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M.Tech(Power Systems) Department of Electrical & Electronics Engg.

LOWER PERIYAR POWER STATION

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CHAPTER-1

INTRODUCTION

The hydroelectric power plant, also called as dam or hydro power plant, is used

for generation of electricity from water on large scale basis. The dam is built across the

large river that has sufficient quantity of water throughout the river. In certain cases

where the river is very large, more than one dam can built across the river at different

locations .among the various renewable natural energy resources; the hydropower

generation has emerged as the most potential option in terms of environmental

cleanliness and cost-effective high capacity generation. The hydel power stations have

the inherent ability for instantaneous starting, stopping and load variations, which ensures

a high reliability of power system. Therefore, hydel power stations are the best option for

meeting the peak demand. Further, the generation cost in hydroelectric projects is

inflation free and reduces substantially over time after repayment of debt. With 41 rivers,

flowing down (westward) from the Western Ghats joining the backwaters and the

Arabian Sea, Kerala has tremendous potential for hydel-power generation.

Power generation started in Kerala in 1947 with the commissioning of the

Pallivasal hydro-electric project at the Ramaswami Ayer Headwork close to the tea

county of Munnar in the erstwhile princely State of Travancore. The Kerala power

system consists of 17 hydel stations including 2 captive power plants, 2 thermal stations,

3 independent power producers, 5 major inter-state transmission lines, one 400 KV sub-

section, and two 220 KV substations with the interconnecting grid. Kerala has a storage

capacity of 3843mu and the present storage is about 72% of the full capacity.

Mullaperiyar dam, Idukki Hydro-electric project, Idamalayar Hydro electric

project and the Lower Periyar are constructed across the Periyar. Kundala Dam,

Mattupetty Dam, Munnar head works, Ponmudi dam and the Kallarkutty Dam are

constructed across the various tributaries of Periyar.

Lower Periyar hydroelectric project (180 MW) envisages utilization of the tail

waters from the existing Neriamangalam power station and the spill from Kallarkutty

head works. The Sengulam hydroelectric project is situated downstream of Pallivasal

Project in Mudirampuzha river, which is an important tributary of Periyar river. Panniyar

hydroelectric project is developed on Panniyar, a tributary of Mudirampuzha river.

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1.1 Hydro-Electric Projects in Kerala

Table 1.1 Hydro-electric Projects in Kerala

Project Capacity Total Dams

Idukki 6 x 130 MW 780 Idukki, Cheruthoni

Sabarigiri 5 x 55MW + 60

MW 335 Kakki,Anathodu,Pampa

Idamalayar 2 x 37.5 MW 75 Idamalayar

Sholayar 3 x 18 MW 54 Sholayar-Main,Sholayar-

Flanking,Sholayar-Saddle Dam

Pallivasal 3 x 4.5 MW + 3 x 8

MW 37.5 Kandla,Madupetty

Kuttiyadi 3 x 25 MW + 3 x 50

MW 225 Kuttiyadi

Panniar 2 x 15 MW 30 Ponmudi,Anayirangal

Neriamangalam 3 x 17.55 MW + 25

MW 77.65 Kallarkutty

Poringalkuthu 4 x 8 MW +16 MW 48 Poringalkuttu-

Sengulam 4 x 12 MW 48 Shengulam

Kakkad 2 x 25 MW 50 Veluthodu, Moozhiyar

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CHAPTER-2

HYDEL POWER PLANTS

Fig 2.1 Hydroelectric Dam

In hydroelectric power plants the potential energy of water due to its high location

is converted into electrical energy. The total power generation capacity of the

hydroelectric power plants depends on the head of water and volume of water flowing towards the water turbine The water flowing in the river possesses two type of energy: the kinetic energy due to flow of water and potential energy due to the height of water. In

hydroelectric power and potential energy of water is utilized to generate electricity.

The formula for total power that can be generated from water in hydroelectric

power plant due to its height is given, P=rhg where, P

and is also head of water .the difference between source of

water (from w

m/second square The formula clearly shows that the total power that can be generated from the

hydroelectric power plants depends on two major factors: the flow rate of water or volume of flow of water and height or head of water. More the volume of water and more the head of water more is the power produced in the hydroelectric power plant.

Based on the facts presented above, hydro-electric power plants can generally be

divided into two categories.
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"High head" power plants are the most common and generally utilize a dam to

store water at an increased elevation. The use of a dam to impound water also provides

the capability of storing water during rainy periods and releasing it during dry periods.

"Low head" hydro-electric plants are power plants which generally utilize heads

of only a few meters or less. Power plants of this type may utilize a low dam or weir to

channel water, or no dam and simply use the "run of the river". Run of the river

generating stations cannot store water, thus their electric output varies with seasonal

flows of water in a river.

Fig 2.2 Hydro power plant

Basic components of a conventional hydropower plant can be categorized into three

major parts:

1. Hydraulic Structures

2. Hydro Turbines

3. Electrical structures

2.1 Hydraulic Structures

Hydraulic structures in a hydro electric power station include dam, spillways,

head-works, surge tank, penstock and accessory works.

Dam Dams are structures built over rivers to stop the water flow and form a reservoir.

The reservoir stores the water flowing down the river. This water is diverted to turbines

in power stations. The dams collect water during the rainy season and store it, thus

allowing for a steady flow through the turbines throughout the year. Dams are also used

for controlling floods and irrigation. The dams should be water-tight and should be able

to withstand the pressure exerted by the water on it. There are different types of dams

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such as arch dams, gravity dams and buttress dams. The height of water in the dam is

called head race.

Spillway

A spillway as the name suggests could be called as a way for spilling of water

from dams. It is used to provide for the release of flood water from a dam. It is used to

prevent over toping of the dams which could result in damage or failure of dams.

Spillways could be controlled type or uncontrolled type. The uncontrolled types start

releasing water upon water rising above a particular level.

Penstock Or Tunnel

Penstocks are pipes which carry water from the reservoir to the turbines inside

power station. They are usually made of steel and are equipped with gate systems. Water

under high pressure flows through the penstock. They are generally made of reinforced

concrete or steel. Concrete penstocks are suitable for low heads (

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conduit rushes back to the surge tank and increases the water level. Thus the conduit is

prevented from bursting. On the other hand when the load on the turbine increases,

additional water is drawn from the surge tank to meet the increased load requirements.

Hence a surge tanks overcomes the abnormal pressure in the conduit when load on the

turbine falls and acts as a reservoir during increase of load on turbine. Open conduits

leading water to the turbine require no protection. However, when closed conduits are

used, protection becomes necessary to limit the abnormal pressure in the conduit. For this

reason, closed conduits are always provided with a surge tank. A surge tank is located

near the beginning of the conduit.

Fig 2.3 Surge Tank

2.2 Hydro Turbines

The water strikes and turns the large blades of a turbine, which is attached to a

generator above it by way of a shaft. The most common type of turbine for hydropower

plants is the Francis Turbine, which looks like a big disc with curved blades. A turbine

can weigh as much as 172 tons and turn at a rate of 90 revolutions per minute. The

principal types of water turbines are:

a) Impulse Turbines b) Reaction Turbines

a) Impulse Turbines change the velocity of a water jet. The jet pushes on the turbine's

curved blades which changes the direction of the flow. The resulting change in

momentum (impulse) causes a force on the turbine blades. Since the turbine is spinning,

the force acts through a distance (work) and the diverted water flow is left with

diminished energy. Prior to hitting the turbine blades, the water's pressure (potential

energy) is converted to kinetic energy by a nozzle and focused on the turbine. Impulse

turbines are most often used in very high (>300m/984 ft) head applications. The example

of this type of turbine is the Pelton Wheel.
http://en.wikipedia.org/wiki/Velocityhttp://en.wikipedia.org/wiki/Impulse_(physics)http://en.wikipedia.org/wiki/Potential_energyhttp://en.wikipedia.org/wiki/Potential_energyhttp://en.wikipedia.org/wiki/Potential_energyhttp://en.wikipedia.org/wiki/Kinetic_energyhttp://en.wikipedia.org/wiki/Nozzle

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Fig 2.4 Impulse Turbine

b) Reaction Turbines as the name implies, is turned by reactive force rather than by a

direct push or impulse. In reaction turbines, there are no nozzles as such. Instead, the

blades that project radially from the periphery of the rotor are formed and mounted

so that the spaces between the blades have, in cross section, the shape of nozzles.

