PREFACE…

It is well evident that work experience is an indispensable part of every professional course. In the same

manner practical training in any organization is a must for each and every individual the engineering

course. The rationale behind visiting the power plant and preparing the Project Report is to study the

electrical overview, mechanical overview, various cycles and processes (viz Steam Generation, Turbo

Generation, Synchronization …etc) of the power generation and details of control and instrumentation

required in Thermal Power Plant.

We have carried out this training under well experienced and qualified engineers and technician from

various departments’ viz. Electrical, Mechanical, Chemical and Control and Instrumentation

departments. We have taken the opportunity to explore the Electrical Department, its use, necessity in

power plant and maintenance of various instruments used for monitoring and controlling the numerous

processes of power generation.

We have tried our best to cover all the aspects of the power plant and their brief detailing in this project

report. All the above mentioned topics will be presented in the following pages of this report. The main

aim to carry out this training is to familiarize ourselves with the real industrial scenario, so that we can

relate with our engineering studies.

Acknowledgment

Inspiration and guidance are invaluable in all aspect of life, especially when it is academic. I acknowledge my gratitude to all those who has given me timely help me in completing my training report. Training work is a major part of our course. It is a period in which we are introduced to the industrial environment or in other words we can say that industrial training is provided for the familiarization with the industrial environment, with the increased automation in the industries to increase their production. I am highly obliged to Mr.Anwar Ali Brohi (CEO) for allowing us to join JTPS, as a trainee. I also want to express deep sense and gratitude to Mr.Rizwan and Mr.Rehan for his personal efforts in taking me to sites, explaining the working of power plant Turbine, Generator and its auxiliaries. his valuable guidance during my training at JamshoroThermal Power Station. The object of this training work is to raise the level of performance in one or more of its aspects and this may be achieved by teaching new trends, by imbuing an individual with new attitudes, motives & other personality characteristics. Practical training is an important part of theoretical studies. It covers all that remains in the classroom i.e. without it our studies remains ineffective & Incomplete. Also it explores a student to an invaluable treasure of experience. Also it is a well known fact that practical training plays a very important role in future building of an

individual. Only gaining theoretical knowledge is just not sufficient for sure success in life, practical

training is must & I have been given an opportunity to gain practical experience at JAMSHORO THERMAL

POWER PLANT. I avail this instance in a very satisfactory manner & think it will be very beneficial for me

in building my future.

Table of Contents

Table of Contents PAGE NO:

Introduction 2

Basic needs and overview of a power plant 3

Jamshoro Thermal Power Station 5-7

Water Handling Plant 7-9

Components of Steam/Water Cycle Furnace and Boiler 9-10

Furnace and Boiler 10-12

Steam Turbine 12-14

Electrical System Overview 15-19

Automatic Voltage Regulator 20

Bibliography 21

INTRODUCTION

Electricity generation is the process of generating electric power from sources of energy. Electricity is most often generated at a power station by electromechanical generators, primarily driven by heat engines fuelled by chemical combustion or nuclear fission but also by other means such as the kinetic energy of flowing water and wind. There are many other technologies that can be and are used to generate electricity such as solar photovoltaic and geothermal power. In Pakistan the abundance of gas and oil leads to establishment of thermal power stations and governing bodies namely PEPCO, IPP’s and PAEC power acts as pioneers in the generation of electricity.

Pakistan Electric Power Company (PEPCO)

The factors responsible for the shift in policies were: generation capacity could not be increased to meet demand; WAPDA's growth caused inefficiencies, 'demand suppression' and high tariff policy, proliferated theft. All these factors, over the years, adversely affected WAPDA's financial condition. As part of this program WAPDA's functions under its Water Wing and Power Wing were to be segregated. It was previously envisaged that all power generation, hydel as well as thermal, would be corporatized. However, later on it was decided that the hydel generation should remain part of the Water Wing or the remaining WAPDA. PEPCO has prepared the conceptual framework and is following a comprehensive strategy whereby WAPDA's vertical-monolithic Power Wing has been restructured into twelve (12) distinct autonomous entities under Companies Ordinance 1984. These are: three generation, one transmission and eight distribution corporate entities.

