ESSAR internship report

1 | P a g e
INDUSTRIAL TRAINING REPORT
On
77 MW POWER-PLANT & PROTECTION
At
Vadinar Power Company Limited,
ESSAR, Jamnagar
During
8th
Dec, 2014 to 10th
Jan, 2015
PREPARED BY:-
 Dipen Kantariya (12DEE007)
 Akshay Nada (12DEE067)
 Milan Patel (12DEE048)
 Denish Boda (12DEE055)
GUIDED BY:-
Mr. Alpesh Dhamsania Prof. Dhirajlal Khokhani
Manager, HOD, Electrical Department,
Electrical Department, Institute of Diploma Studies,
VPCL, Jamnagar Nirma University, Ahmedabad

2 | P a g e
CERTIFICATE
This is to certify that
Mr. Dipen S. Kantariya (12DEE007)
Mr. Akshay V. Nada (12DEE067)
Mr. Milan R. Patel (12DEE048)
Mr. Denish R. Boda (12DEE055)
Students of 6th semester,
Has satisfactorily completed the Industrial Training
At Vadinar Power Company Limited, ESSAR – Jamnagar
During 8th Dec, 2014 to 10th Jan, 2015
Date of Submission :- 21/1/2015
Head of Department

3 | P a g e
ACKNOWLEDGEMENT
We would like to extend our sincere thanks to Mr. K.B. Makadia (Plant Head) for
allowing us to pursue our training at VPCL.
We are equally grateful to Mr. Lalit Jethwa (HOD-Electrical Department) for the
encouragement and support and to make our training successful and fruitful one.
We are also thankful to Mr. Alpesh Dhamsania (Manager) for providing guidance and
giving us his valuable knowledge through-out the training.
We would like to deeply tender gratitude to all the staff and employees of VPCL who
have directly or indirectly contributed in our industrial training.
We are also thankful to Prof. Dhirajlal Khokhani (HOD-Elect. Dept. IDS, NU) for
providing continuous guidance and support from the institute level.
We are also thankful to Institute of Diploma Studies, Nirma University for providing us
such a nice platform.

4 | P a g e
TABLE OF CONTENTS
 TITLE PAGE...............................................................................................1
 CERTIFICATE.............................................................................................2
 ACKNOWLEDGEMENT..............................................................................3
 INTRODUCTION TO ESSAR……………...........................................................7
 INTRODUCTION TO VPCL………………..........................................................8
 POWER DISTRIBUTION DIAGRAM OF VPCL...............................................9
 INTRODUCTION TO 77 MW POWER PLANT..............................................10
 SLD OF 77 MW POWER PLANT.................................................................11
 GENERATOR DESCRIPTION…………….....………….…...…….…....................….12
1) General.................................................................................................................12
2) Stator frame and core..........................................................................................12
3) Stator winding.......................................................................................................13
4) Rotor construction................................................................................................13
5) Rotor winding........................................................................................................14
6) Terminals..............................................................................................................14
7) Cooling air circuit..................................................................................................14
8) Accessories............................................................................................................15
9) Generator excitation system.................................................................................16
 NAME PLATE DETAILS.............................................................................18
1) Steam turbine generator......................................................................................18
2) Generator transformers........................................................................................19
3) Unit auxiliary transformers...................................................................................20
4) 6.6/0.435 KV transformer……………………...............................................................21

5 | P a g e
5) Auxiliaries operated on 6.6 KV..............................................................................22
6) HHP motor............................................................................................................23
7) HP motor...............................................................................................................24
8) FD fan motor.........................................................................................................25
 INTRODUCTION TO PROTECTION OF GENERATOR...................................26
1) Why protection of generator is required? ...........................................................26
2) Abnormalities in generator...................................................................................27
3) Faults in generator................................................................................................27
4) Generator protection system................................................................................28
5) Legends.................................................................................................................29
 TYPES OF GENERATOR PROTECTION.......................................................30
1) Differential protection..........................................................................................30
2) Negative phase sequence protection...................................................................31
3) Balanced earth fault protection............................................................................32
4) Over-current protection........................................................................................33
5) Unbalanced loading protection............................................................................34
6) Stator inter-turn protection..................................................................................35
7) Synchro-check relay..............................................................................................36
8) Volts/Heartz protection........................................................................................37
9) Over/Under frequency protection........................................................................37
10) Over voltage protection........................................................................................37
11) Under voltage protection......................................................................................38
12) Reverse power protection....................................................................................38
13) Field failure protection.........................................................................................38

