“MAHI HYDEL POWER STATION
Submitted in Partial Fulfillment of the Requirements
for the award of the Degree
BACHELOR OF TECHNOLOGY
Submitted By:- Submitted To:-
Suryanshu Jain Dr. Surendra Singh Tanwar
IV B.Tech. VII Sem (Head Of Department)
Department of Electrical Engineering
GOVT ENGINEERING COLLEGE BIKANER
I have completed my practical training of 60 days (20/05/2017 to 19/07/2017) at
MAHI HYDEL POWER STATION, BANSWARA.
I am thankful to all Engineers of MAHI HYDEL POWER STATION,
BANSWARA technicians and other staff to give their king support and help in
my training period.
I am also thankful to Ms.SHASHI JAIN, X.En (O&M) & Mr. MAYANK
JOSHI, A.En.(M-Ph.1, Banswara). and all other technical staff to share their
experience and knowledge to us. Whose valuable guidance, suggestions and
information regarding the operation & maintenance of Power House.
I am also indebted to all my group members for regular and kind support
through all training period.
S.NO. FIG. NO. NAME OF FIGURE PAGE NO.
1 1.1 MAHI DAM 2
2 1.2 MAHI POWER HOUSE-I 4
3 1.3 ONE-LINE DIAGRAM OF ELECTRIC-
4 1.4 SYSTEM OF PARALLELED
GENERATORS AND TRANSFORMER
5 2.1 GENERATOR 8
6 2.2 D.C. EXCITOR(PMG) 9
7 3.1 SHAFT 14
8 3.2 GUIDE BEARING 15
9 3.3 BRACK & JACK 16
10 3.4 OIL PRESSURE PUMP 17
11 3.5 H.S. LUBRICATION MOTOR 18
12 3.6 GREES PRESSURE UNIT 19
13 4.1 AVR Panel 20
14 5.1 FRANCIS TURBINE “RUNNER” 24
15 5.2 PRESSURE PUMP & SERVOMOTOR 26
16 5.3 FLOW METER 27
17 5.4 OIL LEAKAGE UNIT 28
18 6.1 CORE TYPE TRANSFORMER 29
19 6.2 POWER TRANSFORMER 30
20 6.3 TRANSFORMER TANK WITH VACCUME FILLING 31
21 6.4 CONSERVATOR TANK IN TRANSFORMER 32
22 6.5 TRANSFORMER OIL TESTING 33
23 6.6 BUSHING 35
24 6.7 LIGHTINING ARRESTOR 37
25 6.8 CURRENT TRANSFORMER 38
26 6.9 TYPICAL SETUP FOR WYE-CONNECTED CT’S
PROTECTING A LINE OR PIECE OF EQUIPMENT
27 6.10 WATER SPRINKLER SYSTEM FOR COOLING
28 6.11 CO2 SPRINKLER 40
29 7.1 PUMP#CLASSIFICATION#&#CONSTRUCTION 41
30 7.2 CENTRIFUGAL PUMPS SPECIFICATION 42
31 8.1 SWITCH YARD 43
32 8.2 SF6 CIRCUIT BREAKER 46
33 8.3 PLCC EQUIPMENT 47
In hydro power plant we use gravitational force of fluid water to run the turbine
which iscoupled with electric generator to produce electricity. This power plant
plays an important roleto protect our fossil fuel which is limited, because the
generated electricity in hydro powerstation is the use of water which is
renewable source of energy and available in lots of amountwithout any cost.
The big advantage of hydro power is the water which the main stuff toproduce
electricity in hydro power plant is free, it not contain any type of pollution and
aftergenerated electricity the price of electricity is average not too much high.
Hydropower is the cheapest way to generate electricity today. That's because
once a dam hasbeen built and the equipment installed, the energy source—
flowing water—is free. It's a cleanfuel source that is renewable yearly by snow
MAHI HYDEL POWER STATION
The Mahi River is flowing in the southern part of Rajasthan near Banswara. The
power potential of this river has been exploited by constructing following#two#Power#
Mahi Power House-I (2x25MW) Mahi Power House -II (2 x 45MW)
FRL 281.5M(923ft.) Up Stream reservoir level 220.5M(723.5ft)
Live storage capacity 65.45TMCuft Live storage capacity 1.53Million
Mahi Hydel Power Station is R.V.U.N.Ltd. Major Hydel generating station situated
on river Mahi near Banswara city, comprising of 2-phases of installed capacity 140MW.
T/G supplier : BHEL (Bharat Heavy Electrical Ltd.)
HYDEL POWER STATIONS:-
Stage Unit No. Capacity(MW)
I 1 25
2 25 6.2.1986
II 1 45
S. No. Name of
Capacity Date of commissioning
2x0.4 MW Nov., 93
1x0165 MW March, 91
Fig.1.1-: Mahi Dam
Quick facts: Development of the multistate MAHI BAJAJ SAGAR Project started with
laying of the foundation stone in 1960. The project is named after national leader Shri
Jamnalal Bajaj. Major construction activities started in 1972 and the project was dedicated by
Prime Minister Indira Gandhi in Jan 1983. Releases from Mahi Reservoir are to Power House
I (2 x 25 MW), 8km from Banswara city, for sale into Rajasthan. The share of Gujarat state is
routed to Power House II (2x45 MW) 40km from Banswara town on the bank of the ANAS
River, a major tributary of the Mahi.
Mahi Hydel Power Station (140 MW):
Two power houses are operating under this power station having total installed capacity
of 140 MW (2x25 & 2x45 MW). During last three years there had been appreciable
increase in the power generation from this plant due to heavy rains in the region. However,
during the year 2003-04 heavy rains were witnessed in the catchment’s area of river Mahi
and 191.63 MU have been generated from this power station.
PLANT SPECIFICATION’S:- (2 X 25 MW)
Capacity of machines 2 x 25 MW.
Type of turbine FRANCIS TYPE [VERTICALSHAFT]
Date of commissioning of Unit I 22-1-1986
Date of commissioning of Unit II 06-2-1986.
Date of dedication of Nation 13-2-1986
Types of generator UMBRELLA Type.
Capacity of generator 27.778 MVA. At 11 kV, 0.9pf, lag
Rated Speed 150 rpm.
Turbine output at rated head of 40m 25.825 MW.
Capacity of power transformer 11/132 kV,31.5 MVA, 3-Ø.
Diameter of Penstock pipe 4.2m
Length of Penstock pipe 9m
Length of Tail Race tunnel 1462m
Tail Race level max. (from sea level) 238 m
Tail Race level min. (from sea level) 231 m
Capacity of Reservoir (at 281.5 m) 80 TMC
Fig:-1.2 Mahi Power House-I
ELEMENTARY DESCRIPTION OF “MAHI HYDRO POWER
Definition’s: A generating station which utilizes the potential energy of water at a high level
for the generation of electrical energy is known as a hydro electric power station.
It contains the following of the elements:-
A dam is barrier which stores water and creates water head. Dams are built of
concrete or stone masonry, earth or rock hill. The type of arrangement depends upon
the topography of the sight.
2. Penstock: Penstock is open or closed conduits which carry water to the turbines.
They are generally made of reinforced concrete or steel. Concrete penstock is suitable
for low or medium as greater pressure causes rapid deterioration of concrete.
Number of penstock 2
Diameter 4200 mm
Length 92m (each)
Intake level 250.32m
Outlet level 230.15m
Plates 16mm (thick.)
It is constructed behind the dam to store water. From here the water takes to turbine
through the penstock. The generation depends upon the head of the water behind dam.
Generally the required head is about 281m
4. Water turbines:
Water turbines are used to convert the energy of falling water into electrical energy.
