CHAPTER-1

THERMAL POWER PLANT

1.1 INTRODUCTION:-

Now a day’s the electricity has become an essential commodity rather than

luxury. In a state or region thermal power stations will become important, as

hydro resources are inadequate. The concept of modern thermal power stations is

that it should be situated at such a place that the basic requirements of fuel, water

& land should be satisfied. Basically thermal stations are of two types,

1. Pit Head Stations.

2. Load Demand Stations.

Pit head stations are those which are near to the source of fuel and load

demand stations are those which are near to the load centers.

The thermal power station is just like any other industry.

The basic requirements are:

a. Supply of raw materials at competitive costs. Coal and oil are the raw

materials required for thermal plants.

b. Access to the markets for its products.

c. Labour force of the size and quantity required.

d. Means of disposal for any trade effluents that is by-products.

The other factors to be considered for selecting the site are:

1. Load Demand

2. Land

3. Site Requirements

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4. Access for Construction

5. Transmission Lines

6. Clearances

7. Environmental Factors

Generally 1000 MW plant requires 90-200 acre land. The water

requirements for thermal stations come under two main groups. The first

requirement is for steam generation and the second requirement is for cooling

purpose. Water for steam generation is low of the order of 3-4 tones per hour per

megawatt, and make up quantity is 2-3% of the same. Whereas amount of water

required for condensation is quite high. Coal for power stations in India, the

principal source of commercial energy is amounting to 95% of the total primary

energy resources of the country. The coal resources existing in the country are of

the order of 1,30,000 million tones.

The main areas where the coal mines are located are the eastern region i.e.

Bihar, Bengal central region, Singareni coal fields, Tamilnadu, Naively and small

resources located in the rest of the country as well.

Other factors like transport, disposal of effluents, transmission, climatic

conditions, proximity of air fields, fisheries and marine life, personnel required

and amenities are also taken for considerations.

1.2 PRINCIPLE OF OPERATION:-

The fundamental forms of energy with which thermal stations are

principally concerned are heat and work. Heat produces work and this work is

further converts into electrical energy through a medium i.e. electrical generator.

For the purpose of understanding of thermal plants, the phenomenon of

thermodynamic vapour power cycles explained here under.

a. Rankine cycle

b. Reheat cycle

c. Regenerative cycle

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a. RANKINE CYCLE:-

This is the simplest theoretical vapour cycle which is the basis for

operation of a steam plant. Superheated steam from the boiler is fed into the prime

mover and is expanded there. After which it enters the condenser emerging as the

condensate. With the help of a pump this condensate is again fed into the boiler.

The main purpose of superheating steam and supplying it to the prime

mover is to avoid too much wetness at the end of expansion. Moisture content of

steam would result in undue blade erosion. The maximum wetness in the final

stage of the steam that may be tolerated without any appreciable harm to the

turbine blades is about 12%. Also the use of super heater in the boiler helps in

reducing the stack temperature by extracting the heat from the flue gases before

these are passed out of the chimney.

b. REHEAT CYCLE:-

In its simplest form the cycle involves with drawing the steam from the

turbine at some intermediate stage, returning it to the steam generator where a

separate super heater is provided in the gas path re-superheating the steam after

which it is re introduced into the turbine at the following stage. It reduces the

wetness of the steam at final stage and improves the efficiency of the cycle.

c. REGENERATIVE CYCLE:-

This cycle is an attempt to induce reversibility in the ordinary rankine

cycle and thus to increase its efficiency. The mixing of coal condensate with the

saturated steam and water mixture in the boiler constitute the principal irreversible

process of the cycle and generation aims at reducing this irreversibility by heating

the feed water near to the saturation temperature through the utilization of heat of

the steam which is partially expanded in the prime mover. Since the purpose is the

thermal regeneration of the condensate the cycle is known as regenerative cycle.

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1.3 COAL TO STEAM PROCESS:-

Coal from mines is brought to plant through wagons and these wagons are

unloaded in coal handling plant. The coal is transported to raw coal bunkers with

the help of belt conveyors. Coal is then transported to mills through feeders where

the coal is pulverized to powder form. This coal powder is lifted to the boiler with

the help of primary air fans (PA fan). PA fan takes the air from the atmosphere, a

part of which is sent to air pre heater for heating while a part goes directly to the

mills for temperature control. Atmospheric air from FD fan heated in the air

heaters and sent to the furnace as combustion air.

Water from the boiler feed pumps passes through the economizer and

reaches the boiler drum. Water from the drum passes through the down comers

and goes to bottom ring header. Water from the ring header is divided to all four

sides of the furnace. Due to the heat and density difference the water raises up in

the water wall tubes. Water is partially converted to steam as it rises up in the

furnace. This steam and water mixture is taken to the boiler drum where the steam

is separated from the water with the help of turbo separators. Water follows the

same path while the steam is sent to superheaters for superheating. The

superheaters are located inside the furnace and the steam is superheated (540o C)

and finally it goes to turbine.

Flue gases from the furnace is extracted by the induced draft fans (ID

fans), which maintains balance draft in the furnace with forced draft fan. This flue

gases emit their heat energy to various superheaters in the pent house and finally

passes through air preheaters and goes to electrostatic precipitator, where the ash

particles are extracted. Electro static precipitators consist of metal plates, which

are electrically charged. Ash particles are attracted on to these plates, so that they

do not pass through the chimney to pollute the atmosphere. Regular mechanical

hammers blows cause the accumulation of ash to fall to the bottom of the

precipitator, where they are collected in a hopper for disposal. This ash is mixed

with water to form slurry and is pumped to ash pond.

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1.4 STEAM TO MECHANICAL POWER:-

A steam pipe conveys steam to the turbine through stop valve and control

valves that automatically regulate the supply of the steam to the turbine. Steam

from the control valves enters the high-pressure cylinder of the turbine, where it

passes through a ring of stationary blades fixed to the cylinder wall. These act as

nozzles and direct the steam into second ring of moving blades mounted on a disc

secured to the turbine shaft. This second ring turns the shaft as a result of the force

of the steam. The stationary and moving blades together constitute a stage of the

turbine and in practice many stages are necessary so that cylinder contain a

number of rings of stationary blades with rings of moving blades arranged

between them. The steam passes through each stage in turn until it reaches the end

of the high pressure cylinder and in its passage some of its heat energy is changed

in to mechanical energy.

The steam leaving high pressure cylinder goes back to the boiler for

reheating and enters into intermediate pressure cylinder through HRH lines.

Hence it passes through another series of stationary and moving blades.

Finally steam is taken to the low pressure cylinders, each of which it enters

at the center for following outwards in the opposite direction through the rows of

turbine blades- an arrangement is known as double flow to the extremities of the

cylinder. As the steam gives up its heat energy to drive the turbine, its temperature

and pressure fall and it expands. Because of this expansion the blades are much

larger and longer towards the low pressure end of the turbine.

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CHAPTER-2

OVERALL VIEW OF THE PLANT

2.1 UNIT OVERVIEW:-

2.2 COAL HANDLING PLANT:-

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Most thermal stations use coal as the main fuel. Raw coal is transported

from coal mines to a power station site by trucks, barges, bulk cargo

ships or railway cars. Generally, when shipped by railways, the coal cars are sent

as a full train of cars. The coal received at site may be of different sizes. The

railway cars are unloaded at site by rotary dumpers or side tilt dumpers to tip over

onto conveyor belts below. The coal is generally conveyed to crushers which

crushes the coal to about ¾ inch (6 mm) size. The crushed coal is then sent by belt

conveyors to a storage pile. Normally, the crushed coal is compacted by

bulldozers, as compacting of highly volatile coal avoids spontaneous ignition.

The crushed coal is conveyed from the storage pile to silos or hoppers at

the boilers by another belt conveyor system.

At a typical coal-fired power plant, the coal from the mine is typically

delivered to the plant in large trucks or via rail, and dumped into the run-of-mine

(ROM) hopper. Once at the plant, it is fed through a primary crusher and

conveyed to a coal storage building. The coal storage building is used to "blend"

coal from different parts of the mine to make it more consistent for burning.

From the coal storage building, the coal is crushed again and conveyed to

smaller coal storage bunkers in the power plant. From there, the coal is fed to the

pulverizers which grind it to a fine powder which is burned in the boiler.

2.3 BALL MILLS:-

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A ball mill, a type of grinder, is a cylindrical device used in grinding (or

mixing) materials like ores, chemicals, ceramic raw materials and paints. Ball

mills rotate around a horizontal axis, partially filled with the material to be ground

plus the grinding medium. Different materials are used as media,

including ceramic balls, flint pebbles and stainless steel balls. An internal

cascading effect reduces the material to a fine powder. Industrial ball mills can

operate continuously fed at one end and discharged at the other end. Large to

medium-sized ball mills are mechanically rotated on their axis, but small ones

normally consist of a cylindrical capped container that sits on two drive shafts

(pulleys and belts are used to transmit rotary motion). A rock tumbler functions on

the same principle.

Ball mills are also used in pyrotechnics and the manufacture of black

powder, but cannot be used in the preparation of some pyrotechnic mixtures such

as flash powder because of their sensitivity to impact. High-quality ball mills are

potentially expensive and can grind mixture particles to as small as 5 nm,

enormously increasing surface area and reaction rates. The grinding works on

principle of critical speed. The critical speed can be understood as that speed after

which the steel balls (which are responsible for the grinding of particles) start

rotating along the direction of the cylindrical device; thus causing no further

grinding.

