The document acknowledges and thanks various individuals who provided support and guidance during the author's training period at the Narora Atomic Power Station. It expresses gratitude to supervisors in the Finance and Training departments for providing the opportunity and to electrical department staff for their guidance and insights into the power industry. The author also thanks their parents and friends for their support.

2. ACKNOWLEDGEMENT
As I continue with the report it would be only fair to acknowledge the
support and guidance I received throughout the training period at
Narora Atomic Power Station which led to the successful completion of
my training.
I am indebted to Mr. Anurag Varshney, SO/O Finance Department,
Operations for because of his guidance I got this golden opportunity to
carry out the field work at this esteemed Power Station.
Thanks are due to Mr. D.S. Chaudhary, Station Director and Mr. G.D.
Sharma, Training Superintendent for allowing me the opportunity to
work in the organization.
I would like to extend my heartfelt gratitude towards Mr. Khagesh
Chandra Rakesh, Mr. Rahul Pandey and other officers who were
instrumental in providing this training facility. I would also acknowledge
the inspiration, guidance and motivation I received during these 4
weeks.
I would be unfair if I do not acknowledge the resourcefulness of the
Electrical Department and the guides Mr. S.K. Katiyar, Mr. D. Prasad,
Mr. Mukesh Yadav, Mr. R.K. Sharma and Mr. Harish Sharma, for it was
because of their untiring and dedicated efforts that I was able to gain
much insights into the functioning of Power Industry and moreover my
knowledge about the subject was improved.
Last but not the least I would thank my parents and also my friends at
NAPS for being a constant source of support.

3. Index
S.No. Description Page No.
1 Introduction 1
2 Layout of NAPS 2
3 Some Important Data about NAPS 3
4 Principle of Nuclear Reactor 4
a) Turbine Generator Cycle 5
b) Reactor Cycle 5
c) Moderator System 6
d) Reactor Fuel 6
5 Shutdown Systems 7
6 Electrical Systems 8
a) Turbo Generator 8
b) Principle Components 9
7 Cooling of Generator Set 10
8 Generator Excitation System 11
a) Static Excitation System 11
b) Components of Static Excitation System 12
9 Generator Transformer 14
10 Station Unit Transformer 15
11 Power Supply Classifications at NAPS 16
12 Control Power Supply System 18
13 Diesel Generator Set 20
14 Power Motor Generator Set 21
15 Switchyard 23
a) Switchyard Equipments 24
16 Motor Control Centre 28
17 Electrical Protection Systems 29
a) Circuit Breakers 29
b) Protective Relay 31
1. Types of Relay 32
18 Trainee’s Training Experience at NAPS 34
19 Conclusions 36

4. ~ 1 ~
Introduction
The Narora Atomic Power Station is situated at the banks of river Ganga in
Bulandshahr district of Uttar Pradesh. It is 60 KMs away from Aligarh which is
the closest substantial population centre.
The Narora Atomic Power Station (NAPS) is a twin unit module of 220MWe
each of pressurized heavy water reactors. The reactors use natural uranium
available in India as fuel & heavy water produced in the country as moderator
& coolant. The station is connected to high voltage network through five 220
kV lines, one to Moradabad, one to Harduaganj, one to Simbhaoli, one to
Khurja and one to Atrauli. It is designed for base load operation as a
commercial station.
The foundation stone of the plant was laid on 4th
January 1974 and it was
dedicated to the nation as Nuclear Power Plant in the early 90s, ever since it
has stood as an epitome of safe and secure Power Source.
With the synchronization of the Narora Atomic Power Station with northern
grid through five lines of 220kV, it has occupied an important place on the
power map of the India. With this, yet another important milestone in the
Indian nuclear program has been achieved, as NAPS is an effort towards
standardization of PHWR units & a stepping-stone to the 500MWe units. A
significant & unique feature of this project has been the evolution of the
design suitable for seismic sites.
Narora Atomic Power Plant is the fourth Atomic Power Plant installed in India
preceded by Tarapur in Maharashtra, Rawatbhata in Rajasthan and Kalpakkam
in Tamil Nadu. One peculiarity about NAPS is that it is the first indigenous
Power Plant of the country.