Here the water turbine used is FRANCIS type turbine; it is a reaction turbine in which water
enters the runner partly with pressure energy and partly with velocity head.
5. Generating Units:
An alternator is connected with the shaft of turbine. The alternator used is of 3-phase salient
pole type, it is used for low speed. When shaft of water turbine starts to rotate then generator
also rotate and electricity is produced.
HYDROPOWER GENERATING STATIONS:- Hydropower generating stations convert
the energy of moving water into electrical energy by means of a hydraulic turbine coupled to
a synchronous generator. The power that can be extracted from a waterfall depends upon its
height and rate of flow. Therefore, the size and physical location of a hydropower station
depends on these two factors.
The available hydropower can be calculated by the following equation:
P = Available water power (kW)
q = Water rate of flow ( m3
h = Head of water (m)
9.8 = Coefficient used to take care of units.
The mechanical power output of the turbine is actually less than the value calculated
by the preceding equation. This is due to friction losses in the water conduits, turbine casing,
and the turbine itself. However, the efficiency of large hydraulic turbines is between 90 and
94 percent. The generator efficiency is even higher, ranging from 97 to 99 percent, depending
on the size of the generator.
Hydropower stations can be divided into three groups based on the head of water:
1. High-head development
2. Medium-head development
3. Low-head development
High-head developments have heads in excess of 300 m, and high-speed turbines are
used. Such generating stations can be found in mountainous regions, and the amount of
impounded water is usually small. Medium-head developments have heads between 30 m and
300 m, and medium speed turbines are used. The generating station is typically fed by a large
reservoir of water retained by dikes and a dam. A large amount of water is usually
impounded behind the dam. Low-head developments have heads fewer than 30 m, and low-
speed turbines are used. These generating stations often extract the energy from flowing
rivers, and no reservoir is provided. The turbines are designed to handle large volumes of
water at low pressure.
Fig-:1.3 One-line diagram of electric-power system
Fig-:1.4System of paralleled generators and transformer.
GENERATOR TYPES AND DRIVES
GENERATOR TYPES AND DRIVES:-
A large amount of electricity is required to power machinery that supplies to
The generator is the power source for the electrical system. A generator
operates most efficiently at its full-rated power output, and it is not practical to have one large
generator operating constantly at reduced load.
If#one#generator#is shut down because of damage or scheduled maintenance, there is still a
source of power for lighting until the defective generator has been repaired. In addition,
generators are widely spaced in the engineering spaces to decrease the chance
that all electrical plants would be disabled.
2.1 PERMANENT MAGNET GENERATOR (P M G):
The PMG provides a 3-Ø low voltage supply to the turbine governed at a frequency directly
related to the speed of the set. Provision has been made for synchronizing its voltage to that
of main generator during its excitation, if required for turbine governor operation.
PMG:-* Type- APV107M6 ,Pole- 40, Frequency- 50Hz,3-Ø
N=150 rpm, 1.0 KVA, 110V, star connected.
* Stator winding resistance between terminals at 20° at 20°c is 2-359 .
* Field winding resistance (at 20°c) 0- 80.
* Air gap 5 mm.
2.2 COLLECTOR RINGS AND BRUSH GEARS:
The collector rings are attached to and are insulated from the fabricated steel shaft
mounted on the spider. The leads from the collector to the field run along the shaft
and joined at suitable points to facilitate dismantling of the rotor. The brush gear for
the collector is mounted on insulated studs on the top bracket and is easily accessible
for inspiration purpose. A DC generator is a rotating machine that changes
mechanical energy to electrical energy. The power output depends on the size and
design of the dc generator. A typical dc generator is shown PMG:- 3-Ø Low voltage,
supply to turbine govern at a frequency directly related to the speed of the set.
Fig2.2-: D.C. Excitor(PMG)
AC generators are also called alternators. In an ac generator, the field rotates, and the
armature is stationary. To avoid confusion, the rotating members of dc generators are called
armatures; in ac generators, they are called rotors. The general construction of ac generators
is somewhat simpler than that of dc generators. An ac generator, like a dc generator, has
magnetic fields and an armature. In a small ac generator the armature revolves, the field is
stationary, and no commutator is required. In a large ac generator, the field revolves
and the armature is wound on the stationary member or stator. The principal advantages of
the revolving-field generators over the revolving-armature generators are two essential parts
of a dc generator: are as follows: The yoke and field windings, which are the load current
from the stator is stationary, and connected directly to the external circuit
the armature, which rotates without using a commutator.
ADV850M55, 27.778MVA, 25MW,11kV ±15% 3-Ø, 50 Hz, 1458 Amp., 0.9 p.f.
lag, 40 poles, 150 rpm., run away speed 350 rpm,11.55 kV max.-10.45 kV min.
* Air gap at pole center- 20 mm.
* Stator resistance per phase (at 20°c) - 0.0182
* Stator connection- STAR.
* Field winding resistance (at 20°c) -0.08534
* Flywheel effect of generator (GD)² –3.4*10ˆ6 kg m²
* Synchronize reactance (Xd) -0.789 p.v.
* Transient reactance Xd (sat.) – 0.265 p.v.
* Sub transient reactance Xd´ (sat.) – 0.183 p.v.
* S/C ratio – 1.33
* Max. I²t -154722/1968
* Excitation at no load rated voltage – 745 amp.
* Excitation at rated voltage -1217 amp.
* S/R brushes –total 30 no. (15 per ring)
* Brushes size – 25.4*38.1 mm.
* Brushes grade – Mogen EGO.
* Brushes force – 1.7 kg.
The stator core and winding are housed in a fabricated steel frame made in four sections. The
stator core is built of vanished segmental silicon steel laminations held in the frame by
dovetailed key bars, welded to the frame. The core is divided into the packets by narrow
radial steel spears, thus forming ventilating ducts leading from the stator core to the outside
periphery. The core is clamped between the bottom frame plate and segmental flanges on the
top by means of through bolts.
The stator winding is of the double layer three turned diamond pulled coil type,
assembled in open slots. Each coil is made of a number of insulated copper strands, with a
semi-rebel transposition in the end of Epoxy Movolac glass Mica paper tapes and flexible
Mica flakes taps in the end winding. All the coils are identical and interchangeable.
Temperature sensors of resistance type are inserted between coil sides in all three phases to
provide a continuous indication of coil temperature.
The rotor is of the friction held type and is built up of thin sheet steel laminations rigidly
clamped between steel and plates by a large number of through bolts. The clamping force in
the rim is such that the fractional forces between the laminations prevent them from slipping
relative to one another at any speed up to and including runway. The spider which supports
the rim is of fabricated steel construction with dished arms from a central hub. The lower
plane is machined to fit on top of the generator shaft. The driving torque is transmitted from
the shaft to the spider by radial keys. This method of construction permits the lifting of rotor
independent of the shaft. The weight of the rim and poles is supported on the heavy steel bars
welded on the outer end of the spider arms. Each pole carries a field coil made from straight
lengths of copper straps, dovetailed and brazed at the ends. At intervals down each coil, the
copper is increased in width to from fins for improved cooling. The inter turn insulation is of
epoxy resign bonded asbestos paper and the insulation between the coil and pole body is
epoxy glass fabric bored. In addition, each pole is equipped with six damper bars of circular
cross section made of high conductivity copper embedded in semi-closed slots in the pole
face, which are brazed at each end into copper punching clamped between pole and end
plates. Axial flow aero-fill type fans are mounted at each end of the rotor.