Vision To make

Pakistan Power Sector customer friendly, efficient, able and responsive in meeting tee electric energy requirements of industry, business and domestic customers, and move to an energy sufficient model from the current energy deficient scenario, on commercially viable and sustainable basis, in order to support the high growth economy and to meet the government's objective of "Power for All".

Thermal Generation

PEPCO's Thermal Power Generation is mainly based on generation of power from its Steam Turbo-Generators, Gas Turbines (simple as well as Combined Cycle Units) installed at different Power Stations located in Sindh, Punjab and Balochistan provinces. Indigenous Gas & Coal is the main fuel whereas Furnace oil and HSD are also used as alternative fuel. As per Government of Pakistan policy all thermal power generation has been restructured and four corporatized companies namely Jamshoro Power Generation Company Limited (GENCO-1) head quarter at Jamshoro district Dadu near Hyderabad Sindh, Central Power Generation Company Limited (GENCO-2) head quarter at Guddu district Jacobabad Sindh and Northern Power Generation Company Limited (GENCO-3) head quarters at Muzaffargarh and Lakhra Power Generation Company Limited (GENCO-IV) at Khanote (Sindh) have been formed and registered. Functioning of GENCOs has commenced.

Basics Needs and Overview of Thermal Power Plant

SITE REQUIREMENT:- The basic requirements of thermal power plant are determined by the type, size and other specifications of the plant. It is required to know the immediate capacity of the power plant after construction and the extension of capacity in the future, to determine the area required for construction of

the plant. The basic things that are taken into consideration areBasic Needs and Overview of a Thermal Power Plant. The idea that STEAM has potential energy and can be converted into kinetic energy was given by famous scientist, Sir. James Watt. This idea became the governing principal of many mechanical processes and finally led to the success of Thermal Power Energy. The need of establishing a Thermal Power Plant came to engineers by the realization of the fact that Hydel Power could be utilized only for certain period of time in a year. This section will give the basic requirements for Thermal Power Plant.

<1>Station Building, <2>Cooling Towers, <3>Switch yard compound,<4> CLIMATIC.

CONDITION:- The tropical climate is best for erection of thermal power plant, because areas having high humidity

and fluctuating temperature lead to dew point and condensation which as a result damages the electrical machines and

corrodes the insulation and over head cables. Page | 7 TRANSMISSION: -The plant area must have route available for

transmission over head cables to the nearest grid lines or load points which will be capable of accepting the generated

power output of the power station.

EFFLUENTS:-Due to heavy rate of coal combustion residual volume is also high. The main residual product is ash.

The plant must have facilities like ash pond to dispose them safely without harming the environment.

TRANSPORT:- It is one of the another vital factor of the plant as huge burden lies on transportation in daily basis

because of huge need of coal, furnace oil, hydrochloric acid and other chemical products along with mechanical

products.

WATER REQUIREMENT:- Water is required in power plant for two basic needs, first is for steam generation and

second is for cooling purpose. Thermal Power Plant requires huge volume of water, nearly of about 3 to 4 Tons/hr/MW

only for steam generation. So site of plant must also have reliable and huge water sources located near to it.

GEOLOGY:- The geology of the site should be cost effective and the subsoil must be able to with stand huge load of

foundation. Surrounding areas and approaching.

AMENITIES:-Some considerations like availability of hospital, educational institutes and other facilities must be taken

into account.

PERSONNEL REQUIREMENTS:- To run a plant smoothly requirement of skilled and unskilled personnel is very

important. So recruitment of workers and skilled personnel should be made carefully and in adequate amount.

PROXIMITY OF AIRFIELDS:- The airfields must be studied properly to avoid mishaps as the chimney height

ranges from 500 to 600 fts and boiler housing is of 200 fts in general.

Schematic Diagram of Thermal Power Plant

Jamshoro Thermal Power Station

LOCATION

Thermal Power Station Jamshoro is situated in District Jamshoro (Sindh) 5 Km North-West of the village of Jamshoro on Indus High-way at the right bank of River Indus at Mohra Jabal, about 18 Km from center of Hyderabad. The city of Karachi is approximately 150 Km South-West of Jamshoro connected with Super-Highway.

