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Batch: 2010

PRESENTED BY:

Muhammad Suleman

Hammad Rasheed

Abdullah Tahir

UET, Taxila

UET, Lahore

FAST, Lahore

SUBMITTED TO

Director Training

Mr. Haji Muhammad

SUBMISSION DATE

27TH July 2012

INTERNSHIP REPORT (MANGLA POWER STATION)

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TABLE OF CONTENTS

I. ACKNOWLEDGEMENTS….………………………………………………………………………………....... 5

II. EXECUTIVE SUMMARY..………………………………………………………...…………………………… 6

III. WHAT IS HYDRO ELECTRICITY ………………………………...………………………………………… 7

IV. GENERATION METHOD …………………………………………………………….....………………….. 7

A. CONVENTIONAL (DAM)………………………………………………………………………………… 7

B. PUMPED STORAGE…………………………………………………………………….……………… 7

C. RUN OF THE RIVER…………………………………………………………………………………… 7

D. TIDE………………………………………………………………………………………………….…… 7

E. UNDERGROUND……………………………………………………………………………………….. 7

V. DAM BASED HYDRO ELECTRICITY …………………………………………………………….………… 7

VI. DAMS IN PAKISTAN……………………………………........................................................…………………. 8

A. TARBELADAM ……………………………………………………………...……………………………..……. 8

B. MANGLA DAM …………………………………………………………………......………………………….. 8

C. WARSAK DAM ……………………………………………………..……………………………………………. 9

VII. MANGLA POWER STATION ………………………………..……………………………………………………………. 9

A. TURBINE……….………………………………………………………………..................…………….................. 9

a. Impulse Turbine ……………………………………………………………………………………….…………………… 9

b. Reaction Turbine …………………………………………………………………………………………………………… 9

c. Flow of Water from Reservoir to Turbine ……………………………………………….…………………………….. 10

d. Runner ………………………………………………………………………………………………..…………………… 10

e. Lower & Upper Guide Bearings ……………………………………………………………………………………….. 10

B. GENERATOR…..……………… …………………………………………………………………………………. 10

a. How Generator Works ………………………………………………………………………….. …... 10

b. Exciter ………………………………………………………………………………………….............. 11

C. AUTOMATIC VOLTAGE REGULATOR … ………………………………….……………………………. 11

D. TRANSFORMER …………………….……………………………………...….………….…………… 11

a. Step Up Transformer ………………………………………………………………………………………… 12

b. Step Down Transformer ……………………………………………………………………………………… 12

c. Auto Transformer …………………………………………………………………………………………… 12

d. Potential Transformer ……………………………………………………………………………………… 13

e. Current Transformer ………………………………………………………………………………………… 13

E. COOLING SYSTEM AT MANGLA POWER STATION ……………………………………………………… 15

a. Components of Cooling Water System (Valves &Filters) …………………………………………………………… 15

b. Cooling of Transformers ………………………………………………………………………………………………… 17

c. Heat Exchanger ………………………………………………………………………………………………………. 18

F. PROTECTION SYSTEM INSTALLED AT MANGLA POWER STATION ………………….…………… 18

a. Guide Vane Protection ……………………………………………………………………………………….….. 18

b. Generator Protection (Types of Relays)…………………………………………………………..…… 18

c. Transformer Protection …………………………………………………………………………………..…… 20

d. Protection Against Fire…………………………………………………………………………… 20

G. STATION AUXILIARY SUPPLY ………………………………………………………………………….. 20

H. MECHANICAL AUXILIARY ……………………………………………………………………………… 21

a. Pumping System …………………………………………………………………………………………… 21

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b. Over Head Crane System ……………………………………………………………………………………… 21

c. Air System ………………………………………………………………………………………..……….……… 21

I. OPERATION OF HYDRO POWER PLANT ……………………………………………………………………… 22

a. Starting Sequence ……………………………………………………………………………………….…………. 22

b. Off Sequence ………………………………………………………………………………………………… 22

c. Frequency Maintenance …………………………………………………………………………………… 22

d. Hydro Control Desk ………………………………………………………………………………………. 22

e. Auxiliary Control Desk …………………………………………………………………………………… 23

f. Power Control Desk ……………………………………………………………………………………. 23

VIII. SWITCH YARD………..………………….…………...……………………………………..…………………… 23

A. SYSTEM INSTALLED AT MANGLA SWITCH YARD …………………………………………………. 23

a. Circuit Breaker ……………………………………………………………………………………….. 23

b. Isolator Switch ………………………………………………………………………………………. 24

c. One & Half Breaker Scheme ………………………………………………………………………… 24

IX. THE NEW BONG ESCAPE ……………………………………………………..………….………………….. 25

A. CONCEPT DESIGN …………………………………………………………………………………….. 25

B. BULB TURBINE ………………………………………………………………………………………… 25

X. OPERATION & MAINTENANCE OF SPILLWAY ………………………..………………...………………. 26

XI. MANGLA FORT VISIT …………………..………………………………………….……...…………….…. 27

XII. MISC DRAWINGS …………..……………..……………..……………..……………..……………..……… 28

LIST OF ILLUSTRATIONS

Table 1.1. PRIMARY ENERGY MIX BY COUNTRY 2003-04 …………………………………………………... 8

Table 1.2. ENERGY SUPPLYING PAKISTAN 2003-04…. …………………………………………………......... 8

Fig 1.1 TARBELA DAM………..……………………………………………………………………….……………… 8

Fig 1.2 COMPARISON BETWEEN IMPULSE & REACTION TURBINE……………………………….……………… 9

Fig 1.3 TURBINE SPECIFICATIONS…………………………………….……………………………….……………… 10

Fig 1.4 GENERATOR SPECIFICATIONS …………………………….……………………………….……………… 10

Fig 1.5 GENERATOR/TURBINE SCHEMATIC……………………………………………………………………… 10

Fig 1.6 TRANSFORMER BASIC PRINCIPLE……….……………………………………..…………….……………… 11

Fig 1.7 13.2/132 KV TRANSFORMER………………………………..……………………………….……………… 12

Fig 1.8 AUTO TRANSFORMER SPECIFICATIONS…………………….……………………………….……………… 12

Fig 1.9 AUTO TRANSFORMER………………………………………..……………………………….……………… 13

Fig 1.10 COOLING WATER SYSTEM…………………………………………..………………………….……………… 15

Fig 1.11 INDICATION AT GENERATOR………………………………………………………………….……………… 18

Fig 1.12 METERS AT GENERATOR………………………………………………………………….…………..…… 18

Fig 1.13 DPR SCHEME………………….………………………………………………………………….……………… 19

Fig 1.14 UNIT BOARD SECTION………………………………………………………………….…………………… 20

Fig 1.15 CO2 CYLINDER………………..………………………………………………………………….……………… 20

Fig 1.16 GOVERNOR OIL PUMP MECHANISIM………………………………………………………….……………… 20

Fig 1.17 STATION AUXILIARY SUPPLY SCHEMATIC………………………………………………………………… 21

Fig 1.18 OIL TANK…………………………………..………………………………………………………………………. 22

Fig 1.19 HYDROLIC CONTROL DESK……………………….……………………………………………………………. 23

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Fig 2.0 AUXILIARY CONTROL DESK……………………………………………………………………………… 24

