ntpc industrial training

8/22/2019 NTPC Industrial Training

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Summer Industrial Training

at

By:-

Aayush Pandey (09-13-059)

Sudhankar Raw (09-13-049)

Aditya Choudhary (09-13-069)

Gourav Singh (09-13-025)


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A Brief Introduction

NTPC, India's largest power company powering one-fourthIndia

Set up in 1975

A Maharatna Public Sector Company

The total installed capacity of the company is 39,674 MW(including JVs) with 16 coal based and 7 gas based stations,located across the country. In addition under JVs, 7 stationsare coal based & another station uses naptha/LNG as fuel.

Apart from power generation, which is the mainstay of the

company, NTPC has already ventured into consultancy,power trading, ash utilisation and coal mining.

NTPC ranked 337thin the 2012, Forbes Global 2000ranking of the Worlds biggest companies.


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Although the company has 17.75% of the total national

capacity, but it contributes 27.40% of total power

generation due to its focus on high efficiency.

NTPC27%

Others73%

Contribution of NTPC in powering India


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Introduction to

Vindhyachal Super Thermal Power Project Vindhyachal station belongs to the western region.

Presently the total capacity of this project is 3760 MW being the largest powergeneration plant in India.

COAL SOURCE:-

Open cast mines: Northern coal fields limited (NCL) mines at Dudhichua (7Km) and Nigahi

(10Km) and Jayant (5Km).

FUEL OIL SOURCE:-Indian oil corporation limited (IOCL) COLD (Customer operated lubricant and oil deposit)

at Jayant (5Km).

WATER SOURCE:-

Discharge canal of Singrauli Super Thermal Power Station (SSTPS).

BENEFICIARY STATES:-Madhya Pradesh, Chhattisgarh, Maharashtra, Gujarat, Goa, Daman & Diu and Dadar &

Nagerhaveli

The power flows out from Vindhyachal through 400KV power transmission system having

ten lines and one 500KV Rihand-Dadri HVDC line.

Vindhyachal also has Power grids HVDC back to back station connecting Northern andWestern grid region.


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Stage 1

Unit 1 210MW

Unit 2 210MW

Unit 3 210MW

Unit 4 210MWUnit 5 210MW

Unit 6 210MW

Stage 2

Unit 7 500MW

Unit 8 500MW

Stage 3

Unit 9 500MW

Unit 10 500MW

Stage 4

Unit 11 500MW (commissioned during our stay)

Unit 12 500MW (will be commissioned shortly)Stage 5

Unit 13 500MW (project under construction)

TOTAL= 4760 MW*


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Schematic flow chart of coal basedpower plant


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ExciterTurbineValve

Exhaust Steam

Condensor

Cooling

Tower

River

Water

TreatmentChamber

Super

Heater

Coal

Storage

Ash

Handling

Plant

Boiler

Coal

Handling

Plant

Ash

Storage

Economiser

AirPreheater

Chimney

Flue Gases

Flue Gases

Induced

Draft

Fan

R

YB

Feed Water

Heater

Feed Water Pump

Circulating Water PumpCondensate

Extraction Pump

Transformer

Bus Bars

Isolator

CircuitBreaker

Isolator

Alternator

Hot Air

Flue Gases

Forced Drought Fan


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Coal storage & Coal Handling Plant(CHP)


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In CHP, coal is received at track hopper from mines through BOBR (bottom open

bottom reclosed) Wagons.

There are generally two types of wagons used:-

BOBR (coal is loaded from up and dispatched from bottom), used hereBOXN (also known as wagon tippler, wagon is rotated to unload the coal)

The unloaded coal is scooped into conveyor belt & subjected to further process of

removal of extraneous material by passing the coal through suspended magnet,

magnetic separators, metal detectors, belt weighers to ensure that sized coal, free

of foreign material, is supplied to the power station. & then crushing to 20-200

mm size in crusher house.

After crushing, the coal again screened for elimination of extraneous materials,

weighed and sent to boiler bunkers.

Excess coal, if any, is sent to coal yard for stacking where it is stored and retrieved

by using Stacker- Reclaimer.

Water sprinkling is done time to time and compacted by running Dozers. Thisprevents air pockets in coal heaps, helps in fire protection and preserve volatile

materials to maintain calorific value of the fuel.