Fuel (Gas / Furnace Oil) Supplies Sui Southern Gas Company Ltd (SSGCL) is in contract with WAPDA/JPCL to supply Gas for power generation at TPS Jamshoro. The daily Gas allocation is 62 MMCF with minimum guaranteed Gas supply of 53 MMCF. The Maximum requirement of Gas for three dual fired Units is about 140 MMCFD whereas average Gas requirement is 90 MMCFD. Furnace Oil is arranged at competitive bidding by oil marketing companies on fortnightly basis from Karachi through tank Lorries / tank wagons. Installed Capacity This Power Station comprises of four units having total capacity of 850 MW. Unit No.1 250 MW Japan origin is Furnace oil fired, whereas Units 2,3 and 4 of 200 MW China Origin each are dual fired i.e. Gas/Furnace Oil.

Unit No Rated Capacity Dependable Capacity Comm: Date Fuel Type

ST-1 250 MW 194 MW 27-01-1990 Furnace oil

ST-2 200 MW OFF

(Because of shortage of fuel)

03-12-1989 Dual( Gas+F.O)

ST-3 200 MW 130 MW 27-06-1990 Dual( Gas+F.O)

ST-4 200 MW 130 MW 21-01-1991 Dual( Gas+F.O)

Total 850 MW 454 MW

Details of TPS, Generating Units

UNIT-1 (Block I)

Project Digest (Complex-I)

Unit No

Installed Capacity (MW)

Fuel Commissioning Date Project Cost (Mil. Rs.)

Contractor Manufacturer

ST-1 250 Furnace Oil 27.01.1990 6,762 M/s Electric & Co. Japan

M/s Fuji Elect. & Co Japan M/s Mitsui/Relay Japan

Energy Generation Since Commissioning upto 30 June 2008

Unit No

Commissioning Date

Hours of Operation

Energy Generated (GWH)

ST-1 27-01-1990 109625 18198

UNIT-2 (Block I)

Project Digest (Complex-I)

Unit No Installed Capacity (MW)

Fuel Commissioning Date Project Cost (Mil. Rs.)

Contractor Manufacturer

ST-2 200 Dual (Gas/FO) 03.12.1989 8,869 M/s CMEC China

M/s Harbin Turbine, Boiler & Electrical Machinery Co Harbine China

Energy Generation Since Commissioning upto 30 June 2008

Unit No Commissioning Date

Hours of Operation

Energy Generated (GWH)

ST-2 03-12-1989 107821 15848

UNIT-3 (Block II)

Project Digest (Complex-I)

Unit No Installed Capacity (MW)

Fuel Commissioning Date Project Cost (Mil. Rs.)

Contractor Manufacturer

ST-3 200 Dual (Gas/FO) 17.08.1990 8,869 M/s CMEC China

M/s Harbin Turbine, Boiler & Electrical Machinery Co Harbine China

Energy Generation Since Commissioning upto 30 June 2008

Unit No Commissioning Date

Hours of Operation

Energy Generated (GWH)

ST-3 27-01-1990 94640 14137

UNIT-4 (Block II)

Project Digest (Complex-I)

Unit No Installed Capacity (MW)

Fuel Commissioning Date Project Cost (Mil. Rs.)

Contractor Manufacturer

ST-4 200 Dual (Gas/FO) 20.01.1991 8,869 M/s CMEC China

M/s Harbin Turbine, Boiler & Electrical Machinery Co Harbine China

Energy Generation Since Commissioning upto 30 June 2008

Unit No Commissioning Date

Hours of Operation

Energy Generated (GWH)

ST-4 21-01-1991 93404 13665

Water Handling Plant

In Thermal power plants, plenty of water is needed for generation of electricity. Water in a Power Plant is used for:

1. Production of Steam- for rotating turbine.

2. Cooling Purpose- For cooling of various equipments.

Water which is used as a working fluid needs some treatment.

Reasons to choose Water as a Working Fluid: •

It is only common substance available & exists in 3 states (Ice, water, steam)at normal temperature. • Having high

specific heat mean heat carrying capacity is high. • Having low specific volume than air. • Low Cost

• High Availability

• Non-reactive But water is

universal solvent; it dissolves many gases, salts, metals etc. so no source of water is pure so for the formation of

stem water should e pure otherwise generated steam will damage the turbine like rusting.

