Final Report GBHP

Ghazi Brotha Hydro Power Project

Pakistan Water & Power Development Authority

Internship Report

Submitted to:

Mr. Feroz-ud-din

Chief Engineer

Ghazi Brotha Power Complex.

Submitted by:

Waleed Azhar.

11-ME-91

Department of Mechanical Engineering

University of Engineering & Technology (UET), Taxila.


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Table of Contents 1. Power Plants ........................................................................................................................5

1.1 Types of Power Plants ...................................................................................................5

1.1.1 Significance of Hydel Power Plants .......................................................................5

1.1.2 Types of Hydel Power Plants .................................................................................6

2. Ghazi Brotha Hydro Power Project ......................................................................................7

2.1 The Barrage ..................................................................................................................7

2.1.1 Standard Bays ........................................................................................................8

2.1.2 Under Sluice Gates ................................................................................................8

2.1.3 Head Regulator Gates ............................................................................................8

2.2 The Power Channel .......................................................................................................8

2.3 The Power Complex......................................................................................................8

2.3.1 Tail Regulator ........................................................................................................8

2.3.2 Fore Bay ................................................................................................................9

2.3.3 South Head Pond ...................................................................................................9

2.3.4 North Head Pond ................................................................................................. 10

2.3.5 Intake ................................................................................................................... 10

2.3.6 Power House ........................................................................................................ 10

2.3.7 Spill Way ............................................................................................................. 11

2.3.8 Tail Race ............................................................................................................. 11

3. The Main Power Plant ....................................................................................................... 11

3.1 Turbine ....................................................................................................................... 12

3.1.1 Penstock .............................................................................................................. 13

3.1.2 Spiral Casing ....................................................................................................... 14

3.1.3 Wicket Gates ....................................................................................................... 14

3.1.4 Runner: ................................................................................................................ 15

3.1.5 Blading ................................................................................................................ 15

3.1.6 Draft Tube ........................................................................................................... 16

3.2 Governor ..................................................................................................................... 17

3.3 Bearings ...................................................................................................................... 18

3.4 Lubrication and Cooling Systems ................................................................................ 18


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3.5 Braking System: .......................................................................................................... 20

3.6 Generator: ................................................................................................................... 21

3.7 Excitation Transformer ............................................................................................... 23

3.8 Synchronization Circuit Breakers ................................................................................ 23

3.9 Generator Transformer ................................................................................................ 25

3.10 Auxiliary Supply ..................................................................................................... 25

3.11 HVAC: .................................................................................................................... 26

3.12 Control & Instrumentation (C&I) ............................................................................ 26

3.13 Protection & Instrumentation (P&I) ......................................................................... 26

3.14 Switch Yard: ........................................................................................................... 27

3.14.1 Power Transformers ............................................................................................. 28

3.14.2 Bus Bars .............................................................................................................. 28

3.14.3 Breakers ............................................................................................................... 28

3.14.4 Isolators ............................................................................................................... 28

3.14.5 Lightning Arrestors .............................................................................................. 28

3.14.6 Wave Blockers ..................................................................................................... 28

3.14.7 Shunt Reactors ..................................................................................................... 28

3.14.8 CTs & PTs ........................................................................................................... 28


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Acknowledgement

First of all I am grateful to Allah Who Gave me sound mind & sound health to accomplish my

summer placement. Then, I would like to thank my parents who have supported me in every

walk of life. The completion of the task gives me much pleasure. I would also like to thank my

lecturers, Mr. Zahid Sulaiman Butt & Dr. Shehryar, for giving me sufficient technical knowledge

about Fluid Mechanics.

Hereby I want to give my special thanks to “Mr. Feroz-ud-din” Chief Engineer Ghazi Barotha

Hydro Power Project. For giving me the opportunity to learn and get the real work experience.

In addition, I would also like to thank the authority of Ghazi Brotha Power House, for providing

me all the required information and details regarding the available equipment, and for increasing

my practical knowledge of engineering.