Since these blades are mounted on the revolving rotor, they are called moving

blades. Fixed or stationary blades of the same shape as the moving blades are fastened to

the stator (casing) in which the rotor revolves. The fixed blades guide water into the

moving blade system and, since they are also shaped and mounted to provide

nozzle-shaped spaces between the blades, the freed blades also act as nozzles. A reaction

turbine is moved by three main forces: (1) the reactive force produced on the

moving blades as the water increases in velocity as it expands through the nozzle-

shaped spaces between the blades; (2) the reactive force produced on the moving

blades when water changes direction; and (3) the push or impulse of water impinging

upon the blades. Thus, as previously noted, a reaction turbine is moved primarily

by reactive force but also to some extent by direct impulse.

Fig 2.5 Reaction Turbine

Most water turbines in use are reaction turbines and are used in low (

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i) Francis Turbines

ii) Kaplan Turbines

The Francis turbine is one in which the working fluid changes pressure as it moves

through the turbine, giving up its energy. It consists of an outer ring of stationary guide

blades fixed to the turbine casing and an inner ring of rotating blades forming the runner.

The inlet is spiral shaped. Guide vanes direct the water tangentially to the turbine wheel,

known as a runner. This radial flow acts on the runner's vanes, causing the runner to spin.

The guide blades control the flow of water to the turbine. Water flows radially inwards

and changes to a downward direction while passing through the runner. As the water

passes over the rotating blades of the runner, both pressure and velocity of water is

reduced. This causes a reaction force which drives the turbine. The guide vanes (or

wicket gate) may be adjustable to allow efficient turbine operation for a range of water

flow conditions. As the water moves through the r ius decreases,

further acting on the runner. For an analogy, imagine swinging a ball on a string around

in a circle; if the string is pulled short, the ball spins faster due to the conservation of

angular momentum. This property, in addition to the water's pressure, helps Francis and

other inward-flow turbines harness water energy efficiently. A Francis turbine is used for

low to medium heads.

Fig 2.6 Francis Turbine

A Kaplan turbine is used for low heads and large quantities of water. It is similar

to Francis Turbine except that the runner of Kaplan turbine receives water axially. Water

flows radially inwards through regulating gates all around the sides, changing direction in

the runner to axial flow. This causes a reaction force which drives the turbine.
http://en.wikipedia.org/wiki/Conservation_of_angular_momentumhttp://en.wikipedia.org/wiki/Conservation_of_angular_momentumhttp://en.wikipedia.org/wiki/Conservation_of_angular_momentum

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CHAPTER-3

SALIENT FEATURES OF LOWER PERIYAR GENERATING

STATION

Fig 3.1 Lower Periyar Generating Station

Lower Periyar Power House which is situated at Karimanal is the third

biggest generating station of K.S.E.B. The installed capacity of lower Periyar

generating station is 3x60MW and there are 6 nos. 220kV out going feeders. This is

the first generating station in KSEB using microprocessor controlled logic circuit for

the automatic operation of the generators from shutdown status to generator status

and from generator status to shutdown status. It is the second generating

station in Kerala where static excitation system is adopted. These machines are

designed for synchronous condenser operation also. It forms one of the most

important tie station in the power grid of Kerala .The 220 kV feeders from Lower

Periyar powerhouse are l) double circuit feeder to Idukki power house, 2) double

circuit feeder to 400 kV substation Madakkathra, and 3) double circuit feeder to 220

kV substation Bhrahmapuram.

During the tied operation of these lines, the 220kV bus will be the main inter

linking bus for the 4 most important major grid stations of KSE Board viz. Idukki

power house, 400kV substation Madakkathra, and 220 kV substations

Bhrahmapuram which is directly tied with Kayamkulam Thermal station.

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CHAPTER-4

HYDRAULIC SYSTEM OF LOWER PERIYAR

Average annual generation at the power station is approximately 69MW or 609

Mu. Reservoir at Pambla along Mudirampuzha river basin with dam of 31m high above

nominal riverbed and 244m long across river Periyar about 5km downstream of

Panamkutty Power House form the water conductor system. Storage level of reservoir is

approximately 4.55 MCM. The dam is of concrete gravity type with a FRL of 253m.there

are 5 motorized upper vents and 2 hydraulic lower vents for the operation of dam. The

intake arrangement consists of an intake well provided with a trash rack, an intake gate

and also an emergency gate. There is a level difference between dam level and intake

well level. The system also comprises 6.05 m dia, D Shaped, 12.79 km long circular

concrete lined Power Tunnel, a restricted orifice Surge Shaft of 18

meter diameter, a 5.25 meter finished diameter, pressure shaft of length 378

meter, branching in to three steel lined pressure shafts each of 2.96 meter

diameter and of average length of 207 meter.

A surface Power House with three machines located at Karimanal about 18km

downstream of Mudirampuzha, Periyar confluence. The power house is of 180MW

capacity with 3 units of 60 MW each mechanically coupled to Francis turbines. The

generator output is stepped up to 220KV by a 66.6 MVA power transformer and is

distributed among 6 feeder lines, two each to Idukki, Bhrahmapuram and the 400KV

Madakkathra.

4.1 Specifications of the Hydraulic System

Reservoir-Pambla

River basin - Mudirampuzha

Storage - 4.55 MCM

Water usage - 2.17 MCM/MU

Dam

Type - Concrete gravity

Scheme - run off river

Maximum water level - 256 m

Full reservoir level - 253 m

Minimum Draw Down level - 237.76 m

Power Tunnel

Size and shape - 6.05 m, D Shape

Length - 12.791 km

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Sill level at inlet - 229.00 m

Sill level at surge shaft - 186.55 m

Maximum velocity in tunnel

for a discharge of 124.7m3/sec - 4.34 m/sec.

Surge Shaft

Type - restricted orifice

Size - 18m dia

Top level of surge shaft - 285.00

Minimum down surge level - 197.99

Bottom level of surge shaft - 194.10

Control gate - Vertical lift gate

Pressure shaft

No. of pressure shaft - One

Size and shape - 5.25m, circular

Length - 378 m

Manifold (steel lined) size and shape - 5.25m dia.

Branch lines

No. of shafts - 3 Nos.

Size - 2.96 m dia., circular

Average length - 207 m

Fig 4.1 Profile of the Water Conductor System

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CHAPTER-5

HYDRO-TURBINE

Fig 5.1 Francis Turbine

The Lower Periyar Hydroelectric project employs the Francis Turbine. Francis

Turbine has a circular plate fixed to the rotating shaft perpendicular to its surface and

passing through its center. This circular plate has curved channels on it; the plate with

channels is collectively called as runner. The runner is encircled by a ring of stationary

channels called as guide vanes. Water is brought to the turbine and directed to guide

vanes or wicket gates. Guide vanes are housed in a spiral casing called as volute. The exit

of the Francis turbine is at the center of the runner plate. There is a draft tube attached to

the central exit of the runner. The design parameters such as, radius of the runner,

curvature of channel, angle of vanes and the size of the turbine as whole depend on the

available head and type of application altogether.

The modern Francis Turbine is an inward mixed flow reaction turbine i.e., the

water under pressure enters the runner from the guide vanes towards the centre in radial

direction and discharge out of the runner axially. The Francis turbine operates under

medium heads and also requires medium quantity of water. The head acting on the

turbine is transformed into kinetic energy and pressure head. Due to the difference of

pressure between guide vanes and the runner (called reaction pressure), the motion of

runner occurs. That is why a Francis turbine is also known as reaction turbine. The

pressure at inlet is more than that at outlet. In Francis turbine runner is always full of

water. The moment of runner is affected by the change of both the potential and kinetic

energies of water. After doing the work the water is discharged to the tail race through a

closed tube called draft tube.