Impurities in Water Impurities present in water are grouped into 4 categories:

1) Suspended Matter • Mean any matter floating or suspended nature in water • Microorganisms • Grits

2) Dissolved Salts • Ca, Mg, K, Chlorates, Sulphates, Silicates etc.

3) Dissolved Gases Oxygen, Carbon dioxide, Ammonia etc.

Water is recycled and used for various purposes:

Water Cycle

Flow Chart

COMPONENT OF STEAM/WATER CYCLE: A fossil fuel steam generator includes an economizer, a steam drum, and the furnace with its steam generating tubes and super-heater coils. Necessary safety valves are located at suitable points to avoid excessive boiler pressure.

Condenser: The condenser condenses the steam from the exhaust of the turbine into liquid to allow it to be pumped. If the condenser can be made cooler, the pressure of the exhaust steam is reduced and efficiency of the cycle increases. 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. 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.

High Pressure Heater: A heater located downstream of boiler feed pump. Typically, the tube side design pressure is at least 100Kg/cm2, and the steam source is the high pressure turbine. [The heating process by means of extraction of steam is referred to as being regenerative]

Low Pressure Heater: A Heater is located between the condensate pomp and either of the boiler feed pump. It normally extracts steam from low pressure turbine.

GSC: Gland steam condenser is meant for condensing the steam which was used for sealing the LABYRINTH GLAND and reusing it in cycle.

Economizers: These are heat exchange devices that heat fluids, usually water, up to but not normally beyond the boiling point of that fluid. Economizers are so named because they can make use of the enthalpy in fluid streams that are hot, but not hot enough to be used in a boiler, thereby recovering more useful enthalpy and improving the boilers efficiency. They are a device fitted to a boiler which saves energy by using the exhaust gases from the boiler to preheat the feed. Typically the cooling water causes the steam to condense at a temperature of about 35 °C (95 °F) and that creates an absolute pressure in the condenser of about 2–7 kPa (0.59–2.1 in Hg), i.e. a vacuum of about −95 kPa (−28.1 in Hg) relative to atmospheric pressure. The large decrease in volume that occurs when water vapours condenses to liquid creates the low vacuum that helps pull steam through and increase the efficiency of the turbines. 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.

Cooling Towers: The condensate (water) formed in the condenser after

condensation is initially at high temperature. This hot water is passed to cooling

towers. It is a tower- or building-like device in which atmospheric air (the heat receiver)

circulates in direct or indirect contact with warmer water (the heat source) and the

water is thereby cooled. A cooling tower may serve as the heat sink in a conventional

thermodynamic process and when it is convenient or desirable to make final heat

rejection to atmospheric air. Water, acting as the heat-transfer fluid, gives up heat to

atmospheric air, and thus cooled, is recirculate through the system, affording

economical operation of the process. With respect to drawing air through the tower,

there are three types of cooling towers: a).

Natural Draft b).Induced draft c).Forced Draft

Note: Here at JTPS Forced Draft Cooling Method is used.

Forced Draft Cooling Tower

Furnace and Boiler

What is Boiler?

A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including boiler-based power generation, cooking, and sanitation. Here in TPS Jamshoro, the boiler is a rectangular furnace about 50 feet (15 m) on a side and 130feet (40 m) tall. Its walls are made of a web of high pressure steel tubes about 2.3inches (58 mm) in diameter.

Types of Boiler:

Fire Tube Boiler: In fire tube boiler, hot gases pass through the tubes and boiler feed water in the shell side is converted into steam. Fire tube boilers are generally used for relatively small steam capacities and low to medium steam pressures. As a guideline, fire tube boilers are competitive for steam rates up to 12,000 kg/hour and pressures up to 18 kg/cm2. Fire tube boilers are Fire tube Boiler available for operation with oil, gas or solid fuels. For economic reasons, most fire tube boilers are nowadays of “packaged” construction (i.e. manufacturers shop erected) for all fuels.