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From the bunker the coal goes to a RC Feeder/ Gravimetric feeder which controls the

amount of coal to be discharged for the further processing. The feeder consists of a

belt and is used to measure the quantity of coal fed (generally measured in

Tons/hour). From the Feeder, the coal goes to a helical structure (Ribon Shaped Path) which

carries it to the mills for pulverizing.

Generally mills are of two types used here:-

Ball and Tube arrangement: The mill usually consists of a large metal cylinder on

which large steel balls are positioned. The cylinder revolves, forcing the coal under

the balls to crush it. In this way coal is grounded to powder as fine as flour. Used only

in stage II (2X500) in VSTPP.

Bowl and roller arrangement: The mill usually consists of a large metal bowl on which

large steel rollers are positioned. The bowl and roller revolves, forcing the coal under

the roller to crush it. In this way coal is grounded to powder as fine as flour. Used in

other stages at VSTPP. This pulverized coal is such that 70% of it passes the 200 mesh sieve (200 mesh means

a sieve such that there are 200 holes in one square inch of area).


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Boiler


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This pulverized coal is mixed with air (called primary air) and taken to boiler/

furnace using primary air fan (PA fan). Now secondary air is taken using forced draftfan (FD fan) to ignite the coal.

To ignite the boiler for the first time oil is sprinkled. There are two types of oil used:-

LDO (Light Diesel Oil)

HFO (High Furnace Oil)

Boilers are generally of two types:-Fire tube

Water tube (used here)

Natural Circulation (no need of external pump as density of steam and water is

different)

Forced Circulation (external pump is used as at high temp. & pressure the density of

steam and water becomes equal.) used here


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The boiler consists of a large number of tubes extending the full height of the structureand the heat produced in boiler raises the temperature of the water circulating in themto create steam which passes to the steam drum at very high pressure. The steam isthen heated further in the super heater and fed through the outlet valve to the highpressure cylinder of the steam turbine (High pressure turbine).

A fire ball is created in boiler to burn the coal and produce steam. Sensors and scannersare present in boiler to monitor the various parameters of boiler.

The water used in boiler is demineralised water (ph 9.4 with no dissolved minerals) toprevent sludge formation and corrosion of the boiler and turbine blades. For this thereis a DM plant (demineralising plant).

When the steam has been through the first cylinder (High Pressure) of the turbine, it isreturned to the boiler and reheated using reheater before being passed through theother cylinder (Intermediate and Low Pressure) of the turbine.

From the turbine the steam passes into a condenser to be turned back into water called

condensate. Then through CEP (condensate extract pump) condensate is pumped toLow pressure heaters (where it may be heated to about 250C) to the deaerator (wherethe dissolved oxygen is removed according to Henry & Solubility laws i.e. with increasein temp., solubility of dissolved gases decreases) to boiler feed pump (it is most highestpower consuming motor in the power plant i.e. 2% of generating unit), where the mainloss (i.e. 44% loss) is occurred due to phase shift of steam to water making totalefficiency of a power plant about 38%.


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Boiler feed pump of two types are used here:-

a) Motor driven (driven using motor, used when plant is started)

b) Turbine driven (driven using turbine, when plant makes to its full capacity,

motor is stopped and steam rotating the turbine is used. Thus minimizing the

consumption of high power)

Then it is taken to high pressure heaters then to economizer where the

temperature is raised sufficiently for the condensate to be returned to the lower

half of the steam drum of the boiler and finally reconverted to steam.

Where the cooling water for power stations is drawn from large rivers, estuaries

or the coast, it can be returned directly to the source after use. Power stationssituated on smaller rivers and inland do not have such vast water resources

available, so the cooling water is passed through cooling towers (where its heat is

removed by evaporation) and re- used (used here).

There are three types of cooling tower:-

a) Natural (cooling is done naturally by allowing hot water in contact with outeratmosphere)

b) Forced Draft (fan is used to cool the hot water by pushing the heat)

c) Induced Draft (used here, fan is used to pull the heat from hot water)


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There are two type of ash found in boiler:

a) Fly ash (about 80%)

b) Bottom ash (also called slurry)

Then the flue gases are taken to Electrostatic Preceptors (ESP). The electrostaticprecipitator consists of metal plates which are electrically charged .Dust and Grit in

the flue gases are attracted on to these plates (as they are negatively charged

colloid, so they are attracted to the positive charged plate of ESP), so that they do

not pass up the chimney to pollute the atmosphere. Regular mechanical hammer

blows cause the accumulations of ash, dust and grit to fall to the bottom of the

precipitator, where they collect in a hopper for disposal. Additional accumulationsof ash also collect in the hoppers beneath the furnace. The efficiency of ESP is

about 99.8%.