Fig 2.1 POWER CONTROL DESK……………………………………………………….………………………………… 24

Fig 2.2 NEW BONG PROJECT (SIGHT MAP)…………………………………………………………………………… 26

Fig 2.3 NEW BONG PROJECT (CONSTRUCTION)…………………………………………………………………… 27

Fig 2.4 HORIZONTAL BULB TURBINE………………………………………………………………………………… 27

Fig 2.5 SPILLWAY……………………..………………………………………………………………………………….. 28

Fig 2.6 MANGLA FORT VISIT……….…………………………………………………………………………………… 29

Fig 2.7 POWER STATION AUXILIARY SUPPLY………………………………………………………………………… 29

Fig 2.8 MANGLA SWITCH YARD SCHEMATIC………………………………………………………………………… 29

Fig 2.9 OIL SUM TANK………………………………………………..……………………………………………………. 29

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I. ACKNOWLEDGMENTS

The whole praise is to Almighty Allah, creator of this universe, Who made us the super creature with great knowledge and who

able us to accomplish this work. We feel great pleasure in expressing our deepest appreciation and heartiest gratitude to the staff

of Mangla Power Station for their guidance and great help during the internship period.

We would like to express our deepest affection for our parents and our friends who prayed for us success and encouraged us

during this internship period. We appreciate and acknowledge the patience, understanding and love provided by employees of

Mangla Power Station

A token of special thanks to the following people who had been very friendly, co-operated with us throughout our internship

period in E & I department and made it possible for us to learn and gather information. These are the people who in spite of

their busy scheduling took time out to explain to us the procedures and mechanics of work in the organization.

We are very thankful to:

Mr. RiazHussain Resident Engineer

Mr. ChaudarySaleem Chief Engineer

Mr. Haji Muhammad Director

Mr. ZubairBhatti Deputy Director

Mr. AbdurRehman Deputy Director

Mr. Kareem Nawaz Senior Engineer

Mr. Tariq Senior Engineer

Mr.Tanvir Senior Engineer

Mr. Umar Junior Engineer

Mr. Usman Junior Engineer (Operation “Control Room”)

Mr.Imran Junior Engineer (Operation “Control Room”)

Mr.Athar Junior Engineer (Operation “Control Room”)

We would like to express our deepest thanks to Mr. Sufi Wajid and Mr. Hameed Jamal, who really gave their best of time to us

and we really learned a lot from them in a very short period.

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II. EXECUTIVE SUMMARY

The purpose of this report is to explain the working of Mangla Power Station.

Mangla Power Station is hydel Power Station having capacity of 1000MW of electricity. 10 units each of capacity of 100MW

are working at Mangla. Recently a project of extension of reservoir has been completed. In coming years this extension will

definitely increase the efficiency of units. Moreover, advancements in windings of generators are in progress.

Report will describe working of station according to the different departments in the station. Moreover we will discuss about the

maintenance and protection systems installed at Mangla. New Bong Escape project, operation and maintenance of spill way and

Jari Intake gate is also covered.

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III. What is Hydroelectricity

Hydroelectricity is the term referring to electricity generated

by hydropower; the production of electrical power through the

use of the gravitational force of falling or flowing water. It is

the most widely used form of renewable energy, accounting

for 16 percent of global electricity consumption, and 3,427

terawatt-hours of electricity production in 2010, which

continues the rapid rate of increase experienced between 2003

and 2009.

Hydropower is produced in 150 countries, with the Asia-

Pacific region generating 32 percent of global hydropower in

2010. China is the largest hydroelectricity producer, with 721

terawatt-hours of production in 2010, representing around 17

percent of domestic electricity use. There are now three

hydroelectricity plants larger than 10 GW: the Three Gorges

Dam in China, ItaipuDam in Brazil, and Guri Dam in

Venezuela.

The cost of hydroelectricity is relatively low, making it a

competitive source of renewable electricity. The average cost

of electricity from a hydro plant larger than 10 megawatts is 3

to 5 U.S. cents per kilowatt-hour. Hydro is also a flexible

source of electricity since plants can be ramped up and down

very quickly to adapt to changing energy demands. However,

damming interrupts the flow of rivers and can harm local

ecosystems, and building large dams and reservoirs often

involves displacing people and wildlife. Once a hydroelectric

complex is constructed, the project produces no direct waste,

and has a considerably lower output level of the greenhouse

gas carbon dioxide (CO2) than fossil fuel powered energy

plants.

IV. GENERATING METHODS

A. Conventional (dams)

Most hydroelectric power comes from the potential

energy of dammed water driving a water

turbine and generator. The power extracted from the water

depends on the volume and on the difference in height

between the source and the water's outflow. This height

difference is called the head. The amount of potential

energy in water is proportional to the head. A large pipe (the

"penstock") delivers water to the turbine.

B. Pumped-Storage

This method produces electricity to supply high peak demands

by moving water between reservoirs at different elevations. At

times of low electrical demand, excess generation capacity is

used to pump water into the higher reservoir. When there is

higher demand, water is released back into the lower reservoir

through a turbine. Pumped-storage schemes currently provide

the most commercially important means of large-scale grid

energy storage and improve the daily capacity factor of the

generation system.

C. Run-of-the-river

Run-of-the-river hydroelectric stations are those with small or

no reservoir capacity, so that the water coming from upstream

must be used for generation at that moment, or must be

allowed to bypass the dam.

D. Tide

A tidal power plant makes use of the daily rise and fall of

ocean water due to tides; such sources are highly predictable,

and if conditions permit construction of reservoirs, can also

be dispatch able to generate power during high demand

periods. Less common types of hydro schemes use

water's kinetic energy or undammed sources such as

undershot waterwheels.

E. Underground

An underground power station makes use of a large natural

height difference between two waterways, such as a waterfall

or mountain lake. An underground tunnel is constructed to

take water from the high reservoir to the generating hall built

in an underground cavern near the lowest point of the water

tunnel and a horizontal tailrace taking water away to the lower

outlet waterway.

V. DAM BASED HYDROELECTRICITY

Dam based hydroelectricity is the cheapest source of

electricity as water is free of cost. Pakistan is generating

power from water as well as from different other sources

including gas, coal, diesel and nuclear.

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Source wise primary energy supply in Pakistan in 2003-04 is

indicated below:

.

VI. DAMS IN PAKISTAN

Three main dams Mangla, Tarbela and Warsak were

constructed for the purpose of generating electricity and

irrigating agricultural land. In addition, there are 23

barrages/head works/ siphons; main irrigation canals are 45,

which have extended up to 40,000 miles. Similarly, there are

90,000 water courses, which are extended up to one million

miles.

A. Tarbela Dam

The world's largest earth-filled dam on one of the world's

most important rivers the Indus is 103 km from Rawalpindi.