2.3.1 PRIMARY AIR FAN:-

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The main purpose of this fan is to lift the coal from mill to boiler and also

provide air for the combustion of coal in the boiler.

2.3.2 SECONDARY AIR FAN:-

The main purpose of this fan is to provide excess air required for complete

combustion of coal.

2.3.3 INDUCED DRAFT FAN:-

About 60-80% of ash with flue gases is left in the boiler after combustion

of coal. The main purpose of this fan is to suck the flue gases containing the ash

particles from the boiler.

2.4 BOILER FURNACE AND STEAM DRUM:-

Once water enters 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

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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 remove moisture from the wet steam entering the drum from the steam

generating tubes. The dry steam then flows into the super heater coils.

In KTPS V stage the boiler used is Direct Fired Natural Circulation

Balanced Draft Water Tube Boiler. The maximum temperature of the steam in the

boiler is 540oC. The steam pressure is 150 kg/cm2. The efficiency is about 86.6%.

2.4.1 SUPERHEATER:-

Thermal power plants can have a super heater and reheater section in the

steam generating furnace. After the wet steam is separated into steam and water

by the turbo separators inside the steam drum, it is piped from the upper drum area

into tubes inside an area of the furnace known as the super heater, which has an

elaborate set up of tubing where the steam vapor picks up more energy from hot

flue gases outside the tubing and its temperature is now superheated above the

saturation temperature. The superheated steam is then piped through the main

steam lines to the valves before the high pressure turbine.

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2.4.2 REHEATER:-

Power plant furnaces may have a reheater section containing tubes heated

by hot flue gases outside the tubes. Exhaust steam from the high pressure turbine

is rerouted to go inside the reheater tubes to pickup more energy to go drive

intermediate or lower pressure turbines. The arrangement and construction of a

reheater is similar to that of a super heater. In large modern boiler plants, the

reheater sections are mixed equally with super heater sections. The reheater

sections in modern boilers usually consists of pendant assemblies these can be

used in combination with horizontal assemblies are a radiant wall located in the

upper furnace.

2.4.3 ECONOMIZERS:-

A boiler economizer is a heat exchanger device that captures the "lost or

waste heat" from the boiler's hot stack gas. The economizer typically transfers this

waste heat to the boiler's feed-water or return water circuit, but it can also be used

to heat domestic water or other process fluids. Capturing this normally lost heat

reduces the overall fuel requirements for the boiler. Less fuel equates to money

saved as well as fewer emissions - since the boiler now operates at a higher

efficiency. This is possible because the boiler feed-water or return water is pre-

heated by the economizer therefore the boilers main heating circuit does not need

to provide as much heat to produce a given output quantity of steam or hot water.

Again fuel savings are the result. Boiler economizers improve a boiler's efficiency

by extracting heat from the flue gases discharged.

Systems Equipment Corporation Boiler Economizers are fabricated from

uniquely formed tubular elements, similar to a tear drop or diamond shape. Each

economizer is specifically designed to match our client’s boiler characteristics in

order to maximize efficiency and the use of boiler room space. Because Systems

Equipment Corporation Boiler Economizers are manufactured from stainless steel

the usual corrosion problems encountered by our competitions designs are

eliminated.

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Systems Equipment Corporation Boiler Economizers are designed to suit

boilers in the range of 500,000 btu/hr to 60,000,000 btu/hr or 400-lbs to 60,000-

lbs of steam/hr.

2.4.4 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 is almost always be kept significantly

below 100 °C 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.

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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.

2.4.5 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 (joules or Btu)

in the steam is referred to as enthalpy. The condensate pump then pumps

the condensate water through a feedwater heater. The feedwater heating

equipment then raises the temperature of the water by utilizing extraction steam

from various stages of the turbine.

Preheating the feedwater reduces the irreversibility’s involved in steam

generation and therefore improves the thermodynamic efficiency of the

system. This reduces plant operating costs and also helps to avoid thermal

shock to the boiler metal when the feedwater is introduced back into the steam

cycle.

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2.4.6 DEAERATOR:-

A steam generating boiler requires that the boiler feedwater 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 feedwater. A deaerator typically

includes a vertical, domed deaeration section mounted on top of a horizontal

cylindrical vessel which serves as the deaerated boiler feedwater 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. If operated properly, most deaerator manufacturers

will guarantee that oxygen in the deaerated water will not exceed 7 ppb by weight

(0.005cm³/L).

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2.5 DEMINERALIZED WATER PLANT (D. M. PLANT):-

DEIONIZERS:-

Pure Aqua is a leading provider of deionization solutions. Our water

deionizers are rugged, pre-engineered, pre-assembled, standardized units that

minimize expensive installation and start-up costs. We have designed our

Deionization systems to maximize the efficiency and repeatability of the unit

during the service and regeneration modes.

THE PROCESS OF DEIONIZATION OR ION-EXCHANGE:-

In the context of water purification, ion-exchange is a rapid and reversible

process in which impurity ions present in the water are replaced by ions released

by an ion-exchange resin. The impurity ions are taken up by the resin, which must

be periodically regenerated to restore it to the original ionic form. (An ion is an

atom or group of atoms with an electric charge. Positively-charged ions are called

cations and are usually metals; negatively-charged ions are called anions and are

usually non-metals).

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The following ions are widely found in raw waters:

CATIONS ANIONS

Calcium (Ca2+) Chloride (Cl-)

Magnesium (Mg2+) Bicarbonate (HCO3-)

Sodium (Na+) Nitrate (NO3-)

Potassium (K+) Carbonate (CO32-)

Iron (Fe2+) Sulfate (SO42-)

ION EXCHANGE RESINS:-

There are two basic types of resin - cation-exchange and anion-exchange

resins. Cation exchange resins will release Hydrogen (H+) ions or other positively

charged ions in exchange for impurity cations present in the water. Anion

exchange resins will release hydroxyl (OH-) ions or other negatively charged ions

in exchange for impurity anions present in the water.

The application of Ion-Exchange to Water Treatment and Purification:

 There are three ways in which ion-exchange technology can be used in

water treatment and purification:

1. Cation-exchange resins alone can be employed to soften water by

Base Exchange.

2. Anion-exchange resins alone can be used for organic scavenging or

nitrate removal.

3. Combinations of cation-exchange and anion-exchange resins can

be used to remove virtually all the ionic impurities present in the

feed water, a process known as deionization. Water deionizer’s

purification process results in water of exceptionally high quality.

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DEIONIZATION:-

For many laboratory and industrial applications, high-purity water which is

essentially free from ionic contaminants is required. Water of this quality can be

produced by deionization. The two most common types of deionization are:

Two-bed deionization

Mixed-bed deionization

TWO-BED DEIONIZATION:-

The two-bed deionizer consists of two vessels - one containing a cation-

exchange resin in the hydrogen (H+) form and the other containing an anion resin

in the hydroxyl (OH-) form. Water flows through the cation column, whereupon

all the cations are exchanged for hydrogen ions. To keep the water electrically

balanced, for every monovalent cation, e.g. Na+, one hydrogen ion is exchanged

and for every divalent cation, e.g. Ca2+, or Mg2+, two hydrogen ions are

exchanged. The same principle applies when considering anion-exchange. The de-

cationised water then flows through the anion column. This time all the negatively

charged ions are exchanged for hydroxide ions which then combine with the

hydrogen ions to form water (H2O).

MIXED-BED DEIONIZATION:-

In mixed-bed deionizers the cation-exchange and anion-exchange resins

are intimately mixed and contained in a single pressure vessel. The thorough

mixture of cation-exchangers and anion-exchangers in a single column makes a

mixed-bed deionizer equivalent to a lengthy series of two-bed plants. As a result,

the water quality obtained from a mixed-bed deionizer is appreciably higher than

that produced by a two-bed plant.

Although more efficient in purifying the incoming feed water, mixed-bed

plants are more sensitive to impurities in the water supply and involve a more

complicated regeneration process. Mixed-bed deionizers are normally used to

‘polish' the water to higher levels of purity after it has been initially treated by

either a two-bed deionizer or a reverse osmosis unit.

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Electro deionization EDI Electro deionization Systems remove ions from

aqueous streams, typically in conjunction with reverse osmosis (RO) and other

purification devices. Our high-quality deionization modules continually produce

ultrapure water up to 18.2MW/cm. EDI may be run continuously or intermittently.

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2.6 ELECTROSTATIC PRECIPITATOR:- 

This electrical equipment was first introduced by Dr. F.G. COTTELL in

1906 and was first economically used in 1934 for the removal of dust and ash

particles with the exhaust gases of the thermal power plant. The electrostatic

precipitator utilizes electrostatic force to separate the dust particles from the gases

to be cleared. The electrostatic precipitator essentially consists of two sets of

electrodes called “collecting electrodes” and “emitting electrodes” (also called

discharge electrodes). The collecting electrodes are made up of steel sheet pressed

to a special profile and the emitting electrodes are a thin wire drawn to a helical

form. A unidirectional high voltage (70K.V.) is applied between these electrodes,

connecting its positive polarity to the collecting electrodes which are also earthed.

After the combustion of coal in the boiler, 60-80% of the ash along with flue gases

leaves in the boiler. The induced draft fans (ID fans) sucks these flue gases

containing ash particles from the boiler and introduces them the chamber

containing these electrodes. These dust leden flue gases from the boiler passes

between the rows of collecting and discharging electrodes.