6 | P a g e
14) Rotor earth fault protection.................................................................................39
15) Voltage unbalance protection..............................................................................39
16) Stator unbalanced current protection..................................................................39
17) Loss of synchronism protection............................................................................40
18) Breaker failure protection....................................................................................40
 CONCLUSION..........................................................................................42
 REFERENCES...........................................................................................43

7 | P a g e
INTRODUCTION TO ESSAR
The Essar mainly deals with refining of crude oil for arriving at final products like Motor
Spirit, High Speed Diesel, Naphtha, Superior Kerosene Oil, Liquefied Petroleum Gas, Aviation
Fuel etc. It operates 6 refineries all over India and has a separate division for Marketing,
Pipeline and Research and Development.
This training report covers the working of the power plants that is operated by VPCL.
The fulfilment of uninterrupted supply of steam and power is to be maintained by VPCL.
However the utilities like Water treatment plant and Switchyard are maintained by MRSS (Main
Refinery Sub-Station).

8 | P a g e
INTRODUCTION TO VPCL
Vadinar Power Company Ltd. is a company under Essar oil limited whose main function
is to maintain uninterrupted steam and power supply to the Essar refinery.
There are mainly three units:
1) 77 MW (2 x 38.5 MW)
Fuel : HFO (Heavy Furnace Oil), LDO (Light Diesel Oil)
Prime Mover : Steam Turbine
2) PHASE : 1 - 220 MW (2 x 110 MW)
Fuel : Naphtha Gas
Prime Mover : Gas Turbine
3) PHASE : 2 - 325MW (2 X 105 MW, 1 X 92.8MW)
Fuel : Coal
Prime Mover : Steam Turbine

9 | P a g e
POWER DISTRIBUTION DIAGRAM OF VPCL

10 | P a g e
INTRODUCTION TO 77 MW POWER PLANT
•Type of Plant : Cogeneration Plant
•Plant Generating Capacity : 77 MW
•Number of Steam Turbines : 2 (Two)
•Capacity : 2 x 38.5 MW
•Number of Boilers : 3 (Three)
•Capacity of Boilers : 175 TPH (Tons per hour)
•Type of Fuel Fired : Heavy Furnace Oil / Refinery Fuel Gas
•Condenser Cooling : Sea Water / Narmada Reservoir
There are three boilers for producing steam to meet the power generation and steam
requirement of Refinery. There are two turbo-generators of 38.5 MW each and two number of
turbines. The steam pressure in each in of the turbine is 63.24 kg/cm2
.
In normal plant operation, all the three boilers will operate at 100% maximum
continuous rating (MCR) along with two STGs at full load. Boilers are designed to operate under
by firing any or a combination fuel oil or fuel gas. Start-up power required for power plant and
utilities will be drawn from the grid through a 220 kV switchyard. HHP Steam generated in the
power plant is used to run two steam turbines and other steam turbine driven auxiliaries like
FD fan, HHP boiler feed water pump, HP feed water pump, condensate extraction pump & fuel
oil feed pump.
Under the normal operating conditions, both the STGs will remain in synchronism with
the grid. The power generated from generators at 11 kV is stepped up to 33 kV by 50 MVA
Unit Transformers provided for each generator in CPP. Generated power is fed to 33 KV bus
in Main Sub Station. Grid supply is available at 220kV and is stepped down to 33kV by 220/33kV
stepped down transformer. 33kV bus in the main substation is the synchronization bus. Power
at 33 kV is supplied to various substations in the refinery through two parallel feeders for
each substation.