Regards.


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1. Power Plants

A Power Station or Power Plant is an industrial facility for the generation of electric power. At

the center of nearly all power stations is a generator, a rotating machine that converts mechanical

power into electrical power by creating relative motion between a magnetic field and a

conductor. The energy source harnessed to turn the generator varies widely. It depends chiefly on

which fuels are easily available, cheap enough and on the types of technology that the power

company has access to.

1.1 Types of Power Plants

There are namely five major types of Power Plants that are currently working around the globe

for power generation. These are enlisted below:

Hydel Power Plants.

Thermal Power Plants.

Wind Energy Power Plants.

Solar Power Plants.

Nuclear Power Plants.

Pakistan's basic power generation reliance is upon Thermal Power Generation, producing 70 %

of the total power generated, but many Hydel Power projects are also working to fulfill the

country's increasing energy needs.

1.1.1 Significance of Hydel Power Plants

Water is the most easily available and cheap energy source. It is our common observation that

water carries huge amount of energy under flowing condition and this flow energy can be further

amplified when it is allowed to flow from a certain height. This is the main idea used in Hydel

power plants. Water, which is stored in the reservoirs, is allowed to flow over the blades of a

water turbine, due to high pressure energy of water flowing from a high head the blades begin to

rotate. The shaft of the blades is coupled with a generator, which generates electricity. And the

water is then released into the tail race and is returned back into the river. So in this way, we get

energy output from a free source of nature.


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1.1.2 Types of Hydel Power Plants

There are major five types of Hydel Power Plants, which are discussed briefly below:

Conventional hydroelectric such as hydroelectric dams.

Run-of-the-river hydroelectricity, which captures the kinetic energy in rivers or

streams, without the use of dams.

Small hydro projects are 10 megawatts or less and often have no artificial reservoirs.

Micro hydro projects provide a few kilowatts to a few hundred kilowatts to isolated

homes, villages, or small industries.

Pumped-storage hydroelectricity stores water pumped during periods of low demand to

be released for generation when demand is high.


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2. Ghazi Brotha Hydro Power Project It was observed that a useful 74 meters head was available between Ghazi, the tailrace of

Tarbela, and Brotha village. So the idea of Ghazi Brotha Project was proposed and it was

basically designed as a running water power station, regulated by the tailrace of Tarbela Dam.

The project was completed in 2003 under the working of various companies such as:

Voith Hydro, Germany.

Toshiba, Japan.

ABB, Germany.

Alstom Power Generation, Germany.

CMEC, China.

HMC, Pakistan.

OMG, Italy.

VA Tech, Australia.

The total cost of the project was around 2.6 billion US dollars. The power station is capable of

producing 1450 MegaWatts with five Francis turbines each of 290 MW, among which four units

are designed for continuously generating power. During the months of May & June, when other

power station are at minimum generation due to low reservoir level, GBHP is designed to

generate maximum power during the same period, with a plant annual utilization factor of 52%.

The project comprises of three main parts:

The Barrage.

The Power Channel.

The Power Complex.

2.1 The Barrage

The barrage located 7 km downstream of Tarbela Dam, provides at 71 million cubic meters

storage pond allowing for the re-regulation of the daily discharge from Tarbela by diverting the

flow into the power Channel. The bridge is able to pass the design flood of 18,700 cusecs,

equivalent to the flood of record, through the Standard bays and Under sluices at the normal


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pond level of 340 meters. The fuse plug has been provided to pass the extreme floods up to the

capacity of Tarbela’s spillway and tunnel equating 46,200 cusecs.

2.1.1 Standard Bays

Twenty such gates are provided to remove excess water after diverting into the power channel.

2.1.2 Under Sluice Gates

This portion contains 8 gates. It is used for the removal of mud and other materials like stone etc.

These gates are at lower level then head regulator gates, so that to provide temporary filtered

water to power channel.

