TO

Honorable

Chief Engineer (Thermal)

Genco III, Faisalabad

BY

M.Zeeshan Arshad (BEE-FA06-077)

Salah-Ud-Din (BEE-FA06-002)

Tayyab Saeed (2008-EP(H)-08)

Steam Power Station

Steam Power Station of Northern Power Generation Company Limited held in Faisalabad is of 2×66 MW and their working based on crude oil and whole system installed by collaboration of the american which is the part of american aid in 1967.

A steam 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, like Crude oil, coal ,natural gas and nuclear.

Typical diagram of a thermal power station

Main parts of the steam power station.

1. Cooling tower

2. Cooling water pump

3. Transmission line (3-phase)

4. Step-up transformer (3-phase)

5. Electrical generator (3-phase)

6. Low pressure steam turbine

7. Condensate pump

8. Surface condenser

9. Intermediate pressure steam turbine

10. Steam Control valve

11. High pressure steam turbine

12. Deaerator

13. Feedwater heater

14. Crude oil

15. Coal hopper

16. Coal pulverizer

17. Boiler steam drum

18. Ash hopper

19. Superheater

20. Forced draught (draft) fan

21. Reheater

22. Combustion air intake

23. Economizer

24. Air preheater

25. Precipitator

26. Induced draught (draft) fan

27. Flue gas stack

Steam Power Electric generator

The Capacity of Generator in SPS Faisalabad is 85 MVA, speed is 3000 revolution per minute, has 2 poles,3 phase, frequency 50 cycles per second,11000 volts, at Hydrogen pressure (Psig) of 0.5 amperes are 3569 and 68000 KVA, at Hydrogen pressure (Psig) of 15 amperes are 4105 and 78200 KVA, at Hydrogen pressure (Psig) of 30 amperes are 4462 and 85000 KVA, these ratings are at .85 power factor.

The steam turbine-driven generators have auxiliary systems enabling them to work satisfactorily and safely. The steam turbine generator being rotating equipment generally has a heavy, large diameter shaft. The shaft therefore requires not only supports but also has to be kept in position while running. To minimize the frictional resistance to the rotation, the shaft has a number of bearings. The bearing shells, in which the shaft rotates, are lined with a low friction material like Babbitt metal. Oil lubrication is provided to further reduce the friction between shaft and bearing surface and to limit the heat generated.

Barring gear

Barring gear (or "turning gear") is the mechanism provided to rotate the turbine generator shaft at a very low speed after unit stoppages. Once the unit is "tripped" (i.e., the steam inlet valve is closed), the turbine coasts down towards standstill. When it stops completely, there is a tendency for the turbine shaft to deflect or bend if allowed to remain in one position too long.

This is because the heat inside the turbine casing tends to concentrate in the top half of the casing, making the top half portion of the shaft hotter than the bottom half. The shaft therefore could warp or bend by millionths of inches.

This small shaft deflection, only detectable by eccentricity meters, would be enough to cause damaging vibrations to the entire steam turbine generator unit when it is restarted. The shaft is therefore automatically turned at low speed (about one percent rated speed) by the barring gear until it has cooled sufficiently to permit a complete stop.

Condenser

The surface condenser is a shell and tube heat exchanger in which cooling water is circulated through the tubes. The exhaust steam from the low pressure turbine enters the shell where it is cooled and converted to condensate (water) by flowing over the tubes as shown in the adjacent diagram. Such condensers use steam ejectors or rotary motor-driven exhausters for continuous removal of air and gases from the steam side to maintain vacuum.

For best efficiency, the temperature in the condenser must be kept as low as practical in order to achieve the lowest possible pressure in the condensing steam. Since the condenser temperature can almost always be kept significantly below 1000C where the vapor pressure of water is much less than atmospheric pressure, the condenser generally works under vacuum. Thus leaks of non-condensable air into the closed loop must be prevented. Plants operating in hot climates may have to reduce output if their source of

condenser cooling water becomes warmer; unfortunately this usually coincides with periods of high electrical demand for air conditioning.

The condenser generally uses either circulating cooling water from a cooling tower to reject waste heat to the atmosphere, or once-through water from a river, lake or ocean.

Feedwater heater

In the case of a conventional steam-electric power plant utilizing a drum boiler, the surface condenser removes the latent heat of vaporization from the steam as it changes states from vapour to liquid. The heat content (BTU) in the steam is referred to as Enthalpy. The condensate pump then pumps the condensate water through a feed water heater. The feed water heating equipment then raises the temperature of the water by utilizing extraction steam from various stages of the turbine.

Preheating the feed water reduces the irreversibilities involved in steam generation and therefore improves the thermodynamic efficiency of the system.[9] This reduces plant operating costs and also helps to avoid thermal shock to the boiler metal when the feed water is introduced back into the steam cycle.

Superheater

As the steam is conditioned by the drying equipment inside the drum, it is piped from the upper drum area into an elaborate set up of tubing in different areas of the boiler. The areas known as super heater and re heater. The steam vapor picks up energy and its temperature is now superheated above the saturation temperature. The superheated steam is then piped through the main steam lines to the valves of the high pressure turbine.

Deaerator

A steam generating boiler requires that the boiler feed water should be devoid of air and other dissolved gases, particularly corrosive ones, in order to avoid corrosion of the metal.

Generally, power stations use a deaerator to provide for the removal of air and other dissolved gases from the boiler feed water. A deaerator typically includes a vertical, domed deaeration section mounted on top of a horizontal cylindrical vessel which serves as the deaerated boiler feed water storage tank.

There are many different designs for a deaerator and the designs will vary from one manufacturer to another. The adjacent diagram depicts a typical conventional trayed deaerator.

Auxiliary systems

Oil system

An auxiliary oil system pump is used to supply oil at the start-up of the steam turbine generator. It supplies the hydraulic oil system required for steam turbine's main inlet steam stop valve, the governing control valves, the bearing and seal oil systems, the relevant hydraulic relays and other mechanisms.

At a preset speed of the turbine during start-ups, a pump driven by the turbine main shaft takes over the functions of the auxiliary system.

