities, minerals, gases like Oxygen Nitrogen and consists of only pure water (H2O) is called demineralized water”. Demineralized plant is used for the preparation of demineralized water. Demineralized water is used for the preparation of steam, for the cooling of stator of generator and for the cooling of thyristors in the excitation system.

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The plant has total generation capacity of 90 tons/hour. Raw water is used for the preparation of the demi water. Raw water is pumped out by the tube wells and stored in the raw water storage tanks. Demi water is passed through the hollow conductors of stator winding for the stator cooling. It is used for this purpose because demi water acts as an insulator & has a resistivity of 200kOhms.it does not short circuit the windings. Demi water is used for the steam preparation in the boiler for the following reasons: Raw water contains mineral like Calcium, Magnesium and sulphur. These minerals cause the stacks and corrosion in the boiler tubes which causes the heat loses and may damage the boiler tubes. The designed loss of the demi water in the steam cycle is 2%. Make up demi water is done in the hot well and feed water tank. A generalized layout of the demi water plant is shown in the figure below; .

Raw Water

Mech. Clarifier filter

Cation filter

Decarbonized Exhaust

Anion Filter

Storage tank

Mixed bed

Cation 2nd filter

Preparation of demineralized water _____________________________________________________________________________ _ Mech. Clarifier filters: In mechanical clarifier filter coal and gravels are is used to remove the unresolved particles from the water. Cation filter: In the cation filter resins is used which replaces the Na+ & Ca2+ ions in the water from the + H ions. In the end water becomes acidic.

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Decarbonizer exhaust: It removes the carbonates from the water.CO2 is removed by showering of the water against air. It is also known as degasifier. Anion filter: In Anion filter castic soda (NaOH) is used which replaces the Cl- or SO4 ions with the OH- ions forming partial demi water. Cation 2nd filter: It also removes the positive ions from the water. Mixed filter: In the mixed filter both the remaining anions and cations are removed. The water leaving the mixed bed is the pure distilled water. Storage tanks: This prepared demineralized water is then stored in the storage tanks. Water treatment: Ammonium hydroxide, Hydrazine and Trisodium phosphate are dozed at different points in the boiler such as boiler drum, for water treatment. The nature of this water is acidic, to minimize the acidity of this water ammonium hydroxide (NH4OH) is used. Hydrazine (N2H4) removes the Oxygen from water and protects the boiler tubes against corrosion. Trisodium phosphate (Na3PO4) is used in the boiler drum which removes the Ca, Mg and adds Na.

Oil Testing Lab: Different tests of the furnace oil and the lubrication oil are performed in the oil testing laboratory to check their characteristics. The test on the transformer oil is also performed in this lab. The following tests are performed on the furnace and lube oil:1.

Moisture test

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Flash point test. Viscosity test. Specific gravity test. Acidity test. Solubility test. Mechanical impurity test. Chlorification test.

LIST OF SYMBOLS AND ABBREVATIONS

TPS G/R T/F T/R

Thermal power station Generator Transformer Transformer

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M.T A.T H.V.S L.V.S B.B A.S.B C.B C.T P.T R.C L.A Temp. PCB ICs MW MVAR MVA EMF AC DC

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Main Transformer Auxiliary Transformer High Voltage Side Low Voltage Side Bus Bar Auxiliary System Bus Circuit Breaker Current Transformer Potential Transformer Relay Coil Lightning arrestor Temperature Printed Circuit Board Integrated Circuits Mega Watt Mega Volt Ampere Reactive Mega Volt Ampere Electromotive force Alternating current Direct current

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