The high voltage induces ionization of gas molecules adjacent to the

negatively charged emitting electrodes. The positive charges of the ions create

travel towards the discharge electrodes and negative charges towards the

collecting electrodes. And their way to the collecting electrodes, the negative

charges get deposited on the dust particles. Thus dust particles experience a force

which causes the particle to move towards the collecting electrodes and finally get

deposited on them. Minor portion of the dust particles, which have acquired

positive charges, gets deposited on the emitting electrodes also. Periodically these

are dislodged from the electrodes by the process called “rapping”. The particles

then fall into the hoppers at the bottom.

The efficiency of the electrostatic precipitator is very high it is about

99.97%.

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2.7 ASH HANDLING PLANT:-

i. FLY ASH COLLECTION:-

Fly ash is captured and removed from the flue gas by electrostatic

precipitators or fabric bag filters (or sometimes both) located at the outlet of the

furnace and before the induced draft fan. The fly ash is periodically removed from

the collection hoppers below the precipitators or bag filters. Generally, the fly ash

is pneumatically transported to storage silos for subsequent transport by trucks or

railroad cars.

ii. BOTTOM ASH COLLECTION AND DISPOSAL:-

At the bottom of the furnace, there is a hopper for collection

of bottom ash. This hopper is always filled with water to quench the ash and

clinkers falling down from the furnace. Some arrangement is included to crush the

clinkers and for conveying the crushed clinkers and bottom ash to a storage site.

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2.8 ELECTRICAL LAY OUT OF THE PLANT:-

Plant contains many auxiliary equipments, boiler auxiliaries like mills, FD

fans, PD fans, ID fans and turbine auxiliaries’ like vacuum pumps and generator

auxiliaries like seal oil pumps etc. these auxiliaries in turn contribute to increase

the efficiency of the plant. These auxiliaries may be HT auxiliaries (about 6.6 KV)

or LT auxiliaries (less than 3.3 KV). To give supply to these auxiliaries the

generator output is tapped before it is step up by the power transformer and the

tapped output of the generator is stepped down to 6.6 kV by a auxiliary

transformer and this supply is given to turbine auxiliary and boiler auxiliary

boards through I/C breakers again the supply is taken from the boards and the

voltage is stepped down to 415V and given to LT auxiliary boards of turbine and

boiler. All these boards are called unit supply boards since the supply is from the

unit itself.

When ever the plant is in shutdown condition and the generator is not

running. To again take the plant into running condition the auxiliaries have to start

first. In this condition the supply is taken from one of the outgoing feeders and

again it is stepped down to 6.6 KV and given to station auxiliary boards through

tie breakers. Whenever this tie breaker is closed the I/C breaker automatically

open circuited.

Whenever the plant is in shutdown condition and the supply from the

feeder is also not available due to any fault on the feeder then it is called station

dark out condition. Under this condition also some of essential loads have to be

work like scanner fan in the boiler. To give supply to these essential loads DC

battery backup is provided. When this battery bank is also not available then

Diesel-Generator set is used to give supply to these essential loads.

Procedure to be adapted by the shift engineer in case of station dark out

condition is

Safe guard the equipments.

Check whether the DC auxiliaries have come into service or not.

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Start DG set and extend supply EMC board and SSS board.

Switch off DC auxiliaries.

Take the supply from any of the out feeders available.

The below figure shows electrical layout of K.T.P.S. V stage,

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CHAPTER -3

STEAM TURBINE

 3.1 INTRODUCTION:-

Turbine is a machine in which a shaft is rotated steadily by impact or

reaction of current or stream of working substance (steam, air, water, gases etc)

upon blades of a wheel. It converts the potential or kinetic energy of the working

substance into mechanical power by virtue of dynamic action of working

substance.  When the working substance is steam it is called the steam turbine.

3.2 PRINCIPLE OF OPERATION:-

Working of the steam turbine depends wholly upon the dynamic action of

Steam.  The steam is caused to fall in pressure in a passage of nozzle, doe to this

fall in pressure a certain amount of heat energy is converted into mechanical

kinetic energy and the steam is set moving with a greater velocity.  The rapidly

moving particles of steam, enter the moving part of the turbine and here suffer a

change in direction of motion which gives rose to change of momentum and

therefore to a force.  This constitutes the driving force of the machine.  The

processor of expansion and direction changing may occur once or a number of

times in succession and may be carried out with difference of detail.   The

passage of steam through moving part of the commonly called the blade, may take

place in such a manner that the pressure at the outlet side of the blade is equal to

that at the inlet inside.  Such a turbine is broadly termed as impulse turbine.  On

the other hand the pressure of the steam at outlet from the moving blade may be

less than that at the inlet side of the blades; the drop in pressure suffered by the

steam during its flow through the moving causes a further generation of kinetic

energy within the blades and adds to the propelling force which is applied to the

turbine rotor.  Such a turbine is broadly termed as impulse reaction turbine. 

The majority of the steam turbine has two important elements, or Sets of

such elements. These are,

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1. The nozzle in which the system expands from high pressure end a state of

comparative rest to a lower pressure end a status of comparatively rapid

motion.

2. The blade or deflector, in which the steam particles changes its directions

and hence its momentum changes. The blades are attach to the rotating

elements are attached to the stationary part of the turbine which is usually

termed the stator, casing or cylinder.

Although the fundamental principles on which all steam turbine operate

the same, yet the methods where by these principles carried into effect very end as

a result, certain types of turbine have come into existence.

Simple Impulse Steam Turbine.

The Pressure Compounded Impulse Turbine.

Simple Velocity Compounded Impulse Turbine.

Pressure-Velocity Compounded Turbine.

Pure Reaction Turbine.

Impulse Reaction Turbine.

3.3 STEAM FLOW:-

250MW steam turbine is a tandem compound machine with HP, IP & LP

parts. The HP part is single flow cylinder and HP & LP parts are double flow

cylinders.  The individual turbine rotors and generator rotor are rigidly coupled. 

The HP cylinder has a throttle control.  Main steam is admitted before blending by

two combined main stop and control valves.  The HP turbine exhaust (CRH)

leading to reheated have to swing check valves that prevent back flow of hot

steam from reheated, into HP turbine.  The steam coming from reheated called

HRH is passed to turbine via two combined stop and control valves.  The IP

turbine exhausts directly goes to LP turbine by cross ground pipes.

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3.4 HP TURBINE:-

The HP casing is a barrel type casing without axial joint. Because of its

rotation symmetry the barrel type casing remain constant in shape and leak proof

during quick change in temperature.  The inner casing too is cylinder in shape as

horizontal joint flange are relieved by higher pressure arising outside and this can

kept small. Due to this reason barrel type casing are especially suitable for quick

start up and loading.

  The HP turbine consists of 25 reaction stages. The moving and stationary

blades are inserted into appropriately shapes into inner casing and the shaft to

reduce leakage losses at blade tips.

3.5 IP TURBINE:-

The IP part of turbine is of double flow construction. The casing of IP

turbine is split horizontally and is of double shell construction. The double flow

inner casing is supported kinematically in the outer casing. The steam from HP

turbine after reheating enters the inner casing from above and below through two

inlet nozzles.  The centre flow compensates the axial thrust and prevents steam

inlet temperature affecting brackets, bearing etc.  The arrangements of inner

casing confines high steam inlet condition to admission branch of casing, while

the joints of outer casing is subjected only to lower pressure and temperature at

the exhaust of inner casing.  The pressure in outer casing relieves the joint of inner

casing so that this joint is to be sealed only against resulting differential pressure.

The IP turbine consists of 20 reaction stages per flow. The moving and

stationary blades are inserted in appropriately shaped grooves in shaft and inner

casing.

3.6 LP TURBINE:-

The casing of double flow type LP turbine is of three shell design. The

shells are axially split and have rigidly welded construction. The outer casing

consists of the front and rear walls, the lateral longitudinal support bearing and

upper part.

25

The outer casing is supported by the ends of longitudinal beams on the

base plates of foundation.  The double flow inner casing consists of outer shell

and inner shell.  The inner shell is attached to outer shell with provision of free

thermal movement.

Steam admitted to LP turbine from IP turbine flows into the inner casing

from both sides through steam inlet nozzles.

3.7 TECHNICAL DATA OF 250 MW TURBINE:-

Rated Output : 250 MW.

Rated Speed : 3000 rpm. 

Main Steam Pressure : 150 Kg/Cm2

Main Steam Temperature : 535oC.       

  

Reheat Steam Temperature : 535oC.

Weight of Turbine : 475 T approx. 

Overall Length : 16.975 Mtrs. approx.

Single flow HP Turbine with 25 reaction stages.

Double flow IP Turbine with 20 reaction stages per flow.

Double flow LP Turbine with 8 reaction stages per flow.

26

CHAPTER-4

TURBO GENERATOR

4.1 INTRODUCTION:-

Michael Faraday invented the first A.C. generator concept in 1831. In

1889 sir Charles A. parsons developed the first A.C turbo generator. Although

slow speed A.C. generators has been built for sometime, it was not long before

that the high speed generators made its impact.

Development contained until, in 1922, the increased use of solid forging

and improved techniques permitted an increase in generator rating to 20 MW at

3000 RPM. Up to the outbreak of Second World War in 1939, most of the large

generators have order of 30 to 50 MW at 3000 RPM.

During the war, the development and installation of power plants was

delayed in large number of 30MW and 60MW at 3000 RPM units were

constructed during the years immediately following the war. The changes in this

period were relatively small.

