Tata Power 2

8/10/2019 Tata Power 2

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ACKNOWLEDGEMENT:

Our report will remain incomplete if we do not mention the efforts of

those people who helped us in completing this project.Firstly we want to thank Mr. Binay Khalkho Manager-H.R. and

Deepu Minz H.R. Dept TATA POWER Jamshedpur and the electrical

department for letting us use the department data and carry out the

necessary field work.

We would like to express our gratitude to Mr.G.P.Shastry,

Department Head, EMD, for his support, encouragement and all the

technical help without which the completion of this project would

have been impossible.

We are also deeply indebted to Mr. Soumendra Mandal, EMD Project

coordinator, whose technical input, stimulating suggestions and

encouragement helped us in completion of report and provided us

with practical on field knowledge of the subject.

We also want to thank my co-trainees from various colleges who

supported us in work. Their presence made our stay at TATA

POWER a pleasant and learning experience in all aspects of life.


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CONTENTS

Tata power

Jojobera Thermal Power Plant

Areas of operation

Coal Handling Plant

Boiler & Turbine Area

Transformer Yard

Electrical Switchyard

Electrostatic Precipitator

Transformers

Conclusion

Bibliography


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Jojobera Thermal Power plant

The Jojobera Thermal Power Plant, in Jamshedpur has an installed capacity of

547.5MW. It has a 5 generating units comprising of a single 67.5MW unit and

four units of 120MW each.

Units:

Unit#1: 67.5MW (commissioned in 1996)

Unit#2: 120MW (commissioned in 2000)




In total there are total 9 number of transmission lines going to various

substations in the city.

Transmission Lines (each 132kv):

Line1: Golmuri

Line2: Golmuri

Line3: Golmuri

Line4: Main Ring Substation (MRSS4)

Line5: Blower House (TATA STEEL)

Line6: Bara, Sonari



Line9: Tata Growth Shop


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Total number of bus couplers and bus sectionalizers used for transmission are:

Bus sectionalizers: 4

Bus couplers: 3

Total bus sections: 6

The transmission line diagram of the plant is as follows:

RAW MATERIAL

(COAL)CHP

BOILER AND

TURBINE

TRANSFORMER

YARDSWITCHYARD

ELECTROSTATIC

PRECIPITATOR

FLY ASH

AS SIDE

PRODUCT

TO DIFFERENT

PLACES BY

TRANSMISSION

LINES


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Areas of operationThe main area of operation or the division of the thermal power

plant is into the following areas:

Coal Handling Plant

Boiler & Turbine Areas

Transformer Yard

Electrostatic Precipitator

Switchyard

COAL HANDLING PLANT

Coal Handling Plant is the most essential part of any thermal plant. CHP is

responsible for the procurement and the supply of the coal to the coal millbunkers so that the required supply of pulverized coal is obtained for the

generation of power. CHP in thermal power plant comprises the process from

the unloading till filling bunkers of respective coal mills in different units.

Function and Capacity

Procurement of coal

Unloading , sizing and storing of coal

Feeding of coal

The design capacity of CHP is 1176TPH and rated capacity is 100TPH

Middling coal from TISCO West Bokaro Collieries

IB Valley coal from Mahanandi Coalfields Ltd.

Coals are crushed by primary crusher and secondary crusher.


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PROCESS FLOW CHART OF CHP

Step 1 Railway Rakers

Step 2 Wagon Tipplers

Step 3 Hopper

Step 4 Apron Feeder

Step 5 Primary Feeder

Step 6 Eccentric Disk Screen

Step 7 Secondary Crusher

Step 8 Conveyer

Step 9 Bunker

Specifications of Jojobera CHP plant:

Capacity of CHP 1176 ton/hr

Capacity of Wagon Tippler 105 ton

Coal carrying capacity of one wagon 58-60 ton(approx.)

Coal carrying capacity of one rake 3500 ton(approx.)Charging rate of side arm charger 20 wagon/hr

Capacity of primary crusher 1176 ton/hr

Capacity of secondary crusher 1176 ton/hr

Total length of conveyer 3km(approx.)

Input/ Output coal size primary crusher 600mm/150mm

Input/ Output coal size secondary crusher 300mm/25mm

Average coal consumption per day 30004000 ton

Coal storage capacity of stockyard 1000 tons

Major auxiliaries of CHP are:

1. Wagon Tipplers:

The wagon tippler is driven by 110KV motor and the top lamping device is

actuated by hydraulic cylinders. Cylinders are operated by a hydraulic power

pack which gives necessary fluid flow and pressure by means of 30KV


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hydraulic motor to operate the hydraulic cylinder. All these motors are PLC

controlled.