The dam was completed in 1976 at a cost of Rs.18.5 billion.

Over 15,000 Pakistani and 800 foreign workers and engineers

worked during its construction. It is the biggest hydel power

station in Pakistan having a capacity of generating 3,478 MW

of electricity. Its reservoir is 97 km long with a depth of 137

Meters while total area of the lake is 260 Sq Km.

B. Mangla Dam

The Mangla Dam on the River Jhelum is one of the longest

earth-fill dams in the world.The Indus Basin treaty of 1960

with India paved the way for its construction. The

treatyprovided for two dams, one on the River Jhelum at

Mangla and the other on the Indus atTarbela.World's third

largest earth-filled dam is only 115 km south-east of

Rawalpindi. The area of the dam is 100 square Km.The rated

head of the dam is 295 feet. Mangla Power House was

completed in four stages. The initial phase comprising of four

units of 100 MW each was completed in 1967-69. The first

extension of Unit No. 5&6 (2X100 MW) was completed in

1974 while second extension comprising Unit No. 7&8 (X100

MW) was completed in 1981. The project attained its

Fig1.1- Tarbela Dam

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maximum capacity of 1000 MW with the final extension of

Unit No. 9&10 (X 100 MW) in 1993-94.

C. Warsak Dam

The gigantic multi-purpose Warsak Dam on RiverKabul is

situated 30 KMs north-west of Peshawarin the heart of tribal

territory. It has a totalgenerating capacity of 240,000 KW and

willeventually serve to irrigate 110,000 acres of land.

The 250 ft. high and 460 ft. long dam withreservoir of 4

square miles had a live storagecapacity of 25,300 acre-feet of

water for irrigationof 119,000 acres of land and meeting

powergeneration requirement. A spillway with ninegates is

capable to discharge 540,000 cusecs offlood water.

There are also small dams like Dohngi Dam, GomalZam

Dam, Hub Dam, Kahnpur Dam etc.

VII. MANGLA POWER STATION

Mangla power station is generating 1000 MWatt of electricity

at rated capacity and 1500 MW at overload condition.

Numerous machines are using there for generation of

electricity. Main parts of hydel generation are:

Turbine Generator Transformer

A. Turbine

A turbine is a rotary mechanical device that

extracts energy from a fluid flow and converts it into

useful work. A turbine is a turbo machine with at least one

moving part called a rotor assembly, which is a shaft or drum

with blades attached. Moving fluid acts on the blades so that

they move and impart rotational energy to the rotor. Early

turbine examples are windmills and water wheels.

Different types of turbines are used in power generation.

a. Impulse Turbine

In impulse turbine water is thrown through a nozzle on to the

blades of turbine. This water flow moves turbine in a specific

direction. Pelton and Turgo turbines are the examples of

Impulse Turbine.

b. Reaction Turbine

Reaction turbines develop torque by reacting to the water. The

pressure of the water changes as it passes through the turbine

rotor blades. A pressure casement is needed to contain the

water as it acts on the turbine stage(s) or the turbine must be

fully immersed in the fluid flow. The casing contains and

directs the working fluid and, for water turbines,

Fig 1.2- Comparison between Impulse and Reaction Turbine

maintains the suction imparted by the draft tube. Kaplon,

Propeller, Fransist are the examples of the Reaction Turbines.

Fransist type turbine is medium head turbine. In Mangla all

the turbines are Fransist turbines.

Fig1.3- Turbine specifications

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c. Flow of water from reservoir to turbine

Water being stored in the reservoir of 100 Km2 is travelled

through a tunnel of diameter of 30 feet. This tunnel is called

“Penstock”. The 5×30 feet tunnels make “Y” connection and

each tunnel is divided into two tunnels of 15feet diameter.

Here potential energy stored in water is converted into kinetic

energy due to gravity. This high pressure water is thrown to

the runner of the turbine. Cover around the turbine is called

“Spiral Casing”. This casing is designed in such a way that it

gives rotor of the turbine anticlockwise rotation.

Butterfly inlet valves are used to stop the flow of water. In

case of any emergency valve is closed and water is provided a

bypass path through the emergency irrigation valve to release.

d. Runner

The runner of the turbine has 24 blades on which water flow.

There are 24 guide wanes and wicket gates which can be

adjusted to control the flow of the

water. These guide wanes adjust

themselves in order to maintain

the speed of the rotor. All the

gates are operated hydraulically

by using oil and servo motors.

e. Lower and Upper Guide bearings

Whenever we stop our turbine it sits itself onto a base. Now

when we want to run the turbine again we cannot run it in its

rest position. In such condition we pass an impulse through

governor. Oil is filled in the lower guide bearings form the oil

tank which uplifts the rotor 2 mm. Now turbine is ready to

start. These bearings also help to maintain the balance of the

rotor.

B. Generator

Generator is the second most important part of the electricity

generation. The kinetic energy of the water moves turbine and

produces mechanical energy. Generator uses this mechanical

energy and convert it into electrical.

At Mangla Power Station 10 generators are working following

are the specifications of these generators.

Rated Output 125000 KVA Voltage 13200 V

Power Factor 0.8 Amperes 5467 A

Frequency 50 Hz Poles 36

Overload 115% Speed 166.67rpm

Phase 3 Ex. Volts 261 V

Ex.Amperes 990 A

\

Generation voltage at Mangla power house is 13.2 KV. Each

generator of 125000 KVA working at 0.8 power factor is

generating 100 KW of power. The frequency/speed

relationship of the generator/turbine can be find out with the

formula

a. How Generator Works

It works according to the Faraday’s Law of Electromagnetism.

Whenever a coil is moved in a magnetic field an induced

current is produced.

Fig1.5- Generator /Turbine Schematic

Fig1.4- Generator Specifications

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b. Exciter

Theoretically permanent magnets are required to give

magnetic field but in practical we cannot use permanent

magnets because there is a lot of heat inside the generator and

magnetism drastically reduce with heat. Secondly such large

permanent magnets are inevitable to produce and maintain.

That is why we use Electromagnets in generators.

Electromagnets are developed according to Ampere’s Law

which states that:

The magnetic field at a distance r from a very long straight

wire, carrying a steady current I, has a magnitude equal to

To start a generator its field winding must be excited

(magnetized). Generator voltage is directed related to the

excitation current. So if the voltage of the generator is

dropping, it can be managed by increasing excitation current.

There are two type of exciter used in Mangla power Station.

Brush Type Exciter

Static Exciter

Unit 1-6 use brush type exciter while 7-10 use static

exciter.

Brush Type Exciter

The brush type exciter can be mounted on the same shaft as

the AC generator armature and can be housed separately from,

but adjacent to, the generator. When it is housed separately,

the exciter is rotated by the AC generator through a drive belt.

The distinguishing feature of the brush-type exciter is that

stationary brushes are used to transfer the DC exciting current

to the rotating generator field. Current transfer is made via slip

rings that are in contact with the brushes

Static Exciter

Static exciter contains no moving parts. A portion of the AC

from each phase of generator output is fed back to the fields

winding, as DC excitations, through a system of transformers,

rectifiers, thyrestors and reactors.

