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 27 TH July 2012 INTERNSHIP REPORT (MANGLA POWER STATION)
Oct 23, 2015
P a g e | 1
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)
P a g e | 2
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
P a g e | 3
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
P a g e | 4
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
P a g e | 5
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.
P a g e | 6
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.
P a g e | 7
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.
P a g e | 8
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
P a g e | 9
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
P a g e | 10
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
P a g e | 11
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
P a g e | 12
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
P a g e | 13
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
P a g e | 14
“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
P a g e | 28
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
P a g e | 29
Fig 2.8-Oil sump Tank
Fig 2.9-Oil Sump Tank Schematic