Wagons arriving at CHP are placed by hydraulic operated side arm charger

on wagon tippler which is driven by 415V ac, 125KV induction motor.TATA Honeywell PLC performs the entire of wagon tippling.

Individual coal loaded wagons are placed on wagon tippler cradle. Wagon

tippler raise command is given by operator and sequence of tippling

operation starts in auto mode controlled by PLC.

During tippling operation the along with loaded wagons rotates for 135

140 degrees and dumps the coal into the hooper.

2. Side Arm Chargers

It is hydraulic equipment provided at wagon tippler to place coal wagons as

per requirement avoiding the engagement of the locomotive during

unloading operation. A batch of 2022 coal loaded wagon can be handled

at a time. A 450KW motor in side arm chargers is connected with the SAC

hydraulic power pack which delivers necessary torque to the SAC. SAC in

each operation gets connected to the rack of the loaded wagon by swing arm

and brings the individual wagon to cradle for tripling.

3. Conveyer Belts:

A conveyer belt (or belt conveyer) consists of two or more pulleys, with a

continuous loop of materialthe conveyer beltthat rotates about them.

One or both of the pulleys are powered, moving the belt and the material on

the belt forward. The powered pulley is called the drive pulley while the

unpowered pulley is called the idler.

4. Primary Crusher:

It is also known as rotator breaker. It is a horizontal drum having perforated

screen plates inside the drum and is supporting rollers along with two guide

rollers. Lifting shelves are fitted inside the drum which lifts up coal fed at

one end during its rotation the coal is reduced in size and passes through the

perforated screened plates having 150mm diameter holes. The uncrushed


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Practical arrangement in a simple steam power plant working on Rankine cycle

is shown ahead.

Thus in Rankine cycle, isothermal heat addition and heat rejection processes

have been replaced by isobaric processes. Realization of isobaric heat additionand heat rejection in boiler and condenser respectively is in conformity

with nature of operation of these devices. Isobaric heat addition can be had in

boiler from sub cooled liquid to superheated steam without any limitations.

Boiler mountings:

Water level indicator

Safety valve

High steam and low pressure safety valves

Fusible plugs

Pressure gauge

Stop valve

Feed check valve

Blowof cock

Manhole and Mudbox

Boiler accessories:


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Super heater

Economizer

Air preheater

Feed pump

N.B :- Boiler mountings and accessories may vary for different types of boilers.

Some of the boiler accessories and mountings are described below.

Super Heater: Its purpose is to super heat steam and is a type of heat

exchanger in which steam flows inside tubes and hot gases surround it.

Economizer: It is also a heat recovery device in which feed water is

heated from heat available with exhaust gases. Thus hot feed water

available from economizer lowers the fuel requirement in combustion

economizer also helps in removal of dissolved gases by preheating of

water and thus minimizes tendency of corrosion and pitting.

Feed pump: Feed pump is used for sending water into boiler at the

pressure at which steam generation takes place. It is generally of three

types i.e. centrifugal pump, reciprocating pump and injectors.

Safety valve: Its function is to prevent the steam pressure from

exceeding a limiting maximum pressure value. Safety valve should

operate automatically by releasing excess steam and bring pressure

down within safe limits.

Pressure gauge: It is used for pressure measurement. Pressure is

continuously monitored so as to avoid occurrence of over shooting of

boiler pressure, although safety devices to protect boiler against pressure

rising beyond a limit is provided but pressure gauges are also used for

monitoring pressure.

Stop valve: It regulates the flow of steam from the boiler. The is

generally mounted on highest part of boiler shell and performs function

of regulating the flow of steam from boiler. Stop valve generally has

main body of cast steel; valve, valve seat and nut etc. are of brass.

Manhole and Mudbox: Manhole provides opening for cleaning,

inspection and maintenance purpose. Mudbox is a collection chamber

for collecting the mud.


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TURBINE AUXILLARIES:

A steam turbine is a prime mover in which rotary motion is obtained by thegradual change of momentum of the steam. In a steam turbine following are the

main parts:

The nozzle in which energy of high pressure is converted in to kinetic

energy, so that steam issues from nozzle at high velocity.

The blade which change the direction of motion of steam issuing from

the nozzle that force acts on the blade to change momentum and propel

them.

The auxiliaries are:

Condensate extraction pump

Hot well make up pump

Grand stream condenser

Surface condenser

Extraction steam system

LP Heater: A heater located between the condensate pump and either the

boiler feed pump.

HP Heater: A heater located downstream of the boiler feed pump.