C. Automatic Voltage Regulator

Voltage transformers provide signals proportional to line

voltage to the AVR where it is compared to a stable reference

voltage. The difference (error) signal is used to control the

output of the exciter field. For example, if load on the

generator increases, the reduction in output voltage produces

an error signal which increases the exciter field current

resulting in a corresponding increase in rotor current and thus

generator output voltage.

Due to the high inductance of the generator field windings, it

is difficult to make rapid changes in field current.

This introduces a considerable "lag" in the control system

which makes it necessary to include a stabilizing control to

prevent instability and optimize the generator voltage

response to load changes.

Without stabilizing control, the regulator would keep

increasing and reducing excitation and the line voltage would

continually fluctuate above and below the required value.

Modern voltage regulators are designed to maintain the

generator line voltage within better than +/- 1% of nominal for

wide variations of machine load.

D. Transformer

A transformer is a device that transfers electrical

energyfromone circuit to another through inductively

coupled conductors—the transformer's coils. A

varying current in the first or primary winding creates a

varying magnetic flux in the transformer's core and thus a

varying magnetic field through thesecondary winding. This

varying magnetic field induces a varying electromotive force

(EMF), or "voltage", in the secondary winding.

Fig1.6- Transformer’s Basic Principal

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If a load is connected to the secondary, current will flow in the

secondary winding, and electrical energy will be transferred

from the primary circuit through the transformer to the load.

In an ideal transformer, the induced voltage in the secondary

winding (Vs) is in proportion to the primary voltage (Vp) and

is given by the ratio of the number of turns in the secondary

(Ns) to the number of turns in the primary (Np) as follows:

Several transformers are used for different purposes. Just after

generation we need to step up or step down the voltage. Then

we have some auto transformers in Mangla. Many current and

potential transformers are used which will be discussed later.

a. Step-up Transformers

After generation at 13.2 KV at Mangla, step-up transformers

step-up the voltage to 132 KV and 220KV. We have two

13.2/132 KV transformers and eight 13.2/220 KV

transformers. After stepping up voltages these voltages are

transmitted through bus bars.

b. Step-down Transformers

We have two Station Transformers which step down 132 KV

to 11 KV. These two Transformers are of 7.5 MVA each.

Power through these transformers is fed inside the station to

run different equipments at station and in switch yard.

c. Auto Transformers

In an autotransformer portions of the same winding act as both

the primary and secondary. The winding has at least

three taps where electrical connections are made. An

autotransformer can be smaller, lighter and cheaper than a

standard dual-winding transformer however the

autotransformer does not provide electrical isolation.

As an example of the material saving an autotransformer can

provide, consider a double wound 2 kVA transformer

designed to convert 240 volts to 120 volts. Such a transformer

would require 8 amp wire for the 240 volt primary and 16 amp

wire for the secondary. If constructed as an autotransformer,

the output is a simple tap at the centre of the 240 volt winding.

Even though the whole winding can be wound with 8 amp

wire, 16 amps can nevertheless be drawn from the 120 volt

tap. This comes about because the 8 amp 'primary' current is

of opposite phase to the 16 amp 'secondary' current and thus it

is the difference current that flows in the common part of the

winding (8 amps). There is also considerable potential for

savings on the core material as the apertures required to hold

the windings are smaller. The advantage is at its greatest with

a 2:1 ratio transformer and becomes smaller as the ratio is

greater or smaller.

Autotransformers are often used to step up or down between

voltages in the 110-117-120 volt range and voltages in the

220-230-240 volt range, e.g., to output either 110 or 120V

(with taps) from 230V input, allowing equipment from a 100

or 120V region to be used in a 230V region.

We have to working and one stand by auto transformer. The

function of auto-transformer is load sharing between 220KV

and 132 KV bus bars. Whenever we have more load at 132

side, Tx. switches 220 KV to 132 KV and share the load and

vice-versa.

Fig 1.7- 13.2/132 KV Transformer

Fig 1.8- Auto Transformer specifications

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d. Potential Transformers

At transmission side potential Transformers are used. The

purposes of potential transformer are as follows:

Voltage Measurement

Overvoltage protection

Transformers can also be used in electrical instrumentation

systems. Due to transformers' ability to step up or step down

voltage and current, and the electrical isolation they provide,

they can serve as a way of connecting electrical

instrumentation to high-voltage, high current power systems.

Suppose we wanted to accurately measure the voltage of a

13.8 kV power system

Direct measurement of high voltage by a voltmeter is a

potential safety hazard.

Designing, installing, and maintaining a voltmeter capable of

directly measuring 13,800 volts AC would be no easy task.

The safety hazard alone of bringing 13.8 kV conductors into

an instrument panel would be severe, not to mention the

design of the voltmeter itself. However, by using a precision

step-down transformer, we can reduce the 13.8 kV down to a

safe level of voltage at a constant ratio, and isolate it from the

instrument connections, adding an additional level of safety to

the metering system.

Instrumentation application: “Potential transformer” precisely

scales dangerous high voltage to a safe value applicable to a

conventional voltmeter.

Now the voltmeter reads a precise fraction, or ratio, of the

actual system voltage, its scale set to read as though it were

measuring the voltage directly. The transformer keeps the

instrument voltage at a safe level and electrically isolates it

from the power system, so there is no direct connection

between the power lines and the instrument or instrument

wiring. When used in this capacity, the transformer is called

a Potential Transformer, or simply PT.

Potential transformers are designed to provide as accurate a

voltage step-down ratio as possible. To aid in precise voltage

regulation, loading is kept to a minimum: the voltmeter is

made to have high input impedance so as to draw as little

current from the PT as possible. As you can see, a fuse has

been connected in series with the PTs primary winding, for

safety and ease of disconnecting the PT from the circuit.

A standard secondary voltage for a PT is 120 volts AC, for

full-rated power line voltage. The standard voltmeter range to

accompany a PT is 150 volts, full-scale. PTs with custom

winding ratios can be manufactured to suit any application.

This lends itself well to industry standardization of the actual

voltmeter instruments themselves, since the PT will be sized

to step the system voltage down to this standard instrument

level.

d. Current Transformers

These transformers are used for the following purposes:

Current measurement

Over current Protection

Following the same line of thinking, we can use a transformer

to step down current through a power line so that we are able

to safely and easily measure high system currents with

inexpensive ammeters, such a transformer would be connected

in series with the power line.

Fig 1.9- Auto Transformer

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“Current transformer” steps high current down to a value

applicable to a conventional ammeter.

Note that while the PT is a step-down device, the CT is a step-

up device, which is what is needed to step down the power

line current

Current conductor to be measured is threaded through the

opening. Scaled down current is available on wire leads.