Generator heat dissipation

The electricity generator requires cooling to dissipate the heat that it generates. While small units may be cooled by air drawn through filters at the inlet, larger units generally require special cooling arrangements. Hydrogen gas cooling, in an oil-sealed casing, is used because it has the highest known heat transfer coefficient of any gas and for its low viscosity which reduces windage losses. This system requires special handling during start-up, with air in the

chamber first displaced by carbon dioxide before filling with hydrogen. This ensures that the highly flammable hydrogen does not mix with oxygen in the air.

The hydrogen pressure inside the casing is maintained slightly higher than atmospheric pressure to avoid outside air ingress. The hydrogen must be sealed against outward leakage where the shaft emerges from the casing. Mechanical seals around the shaft are installed with a very small annular gap to avoid rubbing between the shaft and the seals. Seal oil is used to prevent the hydrogen gas leakage to atmosphere.

The generator also uses water cooling. Since the generator coils are at a potential of about 22 kV and water is conductive, an insulating barrier such as Teflon is used to interconnect the water line and the generator high voltage windings. Demineralized water of low conductivity is used.

Generator high voltage system

The generator voltage ranges from 11 kV in smaller units to 22 kV in larger units. The generator high voltage leads are normally large aluminum channels because of their high current as compared to the cables used in smaller machines. They are enclosed in well-grounded aluminum bus ducts and are supported on suitable insulators. The generator high voltage channels are connected to step-up transformers for connecting to a high voltage electrical substation (of the order of 115 kV to 132 kV) for further transmission by the local power grid.

The necessary protection and metering devices are included for the high voltage leads. Thus, the steam turbine generator and the transformer form one unit. In smaller units, generating at 11 kV, a breaker is provided to connect it to a common 11 kV bus system.

Steam generator

In fossil-fueled power plants, steam generator refers to a furnace that burns the fossil fuel to boil water to generate steam. In the nuclear plant field, steam generator refers to a specific type of large heat exchanger used in a pressurized water reactor (PWR) to thermally connect the primary (reactor plant) and secondary (steam plant) systems, which of course is used to generate steam. In a nuclear reactor called a boiling water reactor (BWR), water is boiled to generate steam directly in the reactor itself and there are no

units called steam generators. In some industrial settings, there can also be steam-producing heat exchangers called heat recovery steam generators (HRSG) which utilize heat from some industrial process. The steam generating boiler has to produce steam at the high purity, pressure and temperature required for the steam turbine that drives the electrical generator.

Boiler furnace and steam drum

Boiler of Steam power station Faisalabad has 6 lack pounds of steam per hour. Boiler has temperature range of 950+100F.

Once water inside the boiler or steam generator, the process of adding the latent heat of vaporization or enthalpy is underway. The boiler transfers energy to the water by the chemical reaction of burning some type of fuel.

The water enters the boiler through a section in the convection pass called the economizer. From the economizer it passes to the steam drum. Once the water enters the steam drum it goes down the down comers to the lower inlet water wall headers. From the inlet headers the water rises through the water walls and is eventually turned into steam due to the heat being generated by the burners located on the front and rear water walls (typically). As the water is turned into steam/vapor in the water walls, the steam/vapor once again enters the steam drum. The steam/vapor is passed through a series of steam and water separators and then dryers inside the steam drum. The steam separators and dryers remove water droplets from the steam and the cycle through the water walls is repeated. This process is known as natural circulation.

The boiler furnace auxiliary equipment includes coal feed nozzles and igniter guns, soot blowers, water lancing and observation ports (in the furnace walls) for observation of the furnace interior. Furnace explosions due to any accumulation of combustible gases after a trip-out are avoided by flushing out such gases from the combustion zone before igniting the coal.

The steam drum (as well as the super heater coils and headers) have air vents and drains needed for initial startup. The steam drum has internal devices that removes moisture from the wet steam entering the drum from the steam generating tubes. The dry steam then flows into the super-heater coils.

Re-Heater

Power plant furnaces may have a re-heater section containing tubes heated by hot flue gases outside the tubes. Exhaust steam from the high pressure turbine is rerouted to go inside the re-heater tubes to pickup more energy to go drive intermediate or lower pressure turbines. This is what is called as thermal power.

Fuel preparation system

Some power stations burn coal rather than oil. The oil must kept warm (above its pour point) in the fuel oil storage tanks to prevent the oil from congealing and becoming unpumpable. The oil is usually heated to about 100°C before being pumped through the furnace fuel oil spray nozzles.

Boilers in some power stations use processed natural gas as their main fuel. Other power stations may use processed natural gas as auxiliary fuel in the event that their main fuel supply (coal or oil) is interrupted. In such cases, separate gas burners are provided on the boiler furnaces.

Boiler make-up water treatment plant and storage

Since there is continuous withdrawal of steam and continuous return of condensate to the boiler, losses due to blow down and leakages have to be made up to maintain a desired water level in the boiler steam drum. For this, continuous make-up water is added to the boiler water system. Impurities in the raw water input to the plant generally consist of calcium and magnesium salts which impart hardness to the water. Hardness in the make-up water to the boiler will form deposits on the tube water surfaces which will lead to overheating and failure of the tubes. Thus, the salts have to be removed from

the water, and that is done by water demineralising treatment plant (DM). A DM plant generally consists of caution, anion, and mixed bed exchangers. Any ions in the final water from this process consist essentially of hydrogen ions and hydroxide ions, which recombine to form pure water. Very pure DM water becomes highly corrosive once it absorbs oxygen from the atmosphere because of its very high affinity for oxygen.

The capacity of the DM plant is dictated by the type and quantity of salts in the raw water input. However, some storage is essential as the DM plant may be down for maintenance. For this purpose, a storage tank is installed from which DM water is continuously withdrawn for boiler make-up. The storage tank for DM water is made from materials not affected by corrosive water, such as PVC. The piping and valves are generally of stainless steel. Sometimes, a steam blanketing arrangement or stainless steel doughnut float is provided on top of the water in the tank to avoid contact with air. DM water make-up is generally added at the steam space of the surface condenser (i.e., the vacuum side). This arrangement not only sprays the water but also DM water gets de-aerated, with the dissolved gases being removed by an air ejector attached to the condenser.