Deaerator: It is a device that is widely used for the removal of oxygen

and other dissolved gases from the feed water to steam- generating

boilers

Operation:

The steam cycle is working on a heat regeneration cycle. Feed water is supplied

to the drum through the economizer outer limbs. Water in the boiler tubes

absorbs heat from the furnaces. The mixtures of the water and steam is


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discharged into the boiler drums. The separated saturated steam is led to super

heater where it is heated to about 810K.

Superheated steam from the boiler is fed to the turbine via the turbine top valve,

emergency stop and governing valve. Steam first enters the HP turbine, getsexpanded here and then it is directed to the inlet of the LP turbine for further

expansion. In the process the turbine starts rotating which in turn rotates the

prime mover of the generator, thus producing electricity.

Steam undergoing expansion in the allowed to flow through the condenser

where the steam is condensed by cooling water supplied by C.W pumps. The

condensate collected in the hot wells and pumped by vertical condensate

extraction pumps to the de aerator through air ejector, gland steam condenser,

drain cooler and LP heater. From the de aerator feed water storage tank, feed

water is pumped to the economizer inlet header through two HP heater. During

this process, the condensate steam is collected in different system. Heat is

recovered at various points and is fed to the main feed water system.

The ratings of UNIT #2 turbo generator of TATA Power Jojobera Power Plantis given below:

1. K.W : 120000

2. P.F : 0.8

3. KVA : 150000


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TURBO GENERATOR

A turbo generator is a combination of a turbine directly connected to an electric

generator for the generation of electric power. Large steam powered turbo

generators provide the majority of the worlds electricity and are also used by

steam powered turbo electric ships.

Smaller turbogenerators with gas turbine is often used as auxiliary power

units. For base loads diesel generators are usually preferred, since they offer

better fuel efficiency, but on the other hand diesel generator have a lower power

density and hence require more space.

The efficiency of larger gas turbine plants can be enhanced by using a combined

cycle, where the hot exhaust gases are used to generate steam which drives

another turbo generator.

Generator produces alternating current:

The generator is connected to the turbine drive shaft. It has a moving partthe

rotor and a fixed part the stator. The rotors outersurface is covered with

electromagnets. The stators inner surface, or cylinder wall, is made up ofcopper windings. When the rotor turns inside the stator, the electrons in the

copper windings vibrate. Their movement generates an electric currents,

similar to the one created by Michael Faraday in his 1831 experiment on

electromagnetic induction, but on a much larger scale.

Turbine have a constant rotation speed:

All the generators units in a power system must be synchronised. In other words

its essential that they maintain an exact rotation speed. To ensure adequate

power quality. Equipment that runs on electricity is designed to use alternating

current of specific frequencies. This frequency depends on the generating units

rotation speed i.e. the no of times per second that rotor magnet travel past the

stator winding. This frequency is expressed in cycles per second, or hertz(Hz),

named after the German physicist Heinrich Hertz, to prove the existence of

radio waves.


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Stator :-

The stator consists of two party viz. The outer casing and inner framesupporting the core the winding outer casing is of welded construction welded

tubes and ducts provide flow path for cooling. Inner stator consists of stator and

core windings. Stator core stacked with insulated electrical sheet steel

lamination clamping fingers ensures a uniform pressure and intensive cooling of

stator core ends. Stator winding fractional pitched, two layers consisting of

individual bars. To minimize the losses, the bars are separately brazed together

and insulated from each other


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TRANSFORMER YARD

The transformer yard of Jojobera thermal plant comprises of following

transformers:

TYPE OF TRANSFORMER QUANTITY

1. Generating transformer (GT) 5

2. Unit Auxiliary transformer (UAT) 5

3. Station transformer (ST) 3

4. Sub station transformer (SST) 8

Generating Transformer (GT)- 11KV/132KV

The generating transformer is used as a step up transformer which produces

11KV and steps up this voltage to 132KV for transmission. Electricity produced

at 11KV cannot be transmitted owing to large losses due to heavy current at the

voltage level. A generating transformer is used to increase the voltage level to

132KV to meet the transmission requirements GTs are step up transformers

with deltaconnected LV windings are connected to the transmission lines.