11 | P a g e
SLD OF 77 MW POWER PLANT

12 | P a g e
GENERATOR DESCRIPTION
 General:
The turbo-generator is indoor type, single end drive, stationary armature & revolving field
with cylindrical rotor and brushless excitation complete with permanent magnet pilot exciter
and rotating rectifier assembly. It has totally enclosed water-to-air cooled (TEWAC) heat
exchanger mounted on the top of the stator frame. The cooling air required for generator
cooling is circulated by fans located at both the ends of the generator rotor.
 Stator Frame and Core:
The stator frame is an integrated box like structure combining wrapper plates, main
structural webs with longitudinal distance pieces and bars carrying the core. It also includes end
winding compartments and air inlet compartments at each end. Substantial trunnions are
provided for lifting and suitable jacking points are also provided.
The core is built up from segmental laminations of low loss, high permeability, high silicon
content steel, which are located by dovetail key bars, bolted to the stator frame. All laminations
are debarred and insulated with varnish on both sides to reduce eddy current losses to a
minimum and to ensure that these losses are maintained at a low level in service. The stator
core is hydraulically pressed at several stages during assembly to ensure a tight core; the
pressure applied being carefully controlled. The laminations are clamped between two heavy
section pressure plates which are located by circular keys.
The natural frequency of the frame and core is different from the frequency of magnetic
excitation. Radial ventilating ducts are formed in the stator core by ‘H’ section steel spacers.
Uniform distribution of cooling air is ensured by suitable axial sub-divisions of the frame.

13 | P a g e
 Stator Winding:
The stator winding is double layer diamond type, with the half coils completely formed and
insulated before insertion in the open type stator slots. The half coils are built up from a
number of insulated copper strips which are transposed in a regular manner to reduce eddy
current losses to a minimum. After forming the copper strips to the shapes required by the
transposition, they are placed together and a synthetic resin is applied to produce a void free
conductor which is then insulated with layers of mica glass tape bonded with epoxy resin to
form a half coil. During all taping operations, special care is taken to see that no voids are left in
the winding. The tape is wrapped on to the conductors whilst they are heated by passing
current through them. The completely insulated half coils are pressed to size over the straight
portion in heated hydraulic press. Colloidal graphite is then applied to the outside surface of
the coil over the length which will be contained in the slot to form a conducting coating for the
prevention of corona discharge in the slot.
Temperature detectors are embedded in the slots at selected points for connection to
suitable indicating instruments to measure the internal temperatures. Likewise detectors are
fitted in the inlet and exhaust air circuits.
 Rotor Construction:
The rotor consists of a solid forging of high quality alloy steel, the physical analysis of the
material and also the forging and heat treatment processes being carefully controlled by the
steel makers, and subjected to expert metallurgical inspection at every stage.
Axial slots are accurately machined in the periphery of the forgings, suitably shaped and
disposed to carry the windings and retaining wedges. Rotor ventilation channels are machined
between the slots containing the rotor winding. Where ever necessary, cross slots are
machined in the pole faces to avoid double frequency vibration.

14 | P a g e
Axial flow fans made up of aluminium alloy are mounted at each end of the rotor to
circulate cooling air through the generator. Axial and radial ventilating holes are provided in the
rotor core for effective cooling.
The rotor is fitted with a shaft earthing brush made up of copper to ground the induced
circulating current and static charges and ultimately to avoid the pitting of the bearings.
 Rotor Winding:
The rotor winding is manufactured from high conductivity silver copper alloy bent on edge
and pre-formed before winding.
The completed winding is electrically heated and pressed to size by heavy steel clamping
rings. An aluminium damper is fitted below the end caps.
The rotor leads are brought out to the main exciter through a hole bored axially through the
exciter end of the rotor shaft. The completed rotor is balanced and is tested for over speed to
20% above its rated speed for two minutes.
 Terminals:
The terminals are in the form of six epoxy bushings brought out on the underside of the
stator at the exciter end of the machine. The terminals are suitable for non-segregated bus duct
connections.
 Cooling Air Circuit:
Cooling air is driven round the generator by axial fans provided at both sides of the
generator rotor. Cool air is drawn into each end of the generator stator and will then pass
through the air gap between the stator core and rotor body, behind the stator end windings
and through inter slot ducts between the winding slots in the rotor body. The air then flows out
of the rotor through vent slots machined in the rotor surface in the line with the outlet
compartment behind the stator core.