Other systems

Monitoring and alarm system

Most of the power plant operational controls are automatic. However, at times, manual intervention may be required. Thus, the plant is provided with monitors and alarm systems that alert the plant operators when certain operating parameters are seriously deviating from their normal range.

Battery supplied emergency lighting and communication

A central battery system consisting of lead acid cell units is provided to supply emergency electric power, when needed, to essential items such as the power plant's control systems, communication systems, turbine lube oil pumps, and emergency lighting. This is essential for a safe, damage-free shutdown of the units in an emergency situation.

Gas turbine power station

The gas turbine power station of Faisalabad Pakistan is approximately 660´, above sea level and is located at latitude 31026´, longitude 76086´.The equipment of gas turbine power station is designed to operate at temperature rating between 500 C in summer and 00C in winter. The complex is located at 10 Km from Faisalabad city on Faisalabad-Sheikhupura road, Nishatabad Railway station is 4 Km in the West and Rakh Branch canal flow close to the power station in the east.

Gas turbine

A gas turbine, also called a combustion turbine, is a rotary engine that extracts energy from a flow of combustion gas. It has an upstream compressor coupled to a downstream turbine, and a combustion chamber in-between. (Gas turbine may also refer to just the turbine element.)

Energy is added to the gas stream in the combustor, where air is mixed with fuel and ignited. Combustion increases the temperature, velocity and volume of the gas flow. This is directed through a nozzle over the turbine's blades, spinning the turbine and powering the compressor.

Energy is extracted in the form of shaft power, compressed air and thrust, in any combination, and used to power generators.

Combined Cycle Power Plant (CCP)

Applications

Large scale power production

Overview

The Combined Cycle power plant is a combination of a fuel-fired turbine with a Heat Recovery Steam Generator (HRSG) and a steam powered turbine. These plants are very large, typically rated in the hundreds of mega-watts.

Depending on the power requirements at the time, the combined cycle plant may operate only the fired turbine and divert the exhaust. However, this is a substantial loss of efficiency. Large fired turbines are in the low 30% eff. range, while combined cycle plants can exceed 60% efficiency.

Single Shaft Combined Cycle Plant

Multi-Shaft Combined Cycle Plant, steam turbine and generator are on the left side of the diagram.

In a combined cycle power plant (CCPP), or combined cycle gas turbine (CCGT) plant, a gas turbine generator generates electricity and the waste heat is used to make steam to generate additional electricity via a steam turbine; this last step enhances the efficiency ofelectricity generation.

Design Principle:

Working principle of a combined cycle power plant

In a thermal power station water is the working medium. High pressure steam requires strong, bulky

components. High temperatures require expensive alloys made from nickel or cobalt, rather than

inexpensive steel. These alloys limit practical steam temperatures to 655 °C while the lower

temperature of a steam plant is fixed by the boiling point of water. With these limits, a steam plant has

a fixed upper efficiency of 35 to 42%.

An open circuit gas turbine cycle has a compressor, a combustor and a turbine. For gas turbines the

amount of metal that must withstand the high temperatures and pressures is small, and lower

quantities of expensive materials can be used. In this type of cycle, the input temperature to the

turbine (the firing temperature), is relatively high (900 to 1,400 °C). The output temperature of the flue

gas is also high (450 to 650 °C). This is therefore high enough to provide heat for a second cycle

which uses steam as the working fluid; (a Rankine cycle).

In a combined cycle power plant, the heat of the gas turbine's exhaust is used to generate steam by

passing it through a heat recovery steam generator (HRSG) with a live steamtemperature between

420 and 580 °C. The condenser of the Rankine cycle is usually cooled by water from a lake, river, sea

or cooling towers. This temperature can be as low as 15 °C

In an automotive powerplant, an Otto, Diesel, Atkinson or similar engine would provide one part of the

cycle and the waste heat would power a Rankine cycle steam or Stirling engine, which could either

power ancillaries (such as the alternator) or be connected to the crankshaft by a turbo

compounding system.

Typical size of CCGT plants

For large scale power generation a typical set would be a 400 MW gas turbine coupled to a 200 MW

steam turbine giving 600 MW. A typical power station might comprise of between 2 and 6 such sets.

Efficiency of CCGT plants

By combining both gas and steam cycles, high input temperatures and low output temperatures can

be achieved. The efficiency of the cycles add, because they are powered by the same fuel source.

So, a combined cycle plant has a thermodynamic cycle that operates between the gas-turbine's high

firing temperature and the waste heat temperature from the condensers of the steam cycle. This large

range means that the Carnot efficiency of the cycle is high. The actual efficiency, while lower than

this, is still higher than that of either plant on its own. The actual efficiency achievable is a complex

area.

Relative cost of electricity by generation source:

When looking at the costs of electric power, to have any validity and usefulness, competing sources

need to be compared on a similar basis of calculation.

When comparing costs several internal cost factors have to be considered. Note we are not here

talking about price (i.e., actual selling price) since this can be affected by a variety of factors such as

subsidies on some energy and sources and taxes on others:

Capital costs (including waste disposal and decommissioning costs for nuclear energy)

Operating and maintenance costs

Fuel costs (for fossil fuel and biomass sources, and which may be negative for wastes)

Expected annual hours run

To evaluate the cost of production of electricity, the streams of costs are converted to a net present

value using the time value of money. Inherently renewables are on a decreasing cost curve, while

non-renewables are on an increasing cost curve.

There are additional costs for renewables in terms of increased grid interconnection to allow for

diversity of weather and load, but these have been shown in the pan-European case to be quite low,

showing that overall wind energy costs about the same as present day power.

Supplementary firing and blade cooling

The HRSG can be designed with supplementary firing of fuel after the gas turbine in order to increase

the quantity or temperature of the steam generated. Without supplementary firing, the efficiency of the

combined cycle power plant is higher, but supplementary firing lets the plant respond to fluctuations of

electrical load. Supplementary burners are also called duct burners.

More fuel is sometimes added to the turbine's exhaust. This is possible because the turbine exhaust

gas (flue gas) still contains someoxygen. Temperature limits at the gas turbine inlet force the turbine

to use excess air, above the optimal stoichiometric ratio to burn the fuel. Often in gas turbine designs

part of the compressed air flow bypasses the burner and is used to cool the turbine blades.