The economic case for the development of very large turbo generators was

indisputable, and the designer was faced with the problems of increasing the

rating in the case of increasing the limitations of size and weight, which can be

easily transported. Substantial gain could not raise the current load of the

machines so that the increased power rating could be achieved without

proportionate increase in size and weight. The raising of the current load greatly

increased the copper the losses in both stator and rotor windings and these losses

could not be adequately dissipated by use of conventional air cooling. Air as a

coolant was suppressed by hydrogen and increases in generator rating up to 275

MW were obtained bypassing the hydrogen through passages in stator and rotor

conductors. The direct cooling eliminated the high temperature gradients across

the slot insulation, along stator and rotor teeth, and from the iron surfaces to the

cooling medium. Further development was made possible by use of water instead

of hydrogen for cooling medium.

27

The first air cooled generator, a 60 MW machine, was installed in U.K. in

1949. This was a conventionally cooled generator where in hydrogen replaced air

as cooling medium. The hydrogen in the machine frame was at a pressure of

0.1kg/cm2 to obviate the risk of air leaking into the machine frame and forming an

explosive mixture. It was soon founded that the power output from a given frame

size could be increased by increasing the hydrogen pressure with in a short time

3k.g/cm2 had become standard pressure. In 1955 the first 100 MW generators

were commissioned and from the same design followed the 220 MW machines

which came into service from 1958.

The 200 MW generators were installed in 1959. In these machines there

was a complete departure from the conventional method of cooling. Instead of

removing heat from the external surfaces with in the machine the stator and rotor

conductors were directly cooled by causing hydrogen to flow with in the slot of

the generators. Up to 275 MW rating generators were build in accordance with

this principle. The development opened the way to higher rated machines because

it virtually eliminated the large temperature difference, which existed between

cooled surface and the winding conductors in the conventional cooled machines.

The advantage of direct cooling were further emphasized when hydrogen gas was

superseded by use of water for cooling the stator windings, and the ratings of

generators rapidly increased from 275MW to 500 MW.

The next decisive stage must be the development of single shaft generators

in the output range of 750 MW to 1000MW. There are still a number of electrical,

mechanical and thermal problems to be solved. Electrically the progress to the

high rated machines is governed largely by the short circuit ratio and transient

reactance which influences the machine stability during sudden load changes.

4.2 PRINCIPLE:-

The A.C. generator or alternator is based upon the principle of the

Electromagnetic Induction and consists generally of stationary part called stator

and a rotating part called rotor. The stator housed the armature windings. The

rotor houses the field windings; DC voltage is applied to the field windings. When

the rotor is rotated, the lines of the magnetic flux cut through the stator windings.

28

The magnitude of EMF is given by the following expression.

E=4.44 Ǿ f T volts

Where,

Ǿ= flux density in Weber’s/m2

f= frequency in Hz = PN/120

T= number of turns in a coil of stator winding

P= number of poles

N= revolutions per second of the rotor

From the expression it is clear that for the same frequency, number of

poles increases with decrease in the speed and vice versa. Therefore, low speed

hydro turbine drives generators have 14 to 20 poles where as high speed steam

turbine driven generators have generally 2 poles. Pole rotors are used in low

speed generators because the cost advantage as well as easier construction.

4.3 CONSTRUCTION OF GENERATOR:-

4.3.1 STATOR:-

4.3.1.1 STATOR FRAME:-

The stator frame is of a gas tight and pressure resistant welded

construction and accommodates the laminated core, the winding and the coolers

arranged horizontally in the generator housing. Both the gas ducts and the

welded circular ribs provides for the rigidity of the stator frame. End shields

containing the shaft seal and baring components are bolted to the frame and

walls. The flanged connections are sealed gas tight by means of viscous cement.

Feet are welded to the stator frame to bolt the stator to the machine sole plates.

The stator is firmly connected to the foundation with anchor bolts through the

machine sole plates.

29

4.3.1.2 STATOR CORE:-

The armature core of the generator is supported by the stator frame.

It is built up of laminations of special magnetic iron or steel alloy. The core is

laminated to minimize loss due to eddy currents. The laminations are stamped

out in complete rings or in segments. The laminations are insulated from each

other and have space between them for allowing the coolant hydrogen to pass

through. The slots for housing the armature conductors lie along the inner

periphery of the core and are stamped out at the same time when laminations are

formed.

4.3.1.3 STATOR WINDINGS:-

The 3-phase stator winding is a fractional pitch two layer type

consisting of individual bars. Each stator slot accommodates two bars. The slot

bottom bars are displaced from each other by one winding pitch and connected

at their ends to form coil groups. The coil groups are connected together with

phase connectors inside the stator frame.

This arrangement and shape of the bars at the ends result in a one shaped

winding having particularly favorable characteristics both in respect of its

electrical properties and resistance to magnetically induced forces. The bars

afford maximum operating reliability since each coil is one turn. This makes the

turn insulation and the main insulation identical.

4.3.2 ROTOR:-

4.3.2.1 ROTOR SHAFT:-

The rotor shaft is a single-piece solid forging manufactured from a

vacuum casting. Slots for insertion of the field winding are milled into the rotor

body. The longitudinal slots are distributed over the circumference so that two

solid pieces are obtained. The rotor poles are designed with a transverse slot to

reduce twice system frequency rotor vibrations caused by deflections in the

direction of the pole and the natural axis. To ensure that only high quality

forgings are used, strength tests, material analysis and ultrasonic tests are

30

performed during the manufacture of the rotor. After completion, the rotor is

balanced in various planes at different speeds and then subjected to an over

speed test at 120% of its rated speed for 2 minutes.

4.3.2.2 ROTOR WINDINGS:-

The rotor windings consists of several coils, which are inserted into

the slots and series- connected such that two coil groups form one pole. Each

coil consists of several series consented turns, each of which consists of two half

turns which are connected by brazing in the end section. The rotor winding

consists of silver baring de-oxidized copper hallow conductors with two lateral

cooling ducts. L shaped stripes of the laminated epoxy glass fiber fabric with

nomex filler are used for slot insulation. The slot wedges are made up of high

conductivity material and extended below the shrink sheet of retaining ring. The

seat of the retaining ring is silver plated to ensure a good electrical contact

between the slot wedges and rotor retaining rings. This system has long proved

to be a good damper winding.

4.4 RATING OF THE 250 MW TURBO GENERATOR IN KTPS

V STAGE

Type : THRI 108/44

Apparent Power : 294 MVA

Active power : 250 MW

Current : 10,290A

Voltage : 16.5KV +/-825V

Speed : 3000 R.P.M

Frequency : 50 Hz.

Power Factor : 0.85 lag

31

Interconnection of Stator winding : Stat-Star

Coolant : Hydrogen

Hydrogen Pressure : 3.0 bar

Continuous permitted unbalance load : 8%

Rated field current o/p : 2386A D.C

Rated field voltage : 319Volts D.C

No. of rectifier wheels : 2

Excitation system : Brushless type.

4.5 COOLING SYSTEM:-

In KTPS hydrogen cooling system is employed for generator cooling.

Hydrogen is used for cooling medium primarily because of its superior cooling

properties & low density.  Thermal conductivity of hydrogen is 7.3 times of air.  It

also has higher transfer co-efficient.  Its ability to transfer heat through forced

convection is about 75% better than air.  Density of hydrogen is approx. 7/14 of

the air at a given temperature and pressure.  This reduces the windage losses in

high speed machine like turbo-generator.  Increasing the hydrogen pressure the

machine improves its capacity to absorb & remote heat. Relative cooling

properties of air and hydrogen are given below, 

Elimination of fire risk because hydrogen will not support

combustion.

Corona discharge is not harmful to insulation, since oxidation is

not possible.

Smooth operation of machine in view of vertical elimination of

wind age noise & the use of heavy gas light enclosure and dirty

proby casing.

32

At pressure 0.035 atm. of hydrogen heat carrying capacity is 1. But at 2

atm. of hydrogen heat carrying capacity is 1.95 to overcome the serious possibility

of hydrogen explosion within the machine and to ensure the safety of operation

purity of hydrogen on the generator.  Casing must be maintained as high as

possible.  The purity of hydrogen should be 98% above but should not be less than

98%. In case of hydrogen purity drops below 98% an alarm is provided.

4.5.1 HYDROGEN DRYERS:-

Two nos. of dryers are provided to absorb the hydrogen in the Generator.

Moisture in this gas is absorbed by silica gel in the dryer as the absorbed gas

passes through it.  The satural of silica gel is indicated by change in its color from

blue to pink. The silica gel is reactivated by heating. By suitable change over from

drier to the other on un-interrupted drying is achieved.

4.5.2 HYDROGEN FILLING SYSTEM:-

The filling operation is carried out in two steps.

Scavenging the air by CO2 with hydrogen. 

Before filling the hydrogen at a pressure of 2 atm, in the machine it is

necessary to store, at least 18 cylinders of 20 Kg. CO2 & 48 cylinders of

hydrogen.

4.6 BRUSHLESS EXCITATION SYSTEM:-

This system consists of main components as listed below,

a. Three Phase Pilot Exciter.

b. Three Phase Main Exciter.

c. Rotating Rectifier Wheels.

d. Cooler.