Water Tube Boiler: In water tube boiler, boiler feed water flows through the tubes and enters the boiler drum. The circulated water is heated by the combustion gases and converted into steam at the vapor space in the drum. These boilers are selected when the steam demand as well as steam pressure requirements are high as in the case of process cum power boiler / power boilers. Most modern water boiler tube designs are within the capacity range 4,500 – 120,000 kg/hour of steam, at very high-pressures. Many water tube boilers nowadays are of “packaged” construction if oil and /or gas are to be used as fuel. Solid fuel fired water tube designs are available but packaged designs are less common.

Note: At TPS, Jamshoro, Water tube Boilers are incorporated.

Furnace:

A furnace is a device used for heating. The name derives from Latin fornix, oven. The boiler furnace auxiliary equipment include soil or gas 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 fuel i.e. gas or

oil. The gas or oil is blown with part of the combustion air into the boiler plant through a series of burner nozzles. Secondary and tertiary air may also be added. Combustion takes place at temperatures from 1300-1700°C. Particle residence time in the boiler is typically 2 to 5 seconds, and the particles must be small enough for complete combustion to have taken place during this time. This system has many advantages such as ability to fire varying quality of coal, quick responses to changes in load, use of high pre-heat air temperatures etc. One of the most popular systems for firing pulverized coal is the tangential firing using four burners corner to corner to create a fireball at the center of the furnace.

Boiler Drum: -

Boiler Drum is the part of boiler where the dematerialized water is stored and is inserted into the boiler. It is also houses the steam that is formed in the boiler. Water stored in the drum comes down to the top of the boiler and forms a Water Ring which’s then inserted into the boiler through the water walls. Water Walls are basically tubes along the walls of the furnace, it is here where the water is converted into steam at1300 and water separated due to centrifugal force. The pressure of boiler drums is150kg/sq.cm and must be always maintained. Water in the drum comes from feed control station via economizer.

Steam Turbine

The 250/210 MW turbine installed in TPS, Jamshoro is one of condensing-tandem-compound, three cylinder, horizontal, disc, and diaphragm, reheat type with nozzle governing and is directly coupled with A.C generator.

ROTOR: -

The rotor is basically the main rotating part of the turbine which is also called the shaft and is attached with the rotor of the A.C generator via coupling. Rotor is basically divided into 3 categories and they are as follows: -

a) HIGH PRESSURE ROTOR: - This is basically made of single Cr-Mo-V steel forged with internal disc attached to T-shoot fastening designed especially for stabilizing the HPT and preventing the axial shift. b) INTERMEDIATE PRESSURE ROTOR: - This is made from high creep resisting Cr- Mo-V steel forging and the shrunk fit disc are machined from nickel-steel forging. This basically adjusts the frequency of the blades. c) LOW PRESSURE ROTOR: - This is made from the above mention alloy used in IP Rotors; blades are secured to the respective disc by riveted fork root fastening. Wires are provided in all stages of this to adjust the frequently of the blades.

BLADES: - Blades are single

most costly element fitted in the turbine. Blades fitted in the stationary part are called guide blades and those

fitted in the rotor are called moving or working blades. Blades are of basically three types, they are as follows: -

a) Cylindrical ( constant profile) blade

b) Tapered cylindrical blade

c) Twisted and varying profile blade

SEALING GLANDS: -

To eliminate the possibility of steam leakage to the atmosphere from the inlet and the exhaust end

of the cylinder, labyrinth glands of the radial clearance type are provided which provide a trouble free

frictionless sealing.

EMERGENCY STOP VALVES AND CONTROL VALVES: -

Turbine is equipped with emergency stop valves to cut off steam supply and with control valve regulate

steam supply. Emergency stop valves are provided in main stream line and control valves are provided in the hot

reheat line.

COUPLING: -

Since the rotor is made in small parts due to forging limitations and other technological and economic

reasons, the couplings are required between any two rotors. The coupling permits angular misalignment, transmits

axial thrust and ensures axial location.

BEARING: -

Journal bearing are manufactured in two halves and usually consist of bearing body faced with anti-friction

tin based habiting to decrease coefficient of friction. Bearings are usually force lubricated and have provision for

admission of jacking oil. Thrust bearing is normally Mitchell type and is usually combined with a journal bearing,

housed in spherically machined steel shell. The bearing between HP and IP rotor is of this type. The rest is of

journal type.