Fuel for combined cycle power plants

Combined cycle plants are usually powered by natural gas, although fuel oil, synthesis gas or other

fuels can be used. The supplementary fuel may be natural gas, fuel oil, or coal. Biofuels can also be

used. Integrated solar combined cycle power stations are currently under construction at Hassi

R'mel, Algeria and Ain Beni Mathar, Morocco [5]. Next generation nuclear power plants are also on the

drawing board which will take advantage of the higher temperature range made available by the

Brayton top cycle, as well as the increase in thermal efficiency offered by a Rankine bottoming cycle.

Heat recovery steam generator

HRSG:

A heat recovery steam generator or HRSG is an energy recovery heat exchanger that recovers heat from a hot gas stream. It producessteam that can be used in a process or used to drive a steam turbine. A common application for an HRSG is in a combined-cycle power station, where hot exhaust from a gas turbine is fed to an HRSG to generate steam which in turn drives a steam turbine. This combination produces electricity more efficiently than either the gas turbine or steam turbine alone. Another application for an HRSG is in diesel engine combined cycle power plants, where hot exhaust from a diesel engine is fed to an HRSG to generate steam which in turn drives a steam turbine. The HRSG is also an important component in cogeneration plants. Cogeneration plants typically have a higher overall efficiency in comparison to a combined cycle plant. This is due to the loss of energy associated with the steam turbine

HRSGs consist of three major components. They are the Evaporator, Superheater, andEconomizer. The different components are put together to meet the operating requirements of the unit.

Evaporator:

Within a downstream processing system, several stages are used to further isolate and purify the desired product. The overall structure of the process includes pre-treatment, solid-liquid separation, concentration, and purification and formulation. Evaporation falls into the concentration stage of downstream processing and is widely used to concentrate foods, chemicals, and salvage solvents. The goal of evaporation is to vaporize most of the water from a solution containing a desired product. After initial pre-treatment and separation, a solution often contains over 85% water. This is not suitable for industry usage because of the cost associated with processing such a large quantity of solution, such as the need for larger equipment.

Superheater

 superheater is a device used to convert saturated steam or wet steam intodry steam used for

power generation or processes. There are three types of superheaters namely: radiant, convection,

and separately fired. A superheater can vary in size from a few tens of feet to several hundred feet (a

few meters or some hundred meters).

A radiant superheater is placed directly in the combustion chamber.

A convection superheater is located in the path of the hot gases.

A separately fired superheater, as its name implies, is totally separated from the boiler.

A superheater is a device in a steam engine, when considering locomotives, that heats the steam

generated by the boiler again, increasing its thermal energy and decreasing the likelihood that it

will condense inside the engine [1] [2]. Superheaters 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. Superheaters were applied

to steam locomotives in quantity from the early 20th century, to most steam vehicles, and to stationary

steam engines. This equipment is still an integral part of power generating stations throughout the

world.

General arrangement of a superheater installation in a steam locomotive.

Applications

Heat recovery can be used extensively in energy projects.

In the energy-rich Persian Gulf region, the steam from the HRSG is used for desalinationplants.

Universities are ideal candidates for HRSG applications. They can use a gas turbine to produce

high reliability electricity for campus use. The HRSG can recover the heat from the gas turbine to

produce steam/hot water for district heating or cooling.

Economizer:

Economizers, or in British English economisers, 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, powerplant, and heating, ventilating, and air-conditioning (HVAC) uses are discussed in this article. In simple terms, an economizer is a heat exchanger.

Gas turbine operation

Gas turbines are described thermodynamically by the Brayton cycle, in which air is compressed isentropically, combustion occurs at constant pressure, and expansion over the turbine occurs isentropically back to the starting pressure.

In practice, friction and turbulence cause:

1. Non-isentropic compression: for a given overall pressure ratio, the compressor delivery temperature is higher than ideal.

2. Non-isentropic expansion: although the turbine temperature drop necessary to drive the compressor is unaffected, the associated pressure ratio is greater, which decreases the expansion available to provide useful work.

3. Pressure losses in the air intake, combustor and exhaust: reduces the expansion available to provide useful work.

As with all cyclic heat engines, higher combustion temperature means greater efficiency. The limiting factor is the ability of the steel, nickel, ceramic, or other materials that make up the engine to withstand heat and pressure. Considerable engineering goes into keeping the turbine parts cool. Most turbines also try to recover exhaust heat, which otherwise is wasted energy. Recuperators are heat exchangers that pass exhaust heat to the compressed air, prior to combustion. Combined cycle designs pass waste heat to steam turbine systems. And combined heat and power (co-generation) uses waste heat for hot water production.

Mechanically, gas turbines can be considerably less complex than internal combustion piston engines. Simple turbines might have one moving part: the shaft/compressor/turbine/alternative-rotor assembly (see image above), not counting the fuel system. However, the required precision manufacturing for components and temperature resistant alloys necessary for high efficiency often make the construction of a simple turbine more complicated than piston engines.

More sophisticated turbines (such as those found in modern jet engines) may have multiple shafts (spools), hundreds of turbine blades, movable stator blades, and a vast system of complex piping, combustors and heat exchangers.

As a general rule, the smaller the engine the higher the rotation rate of the shaft(s) needs to be to maintain top speed. Turbine blade top speed determines the maximum pressure that can be gained, this produces the maximum power possible independent of the size of the engine. Their are eight gas turbine in Faisalabad power plant and normal turbine speed is 51000rpm.

Turbine

A turbine is a rotary engine that extracts energy from a fluid or air flow and converts it into useful work.

The Exhaust temperature of turbine in gas turbine power station (1-8) has 4830C .It has 2 stages. Normal turbine speed is 51000 RPM.

The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum, with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and impart rotational energy to the rotor. Early turbine examples are windmills and water wheels.

Gas, steam, and water turbines usually have a casing around the blades that contains and controls the working fluid. Credit for invention of the steam turbine is given both to the British Engineer Sir Charles Parsons (1854-1931), for invention of the reaction turbine and to Swedish Engineer Gustav de Laval (1845-1913), for invention of the impulse turbine. Modern steam turbines frequently employ both reaction and impulse in the same unit, typically varying the degree of reaction and impulse from the blade root to its periphery.