15 | P a g e
 Accessories:
1) 6- Stator winding 100 ohm Platinum RTD’s
2) 2- Bearing Drain 100 ohm Platinum RTD’s (1 per Bearing)
3) 2- Bearing Metal 100 ohm Platinum RTD’s (1 per Bearing, Duplex)
4) 4- Air Circuit 100 ohm Platinum RTD’s
5) 4- Bentley Nevada Proximities and Probes (2 per Bearing)
6) Rotor shaft earthing brush.
7) Stator earthing pads.
8) Water leakage detectors.

16 | P a g e
GENERATOR EXCITATION SYSTEM
Generator is provided with brushless excitation system. A permanent magnet generator
(PMG - 2.1 KVA) mounted on the main generator shaft generates 3-phase 110 volt AC voltage
required for excitation at 200 Hz. This is the input power source to the AVR (Automatic Voltage
Regulator) and gets rectified.
The controlled DC excitation which is AVR output is given to the stationary field winding
of main exciter (185 KVA, 225 V, 419A, 100 HZ). The AC power generated by main exciter is
rectified by rotating ring diodes. Leads coming out of the rotating diodes are connected to the
generator main field winding.

17 | P a g e
 Main Exciter:
The main exciter is of the overhung duct ventilated direct drive brushless type, with
stationary field and revolving armature.
The armature is provided with a three phase fused rotating rectifier assembly. This will
rectify the A.C output of the exciter into DC for the generator field winding. The generator field
will be connected to the rectifier assembly via insulated conductors inside a hole bored in the
end of the generator rotor shaft. Cooling air for the exciter is ducted from and returned to the
generator cooling air circuit.
 Pilot Exciter:
The pilot exciter is a permanent magnet revolving field, three phase stationary armature AC
generator to supply excitation power to the automatic voltage regulator. It is mounted at the
extreme end of the generator shaft.

18 | P a g e
STEAM TURBINE GENERATOR (STG-1 & STG-2)
Make Meidensha Corporation, Japan
Output 48125 KVA
Power factor 0.8
Voltage 11000 V
Current 2526 Amp
Number of phases 3
Terminal frequency 50 Hz
Rated speed 3000 rpm
Field voltage 315 V
Generator AVR range of control 80 to 105% (8800 – 11500 V)
Efficiency (Including loss in the excitation system)
Load 100% 75% 50% 25%
At cos = 1 98.57 98.4 97.93 96.3
At cosrated =0.8 98.13 97.91 97.33 95.33
Excitation requirement of synchronous generator (at operating temp.)
At rated speed & rated voltage current voltage
No load 150 86
Rated output 438 251

19 | P a g e
GENERATOR TRANSFORMERS : 11/33 KV (GT-1 & GT-2)
 KVA : 50000 (50 MVA)
 Make : Verbano Transformer, Novara- Italy
 H.V No load volts : 35000 2 x 2.5 % Volts
 L.V No load Volts : 11000 Volts
 Winding Connection : Delta / Star Neutral
 Insulation level of : H.V-IA 250 FI 95
Transformer L.V-IA 60 FI 28
 Impendence at 50 MVA : 14.43 %
 Core & Coil Weight : 40 Tons
 H.V. Current : 824.8 Amps.
 L.V. Current : 2624.3 Amps.
 Oil Weight : 15 Tons
 Total Weight : 68 Tons
 Type of Cooling : ONAF (Oil Natural Air Forced)
 Frequency : 50Hz
 Year of Manufactured : 1998

20 | P a g e
UNIT AUXILIARY TRANSFORMERS : 33/6.6 KV (UAT-1 & UAT-2)
 KVA : 8000 (8 MVA)
 Make : SEA - Italy
 Insulation level of : MV KV 36-70-170
Transformer LV KV 7.2- 20-60
 Impendence at 8 MVA : 8.23 %
 Core & Coil Weight : 8260 Kgs.
 H.V. Current : 139.9 Amps.
 Oil Weight : 3000 Kgs.
 Total Weight : 16000 Kgs.
 Type of Cooling : ONAN (Oil Natural Air Natural)