Specifications:

GT#1

Make BHEL


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Rating 90MVA

Voltage 11/132KV

CoolingHV

LV

ONAF ONAN30MVA 55MVA

90MVA 55MVANo Load Voltage

HV

LV

ONAF ONAN

133V 139V

10.5V 10.5V

Line Current

HVLV

ONAF ONAN

373.8A 228.4A4943.7A 3024.5A

Phase 3

Connection Y

Frequency 50HzInsulation level

HV

LV

ONAF ONAN

660KV 275KV

75KV 25KV

Weight (of oil)

(total)

30500Kg

116000Kg

GT#2, GT#3, and GT#4

Make BHEL

Rating 90/120/150 MVA

Voltage 11/132KV

Cooling

HV

LV

ONAF ONAN

30MVA 55MVA

90MVA 55MVA

No Load Voltage

HV

LV

ONAF ONAN

133V 139V

10.5V 10.5V

Line Current

HV

LV

ONAF ONAN

373.8A 228.4A

4943.7A 3024.5A

Phase 3

Connection Y

Frequency 50Hz

Insulation level

HV

LV

ONAF ONAN

275KV 650KV

28KV 75KV

Weight (of oil) 30500Kg


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(total) 116000Kg

Unit Auxiliary Transformer (UAT) 11KV/6.6KV

UAT is a power transformer that supplies power to the auxiliary equipment of

the power generating station during its normal operation. This transformer is

connected directly to the generator output by a tapoff of the isolated phase

bus duct and thus becomes the cheapest source of power to the generating

station.

It is generally a threewinding transformer where the primary winding is equal

to the main generator voltage rating. The UATs are connected to the generators

as step down transformers. Rated KVA of UAT is approximately 15% of thegenerator rating.

Specifications:

UAT#1

Make BHEL

Rating 11/6.6KV

No Load VoltageHV

LV

11000V

6600V

Line Current

HV

LV

656.1/787.3A

1045.9/1255.1A

Phase 3

Vector group DdO

Cooling ONAF/ONAN

Impedance at normal temperature 8.76%Impedance at extreme temperature 8.05%

Weight (of oil )

(total)

6265Kg

16500Kg

Station Transformer (ST)132KV/33KV/6.6KV

A critical function of any electricity generation and distribution system is

stepping up or down of voltage at various points in the delivery network. Thevoltage is stepped up or down at substations using station transformers. The se


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may come in various sizes, depending upon the site transformers, but are

normally connected to the network through overhead connections which results

in exposed HV or LV bushings that necessitate a fence or other protective

enclosure for personnel safety and security.

At Tata Power Jojobera plant, there are three numbers of 3 winding

132/22/6.6KV station transformers (ST#1, ST#2, ST#3) to cater to station loads

such as CHP,DM water plant, AIC plant, ESP unit etc. These also supply power

to the customers as Tata Motors, Tata Cummins, and Lafarge Cement at 33KV.

There are two numbers of feeders for each recipient, normally which are kept

ON from the Jojobera plant end.

Specifications:

ST#1, ST#2, ST#3

Make BHEL

Rating 75MVA

Voltage 132/33/6.6KV

Oil quantity 32250 Lts

Cooling ONAF/ONAN

Connection HVStar, MVStar, LVDelta

Vector group HVMV: YNynoHVLV: YNd1

Insulation level

1.) Impulse withstand voltage2.) 1 min. Power frequency

withstand voltage

HV MV LV

550 75 60230 28 20

No load losses at rated voltage andfrequency

42 KW

Load losses at principal tap and rated

output

268 KW

Auxiliary losses 5.2KW (Max.)

Weight (of oil )

(total)

30500Kg

116000Kg

TRANSFORMERS AT JOJOBERA PLANT AND THEIR USES:


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USTs are located in power plant to step down the voltage level from

6.6KV to 415V. The rating for this transformer corresponds to the rating

of the auxiliary load to be borne. Generally, these are stationed indoor

and are dry type transformers.

Power at Jojobera plant of Tata Power is evacuated at 132KV

33KV system supplies power to Lafarge cement plant, Tata Cummins and

TELCO. For each of the aforesaid units, there are two feeders of 33KV

each. To facilitate this is a 33 kV bus with two incomers and one bus

couplers. Each incomer is capable of bearing the full load.

There are six 6.6 kV buses. All the HT motors, 6.6kV/440V transformers

are connected to the 6.6kV buses employ SF6 breakers. If the unit trips

then all the load gets transferred to the station transformer automatically.

There are 14 415 V buses, all the 415V motors like ACW pumps, CCW

pumps, valves, blowers, ACs are connected to the 415V bus system.

SWITCHYARD

Switchyard is protected area where all the switchgears and its equipment are

installed power transmission. Switchgear is used for switching, controlling and

protecting device. Switchgear equipment is essentially concerned with

switching and interrupting currents either under normal or abnormal operatingconditions. Switchyard is hub for electrical power sources, transformers,

remotely controlled arc snuffing breakers, metering devices etc.