It is employed in the medium head power plants. This type of turbine covers a

wide range of heads (30m to 450m). allow the water to fall freely

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to the tailrace level as in the case of Pelton turbine. The free end of the draft tube is

submerged deep in the tail water, thus making the entire water passage, right from the

head race up to the tail race totally enclosed.

The draft tube converts kinetic head to pressure head. About 70% conversion is

possible. By recovering pressure head in the draft tube the pressure at the runner exit is

reduced below atmosphere. This makes it possible to install the turbine above the tail race

without any loss in available head. This is an important advantage in the reaction over

Pelton turbine.

The turbine has its own thrust bearing capable of carrying the additional load of

turbine shaft, runner and hydraulic thrust making a total of three guide bearings for the

complete unit.

5.1 Specifications

Type - Vertical Francis

Rated/Max output - 61300/67400KW

Design Net head - 184m

Max Gross head - 204.58m

Min.net head - 165m

Rated /Max. Discharge - 36.2/40.2 Cub m3/sec.

Rated speed - 333.3RPM

Run away speed - 585RPM

Direction of rotation - Clockwise

Maximum pressure rise - 50%

Maximum speed rise - 50%

The vertical shaft Francis type turbine comprise of a draft tube, spiral casing

and stay rings, guide apparatus, shaft, runner, guide bearing, shaft seal and auxiliary

items. The guide apparatus regulates the flow of water with, change in load and also

serves as a closing device. It includes top cover, pivot ring, guide vanes and turning

machinery. The mechanism for turning the guide vanes (regulating ring) is designed to

ensure simultaneous turning of guide vanes during opening or closing of guide

apparatus. Two servomotors, housed inside the pit liner, actuate the regulating ring

which in turn operates the guide vanes through regulating gear. To facilitate atmospheric

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air supply below the runner during part load operation of turbine, the necessary

connections from the aeration valve are made in the upper cone.

The shaft sealing prevents leakage of water through clearance between top cover

and shaft sleeve. It is located below turbine guide bearing. To prevent the abrasive

particles and dirty water corning in contact with the rubber-sealing ring, water at a

pressure slightly higher than that above the runner is supplied at three points of the

shaft seal through a micro filter from the main cooling water system.

Oil level relay is provided on the bearing housing to indicate high and low oil

levels of the bearings at Unit control board [UCB]. Temperatures of guide bearing pads

are monitored by a set of resistance temperature detectors [RTD] and dial type

thermometers [DTT]. Out of eight pads, temperatures of four pads are measured by

RTDS and the remaining four by DTTS. Two RTDs measure temperature in the oil bath.

5.2 Guide Vane Servomotors

Guide vanes are fixed aerofoils that direct air, gas, or water into the moving blades

of a turbine or into or around bends in ducts with minimum loss of energy. The runner of

turbine is encircled by a ring of guide vanes. Guide Vanes are installed in the turbine to

regulate the quantity of water to the runner with change in load. These are operated by

two servomotors through guide vane operating mechanism via links & levers. The

servomotors get signals from Governor. The guide vanes are of aero flow section, which

allows the flow of water without formation of eddies in all positions. Depending upon silt

flow, the guide vanes may be made of mild steel or stainless steel with integral machined

stems, which are drilled for grease lubrication of bushes. Two servomotors are provided

for turning the regulating ring during regulation of load on turbine and closing /opening of

the guide apparatus. When the turbine load changes during generating operation, the

servo motor shall operate the guide vane smoothly coordinating with the speed governor

Fig 5.2 Guide Vanes

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.CHAPTER-6

GOVERNOR MECHANISM

The primary purpose of a governor for a hydroelectric unit is to control the speed and

loading of the unit. It accomplishes this by controlling the flow of water through the turbine

by adjusting the opening of the Needles / Guide vanes and by sensing the Speed of the

Machine. The governing system consists of two parts (i) the sensing and signal

processing part. (ii) The operational part. In the operational part hydraulic oil pressure is

used for operating vanes and valves.

Fig 6.1 Block diagram of electronic governor

6.1 Electro hydraulic transducer

The electro- hydraulic transducer is the interface between the electronic signal

processing part and the hydraulic operating part. This transducer receives the electric

signal from electronic part and converts the signal into a hydraulic flow. This hydraulic

signal is hydraulically amplified and used for operating the vanes or the jets and

deflectors.

Fig 6.2 Distributing valve controlling a Servomotor

When an opening signal is received from the electronic governor, the actuator will

pull the floating valve piston to go down and pressure oil is admitted to opening side of

servomotor and servomotor gradually opens. As the servomotor opens, the feedback lever

pushes the floating lever upwards. When feedback push equals the feed forward pull, the

distributing valve piston will return to the original position and steady state is achieved.

Arrangement of Distributing valve controlling a Servomotor.

Feed Forward pull from Actuator

Servo motor

Feed back push from servo motor

Floating

liver

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CHAPTER-7

VALVE GALLERY

Fig 7.1 Valve system

On the upstream side there is valve gallery throughout the length of the floor.

The main equipments on this floor are Butterfly [BF] valve, water operated

servomotors, oil leakage units and the pipelines for the same. The access to the draft

tube cone and the removal of the runner for maintenance is also from this floor.

The station drainage system is installed on the left hand side of the Power Station

when viewed from the downstream side.

A 2.2 m dia. double door BF valve has been provided as main inlet valve on each

penstock branch. Water operated double acting servomotor(20 kg/cm2) has been provided

on the left hand side of the BF valve and is mechanically connected with a lever and keyed

to the door turn-on of the BF valve. A 100 NB drain valve is provided on the bottom

side of the BF valve to drain the water in between the two doors of the BF valves and is

connected to the penstock drain pipe.

The servomotor is water operated. An oil operated control valve (40 kg/cm2) is

provided to adjust opening and closing of the valve. For the opening of the main inlet

valve [MIV], water under pressure is taken from the spiral side and for the closing the

same is taken from the penstock side through isolating 40 NB valves and duplex

strainers. Time of closing is 50-55 sec. The operation of the control valve is carried out

by oil pressure through a solenoid valve mounted on the MIV control panel. If the oil

pressure is low due to control failure or any other fault, when the MIV is open, the

control spring will force the operating piston down to its closed position. This will

close the MIV automatically. All these assembly has been provided on the left side of

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BF valve. From the upstream of inlet pipe of the BF valve tapping and connections are

taken with isolating valves, for operating control valve, ejector, and pressure gauges.

Fig. 7.2 Bypass Valve

Oil operated by-pass valve and piping are provided over the top of the BF valve

for balancing the pressure on either side of the BF valve. The opening and dosing of the

valve is carried out with the help of pressurized oil taken from the oil pressure system

through a solenoid valve which is mounted on the MIV control panel. Limit switches are

provided to get the opening and closing indications for the by-pass valve and BF valve.

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CHAPTER-8

GENERATOR

An alternator is an electromechanical device that converts mechanical energy to

electrical energy in the form of alternating current.

Alternators generate electricity based on the principle that, when the magnetic

field around a conductor changes, a current is induced in the conductor. Typically, a

rotating magnet, called the rotor turns within a stationary set of conductors wound in

coils on an iron core, called the stator. The field cuts across the conductors, generating an

induced emf (electromotive force), as the mechanical input causes the rotor to turn.

The rotating magnetic field induces an AC voltage in the stator windings. Often

there are three sets of stator windings, physically offset so that the rotating magnetic field

produces a three phase current, displaced by one-third of a period with respect to each

other.

The rotors magnetic field may be produced by induction (as in a "brush-less"

alternator), by permanent magnets (as in very small machines), or by a rotor winding

energized with direct current through slip rings and brushes.