Some CTs are made to hinge open, allowing insertion around

a power conductor without disturbing the conductor at all. The

industry standard secondary current for a CT is a range of 0 to

5 amps AC. Like PTs, CTs can be made with custom winding

ratios to fit almost any application. Because their “full load”

secondary current is 5 amps, CT ratios are usually described

in terms of full-load primary amps to 5 amps, like this:

Because CTs are designed to be powering ammeters, which

are low-impedance loads, and they are wound as voltage step-

up transformers, they should never, ever be operated with an

open-circuited secondary winding. Failure to heed this

warning will result in the CT producing extremely high

secondary voltages, dangerous to equipment and personnel

alike. To facilitate maintenance of ammeter instrumentation,

short-circuiting switches are often installed in parallel with the

CT's secondary winding, to be closed whenever the ammeter

is removed for service.

Short-circuit switch allows ammeter to be removed from an

active current transformer circuit.

Though it may seem strange to intentionally short-circuit a

power system component, it is perfectly proper and quite

necessary when working with current transformers.

P a g e | 15

E. Cooling system at Mangla Power Station

Cooling of heavy equipment is very important at

Mangla. Huge amount of current and voltages makes

equipments very hot specially generators and

transformers. Due to the importance of cooling we have

working as well as multiple stand-by cooling systems in

Mangla. Water is taken from reservoir through 24 inch

pipeline and then distributed to the different sections in

Mangla in green pipes. Following is the Schematic

diagram of cooling of two of the units.

Following valves are used as per different requirement.

Normally open

Normally closed

No return valve

Safety valve

Motor opened valve

Pressure reducing valve

Following filters and strainers are used for filtering of

water

Vokes Filter

Y- Strainer

Duplex Filter

C.W Strainer

a. components of cooling water system

Pressure reducing Valve

This valve reduces the pressure of the water that goes

through it, and is used to obtaining a regulated and

constant value at its outlet.

It is installed at the water mains (for a bungalow as for a

flat). It protects the whole installation from problems

due to excess pressure noises in the pipes, water

hammer, splashes, premature wear of household

electrical appliances and taps. The pressure reducing

valves are completely automatic.

Types of Pressure reducing valve

There are two types of water pressure reducing valves,

direct acting and pilot operated. Both use globe or angle

style bodies. Valves used on smaller piping diameter

units are cast from brass; larger piping diameter units

are made from ductile iron. Direct acting valves, the

more popular type of a water pressure reducing valves,

consist of globe-type bodies with a spring-loaded, heat-

resistant diaphragm connected to the outlet of the valve

that acts upon a spring. This spring holds a pre-set

tension on the valve seat installed with a pressure

equalizing mechanism for precise water pressure

control.

Fig 1.10- Cooling water system

P a g e | 16

Motor Operated Valve:

Motor Operated valve is a valve where the Actuator Part

of the Valve is replaced by a motor instead of

pneumatic. MOV are normally used for Larger Process

lines where the Pneumatic pressure is not enough to

provide torque or pressure for the Valves movement.

Since Motors have good torque they are used to open or

close the valves, these are also called as electrical

Actuators.

Advantage of MOV over Pneumatic valve:

Usually motor operated valve used in big pipe

lines sizes which it is need strong torque and for

ON/OFF condition not to control the process, We can

use rather than M.O.V pneumatic ON/OFF valve with

piston actuator (Double Acting) but in this case the

accessories it will cost you more because you need to

provide pneumatic amplifier and big actuator depend on

the pipe size.

That is why better to use M.O.V the motor will rotate

the gears and the gears will rotate the valve with low

cost.

Non Return Valve :

A device for automatically limiting flow in a

piping system to a single direction.Also known as no

return valve.

Vokes Filter:

The Vokes Filter Coalescer is a static device

for the removal of solids and free water from Distillate

and Light Liquid Fuels and Mineral Lubricating Oils.

The cartridge combines a long life depth type

pre-filter media designed to give extended life by the

removal of pipe scale, rust, waxes and asphaltenes that

would otherwise cause the coalescent media to blind.

The pre-filter, together with the first and

second stage coalescing Medias effectively combine

small droplets of water into large droplets which are

then separated from the oil flow by gravity.

A final stripper screen is fitted to further

minimize any risk of carryover of small droplets into the

clean oil discharge.

The purified oil is discharged at the top of the

housing, while the water is drained from the bottom.

Principal of Operation

The small droplets of water are intercepted by fibers and

because of the hydrophilic nature of the fibers, are

retained. As the number of droplets collected increases

they join together to form a layer of water.

P a g e | 17

The flow of the oil then pushes this water through the

media to the outside where it forms large droplets on the

sock surrounding the cartridge.

These droplets then grow until they reach a size which

causes them to fall off and drop to the bottom of the

housing through gravity.

Y.Strainer :

Eaton Y strainers are a cost-effective solution

for the mechanical removal of unwanted solids from

liquid, gas or steam lines by means of a perforated or

wire mesh straining element. They are used in pipelines

to protect pumps, meters, control valves, steam traps,

regulators and other process

equipment.

Duplex Strainer

A duplex strainer is used in applications where

fluid flow cannot be interrupted when the basket is

removed for cleaning. It maintains a continuous flow by

utilizing two separate basket chambers with integral

valves to direct flow into one of the basket chambers

After filtering of water, water is fed to the different

sections of the generator and to the transformer where it

cools down the temperature of oil used in transformer.

The sections are:

Generator Surface air cooler

Main Guide Bearing

Thrust lower guide bearing

Upper guide bearing

Stuffing box

Governor oil sump tank

b. Cooling of Transformers

Though it is not uncommon for oil-filled transformers to

have today been in operation for over fifty years .High

temperature damages winding insulation, the accepted

rule of thumb being that transformer life expectancy is

halved for every 8 oC increase in operating temperature.

At the lower end of the power rating range, dry and

liquid-immersed transformers are often self-cooled by

natural convection andradiation heat dissipation. As

power ratings increase, transformers are often cooled by

such other means as forced-air cooling, force-oil

cooling, water-cooling, or a combinations of these. The

dielectric coolant used in many outdoor utility and

industrial service transformers is transformer oil that

both cools and insulates the windings. Transformer oil

is a highly refined mineral oil that inherently helps

thermally stabilize winding conductor insulation, within

acceptable insulation temperature rating limitations.

However, the heat removal problem is central to all

electrical apparatus such that in the case of high value

transformer assets, this often translates in a need to

monitor, model, forecast and manage oil and winding

conductor insulation temperature conditions under

varying, possibly difficult, power loading conditions.

Air-cooled dry transformers are preferred for indoor

applications even at capacity ratings where oil-cooled

construction would be more economical, because their

cost is offset by the reduced building construction cost.

The oil-filled tank often has radiators through which the

oil circulates by natural convection. Some large

transformers employ electric-operated fans or pumps for

forced-air or forced-oil cooling or heat exchanger-based

water-cooling. Oil-filled transformers undergo

prolonged drying processes to ensure that the

transformer is completely free of water vapor before the

cooling oil is introduced. This helps prevent electrical

breakdown under load. Oil-filled transformers may be

equipped with relays, which detect gas evolved during

internal arcing and rapidly de-energize the transformer

to avert catastrophic failure. Oil-filled transformers may

P a g e | 18

fail, rupture, and burn, causing power outages and

losses. Installations of oil-filled transformers usually

include fire protection measures. They have properties

that once favored their use as a dialectic coolant, though

concerns over their environmental persistence led to a

widespread ban on their use. Today, non-toxic,

stable silicone-based oils, or fluorinated

hydrocarbons may be used where the expense of a fire-

resistant liquid offsets additional building cost for a

transformer vault. Some "dry" transformers (containing

no liquid) are enclosed in sealed, pressurized tanks and

cooled by nitrogen or sulfur hexafluoride gas.