Switchyard forms the integral part of any power plant. These power plants have

their main plant equipment integral controls as well as Plant Distributive

Control System (DCS). While the entire plant is integrated at the DCS level,

true unification is achieved by incorporating/integrating switchyard controls.

Features:

1.) Monitoring of status of switchyard equipment like isolators, circuit

breakers etc.

2.) Issue of close/open commands to isolators, breakers, etc.

3.) Monitoring of system parameters like voltage, current, frequency, MW,

MVAR, energy.

4.) Controlling operations of protective relays.

5.)Presentation of information useful to operator in different forms.

6.) Generation of reports.


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7.) Storage and revival of reports.

8.) Remote control and monitoring of different kinds of frequencies

through fibre optics/PLCC communication like wave traps.

Switchyard Equipments

CURRENT TRANSFORMER (CT)

Current transformer is used to measure current at reduced current as well as for

the protection of the system. It is mainly a step down current to known ratio.

The primary of this transformer consists of one or more turns of thick wire

connected in series with the line. The secondary consists of large number ofturns of fine wire which provides measuring instrument and relay a current

which is a constant fraction of current in the line. It reduces heavy current

flowing in the element of a power system to low values that are suitable for

relay operation. Nickel iron is used for the construction of CT because it gives a

good accuracy up to 5 times the rated current.

Types of CT:

a) Live Tank Current Transformer: In the live tank design, active part (i.e.core with secondary and primary duly insulated) is in the top tank. Top

tank is live and secondary is insulated and taken to the bottom tank.

b) Dead Tank Current Transformer: in dead tank design, active part is in

bottom tank is in ground potential (i.e. dead) and the primary is insulated

and taken to the top tank for primary termination.

POTENTIAL TRANSFER (PT)

Potential transformer is mainly a step down transformer which steps down thevoltage to known ratio. It is used for protection as well as measurement of

voltage in the system. The primary of this transformer consists of a large

number of turns which provides measuring instruments and relays, a voltage

which is known fraction of line voltage.

Types of PT:

a) Capacitive Voltage Transformer (CVT): CVT is used to measure high ac

voltage. It consists of capacitive potential divider and step down


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transformer. Primary side of transformer is connected to the high voltage

side together with capacitive and secondary side of transformer is having

measuring instrument.

Advantages of CVT are:

Low impedance measuring device is used in CVT

Cost of device reduced

Loss is less

b) Inductive Voltage Transformer (IVT): IVT are used for voltage metering

and protection in high voltage network systems. They transform the high

voltage into low voltage adequate to be processed in measuring and

protection instruments secondary equipment, such as relays & recorders.

ISOLATORS

It is a disconnection switch which operates at no load condition both manually

as well as remote. During faulty conditions circuit breaker operates first and

then isolator is opened. After getting recovered from the fault, the isolator is

closed first then the circuit breaker in order to avoid flashover.

Isolators have provisions for a padlock so that inadvertent operation is not

possible. In high-voltage or complex systems, these padlocks may be part of

a trapped key-interlock system to ensure proper sequence of operation. In some

designs, the isolator switch has the additional ability to earth the isolated circuit

thereby providing additional safety. Such an arrangement would apply to

circuits which inter-connect power distribution systems where both ends of the

circuit need to be isolated.

So definition of isolator can be rewritten as Isolator is a manually operated

mechanical switch which separates a part of the electrical power system

The main difference in isolator and a circuit breaker is that an isolator is an off

load device intended to be opened only after a current has been interrupted by

some other control device. Safety regulations of the utility must prevent any

attempt to open the disconnector while it supplies current.

Classification of isolators


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Isolators are classified into three categories based on its breaking method.

Horizontal break: In these isolators the operating arm moves in a

horizontal plane. It can be further classified into:-

1. Centre break2. Double break

Vertical break

Pantograph


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CIRCUIT BREAKER

The circuit breakers are the device, which is capable of making and breaking of

an electrical circuit under normal and abnormal conditions. During normal

operating condition the Circuit Breaker(CB) can be opened or closed by astation operator for the purpose of switching and maintenance. During the

abnormal or faulty conditions the relays senses the fault and closes the trip

circuit breaker. Thereafter the circuit breaker opens. The circuit breaker has two

working positions, open & closed. These correspond to open circuit breaker

contact and closed circuit breaker contact respectively. The operation of

automatic opening and closing the contact is achieved by means of operating of

the circuit breaker. As the relay contact closes the trip circuit is closed and the

operating mechanism. In Tata Power, the 132kV breakers for GT#1,2,3 all ABBand arc SF6 circuit breaker in which closing and tripping charged spring.