2.1.3 Head Regulator Gates

Head regulator gates are used to control the flow of water into power channel. It consists of eight

gates.

2.2 The Power Channel

The power channel is 52 km long and is concrete lined. It is 9 meters deep and can allow a flow

of 1600 cumecs of water. The average velocity of water in the channel is found to be 2.3 m/s,

which is approximately 9 kph. It is named as power channel because it is used for power

generation.

Two 11 kV lines on both side of the channel. Eight feeders are available to feed these lines. 25

kVA transformers step down 11 kV to 400 V to operate the pumps for maintain the channel

level.

2.3 The Power Complex

The power complex begins with fore bay and two head ponds with a combined live storage of 25

million cubic meters. The five generating units each of 290 MW in the powerhouse are each fed

by a steel linked penstock of 10.6m diameter, with a peak flow 460 cumecs. The power complex

consists of following main features which are enlisted and described below:

2.3.1 Tail Regulator

It is located at the end of power channel. It has four radial gates which are used to regulate the

flow. The major job of tail regulator is to keep the water level of the pond at 334 meters above

sea level. Depth of the tail regulator is 9 meters and width is 18.5m. The gates are opened


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hydraulically and are closed with the help of gravity. Each gate is installed at a distance of 200

mm from each other. Tail regulator is provided with a control room from where the opening and

closing of gates is done manually

2.3.2 Fore Bay

A central pond with a water storage capacity of 1,450 Million cubic Meters between elevations

of 329.00m and 334.00m.

2.3.3 South Head Pond

An auxiliary pond connected with fore bay through south sill opening and with live storage

capacity of 5,932 Million Cubic Meters of water between Elevations 329.00m and 334.00 m.


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2.3.4 North Head Pond

An auxiliary pond connected with fore bay through North sill opening with a live storage

capacity of 17,192 Million Cubic Meters of water between Elevation of 329.00 m and 334.00 m.

2.3.5 Intake

Intake is the sending point of fore bay. The water levels of fore bay are 334.34 meters. There are

five sets of power in take surviving the five hydraulic turbines and the control room.

Each intake is divided by a centre pier and contains two intakes gates. The intake gates are

connected with the power house through 10.6 meters diameters steel penstock.

2.3.6 Power House

Power House consists of Five Francis turbines with a capacity of 290 MW each and its control

room and its switchyard structure is connected with Power House via transmission lines.


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2.3.7 Spill Way

The structure to release the excess water in the fore bay when the level reaches the elevation of

334.50. It is a siphon type with Eight discharge gates having capacity of 1600 cumecs.

2.3.8 Tail Race

A structure for conveying the discharge water from the units and the spill way to the Indus River.

It starts at the end of draft tubes from each turbine and all the cooling water outlets exit in the

Tail Race.

3. The Main Power Plant

Power plant is the area in which power is generated. The water flow downward from the intake,

sets the turbine into motion and exits. The turbine rotates the generator and electric power is

generated rate at 18 kV from each rotor, which is supplied to the power transformer. Power

transformer step up 18 kV to 500 kV to be transmitted to different cities.


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3.1 Turbine

The power house is equipped by five Francis Turbines. The Francis turbines are Reaction

turbines as it utilizes pressure energy of water, and are used under low or medium heads. The

head at Ghazi Brotha is rated as medium head therefore Francis turbines were selected. The

turbine has its own accessories which included the Penstock and the Draft tube.


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The turbine has the following technical specifications:

Turbine Name Francis

Turbine Type Reaction

Flow Types Radial at inlet & Axial at outlet

Manufacturer MS Voith Hydro, Germany

Normal Operating speed (N) 100rpm

Rated Turbine Discharge (Q) 460m3/s

Max. Rated Output (P) 295 MW

Weight of Runner 122 tons

Diameter of Runner 6.7 m

Rated Net Head (H) 69 m

Max. Achievable Efficiency 98 %

Following are the key features of the turbine:

3.1.1 Penstock

It is the main inlet of the turbine. It is 10.6 meters in diameter and is made up of Steel to give

high mechanical strength. It allows the water to enter the turbine radially via spiral casing.