21 | P a g e
6.6/0.435 KV TRANSFORMER (ST-1 & ST-2)
 KVA : 1600 (1.6 MVA)
 Make : SEA - Italy
 Insulation level of : HV L140 AC 20-11
Transformer LV KV 7.2 / 20-60
 Impendence at 1.6 MVA : 5.9 %
 Core & Coil Weight : 2260 Kgs.
 H.V. Current : 140 Amps.
 Oil Weight : 760 Kgs.
 Total Weight : 4100 Kgs.
 Type of Cooling : ONAN (Oil Natural Air Natural)

22 | P a g e
AUXILIARIES OPERATED ON 6.6 KV
 HHP Feed Water Pump : 4 no.s
1 – Turbine Driven
2 – Motor Driven (6.6 KV, 750 KW)
 HP Feed Water Pump: 3 no.s
 Forced Draught Fan (FD Fan) : 6 no.s (2 FD Fans per Boiler)
Total: 3 (Turbo Driven) + 3 (Motor Driven) = 6

23 | P a g e
NAME PLATE DETAILS OF 3-PHASE, 6.6KV HHP MOTOR
 Service : Motor Driven HHP Boiler Feed Water Pump
 Make : Loher Flender AG
 KW : 750
 RPM : 2986
 Voltage : 6600 Volts
 Full Load Current (FLC) : 74 Amps.
 Frequency : 50 Hz
 Power Factor : 0.92 lagging
 Connection : Star
 Mounting : B3
 Insulation Class : F
 Area/ Zone : Non-hazardous
 Ambient Temperature : 46 °C

24 | P a g e
NAME PLATE DETAILS OF 3-PHASE, 6.6KV HP MOTOR
 Service : Motor Driven HP Feed Water Pump
 KW : 500
 RPM : 2982
 Mounting : B3

25 | P a g e
NAME PLATE DETAILS OF 3-PHASE, 6.6KV FD FAN MOTOR
 Service : Motor Driven FD Fan Motor Pump
 KW : 510
 RPM : 1490
 Mounting : B3

26 | P a g e
INTRODUCTION TO PROTECTION OF GENERATOR
The protection system of any modern electric power grid is the most crucial function in
the system.
The key function of any protective system is to minimize the possibility of physical
damage to equipment due to a fault anywhere in the system or from abnormal operation of the
equipment i.e., over speed, under voltage, etc.
However, the most critical function of any protective scheme is to safeguard those
persons who operate the equipment that produces, transmits and utilizes electricity.
Purchasing, installing, setting, coordinating and properly maintaining protective systems are not
an insignificant expense. Therefore the extent any device or electric circuit is protected
depends on the potential cost of not doing so adequately.
Electric power generators are most often the most critical electrical apparatus in any
power plant. In fact, the generator and the main step-up transformer are those two most
important apparatus which share some of the protective functions.
Protection systems can be divided into systems monitoring current, voltage, windings
and cooling media temperature and pressure, and systems monitoring internal activity, such as
partial discharge, decomposition of organic insulation materials, water content, hydrogen
impurities, and flux probes.
Protection devices are designed to monitor certain conditions, and subsequently, to
alarm or trip if a specified condition is detected.
WHY PROTECTION OF GENERATOR IS REQUIRED?
 The generating units, especially the larger ones are relatively few in number and higher
in individual cost than most other equipment’s, therefore it is desirable and necessary
to provide protection to the generator.
 In generating station, as a continuous operation of generators is much more necessary
so the faulty part has to be cleared very quickly for uninterruptable power supply.
 Unlike other apparatus, opening a breaker to isolate the faulty generator is not
sufficient to prevent further damage.