Classification of Circuit Breaker

a) Oil Circuit Breaker: It employs the basic technique of oil for arc

extinction. Upon interruption of the electric circuit, an electric arc forms

between the contacts of the circuit breaker. Because of the high

temperature of the arc the oil is evaporated and oil vapours are partially

decomposed liberating ethylene, methane and other gases. A gas bubble

is formed in the arcing zone; the pressure in the bubble may be as high as

several dozen mega N/m2. The arc is then extinguished, both because of

its elongation upon parting of contacts and because of intensive cooling

by the gases and oil vapour.

b) Vacuum Circuit Breaker: Vacuum circuit breakers are circuit breakers

which are used to protect medium and high voltage circuits from

dangerous electrical situations. A vacuum circuit breaker is such kind ofcircuit-breaker where the arc-quenching takes place in vacuum. The

technology is suitable for mainly medium voltage application. For higher

voltage vacuum technology has been developed but not commercially

viable. The operation of opening and closing of current carrying contacts

and associated arc interruption take place in a vacuum chamber in the

breaker which is called vacuum interrupter. The vacuum interrupter

consists of a steel arc chamber in the centre symmetrically arranged

ceramic insulators. The vacuum pressure inside a vacuum interrupter is

normally maintained at 10- 6

bar.


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c) Air Blast Circuit Breaker: It uses compressed air or gas as the interrupting

or the breaking medium. Gases such as hydrogen, carbon-dioxide,

nitrogen and Freon can be used as arc interrupting medium, but

compressed air is the most suitable arc interrupting medium. The reason

is nitrogen has the similar circuit breaking properties as that of

compressed air medium. Carbon-dioxide has a drawback that is difficult

to control owing to the freezing at valves and other restricted passages.

Hydrogen has increased breaking capacity bit it is costlier. The air blast

circuit breaker requires an auxiliary compressed air system which

supplies air to the breaker air receiver.

d) SF6 Circuit Breaker: A circuit breaker in which the current carrying

contacts operate in sulphur hexafluoride or SF6 gas is known as an

SF6 circuit breaker. SF6 has excellent insulating property. SF6has high

electro-negativity. That means it has high affinity of absorbing free

electron. Hence, for heavier and less mobile charged particles in SF6 gas,

it acquires very high dielectric strength. Not only the gas has a good

dielectric strength but also it has the unique property of fast

recombination after the source energizing the spark is removed. The gas

has also very good heat transfer property. Due to its low gaseous

viscosity (because of less molecular mobility) SF6gas can efficiently

transfer heat by convection. So due to its high dielectric strength and high

cooling effect SF6 gas is approximately 100 times more effective arc

quenching media than air. Due to these unique properties of this

gas SF6 circuit breaker is used in complete range of medium voltage and

high voltage electrical power system. These circuit breakers are available

for the voltage ranges from 33KV to 800KV and even more.


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LIGHTNING ARRESTER

A lightning arrester is a device used electrical power systems and

telecommunications systems to protect the insulation conductors of the system

from the damaging effects of lightning. The typical lightning arrester has a highvoltage terminal and a ground terminal. When a lightning surge (or switching

surge, which is very similar) travels along the power line to the arrester, the

current from the surge is diverted through the arrester to earth.

If protection fails or is absent, lightning that strikes the electrical system

introduces thousands of kilovolts that may damage the transmission lines, and

can also cause severe damage to transformers and other electrical or electronic

devices. Lightning produced extreme voltage spikes in incoming power lines

can damage electrical home appliances.

Here zinc oxide arresters are used. Zinc oxide arresters have energy absorption

level.

Types:

1. Rod gap arrester

2. Horn gap arrester

3. Multi gap arrester4. Expulsion type lightning arrester

5. Valve type lightning arrester


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RELAYS

A relay is an electrically operated switch. Many relays use an electromagnet to

mechanically operate a switch, but other operating principles are also used, such

as solid-state relays. Relays are used where it is necessary to control a circuit bya low-power signal (with complete electrical isolation between control and

controlled circuits), or where several circuits must be controlled by one signal.

The first relays were used in long distance telegraph circuits as amplifiers: they

repeated the signal coming in from one circuit and re-transmitted it on another

circuit. Relays were used extensively in telephone exchanges and early

computers to perform logical operations.

A type of relay that can handle the high power required to directly control an

electric motor or other loads is called a contactor. Solid-state relays control

power circuits with no moving parts, instead using a semiconductor device to

perform switching. Relays with calibrated operating characteristics and

sometimes multiple operating coils are used to protect electrical circuits from

overload or faults; in modern electric power systems these functions are

performed by digital instruments still called "protective relays".