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3.1.2 Spiral Casing

The spiral casing is provided at the end of each penstock, and it is the main outer housing of the

turbine. It increases the pressure head by gradual decrease in area of the casing. It is also

designed to avoid cavitation within the turbine. Water pipeline for cooling or other purposes is

taken from the spiral casing, which is at a pressure of 7 bar.

3.1.3 Wicket Gates

Each turbine is provided with 24 wicket gates which are operated hydraulically with the help of

two servomotors. These servomotors are controlled by governor according to the load

requirements. These gates allow water to enter radially into the turbine along the periphery of the

spiral casing.


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3.1.4 Runner:

The runner is the main rotating body of the turbine. It is coupled with the rotor of generator via a

hollow steel shaft. The purpose of keeping the shaft hollow is that it also acts as a Surge Tank for

the turbine, and absorbs sudden rises of pressure, as well as to quickly provide extra water during

brief drop in pressure. The blades are pinned to the runner.

3.1.5 Blading

The material proposed for the blades is composes of 83% Stainless Steel, 13% Chromium and

4% Nickel. Chromium and Nickel are added as to give anti-corrosive properties to the runner.

The runner is provided with three sets of blades. The guide blades are used to direct the water

onto the moving blades, and they can be adjusted according to the running conditions of the

turbine. The stationary blades are provided which act as nozzles to accelerate the water flow.

Then comes the set of moving blades, they are pinned to a shaft which is coupled with the

generator rotor.


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3.1.6 Draft Tube

Draft tube is provided with each unit to compensate the loss of head if the turbine is installed

above the tail race level, and to increase turbine's net efficiency. The draft tube installed here, is

slightly hook shaped as to avoid erosion at the exiting edge of draft tube. The tube is rectangular

in cross-section, while the exit is circular.


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3.2 Governor

Governor is an auto decision making unit controlling which alter the opening of the wicket gates

according to the load requirements by operating the servomotors hydraulically. The governor

used at GBHP is of Digital type equipped with a microprocessor. The governor has two pumps

installed with it, which operate alternatively to pump the compressed oil at 65 bar into the

servomotors. The storage tank of oil has a mixed of oil and compressed air in it, to maintain the

internal pressure without any external source ideally. We have to set either of two parameters

power or frequency. We mostly set power, for example if we set power to 290 MW, the governor

will automatically open the wicket gates up to 79% allowing a flow of 479 m3/s. Governor also

takes protection step i.e. if there is water leakage from the seals of the shaft at the axis of turbine,

the governor will automatically close all the wicket gates without any manual command.


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3.3 Bearings

Bearing is a machine element that constrains relative motion between moving parts to only the

desired motion. Various bearings are provided with the turbine and generator to minimize

rotational friction. Most common are Guide bearings, which are installed about the shaft and

below to keep the shaft intact. Turbine bearing and Generator bearing are provided with the

upper side of turbine and the lower end of generator respectively. Thrust bearing is installed

with the lower end of the turbine to absorb the axial thrust of the runner. These bearing are

provided with cooling water systems for their cooling.

3.4 Lubrication and Cooling Systems

All the rotating parts in the power plant are provided with lubrication. The bearing are provided

with lubrication oils which are filtered and cooled gradually by water coolers, to prevent the


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bearings from over-heating. The hot oil is cooled up to 10 Celsius. The lubricating oil used in

bearings is LHM46, while the hydraulic oil used in intake gates as well as in governing system is

T60. These oils are selected on the basis of different factors such as lubrication capacity, thermal

stability, viscosity, compressibility etc.