The generator has a closed circuit system of ventilation. Four twin sets of air coolers
are located at the corners of generator housing and the cooled air is discharged into the space
between the coolers and generator barrel from which part of this air will then return to fan
below the rotor through. The ducts in the foundation below the air coolers and the remainder
of the cooled air will return to the fan above the rotor. The air is then circulated through the
closed system by the combined action of the rotor poles and of the fans. The fan consists of a
large number of specially shaped Aluminum blades. The fans are surrounded by suitable
shaped air guides to ensure proper distribution of air. The inlet and outlet connections are
made to the bus pipes running around the machine.
3.4 AIR COOLER:
Each of the twin shades of air coolers consists of a nest of admiralty Brass cubes
wound with copper wire covered in a mild steel frame. The tube ends are roller expanded into
Brass plates on which are mounted the inlet and return end water boxes fabricated from mild
steel. The thickness of water box includes generous corrosion allowance and these are
internally subdivided to provide for multiple water passes for requisite flow pattern. The inlet
water box is filled with vent valve and with drain valve. The differential thermal expansion
between tubes and frame is absorbed by the action of neoprene packing between the frame
and the tube plate. The coolers are provided with support foot plates at the bottom for baling
down to the concrete foundations. A drip tray is provided below the cooler for collecting any
3.5 OIL COOLERS:
Each of the four plug-in-type oil coolers consists of a bank of 'U' shapes admiralty
Brass tube with Copper wire carried in a Steel frame with inlet end terminating in a rolled
Brass tube plate and the other 'U' end supported in a tube support fixed frame. The tube
rollers expanded into the tube plate. The water box which is of mild steel fabrication is belted
to the tube plate and amply proportional to reduce turbulence and pressure drop. The
differential thermal expansion between tube and frame is absorbed by the 'U' shaped tubes.
3.6 BEARINGS: - » Thrust bearing type –spring matters supported:
(No. of pads – 8)
» Guide bearing type – Pivoted type:
(No. of pads – 18)
» Normal operating temperature of bearing pads: 60°c
This type of Bearing is taking the whole machinery weight. It located at below the
rotor-stator frame housing of core &winding. It has construction of four sectional steel
3.6.1 SHAFT AND THRUST BLOCK:
The generator shaft and thrust block is a one piece steel forging. The bottom surface of
the thrust block forms rotating thrust bearing surface and is machined to be accurately
perpendicular to the axis of the shaft. It is ground to an optical finish. The journal surface is
machined and ground on the circumference of the thrust block. Over the top of support into
the reservoir. The air space above the oil surface is vented to atmosphere by means of an oil
vapor seal fitted to prevent the escape of oil vapor into the generator air circuit.
The bearing parts are self lubricated. The hot oil coming out of the bearing is cooled
by means of oil to water heat exchangers inserted into the bearing housing itself. The cool oil
will again sucked by rotating parts of the bearing. During starting when the hydro-dynamic
oil film is not likely to be formed, provision is made to inject oil at high pressure through the
thrust pads. The system is designed to come into operation automatically on starting and also
stopping the machine. The thrust bearing housing is designed to give the best possible
accessibility to the thrust bearing. Openings with removable covers are provided in the wall
of housing, so that the thrust pads and the thrust face can be inspected after the housing has
been drained and the rotor jacked up. A special tackle is provided to enable the thrust pads to
be withdrawn through the openings, if necessary. It is possible to inspect the pads and spring
units without dismantling the bearing or removing the generator rotor. It is used to prevent
the bubbling of rotor. It situated at D.C. exciter portion or PMG part.
3.6.2 THRUST AND GUIDE BEARING ASSEMBLY:
The thrust bearing of the spring supported type in which the stationary part
consists of white metal segmental thrust pads supported on mattress of helical springs. The
bearing operates immersed in oil.The thrust pads are stress relieved mild steel and are paced
with a high quality white metal. Each pad rests on pre-compressed spring finished to standard
overall length. The springs are assembled on a heavy steel spring plate which is fixed to the
bottom bracket by screws and dowels. The thrust pads are prevented from rotation by means
of pad stop secured to the spring plate. Radial movement of the pads is prevented by dog
clamps which also prevents them from rising with the thrust collar when jacking up the rotor.
The guide bearing comprises white metal faced pads arranged inside a cylindrical support in
the thrust bearing housing and bearing on a journal surface machined on the thrust collar.
Fig-3.2 GUIDE BEARING
A pivot bar double curvature is screwed to the back of each guide bearing pad, to
enable the pad to rock slightly to take up a suitable position and to facilitate the formation of
the oil film when running. The clearance between individual pads and pivot bar. The lower
part of the plates are permanently immersed, in oil and by centrifugal action, the oil is
pumped between the pads and spills.
3.6.3 THRUST AND GUIDE BEARING BRACKET:
The thrust and guide bearing bracket below the rotor is a fabricated bridge type
construction. It is designed to support the hydraulic thrust form the turbine in addition to the
weight of the rotating parts of the generator and turbine. The bracket arms rest on sole plates
grouted into the concrete foundation. Shims are provided for leveling purpose. Jack screws
are provided for using leveling and centering the whole bracket. Sheet covers are bolted to
the underside of the bracket seal and machine enclose from the turbine pit. The complete
bracket is designed such that it can be lifted through the stator bore.
3.6.4 TOP BRACKET:
The top bracket is also of fabricated steel construction and support the stationary
part of the PMG, brush gear and DC exciter. The bracket arm rest on machined facings at the
top of stator frame and shims are provided for leveling purpose. Jacking screws are provided
for adjusting the bracket during leveling and centering. The bracket also supports the steel
flooring on top generator pit.
3.6.5 BRAKES AND JACKS:
Polished steel segmental to the button of spider hub BRAKES &JACKS:-Brake air
pressure-4 kg/cm², recently -7 kg/cm².
Fig-3.3 BRACK & JACK
Fig- 3.4 OIL PRESSURE PUMP
The generator equipped with combined brake and jack units on the lower bearing bracket.
They are designed to operate on air pressure as brakes and with high pressure oil as jacks for
raising the rotor. A portable high pressure oil pump is furnished to supply the necessary high
pressure oil for jacking. In order that the rotor might be held in the raised position for an
extended period of time, a locking device is provided on the brake units. Each brake is
provided with a limit switch. The brakes are capable of bringing the unit to a dead stop from
33% speed within 5 min with the turbine gates closed and without field excitation.
3.6.6 H.S. LUBRICATION FOR THRUST BEARING:
It is large size of bearing at middle of the machinery. It connects to generator & turbine part.
It is oil filled for cooling purpose, it also used as lubricant. For oil film generate H.S. Lub
(High Sped Lubrication) motor.(H.S. Lub Motor figure) It is oil filled, water cooled, air
cooled fully packed chamber & oil pressure (40 kg.) adopted bearing. Maintain of 40 kg.
Pressure by two 5 HP (Horse Power), 120 kg. weighted Induction Motor’s. Each motor can
generate to 40kg pressure but both running at a time for safety point of view. Each 25-25
MW units we use that pair of motors different. They will run in whole generation of power.
Fig- 3.5 H.S. LUBRICATION MOTOR
H.S.Lub:- Oil film unit between the thrust body and the runner during start/stop. (Hydro-
dynamic oil film).This will take the whole weight & Balance of Shaft & connected
3.7 Analysis of industrial oils and greases:-
Many different oils and greases are used in industry, including fuel oils, engine oils,
lubricating oils and hydraulic oils. We analyses industrial oils from all sorts of plants,
including mechanical and rotating, moving plant / vehicles, hydraulic systems, pumps,
engines and bearings. When analyzing industrial oils, we first look at the quality of the oil to
ensure it is the correct oil and that it is doing its job. If not, we look at the potential to 'repair'
oil via additives, etc.Industrial oils can also be used to ascertain equipment condition,
maintenance requirements and diagnose faults. This is possible because oil, like blood, flows
freely in plants, picking up information on its journey, and oil analysis can unlock this
information. Techniques employed include microscopic analysis of wear metals and particles
in the oil, ICP (plasma), spectroscopy (emissions), infrared, ferro-graphy, etc.