In alternators, the armature may be the rotor or stator. The rotating-field alternator

has a stationary armature winding and a rotating-field winding. The advantage of having

a stationary armature winding is that the generated voltage can be connected directly to

the load. The stationary armature, or stator, of this type of alternator holds the windings

that are cut by the rotating magnetic field. Rotating-field ac generator consists of an

alternator and a static excitation system. In the case of a machine with field coils, a

current must flow in the coils to generate the field; otherwise no power is transferred to or

from the rotor. The process of generating a magnetic field by means of an electric current

is called excitation. The output of the alternator section supplies alternating voltage to the

load. The only purpose for the exciter is to supply the direct current required to maintain

the alternator field. Thus, a fixed-polarity magnetic field is maintained at all times in the

alternator field windings. When the alternator field is rotated, its magnetic flux is passed

through and across the alternator armature windings. There are two types of rotors used

in rotating-field alternators. They are called the turbine-driven and salient-pole rotors.
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The windings can be lap or wave. Generators can be installed horizontally as well as

vertically based on the weight.

The Generators installed at Lower Periyar Power House are of vertical type, salient

pole, and suspended type construction. The stator winding is of two-layer bar type wave

winding. The Generator has a guide bearing positioned above the rotor, and one guide

bearing below the rotor.

Hydro Static [HS] lubrication system for injection of oil to the thrust bearing

pads have been provided for use during starting and stopping. The generator slip rings

and speed signal generators are located at the top. The generator excitation is provided

by separate static excitation equipment.

8.1 Technical Data Of The Generator

Maximum continuous rating - 66.67 MVA

Rated power - 60 MW

Rated voltage - 11000 volts

Rated power factor - 0.9 lagging

Rated frequency - 50 Hz

Rated speed - 333.33 RPM

No. of poles - 18

Direction of rotation - clockwise

Air gap at pole centre - 26 mm

Stator Resistance/Phase - 0.00505 Ohm

Stator winding connection - Star (Wave)

Field winding Resistance - 0.14255 Ohm

Excitation current at no load - 607 Amps

Excitation current at rated load - 1250A,230V 287.5kW

Stator current at rated load - 3500 A

8.2 Stator

The different parts are

Frame-The stator frame is used to hold the armature windings in alternators, and in case

of larger diameter alternators (which are slow speed) the stator frame is cast out of

sections and there are holes for ventilation in the casting itself. The recent trends towards

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such stator construction are more in favour of using mild steel plates which are welded

together rather than castings. The stator frame is built of welded steel structure and to

facilitate transport, it is dispatched from the factory in three parts. It has adequate

depth to prevent distortion during transport and under any operating conditions.

Core- Another integral part of the stator is the stator core. The core is constructed in the

form of laminations and the material used for the same is either magnetic iron or steel

alloy. The main purpose of lamination is to prevent loss of energy in the form of eddy

currents. There are different types of armature slots provided in the core to insert the

conductors and the three various types are as follows.

Wide open type slots

Semi closed type slots

Close type slots

The core is securely clamped by a large number of studs. Ventilation ducts

are provided at intervals along the stator core, being formed by means of non

magnetic steel spacing is securely welded to adjacent steel stampings. Jacking screws

are provided at the outer edge of end plates to enable the pressure of the teeth to be

adjusted.

Fig 8.1 60 MW Alternator

Windings-The stator winding is of two layer bar type wave winding. All the bars are

formed, insulated and tested before being placed in the slots. Each bar consists of a

number of individual copper strands of rectangular section to minimize eddy current

losses. Each strand is insulated with polyesterimide varnished glass brainding. The

bars are insulated along the slot portion by adequate presses and consolidated in a

heated press. This ensures complete elimination of voids and high factor of safety

against breakdown. The end portion of the bar have flexible insulation consisting of

polyester film and glass backed mica flake tape, reinforced at intervals with layers of
http://www.brighthub.com/guides/energy.aspx

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varnish treated terylene tape and with glass tape for protection and finish. The joints

between the bars are made by brazing and are insulated. All connections between

bars and terminals are securely clamped. Both ends of each phase windings are

brought out to suit the terminals near the top of the stator frame.

Fig 8.2 Stator

8.3 Rotor

The rotor consists of a coil of wire wrapped around an iron core. Current through

the wire coil - called "field" current - produces a magnetic field around the core. The

strength of the field current determines the strength of the magnetic field. The field

current is D/C, or direct current. In other words, the current flows in one direction only,

and is supplied to the wire coil by a set of brushes and slip rings. The magnetic field

produced has, as any magnet, a north and a south pole. The rotor is driven by the

alternator pulley, rotating as the engine runs, hence the name "rotor." The rotor is

constructed with a high strength alloy steel shaft forging that is precision machined,

ground and finished to exact tolerances.

Fig 8.3 rotor

Poles-There are 18 magnet blocks on each rotor. Each magnet block has a north pole and

a south pole. The poles are arranged alternately, so north faces the stator on one block

and south on the next. The poles on the other magnet rotor are arranged in the opposite

polarity so that the north poles face south poles across the stator. In this way, a strong

magnetic flux is created through the stator between the magnet rotors. The coils

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embedded in the stator are dimensioned such as to encircle the flux from one magnet pole

at a time. As the magnet blocks pass a coil, the flux through the coil alternates in

direction. This induces an alternating voltage in each turn of the coil. The voltage is

proportional to the rate of change of flux.

Damper Winding-The rotor is equipped with damper windings. They stabilize the

speed of AC generator to reduce hunting under changing loads. If speed tends to

increase induction-generator action occurs in damper winding. This action places a

load on the rotor tending to slow down the machine. In case of speed decrease

induction-motor action takes place.

The damper winding is of major importance to the stable operation of the

generator. While the generator is operating in exact synchronism with the power system,

rotating field and rotor speed exactly matched, there is no current in the damper winding

and it essentially has no effect on the generator operation. If there is a small disturbance

in the power system, and the frequency tends to change slightly, the rotor speed and the

rotating field speed will be slightly different. This may result in oscillation, which can

result in generator pulling out of step with possible consequential damage.

Damping bars are of circular sections of copper which are semi closed in the

pole faces. The ends of the bars are short circuited together by copper stampings.

The damper winding is inter-connected between poles.

Field Winding-The magnetic field in the synchronous generator is created by field

winding. The field coils are square ended being fabricated from a straight length of

copper strips dove tailed and braced at the ends. At intervals down each coil the

copper is increased in width to give fins for cooling purposes.

All connections between adjacent field coils and also between field coils and

slip rings are firmly secured to the rotor.

Temperature detectors- Resistance temperature detectors are built into the

generator stator core and windings. The detectors are of three wire resistance type

having 100 ohms resistance at 00C and 138.5 ohms at 100

0C. The loads from the

detectors are brought out to a metal clad terminal box located in a conveniently

accessible position from which cables could be run to the indicating instrument via

generator marshalling box.

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CHAPTER-9

BEARINGS

Conventional alternators comprise of top-mounted thrust and guide bearing

supported on heavy brackets, capable of supporting total weight of generator. A guide

bearing is a plain bearing used to guide a machine element in its lengthwise motion,

usually without rotation of the element. A bottom guide bearing combined with turbine

shaft is usually provided. This conventional design is used for high speeds (up to 1000

rpm) generators.

9.1 Thrust Bearing

Thrust bearing in any turbo machine is used to prevent axial tolerance on the

shaft. The thrust bearing is a spring supported type in which the stationary part consist

segmental pads supported on mattress of helical springs. The rotating bearing surface is

machined accurately perpendicular to the axis of the shaft. The bearing surface is

polished to fine surface finish. The thrust pads are of stress relived mild steel and are

faced with a high quality white metal. Each pad rests on a number of springs which are pre-

compressed by a permanently locked centre screw and finished to a standard overall

length. The springs are assembled on a heavy fabricated spring plate which is an integral

part of the thrust bearing housing. The thrust pads are prevented from moving

circumferentially by pad stops secured to the spring plate. Radial movement is prevented

by-dog damps which would also prevent the pad from rising with the thrust block

during rotor jacking operation. The thrust bearing pads are completely immersed in oil

bath. The oil is cooled by plug in oil coolers.

Transferring the weight of Rotating mass through the thrust bearing, upper

Bracket & to the Foundation.