Operation of turbine

A working fluid contains potential energy (pressure head) and kinetic energy (velocity head). The fluid may be compressible or incompressible. Several physical principles are employed by turbines to collect this energy:

Impulse turbines 

These turbines change the direction of flow of a high velocity fluid or gas jet. The resulting impulse spins the turbine and leaves the fluid flow with diminished kinetic energy.

There is no pressure change of the fluid or gas in the turbine rotor blades (the moving blades), as in the case of a steam or gas turbine, all the pressure drop takes place in the stationary blades (the nozzles).

Before reaching the turbine, the fluid's pressure head is changed to velocity head by accelerating the fluid with a nozzle. Pelton wheels and de Laval turbines use this process exclusively. Impulse turbines do not require a pressure casement around the rotor since the fluid jet is created by the nozzle prior to reaching the blading on the rotor. Newton's second law describes the transfer of energy for impulse turbines.

Reaction turbines 

These turbines develop torque by reacting to the gas or fluid's pressure or mass. The pressure of the gas or fluid changes as it passes through the turbine rotor blades. A pressure casement is needed to contain the working fluid as it acts on the turbine stage(s) or the turbine must be fully immersed in the fluid flow (such as with wind turbines). The casing contains and directs the working fluid and, for water turbines, maintains the suction imparted by the draft tube. Francis turbines and most steam turbines use this concept. For compressible working fluids, multiple turbine stages are usually used to harness the expanding gas efficiently. Newton's third law describes the transfer of energy for reaction turbines.

Electrical generator

In electricity generation, an electrical generator is a device that converts mechanical energy to electrical energy. The reverse conversion of electrical energy into mechanical energy is done by a motor; motors and generators have many similarities. A generator forces electric charges to move through an external electrical circuit, but it does not create electricity or charge, which is already present in the wire of its windings. It is somewhat analogous to a water pump, which creates a flow of water but does not create the water inside. The source of mechanical energy

may be a reciprocating or turbine steam engine, water falling through a turbine or waterwheel, an internal combustion engine, a wind turbine, a hand crank, compressed air or any other source of mechanical energy. Generators of gas turbines (1-8) are air cooled capacity of 32000 KVA. Voltage are 10.5 KV. Exciting Voltage are 140V, excitation current is 540 Amps and speed is 3000 RPM.

Equivalent circuit

The equivalent circuit of a generator and load is shown in the diagram to the right. To determine the generator's VG and RG parameters, follow this procedure: -

Before starting the generator, measure the resistance across its terminals using an ohmmeter. This is its DC internal resistance RGDC.

Start the generator. Before connecting the load RL, measure the voltage across the generator's terminals. This is the open-circuit voltage VG.

Connect the load as shown in the diagram, and measure the voltage across it with the generator running. This is the on-load voltage VL.

Measure the load resistance RL, if you don't already know it.

Calculate the generator's AC internal resistance RGAC from the following formula:

Equivalent circuit of generator and load.G = generator

VG=generator open-circuit voltageRG=generator internal resistanceVL=generator on-load voltageRL=load resistance

Note 1: The AC internal resistance of the generator when running is generally slightly higher than its DC resistance when idle. The above procedure allows you to measure both values. For rough calculations, you can omit the measurement of RGAC and assume that RGAC and RGDC are equal.

Note 2: If the generator is an AC type, use an AC voltmeter for the voltage measurements.

The maximum power theorem states that the maximum power can be obtained from the generator by making the resistance of the load equal to that of the generator. This is inefficient since half the power is wasted in the generator's internal resistance; practical electric power generators operate with load resistance much higher than internal resistance, so the efficiency is greater.

Generator terminology

The two main parts of a generator or motor can be described in either mechanical or electrical terms

Mechanical:

Rotor: The rotating part of an electrical machine

Stator: The stationary part of an electrical machine

Electrical:

Armature: The power-producing component of an electrical machine. In a generator, alternator, or dynamo the armature windings generate the electrical current. The armature can be on either the rotor or the stator.

Field: The magnetic field component of an electrical machine. The magnetic field of the dynamo or alternator can be provided by either electromagnets or permanent magnets mounted on either the rotor or the stator.

Because power transferred into the field circuit is much less than in the armature circuit, AC generators nearly always have the field winding on the rotor and the stator as the armature winding. Only a small amount of field current must be transferred to the moving rotor, using slip rings. Direct current machines necessarily have the commutator on the rotating shaft, so the armature winding is on the rotor of the machine.

Excitation

An electric generator or electric motor that uses field coils rather than permanent magnets will require a current flow to be present in the field coils for the device to be able to work. If the field coils are not powered, the rotor in a generator can spin without producing any usable electrical energy, while the rotor of a motor may not spin at all. Very large power station generators often utilize a separate smaller generator to excite the field coils of the larger.

Transformer

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core, and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF) or "voltage" in the secondary winding. This effect is called mutual induction.

If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding (VS) is in proportion to the primary

voltage (VP), and is given by the ratio of the number of turns in the secondary (NS) to the number of turns in the primary (NP) as follows:

By appropriate selection of the ratio of turns, a transformer thus allows an alternating current (AC) voltage to be "stepped up" by making NS greater than NP, or "stepped down" by making NS less than NP.

In the vast majority of transformers, the coils are wound around a ferromagnetic core, air-core transformers being a notable exception.

Transformers come in a range of sizes from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of national power grids. All operate with the same basic principles, although the range of designs is wide. While new technologies have eliminated the need for transformers in some electronic circuits, transformers are still found in nearly all electronic devices designed for household ("mains") voltage. Transformers are essential for high voltage power transmission, which makes long distance transmission economically practical.

Combined cycle operation

This design consists of a combustion turbine/generator, a heat recovery steam generator, and a steam turbine/generator. The exhaust heat from the combustion turbine is recovered in the heat recovery steam generator to produce steam. This steam then passes through a steam turbine to power another generator, which produces more electricity. Combined cycle is more efficient than conventional power generating systems because it re-uses waste heat to produce more electricity. The integration of these technologies provides the high efficiency of the combined-cycle design with the low cost of coal for fuel.