Fig-3.6 GREES PRESSURE UNIT
Automatic Voltage Regulator
Automatic Voltage Regulator: [ A V R ]
AVR type V × B 32 automatically regulate the output voltage of the generator by providing
it with a controlled field supply via an exciter generator. The equipment is active over the
whole load range with negligible dead band. Other facilities in addition to generator output
voltage regulation. Manual control of excitation is available in the event of failure of
automatic control. The basic system as shown in figure consists of a closed loop generator
voltage control employing a thyristor converter. Output stage and an open loop manual
control of excitation and when necessary potentiometer 70 volts set the required generator
output voltage. The output of manual circuit is single phase full wave rectifier DC voltage
The auto control output is a full controlled thyristor converter fed on a single phase
AC supply. The converter output is the exciter field current. The converter output level is
determined by the thyristor control signal regenerated as already described. The manual
control stage is a diode bridge fed from a manually controlled single phase auto transformer
whereas of a step down transformer.
Fig4.1:- AVR Panel
4.1WORKING OF AVR:
Relays may be fitted with a variety of contact systems for providing electrical outputs for
tripping and remote indication purposes. The most common types encountered are as follows:
The contacts remain in the operated condition only while the controlling quantity is
applied, returning to their original condition when it is removed.
(b). Hand or electrical reset
These contacts remain in the operated condition after the controlling quantity is
removed. They can be reset either by hand or by an auxiliary electromagnetic element.
The majority of protection relay elements have self-reset contact systems, which, if so
desired, can be modified to provide hand reset output contacts by the use of auxiliary
elements. Hand or electrically reset relays are used when it is necessary to maintain a signal
or lockout condition. Contacts are shown on diagrams in the position corresponding to the
un-operated or de-energized condition, regardless of the continuous service condition of the
equipment. For example, an under voltage relay, which is continually energized in normal
circumstances, would still be shown in the de-energized condition. A 'make' contact is one
that closes when the relay picks up, whereas a 'break' contact is one that is closed when the
relay is de-energized and opens when the relay picks up.
A protection relay is usually required to trip a circuit breaker, the tripping mechanism
of which may be a solenoid with a plunger acting directly on the mechanism latch or an
electrically operated valve. The power required by the trip coil of the circuit breaker may
range from up to 50 watts for a small 'distribution' circuit breaker, to 3000 watts for a large,
extra-high voltage circuit breaker.
The relay may therefore energize the tripping coil directly, or, according to the coil
rating and the number of circuits to be energized, may do so through the agency of another
multi-contact auxiliary relay. The basic trip circuit is simple, being made up of a hand trip
control switch and the contacts of the protection relays in parallel to energize the trip coil
from a battery, through a normally open auxiliary switch operated by the circuit breaker. This
auxiliary switch is needed to open the trip circuit when the circuit breaker opens since the
protection relay contacts will usually be quite incapable of performing the interrupting duty.
The auxiliary switch will be adjusted to close as early as possible in the closing stroke, to
make the protection effective in case the breaker is being closed on to a fault.
Each of vertical shaft Francis type turbine comprises of a shaft tube, spiral casing ,and
stay ring, guide apparatus, shaft ,runner, guide bearings ,shaft seal and ancillary item, The
turbine equipment for each unit includes one electro hydraulic governor and oil pressure unit.
The machine has been designed to run has synchronous condenser also by depressing the
water in the runner chamber. Further descriptions of the major component of the turbine are
given as below.
5.1 DRAFT TUBE:
The draft tube consists of cone and knee liner. The draft tube cone consists of upper
cone and lower cone which is further split into equal halves for transportation facility. The
top segments of upper cone made of stainless steel plate and are welded.
To mild steel plate in the bottom portion. An allowance of 50 mm is kept in the total
height of the cone so as to maintain the elevation and level of total flange of upper cone. The
top flange of upper cone supports runner with shaft on it when it is decoupled from generator
shaft. A trapping for vacuum gauge is provided on it. Machine door is provided in upper cone
for providing access to runner is assembled condition.The test cock is provided below the
main whole door to check the water level before opening the main whole door. The draft
tube knee liner is of welded structural steel construction and rigidly held in concrete with
help of anchors and turn buck-less. Leveling bolts have been provided at the base of knee
liner for leveling it during installation. The top draft tube knee liner is welded to lower cone
at site. Drainage box with removable grill is provided on the draft tube concrete wall.
Drainage wall is connected to draft tube drain valve. It is placed in dewatering pit and can be
operated from floor at elevation 227.0 m.
The leakage water from shaft seal and middle journal of guide vane, is connected
inside to cover and drained through stay vane hales. Additional facility is provided for
automatic draining of top cover through ejector in case level of water rises in top cover. For
measuring top cover pressure a tapping is provided which is further connected to pressure
gauge. The pivot ring houses the lower bush for lower steam of guide vane, It is fabricated in
to pieces and attached to stay ring along guide vane P C D.
Top face of pivot ring is provided with belted stainless steel is provided with bolted
stainless steel plate. Lower labyrinth is also bolted with pivot ring. Four tapped holes are
provided, in pivot ring for measuring the labyrinth deceases. Hales are plugged with both
upper and lower labyrinth rings are machined to provide 1.2 to 1.5 mm clearance to runner.
The guide vanes are case solid from cast steel. The upper and middle journals sheets, kept
pressed by distance ring and cover plate against stainless steel sleeve bolted on shaft.The
branch pipe line also has flow switch with electrical contacts for low flow alarm and starting
inter lock and a tapping for pressure gauge. The shaft sealing can be inspected are repaired
when the runner is stationary by applying isolating seal located at the bottom of housing. It
comprises of a wedge sectioned, nitrite rubber ring normally held clear of the shaft.
5.2 SPIRAL CASING & INLET PIPE:
It is a welded construction from bailer quality steel plates. It is of logarithmic form
and circular cross section to maintain a constant velocity throughout its length. The plates are
gradually reduced in thickness to suit the load and shop welded to each other in group of two
to four segments considering ease of handling & transport limitations. Three make up
segments are supplied with fitting allowances which are to be welded after making proper
edge preparation for site welding as shown in dewatering.The spiral casing at inlet section is
welded to inlet pipe at site. The inlet pipe is provided with fitting allowances for welding it to
the penstock. The spiral casing has all necessary lifting lugs, feet, pads, eyes belts, and
jacking screw for leveling during erection.
The runner is cast stainless steel with stream lined vanes and complete with central
coupling flange for coupling with the shaft. The runner is provided with top and bottom
labyrinth rings. These rings are accurately machined to give 1.2 to 1.5 mm clearance with
labyrinth rings in top cover and pivot ring. The runner cone is fabricated from steel plates in
one piece. It has fit in the recess on the face of runner coupling flange held in position by
studs and nuts. On coupling flange 12 unloading holes are provided for balancing the
pressure on the upper & lower side of runner. The runner is statically balanced in the works.
Fig- 5.1 FRANCIS TURBINE “RUNNER”.
5.4 TURBINE SHAFT:
The turbine shaft is of forged steel with forged bearing skirt and coupling flanges. It is bored
throughout the length to ascertain soundness. The shaft is coupled to the generator shaft by
fitted bolts. The coupling holes in runner end of turbine shaft and runner are accurately
drilled using special jig to achieve interchangeability of runner.The bearings surfaces is fine
machined and polished and the shaft is aligned with generator shaft at works. A fine
machined band is provided on the shaft for checking alignment at site. Stainless steel sleeve
is bolted on the shaft for providing wearing surfaces for shaft seal.