27 | P a g e
ABNORMALITIES IN GENERATOR
 Failure of prime mover
 Failure of exciter
 Over-loading
 Unbalanced loading
 Over voltage
 Over speed
FAULTS IN GENERATOR
 STATOR FAULTS:
1. Phase to phase faults
2. Phase to earth faults
3. Inter turn faults
 ROTOR FAULTS:
1. Earth faults
2. Inter turn faults

28 | P a g e
GENERATOR PROTECTION SYSTEM

30 | P a g e
1.DIFFERENTIAL PROTECTION
 It provides protection against phase to phase and phase to ground.
 When the stator winding (armature winding) is healthy and when there is no internal
fault, equal currents flow the through the secondary windings of CTs.
 So no current flows through any winding of the relay.
 But the current balance is distributed when there is earth fault in one phase or when
there is phase to phase fault, current flows through one or winding of the relay and the
circuit breaker is tripped.

31 | P a g e
2. NEGATIVE PHASE SEQUENCE PROTECTION
 The negative sequence component is produced when the load is become unbalanced.
 Unbalance may cause due to single phase fault or unbalanced loading and it gives rise to
negative sequence current.
 This current in rotor causes rotor overheating and damage to the rotor.
 This component rotates with synchronous speed in the direction opposite to that of the
rotor.
 This can be protected by negative sequence current filter with over current relay.

32 | P a g e
3.BALANCED EARTH FAULT PROTECTION
 The value of the pickup current for the over current relay is more so the relay cannot
operate with low value of the earth fault current.
 So, to give earth fault protection, an earth fault relay is connected in the neutral circuit
through CT as shown in fig.
 Balanced earth fault protection is used for those alternators in which neutral ends of the
three phases are connected internally to a single terminal.
 It provides no protection against phase to phase fault.

33 | P a g e
4.OVER-CURRENT PROTECTION
 The time setting of the over current relay is kept higher than that of differential
protection.
 Because the first differential protection should work and if it fails to operate, after some
time this over current protection system will work.
 Overloading of the machine causes overheating in the stator winding.
 This can be prevented by using over-current relay with time delay adjustment.
 But overheating not only depends on over-current but also the failure of the cooling
system in the generator.
 So temperature detector coils such as thermistors or thermocouples are used at various
points in stator winding for indication of the temperature.

34 | P a g e
5.UNBALANCED LOADING PROTECTION
 Unbalanced loading arises from fault to earth or faults between phases on the circuits
external to the alternator.
 Unbalanced current may burn the mechanical fixing of the rotor core or damage the
field winding.
 Under normal operating condition, algebraic sum of three currents flowing through the
relay is zero and relay does not operate.
 When unbalancing occurs, resultant current flows through the relay and relay trips the
circuit breaker to disconnect the alternator from the system.

35 | P a g e
6.STATOR INTER-TURN PROTECTION
 When a short circuit develops between adjacent turns in one of the armature windings,
unbalanced current flows in two winding.
 This unbalanced current flow through the relay to operate the circuit breaker.

36 | P a g e
7.SYNCHRO-CHECK RELAY
 A synchro-check relay electrically determines if the difference in voltage magnitude,
frequency and phase angle falls within allowable limits.
 The allowable limits will vary with the location on the power system. Typically, the
further away from generation and load, the more phase angle difference can be
tolerated.
 Synch-check relays typically do not provide indication of the voltage magnitude,
frequency or phase angle.
 A synch-check relay decides internally whether its conditions for closing are satisfied.
 The synch-check relay will either allow or prevent closing depending on its settings.