33

a. Three Phase Pilot Exciter:-

Three phase pilot exciter has a revolving field with permanent magnet

poles. The controlled rectified D.C is fed to the main exciter field. The induced

Three Phase A.C voltage is rectified in the rotating rectifier bridge and is fed to

the generator rotor winding through the D.C leads in the shaft. The pilot exciter

has 16 poles. The output is 220V + - 10%, 400 Hz. Ten magnets are housed

together in a non magnetic enclosure and this make one pole. These magnets are

braced between the hub and external pole shoe with bolts.

b. Three Phase Main Exciter:-

The three phase main exciter is a six pole rotating armature unit. The field

poles with the damper windings are arranged in the stator frame. Laminated

magnetic poles are arranged to form the field winding. To measure the exciter

current a quadrature axis coil is fitted between two poles.

The winding conductors are transposed within the core length, and the end

turns of the rotor windings are secured with steel bands. The connections are made

at rectifier wheel end. A ring bus formed at the winding end and leads to rotating

rectifier wheel are also connected to the same. The complete rotor is shrunk fit on

the shaft. The rotor is supported on a journal bearing positioned between the main

and the pilot exciters. Lubrication of the bearing is formed from the turbine oil

system.

c. Rotating Rectifier Wheels:-

The silicon diodes are arranged on the rectifier wheels in three

configurations. The diodes are so made that the contact pressure increases during

rotation due to the centrifugal force. There are two diodes.

d. Coolers:-

Because of these properties, hydrogen will extract more heat per unit

volume/min. Thus for a given rise of temperature, machine capacity can be

increased. It has been estimated that by use of Hydrogen 20% reduction in active

34

construction materials can be affected. At 0.035 kg/cm² of hydrogen, machine

rating is increased by 22-25% and at 2.109 kg/cm² the rating increase is 35%.

Below figure shows the block diagram of brushless excitation system of Turbo

Generator.

4.7 RATINGS OF BRUSHLESS EXCITER:-

KW : 1350

Volts : DC- 420

Amps : DC- 3200

Excitation in Voltage : DC- 106

Excitation in Amps : DC- 36.5

RPM : 3000

Coolant : Air

Insulation class : F

35

CHAPTER-5

PROTECTION OF GENERATOR

5.1 NEED FOR PROTECTIVE SCHEME:-

An electrical power system consists of generators, transformers and

transmission and distribution lines. Faults can occur in any part of the power

system. Short circuits and all the abnormal operating conditions of the

components of power system are referred as faults. A fault free power system is

neither economically justifiable nor technically feasible. So, for the protection of

the components of the power system, protective schemes are required.

The protective scheme includes circuit breakers and protective relays to

isolate the faulty section of the system from the healthy section. The protective

relay detects any of the faults in the power system and issues necessary commands

to the circuit breakers to disconnect the faulty element. Protective relays utilize

one or more of the basic electrical quantities such as current, voltage, frequency

and phase angle to detect abnormal operating conditions on a power system.

A protective relay does not anticipate or present the occurrence of a fault;

rather it takes action only after a fault has occurred. The cost of protective

equipment generally works out to be about 5% of the total cost of the system.

5.2 TYPES OF FAULTS AND THEIR EFFECTS:-

Faults are caused either by insulation failure or by conducting path

failures. The failure of insulation results in short circuits, which are very harmful

as they may damage some equipment of the power system. Opening of conducting

paths results in unbalanced operation of the system. Unbalanced currents flowing

in rotating machines set up harmonics, thereby heating the machines in short

periods of time, so unbalanced operation is not allowed in normal operation of

power system. Sometimes even during the normal operation, circuit breakers may

trip due to errors in switching operation, testing or maintenance work, wrong

connections, defects in protective devices improving the system design, by

36

employing good quality components and by better operation and maintenance, can

reduce occurrence of such faults.

The faults are mainly classified as,

a. Symmetrical Faults.

b. Unsymmetrical Faults.

a. Symmetrical Faults:-

A 3-phase fault is called a symmetrical fault. All the three phase may be

short-circuited to the ground or they may be short-circuited without involving the

ground. It is a standard fault and is used to determine systems fault level.

b. Unsymmetrical Faults:-

Single phase to ground, phase-to-phase short circuits, single-phase open

circuit and two-phase open circuit are unsymmetrical types of faults. In addition to

above faults, the short-circuiting of turns, which occurs in machine windings, also

occur referred as winding faults. Two or more faults occurring simultaneously on

a system are known as multiple or simultaneous faults.

Of all the faults short circuit fault is most dangerous which has the

following consequences on the system.

1. Heavy short circuit current may cause damage to the equipment or any

other element of the system due to over heating and high mechanical

forces set up due to heavy current.

2. Arcs associated with short circuits may cause fire hazards.

3. Short circuits may cause the unbalancing of supply voltages and

currents, thereby heating rotating machines.

4. There may be loss in system stability and individual generators in

system may loose synchronism, resulting in a complete shutdown of

the system.

37

5.3 GENERATOR FAULTS AND THEIR EFFECTS:-

All the generator faults can be classified as:

1. Stator Faults

2. Rotor Faults

3. Miscellaneous Faults or Abnormal Operating Conditions

1. STATOR FAULTS:-

The stator faults include

i. Phase to Earth Faults

ii. Phase to Phase Faults

iii. Inter Turn Faults

Most faults occur in the stator windings, of which majority are earth faults.

Phase faults & inter faults are less common, these usually develop an earth fault.

The effect of earth in the stator is two fold,

1. Arcing to core which welds laminations together causing eddy current

hot spots on subsequent occurrence, repairs to this condition involve

considerable expenditure of time and money.

2. Severe heating in the conductors damaging them & the insulation, with

possible fire risks.

2. ROTOR FAULTS:-

Faults in the rotor circuit may be either earth faults or between turns. But

as the rotor field circuit is operated ungrounded a single ground fault does not

affect the operation of generator or cause any damage. However, It increases the

stress to ground in the field when stator transients induce an extra voltage in the

field winding. Thus the probability of occurrence of the second fault is increased.

If a second ground fault occurs a part of the filed winding is by passed, thereby

increasing the current through the remaining portion of the field winding. This

causes an unbalance in the air gap fluxes, leading to severe vibration of the rotor.

38

a. Loss of Excitation:-

Failure of excitation system is one of the serious abnormal operations of

the alternator. It may occur due to the failure or mal operation of a faulty field

breaker. The alternator speeds up slightly & operates as an induction generator.

Round rotor generators don’t have damper windings & hence they are not suitable

for such an operation. The rotor is over heated quickly due to heavy induced

currents in the rotor iron. Stator also gets over heated due to wattles current drawn

by the machine as magnetizing current drawn from the system but slower then

rotor heating. A large machine like a Turbo alternator may upset the system

stability because it draws reactive power from the system stability because it

draws reactive power from the system when working as n induction generator.

b. Unbalanced Three – Phase Faults:-

The unbalanced operation of the Alternator may arise due to,

i. Fault in stator winding.

ii. An unbalanced external fault, which is not cleared quickly.

iii. Open circuiting of a phase.

iv. Failure of one contact of the circuit breaker.

The unbalanced operation gives rise to negative sequence currents, which

rotate in a direction opposite to that of the rotor and hence produced a flux, which

sweeps through the rotor with twice the rotational speed. Hence spurious currents

of twice the machine frequency are induced in rotor body leading to overheating

of the rotor.

3. MISCELLANEOUS FAULTS OR ABNORMAL OPERATING

CONDITIONS:-

Many abnormal operating conditions such as over voltage, over speed,

High vibration effects, over heating of bearings, auxiliary failure, pole slipping

and voltage regulators are referred to as miscellaneous faults. These are explained

overtly in the following chapters.

39

CHAPTER-6

PROTECTION OF STATOR

6.1 DIFFERENTIAL PROTECTION FOR GENERATORS:-

Differential protection is used for protection of the generator against phase

to earth and phase to phase fault. Differential protection is based on the circulating

current principle.

In this type of protection scheme currents at two ends of the protection

system are compared. Under normal conditions, currents at two ends will be same.

But when the fault occurs, current at one end will be different from the current at

the end and this difference of current is made to flow through relay operating

coils. The relays then closes its contacts and makes the circuit breaker to trip, thus

isolate the faulty section. This type of protection is called the merz price

circulating current system.

Fig. Differential Protection for Generators

Limitations of this method:-

The earth fault is limited by the resistance of the neural earthing. When the

fault occurs near the neutral point, this causes a small current to flow through the

40

operating coil and it is further reduced by the neutral resistance. Thus this current

is not sufficient to trip the circuit breaker. By this protection scheme, one can

protect only 80 to 85 percent of the stator winding. If the relays with low settings

are used then it will not provide desire stability. This difficulty is overcome by

using the modified differential protection.

6.2 MODIFIED DIFFERENTIAL PROTECTION:-

In modified differential protection setting of the earth faults can be

reduced without any effect on the stability.

In this method two relays are used for the phase to phase fault and one

relay is used for the protection of earth fault. In this method the two relays and the

balancing resistance are connected in star and the phase fault relay is connected

between the star point and the neutral pilot wire. The star connected circuit is

symmetrical in terms of impedance. So when the fault current occurs due to the

phase to phase fault, it cancels at the star point due to the equal impedance. Thus it

is possible with this scheme to operate with the sensitive earth fault relays. Thus

this scheme provides protection to the greater percentage of the stator winding.