5.5 SHAFT SEALING:
The shaft sealing prevents leakage of water through clearance between shaft and top cover. It
is located below turbine guide bearing and supported on the top cover by bolts. The sealing
elements are in two layers of sealing ring in the form of rubber. Applied when required
through isolating valve. The seal is released through isolating valve. The seal is released
through isolating valve.
5.6 GUIDE BEARING:
The guide bearing is pivoted pad type with self contained oil bath lubrication and external oil
coolers. It consists of 8 Babbitt lines pads arranged along the outer circumference of skirt of
the shaft .Each pad is adjustable by means of lockable screw bearing on thrust disc at the
back of pad and is kept pivoted against spherical ends of the studs. The bearing body is bolted
with top cover. The centre piece located inside shaft caller is built up by welding and
matching around the shaft. Under stationary condition, the pads are kept immersed in oil bath
approximately up to centre line of bearing when the shaft rotates, the oil flows through the
holes in the skirt due to centrifugal force and rises along the bearing body lubricating pads.
The guide bearings comprise of two chambers, chamber 1 is cool oil which is inside
the shaft and in lower portion. Chamber 2 is outside the skirt of shaft around the pads and it
consists of hot oil. The flow of oil from chamber 1 to chamber 2 takes place through hale
provided on the skirt of the shaft. The difference between the oil level in chamber 1 and
chamber 2 is the total energy available which assume the circulation of oil from chamber 2 of
guide bearing to the oil cooler and back from oil cooler remains in between to two oil level in
the chambers of guide bearing. The oil cooler is out side the generator barrel in a pit and is
connected to the guide bearing by oil pipes.
A visual oil level indicator and two level relays with electrical contacts are provided
on the oil tank for cooler for indicating the oil level in the guide bearing and for monitoring
high and low level the procedure for setting the levels is given on the above referred drawing.
The exact limit of oil level is to be decided after the mechanical run of the machine. Oil
levels on the coolers can be regulated by means of plugs provided in holes of skirt of shaft.
Guide bearing temperature is monitored by two thermometers with alarm and trip
contacts and two RTD’s for temperature recordings on the turbine gauge panel. RTD
monitors the guide bearing oil temperature. Pad and oil temperature are set to operate an
alarm at 5˚cabove normal and trip at 10˚c above normal temperature.
5.7 GUIDE VANE SERVOMOTERS:
Two servomotors are provided for turning the regulating ring. They are identified as:
1. Guide vane servomotor with stopper.
2. Guide vane servomotor without stopper.
Fig- 5.2 PRESSURE PUMP & SERVOMOTOR
Each servomotor comprises of, basically a cylinder housing a cast iron piston, with cast iron
piston rings to minimize the leakage thorough it. The end faces of the cylinder are closed
with the help of covers through one of which the sleeve is provided by rubber cup sealings.
The piston rod is made in two parts which are connected together with a turn buckle having
right hand possible to adjust the length of the piston rod by rotating the turn buckle. Lock
nuts are provided on its both ends for locking the position of turn buckle after its final setting.
Near the end of its stroke for closing, the piston is decelerated by throttling the oil through
special vanes. These vanes protected the system from impact and hydraulic hammer. The oil
drained into the tank of oil leakage unit. Emptying of servomotor is also carried out through
the oil leakage unit. A scale has been provided on servomotor with stopper on which the
servo stroke is indicated. One tapping each in opening and closing pipe line provided for
connecting to pressure gauge.
Stopper is provided on servomotor to hold the guide vanes is closed position. The
stopper is provided with contact switches to indicate closed or open position on the panel.
The stopper is designed for hydraulic load which may occur in closed position of guide vane.
No pressure is allowed inside the servomotor when stopper is closed.
5.8 FEED BACK CONNECTION:
The feedback mechanism is intended for the restoration of the governor main slide valve to
the mean position in the process of governing the guide vane servomotor. It consists of rope
drive, which transmits the moments of servomotor connecting rod through the system of
rollers to the main slide valve. On the feedback gear a motor switch is also installed.
The ejector system is used for automatic draining of top cover as an additional facility
over normal gravity draining through holes in two stay vanes. For this purpose high pressure
water tapped from penstock is passed through an ejector, which sucks water from top cover,
and discharge in gutter from where it goes in drainage pit.
5.10 FLOW METER:
Fig:- 5.3 Flow Meter
The measuring turbine discharge suitable tapping points are provided on spiral casing. The
general scheme for the measure meant for these measurements is as. The electronics
differential pressure transmitter with transducer is suitable for measuring static or dynamic
fluid pressure. The two pressure p1 and p2 are applied the diaphragm of the pressure
transducer. The differential pressure transducer converts the fluid pressure into electrical
signal utilizing for strain gauge, bonded on one side diaphragm, arranged in form of
5.11 VACCUM BREAKING VALVES:
These valves are mounted on top cover with an isolating valve. These will be use supplying
air under ATM pressure below the top cover to break the vacuum in case of sudden closer of
guide apparatus; these are spring loaded valve and oil pipe lines and periodic pumping of the
oil to the sump of oil pressure unit. The oil leakage unit consists of a tank and mounted on it
is a pump and electric motor in the tank a level relay is mounted for automatic controlling of
the pump and alarm check.
5.12 OIL LEAKAGE UNIT:
It is intended for collection of oil leakage from servomotors for draining oil from servomotor,
controlling valves and oil pipe lines and periodic pumping of the oil to the sump of oil
pressure unit. The oil leakage unit consists of a tank and mounded on it is a pump electric
motor in the tank a level relay is mounted for automatic controlling of the pump and alarm
Fig:- 5.4 Oil Leakage Unit
6.1 TRASNFORMER CONSTRUCTION:
There are two basic types of core assembly, core form and shell form. In the core
form, the windings are wrapped around the core, and the only return path for the flux is
through the center of the core. Since the core is located entirely inside the windings, it adds a
little to the structural integrity of the transformer’s frame. Core construction is desirable when
compactness is a major requirement. Figure Z-6 illustrates a number of core type
configurations for both single and multi-phase transformers.
Fig:- 6.1 Core Type Transformer
Fig:-6.2 Power Transformer
This manu-aclontaions a generalized overview of the fundamentals of transformer
theory and operation. The transformer is one of the most reliable pieces of electrical
distribution equipment. It has no moving parts, requires minimal maintenance, and is capable
of withstanding overloads, surges, faults, and physical abuse that may damage or destroy
other items in the circuit. Often, the electrical event that burns up a motor, opens a circuit
breaker, or blows a fuse has a subtle effect on the transformer. Although the transformer may
continue to operate as before, repeat occurrences of such damaging electrical events, or lack
of even minimal maintenance can greatly accelerate the evenhml failure of the transformer.
The fact that a transformer continues to operate satisfactorily in spite of neglect and
abuse is a testament to its durability. However, this durability is no excuse for not providing
the proper care. Most of the effects of aging, faults, or abuse can be detected and corrected by
a comprehensive maintenance#and#testing#program.
Fig.6.3 Transformer Tank With Vaccume Filling
6.2 COSERVATOR TANK:
Conservator or expansion type tanks use a separate tank to minimize the contact
between the transformer oil and the outside air (see figure). This conservator tank is usually
between 3 and 10 percent of the main tank’s size. The main tank is completely filed with oil,
and a small conservator tank is mounted above the main tank level. A sump system is used to
connect the two tanks, and only the conservator tank is allowed to be in contact with the
outside of transformer oil flow.