5. ~ 2 ~
Layout of NAPS
NAPS have the following main parts:-
1. Administration Building
2. Overhead Water Tank
3. Canteen
4. Natural Draft Cooling Towers (NDCT).
5. 220KV Switch Yard
6. Stack Tower
7. Service Building
8. Supplementary Control Room
9. Reactor Building
10.Purification Building
11.Turbine Building
12.Pump House
13.Station Training Centre

6. ~ 3 ~
SOME IMPORTANT DATA OF NAPS
DATA SPECIFICATION
Transmission Lines
1. Moradabad
2. Atrauli
3. Khurja
4. Simbhaoli
5. Harduaganj
Single Line
Single Line
Single Line
Single Line
Single Line
Stack Height 142 Meters
NDCT Height 128 Meters
NDCT Top Diameter 58 Meters
NDCT Base Diameter 107 Meters
NDCT Throat Diameter 53 Meters
Steam Flow 1314 Ton/hr
PHT Flow 12700 Ton/hr
Steam Pressure 40-48 kg/cm2
PHT Pressure 87.0 kg/cm2
CCW Flow 39000 Ton/hr
Coolant Tubes 306
No. of Fuel Bundles in one channel 12
Fuel Bundle UO2 – Weight 15kgs
No. of Bundles in a core 3672
Condenser Pressure 680 mm of Hg
RB Design Pressure 1.25 kg/cm2
Station Load 18 – 20 MW
Generator Power 220 MW
Grid Voltage 220 kV
ISO-14001 certification 19th AUGUST 1999

7. ~ 4 ~
PRINCIPLE OF NUCLEAR REACTOR
A Nuclear Power reactor is only a source of heat, the heat being produced
when the uranium atom splits (fission). Nuclear fission is a nuclear reaction in
which the nucleus of an atom splits into smaller parts (lighter nuclei). The
fission process often produces free neutrons and photons (in the form of
gamma rays), and releases a very large amount of energy even by the energetic
standards of radioactive decay. The heat produces steam, which drives the
turbo-generator & produces electricity. Natural uranium, the fuel used in this
reactor, consist of two types (isotopes) of uranium namely U-235 and U-238 in
the ratio of 1:139. It is the less abundant i.e. U-235 isotope that fissions and
produces energy. When a U-235 atom is struck by a slow (or thermal) neutron,
it splits into two or more fragments. Splitting is accompanied by tremendous
release of energy in the form of heat, radioactivity & two or three fast
neutrons. These fast neutrons, which fly out of the split atom at high speeds,
are made to slow down with the help of moderator (heavy water). So that they
have high probability to hit other 92U235
atoms which in turn releases more
energy & further sets of neutrons and fission. Attainment of self-sustained
fission of uranium atoms is called a ‘Chain Reaction’. At this stage the reactor is
said to have attained “criticality”.
The basic nuclear reaction is as follows:
𝑈92
235
+ 𝑛0
1
𝑆𝑟38
94
+ 𝑋𝑒54
140
+ 2 𝑛0
1
+ (Heat Energy) + γ
(Natural Uranium Oxide)
𝑈92
235
+ 𝑛0
1
𝐵𝑎56
141
+ 𝐾𝑟36
92
+3 𝑛0
1
+ (Heat Energy) + γ

8. ~ 5 ~
TURBINE GENERATOR CYCLE
REACTOR CYCLE
Heavy Water is used in the Reactors as moderator and as coolant for the
Reactor fuel. The two functions are separate, each having its own closed
circulating system. The fuel coolant system is called the Primary Heat Transport
System, and is a high pressure, high temperature circuit. The moderator and
reflector circuit is called the moderator system, and is a low pressure, low
temperature circuit. The Pressure tubes & Calandria Tubes are insulated from
each other in the Reactor core by Carbon di-oxide Gas in the annular space
between the calandria tubes and the coolant tubes. Figure shown above is a
simplified schematic diagram of the Reactor Cycle. Heavy water at 293 0
C
enters the Steam Generator tubes to raise steam from Demineralized Water in
shell side, for the turbine and returns back to the Reactor at 249 0
C. The
working pressure, which is the mean of the pressure, in the Reactor inlet &
outlet headers is 87.0 kg/cm2
.

9. ~ 6 ~
Moderator System
The moderator system is a Heavy Water with Cover Gas as Helium. Calandria is
always kept full of heavy water up to 96% Level. Remaining volume is covered
by Helium Gas, which acts as Cover Gas to avoid downgrading of Moderator
D2O. Moderator is used to slow down the speed of fast neutron. Moderator
(D2O) system circulating pump take suction from bottom of calandria and
discharge back to calandria through moderator heat exchanger for maintaining
moderator temp. Working pressure and temperature of moderator system are
8kg/cm 2
and 63o
C respectively.
In order to avoid escape & loss of Heavy Water from PHT / Moderator System,
a high standard of integrity is maintained by using multiple seals & leakage
collection system in the liquid phase. D2O Vapour recovery Dryer Systems is
used for the vapour phase collection.
Reactor Fuel
Fuel from the reactor is in the form of bundles 49.53 cm long & 8.17cm dia. &
each bundle consists of 19 hermetically sealed zinc alloy tubes containing
compact & sintered pallets of natural uranium. Twelve such bundles are
located in each fuel channel.