Finally, flue gases and remaining particles are drawn by the Induced Draught (ID)

Fan (i.e. synchronous motor) into the main flue and to the chimney and then to

atmosphere.


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Turbine


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Turbines are of two types:-

Reaction (used here)

Impulse

There are three level of turbine:-

High Pressure (17 stages)

Intermediate Pressure (12X2 stages)

Low Pressure (6X2 stages)

From the boiler, a steam pipe conveys steam to the turbine through a stop valve

(which can be used to shut off steam in an emergency) and through control valves

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

Stop valve and control valves are located in a steam chest and a governor, driven

from the main turbine shaft, operates the control valves to regulate the amount of

steam used. (This depends upon the speed of the turbine and the amount of

electricity required from the generator).

The turbine shaft usually rotates at 3000 revolutions per minute. This speed is

determines by the frequency of the electricity system used in this country and is

the speed at which a 2- pole generator must be driven to generate alternating

current at a frequency of 50 /cycles per second.

When as much energy as possible has been taken from the steam it is exhausted

directly to the condenser.


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Generator


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The AC generator or alternator is based upon the principle of faradays law of

electromagnetic induction (i.e. when there is a flux linkage change across a

conductor an induced emf comes into existence and if conductor is shorted,

current passes through it)

Consists generally of a stationary part called stator and a rotating part called rotor. The stator housed the armature windings. The rotor houses the field windings.

D.C. Voltage is supplied to the field windings called excitation of generator.

It is of three types:

Static Excitation: Here first, excitation is given by battery, then after proper voltage

build up, an output of generator is taken and then step down to required voltageand then rectified using rectifier before feeding the rotor as input to generator

field winding. (Used only in Stage 1 of VSTPP).

Brushless Excitation: Here there is Main exciter & Pilot exciter.

The rotor of pilot exciter is a permanent magnet, which produces ac in stator

winding. This ac is given to stator of main exciter after rectification. The main

exciter output is directly connected to input of generator field winding after

rectification through hollow shaft where the rectifier is mounted on the same

shaft. Since there is no use of brush so called brushless excitation. (Used in other

Stages of VSTPP)


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DC exciter: Herethe pilot exciter is a dc shunt generator feeding the field winding

of main exciter which is a separately excited dc generator .The dc output of main

exciter is given to the field winding of alternator through brushes and sliprings.

The turbine is mechanically coupled with shaft/ rotor of the turbo generator.

When steam rotates the turbine, the rotor also rotates. When the rotor is rotated,

the line of magnetic field flux cut through the stator windings. This induces an

electromagnetic force in the stator windings.


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Specification of generator used here:

Manufactured: BHEL

Cooling of stator winding: Directly water cooled

Cooling of stator core & rotor: Directly hydrogen cooled

Stator inner connection: YY

Phase: 3

Frequency: 50Hz

RPM: 3000

Active Power: 500 MW

Apparent Power: 588 MVA

Power Factor: 0.85(lag)

Stator Voltage: 21 KV +- 1.05 KV (Stage II and III) and 15.75 KV (Stage I :: 210 MW)

Stator Current: 16200 amps

Rotor voltage: 340 volts

Rotor Current: 4040 amps


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Generator Cooling

The winding of rotor and stator produces heat. This heat raises the temperature of

the Generator. lf the temperature rises too much then the insulation breaks off

and the Generator gets short circuited. As the whole Generator is synchronized, so

it will affect all the Generator. So there must be a regular cooling of the generator

to avoid Rise of temperature in the Generator.

Cooling of stator winding: Directly water cooled i,e, Distilled Water

Cooling of stator core & rotor: Directly hydrogen cooled


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Hydrogen cooling system

Hydrogen is used as a cooling medium in large capacity generatorin view of its high heat carrying capacity and low density. But in view of its

forming an explosive mixture with oxygen, proper arrangement for filling, purging

and maintaining its purity inside the generator have to be made.

Also, in order to prevent escape of hydrogen from the generator casing, shaft

sealing system is used to provide oil sealing.

GENERATOR SEALING SYSTEM

Seals are employed to prevent leakage of hydrogen from the stator at the point of

rotor exit.