Central thermal workshop

In central thermal workshop there are many processes that have been done on the heavy parts of gas turbines or steam power stations like rotors, diaframes (first stage, second stage etc) different types of bearings, blasters etc

During my internship period in thermal work shop a generator rotor of gas turbine power station also repaired so its report also included in this.

The whole process is divided into different steps

Chemical cleaning Cleaning shop Non destructive test shop Cutting, Welding & grinding

Chemical cleaning:

Those parts that have high scaling can dip in the chemical for the cleaning proposes.

Cleaning shop:

There are different processes to clean the heavy jobs (parts of the machine).

Decreasing plant Vacuum blast junior Vapors blasting Steam jet cleaner Sand blasting

Decreasing plant:

This is just like a big container or tub which is use to dip the parts that we need to clean. In this tryo chloro ethylene is used. The normal temperature of this is

87 c. at this temperature the steam is produce and it will remove the oil and grease from the small point and curves in the job.

Vacuum blast junior:

This is a small machine used for cleaning purposes of small parts.

Vapors blasting:

Is also used for cleaning propose Zyte 35% +air +water65%

Steam jet cleaner:

It is Portable machine in which we use different materials is used according to our requirements like Chemical, water, any cleaning liquid.

Sand blasting:

This process is used for cleaning propose. Basically sand is used in this process the sand is throwing with a high speed on the job to clean

Non destructive test shop

The five major test perform that can be performed in non destructive test shop means these test perform on the jobs without any damage.

These are included:

visual inspection penitent method magnetic practical inspection ultrasonic method x ray radio graphy

Visual inspection:

In visual inspection the job can be inspected simply without any other machine.

Penitent method:

In penitent method there are two processes

Day light dark light

Spot checking self emulsifying oil use as penitent Red penitent + it penetrate on a small cracks and water

Cleaner + wash able.Developer Fluorescent powder is used as developer and check through ultraviolet light.

Process time Process time 20-30 min20-30 min

Magnetic practical inspection:

In this process the material must be ferrous base

Max 4000amp – min 5 amp current when magnetize.

Day light dark light

Ferro flux flu flux Job base must be check through ultraviolet light

White crack lines grenish

Cutting & Welding:

The damaged parts of the job are removed by cutting and then after this the cut portion is filled by welding of the same material of the job.

5 types of welding are used to done this process

Arc welding Gas welding Tig welding Mig welding Spot welding

Arc welding:

Electricity is used in this process

Gas welding:

Oxygen + astalene gas is used

Tig welding:

Tungsten inert gas welding (helium + organ gas is used) also known as organ welding

Mig welding:

Metal inert gas welding

Spot welding:

Spot welding is just like between two points such as cars body.

Some other heavy machines also there

cnc machine

Horizontal Lath machine

Vertical lath machine Drilling machine Balancing machine Types of rotors

REPAIR REPORT

Cleaning of Rotor Shaft Bore of 25 MW Generator Rotor GTPS Faisalabad

REPAIR OF 25 MW GENERATOR ROTORGTPS FAISALABAD

TABLE OF CONTENTS

S/N DESCRIPTION PAGE NO.

1. INTRODUCTION OF WORKSHOP. 30

2. SPECIFICATIONS OF 25 MW GENERATOR ROTOR GTPS FAISALABAD.

32

3. CASE STUDY / REPAIR PROCEDURE STEPS.

33 - 35

4. NON DESTRUCTIVE TESTING REPORT.

36

5. DYNAMIC BALANCING REPORT. 37

6. PICTURES OF GENERATOR ROTOR

38 - 47

7. SUM UP COMPONENTS REPAIRED FROM 1982 TO 6/2009

48 - 49

8. SOME SPECIAL JOB REPAIRED IN THIS WORKSHOP

20 - 25

CENTRAL GAS TURBINE MAINTENANCE WORKSHOP WAPDA FAISALABAD

Central Gas Turbine Maintenance Workshop at Faisalabad was established in 1983 to cater for the repair needs of all types of Gas Turbine parts, especially Hot Gas Path Components of the whole WAPDA Power Generation System.

Initially this Workshop was established to provide repair facilities only to Gas Turbine power station Faisalabad but later on repair facilities were extended to other power stations. Keeping in view the rising importance of this Workshop Authority decided to upgrade it. For this purpose in 1995 new machines and T&P were imported from abroad and now this Workshop can handle all turbines parts of Thermal Power Stations of Wapda.

Heavy Duty CNC Horizontal and Vertical Lathe machines, Radial Arm Drill machine, Milling machines Overhead cranes, Heavy Duty Dynamical Balancing and Moment Weighing Balancing machines, Alloy analyzer, Plasma Spray Coating System, Vacuum Annealing Furnace, NDT equipments and many other T&P is available to carry out satisfactory repair of sophisticated turbines parts including Turbine Rotors, Generator Rotors, Heavy Duty Motors, Turbine Casings, Diaphragms, Combustor Liners, Transition Pieces, Shroud Blocks etc.

In short now this Workshop is capable to provide repair facilities to all Thermal Power Stations. This workshop has proved it importance in the Wapda by putting best efforts to bring damaged power turbines back in operation within minimum possible time and cutting down their outage time and make them available for production of extra electric power for the country. By repairing turbine parts of Wapda formations within country, this Workshop has saved precious foreign exchange of billions of rupees.

In addition to precious foreign exchange saving for Wapda, this Workshop has also earned hard cash amounting to Rs.178.254 Millions from Private Industry since it’s commissioning. This became possible only due to additional un-tired efforts of Engineers, Workers and Management of this Workshop.

SPECIFICATIONS OF 25 MW GENERATOR ROTOR GTPS FAISALABAD

1 Make M/S AEG-KANIS Germany

2 Capacity 32 MVA

3 Power Factor 0.8

4 Speed 3000 RPM

5 Voltage 10.5 KV

6 Current 1682 A

7 Type of Cooling Cir-Cooled

8 Grounding Resistance Grounding

9 Frequency 50 Hz

10 No. of Poles 02 Nos.

11 Insulation Class-F

CASE STUDY

HISTORY AND SCOPE.