[A]. By mounting the sump at a higher level in the conservator tank, sludge and water
can form at the bottom of the conservator tank and not be passed into the main tank. The
level in the main tank never changes, and the conservator tank can be drained periodically to
remove the accumulated water and sludge.
Fig:-6.4 Conservator Tank In Transformer
[B]. Although this design minimizes contact with the oil in the main tank, the auxiliary tank’s
oil is subjected to a higher degree of contamination because it is making up for the expansion
and contraction of the main tank. Dangerous gases can form in the head space of the auxiliary
tank, and extreme caution should be exercised when working around this type of transformer.
The auxiliary tank’s oil must be changed periodically, along with a periodic draining of the
6.3 TRANSFORMER OIL TESTING:
Oil is analyzed from high voltage electrical systems and plant, including generators,
transformers, switchgear and cables that contain insulating oil. Aside from power stations and
electricity distributors, many large industrials have their own high voltage network that can
benefit from oil analysis. Train operators and airports are other examples of users.
Fig:-6.5 Transformer Oil Testing
Basic tests are used to look at the oil's quality; they include testing for water, acidity, electric
strength, resistively, color, fibers, odors and oxidation. To evaluate the condition of the plant
from the oil, more complicated techniques of high-pressure liquid and gas chromatography
are used to determine the combination of gasses and debris in the oil.
[A]. Insulating fluid plays a dual function in the transformer. The fluid helps to draw the heat
away from the core, keeping temperatures low and extending the life of the insulation. It also
acts as a dielectric material, and intensifies the insulation strength between the windings. To
keep the transformer operating properly, both of these qualities must be maintained.
[B].The oil’s ability to transfer the heat, or its “thermal efficiency,” largely depends on its
ability to flow in and around the windings. When exposed to oxygen or water, transformer
oils will form sludge and acidic compounds. Sludge deposits restrict the flow of oil around
the winding and cause the transformer to overheat. Overheating increases the rate of sludge
formation (the rate doubles for every 10 “C rise) and the whole process becomes a “vicious
[C]. The oil’s dielectric strength will be lowered any time there are contaminants. If leaks are
present, water will enter the transformer and condense around the relatively cooler tank walls
and on top of the oil as the transformer goes through the temperature and pressure changes
caused by the varying load. Once the water condenses and enters the oil, most of it will sink
to the bottom of the tank, while a small portion of it will remain suspended in the oil, where it
is subjected to hydrolysis. Acids and other compounds are formed as a by-product of sludge
formation and by the hydrolysis of water due to the temperature changes.
[D]. The two most detrimental factors for insulating fluids are heat and contamination. The
best way to prevent insulating fluid deterioration is to control overloading (and the resulting
temperature increase), and to prevent tank leaks. Careful inspection and documentation of the
temperature and pressures level of the tank can detect these problems before they cause
damage to the fluid. However, a regular sampling and testing routine is effective tool for
detecting the onset of problems before any damage is
The leads from the primary and secondary windings most be safely brought through
the tank to form a terminal connection point for the lie and load connections. The bushing
insulator is constructed to minimize the stresses at these points, and to provide a convenient
connection point. The bushing is designed to insulate a conductor from a barrier, such as a
transformer lid, and to safely conduct current from one side of the barrier to the other. Not
only must the bushing insulate the live lead from the tank surfaces, but it must also preserve
the integrity of the tank’s seal and not allow any water, air, or other outside contaminants to
enter the tank.
Fig:- 6.6 Bushing
[A]. There are several types of bushing construction; they are usually distinguished by
their voltage ratings, although the classifications do overlap:
1. Solid (high alumina) ceramic-(up to w5kv).
2. Porcelain-oil filled (25 to 69Kv).
3. Porcelain-compound (epoxy) filled (25 to 69kV).
4. Porcelain--synthetic resin bonded paper-filled (34.5 to 115kV).
5. Porcelain-oil-impregnated paper-filled (above 69kV, but especially above 275kv).
[B]. For outdoor applications, the distance over the outside surface of the bushing is
increased by adding “petticoats” or “watersheds” to increase the creep age distance between
the line terminal and the tank. Contaminants will collect on the surfaces of the bushing and
form a conductive path. When this creep age distance is bridged by contaminants, the voltage
will flashover between the tank and the conductor. This is the reason why bushings must be
kept clean and free of contaminants.
[C]. Transformer bushings have traditionally been externally clad in porcelain because of its
excellent electrical and mechanical qualities. Porcelain insulators are generally oil-filled
beyond 35 kV to take advantage of the oil’s high dielectric strength. There are a number of
newer materials being used for bushings, including: fiberglass, epoxy, synthetic rubbers,
Teflon, and silica compounds. These materials have been in use for a relatively short tile, and
the manufacturer’s instructional literature should be consulted when working with these
[D].Maintenance. Bushings require little maintenance other than an occasional cleaning and
checking the connections. Bushings should be inspected for cracks and chips, and if found,
should be touched-up with Glyptic paint or a similar type compound. Because, bushings are
often called on to support a potion of the line cable’s weight, it is important to verify that any
cracks have not influenced the mechanical strength of the bushing assembly.
[E]. Testing. Most bushings are provided with a voltage tap to allow for power factor testing
of the insulator. If they have no tap, then the power factor test must be performed using the
“hot collar” attachment of the test set. The insulation resistance-dielectric absorption test can
also be performed between the conductor and the ground connection.
6.5 LIGHTNING (SURGE) ARRESTERS:
Most transformer installations are subject to surge voltages originating from lightning
disturbances, switching operations, or circuit faults. Some of these transient conditions may
create abnormally high voltages from turn to turn, winding to winding, and from winding to
ground. The lightning arrester is designed and positioned so as to intercept and reduce the surge
[A]. Construction. Lightning arresters are similar to big voltage bushings in both appearance
and construction. They use a porcelain exterior shell to provide insulation and mechanical
strength, and they use a dielectric filler material (oil, epoxy, or other materials) to increase the
dielectric strength (see Figure). Lightning arresters, however, are called on to insulate normal
operating voltages, and to conduct high level surges to ground. In its simplest form, a lightning
arrester is nothing more than a controlled gap across which normal operating voltages cannot
jump. When the voltages exceeds a predetermined level, it will be directed to ground, away
from the various components (including the transformer) of the circuit. Some arresters use a
series of capacitances to achieve a controlled resistance value, while other types use a dielectric
element to act as a valve material that will throttle the surge current and divert it to ground.
Fig-: 6.7LIGHTINING ARRESTOR
[B]. Mechanism.Lightning arresters use petticoats to increase the creep age distances across
the outer sm. face to ground. Lightning arresters should be kept clean to prevent surface
contaminants from forming a flashover path. Lightning arresters have a metallic connection
on top and bottom. The connectors should be kept free of corrosion.
[C]. Testing. Lightning arresters are sometimes constructed by stacking a series of the
capacitive/dielectric elements to achieve the desired voltage rating. Power factor testing is
usually conducted across each of the individual elements, and, much like the power factor test
on the transformer’s windings, a ratio is computed between the real and apparent current
values to determine the power factor.
6.6 CURRENT TRANSFORMER’S:
Fig:-6.8 Current Transformer
(B) TOP VIEW OF C.T.