Experimental power transformers in the 2 MVA range

have been built with superconducting windings which

eliminates the copper losses, but not the core steel loss.

These are cooled by liquid nitrogen.

c. Heat Exchanger

A heat exchanger is a specialized device that assists in

the transfer of heat from one fluid to the other. In some

cases, a solid wall may separate the fluids and prevent

them from mixing. In other designs, the fluids may be in

direct contact with each other. In the most efficient heat

exchangers, the surface area of the wall between the

fluids is maximized while simultaneously minimizing

the fluid flow resistance. Fins or corrugations are

sometimes used with the wall in order to increase the

surface area and to induce turbulence.

Common appliances containing a heat exchanger

include air conditioners, refrigerators, and space heaters.

Heat exchangers are also used in chemical processing

and power production

There are three primary flow arrangements with heat

exchangers: counter-flow, parallel-flow, and cross-flow.

In the counter-flow heat exchanger, the fluids enter the

exchanger from opposite sides. This is the most efficient

design because it transfers the greatest amount of heat.

In the parallel-flow heat exchanger, the fluids come in

from the same end and move parallel to each other as

they flow to the other side. The cross-flow heat

exchanger moves the fluids in a perpendicular fashion.

AT MANGLA

Each unit installed have 2 external heat exchanger

installed which include one stand by while the other one

used as a main heat exchange system .this is used for the

same purpose as of cooling water system.

Heat exchanger include boiler through which hot oil (

passed from machine) is cooled down by using tubes of

cooling water supply system .

F. Protection System Installed at Mangla

Different protection system for different equipments is

installed at Mangla Power Station.

a. Guide Vane Protection

Sometimes large stuff like trunk of trees or large stones

comes into the penstock with the flow of water. These

things stuck in the runner and stop the operation of

guide vanes and hence wicket gates cannot move. In

such situation the share pin installed with the vane is

broken and control room gets the indication of problem

in guide vane and is alarmed.

b. Generator Protection

At the front of the units different gauges and meters are

installed. These meters measure the temperature,

voltage, oil level, generation capacity; speed etc. in case

of any problem alarm is active. Moreover generators

have auto switch of system in case of very serious

problem.

Fig 1.11- Indications at Generator

Fig 2.0- Meters at Generator

Fig 1.12- Meters at Generator

P a g e | 19

GENERATOR PROTECTION RELAYS

This includes

Generator Differential Relays

Split Phase Relay

Restricted Earth Fault (REF)

Stator Earth Leakage

A Symmetrical load

Loss of Excitation

Generator Differential Relays

The generator differential relay is sensitive enough to

detect winding ground fault with low impedance

grounding. It is operate due to Phase Split relay and

restricted earth fault.

Split Phase Relay

At output there are three windings and each is

then divided into three parallel path. Four Current

Transformer is connected to each winding. If any open

circuit fault is occurs the current passes from other path

and the relative CT noted high current and relay sense it

and give relative indication.

Restricted Earth Fault relay

This relay is connected in between 13.2kv and

132kv or 220kv.The neutral point of CT feed and the CT

of HV side is also feed and when fault occurs at any side

relay sense it and trip frequently.

Stator Earth Leakage relay

There is protection of generator winding.

Current transformer is connected to the neutral point. If

three phase supply is short to neutral then this relay

activate immediately and trip the unit.

A symmetrical Load relay

This relay continuously sensing the

unbalancing in three phase voltage. Three phase voltage

will be unbalance when the load is unbalance. If the

symmetrical load is 7% then relay activate alarm and

when it increases to 20% then it trips the unit.

Loss of Excitation

Excitation is concern to maintain the terminal voltage of

generator. It is necessary to stable the terminal voltage.

This relay is activate after some specific time period

when there is suddenly load surge then it decrease the

frequency and AVR sense it if due to any reason AVR

couldn’t sense it then field loss is occur and if AVR do

not sense it for 40sec then this relay trip the unit.

LINE RELAYS

Those relays which are used in switchyard is

known is line relays.

Line relays includes:-

Distance Protection Relay

Over current Relay

Under Frequency

Distance Protection Relay

This is line protection. Each line is divided into

three zones and it is depend upon impedence. Each zone

has a relay if any fault is occur at any zones the relative

relay sense it and give indication.

Over Current Relay

These relays simply sense the over current when there is

high current then this relay is activated.

Under Frequency

At Mangla Power Plant the frequency of generated

power is 50Hz. If frequency decreases due to any reason

and reach 48.6Hz to 48.8Hz

Then this relay produce indication.

Fig 1.13- DPR scheme

P a g e | 20

c. Transformer Protection

In Transformers we have bubble sensors in order to

sense any chemical reaction present in transformer.

Conservation tanks are there for extra oil. In case if oil

expands all the extra oil is transferred to conservation

tank. Water cooling system cools down the oil. We have

spare tank for transformer oil. The top of the tanks is

filled with nitrogen gas.

d. Protection Against fire

In Mangla fool proof system against fire is present. A

bank of cylinders containing CO2 is for generators for

fire. Water nozzles are installed all around the

Transformers. As soon as sensors sense fire, nozzles

start sprinkling water onto the transformers and CO2 to

the Generators. Red color pipes throughout station

contain water for fire protection.

G. Station Auxiliary Supply

Two station transformers each of 750 MVA step down

132 KV/11 KV for station aux supply. This supply,

through 11 KV bus bar, transmitted inside the station.

Unit board is the section where all the equipments

regarding protection and working of generators are

present like circuit breakers, switches etc. 11 KV is

further step down to 440 V and 440 V is fed to the all

the equipments in unit board section. For protection

isolators are used here.

The 440 V supply is transmitted to the following units

inside and outside the power station.

Switch Yard Plant House Board

Common Services Board

Intake Control Station

Essential Services Board

Spill Way Switch Fuse Board

11 KV is supplied to the following units

Mangla Grid

P/T Adit Tunnel

Instrument House

Right Bank Drawing

L.B.G Station

Fig 1.15- CO2 cylinder

Fig 1.14- Unit Board Section

Fig 2.5- Circuit Breaker at UBS

Fig 1.16- Governor Oil pump mechanism

P a g e | 21

H. MECHANICAL AUXILLARY

a. PUMPING SYSTEM

There is oil pumping system along with two motors.

One pump is on main and other one is standby. When

there is pressure of 310 psi then pump will operate and

load oil from sump tank when pressure increases to 340

psi then pump will OFF automatically. In case of fault

when pressure increases to 375 psi then safety valve will

operate and it will close and vice versa.