10. ~ 7 ~
Shutdown System
NAPS have two diverse & independent shut down system, one of them is fast
acting & other is slow acting.
1. Primary Shutdown System
The system is meant to shut down the Reactor whenever any operating
parameter crosses a set limit. The system operates automatically & can also be
operated manually. The system has 14 rods of cadmium sandwiched in
stainless steel as neutron absorbing element. Any trip signal actuates the
mechanical drum assembly and the criticality is reduced to sub criticality in a
span of 2.3 seconds.
2. Secondary Shutdown System
The Secondary Shutdown system comes into action when the primary
shutdown system fails to operate. It is provided as a backup protective system.
It consists of 12 liquid poison tubes which remain empty during normal course
of operation. But during operation the system enables the filling of tubes with
a neutron absorbing liquid. The principle is such that four when liquid filled
tanks are pressurized than the liquid rises up in liquid tubes located inside
reactor. It makes the reactor sub-critical in 1.4 seconds.
3. Automatic Liquid Poison Addition System
The primary and secondary shut down systems are unable to maintain the
state of sub criticality for long enough therefore an additional system known as
Automatic Liquid Poison Addition System is employed. Liquid poison is added
in the moderator. This poison will absorb the neutrons and thus will interrupt
chain reaction. Poison can be added either manually or automatically.

11. ~ 8 ~
Electrical Systems
The electrical system deals with generation of electrical energy from heat
energy obtained from nuclear reaction and its subsequent transmission and
utilization.
Turbo Generator
TECHNICAL SPECIFICATION
1. Active Power - 237.7 MW
2. Power factor - 0.90
3. Total Power - 264.0 MVA
4. Stator - 16.5kV, 9240 A
5. Rotor - 326 V, 2755 A
6. RPM - 3000 RPM
7. Short circuit ratio - 0.58
8. Response time - 50ms
9. Efficiency at full load - 98.6%
10. Frequency - 50 Hz
11. Connection - 3 phase
12. Coolant - a) DM water, b) Hydrogen
13. Insulation - Class B
14. Production - 1991-92
15. Made by - BHEL – Haridwar

12. ~ 9 ~
Principal Components:
Stator
The stator is the stationary part of the generator. It is made up of stacked
laminations of Cold Rolled Grain Oriented Silicon Steel. All these laminations
are insulated from each other. The core is provided with number of ducts both
in the plane of the core and in perpendicular plane to facilitate rapid cooling.
The stator is wound for three phase windings and is star connected.
Rotor
It is made up of Chromium-Nickel steel. Field winding conductors are placed in
rotor slots and are connected to form a series winding. A D.C voltage is applied
to the field winding to provide necessary excitation.
Damper windings are also provided. It is used to damp out the oscillations
produced due to abrupt change of load.
Slip Ring
Slips rings are made of copper, brush gear is provided in the generator shaft to
inject excitation current from the static rectifier unit to the rotating main field.
The slip rings are provided with inclined holes for self ventilation.
Principal of Operation of Turbo Generator
The electric generator is based on the principal of faraday laws of
electromagnetic Induction discovered by Michael Faraday in 1831.
 When the magnetic flux linked by a conductor changes, an EMF is
induced in it.
 Magnitude of EMF is directly proportional to the rate of change of flux.

13. ~ 10 ~
Cooling Of Generator Set
Stator Cooling
Generator stator windings are cooled by DM water passing through the hollow
conductor. DM water is used for stator winding cooling purpose because of it
has:
 Low viscosity
 No fire hazards
 Better heat removal capacity
 Non conducting
Rotor Cooling
Stator core, rotor winding and core are cooled by hydrogen present in the
stator and rotor air gap. Two axial shaft fans mounted on both end of rotor
body are provided to circulate hydrogen gas in the independent and
symmetrically closed circuit.
Gas coolers are mounted in the stator body for hydrogen cooling. Hydrogen
gas is used for generator because of its
 High heat conductivity
 Less density
 High heat removing capacity
 Low voltage loss across it

14. ~ 11 ~
Generator Excitation System
The excitation systems are basically classified as:-
i) DC Excitation System: It utilizes generator as source of power driven by
motor or shaft of main generator. It can be self or separately excited.
ii) AC Excitation System: It uses AC machine as source of power. Usually the
exciter is on the same shaft as turbine generator. The AC output is rectified by
either controlled or non controlled rectifiers.
iii) Static Excitation System: In static Excitation system, all components are
stationary. It supplies DC current directly to the field of the main generator
through slip rings.
Static Excitation System
Static excitation for 235MW is preferred because of following reasons:
 Fast response time
 High reliability
 Interchangeability of part during operation
 Very low maintenance
 Less space requirement