(C) POSITION ON TRANSFORMER (Location)
(D) C.T. OPEN FOR MENTINANCE
The primary winding of a current transformer is connected in series with the power
circuit and the impedance is negligible compared with that of the power circuit. The power
system impedance governs the current passing through the primary winding of the current
transformer. A current transformer is specified as being 600 A, 5 A class C200. Determine its
characteristics. This designation is based on ANSI Std. C57.13–1978. 600 A is the
continuous primary current rating, 5 A is the continuous secondary current rating, and the
turns ratio is 600/5=120. C is the accuracy class, as defined in the standard. The number
following the C, which in this case is 200, is the voltage that the CT will deliver to the rated
burden impedance at 20 times rated current without exceeding 10 percent error. Therefore,
the rated burden impedance is This CT is able to deliver up to 100 A secondary current to
load burdens of up to 20 with less than 10 percent error. Note that the primary source of error
is the saturation of the CT iron core and that 200 V will be approximately the knee voltage on
the CT saturation curve.
A typical wye CT connection is shown in Fig. The neutral points of the CT’s are tied
together, forming a residual point. Four wires, the three-phase leads and the residual, are
taken to the relay and instrument location. Additional relays are often connected in the
residual, as the current in this circuit is proportional to the sum of the phase currents.
Fig:-6.9 Typical setup for wye-connected CT’s protecting a line or piece of equipment
6.7.1 WATER COOLING(SPRINKLER):-This type of cooling system pressure pumps
used for water pressure flow. At cooling place use pipe lines with sprinkler equipment.
Fig:-6.10 Water Sprinkler System For Cooling Substation
6.7.2 CO2 SPRINKLER:- This system use at around the transformer for fir-fighting.
The color of the pipes is Yellow painted. At nosel of the pipe, glass flask filled with
either. When burn or temperature rise of the transformer flask will blast and CO2
spray on transformer for safety.
FIG 6.11-: CO2 SPRINKLER
Circulate cooling water for coolers and condensers,#pump#out bilges,#transfer fuel
oil,supply water#to the distilling plants, and are used for many other purposes. The operation
of the plant and of almost all the auxiliary machinery depends on the proper operation of
pumps Although most plants have two pumps, a main pump and a standby pump, pump
failure may cause failure of an entire power plant. If they fail, the power plant they serve also
fails. In an emergency,#pump#failures#can prove disastrous.#Maintaining pumps in an
efficient working order is a very important task of the engineering department. The pumps
with which you are primarily concerned are used for such purposes as circulating lubricating
(lube) oil to the bearings and gears, supplying water for the coolers, transferring fuel oil to
various storage and service tanks. Centrifugal pumps of various sizes are driven by electric
motors to move different types of liquid. The fire pump and water service pump are two
examples of this type of pump.
Centrifugal pumps may be classified in several ways. A single-stage pump has only
one#impeller,#a multistage pump#has two or more#impellers housed together#in one#casing.
In a#multistage#pump, each impeller usually actsseparately, discharging to the suction of the
next-stage impeller. Centrifugal pumps are also classified as horizontal or vertical, depending
on the position of the pump shaft. Impellers used in centrifugal pumps may be
classified as single-suction or double-suction, depending on the way in which liquid enters
the eye of the impeller. The double-suction arrangement has the advantage of balancing
the end thrust in one direction with the end thrust in the other direction. Impellers are also
classified as CLOSED or OPEN. A closed impeller has side walls that extend from the eye to
the outer edge of the vane tips; an open impeller does not have side walls.
CENTRIFUGAL PUMPS SPECIFICATION:-
Fig:- 7.2 CENTRIFUGAL PUMPS SPECIFICATION
FIG-:8.1 SWITCH YARD
An isolator is one which comes brake the electric circuit when the circuit to be
switched on no load these are normally used in various circuits for the purpose of isolation
for a certain portion required for maintenance.
SWITCHING ISOLATORS:- They are capable of-
1) Interrupting transformer magnetizing currents.
2) Interrupting charging currents.
3) Load transformer switching.
The main application is in connection with feed or bank transformer feeders. This unit makes
it possible to switch out one transformer while the other is on still load.
8.2 CIRCUIT BREAKERS:-
A circuit’s breaker is a device that can make or break circuit on load & even on faults,
this is most important and heavy duty equipments moving utilized for protection of various
circuit and separation at load. The circuit breaker is a switch yard is installed on movable. It
is tripped by relay of by a manual signal. The CB used in switch gear. now a days are
minimum oil circuit breaker, oil circuit breaker, vacuum CB and other types are used in the
switch gear the required from the CB is such that it should be compare to
* carry continuously minimum current of the system at P.B. of installation.
* make & break circuit under normal working condition.
8.2.1 OIL CIRCUIT BREAKERS:
Oil circuit breakers are used for transmission voltages up to 300kV, and can be
subdivided into the two types: ‘bulk oil’ and ‘small oil volume’. The latter is a design aimed
at reducing the fire hazard associated with the large volume of oil contained in the bulk oil
breaker. The operating mechanisms of oil circuit breakers are of two types, ‘fixed trip’ and
‘trip free’, of which the latter is the most common. With trip-free types, the reclosing cycle
must allow time for the mechanism to reset after tripping before applying the closing
impulse. Various types of tripping mechanism have been developed to meet this requirement.
The three types of closing mechanism fitted to oil circuit breakers are:
CB’s with solenoid closing are not suitable for high-speed auto-re-close due to the
long time constant involved. Spring, hydraulic or pneumatic closing mechanisms are
universal at the upper end of the EHV range and give the fastest closing time. Shows the
operation times for various types of EHV circuit breakers, including the dead time that can be
8.2.2 AIR BLAST CIRCUIT BREAKERS:
Air blast breakers have been developed for voltages up to the highest at present in use on
transmission lines. They fall into two categories:
A . Pressurized head circuit breakers.
B . Non-pressurized head circuit breakers. In pressurized head circuit breakers,
compressed air is maintained in the chamber surrounding the main contacts. When a tripping
signal is received, an auxiliary air system separates the main contacts and allows compressed
air to blast through the gap to the atmosphere, extinguishing the arc. With the contacts fully
open, compressed air is maintained in the chamber. Loss of air pressure could result in the
contacts re-closing, or, if a mechanical latch is employed, re-striking of the arc in the de-
pressurized chamber. For this reason, sequential series isolators, which isolate the main
contacts after tripping, are commonly used with air blast breakers. Since these are
comparatively slow in opening, their operation must be inhibited when auto-re-closing is
required. A contact on the auto-re-close relay is made available for this purpose. Non-
pressurized head circuit breakers are slower in operation than the pressurized head type and
are not usually applied in high-speed re-closing schemes.
8.2.3 SF6 CIRCUIT BREAKERS:
Most EHV circuit breaker designs now manufactured use SF6 gas as an insulating and
arc-quenching medium. The basic design of such circuit breakers is in many ways similar to
that of pressurized head air blast circuit breakers, and normally retains all, or almost all, of
their voltage withstand capability, even if the SF6 pressure level falls to atmospheric
Sequential series isolators are therefore not normally used, but they are sometimes
specified to prevent damage to the circuit breaker in the event of a lightning strike on an open
ended conductor. Provision should therefore be made to inhibit sequential series isolation
during an auto-re-close cycle.
FIG-:8.2 SF6 CIRCUIT BREAKER
8.3 BUS BAR:
Bus bars are defined as conductors which several incoming and outgoing lines are
connecting. This is essential component of switch gear. These are made of copper or
Aluminum. The bus bar section of high boring unit is connected by aluminum link. The
incoming and outgoing cables are provided with cables vanes, which welded steel
conductors. C.T. and P.T. used are of ring type they are fitted or insulation the installation
provided by cast-epoxy resin fitting.
8.4 POTENTIAL TRANSFORMER:
Transformer for measurement the voltage is called “Voltage transformer” or P.T. as
short. For the measurement of voltage the primary is connected to the voltage being measured
and the secondary to voltmeter. The potential transformer step down’s the voltage to level of
C.T. is never open circuit.