Generator Rotor of 25 MW Gas Turbine Power Plant (Unit No.7) operating at 200 MW Gas Turbine Power Plant Faisalabad was received in Workshop for inspection and repair purposes on 05-08-2009. At 200 MW GTPS Faisalabad total eight units of 25 MW capacity each are operating since 1973. Turbines have been supplied by M/S G.E USA whereas generators have been provided by M/S AEG KANIS. The capacity of each generator is 32 MVA.

The Rotor of the generator keeping in view the speed of turbine and operating frequency in our country i.e. 50 c/s has been designed as two pole generator. The rotor has been provided with latest excitation system i.e. ROTA DUCT. To supply excitation current to both coils a bore of 80 mm dia. & 2000 mm in length has been drilled in the rotor body. In this bore glass fibre rod which accommodates two copper main lead (25x2000 mm) has been fitted. From these excitation copper strips current is supplied to both coils of the rotor.

Fiber glass rod keeping in view the maintenance of rotor has been designed in two pieces. The length of each half is approximately one meter.

FAULT DIAGNOSIS.

During preliminary inspection the rotor body was found dead short with the body. First of all after the removal of both axial fans both end rings were also removed from rotor windings. After necessary cleaning of the windings improvement in winding resistance was not noted. So next step was to disconnect the connecting leads from both coils and removal of the both leads alongwith its fiber glass fitting from the bore.

After disconnecting the leads from both ends again insulation of both coils was noted which was found as infinity. So it was concluded that the fault was with the main exciting current supply leads.

When the main leads was pulled out from the bore only half portion with its fiber glass & fitting came out where as the 2nd half remained in the body which indicated occurrence of major damage to the supply leads inside the Rotor bore.

Following were the extent of damages noted:-

1. Main copper strips which are two meter long had broken into two pieces due to short circuiting.

2. Fibre glass rod in which the copper strips are adjusted had burnt due to flash of short circuit.

3. Molten copper in the form of spatters and pieces had stuck with the rotor body inside the bore.

4. Both bolts joining the coils with main copper strips had also given way at their joining points with the strips

5. 2nd half of the fiber glass rod with damaged strips has stuck inside the rotor body and was very difficult to remove.

6. The bore of the rotor body which had damaged due to short circuiting needed through cleaning/polishing.

REPAIR STEPS.

For the removal of the 2nd half of fibre rod fitting left inside the bore and cleaning/polishing of the bore following steps were carried out:-

1. Borescopic inspection of the available bore was carried out to check the exact position inside the bore.

2. A 3.5 meter long cutting tool was fabricated to reduce the diameter of the fibre rod from 80 mm to 70 mm dia & also to remove stickings of fibre rod with rotor body.

3. Rotor was fitted on the lathe machine and with the help of the above mentioned tool the fiber rod was machined from 80 to 70 mm dia.

4. After machining another fixture was designed/fabricated to pull out the machine fibre rod from the body.

5. After removal of the whole fibre glass fitting boroscopic inspection of the bore was carried out in which lot of copper spatter and pieces was found stuck with the rotor body.

6. To clean the rotor bore honing tool was designed with which the bore was thoroughly cleaned and polished.

7. After detail market survey material was purchased/tested as per our requirement & then new fittings were fabricated. This activity was carried in parallel to cut down the down time of the repair time.

8. During fabrication numerous difficulties were faced which were solved one by one.

9. Complete new fitting was adjusted in side the rotor bore and connecting rods were screwed and same were brazed with the field windings of the rotor.

10.Insulation strength of the winding was checked and found satisfactory. 11.Both End Rings and Cooling Fans were fitted back on the rotor body with

the help of special fixtures.12.Finally rotor was dynamically balanced and sent to the Power Station for

fitting in the machine.

FINAL CONCLUSIONS.

As far as the fault finding is concerned it is crystal clear that the fault has occurred as a result of short circuiting between the excitation bars & rotor body due to face to face of the two fibre rods which accommodates both the exciting bars by the original manufacturer. Due to wrong machining/fitting carbon made a path between the bars & rotor body. At this point slowly short circuiting took place and ultimately the fibre burnt away, copper strips melted and broke into two pieces which stopped the flow of field current to both coils and caused tripped of Power Plant.

This was a original manufacturing fault (straight joint) which has been modified by providing overlap joint. This will not allow the carbon to make a short circuit path between the strips & rotor body for longer time.

It is suggested that in order to avoid the repetition of such fault on other units same modification may please be got done at the time of replacement/removal of end rings of the rotor.

NON DESTRUCTIVE TESTING REPORT OF 25 MW GENERATOR ROTOR RETAINING RINGS

INSPECTION TECHNIQUE.

In this method of inspection after proper cleaning of the job dye penetrant is applied to the job and at least half an hour is given to this dye penetrant for penetration. Then the job surface is cleaned very carefully and job is dried up. Finally the Developer is applied on the surface of the job. This developer sucks out the penetrant from the cracks by anti capillary action and makes it visible.

DYNAMIC BALANCING REPORT OF

25 MW GENERATOR ROTOR GTPS FAISALABAD

SUM UP OF COMPONENTS REPAIRED FROM

SINCE COMMISSIONING FROM 1982 TO 2009

S/N DESCRIPTION QTY.