Guide Bearing

Thrust Bearing

Fig 9.1 Generator Bearing

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9.2 Top Guide Bearing

The top and bottom guide bearings are of the pivoted pad type consisting of a

row of white metalloid pads arranged in a support ring. Top guide bearing is located

above the thrust bearing, on a journal surface machined on the periphery of the thrust

collar. Sufficient insulation and protection is provided in top guide bearing to prevent

flow of shaft current through the bearing pads. The same oil bath for the thrust pads is

used for the guide bearing.

9.3 Bottom Guide Bearing

Bottom guide bearing is located on a journal integrally forged with the shaft. A

pivot bar is bolted to the back or each guide bearing pad to enable the pad to rock slightly

to take up a suitable position and facilitate formation of the oil film, when running. The

clearance between individual pads and the journal is set by adjusting the shims

between the back of the pad and the pivot bar. The pads are cooled by an oil bath with

plug in type coolers.

Lower Guide Bearing .Coupling

Flange

Rotor Fan

Rotor Poles

Fig 9.2 Lower Guide Bearing

9.4 Hydro Static [HS] Lubrication System

Lubricants (solid or fluid film) are deliberately applied to produce low friction

and low wear. In hydrostatic lubrication, a thick fluid film is maintained between two

surfaces, with little or no relative motion, by an external pumping agency: a pump, which

feeds pressurized fluid to the film.

Hydrostatic lubrication requires an external pumping agency. HS bearings provide

high load-carrying capacity. Since HS bearings do not require relative motion of the

bearing surfaces to build up the load-supporting pressures as necessary in hydrodynamic

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(HD) bearings by viscous shear/drag, HS bearings can be used in applications with little

or no relative motion between the surfaces.

The hydro static lubrication system has been designed to provide an oil film

between the thrust pads and the runner disc during starting and stopping when there is

little likelihood of formation of hydrodynamic oil film. Therefore, it should always be put

on service before starting the unit. However, if for any reason the HS lubrication system is

out of order, the rotor shall be jacked up and released just before starting the unit, to

ensure formation of oil film. This operation is not necessary If the machine has been at

stand still for less than 12 hours.

9.5 Brakes and Jacks

The generator brakes consists of a number of 'Ferodo' lined shoes which

operates against a polished circular steel brake track to the underside of the rotor

spider hub. Each brake shoe is mounted on a vertical piston moving in a small cylinder.

To apply/release the brakes, air would be forced into the brake cylinder in appropriate

direction from the station compressed air supply. The brake cylinders are mounted on

the bottom bracket.

The brakes are to be applied continuously starting from 30 rpm, with HS. Lube

ON and with air pressure of 4 to 5 bars for minimizing brake -dust problems. When the

machine has come to a full stop, the brake should be left on for about 5 minutes more, to

flow static friction to be established between the rotating parts and the bearing pads. If

sufficient time is not allowed for the oil to squeeze out from between the bearing

surface to establish static friction, the turbine gate leakage torque may cause the rotor to

creep, which could cause damage to the thrust bearing pads.

No. of units - 6

Brake material - Ferodo India Grade

Brake pad and size - 325mmx325mm

Brake operating pressure - 4 to 5 Kg/ sq. cm

Jacking oil pressure required - 70 Kg/sq. cm

Brake application speed - 30 RPM with HS

Time to bring the machine to rest after brake - 3 to 5 minutes

Rotor jacking limit - 15mm

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CHAPTER-10

STATIC EXCITATION

Lower Periyar is the second power house using static excitation in Kerala State

Electricity Board. The static excitation system consists of excitation transformer, thyristor

converter and voltage regulator. A complete system also includes control and de-excitation

circuits. It is called static excitation when you make use of solid state components like

diode and thyristors to convert to pure dc and to use this dc for field excitation of

synchronous generators.

The Thyristor-type static excitation system, due to its many advantages, excellent

response characteristics, easy maintenance and simplified main machine construction, is

now extensively used for medium-and large-capacity hydro-or steam-turbine generators.

suppression via a de-excitation D.C. circuit breaker and a discharge resistor is accomplished.

The excitation system is equipped with a microprocessor control system that enables voltage

control, supervision, protection, communication and signalization. The system is completely

automated and adapted for no-crew plants and for remote control from the superimposed

control centre.

The main types of Exciters are:

1) Conventional D.C. Exciter.

2) Static Exciter.

3) Brushless Exciter

In modern generators, magnetic field is produced by an electromagnet. Equipments

required to produce a controlled amount of field current is known as Excitation System.

10.1 Static Excitation Equipment

It consists of Regulation Cubicle, field flashing & field breaker cubicle, thyristor

cubicles, and transformer cubicle. All excitation power is normally derived from the

synchronous machine terminals through the step down excitation transformer of 850 kVA

rating, generally termed as the rectifier Transformer or the Excitation Transformer,

housed inside a cubicle and the thyristor converter. The voltage regulator via pulse-

triggering unit controls the thyristor converter.

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As synchronous machine has low remnant voltage, the voltage built-up in the self-

excitation mode is accomplished by flashing the field from an external D.C. supply (station

battery) or with A.C. supply (station auxiliary) through a diode rectifier. The control circuit

is suitable to accept supervisory command signal contacts from remote Supervisory control

equipment.

The AC input supply of all electronic power supplies are given from the secondary of

the Excitation Transformer through suitable intermediate transformers. The secondary of the

Excitation Transformer feeds the thyristor bridge which consists of parallel connected bridges

to meet the field current requirement of the Machine.

The DC output of the Thyristor Bridge is fed to the generator field through field

breakers. The discharge resistance in the field circuit enables faster suppression of stored

energy in the field.

Fig.10.1 Static Excitation

Power Rectifier-Three phase 6-pulse fully controlled thyristor bridges with fuse RC

circuit, gate circuit and de coupling reactors are provided with conduction monitoring unit

to indicate with the help of LEDs the non-conduction of any thyristor in the bridge. De-

coupling reactors provided in each arm of the bridge for di/dt protection also improves

the paralleled sharing between thyristor bridges. One redundant bridge is built in the system

such that in the event of -failure of one bridge rest of the bridges can carry full rated

excitation requirement of the machine. With 2 bridges out of service, machine can be

operated at reduced load with the remaining bridge.

Voltage Build up/ field flashing- Electrical generators that are self excited depend on

residual magnetism in the field to start generating. If the residual magnetism has been

lost, it may be restored by briefly applying power from an external source. The brief

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application of power for that purpose is called "flashing the field." Flashing is sometimes

done manually to start a small generator.

Voltage build up (field flashing) can be done either with the help of station battery

supply through a dropping resistor and blocking diodes stack or Station Auxiliary supply

through a step down transformer and diode bridge. At 30% of the rated generator voltage

pulses to the thyristors in the main circuits are released and they take over the build process at

about 40% of the rated generator voltage. For checking the healthiness of the main circuit, the

field flashing is kept in circuit up to 70% of the rated generator voltage after which the field

flashing circuit is automatically disconnected.

If a successful start up is not achieved during this period of time, a timer provided

in the excitation circuit, switches off the field flashing process. It is to be noted that a

minimum period of 10 minutes must elapse before field flashing is resorted once again.

For AC field flashing a diode bridge stack consists of six screws in type diode mounted

on suitable heat sink assembled side by side and can be easily replaced from the front.

The six diodes are connected to from a three-phase bridge.

10.2 Modes of Operation

Two independent modes of operation are envisaged namely

1. Automatic mode

2. Manual mode.

Automatic mode:-In the Automatic Mode excitation is regulated by the AVR. The AVR

compares the actual value of generator voltage which is sensed through PT after suitably

stepping down and converting into DC with the reference value set on the Auto Reference

Potentiometer. The amplified error (output of AVR) is used as control signal to control the

Grid control unit (Firing Circuit) for the Auto Channel. The output pulse of the Grid control

unit is amplified to boost the voltage level in the pulse Intermediate amplifying stage and

power supply unit. The power supply unit of me pulse Intermediate Amplifying Stage feeds

the AVR and the Auto; / and is termed as supply A.