The cooling water used all over the power house is taken from the spiral casing of each turbine

housing. This water is approximately at 16° Celsius and at 7 bar, and reaches every part of the

power house without any pumping action. It is strained and filtered at its inlet to avoid any

blockage in the cooling pipeline. This water is used to cool the bearing, generator transformers

and governor oil pumping set.


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3.5 Braking System:

For stopping any unit , braking systems are provided with the shaft of the turbine. These brakes

are pneumatically operated with the help of compressed air. Two central compressed air

cylinders are provided and also each unit has its own air storage cylinder. The air is kept at 10

bar pressure. The compressed air is released when the brakes are applied, which push the

graphite brake pads onto the shaft and stops it. A dust collector is also provided with it to

collecting the dust by creating a vacuum, produced by sliding of pads with the shaft. The brakes

are applied below 25 rpm otherwise it can cause heavy damage to the braking pads and cause

immense mechanical vibrations that can disturb the whole system. If brakes are applied at high

speeds then excessive amount of heat will also be generated , which will cause the CO2 to be

released. There are two banks of CO2. Primary bank has 58 cylinders, while the secondary bank

is kept as a backup having 30 cylinders.


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3.6 Generator:

Five Self-exciting generators are installed with each turbine unit via a shaft. There are air ducts

with each generator which are installed as to remove air humidity from the inside casing of

generator. If there is, then it will cause corrosion. Units has to be synchronized with the system,

this is done by synchronoscope.


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Following are the technical specifications of each generator:

Manufacturer Toshiba, Japan

No. Of Phase 3

Rated Output 322200 kVA.

Rated Voltage 18000 Volts

Rated Current 10335A

Power Factor 0.9 Lagging

No. Of Poles 60

Frequency 50Hz

Rated Speed 100 rpm

Rotation Direction Anti-Clockwise

Power Source Francis Turbine

Stator Coil Star Connection.

Stator Insulation Class F

Rotor Insulation Class F

Armature Connection Y

Armature Temp. Rise 78.5 K

Natural Point Transformer Grounding

Cooling Method Radial Ventilation Air

Cooling method

Excitation Method Thyrister exciting method

Exciting Current 2439A

Excitation voltage 400 V


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3.7 Excitation Transformer

Excitation Transformer are used to provide D.C voltage to the rotor of generator. The 18 kV AC

line coming from the generator is tapped before entering the synchronizing breaker, and is given

to the excitation transformer where it is stepped down from 18kV to 400V. This 400V AC line is

then transferred to AVR unit where Bridge Rectifiers are used to convert it into 400V D.C. This

D.C line is then given to the rotor of the generator to magnetize its poles.

3.8 Synchronization Circuit Breakers

Circuit breakers are provided at 18 kV on each line coming from generator, they are also filled

with compressed air at 6 bar to avoid any contamination and ionization.


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Technical specifications of the breakers are as under:

Type HEC 2

Rated Voltage 24

Rated frequency 50 Hz

Rated Normal Current 120000 A

Rated S C breaking current 100 kA

Rated peak withstand current 300 kA

Rated power frequency withstand voltage 60 kV / 70 kV

Rated lightning impulse withstand peak voltage 125 kV / 145 kV

Capacitor on generation side 130 nF

Capacitor on transformer side 260 nF

Total weight of the breaker system 5350 Kg

Control voltage for closing coil 220V D.C

Control voltage for tripped coil 220V D.C

Rated voltage for motor drive 220V D.C


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3.9 Generator Transformer

Rated output of the three phase generator is 18 kV which is stepped up to 500 kV by the main

generator transformer. Each generator has Three Generator Transformers for the

different Phases. One for Blue phase, one for Red phase and one for Yellow phase. In total there

are fifteen Generator Transformers for five units located at the Transformer Deck.