1 Turbine Moving Buckets. 12756

2 Combustion Liners. 2993

3 Transition Pieces. 2352

4 Cross Fire Tubes. 2515

5 Shrouds Blocks. 1915

6 Bearings. 1606

7 Compressor Blades. 1513

8 Retainer Plates. 1645

9 Floating Seals. 1191

10 Bearing Pads. 1072

11 Swirl Tips. 918

12 End Seals. 907

13 Vane Segments. 682

14 Scrapper Chain Links. 517

15 Bull Horns. 664

16 Light / Heavy Motors. 370

17 Turbine Nozzle Support Rings 339

18 Turbine Nozzle. 325

19 Pressure Gauges. 300

20 Turbine Diaphragms. 257

21 Electronic Cards. 203

22 Track Block. 181

23 Labyrinth Seals. 134

24 Turbine Rotors. 138

25 Heavy Motor Rotors. 112

26 Stuffing Box Seals. 83

27 Bushes. 64

28 Contactors. 75

29 Generator Rotors. 63

30 Pumps. 62

31 Slip Rings. 55

32 Steam Turbine Diaphragm Support Ring. 49

33 Heavy Duty Shafts. 44

34 Hydrogen Seals. 60

35 Impellers. 34

36 Pressure Switches 28

37 Gears. 21

38 Diffusers. 21

39 Control Valves. 19

40 Solenoid Valves. 18

41 Multiple Disc Jaw Clutches. 15

42 Shaft Sleeves. 28

43 Combustor Wrapper. 13

44 Turbine Nozzle Discs. 14

45 Spring Seals. 13

46 Shaft Sleeves 14

47 Wiper Seal 2

48 Casings 4

SOME SPECIAL MAJOR JOBS REPAIRED

IN CENTRAL MAINTENANCE WORKSHOP

RE-BLADING OF 100 MW GAS TURBINE

AXIAL AIR COMPRESSOR TPS GUDDU

Re-blading of 100 Mw Axial Air Compressor Ge

Frame-9 TPS Guddu was carried out in this

Workshop. This job was done first time in our

country. Said Rotor is in operation at Thermal

Power Station Guddu.

One blade of 2nd stage had broken due to F.O.D which ultimately bended,

broken and cracked almost all the blades of the compressor. Physical

inspection revealed that all the blades need replacement with new one.

Axial compress rotor of GE Frame-9 machines was of very complex nature. It

consisted of 17 stages, each stage carriers different number of blade & size.

Hubs of each disc are fitted in next disc with negligible clearance. All the 17

discs were assembled with 18 stud bolts. These stud bolts were made of

special material were opened & tightened with special type of Bolt Tensioning

Machine which stretch the stud bolts upto 12000 Psi to opened re-tight the

nuts.

After fixing new blades in each disc, these were threaded in 18 Nos. stud bolts.

These stud bolts were tightened to 12000 Psi. locked. Finally rotor was

dynamically balanced and sent back to Guddu Thermal Power Station.

REPAIR OF AXIAL AIR COMPRESSOR OF

15 MW GAS TURBINE TPS KOTRI.

The rehabilitation work of Axial

Compressor was started on 27-02-2007

and within 30 days job was completed

and sent back to Kotri Power Station on

27-03-2007 for refitting back in the

housings.

It is 17 stages compressor. Numbers of blades in each stage vary from 56 to 60.

Blades in each stage are locked with special type of lock. So to remove blades

first of all the 17 locks were detached, grinded and pulled out with a specially

locally fabricated puller. Later on by hammering and sliding all the blades were

removed from compressor body. In total 972 blades are removed. Each blade

is a parted from the next one with the help of a wedge so all the wedges were

also checked. Damaged were replaced with new ones. All the blades were also

replaced with new one. Rotor was mechanically cleaned, NDT was carried out,

blades, wedges, locks wire were refitted and finally locks were adjusted.

Labyrinth Seals were also replaced with new ones, journal were polished.

Rotor was shifted on balancing machine. Necessary balancing weights were

added.

Repair work of Axial Compressor was completed in 30 days after balancing

Rotor was sent back to Kotri Power Station on 26-03-2007.

REPAIR OF TURBINE ROTOR OF 15 MW

GAS TURBINE TPS KOTRI

It is seven stages Rotor. Total numbers of

blades installed in seven stages are 609.

Each stage is provided with special type of

lock. So to remove blades all the locks

were grinded and pulled out with a special

type of locally fabricated puller. After

removing wedge, blades, locking wire Rotor was sent out side for mechanical

cleaning, NDT of Rotor was carried out. After chemical and mechanical

cleaning, NDT of blades was also carried out. Healthy blades were retained,

repair work on some of the blades was carried out were as the damaged

blades were replaced with healthy ones.

After fixing locking wire, wedges & blades seals were rectified, Rotor was

shifted on balancing machine where after successful balancing Turbine Rotor

was competed in 25 days. Rotor was despatched back to Kotri Power Station

on 23-04-2007.

RE-BLADING OF 210 MW L.P TURBINE ROTOR OF TPS GUDDU.

Re-blading of 210 MW L.P Turbine Rotor of

TPS Guddu was carried out in this Workshop.

This job was done first time in our country.

Said Rotor is in operation at Thermal Power

Station Guddu. By repairing this Workshop

was able to save 8.10 Billions (approximately)

by commissioning the Plant 435 days earlier in terms of cost of power

generation and 20 Millions in respect if said Rotor has been sent abroad for

repair.

RE-BLADING OF 65 MW STEAM TURBINE ROTOR & REPAIR OF HP CASING OF SPS FAISALABAD.

Re-blading of 65 MW Steam Turbine Rotor,

repair of HP Casing and other miscellaneous

works of SPS Faisalabad were carried out from

16-02-2007 to 19-03-2007 which helped to

boost up the output of machine. Moreover,

approximately 995 Millions were saved in terms of cost of power generation by

doing the repair work in this Workshop and bringing back the Power Unit on

bar 240 days earlier.

RE-BLADING OF 320 MW STEAM TURBINE ROTOR OF TPS MUZAFFARGARH.

L.P Rotor of 320 MW Steam Turbine was

received in Workshop on 15-02-2008 and was

despatched back to TPS Muzaffargarh on 29-

02-2008. Staff & Engineers worked day &

night and completed the re-blading work in

shortest possible time of 12 days.

If this Rotor had to sent out of country for re-blading then at least 30 months

period was required for tendering, insurance, completing documents sending

Rotor abroad to either country for repair work actual repair time and then

bring the same back to TPS Muzaffargarh. Now this plant generates 6240000

KWH per day. Thus Billions of rupees have been saved in respect of time

saving/extra power generation and repair cost if same Rotor was sent abroad

for repair.

CONCLUSION

During my internship training at northern power Generation Company limited

Faisalabad. I have learned a lot. It was a good experience for me.

GOOD FEATURES

The staffs of all departments are highly professional. All the members of this

departments are highly educated and trained they work in a proper way and

follow all the ruled and regulations.