Manual mode:-In the manual mode the Grid control unit of the Manual channel is

directly controlled by the Manual reference potentiometer. The pulse generated by the

Manual Grid Control unit is amplified in the pulse Intermediate stage and power supply

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unit of the manual channel. The power supply unit of the pulse Intermediate Amplifying

stage feeds reference voltage to the manual chan

Fig 10.2 Block Diagram Static Excitation

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CHAPTER-11

STATION AUXILIARIES

11.1 Cooling Water System

Normally cooling water is tapped from the penstocks and connected to a common

inlet header through a duplex strainer with isolating valves on either side. The inlet

header is connected to an outlet header through many numbers of cooling water pumps

and a non-return valve. Isolating valves are provided on either side of the pumps.

Normally cooling water for generator and transformer is taken from the outlet header

through valves. The cooling water pressure at outlet header is sufficient as the same is

tapped from the penstock; hence the cooling water pumps are normally not started.

Fig 11.1 Cooling water system

The cooling water system will be used for the following service.

1.Cooling water for turbine bearing and shaft seal.

2.Cooling water for Generator coolers and bearing.

3.Station services.

4. Transformers.

Cooling water for the above requirements is taken from cooling water pit which is

connected to the tail races. The cooling water from the pit pushes through a -duplex

strainer pump motor sets with non return valve [NRV]. Pressure switch has been

provided in each line which helps in the automatic start/stop of main and stand by pump.

Discharge of each pump is connected to common header. Cooling water is supplied to

Generator and turbine components through motor (4 Nos. 110HP) operated valve.

Cooling water connection for transformer and station services are provided on the

common header. Out of 4 pumps 3 pumps works as main pump for each unit and one

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pump is common as stand by. An emergency cooling water system is also provided to

feed the cooling during total shutdown of the power supply.

11.2 High and Low Pressure Air System

H.P Air system consists of two H.P. compressor sets with air-cooled systems. Air

from compressors pass through non-return valve, isolating valve, air cooled after

coolers and finally to the H.P air receiver. Isolating valve in the H.P. airline shall be

kept open. The H.P receiver has pressure gauge and safety valve mounted on it. Low

pressure (LP) air receivers are provided to supply low-pressure air to shaft seal, Brake &

Jack panel and station service. The feeding of air to the, LP receiver is earned out from the

H.P. receiver through a pressure reducer. Pressure switches have been provided on the H.P.

receiver to work the compressors automatically. The main compressor starts when the

pressure drops below 37kg/sq cm and stop at 40kg/sq cm. The stand by compressor will

start at 34kg/sq cm and stop at 40kg/sq cm. One pressure switch is set to give alarm at

32kg/sq cm

11.3 Dewatering System

The de-watering system has been provided to remove water passage via. a de-

watering pump to tailrace. The de-watering sump has two oil lubricated vertical turbine

pump set (110HP) placed at turbine floor on the left hand side (near Unit -3) of the

Power House. The discharge from the two pumps is connected to a common header via

non-return valve and is lead to the tailrace.

Level control relays nave been provided for the automatic operation or the pump

sets. Pumps can also be operated manually by push buttons provided in the starter

panels. A high level alarm is also provided in the sump to avoid flooding of the sump.

11.4 Drainage System

Water from the seepage, turbine leakage delivery water during the operation of

BF valve and ejectors are taken to the drainage sump. This sump has got two vertical

turbine pumps, (2x20HP) set with motors. The discharge from the two pumps is

connected to a common header and leads to the tailrace. Level control relays have been

provided for automatic starting and stopping of pump sets and can also operate manually by

push buttons. A high level alarm is also provided in the sump.

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11.5 Centralized Grease Lubrication System

To facilitate grease lubrication of every moving part of Inlet valve and turbine, a

centralized grease lubrication system has been provided. The system is completely

automatic with a synchronous time adjustable between 6 to 120 hours for repeating

greasing cycles. The system consist of a heavy duty reciprocating pump drives plungers

type pump with built in reduction gear, a four way solenoid valve, a set of dose feeders

with high pressure pipes and fittings. The grease lubrication have provided on the valve

door turnings on both sides with non return valves, servomotor lines of BF valve, guide

vane lower bushing through non-return valves, upper bushings, guide vane servo

motor pins and the regulating ring supporting bushes.

Lubrication systems increase the life span of machine components and they

protect from wear and corrosion. As a result, they are an inevitable part of modern

service and maintenance concepts. Lubrication systems have the task of bringing the

lubricant to the appropriate point in an exact measured quantity, at the right time. In the

field, single-line and progressive lubrication systems are largely used. The choice of a

suitable lubricant is largely dependent on the operational method of the lubrication

system and the application. This is why both these factors need to be carefully

scrutinized.

11.6 Synchronous Condenser Operation

A synchronous condenser (sometimes synchronous capacitor or synchronous

compensator) is a device identical to a synchronous motor, whose shaft is not connected

to anything but spin freely. Its purpose is not to convert electric power to mechanical

power or vice versa, but to adjust conditions on the electric power transmission grid. Its

field is controlled by a voltage regulator to either generate or absorb reactive power as

needed to adjust the grid's voltage, or to improve power factor.

Increasing the device's field excitation, results in furnishing magnetizing power

(kVARs) to the system. Its principal advantage is the ease with which the amount of

correction can be adjusted. The energy stored in the rotor of the machine can also help

stabilize a power system during short circuits or rapidly fluctuating loads such as electric

arc furnaces. Large installations of synchronous condensers are sometimes used in

association with high-voltage direct current converter stations to supply reactive power.
http://en.wikipedia.org/wiki/Synchronous_motorhttp://en.wikipedia.org/wiki/Electric_powerhttp://en.wikipedia.org/wiki/Electric_power_transmission_gridhttp://en.wikipedia.org/wiki/AC_power#Real.2C_reactive.2C_and_apparent_powerhttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Power_factorhttp://en.wikipedia.org/wiki/Volt-amperes_reactivehttp://en.wikipedia.org/wiki/Inertiahttp://en.wikipedia.org/wiki/Short_circuithttp://en.wikipedia.org/wiki/Electric_arc_furnacehttp://en.wikipedia.org/wiki/Electric_arc_furnacehttp://en.wikipedia.org/wiki/Electric_arc_furnacehttp://en.wikipedia.org/wiki/High-voltage_direct_current

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CHAPTER-13

MAIN CIRCUIT BREAKERS AND POWER TRNSFORMERS

Fig 13.1 11kV/220kV Transformer

The combined electrical, physical, chemical and thermal properties offer many

advantages when used in power switchgears. Some of the outstanding properties of SF6

making it desirable to use in power applications are:

High dielectric strength

Unique arc-quenching ability

Excellent thermal stability

Good thermal conductivity

SF6 circuit breakers of capacity 1250 A, 40 kA, 245 KV are used in this power house.

These are of air operated single break, with individual operating mechanism with one

common air compressor unit coupled to the three limbs with pipe. AH control equipment and

compressor are housed in the center limb. The opening of the breaker is done by 15 Kg/sq.

cm air pressure. While opening, the closing spring is automatically charged this is used

for subsequent closing. The breaker can be operated locally or remotely according to the

switch position. Different air and gas pressure for the breaker operation is as follows.

1) Low air pressure alarm - 13.2 to 14.2 Kg/sq. cm.

2) Low air pressure cut off - 12 to 13 Kg/sq. cm

3) Auto re close cut off - 14.3 to 14.8 Kg/sq. cm.

4) Normal SF6 gas pressure - 6.5 to 6.8 Kg/sq. cm

5) Low gas pressure alarm. - 5.5 Kg/sq. cm.

6) Circuit Breaker lockout - 5 Kg/sq. cm.

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13.1 Power Transformer

Technical data:

Make - Crompton greaves make

No load voltage ratio - 11 KV/220 kV.

Tap changing circuit - OFF load provided on HV side

Vector simple - Ynd1

Type of cooling - OD WF [Oil drive, water forced].