While indication & alarm for emergency shutdown is at

245 psi.

b. Overhead crane system

Twooverhead cranes are installed at Mangla power

station each having weight 200 tons (along with spare

30 tons weight).These are used for lifting heavy

machinery like rotor, runner etc.

c. AIR SYSTEM

The Air compressor system uses pre-compressed air

from an available compressed air network or is supplied

directly by a dedicated compressor set to its standard

pressure of 10 Bar.

The pre-compressed air (intake pressure up to 10 bars) is

compressed to the desired higher final pressure - simply,

safely, economically. There is no need therefore to

Fig 1.17- Station Auxiliary Supply Schematic

Fig 1.18- Oil tank

P a g e | 22

invest in a dedicated high-pressure network or to have a

separate, decentralized compressor system. The slow-

running, air-cooled compressors can be adapted to

almost all operating conditions due to their well-

designed modular principle. This also applies to the

robust Booster (located after the compressor) for

operating pressures of up to 40 bars

I. OPERATION OF HYDEL POWER PLAN

It includes

Starting &stopping sequence of Machines

Frequency maintenance

Hydraulic control desk

Auxiliary control desk

Power control desk

a. STARTING SEQUENCE:

First open inlet valve from Hydraulic control

desk

Give starting impulse to turbine

Thus transformer oil pump along with T.B

oilinjunction pump and cooling water system is

operated. ThenGovernorOil pump is operated

at the mean time. But space heaters are OFF.

At 50 R.P.M T.B oilinjunction pump get OFF

and Hydraulic locking is disengaged.

After achieving rated speed closed field switch

(70 E) placed at Power control desk which

reduces field resistance and maintain terminal

voltage .Then AVR is introduce into circuit.

Then using Power control desk generator is

synchronized and feed the particular

circuit(synchronizing time is 4 mint).

b. OFF SEQUENCE:

First load is taken to zero

Field is switch is open (1-8) thus excitation or

generator gets OFF.

Breaker is OFF (open) mean isolator get open.

Then stopping pulse is given as a result space

heater is getting OFF and transformer and

governor oil pump get OFF.

As speed reached to 50 rpm,then breaking

system is introduced.

Speed reached to zero T.B oilinjunction is zero

and break is done.

c. FREQUENCY MAINTENANCE

As load increases speed of generator is decreased,thus

frequency get depressed ultimately because

“frequency is directly proportional to speed”

Now permanent magnet generator sense the speed and

signal is given to reaction motor installed at governor

which runs the oil pump then servor motor is operate

and as a result guide vanes are open as per load

requirement and as result frequency is maintain to 50

Hz.

d. HYDRAULIC CONTROL DESK

It is basically used for mechanical operations. By using

hydraulic control desk we can provide starting and

stopping pulse along with operation of guide valve is

maintained.

Here different meters are installed which shows the

amount of water coming and exhaust through outlet.

Fig 1.19-Hydraulic control Desk

P a g e | 23

e. AUXILLARY CONTROL DESK

Following boards are control by auxiliary control desk:

Essential service board

Unit board

Common service board

All the auxiliary system of the machine installed at

power station is fed by these above mention boards.

f. POWER CONTROL DESK (PCD)

19 bays (circuit) are operated manually from power

control desk .one and a half breaker scheme is used

while 2 bus bars are used to energized.

VIII. SWITCHYARD

Switchyard is compromise of 2 bus bar and one and a

half breaker scheme and is consist of 19 bays(circuits)

from -3 to 15 from which 18 are functional while 1 is on

maintenance .

Here bay from -3 to 6 is consist of 132 kV lines while

remaining (7-15)are of 220 kV lines and in between

these two partitions 4 autotransformers are operated

which are used as interconnected transformers. If load

exceed at 132 kV lines then autotransformer operate

automatically and transform power from 220 KV line to

132 kV line or vice versa.

From 4 autotransformers:

2 are working

1 is on maintenance

While remaining 1 is spare

In previous years oil filled underground cables (used to

connect switchyard to power station) are replaced by

overhead conductors while only 9 & 10 bay are still

operating with underground system. In the mean time

bay 14 have 2 generators as well.

Switchyard is also operated with 8 compressors which

compressed 40 kg air at a time (26 kg is utilized by air

blast circuit breaker while 16 kg by isolator)

Isolators installed at switchyard have 2 contacts

Male

Female

A. SYSTEM INSTALLED AT MANGLA

SWITCHYARD

a. Circuit Breaker

A circuit breaker is an electrical device used in an

electrical panel that monitors and controls the amount of

amperes (amps) being sent through the electrical wiring.

Circuit breakers come in a variety of sizes. Its basic

function is to detect a fault condition and, by

interrupting continuity, to immediately discontinue

electrical flow.

If a power surge occurs in the electrical wiring, the

breaker will trip. This means that a breaker that was in

the "on" position will flip to the "off" position and shut

down the electrical power leading from that breaker.

Fig 2.0- Auxiliary control Desk

Fig 2.1-Power control Desk

P a g e | 24

Essentially, a circuit breaker is a safety device. When a

circuit breaker is tripped, it may prevent a fire from

starting on an overloaded circuit; it can also prevent the

destruction of the device that is drawing the electricity.

There are two type of circuit breaker are used in Mangla

Power Station.

Air Circuit Breaker

SF6 Circuit Breaker

Air Circuit Breaker:

If a power surge occurs in the electrical wiring, the

breaker will trip. This means that a breaker that was in

the "on" position will flip to the "off" position and shut

down the electrical power leading from that breaker.

Essentially, a circuitbreaker is a safety device. When a

circuitbreaker is tripped, it may prevent a fire from

starting on an overloaded circuit; it can also prevent the

destruction of the device that is drawing the electricity.

The main function of air circuit breaker is

Open and close a 3 phase circuit, manually or

automatically.

Open the circuit automatically when a fault

occurs. Faults can be of various types under or

over voltage, under or over frequency, short

circuit, reverse power, earth fault etc.

The main feature of ACB is that it dampens or

quenches the arcing during overloading.

SF6 Circuit Breaker:

In this circuit breaker, sulphurhexa fluoride(SF6) gas is

used as the arc quenching medium. The SF6 gas is an

electro negative gas and has a strong tendency to absorb

free electrons. The contacts of the breaker are opened in

a high pressure flow of SF6 gas and an arc is struck

between them. The conducting free electrons in the arc

are rapidly captured by the gas to form relatively

immobile negative ions. This loss of conducting

electrons in the arc quickly builds up enough insulation

strength to extinguish the arc. The SF6 circuit breakers

are very effective for high power and high voltage

service

Why air Circuit Breaker are replace by SF6 Circuit

Breaker:

It is because of two reasons:

Its spare parts are not available in Pakistani

Markets.

Current making capacity is low.

b. Isolator Switch

Circuit breaker always trip the circuit but open contacts

of breaker cannot be visible physically from outside of

the breaker and that is why it is recommended not to

touch any electrical circuit just by switching off the

circuit breaker. So for better safety there must be some

arrangement so that one can see open condition of the

section of the circuit before touching it. Isolator is a

mechanical switch which isolates a part of circuit from

system as when required. Electrical isolators separate a

part of the system from rest for safe maintenance works.