A continuous film between the rotor collar and the seal liner is maintained by

means of oil at a pressure which is about 0.5 atm above the casing Hydrogen gaspressure. .


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Generator Protection

Since the generator is very costly as it is the main equipment for production. So

several types of protection is given for the Generator. This protection includes

different types of fault in the generator and use relay for the tripping signal of the

generator. Some fault is controlled automatically but in case it cant be solvedautomatically the generator stop production of power and the unit trips out.

The different types of protection include the following:-

1) Over current protection

2) Over voltage protection

3) Earth fault protection4) Differential protection

5) Over fluxing protection

6) Loss of excitation protection

7) Loss of synchronism protection

8) Inter turn protection9) Negative sequence protection

10) Temperature alarm


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Transformers


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Transformers used in the power plant

The transformer used in the stage 1 (210MW) of the power plant is a 3 phase

transformer with connection i.e. on L.V. side and on H.V. side. The reason

for doing so is that the 3rdharmonic component of the voltage doesnt appear inthe line voltage in a 3phase connection.

The transformers used in stage 2 are single phase transformers that 3 single phase

transformers. The rating there is 600 MVA out of which the real power output is

500 MW. The input in this case is 21 kV. The reason for using 3 different

transformers in this case is due to the high power rating.

To reduce the losses the core is made up of a special type of material which is CRGO

(Cold Rolled Grain Oriented) steel which is further laminated to reduce the eddy

current losses.


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Generator transformer (GT)

The generator is connected to this transformer by means of isolated bus duct. This

transformer is used to step up the generating voltage of 15.75 KV (in Stage 1) or 21

KV (in stage II III) to grid voltage i.e 400 kV.

This transformer is generally provided with OFAF cooling.Specification:

Manufactured: BHEL

No of units: 3 nos. per unit

Power Rating: 200 MVA each

No load HV voltage: 400/1.732 KVNo load LV voltage: 21 KV

Rated HV current: 824.8 amps

Rated LV current: 9523.8 amps

Phase: 1

Cooling: OFAF (oil forced air forced)

Connection: YNd11

On Load Tap Changer: Tapping in 13 equal steps of 2.25% each provided on HV

winding to give 5% to 10%


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Unit Auxiliary Transformer (UAT):-

The UAT draws its input from the main bus duct connecting generator to the

generator transformer.

It is used for the working of large devices such as boilers, heavy motors etc.

For large units, it has become necessary to use more than one auxiliary transformer. Ituses the generated 15.75kV or 21 kV to convert into 6.6 kV.

Specification:

Manufactured: BHEL

No of units: 2 nos. per unitPower Rating: 7.5 MVA each

Voltage Ratio: 11/3.4 KV

Current Ratio: 393.6/1255 amps

Cooling: ONAN (oil natural air natural)

Connection: dyn1

Type of neutral grounding: LV-NGR

U it T f


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Unit Transformer

A part of power generated is given back to the unit for feeding the plant accessories.

Specification:

Manufactured: BHELNo of units: 2 nos. per unit

Power Rating: 50 MVA each

Voltage Ratio: 21/11.5 KV

Current Ratio: 1374.4/2510.22 amps

Cooling: ONAF (oil natural air forced)

Connection: dyn1

Type of neutral grounding: LV-NGR


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Station Transformer:

The station transformer is used to feed the power to the auxiliaries during the start

of the unit.

This transformer normally rated for the initial auxiliary load requirements of unit.

In physical cases this load is of order of 60% of the load at full generating capacity.

It is also provided with on load tap changer to cater to the fluctuating voltage of the

grid.

Specification:

Manufactured: BHEL

No of units: 1 nos. per unit

Power Rating: 80/40/40 MVA each

Voltage Ratio: 132/11 KV

Cooling: OFAF (oil forced air forced)

Connection: yn/yn0/yn0

Type of neutral grounding: LV1 and LV2-NGR


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Cooling of transformer

Heat is produced in the winding due to the current flowing in the conductors (I 2R) and

in the core on account of eddy currents and hysteresis losses. In small dry type

transformer heat is dissipated directly to the atmosphere. In oil immersed

transformer heat is dissipated by thermo siphon action.The purpose of using oil is:-

1. Cooling: Provides a better cooling and helps in exchanging heat

2. Insulation: A non conductor of electricity so good insulator.

The oil used is such that its flash point is pretty high so that it doesnt have any

possibility to catch fire.