BARRING GEAR: -

The barring gear is mounted on the L.P rear bearing cover to mesh with spur gear L.P rotor rear coupling.

The primary function of the barring gear is to rotate the rotor of the turbo generator slowly and continuously during

the start-up and shut sown process when the temperature of the rotor changes.

TURBINE LUBRICATION OIL SYSTEM: -

The LUB-OIL system of turbine comprises of following category.

a) MAIN OIL PUMP: - It is mounted on the front bearing pedestal and coupled through gear coupling to the rotor.

When the turbine is running at its normal speed of 3000rpmthen the oil to the governing system (at 20 kg/sq.cm)

and to the lubrication system (at 1 kg/sq.cm) is supplied by this pump.

b) STARTING OIL PUMP: - It is a multi-staged centrifugal oil pump driven by A.C powered electric motor. It

provides the oil requirement for starting up and stopping of the turbine. It provides oil to the governing system and to

the lubrication system until the turbine is running at speed lower than 2800rpm.

c) STANDBY OIL PUMP: - This is a centrifugal pump driven by A.C motor. It runs for initial10 minutes at the

starting to remove air from the governing system and fill up oil to it. d) EMERGENCY OIL PUMP: -

This is a centrifugal pump driven by D.C motor. This pump is foreseen as a backup oil pump to A.C oil pumps. This

pump automatically cuts in when the A.C power fails in the power station.

e) JACKING OIL PUMP: - This pump enables the complete rotor assembly to be raised upon to be floated in the

bearing assembly during the start-up and shut down process of the process. Thus this prevents the damage to the

bearings when the shaft is too low for hydrodynamic lubrication to take place. JOP sucks and delivers oil to the

journal bearings at 120kg/sq.cm for lifting of the rotor.

f) OIL COOLERS: - The oil of governing and lubrication system is cooled in the oil coolers by the circulating water.

There are five such coolers; four are for continuous operation and one for standby.

Electrical System Overview

ELECTRICAL STSTEM OF THERMAL POWER BASCICALLY CONSISTS OF FOLLOWING PARTS:

GENERATORS

SWITCHYARD

POWER DISTRIBUTION SYSYTEM

Generator

The transformation of mechanical energy into electrical energy is carried out by

generator. The A.C generator or alternator is based on the principal of electromagnetic induction and

generally consists of a stationary part called stator and a rotating part called rotor. The stator houses the

armature windings and the rotor houses the field windings. A D.C voltage is applied to the field winding

in the rotor through slip rings, when the rotor is rotated, the lines of magnetic flux is cut through the

stator windings. This as a result produces an induced e.m.f (electromotive force) in the stator winding

which is tapped out as output.

The magnitude of this output is determined by the following equation:-

E = 4.44/O f N volts

Where E = e.m.f induced; O =Strength of magnetic field in Weber; f= Frequency in cycles per second or in

hertz; N = Number of turns in the winding of the stator;

Again, f = P n/120;

Where P = Number of poles; n = revolutions per second of the rotor.

From the above expression it is clear that for the same frequency number of poles increases with

decrease in speed and vice versa. Therefore low speed hydro turbine drives generators have 14to

20poles where as for high speed steam turbine driven generators have 2 poles. Generator Components

Rotor: Rotor is the most difficult part to construct; it revolves at a speed of 3000rpm. The massive non-

uniform shaft subjected to a multiplicity of differential stresses must operate in oil lubricated sleeve

bearings supported by a structure mounted on foundations all of which poses complex dynamic behavior

peculiar to them. It is also an electromagnet and to give it the necessary magnetic strength the windings

must carry a fairly high current. The rotor is a cast steel ingot and it is further forged and machined. Very

often a hole bored through the centre of the rotor axially from one end to the other for inspection. Slots

are then machined for windings and ventilation.