So definition of isolator can be rewritten as “Isolator is a

manually operated mechanical switch which separates a

part of the electrical power system normally at off load

condition.”

A switch intended for isolating an electric circuit from

the source of power; it has no interrupting rating and is

intended to be operated only after the circuit has been

opened by some other means.

c. ONE & Half Breaker Scheme

A method of interconnecting several circuits and

breakers in a switchyard so that three circuit breakers

can provide dual switching to each of two circuits by

having the circuits share one of the breakers, thus a

breaker and one-half per circuit; this scheme provides

reliability and operating flexibility, and is generally used

at 500 kV when more than five lines terminate in a

substation.

Advantages of this Scheme are

Flexible operation and high reliability.

P a g e | 25

Isolation of either bus without service

disruption. Isolation of any breaker for

maintenance without service disruption.

Double feed to each circuit. Bus fault does not

interrupt service to any circuits.

All switching is done with circuit breakers.

IX. The New Bong Escape

The Project involves construction of a run-of-the-river,

low head, 84MW hydel power generating complex. Four

generators of 21MW of each are used. It is located at the

New Bong escape, some 7.5 km downstream of the

Mangla Dam, on the Jhelum River, in AJ&K. It will be

fed by water originating from the Mangla Reservoir,

which is released, through the Mangla powerhouse into

the Bong Canal. There is no new reservoir or other

water storage envisaged for the Project. .

Bulb units horizontal type units are used. Bulb units

have high efficiency, low maintenance and are suitable

for such sites with low head, large and variable water

flow. Four low speed bulb-turbine units and

synchronous direct drive generators within the bulb

housing which, together with transformers and balance

of electrical plant will provide basis of the generating

equipment. The selected bulb turbine/generators will

operate at about 100 rpm. It is proposed to procure the

bulb units, governing, protection, and automation and

control systems from Alstom Power Hydro.

The direct-drive generator placed within the turbine

housing will have a rated capacity of about 23MVA

without undue stress.

A. Concept Design

The key components of the Project include intake,

headrace channel, powerhouse complex, and tailrace

channel, switchyard, interconnection facility, road-

bridge and subsidiary outfall structure. The switchyard

will provide connectivity with the existing 132 kV grid

system. All the power generated by the Project will be

sold to the National Transmission and Dispatch

Company (NTDC) under a long term power purchase

agreement with a 25 year term.

B. Bulb Turbine

Bulb turbine used at Bong project has 4 blades.

Following are the key benefits to use bulb turbines

instead of Francis turbines.

Fig 2.2-New Bong Project Site Map

P a g e | 26

Most efficient solution for low heads up to 30

meters

Negligible need for flooding of landscape due

to run-off-river type of the operation

Reduced size, cost and civil works

requirements of up to 25% thanks to the

straight water passage in the draft tube that

improves the hydraulic behavior of the bulb

unit and also results in a lower need for

excavation

Meet the needs of any particular application

our Bulb turbines also operate as pumps in both

flow directions for tidal plant applications

Sluice operation may also impact favorably

both the hydro mechanics and the navigability

close to the dam

X. Operation and Maintenance of

Spillway

A spillway is a structure used to provide the controlled

release of flows from a dam or levee into a downstream

area, typically being the river that was dammed. In the

UK they may be known as overflow channels. Spillways

release floods so that the water does not overtop and

Fig 2.4- Horizontal Bulb Turbine

Fig 2.3- New Bong Project (Construction Phase)

P a g e | 27

damage or even destroy the dam. Except during flood

periods, water does not normally flow over a spillway.

In contrast, an intake is a structure used to release water

on a regular basis for water supply, hydroelectricity

generation, etc. Floodgates and fuse plugs may be

designed into spillways to regulate water flow and dam

height. Other uses of the term "spillway" include

bypasses of dams or outlets of a channels used during

high water, and outlet channels carved through natural

dams such as moraines. Spillway gates may operate

suddenly without warning, under remote control.

Trespassers within the spillway run the risk of

drowning. Spillways are usually fenced and equipped

with locked gates to prevent casual trespassing within

the structure. Warning signs, sirens, and other measures

may be in place to warn users of the downstream area of

sudden release of water. Operating protocols may

require "cracking" a gate to release a small amount of

water to warn persons downstream.

A spillway is located at the top of the reservoir pool.

Dams may also have bottom outlets with valves or gates

which may be operated to release flood flow, and a few

dams lack overflow spillways and rely entirely on

bottom outlets.

There are two main types of spillways

Controlled and Uncontrolled.

A controlled spillway has mechanical structures or gates

to regulate the rate of flow. This design allows nearly

the full height of the dam to be used for water storage

year-round, and flood waters can be released as required

by opening one or more gates.

An uncontrolled spillway, in contrast, does not have

gates; when the water rises above the lip or crest of the

spillway it begins to be released from the reservoir. The

rate of discharge is controlled only by the depth of water

within the reservoir. All of the storage volume in the

reservoir above the spillway crest can be used only for

the temporary storage of floodwater, and cannot be used

as water supply storage because it is normally empty.

In an intermediate type, normal level regulation of the

reservoir is controlled by the mechanical gates. If inflow

to the reservoir exceeds the gate's capacity, an artificial

channel called either an auxiliary or emergency spillway

that is blocked by a fuse plug dike will operate. The fuse

plug is designed to over-top and wash out in case of a

large flood, greater than the discharge capacity of the

spillway gates. Although it may take many months to

restore the fuse plug and channel after such an

operation, the total damage and cost to repair is less than

if the main water-retaining structures had been

overtopped. The fuse plug concept is used where it

would be very costly to build a spillway with capacity

for the probable maximum flood.

There are two spillways at Mangla dam

Main spillway

Emergency Spillway

Each spillway comprises of 9 gates each gate of capacity

100000 cusec so one spillway can flow total 900000

cusec of water in normal days main spillway is operated

as required and emergency spillway is functional in an

emergency or in high flood seasons so the structure of

dam can be safe and would not be damaged by

overflow.

XI. Mangla Fort Visit

After hectic routine of working we planned one day to

visit Mangla fort. Mangla Fort,named after Mangla

Devi, the daughter of King Porus, is situated on the hill

feature dominating the Mangla Dam lake. The fort dates

back to times before Christ. The fort is almost at the

same place from where Alexander the Great crossed the

Jhelum River, and 10 miles away at a place called

"Khari" the forces of Alexander and Raja Porus fought a

final battle in which Alexander's armies succeeded.

Fig 2.5- Spillway

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XII. Misc Drawings

Following are the drawings we found in Mangla Power

station which help us a lot in understanding different

sections of Power Station.

Fig 2.8-Mangla Switchyard Schematic

Fig 2.7-Power Station Auxiliary Supply

Fig 2.6-Mangla Fort visit

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Fig 2.8-Oil sump Tank

Fig 2.9-Oil Sump Tank Schematic