Fig. Modified Differential Protection for Generators

41

6.3 BIASED CIRCULATING CURRENT PROTECTION

(PERCENTAGE DIFFERENTIAL RELAY PROTECTION):-

With the differential protection relaying, the CTs at both end of the stator

windings must be same. If there is any difference in the accuracy of the CTs the

mal-operation of the relay will occurs. To overcome this difficulty, biased

circulating current protection is used. In this protection system we can

automatically increase the relay setting in proportion to the fault current. By

suitable proportioning of the ratio of the relay restraining coil to the relay

operating coil any biased can be achieved.

Fig. Biased Protection of the Stator Winding

Under normal operating condition current in secondary of the line CTs will

be same as the current in the secondary of the CTs at the neutral end. Hence there

are balanced current flows in the restraining coils and no current flows in the

operating coil. If there is any phase to phase or phase to earth fault occurs then it

causes the differences in the secondary current of the two CTs. Thus the current

flows through the operating coil and make the circuit breaker to trip.

42

Advantages of this method:-

a) It does not require the CTs with balancing features.

b) It also permit the low fault setting of the relay, thus protects the greater

percentage of the stator winding.

6.4 SELF BALANCE PROTECTION SYSTEM:-

This type of protection is employed for earth fault and also for the phase to

phase fault.

Fig. Self Biasing Protection of the Stator Windings

In this type of protection two cables are required which is connected to the

two ends of the each phase. These two cables are passed through the circular

43

aperture of the ring type CTs. Under normal conditions the current flowing in the

two leads of the cable will be in the same direction and no magnetization occurs in

the ring type CTs. When the earth fault occurs in any phase the fault current

occurs only once through the CTs and thus magnetic flux induced, this induces the

E.M.F in the relay circuit causes the circuit breaker to trip.

This is very sensitive type earth fault protection but it also has some

limitations,

a) A different design of the cable lead is required in this scheme.

b) Large electromagnetic forces are developed in the CT ring under

the condition of heavy short circuit.

6.5 STATOR GROUND FAULT PROTECTION:-

The method of grounding affects the degree of protection which is

employed by the differential protection. High impedance reduces the fault current

and thus it is very difficult to detect the high impedance faults. So the differential

protection does not work for the high impedance grounding. The separate relay to

the ground neutral provides the sensitive protection. But ground relay can also

detect the fault beyond the generator, it the time co-ordination is necessary to over

come this difficulty.

If we use the star- delta transformer bank, then it will block the flow of

ground currents, thus preventing the occurrence of the fault on other side of the

bank from operating ground relays. In unit protection scheme the transformer

bank limits the operation of the fault relay to the generator.

Unit Connected Schemes:-

In this scheme high resistance grounding is used and system is grounded

through the transformer bank and through the resistors.

95% Scheme:-

Relay which uses in the unit connected schemes must be insensitive to the

normal third harmonics voltage that may be present between the neutral and the

44

ground, and it must be sensitive to the fundamental harmonics voltage that is the

cause of the fault. The magnitude of the neutral shift depends upon its location in

the winding of the ground fault. And the general choice of the relay sensitive and

distribution transformer voltage provide 95% protection of the winding so this

scheme is called 95% scheme.

Neutral third harmonic under voltage:-

There is the third harmonic present between the neutral and the ground ,

and other schemes takes advantages of this and respond to the under voltage

between the neutral and the ground.

100% Scheme:-

This scheme provides complete protection of the stator winding by

injecting the signal between the stator winding and monitors it for change. 95%

scheme and third harmonics protection scheme provide protection only at rated

speed and rated voltage but it 100% scheme also provide protection at standstill.

6.6 STATOR INTERTURN FAULT PROTECTION:-

Differential protection for stator does not provide protection against the

inter-turn faults on the same phase winding of the stator. The reason is that the

current produced by the turn to turn fault flows in the local circuit between the

turns involved and thus it does not create any difference between the current

entering and leaving the windings at its two ends where the CTs are mounted.

The coils of the modern turbo generator are single- turn, so there is no

needs to provide inter –turn fault protection for the turbo generator. But the inter

turn protection is necessary for the multi turn generator like hydro electric

generator. Some times stator windings are duplicated to carry heavy current. In

this case stator winding have two different paths.

In this type of protection primaries of the CTs are inserted in the parallel

paths and secondaries are interconnected. Under the normal condition current

flowing through the two parallel paths of the stator winding will be same and no

current flowing through the relay operating coil. Under the inter turn fault, current

45

flowing through the two parallel path will be different and this difference in

current flowing through the operating coil and thus causes the circuit breaker to

trip and disconnect the faulty section. This type of protection is very sensitive.

Fig. Inter Turn Protection of the Stator Winding

6.7 STATOR OVER HEATING PROTECTION:-

Stator over heating is caused due to the overloads and failure in cooling

system. It is very difficult to detect the over heating due to the short circuiting of

the lamination before any serious damage is caused. Temperature rise depend

upon I2Rt and also on the cooling. Over current relays can not detect the winding

temperature because electrical protection can not detect the failure of the cooling

system.

So to protect the stator against over heating, embed resistance temperature

detector or thermocouples are used in the slots below the stator coils. These

detectors are located on the different places in the windings so that to detect the

temperature throughout the stator. Detectors which provide the indication of

temperature change are arranged to operate the temperature relay to sound an

alarm.

46

CHAPTER-7

PROTECTION OF ROTOR

Different Protection schemes are used for protection of faults occurring in

rotor. These schemes are,

7.1 ROTOR EARTH FAULT PROTECTION:-

As the field circuits are operating unearthed a single earth fault does not

affect the operation of the generator. But this fault increases the stress to the

ground because stator transients induce an extra voltage in the field winding. So if

there is only single earth fault but relay should be provided to give the knowledge

that fault has occurred so the generator may take out of service until second fault

occurs and cause serious damage. Two methods are used for rotor earth fault

protection.

Method I:-

In this method a high resistance is connected across the rotor circuit and its

mid point is grounded through a sensitive relay. This relay detects the earth fault

for whole circuit except the rotor center point.

Fig. Rotor Earth Fault Protection Method I

47

Method II:-

In this method dc injection or ac injection method is used. In it either dc or

ac voltage is connected between the field circuit and ground through a sensitive

over voltage relay and current limiting resistor or capacitor. A single earth fault in

the rotor circuit will complete the circuit including voltage source, sensitive over

voltage relay and earth fault. DC injection method is simple and has no problems

of leakage currents. If we use dc the over voltage relay will be more sensitive than

if we use ac because in case when we use ac the relay not picking up the current

that flows normally through capacitance to ground and also care should be taken

to avoid resonance between capacitance and inductance.

Fig. Rotor Earth Fault Protection Method II

48

7.2 ROTOR OVERHEATING PROTECTION:-

Negative sequence component of the unbalanced currents of the stator

winding causes double frequency current to be induced in the rotor winding due to

this component overheating of the rotor take place. In case of over current due to

over excitation in the rotor circuit, a dc relay is used. This relay senses and

initiates alarm. Application of such relay is limited because relaying of dc

quantities is relatively uncommon.

Rotor Temperature Alarm:-

This kind of protection is only provided in case of large generators. It

gives the level of temperature. In it resistance is measured by comparing voltage

and current by a double actuating quantity moving coil relay. The operating coil

being used as voltage coil and restraining coil used as current coil. The relay

measures the ratio of voltage and current because resistance gives the measure of

rotor temperature.

Fig. Rotor Overheating Protection

49

Automatic Field Suppression and Use of Neutral Circuit Breaker:-

When a fault on the generator winding exist even through the generator

circuit breaker is tripped, the fault continues to be fed as long as the excitation will

exist. For the quick removal of the fault, it is necessary to disconnect the field

simultaneously with disconnection of the generator. So it is very necessary to

discharge its magnetic field as soon as possible in short duration. Hence it should

be ensured that all protection system not only the trip the generator circuit breaker

but also trip the automatic field discharge switch.

7.3 LOSS OF EXCITATION PROTECTION:-

Loss of field failure of or loss of excitation is same phenomena and same

kind of protection is used. It is discussed here in the field failure topic.

Loss of Field Protection:-

Loss of field occurs due to tripping of the supply of the field current which

occurs because of the reasons.

i. Loss of field to the main exciter.

ii. Accidental tripping of the field breaker.

iii. Short circuit in field circuits.

iv. Poor brush contact in the exciter.

v. Loss of A.C supply to the excitation system.

vi. Operating errors.

Field Protection Phenomena:-

When the field supply is tripped, it speed increased and it start behaving as

induction generator so heavy currents are produced in the teeth and wedges of the

rotor. Because of the drop in excitation voltage the generator output voltage drops

slowly to compensate this voltage current start increasing then generator become

under excited and start drawing reactive power 2 to 4 times the generator load.

50

Before losing excitation, the generator is delivering power to the system.

But when loss of field occur this large reactive load thrown on the system abruptly

with loss of generator’s reactive power and it further causes voltage reduction and

extensive instability.

Protection against Loss of Field:-

If the system has capability to tolerate the difference of reactive power

then automatic protection is not required but if the system will be instable

in this condition and has not capability to tolerate then automatic

protection is required.

Under current Moving coil relay is connected across a shunt in series with

field winding. But in case of large generators which operate over a wide

range of field excitation then this relay will not work properly because

field failure due to the failure of the excitation is not detected by it because

it is held in by the ac induced from the stator.