Rotor winding: Silver bearing copper is used for the winding with mica as insulation between

conductors. A mechanically strong insulator such as micanite is used for lining the slots. For cooling

purpose slots and holes are provided for circulation of cooling gas. The wedges the windings when the

centrifugal force developed due to high speed rotation tries to lift the windings. The two ends of the

winding are connected to slip-rings made of forged steel and mounted on insulated sleeves.

Stator: The major part of the stator frame is the stator core, it comprises of inner and outer frame. The

stator core is built up of a large number of punching or section of thin steel plates. The use of cold rolled

grain-oriented steel can contribute to reduction of stator core. Stator windings: Each stator conductor

must be capable of carrying the rated current without overheating. The insulation must be sufficient to

prevent leakage current flowing between the phases to earth. Windings for the stator are made up from

copper strips wound with insulated tape switch is impregnated with varnish, dried under vacuum and

hot pressed to form a solid insulation bar. In 210MW generators the windings are made up of copper

tubes through which water is circulated for cooling purpose.

Generator Cooling and Sealing System

1) HYDROGEN COOLING SYSTEM:

Hydrogen is used as cooling medium in large capacity generators in view of its high heat carrying capacity

and low density. But in view of its explosive mixture with oxygen, proper arrangement for filling, purging

and maintaining its purity inside the generator have to be made. Also in order to prevent escape of

hydrogen from the generator casing, shaft sealing system is used to provide oil sealing.

The system is capable of performing the following functions:-

a) Filling in and purging of hydrogen safely.

b) Maintaining the gas pressure inside the machine at the desired value all the time.

c) Provide indication of pressure, temperature and purity of hydrogen.

d) Indication of liquid level inside the generator.

2) Generator Sealing System:

Seals are employed to prevent leakage of hydrogen from the stator at the point of rotor exit. A

continuous film between the rotor collar and the seal liner is maintained by means of oil at the pressure

which is about above the casing hydrogen gas pressure. The thrust pad is held against the collar of rotor

by means of thrust oil pressure, which is regulated in relation to the hydrogen pressure and provides the

positive maintenance of the oil film thickness.

The shaft sealing system contains the following components.

a) A.C Oil Pump

b) D.C Oil Pump

c) Oil injector

d) Differential Pressure Regulator

e) Damper Tank.

Excitation System:

1).Static Excitation:

•Alternator terminal voltage is used here.

•SCR gate signal are derived from alternator output through CT and P.T.

• SCR- based controlled rectifier is supplied is supplied from alternator output through step down

transformer.

• Alternator terminal voltage is used here.

• To generate the alternator output, it is run at rated speed with its field supplied from a separate

D.C supply bank.

• Rectifier output voltage is fed to the alternator field winding.

• This scheme is less expensive requires little maintenance.

• Excitation energy depends on alternator speed.

2) BRUSHLESS EXCITATION:

•Main shaft of prime movers drives pilot exciter, main exciter and the main alternator.

•Main exciter supplies A.C power to silicon diode bridge rectifier through hollow shaft which feeds the

D.C to the field of main alternator.

• Pilot exciter feeds 3-phase power to main exciter.

• Pilot exciter is a permanent magnet alternator.

•This scheme is mainly employed in turbo alternators.

Specification of Generators

PARAMETERS UNIT-1 UNIT-2 UNIT-3 UNIT-4 Maker JAPAN CHINA CHINA CHINA Rated O/P(KW) 250000 210000 210000 210000 Power Factor 0.85 0.85 0.85 0.85 KVA 294100 247000 247000 247000 Stator Voltage-

16500V Current-10750A

Voltage-15700V Current-9056A

Voltage-15700V Current-9056A

Voltage-15700V Current-9056

Rotor Voltage-290V Current-2395A

Voltage-310 V Current-2600A

Voltage-310V Current-2600A

Voltage-310V Current-2600A

R.P.M 3000 3000 3000 3000 Frequency(Hz) 50 50 50 50 Phase 3 3 3 3 Connection YY YY YY YY Coolant H2 H2 and H2O H2 and H2O H2 and H2O Gas Pressure 3.0BAR 3.5BAR 3.5BAR 3.5BAR Insulation Class Class-F Class-F Class-F Class-F Year of Manufacture 1985 1988 1988 1988

TRANSFORMERS

It is a static device which transfers electric powers from one circuit to the other without any change in

frequency, but with a change in voltage and corresponding current levels also.