P.T. is never short circuit.
Infect instrument transformer are so important for insulating and range
extension purpose that it is difficult to imagine the operation of A.C. system without
There is low power consumption in metering circuit. the metering circuit is isolates
from the high power circuit hence insulation is no problem and the safety is assumed for the
8.5 Power Line Carrier Communications Techniques [PLCC]:
Where long line sections are involved, or if the route involves installation difficulties,
the expense of providing physical pilot connections or operational restrictions associated with
the route length require that other means of providing signaling facilities are required. Power
Line Carrier Communications (PLCC) is a technique that involves high frequency signal
transmission along the overhead power line. It is robust and there fore reliable, constituting a
low loss transmission path that is fully controlled by the Utility.
FIG-:8.3 PLCC EQUIPMENT
High voltage capacitors are used, along with drainage coils, for the purpose of
injecting the signal to and extracting it from the line. Injection can be carried out by
impressing the carrier signal voltage between one conductor and earth or between any two
phase conductors. The basic units can be built up into a high pass or band pass filter.The
single frequency line trap may be treated as an integral part of the complete injection
equipment to accommodate two or more carrier systems. However, difficulties may arise in
an overall design, as, at certain frequencies, the actual station reactance, which is normally
capacitive, will tune with the trap, which is inductive below its resonant frequency; the result
will be a low impedance across the transmission path, preventing operation at these
frequencies. This situation can be avoided by the use of an independent 'double frequency' or
The coupling filter and the carrier equipment are connected by high frequency cable
of preferred characteristic impedance 75 ohms. A matching transformer is incorporated in the
line coupling filter to match it to the HV cable. Surge diverters are fitted to protect the
components against transient over voltages. The attenuation of a channel is of prime
importance in the application of carrier signaling, because it determines the amount of
transmitted energy available at the receiving end.
START AND STOP SEQUENCE
OPERARING INSTRUCTIONS FOR MAHI UNITS:
Before starting the units the following precautions must be checked and ensured:-
1. AC-DC supply to control panels is on and all indicating lamps are healthy.
2. Draft tube gates are in fully raised portion and supported properly.
3. Penstock gates is fully raised and penstock gates ' opened' indication appearing on
UCB and control desk.
4. Draft tube drainage and dewatering system is healthy.
5. Cooling water system is charged and cooling water pressure after pressure reduces
is 2/3 Kg/Cm2.
6. H.P. air supply system is healthy and pressure reduce is 42Kg/Cm2.
7. L.P. air supply system for brakes and turbine seal system is healthy and pressure in
L.P. air receiver is 5.0 Kg/Cm2.
8. Oil pumping unit system is operating and auto mode and maintaining normal
working pressure 37-40 Kg/Cm2.
9. ESV for emergency closing of guide apparatus is healthy and in reset position.
10. Air level in OPU sump and pressure vessel is normal.
11. Governor is in 'auto' mode.
12. OLU is healthy and operating on auto/manual mode.
13. CO2 fire extinguishing system is healthy and operating.
14. CGL system is healthy.
15. Oil level in all the bearing is normal.
16. Pressure in casing is normal i.e. 08.50Kg/Cm2.
17. Cooling water to turbine guide bearing is 'ON' and flow normal.
18. Clean water supply to turbine ceiling is on and flow normal.
19. Air pressure for isolating seal normal and seal disengaged.
20. Servomotor lock is raised.
21. Indication appearing on UCB and governor, before raising servomotor lock
ensures that governor limiter position is below 'Zero' -'ON'.
22. RTDs and TSDs are operative.
23. Cooling water to generator bearings are stator air cooler is 'ON' and flow normal.
24. Brake air pressure is normal to 45Kg/Cm2.
25. Brakes are released and brake relieves indication appearing on UCB.
26. All electrical and mechanical protection relays are reset condition and no any fault
abnormal indication appearing on communication panel and control panel.
27. PMGs switch (for governor supply) and station DC supply switch in electrical
cabinet of EHG is switch 'ON'.
28. Ensure generation circuit (GCB) and field circuit breaker (FCB) in 'OFF' position.
29. Ensure cooling water supply, pre-start check 'OK' unit ready to start indication
appearing on UCB.
-: AND UNIT IS READY TO START :-
SYNCHRONISING OF TWO ALTERNATORS:
For proper operation of alternators for synchronizing the following conditions must be
The incoming feed alternator must be it's terminal Voltage, Same as bus bar
The speed of incoming machine must be such that it's frequency must be equal
to PN/120 equals to bus bar frequency
The phase of the alternator voltage must be intended with the phase of the bus
bar Voltage. It means that the switch must be closed at instant when two voltages have direct
The following steps have to be taken:-
1. Put check synchronizing switch (at bus coupler relay panel unit) at 'Synch In'
2. Select Sync switch SS-1 (at control desk) at manual mode and put on the
synchronous cope ON/OFF switch SS-3 (on Sync cope swing panel).
3. Compare and match Voltage and frequency by adjust AVR control switch and
speed setting case load switch.
When the synchronous scopes pointer is rotating clockwise and it is just crossing 12
O'clock position and synchronizes lamp can synchronoscope and sync panel glowing bright
close the MCB.
4. Put of SS-1 on Control desk and SS-3 on synchroscope.
5. Now increase load on unit by raising gate setting switch C4-4 (control desks up to
6. Loading should be done by the raise/lower switch for speed/load setting on control
desk. If the balance current exceeds, the limit should be raised suitably by switch. If full load
is already reached. Lower by switch, whenever balance current exceeds the depending on the
grid frequency condition.
1. Reduce load to about 2Mw by gate setting.
2. Trip generator circuit breaker.
3. Hang over LT supply to station supply (LT panel at EL240)
4. Bring excitation to zero level.
5. Trip field circuit breaker.
6. Give unit stop command by IC0.
7. Watch application of break around 15Hz and starting of HS lab at about 35 Hz.
8. Gate limiter control switch should be left on AUTO mode for the next starting
9. Observe the stopping of HP cubical when speed comes to zero (If it does not stop in
auto mode put it OFF) Brakes will also be released.
10. Put guide vein lock in.
11. Close cooling water supply to turbine bearing and gland generator bearing and air
coolers transformers oil coolers after 30 min of stopping the unit.
Practice makes a man perfect.A student gets theoretical knowledge from classroom
and gets practical knowledge from industrial training. When these two aspects of theoretical
knowledge and practical experience together then a student is full equipped to secure his best.
In conducting the project study in an industry, students get exposed and have
knowledge of real situation in the work field and gains experience from them. The object of
the summer training cum project is to provide an opportunity to experience the practical
aspect of Technology in any organization. It provides a chance to get the feel of the
organization and its function.
I have privilege taking my practical training at " MAHI HYDRO POWER HOUSE - I
" where power generation takes place in bulk. The fact that Hydro energy is the major source
of power generation itself shows the importance of Hydro power generation in India
In Hydro power plants, the potential energy of water is utilized by the turbine to rotate
coil at high torque. The torque so produced is used in driving the coil coupled to generators
and thus in generating ELECTRICAL ENERGY.
1.PLANT RECORD (Notes) : Files
2.A COURSE IN ELECTRICAL POWER : J.B. Gupta
3.PROTECTION OF POWER SYSTEM : B. Ram
4.POWER TRANSFORMER : Tata Magr. Hill
5.ELECTRICAL ENGINEERING : Tata Magr. Hill
6. MY GUIDE & FACULTY MEMBER
7. GENERATION OF ELECTRICAL ENERGY : B.R. Gupta