Fig. Loss of Field Protection

The most valid type of protection in this case is by using directional-

distance type relay operating by alternating current and voltage at the generator

terminals. In offset-mho relay is used and its setting is like that when the

excitation goes certain value then this relay start operating because machine start

running asynchronously. Its characteristics are shown on R-X diagram. When

excitation is lost the generator impedance start a curve from the first quadrant to

the fourth quadrant. This region is enclosed in the operating area of the relay so

51

the relay will operate when the generator starts to slip poles and will trip the field

breaker and disconnect the generator from the system. The generator may then

return to service when the cause of failure is cleared.

Fig. Loss of Field Relay and system characteristics

Effects Produced by Loss of Field:-

i. It can endanger the generator, connected system or both.

ii. Loss of synchronism.

iii. Overheating of stator winding.

iv. Increased Rotor Losses.

7.4 POLE SLIPPING:-

When angular displacement of the rotor exceeds the stability limit then rotor

slips a pole pitch or we can say rotor flux slips with respect to stator flux. This

condition is called pole slipping.

Causes:-

i. Power system fault that persists for long duration.

ii. Connecting line between two systems is opened.

iii. Because of the insufficient electromagnetic torque that keep rotor

in Synchronism.

iv. Faulty excitation system.

v. Operating errors.

52

Pole Slipping Phenomena:-

Pole slipping does not occur very often when faults are cleared very fast.

When pole slipping occurs due to this synchronizing power will start flowing in

reverse direction twice for very slip cycle. On drawing this synchronizing power

on the impedance plane the flow of it characterized by cyclic change in the load

impedance and load impedance locus passes between +R and –R quadrants

because real power flows in reverse direction. When the load impedance is very

reactive in nature then two systems are 180 degree out of phase, this instant is

when drawn on the jx axis the point corresponding to this instant is called

transition point. At this stage only reactive power flows and system voltage

reached to zero at the electrical mid point of the two systems. Mid point is that

point where pole slipping take place and its location can be determined from the

apparent load impedance to the point where the locus crosses the jx axis. Three

parameters magnitude, direction and rate of change of load impedance with

respect to the generator terminals tell us about the pole slipping, that is it taking

place.

Fig. Offset Mho type Pole slipping Protection

Need of Pole Slipping Protection:-

High currents and torques can,

Loosen or causes wear off stator windings.

Damage shaft and coupling.

Stator and rotor overheating.

Excitation system damage.

53

CHAPTER-8

PROTECTION AGAINST MISCELLANEOUS FAULTS

8.1 UNDER/OVER FREQUENCY PROTECTION:-

8.1.1 OVER FREQUENCY OPERATION:-

Over frequency results from the excess generation and it can easily be

corrected by reduction in the power outputs with the help of the governor or

manual control.

8.1.2 UNDER FREQUENCY OPERATION:-

Under frequency occurs due to the excess. During an overload, generation

capability of the generator increases and reduction in frequency occurs. The power

system survives only if we drop the load so that the generator output becomes

equal or greater than the connected load. If the load increases the generation, then

frequency will drop and load need to shed down to create the balance between the

generator and the connected load. The rate at which frequency drops depends on

the time, amount of overload, load and generator variations as the frequency

changes. Frequency decay occurs within the seconds so we can not correct it

manually. Therefore automatic load shedding facility needs to be applied.

These schemes drops load in steps as the frequency decays. Generally load

shedding drops 20 to 50% of load in four to six frequency steps. Load sharing

scheme works by tripping the substation feeders to decrease the system load.

Generally automatic load shedding schemes are designed to maintain the balance

between the load connected and the generator.

The present practice is to use the under frequency relays at various load

points so as to drop the load in steps until the declined frequency return to normal.

Non essential load is removed first when decline in frequency occurs. The setting

of the under frequency relays based on the most probable condition occurs and

also depend upon the worst case possibilities.

During the overload conditions, load shedding must occur before the

operation of the under frequency relays. In other words load must be shed before

the generators are tripped.

54

8.2 UNDER/OVER VOLTAGE PROTECTION:-

8.2.1 OVER VOLTAGE PROTECTION:-

Over voltage occurs because of the increase in the speed of the prime

mover due to sudden loss in the load on the generator. Generator over voltage

does not occur in the turbo generator because the control governors of the turbo

generators are very sensitive to the speed variation. But the over voltage

protection is required for the hydro generator or gas turbine generators. The over

voltage protection is provided by two over voltage relays have two units – one is

the instantaneous relays which is set to pick up at 130 to 150% of the rated voltage

and another unit is IDMT which is set to pick up at 110% of rated voltage. Over

voltage may occur due to the defective voltage regulator and also due to manual

control errors.

8.2.2 UNDER VOLTAGE PROTECTION:-

If more than one generator supply the load and due to some reason one

generator is suddenly trip, then another generator try to supply the load. Each of

these generators will experience a sudden increase in current and thus decreases

the terminal voltage. Automatic voltage regulator connected to the system try to

restore the voltage. And under voltage relay type-27 is also used for the under

voltage protection.

8.3 PROTECTION OF THE GENERATOR DUE TO

UNBALANCE LOADING:-

Due to fault there is an imbalance in the three phase stator currents and due

to these imbalance currents, double frequency currents are induced in the rotor

core. This causes the over heating of the rotor and thus the rotor damage.

Unbalanced stator currents also damage the stator.

Negative sequence filter provided with the over current relay is used for

the protection against unbalance loading. From the theory of the symmetrical

components, we know that an unbalanced three phase currents contain the

negative sequence component. This negative phase sequence current causes

55

heating of the stator. The negative heating follows the resistance law so it is

proportional to the square of the current. The heating time constant usually depend

upon the cooling system used and is equal to I²t=k where I is the negative

sequence current and t is the current duration in seconds and k is the constant

usually lies between 3 and 20.

Its general practice to use negative current relays which matches with the

above heating characteristics of the generator. In this type of protection three CTs

are connected to three phases and the output from the secondary of the CTs is fed

to the coil of over current relay through negative sequence filter. Negative

sequence circuit consists of the resistors and capacitors and these are connected in

such way that negative sequence currents flows through the relay coil. The relay

can be set to operate at any particular value of the unbalance currents or the

negative sequence component current.

Fig. Protection against Unbalance Loading

8.4 NEGATIVE SEQUENCE OR CURRENT UNBALANCE

PROTECTION:-

When the machine delivering the equal currents in three phases, no

unbalance or negative phase sequence current is produced as the vector sum of

these currents is zero, when the generator is supplying an unbalanced load to a

system, a negative phase sequence current is imposed on the generator. The

56

system unbalance may be due to opening of lines, breaker failures or system

faults. The negative sequence current in the stator winding creates a magnetic flux

wave in the air gap which rotates in opposite direction to that of rotor synchronous

speed. This flux induces currents in the rotor body, wedges, retaining rings at

twice the line frequency. Heating occurs in these areas and the resulting

temperatures depend upon the level and duration of the unbalanced currents.

Under these conditions it is possible to reach temperatures at which the rotor

material no longer contain the centrifugal forces imposed on them resulting in

serious damage to the turbine-generator set. Any machine as per design data will

permit some level of negative sequence currents for continuous period. 

An alarm will annunciate at annunciation panel if negative sequence

currents exceeds a normal level. Reduce the MVAR power on the machine if

necessary load also and keep the machine for some time till the alarm vanishes at

annunciation panel. If the machine trips on the negative sequence protection never

take the machine into service until the temperatures on the rotor parts settle down

to its lower value. Resynchronize the machine to the grid after considerable time

under grid & feeder parameters are within limits. If the unit trips again on the

same protection, stop the machine after consideration time so as to cool down the

rotor parts and inform to the maintenance staff for thorough examination of the

system.

8.5 SYSTEM BACKUP PROTECTION:-

Generator backup protection is not applied to generator faults but rather to

system faults that have not been cleared in time by the system primary protection,

but which require generator removal in order for the fault to be eliminated. By

definition, these are time-delayed protective functions that must coordinate with

the primary protective system.

System backup protection must provide protection for both phase faults

and ground faults.

For the purpose of protecting against phase faults, two solutions are most

commonly applied, the use of over current relays with either voltage restraint or

voltage control, or impedance-type relays.

57

The basic principle behind the concept of supervising the over current

relay by voltage is that a fault external to the generator and on the system will

have the effect of reducing the voltage at the generator terminal. This effect is

being used in both types of over current applications: the voltage controlled over

current relay will block the over current element unless the voltage gets below a

pre-set value, and the voltage restraint over current element will have its pick-up

current reduced by an amount proportional to the voltage reduction.

The impedance type backup protection could be applied to the low or high

side of the step-up transformer. Normally, three 21 elements will cover all types

of phase faults on the system as in a line.

8.6 CLASSIFICATION OF GENERATOR PROTECTION

SCHEMES:-

Unit protection can be classified into following three categories,

Class -- A

Class -- B

Class -- C

Class – A Protection:-

1. Turbine and Generator tripped simultaneously due to sevearity of the

fault.

2. It covers all types of major electrical faults in the Generator, GT and

UATs.