There various types of cooling:-

AN - Air Natural

ON - Oil Natural

AF - Air forced

OF - Oil forcedONAF - Oil natural Air forced

OFAN -Oil forced Air natural

OFAF - Oil forced Air forced


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The oil serves as the medium for transferring the heat produced inside thetransformer to the outside transformer. Thermo Siphon action refers to thecirculating currents set up in a liquid because of temperature difference betweenone part of the container and other.

When oil gets heated up the oil with greater temperature goes to the upper side ofthe transformer. Now, if it is Oil natural it is cooled in it as is whereas in Oil Forced,a radiator is being constructed and a pump is being attached to it to pull the oilfrom the upper part of the transformer.

Now this oil in the chamber gets cooled either by direct heat exchanging through theatmosphere which is called Air Natural or by forced air draft cooling by a radiatorwith many electric fans which are automatically switched on and off dependingupon the loading of transformer which is known as Air Forced cooling.

As the oil gets cooled it becomes heavier and sinks to the bottom.


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Transformer accessories

Conservator: With the variation of temperature there is corresponding variation in the

oil volume. To account for this an expansion vessel called conservator is added tothe transformer with a connecting pipe to the main tank. It is also used to store

the oil and makeup of the oil in case of leakage.

Breather: In conservator the moisture from the oil is excluded from the oil through

breather it has a silica gel column, which absorbs the moisture in air before it

enters the conservator air surface. Normally dehydrating gel is blue in appearance

after the saturation it turns into pink.

Radiator: This a chamber connected to the transformer to provide cooling of the oil. It

has got fans attached to it to provide better cooling.


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TRANSFORMER AGING

Aging of the insulation system reduces both the mechanical and dielectric-withstand

strength of the transformer. As the transformer ages, it is subjected to faults that

result in high radial and compressive forces. As the load increases, with systemgrowth, the operating stresses increase. In an aging transformer failure, typically

the conductor insulation is weakened to the point where it can no longer sustain

mechanical stresses of a fault. Turn to turn insulation then suffers a dielectric

failure, or a fault causes a loosening of winding clamping pressure, which reduces

the transformer's ability to withstand future short circuit forces.

Oil contamination can be regularly checked with periodic test (DGA) and regular

monitoring of data.

Transformer Protection

There are two types of protections:

Mechanical

Electrical


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Mechanical Protection:

Pressure regulating valve: Transformer tank is a pressure vessel as the inside pressure

can grows steeply whenever there is a fault in the windings and the surrounding

oil is suddenly vaporized. Tanks as such are tested for the pressure with standcapacity of 0.35 kg/cm to prevent bursting of tank and thus the catastrophe; these

tanks in addition are provided with expansion vents with a thin diaphragm made

of bakelite/copper/ glass at the end. This diaphragm is the Pressure Relief Device/

Expansion Vent which senses the pressure and releases the valve when the

pressure is more than the specified limit.

Bucholzs relay: This has 2 floats, one of them with surge catching baffle and gas

collecting space at top. This is mounted in the connecting pipe line between

conservator and main tank. Gas evolution at a slow rate, which is associated with

minor fault inside the transformers i.e insapient fault, gives rise to the operation or

top float whose contacts are wired for alarm. There is a glass window with marking

to read the volume of gas collected in the relay. Any major fault in the transformer

creates a surge element in the relay, and trips the transformer. Size of the relay

varies with oil volume in the transformer and the mounting angle also is specified

for proper operation of the relay.


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Temp. Indicators: Most of the transformers are provided with indicators that displace

oil temperature and winding temperature there are thermometers pockets

provided in the tank top cover which hold the sensing bulls in them. Oil

temperature measured that of the top oil, where as the winding temperature

measurement is indirect. This is done by adding the temperature rise due to theheat produced in a heater coil when a current proportional to that following in

windings is passed in it to that or top oil. For proper functioning of OTI and WTI it

is essential to keep the thermometers pocket clean and filled with oil. Nowadays,

the temp. In the transformer is measured by a device called RTD (Resistance Temp.

Detector). This works on the principle that the change in resistance is directly

proportional to the change in temp. And thus, the temp. is monitored by keepingtrack of the resistance.