37 | P a g e
8.VOLTS/HEARTZ PROTECTION
 Core damage due to over excitation is a rare event.
 However, when a severe over excitation occurs, the most probable result is partial or
complete destruction of the core’s insulation, with the consequential need to replace it.
 Therefore it is critical that V/Hz protection be applied and properly set.
 Almost invariably, the cases of severe over excitation occur during run-up, prior to
synchronization.
 One vital component in all V/Hz schemes for any turbo generator is double feed from
two independent potential transformers (PTs).
 Otherwise, loss of a single PT connection may give the excitation system wrong
information about the terminal voltage, forcing the field current and terminal voltage
beyond the V/Hz capability of the machine.
9.OVER/UNDER FREQUENCY PROTECTION
 Over and under frequency operation generally results from full or partial load rejection
or overloading conditions.
 Load rejection can be caused by a fault in the system or load shedding.
 Overload conditions may arise from tripping a large generator or a transmission line.
 What frequency the machine will attain following load rejection or overload is a function
of how much load has changed and the governor droop characteristics.
 For instance, a governor with a 5% droop characteristic will cause a 1.5% speed increase
for a 30% load rejection.
 The manufacturers provide withstand curves that should be used in setting the Function
(81) relay.
10.OVER VOLTAGE PROTECTION
 Overvoltage relays are also used as backup to the over excitation during normal
operation of the machine.
 Generator overvoltage may occur without necessarily exceeding the V/Hz limits of the
machine.
 Protection for generator overvoltage is provided with a frequency-compensated
overvoltage relay.
 The relay should have both an instantaneous unit and a time delay unit with an inverse
time characteristic.
 Two definite time delay relays can also be applied.

38 | P a g e
11.UNDER VOLTAGE PROTECTION
 Generators are usually designed to operate continuously at a minimum voltage of 95%
of its rated voltage, while delivering rated power at rated frequency.
 Operating generator with terminal voltage lower than 95% of its rated voltage may
result in undesirable effects such as reduction in stability limit, import of excessive
reactive power from the grid to which it is connected and malfunctioning of voltage
sensitive devices and equipment.
 The under voltage relays are mainly installed for the purpose of identifying loss of PT
voltage or to identify dead-bus condition for certain alignments.
12.REVERSE POWER PROTECTION
 This protective function trips the unit when power flows from the system to the
generator.
 In this situation, depending on the generator’s field condition, the alternator is driven as
a synchronous or induction motor.
 If it is driven as an induction motor, negative-sequence currents will be established in
the rotor, potentially damaging damper windings, wedges, retaining-rings, and forging.
 Reverse power condition may adversely affect the integrity of the prime mover.
13.FIELD FAILURE PROTECTION
 There are a number of events that may result in an accidental removal of the source of
excitation to the generator.
 This can happen for both brushless and externally excited units.
 For instance, a unplanned opening of the field breaker, a failure of the exciter, a
flashover in the brush-rigging, failure of the automatic voltage regulator (AVR) and a
short-circuit in the field winding can all result in a loss-of-excitation condition.
 When the excitation of generator is lost it operate as an Induction generator.
 It derives excitation from the system and supply power at leading power factor.
 It may cause fall in voltage & so loss of synchronism & system instability and
overheating of rotor due to induction current on it.
 The most widely utilized method of protecting against loss-of-field conditions is that
relying on impedance elements.
 Sometimes two relays are used, each looking at the impedance within a different region
of operation, so that a loss-of-field condition is captured.
 Sensing the field current directly or sensing the VAR power flowing into the generator is
sometimes used for alarm and trip.

39 | P a g e
14.ROTOR EARTH FAULT PROTECTION
 The field circuit of a generator is an ungrounded system. As such, a single ground fault
will not generally affect the operation of a generator.
 However, if a second ground fault occurs, a portion of the field winding will be short
circuited, thereby producing unbalanced air gap fluxes in the machine.
 These unbalanced fluxes may cause rotor vibration that may quickly damage the
machine; also, unbalanced rotor winding and rotor body temperatures caused by
uneven rotor winding currents may cause similar damaging vibrations.
 The first rotor earth fault of generator shall be detected by means of super imposing of
separate DC bias on the field winding.
 The DC bias shall be such that the faults at any point in the winding are covered by the
protection. Also the relay shall withstand the voltage encountered.
 Second rotor earth fault protection for generators shall also be provided, with suitable
relays common for two units.
 The protection shall incorporate feature for compensating the effects of induced
alternating currents in rotor circuit and shall have minimum dead zone.
15.VOLTAGE BALANCE PROTECTION
 The main function of the voltage balance relay is to avoid false tripping of other
protection relays due to a loss of secondary voltage feed for instance, by a blown
potential transformer fuse.
 Voltage balance schemes are possible in most modern and large generators because
such units have at least two PTs feeding the protection and monitoring systems.
 The voltage balance relays senses and compares the secondary voltage of different PTs,
and when it determines that a “blown-fuse” situation arises, it blocks the operation of
certain voltage controlled relays and alarms.
16.STATOR UNBALANCED CURRENT PROTECTION
 There are a number of incidents that may result in unbalanced three-phase currents at
the terminals of an alternator: for instance, unbalance loads, single-pole opening of a
breaker, asymmetrical transmission systems and open circuits.
 Unbalanced currents will result in negative-sequence current components flowing on
the rotor forging surfaces, retaining-rings, rotor wedges, and to some extent in the field
windings.