BUS COUPLER

The main function of bus coupler is to couple the busses. For each and every

instrument a cable comes at the input terminal of bus coupler. Output terminal

of this coupler goes to the control room. Thus each equipment can be controlled

either manually or by control room. It comes into action if any fault occurs in

the bus.

Bus coupler configurations are available as non-terminated or internally

terminated. If two or more non-terminated couplers are used on a bus, then the

couplers at each end of the bus must be terminated externally with 78ohm terminators on the unused bus connections of the end couplers. Alternately,

internally single terminated couplers (with or without the non-functional bus

connectors) can be supplied.

BUS SECTIONALIZERS

The sectionalizer is a self-contained, circuit-opening device used in conjunctionwith source-side protective devices, such as reclosers or circuit breakers, to

automatically isolate faulted sections of electrical distribution systems. Power tooperate the control circuitry and the mechanism is obtained from the line


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ELECTROSTATIC PRECIPITATOR

(E.S.P)

An electrostatic precipitator (ESP) is a highly efficient filtration device that

removes fine particles, like dust and smoke, from a flowing gas using the force

of an induced electrostatic charge minimally impeding the flow of gases

through the unit.

In contrast to wet scrubbers which apply energy directly to the flowing fluid

medium, an ESP applies energy only to the particulate matter being collected

and therefore is very efficient in its consumption of energy (in the form of

electricity

Exhaust gases contain large quantity dust particles which are emitted into the

atmosphere. This poses threat to mankind as devastating health hazard.

The dust issuing from exhaust of the plant can most effectively be prevented

from entering into atmosphere by employing ESP.

Here de dusting of exhaust gases from boiler is done.

Exhaust gases contain large quantity dust particles which are emitted into the

atmosphere. This poses threat to mankind as devastating health hazard.


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E.S.P advantages:

Ability to treat volume of gases at high temperature.

Ability to cope up with corrosive atmosphere.

Offers low resistance path to gas flow. E.S.P uses intense electric forces to separate suspended particles from the

flue gases.

Processes involved:

Electric charging of suspended particles.

Collection of charged particles on collecting diodes.

Removal of particles from collecting diodes.

Five fields to keep emission within limits.

Electromagnetic control system is used.


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TRANSFORMERS

A transformer is an electrical device that can change electrical energy of a

given voltage into electrical energy at a different voltage level. It consists of twocoils arranged in such a way that the magnetic field surrounding of one coil cuts

through the other coil. When an alternating voltage is applied to (across) one

coil induces an alternating voltage in the other coil. Transformers will not work

with direct current, since no changing magnetic field is produced, and therefore

no current can be induced. The factor which determines whether a transformer

is a step up or step down type is the turns ratio. The turns ratio in the primary

winding to the number of turns in the secondary winding.

The TATA power Jojobera division has got the following types of transformers:

Generating Transformer (GT)5

Station Transformer (ST)3

Substation Transformer (SST)8

Unit Auxiliary Transformer (UAT)5

Essential parts of a Transformer:

LV Winding:

The LV Winding or Low Voltage winding is that winding of a

transformer which has less number of turns compared to the high

voltage winding. As a result, the voltage generated in this winding i.e.

LV winding, also the LV winding is generally Delta connected.

HV Winding:The HV winding or High Voltage winding has more number of turns

as compared to the LV winding so voltage regulation is better. So the

voltage required in this type of winding is more than the LV side. The

HV winding is generally Star connected.

Transformer Core:

The core makes up the bulk of the transformer and so selection of proper

material plays an important role in the transformers overall function,working and efficiency. A range of different cores exist viz... steel


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Transformer tank:

Most power transformers are filled with transformer oil, a high dielectric

fluid that both cools and insulates the windings. Transformer oil is ahighly refined mineral oil that cools the windings and insulation bu

circulating within the transformer tank.

Radiator:

Radiators are used to circulate the oil in a transformer by natural

convection.

Conservator:

A conservator as the name suggests is a reservoir used in conserving or

storing oil. If the transformer tank oil reduces due to a kind of overload

or any other ambient conditions, the conservator will feed the oil into the

main tank and if expansion occurs in the transformer oil, that oil will go

to the conservator.

Buchholz relay:

In the field of electric power distribution and transmission, a buchholz

relay is a safety device mounted on some oil filled transformers

equipped with an external overhead oil reservoir/conservator. It is used

as a protective device sensitive to the effects of dielectric failure inside

the equipment.

On a slow accumulation of gas, due to slight overload or any ambient

condition, gas produced by decomposition of insulating oil accumulates

in the top of the relay and forces the oil level downward.


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On load Tap Changer (OLTC):

The OLTC is located in HV winding of a transformer. The tapping is

taken from HV winding because..