Constructional details:

HV Line end - 3 Nos., 245kV Oil filled condenser type

bushing

LV Line end - 3Nos, 24kV, 4000A, Outdoor type bushing

HV Neutral end - 1 outdoor type bushing

Supervisory Apparatus:

A double float type Buchholz relay with a set of alarm and trip contacts

A dial type oil temperature indicator with two sets of contacts for alarm and trip and

maximum reading pointer

A winding temperature indicator with maximum reading pointer, heater bulb/ and

four sets of contacts for alarm, trip, fan control, and oil pump.

A magnetic oil gauge, 2 oil flow indicators, 2 water flow indicators.

A No pressure release valve, pressure gauges in oil and water circuits.

Differential pressure gauge with a set of alarm contacts

The oil is pumped through heat exchangers using motor. Water to the heat

exchangers is taken from the cooling water system controlled by motor operated

valve followed by gate valve. While putting the transformer in service first oil

pump must be started and then only the cooling water valve is opened.

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CHAPTER-14

PROTECTION SYSTEM

14.1 Protection of Generator and Line

In this powerhouse modern solid-state type protection relays are installed for

generators and feeders. All the protective relays are of ABB make.

Generator - Transformer differential relay

It is s three phase differential relay intended for all types of auto- transformers, multi

winding transformers, generator with step up transformer over all protection, often

including the auxiliary transformer in the protected zone. In our power house overall

protection of generator and transformer is adopted. The CT wiring is taken from the

generator neutral side and from 220 kV side of the corresponding unit. A differential relay

is connected so that it is supplied with current proportional to the current to the power

transformer, and current out from the transformer. The relay is connected to the current

transformers and possible auxiliary current transformers.

For transformers with tap- changers for voltage control, the average ratio of the taps

should be used for calculation. During normal operating conditions, small current flows

through the differential circuit of the relay. This current corresponds to the excitation

current of the transformer and to a current depending on the ratio error to the current

transformers. Normally these two currents only comprise a small percentage of the rated

current. The duty of the relay is to detect the internal faults (that is the faults within the

generator, power transformer, or on the connecting lines and bus duct etc) and then rapidly

initiate disconnection of the power supply. The internal faults that can occur are

1. Short circuit.

2. Ground faults

3. Turn-to- turn faults.

When faults arise outside the current transformer, the differential circuit of the relay

maybe supplied with a relatively large current, which can be caused by ratio errors in the

current transformers or by the tap changer not being in the centre tap position. If the tap

changer is in a position 20% from the centre tap position, and the short circuit current is 10

times the rated current/a differential current of twice the rated current is obtained. The

differential shall not operate for this differential current. In order to make an operate value

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setting for such high over current unnecessary, the differential relay is provided with a

through fault restraint with restraining circuits. The relay then will not react for the

absolute value of the differential current, but for a certain percentage differential current

related to the current through the power transformer. When energizing a power

transformer, it is possible to obtain a large inrush current in the exciting winding and then

proportionally large-current in the differential circuits of the relay. The magnitude and

direction of the inrush current depends on the instant of switching in the power transformer,

power transformer remanance, the design of the transformer, the type of the transformer

connection, the method of neutral grounding, the fault MVA rating of the power system and

power transformers connected in parallel.

In modern system the current can be 5 to 10 times the rated current when switching in

into the high voltage side, and 10- 20 times the rated current when switching to the low

voltage side. To prevent the relay from operating when energizing power transformer, it is

not possible, as a rule, to delay the operation during such a long time as required. Thus an

instantaneous relay must have a magnetizing Inrush restraint and there by utilize a certain

characteristic difference between the inrush current and the fault current.

Auxiliary CTs are used to balance the current to the relay. In addition auxiliary CT

may be used to reduce the effective leakage burden of the long secondary leads. The

differential zone of the relay can include up to one kilometre of high voltage cable since

adequate filtering provides security against high current oscillations.

Bus bar protection differential relay

Internal bus faults occur less frequently than line-faults. On the other hand, a bus fault

tends to be appreciably more severe, both with respect to the safety of personnel, system

stability and the damage at the point of fault. The fact that bus faults occur relatively seldom

is therefore of little comfort to the engineer in-charge subsequent to a major system

shutdown caused by the Sack of adequate bus relay.

When an internal bus fault occurs the magnitude of the fault current and its D.C.

component may be so large that the line CT's (current transformers) saturate within 2-3ms.

In such cases it is essential that the bus differential relay operates and seals in within 2ms,

i.e. Prior to the saturation of the line CT's. This high speed is necessary because when a line

CT saturates its output e.m.f. tend to drop to zero.

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In the event of an external fault, just outside the line CT's of a relatively small

feeder, the fault current may in an extreme case be as large as 500 times the rating of the

feeder. The line CT's of the faulty feeder are then likely to saturate at an even higher speed,

particularly so if the remanence left in the core from a previous fault has an

unfavourable polarity. The response of the restraint circuit of the differential relay must

therefore be at least the same high speed as that of the operating circuit, if mal-operation is

to be avoided.

Distance relay for feeder protection

Distance relaying is used to a large extent to provide protection against ground

and phase faults on HV and EHV networks, The operation of all distance relays is based

on information available through main current and voltage transformers. Sometimes

additional information may be required from other apparatus such as receiver equipment

in a communication link between two distance relays. But, the action of a protective relay

cannot only be based on the sole estimation of currents and voltages in the primary

system/ but must also take into consideration the steady-state and transient

characteristics of the relay input sources, namely the instrument current and voltage

transformers. The demands made on protective relays are steadily increasing owing to

such factors as the growing short-circuiting power and the demand of consumers for

greater reliability in their power supply.

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CHAPTER-15

COMMUNICATION

15.1 Power Line Carrier Communication (PLCC)

PLCC System is established at LP Power Station through the 220 KV feeders LP-

Brahmapuram, LP-Madakkathara & LP-Moolamattom. Inter Circuit phase to phase

coupling is used for the system. The feeders are provided with carrier inter trip protection

coupler system. BPL make 9505 and 6515 model panels are used for the communication

system. An exchange MDX 50 BPL make is used for linking PLCC phones to the panels.

The st

48V DC.

The data and status of Generators and feeders are transmitted to the Load

Despatch (LD) station Kalamassery through the PUNCOM make PLCC panel established

the scheme up to Madakkathara and from there to LD station through optical fibre cable.

AC Supply fail alarm for the PLCC Battery charger is wired to Unit No 1

annunciation panel. On initiation of this alarm in the C/R, the operator must inspect the

carrier room for the reason of power failure.

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CHAPTER-16

OPERATION OF DIFFERENT EQUIPMENTS

16.1 Procedure For Stand By Cooling Water Pump Operations

In case the main pump of any unit is not functional, Stand by Cooling Water

Pump (CW4) can be used for starting and running of any machine. Stand by Cooling

Water Pump runs on station auxiliary supply.

Sequence of Operation During Starting

Switch OFF the MCCB of the faulty C.W.P and put the selector switch in NORMAL

position. Start the machine as usual. When the C.W. Valve of the machine is opened,

Switch ON the Stand By Pump from the UCB of the respective machine. (The Stand By

Pump can be Switched ON locally by putting switch to TEST position and pressing the

START button locally from the C.W. Pump control panel at Turbine floor).

At the same time short the terminals 64 & 67 in terminal block TB3 of the respective

machine in Auto Sequencer Panel in Control Room, for getting the command from the

sequencer for executing next step. When next step is executed the shorting can be

removed. The remaining procedures are same as usual for starting the machine.

While changing the machine supply Stand By Pump will not be affected.

After synchronization of the machine, if the Stand by pump is switched on in TEST

position, the selector switch can be put back to norma

Note: - If a machine is to be run using Stand By Pump it is better to put the machine in

service as last one.

Sequence Of Operation During Stopping

While Stopping Switch OFF the machine having Stand By Pump first.