40 | P a g e
 These rotor negative-sequence currents have the potential of generating high
temperatures within seconds, with severe detrimental effects to other rotor
components.
 Generators must meet minimal requirements for sustaining unbalance currents without
damage.
 The protection against unbalanced currents is implemented by using over current relays
that measure negative-sequence components.
17.LOSS OF SYNCHRONISM PROTECTION
 Loss of synchronization (out of step) can have serious effects to the generator.
 Rotor and coupling damage is possible.
 To minimize any harmful effects, the protection should separate the generator from the
system as soon as possible.
 Protection against out-of-step condition is based on the fact that the apparent
impedance, as seen at the generator’s terminals, changes in a predicted manner during
an unstable condition.
 This is similar to the loss-of-excitation condition.
 Therefore to fully protect against out-of-step condition, a dedicated relay must be
included in the protection package.
 This fast protective action tends to reduce considerably the very large oscillating shaft
torque that can otherwise occur.
18.BREAKER FAILURE PROTECTION
 Most faults involving the generator require tripping the line breakers.
 Failure of any such breaker to operate properly results in loss of protection and other
abnormal conditions, such as motoring.
 Activation of a breaker failure scheme is carried out by a combination of triggering
signals from the generator protective relays, over current relays and breaker auxiliary
switches, via a timer.
 Some modified schemes also included in their triggering circuit the trip signal from the
neutral of the main step-up transformer’s over current relay.

41 | P a g e
NAME INPUT PROTECTION TO
Differential
protection
Differential
Current
Stator core &
winding
Stator earth fault Voltage Stator core &
winding
Over current Current Stator core &
winding
Over voltage Voltage Stator core &
winding
Inter-turn short
circuit
Current Stator core &
winding
Rotor Earth Fault Current Rotor winding
Over & under
frequency
Frequency Turbine protection
Reverse power flow Voltage &
current
Turbine protection
Loss of excitation Voltage &
current
Power System
Protection
Back up protection
for lines
Voltage &
current
Generator
protection

42 | P a g e
CONCLUSION
Working with Vadinar Power Company Limited as an industrial training was a very nice
experience. We learnt a lot about different types of machines and equipment’s used in power
plant, their working, their construction and protection required for each equipments. We have
seen Alternators, Transformers, HT motors, Circuit Breakers practically. It is easy for us to just
switch-on the fan and get cooled air in hot summer but here we have seen that the generation
of electricity is not an easy task. It requires very high degree of safety arrangements, regular
maintenance and very complex protection system.
We also practiced what we learnt in the university and applied it on field. Working with
Electrical department enhanced our major understanding. In addition, we gained a good
experience in term of self-confidence, real life working situation, interactions among people in
the same field and working with others with different professional background. Also, the
training was an opportunity for us to increase our human relation both socially and
professionally.

43 | P a g e
REFERENCES
 Technical Dairy of 77 MW Power Plant.
 Data-Sheets of Generator, Transformer and HT Motors.
 Book :- POWER SYSTEM PROTECTION & SWITCHGEAR
By Badri Ram and N. D. Vishwakarma
 Websites :
 www.essar.com
 www.essarenergy.com
 www.electrical4u.com
 www.electrical-engineering-portal.com

ESSAR internship report

Recommended

Recommended

More Related Content

What's hot

What's hot (12)

Similar to ESSAR internship report

Similar to ESSAR internship report (20)

More from Dipen Kantariya

More from Dipen Kantariya (9)

Recently uploaded

Recently uploaded (20)

ESSAR internship report