3.10 Auxiliary Supply

Auxiliary supply to the power house, switch yard, tail regulator and intake are provided by 3 unit

transformers which convert 18 kV generated from turbines into 11 kV. Unit transformers are

only attached with unit 1, 3 & 5. In case, we run out of this supply then 220V DC battery rooms

are provided in each section of the power house for immediate power supply as power house

needs continuous voltage supply for safe operations. A pair of Caterpillar Diesel Generators is

also provided which can give 0.7 MW each to give a backup power supply to the power house.


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3.11 HVAC:

HVAC stands for "Heating, Ventilation & Air conditioning". It is an important system for this

power plant as to avoid excessive heating of the machinery. It provides fresh air for breathing as

the power house is several stories underground. The air conditioning system maintains fresh and

healthy working environment for the workers. The air conditioners for this purpose are installed

which provide conditioned air centrally throughout the power house. These conditioners work on

the same principle as that of conventional air conditioners. The circulating air is ot used again

and again to avoid contamination. It is fixed with some fresh air in each cycle to decrease air

conditioners working load. The air conditioner sucks air from the environment and the

refrigerant extracts the heat from the air and cools it This air is then circulated around the power

house. The refrigerant is first compressed and is then condensed and then passed through an

expansion device, which causes cooling. It is then used to cool the air entering the air

conditioned space.

3.12 Control & Instrumentation (C&I)

The overall control of the Power complex is microprocessor based Distributed Control System

(DCS). The DCS is equipped with dual redundant processor and redundant data highway

network and related communication devices. The data highway uses fiber optic cable. Each

generating unit, tail regulator gates, high voltage switchgear , medium voltage switchboard and

low voltage switchboard has their own dedicated dual redundant processors.

3.13 Protection & Instrumentation (P&I)

The role of this department in the power house is to identify the problem by analyzing the date

given by C&I and solve it, and to assign the reason behind the problem, how the problem is

caused and what is the solution to that problem.

The whole power station is divided into two section. First section which comprises of the whole

power house to the intake, all comes under the control of C&I. While the second section,

consisting of few areas of power house and the switch yard are controlled by P&I. All the data

related to tripping of any transmission line is analyzed, debugged and solved by P&I.


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3.14 Switch Yard:

The switch yard is the heart of all the transmission done from GBHP. It has two grid stations.

The main grid transmits six 500 kV lines to different cities which are Tarbela (I), Tarbela (II),

Gatti (I), Gatti (II), Rawat (I) & Rawat (II). The smaller grid transmits two 220 kV lines directly

to Peshawar.


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Following are the common components to be discussed briefly installed at the switch yard:

3.14.1 Power Transformers

These transformers are used to step up 18 kV to 500 kV. These are insulated by SF6 gas, and are

also provided with cooling fans and radiators.

3.14.2 Bus Bars

Two bus bars are interconnected to each other. The 550 kV lines from transformers are

connected one bus bar and is transmitted to the next bus bar after transmitting through sets of

circuit breakers and isolators.

3.14.3 Breakers

Breakers are On load devices. There are T-shaped breakers connected to 3 phase lines. These are

auto closure breakers. The breaker prevents heavy currents from flowing along the bus bars by

opening the circuit.

3.14.4 Isolators

Isolators are off load devices. It can only be switched when there is no flow of current. They are

also known as disconnector, as they prevent the fault to be transmitted.

3.14.5 Lightning Arrestors

These are provided among all the high towers to protect from lightning. They are also known as

Surge Arrestors.

3.14.6 Wave Blockers

Wave blocker is a low pass capacitive circuit. which allows a limited frequency up to 50 Hz to

pass through them.

3.14.7 Shunt Reactors

These are provided at the transmission side that is at the second bus bar, to provide equivalent

inductance against the capacitance produced while transmitting high voltages. They are installed

both at the transmitting end as well as at the receiving end.

3.14.8 CTs & PTs

These are small transformers which are used to measure high currents and voltages respectively.

They when coupled can also give the value of real power transmitted and can act as a Wattmeter.

Final Report GBHP

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