3. It causes over speed of the TG set.

4. Over speed is tolerated in view of the severity of the fault.

5. It is known as simultaneous trip.

58

Class-A

Protection

Turbine

Trip

Generator

Trip

The faults which come under this category are as follows,

1. Generator overall differential relay

2. Generator differential relay

3. Generator 100% stator earth fault relay

4. Generator backup protection relay

5. Generator loss of excitation with under voltage

6. Generator over voltage protection

7. Stator earth fault relay

8. Rotor earth fault relay etc.

Class – B Protection:-

1. No immediate danger or damage.

2. Turbine trips instantaneously.

3. Then the generator trips on low forward power relay interlock.

4. Back up is the reverse power relay.

5. Faults in UAT & GT which are not severe covered by this protection.

6. No over speed in the TG set.

7. It is also known as sequential trip.

2 sec

59

Class-B

Protection

Turbine Trip

Low Forward Power Relay

Reverse Power Relay

Generator Trip

Reverse Power Relay

The faults which come under this category are as follows,

1. GT winding temperature high.

2. GT oil temperature high.

3. GT OLTC buchholz relay.

Class – C Protection:-

1. Faults in the grid.

2. Only 220 KV Circuit Breaker will be opened.

3. TG set maintains house load operation.

4. Unit can be reconnected to the grid after isolating the fault.

Faults covered in this protection are as follows,

1. Negative Phase Sequence Relay

2. Back Up Impedance Relay

3. GT Over Current Relay

60

8.7 DIFFERENT RELAYS USED IN PROTECTION OF

GENERATOR IN KTPS V STAGE:-

61

CHAPTER-9

CASE STUDY

Generator 10 was tripped in the month of October 2006 with 95% earth

fault (64 GA) and standby earth faults (64 GC) relay operated. The same kind of

fault occurred thrice in the total year (twice in 9 th plant and once in 10th plant). To

know the healthiness of insulation anywhere in power system, IR values of stator

windings is to be measured.

Finding the IR values here means that we have to calculate the value of

resistance. This is also called Megger test. In this test, a DC voltage is connected

to each phase and it is grounded in one side and the other side is connected to each

phase. When the phase is healthy, only a small current called capacitive current

flows through the circuit and resistance is very high and when an earth fault

occurs, a very high current flows through the circuit so current if very low or

approximately zero.

IR values are measured at 5KV with insulation meter and the results are as

follows,

R-E 45 M ohm

Y-E 50 M ohm

B-E 0 M ohm

So from the above results it is known that the earth fault is in the B-Phase

but it is very difficult to find out the exact location where the earth fault occurred

because of the large volume of the stator core and winding. Even then the entire

stator core and winding inspected physically for locating the earth fault. But it was

not visible. So in order to find out the exact location of the earth fault, smoke test

is to be conducted and it is as follows:

At around 32V from the 1-phase variac and a current of about 8 amps,

smoke was observed at 27th slot topbar (double layered winding) nearer to end

winding. Immediately voltage switched off. The area where the smoke was

62

observed is fully cleaned with contact cleaners. It is observed that, the core

stamping (laminated stamping) came outside from the core and it was pierced into

27th topbar which created earth fault. So the earth fault is at the 27 th topbar. Hence

27th topbar is debrazed from the winding and high voltage test is conducted for

rest of the winding and the results are as follows,

HV Test:-

Voltage Applied Leakage Current

R-> E with Y+B-> E 22.6 KV 2.91 A

Y-> E with R+B-> E 22.9 KV 2.92 A

B-> E with Y+R-> E 23.1 KV 2.87 A

So from the results it can be seen that all the three phases are healthy.

IR values are found again with 5 KV source:-

15 sec (in M ohm) 60 sec (in M ohm)

R-E 500 2000

Y-E 500 1750

B-E 350 1950

R-Y 1000 2750

Y-B 1250 4500

B-R 1000 3250

From the above results, it is found that the remaining winding is healthy.

63

New topbar placed at site, tested for high voltage and IR values are also measured.

HV Test Current

31 KV (for 1 minute) 90 mA

IR values at 5 KV:-

15 Sec 30 sec 60sec

5 KV 1, 00,000 M ohm 2, 00,000 M ohm 40, 00,000 M ohm

Topbar is placed in the 27th slot and brazing was done on both turbine and

exciter end sides. Insulating tapes were wound on the brazed winding. Insulating

liquids are also applied on the brazed positions.

Stator overhang position was kept for heating for 24 hours. Again the test

was conducted and IR values are also measured.

Voltage Applied Leakage Currents

R-> E with Y+B-> E 23.0 KV 2.92 A

Y-> E with R+B-> E 22.7 KV 2.88 A

B-> E with Y+R-> E 23.0 KV 2.93 A

IR values at 5 KV:-

64

15 sec 60 sec

R-E 550 2500

Y-E 450 1850

B-E 450 2000

R-Y 1050 3000

Y-B 1300 4000

B-R 1500 3900

It can be observed from the above results that the entire stator winding is

healthy.

There was also some special tests were conducted both on stator and rotor.

ELCID Test (Electromagnetic core imperfection detector test)

It is to find out the healthiness of laminations of stator core. The maximum

shootout current should be less than 100 mA for better operation.

Wedge deflection test

It is to find out the stiffness of the wedges fixed on the stator winding with

hydraulic jerks. A dial gauge will be placed on the wedge and a pressure of

about 100kg/cm sq. will be applied with the hydraulic jerk. The maximum

deflection of the dial gauge will be measured and is found to be normal for the

total stator wedges.

RSO Test (Recurrence Surge Oscillogram)

It is done for rotor winding. It is to find out if there are any internal short

or earth faults in the rotor winding.

Modern Technique

65

A new technique is implemented at Rayalaseema thermal plant (RTTP) in

stage-2 in which there is negligible chance of vibrations which caused trips in

KTPS V stage thrice last year. In the slots, the insulator is poured at the time of

construction and then conductor is directly poured on that so that, the whole stator

is a single and strong piece and less damage is done to the system during

vibrations.

66

CHAPTER-10

CONCLUSION

Thermal power plants are industrial goods that produce electricity.

Moreover, these plants are important to customers and are presumed to have a

service life of greater than twenty years. Accordingly, the reliability of a power

plant is considered most important, followed by economic efficiency. As demand

for electrical power increases throughout the world, APGENCO intends to

continue to strive to supply power plants that provide reliability, high performance

and low price in accordance with the needs of customers.

Thus the generator being the costliest and most important equipment of the

power system and is subjected to more number of faults than any other equipment

of the power system, protection of alternators requires a large number of

protection relays, which control a number of auxiliary relays with logic

interconnections to perform various tripping and alarm functions. This results in

large protection panels, complicated external wiring and a lot number cost,

complex testing, maintenance and trouble shooting procedures.

A number of trip out puts are also required for controlling different circuit

breakers of the generating plant. Selection of the trip out puts will depend on the

type of conditions detected. This is mainly due to the necessity of safeguarding the

generating plant and ensuring maximum plant availability. Therefore, tripping

logic is normally required as part of the protection system. In some applications,

more complex logic such as blocking and interlocking may need to be including

as well.

Microprocessor based relays are the present day advanced equipment used

in practical installations. Supervisory control and data acquisition systems

employing digital panels and computers are the advanced equipment adopted for

efficient interface between different elements of the power system leading to

excellent monitoring system, data collection and storage process over specific

period of time and performance of the whole power system.

67

BIBLIOGRAPHY:-

1. BHEL -- Manual for Alternators KTPS, Paloncha

2. Electrical Power Systems -- CL.Wadhwa

3. The Art and Science of Protective Relaying -- Crussel Masan

4. Power System Protection and Switch Gear -- Badri Ram

5. www.apgenco.com

6. www.wikipedia.com

7. www.scribd.com

8. www.123eng.com

68

INDEX

A

Auxiliaries, 21

A.C. Generators, 27

Air Cooling, 27

Arcing, 38

B

Blend, 7

Black Powder, 8

Bottom Ash, 20

C

Condensate, 3

Condenser, 12

Chimney, 3

Coal Bunkers, 4

Collecting Electrodes, 19

Combustion, 9

Coolant, 33

D

D.C. Injection Method, 48

Deaerator, 24

Deionizers, 15

Detectors, 46

DG Set, 21

E

Economiser, 11

Emitting Electrodes, 19

Enthalpy, 9

EDI (Electro Deionization

system),18

Electromagnetic Induction, 28

ELCID Test, 65

Excitation System, 32

F

Furnace, 9

Field Protection, 50

Feedwater Heater, 13

Fly Ash, 20

H

Hot Flue Gases, 10

Hydrogen Dryers, 33

I

Induced Draft Fan, 9

Impulse Reaction Turbine, 23

Ion Exchange, 15

I/C Breakers, 21

L

Load Demand Station, 1

69

M

Mixed Bed Deionization, 17

Main Exciter, 33

Merz Price Circulating Current

System, 40

Megger Test, 62

N

Natural Circulation, 9

O

Off Set mho Relay, 51

P

Pit Head Station, 1

Pilot Exciter, 33

Pilot Wire, 41

Pulverizers, 7

Primary Air Fan, 9

R

Rankine Cycle, 2

Rapping, 19

Rectifier Wheels, 33

Reheat Cycle, 2

Reheater, 11

Regenerative Cycle, 2

Resins, 16

RO (Reverse Osmosis), 18

Rotor Shaft, 31

Rotor Windings, 31

RSO Test, 65

Run of Mine Hopper, 7

RX Diagram, 51

S

Stack, 3

Secondary Air Fan, 9

Self-Biasing Protection, 43

Super Heater, 10

Silos, 20

Station Dark Out, 21

Stator Frame, 29

Stator Core, 30

Stator Windings, 30

Symmetrical Faults, 37

T

Two Bed Deionization, 17

Tie Breakers, 21

Temperature Alarm, 49

TG Set, 58

Topbar, 63

U

Unit Supply Boards, 21

Unit Connected Schemes, 44

Unsymmetrical Faults, 3

70