Here the transformers used are to transfer electric power from 15.75KV to 220KV or 400KVthat are provided

to the national grid.

The step-up generator transformers are of ONAN/ANOF/AFOF cooling type.

Power Transformers Power Transformers enhances the productivity as well as maximizes the capacity level of the high power

supply equipments. These are ultimate for the regular power without any cut off. They are used for control high voltage and

frequency for the different systems. Power transformers having the following standards: They can assist three phases. There ratings are up to

2000 KVA. Copper and aluminum winding material is used in this. Applicable Standards are IS, IEC, ANSI,

JIS, etc. It is sufficient for primary as well as secondary voltage.

Auto Transformer

High voltage auto-transformers represent an important component of bulk transmission systems and are

used to transform voltage from one level to another. These auto-transformers are critical for regional load supply, inter-regional load transfers and for certain

generator/load connections. To minimize the impact of this type of failures, utilities may carry some spare units to guard against such

events. These spare units are going to cost utilities money (utility cost) to purchase, to store and to maintain

and utilities should try to strike the right balance between the utility cost and the risk cost (if spare units are

not there). Major or catastrophic failures to this equipment can have severe consequences to electric utilities in terms

of increased operating costs and customer load losses.

Advantages of Autotransformers:

1. Its efficiency is more when compared with the conventional one.

2. Its size is relatively very smaller.

3. Voltage regulation of autotransformer is much better.

4. Lower cost.

5. Low requirements of excitation current.

6. Less copper is used in its design and construction.

7. In conventional transformer the voltage step up or step down value is fixed while in autotransformer, we can

vary the output voltage as per out requirements and can smoothly increase or decrease its value as per our

requirement.

Applications:

1. Used in both Synchronous Motor and Induction Motor.

2. Used in electrical apparatus testing labs since the voltage can be smoothly and continuously varied.

3. They find application as boosters in AC feeders to increase the voltage levels.

Transformer Cooling

The load that a transformer carries without heat damage can be increased by using an adequate cooling system.

This is due to the fact that a transformers loading capacity is partly decided by its ability to dissipate heat.

1. Dry Type Cooling

2. Air Forced/Air Naturel(AF/AN) - Transformers temperature is being kept at acceptable levels by forced/naturel

air from a fan/air circulation. Cooling fins are attached to increase the surface area of heat radiation.

3. Oil Forced/Oil Naturel (OF/ON) – Oil are used in transformer to provide insulation and as a coolent agent. If the

oil is circulated by pump than it is known as Oil Forced cooling system, otherwise Oil Naturel Cooling System.

In Jamshoro TPS naturally ONAN, ONAF, OFAN, OFAF and dry cooling system are used for transformer cooling

purpose.

AUTOMATIC VOLTAGE REGULATOR (AVR)

It is a regulator which regulates the output voltage at a nominal constant voltage level.

Role of AVR AVR (Automatic voltage regulator) has following roles.

1) To regulate generator terminal voltage

Mainly generator under no-load condition, AVR regulates the generator voltage to voltage setter

(90R).

*AVR detects terminal voltage and compare with voltage setter (90R).

*AVR regulates field current via the Exciter.

*Generator terminal voltage is regulated by field current.

Vt < 90R _ Field current will be increase

Vt > 90R _ Field current will be decrease

2) To adjust MVars (Reactive power)

When the generator connected to power grid, AVR adjust reactive power by regulate generator

voltage.

Reactive Power (Q) =(Vt-VS)

MVar (Reactive power: Q) is regulated by generator terminal voltage. Therefore AVRcan regulate

MVars.

Vt is increased _ MVars will be increase

Vt is decreased _ MVars will be decrease

3) To Improve the Power System Stability

There are two stabilities:

-Transient Stability…….Improved by AVR

-Dynamic Stability……Improved by PSS(Power System Stabilizer)

Bibliography

List of Websites:

www.wikipedia.org/

www.google.com/

www.jpcl.com.pk

Books:

Elements of Electrical Power Station Design by: Professor M.V Deshpande

Power Plant Engineering By: Balleney