In HV winding, no. of turns is more, so voltage regulation is good.

The LV winding is nearer to the core, so that less insulation can be

provided between core and winding.

In HV winding, current carrying capacity is less than LV winding.

The function of OLTC is to give constant voltage to the secondary

winding, rather maintain/regulate the output voltage of a transformer.

Breather:

When load on transformer increases or when the transformer is under fullload, the insulating oil in the transformer gets heated up, expands and

gets expelled out into the conservator, thus subsequently pushing the dry

air out of the conservator tank through the silica gel breather.

When the oil cools down, air from the atmosphere is drawn into the

transformer. This is called Breathing in of the transformer.

During the breathing process, the incoming air may contain moisture and

dirt which should be removed in order to prevent any physical damage.

Hence the air is made to pass through Silica gel breather, which willabsorb the moisture in the air and ensure that only dry air enters into the

transformer.

Silica gel in the breather is blue when installed and they turn to pink

colour after absorbing moisture, thus indicating replacement of the

crystals. Thus silica gel breathers provide an economic and efficient

means of controlling the level of moisture entering into the conservator

tank during the breathing process.

Neutral Grounding Resistor:

The purpose of a Neutral Grounding Resistor (NGR) is to limit the

ground fault current to a safe level so that all the electrical equipment in

the power system is protected. The resistor should be the only current

path between the neutral of the power transformers and ground.

Cooling Fans:

Oil Natural Air Forced (ONAF):


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For oil filled transformers, the cooling ducts in the coils must be in

sufficient number and size to allow dielectric fluid to flow through

the coils to remove heat. This oil can move by simple convection

(Oil Natural Air Natural) or it can be forced cooled by pumping

fluid. Additionally, the tank surface must be large enough to

transfer heat away from the fluid by the combined actions of

conduction, convection or radiation. To maximise the cooling

effect, cooling fans are added to expedite the heat removal through

radiators.

Thus ONAF uses natural circulation of the oil with the help of fans

to increase the air flow and thus increase the rating of the

transformer.

Oil Natural Air Natural (ONAN):

This is the simplest transformer cooling system. The full form of

ONAN is "Oil Natural Air Natural". Here natural convectional

flow of hot oil is utilized for cooling. In convectional circulation

of oil, the hot oil flows to the upper portion of the transformer tank

and the vacant place is occupied by cold oil. This hot oil which

comes to upper side, will dissipate heat in the atmosphere by

natural conduction, convection & radiation in air and will become

cold. In this way the oil in the transformer tank continually

circulate when the transformer put into load. As the rate of

dissipation of heat in air depends upon dissipating surface of the

oil tank, it is essential to increase the effective surface area of the

tank. So additional dissipating surface in the form of tubes or

radiators connected to the transformer tank.

Oil Forced Air Forced (OFAF):

OFAF means "Oil Forced Air Forced" cooling methods of

transformer. In oil forced air natural cooling system of

transformer, the heat dissipation is accelerated by using forced air

on the dissipating surface but circulation of the hot oil in

transformer tank is natural convectional flow.

The heat dissipation rate can be still increased further if this oil

circulation is accelerated by applying some force. In OFAF

cooling system the oil is forced to circulate within the closed loop

of transformer tank by means of oil pumps.


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Minimum Oil Gauge (MOG):

MOG in transformer is used to show analogic indication of oil level

inside the conservator tank and upon requirement; it also gives alarm

signals when the oil level reduces below minimum/maximum level.

Oil Temperature Indicator (OTI) & Winding Temperature

Indicator (WTI):

Oil Temperature Indicator (OTI): The OTI measures the Top Oil

Temperature. It is used for control and protection for all

transformers. This device measures top oil temperature with the

help of sensing bulb immersed in the pocket by using liquid

expansion in the bulb through a capillary line to operatingmechanism. A link and lever mechanism amplifies this movement

to the disc carrying pointer and mercury switches. When volume

of the liquid in operating mechanism changes, the bellow attached

to end of capillary tube expands and contracts. This movement of

bellow is transmitted to the pointer in temperature indicator of

transformer through a lever linkage mechanism.

Winding Temperature Indicator (WTI):

This device measures the LV and HV winding temperature. A

winding temperature indicator or WTI is also used as protection of

transformer. The basic operating principle of WTI is same as OTI.

But only difference is that the sensing bulb pocket on transformer

top cover is heated by a heater coil surrounded it. This heater coilis fed by secondary of current transformers associated with

transformer winding. Hence the current through the heater coil is

directly proportional to the electric current flowing through

transformer winding.


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Tata Power 2