El i l i


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Electrical protection:

I. Biased Differential Protection: It responds to the vector difference between two

similar quantities. Here CTs are connected at each end of transformer. The CTs

secondary are connected in star (when transformer winding are connected in

delta) or delta(when transformer winding are connected in star) and pilot wires

are connected between the CTs of each end. During normal condition and for

through fault current fed into pilot wires are equal from both ends During internal

faults such as phase to phase or phase to ground ,the balance is disturbed. The out

of balance current flows through the relay operating coil. To avoid unwanted

operation on through fault restoring coil are provided in series with pilot wires.

II. Earth fault Protection:Earth fault relays connected in residual circuit of line CTs

give protection against earth faults on the delta or unearthed star connected

winding of transformer. Earth faults on secondary side are not reflected on primary

side, when the primary winding is delta connected or has unearthened star point.

In such cases an earth fault relay connected in residual circuit of 3 CTs on primary

side operation internal earth fault in primary winding only. Because earth faults onsecondary side do not produce zero sequence currents on primary side.

III. Over load Protection: Protected by using over current relays and thermal relays

IV.Over fluxing Protection: V/F Relays are used for over flux protection


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Switchyard


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BUS SECTIONALISER

MAIN BUS 1

MAIN BUS 2

TRANSFER BUS

BUS COUPLER

MAIN BUS 3

MAIN BUS 4

MAIN BUS 5

MAIN BUS 6

400 KV SWITCHYARD


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The basic purpose of switchyard is to protect the system and transmit power to the

consumer premises. The switchyard mainly comprises of the following

Switchgear equipment:

Isolators: - An isolator is one which can break an electric circuit when the circuit is

to be switched on no-load. These are normally used in various circuits for the

purpose of isolating a certain portion when required for maintenance etc.

The most common form of isolator is:-

Rotating centre post type: In which each phase has three insulators post, with the

outer post carrying fixed contacts and connections while the centre post having

the contact arm which is arranged to move through 90 on its axis.

Centre break isolator: It breaks the circuit from centre. Both the arms of isolator

are detached to break the circuit.

The isolators are driven by an operating mechanism box normally installed nearthe ground level. Isolator cannot operate unless the breaker is open.


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Circuit Breaker: - A circuit breaker is one which can break or make the circuit on

load and even on faults. There are two medium used in CB. Quenching medium

absorbs the arc produced during contact while operating medium is the medium by

which circuit breaks. The circuit breaker can be classified in different ways.

On the basis of quenching medium

i. Air blast circuit breaker

ii. Sulphur hexa-fluoride circuit breaker

iii. Oil immersed circuit breaker

Inter connecting transformer:- This is a transformer used to connect two buses at

different voltage.

Bus coupler:- It is used to couple two bus bar at the same voltage.

Bus sectionaliser:- It is used to divide a bus into two parts, one carrying current and other

isolated.

Lightening arrestor:- Lightening arrestor are provide at the terminals of the


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Lightening arrestor: Lightening arrestor are provide at the terminals of the

transformers for protection against lightening or any surges developing in the

system. There is a practice to install lightening arrestor at the incoming terminals

of the line. Shielding of the substation from the direct lightening stroke is provided

through earth wires located at structure's peaks. Recently, mesh are also being

considered for the purpose of shielding the sub-station.

Current transformer: - The current transformer is single phase oil immersed type. It is

used to measure the amount of current entering the CB. The secondary current is

generally 1 amp. Or 5 amp. in some cases

CVT's (Capacitor voltage transformer):-

They are used at 220KV and above, for the lower voltage, electro-magnetic type of

voltage transformer are mostly used. The secondary voltage is 110/3 volts.

(h)Relay port system:- In this system different relays are equipped to measure anyfault in the circuit. If there is any fault found then the system automatically breaks

the circuit through CB.

( )


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(e)PLCC:

It provide high frequency signal to the transmitting side of the main line.

Function

Communication: It can be used for communicating purpose for long distance.

Safety: If there is any delay in giving command for relay or any delay in the breaker to

break the circuit. It gives backup command to circuit breaker to break the circuit.

PLCC is provided from the CVT's

(f)Wave trap:

It is used to restrict the high frequency signal to the input side (generator side).

(g)Corona Ring

Air get ionized when there is a high voltage flow through the conductor and produces

a hiss sound and forms a blue ring this result in corona loss which is maximum at

sharp edges. This is reduced by using corona ring.


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Thank You

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