Do the Stopping procedure as Usual. After breaking, when the machine comes to stand

still, Switch OFF the stand by pump either from the UCB ( Stop command is to be given

from the UCBs of all machines ) or by putting the Selector Switch in TEST position and

press the OFF push button locally. When Machine comes to standstill change the selector

switch, of Stand by Pump, back to NORMAL.

16.2

System

Avail the Station Supply from DG Set.

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To start a machine from Black Out, Switch OFF the CWP MCCB of the concerned

machine and Switch OFF the MCCB of Stand By Pump. The selector switch of both

the Pumps should be in NORMAL position.

Initiate machine Start Up sequence from Control Desk.

When the CW Valve of the machine opens, OPEN the Emergency Cooling Water

Valve fully. ( If required the Emergency Cooling Water Pumps can be put in to service

from DG supply)

Short the concerned terminals of the Main and Stand pumps at Sequencer panel. (Main

pump TB3 64,67, Stand by TB3 68,71- if required).

When the machine Voltage and Frequency reaches the required level (before

synchronization) change the supply from G A to G B.

Put the Main Cooling Water Pump selector in TEST, Switch ON the Main Cooling

Water Pump MCCB and put the selector to NORMAL (the CWP will start

automatically).

Close the Emergency cooling water valve.

Synchronize the Machine and Normalize the Auxiliary supply.

16.3 Procedure To Be Followed During Tripping Of All MACHINES

If auxiliary Supply is Available

Switch off the MCCBs of the Standby and any of the two (say #2 and #3) Main

Cooling Water Pumps immediately and then change the station supply (otherwise the LT

Breaker may trip). Change the Auxiliary supply of all Machines. Open the Emergency

Cooling Water valve (Emergency Cooling Water Pump can be put into service if

required). Confirm that all the Governor Pumps are running. If not try to switch ON

locally. Otherwise close the Isolation valve at Pressure Receiver Tank. Now stop the

Machines one by one. After the machines comes to standstill, close the Emergency

Cooling Water valve. Give stop command to the Cooling Water Pump of U#2 and U#3

from UCB. Close the cooling water valve from UCB and confirm. Check the Break

Dust collector in OFF condition.

If auxiliary Supply is Not Available

Switch off the MCCBs of the Standby and all the Main Cooling Water Pumps

immediately. Then only avail DG Set Supply and change the station supply (otherwise

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the LT Breaker/DG Set may trip). Change the Auxiliary supply of all Machines. Open the

Emergency Cooling Water valve (Emergency Cooling Water Pump can be put into

service if required). Confirm that all the Governor Pumps are running. If not try to

switch ON locally. Otherwise close the Isolation valve at Pressure Receiver Tank. Now

stop the Machines one by one.

After the machines comes to standstill, close the Emergency Cooling Water valve.

Give stop command to the Cooling Water Pumps from UCB. Close the cooling water

valve from UCB and confirm. Check the Break Dust collector in OFF condition.

16.4 Procedure For Pneumatic Breaking

Breaking of Machine during Stopping

When the Machine speed reaches 10 Hz (20% of rated speed) and getting

confirmation from Chief Operator, (AE should confirm that the HS Pump is ON, if not,

start locally). Fully open the Air valve Near the LP air receiver Tank in Turbine Floor.

Open the Air admission Valve near the Brake & Jack panel in the Shaft Room. Press the

RESET Button until the pressure inside the Brake cylinder fully released (the hissing

sound stops). Apply brakes by pressing APPLY push button. Confirm that ANY ON

and ALL ON indications are obtained. When the machine speed reaches Zero and

Mechanical Brakes Off status is displayed on the CD, the Chief Operator should inform

the concerned to release the Brakes.

For releasing the brakes, apply RESET button as above. Apply RELEASE push

button until the ALL OFF indication is obtained. If ALL OFF indication is not getting,

close the air valve at shaft room and apply RELEASE until the pressure gauge reads

Zero, then conduct a visual checkup inside the Barrel to confirm that, all brakes are

released.

Procedures to be followed at Brake Jack panel before Starting of Machine

Fully open the Air valve Near the LP receiver Tank in Turbine Floor. Open the

Air admission Valve near the Brake & Jack panel in the Shaft Room. Press the RESET

Button and confirm that ANY ON and ALL ON indications are OFF and ALL OFF

indication is ON. The indications GEN Start Not Ready and Syn. Start Not Ready in

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16.5 Machine Start Procedure

Status check before starting machine

Select Display ON/OFF -

Select Spin Generator - indication glows

Select Accept - Status Display Unit

Select Recall criteria -

Again Select Recall criteria -

Check for any other conditions to be satisfied in display unit

Select Pre Sel. Reset -

Select Display ON/OFF

Start procedure:

Close the 220 KV Isolator of machine from Control Desk.

Select Release + Close (A or B Bus)

Physical verification of Isolator contacts for proper closing must be done by AE.

Give direction to the Generator Floor AE to make ready the machine for Starting

OPEN Air Valve and RESET brakes.

The Machine is now READY for Starting.

Set the Speed Setting Indicator in its marked position using Raise-Lower Speed Setting

push button

Switch ON the MCBs in the Transformer Annunciation Panel, Machine Annunciation

panel and Vibration & Rotor Temperature Indicator Panel

Switch ON Transformer Oil Pump and Cooling water Valve from the Transformer

Control Desk.

Synchronizing

Put the key, open the lock and put the Synchronising Selector S/W in CD to CHECK

position. Select

Adjust the voltage and frequency of the incoming M/c to that of Bus using excitation auto

sel. and speed setting Raise-Lower Push Button

When the Incoming Machine frequency approaches the Bus frequency, Switch ON the

Synchronoscope Selection Switch in Vertical panel.

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When the machine frequency matches system frequency and the green lamp of

synchroscope glows steadily, Synchronize the machine .Select Release + CB ON

Increase the Load Suddenly to 15MW using R-L of Guide vane position (MW)

Increase the Load gradually to 45MW using G.V limit PB.

Change the Auxiliary supply from Bus to Machine

16.6 Shut Down Procedure (Normal Stopping)

Load reduced to 45MW for All Machines

(Change the station auxiliary to other Machine or Karimanal Feeder)

Change Machine Auxiliary to Station Auxiliary


Using Speed Setting Push Button Reduce the Load to 40 MW

By using Guide Vane Raise - Lower (MW) reduce the load to 20 MW

(During this time the Output Setting must be >50)

Select Shutdown

Select Recall Criteria

Release +Execute

Guide vane closes

Main CB OFF

Field Breaker OFF

Select Release + Open Isolator Push Button

Select Release + Close MIV

When speed reduced to 10 Hz Apply brake

When Speed Zero and when status comes in the display as

Release Brakes.

Shut down Push Button Glows


S/OFF the MCBs in Panels and Transformer Control Desk

Reset the annunciation panels.

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SINGLE LINE DIAGRAM OF LOWER PERIYAR POWER HOUSE

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BRAHMAPURAM DIESEL POWER

PLANT

31st DECEMBER 2012-11

th JANUARY 2013-03-28

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CHAPTER 1

INTRODUCTION

Kerala depends on Hydro electric, Thermal, Diesel and non-conventional methods

for power. We have our main supply of power from hydroelectric power plants which are

19 in number. We use hydroelectric plant for the base load and thermal and diesel for

peak loads.

The Brahmapuram Diesel Power Project comes at a time when Kerala badly

needs it. This, the first non hydro project in the State will bring welcome relief to a

critical power situation.

In Kerala, we have 3 diesel power plants in Kozhikode, Brahmapuram and one in

Kasarkode (private). BDPP generates a maximum power of 106.6 MW. It was

commissioned in the year 1998. The power is generated using five 21.32 MW engines. A

low voltage system is provided for the internal power demands. The prime mover used is

SEMT Pielstick. Alternators are of GEC-Alstom. The whole control of the plant is

controlled and monitored by PLC system.

Fig.1.1 Brahmapuram Diesel Power Plant

tcl

Documents

hydelpower generation

hydel power stations

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kerala power system

hydroelectric power

kallarkutty dam

idukki hydroelectric

pallivasal project