15. ~ 12 ~
Components of Static Excitation System
1. Excitation transformer
2. Controlled Rectifier Bridge
3. Automatic Voltage regulator
4. Field breaker
Excitation Transformer
Three single phase transformer rated at 833KVA, 16.5KV/332V are connected
in delta to the 16.5KV system through tap of bus duct from main generator.
The LV side of the transformer is connected in star and feeds the input to the
rectifier.
Controlled Bridge Rectifier
There are total of 4 three phase thyristor based rectifier bridges to convert the
AC into DC. These bridges are fed from excitation transformer and are
connected in parallel at the output. Three bridges are used to convert AC into
Dc during normal operation while the fourth one is used as a backup in case
any one of the bridges fails. The control of firing pulses is given through AVR
cubicle.
Automatic Voltage Regulator (AVR)
Control signals are generated here for rectifier. The AVR derives its input from
the PT and CT of the generator and controls the excitation for varying the
machine terminal voltage and reactive overflow in addition to this basic
function of AVR in voltage regulator.

16. ~ 13 ~
The AVR incorporates the following addition feature:-
1. Rotor Current Limiter
AVR protect rotor from overloading and the excitation system from suffering
voltage in excess of the ceiling voltage.
2. Stator Current Limiter
This limiter monitors the stator current limits the excitation in case there is
stator over load.
3. Load Angle Limiter
It monitors the load angle and ensures that generator does not enter unstable
region.
Field Breaker
The field breaker is of air blast type. In this breaker provision is provided to
discharge the energy stored in the field though a non-linear resistance
whenever the breaker is open the means of a special contact of the breaker
when classes before the field breaker opens.

17. ~ 14 ~
Generating Transformer
Technical Specification
1) Capacity - 265 MVA
2) LV side Voltage - 16.5KV
3) HV Side Voltage - 235KV
4) Power factor - 0.9
5) Impedance - 0.14 pµ
6) Coolant - Oil Natural Air forced
The HV voltage of 235 KV is about 6.8 % above 220 KV .The 14 % impedance
specified will result in voltage drop of about 7 % at full load and 0.9 pf. Thus
the full load voltage drop in transformer is almost neutralized by higher ratio
specified.
OFF load tap changers are provided for GTs as the plant has to work normally
as a base load station in the grid. A range of +/-10 % in steps of 2.5 % has been
provided for varying the output voltage of transformer.

18. ~ 15 ~
Station Unit Transformer
Technical Specification
1) Normal load of SUT specified - 20.8 MVA
2) Type of transformer - Outdoor, 3 phase core type
3) Rated voltage - 220/6.6 KV
4) Frequency - 50 Hz
5) Winding impedance % (HV-LV) - 9%.
The transformer is specified with a voltage rate of 220/6.6 KV. The HV voltage
corresponds to the voltage of the HV buses of the main output system. The L.V.
voltage of 6.6 KV is the no load voltage of the LV side on load the voltage drop
in the SUT will reduce the terminal voltage to 6.6 KV with the proper selection
of tap.
The star/star connections for HV/LV winding were chosen in order to obtain
proper vector matching of 6.6 KV unit and station system. The SUT is also
specified with an unloaded tertiary. The tertiary has a power rating of about
1/3 of the main winding. The tertiary winding in delta is provided so as to
provide ground path to the harmonics.
The transformer is specified with an onload tap changer to maintain steady
voltage at the 6.6 KV bus. The on load tap changer has range of +/- 12%.
Insteps of 1- 5%. Here only two SUT are available for initial start up to supply
power to station auxiliary when unit is shut down. SUT take supply from 220 KV
grid & feeds power to station auxiliaries. The capacity of UT is 31.5MV.

19. ~ 16 ~
Power Supply Classification at NAPS
Each load within the station has been classified according to degree of
reliability required for its supply. There are four classes of power supply at
NAPS.
Power Voltage Nature Source
Class-I 250V DC Uninterrupted Battery bank
Class-II 415V AC Uninterrupted Power MG set
Class-III 415V AC Interruptible Diesel generator
Class-IV 415V AC & 6.6 kV interruptible Grid supply & TG
Set
Class IV Power
Power for the class IV station service is normally available from two sources.
These are the unit transformer, which are directly connected to the generator
output terminals, and the start up transformer, which is connected to the 220
kV bus system of the station.
Class IV supply is arranged in two voltages viz. 6.6 kV and 415 volts. Motors
loads above 200 kW are fed at 6.6 kV whereas motors below 200kW rating are
fed at the medium voltage of 415 volts.
Class III Power
This system feeds to those loads which can be interrupted shortly. These loads
are required to run even when Reactor is shut down. System is normally
charged from 6.6 KV system and when the 6.6 KV supply fails DGs
automatically start and recharge the system.

20. ~ 17 ~
The class III supply system consists of two main buses P and Q. Bus P is fed
from 6.6 KV switchgear ( UT side) through a 2000 KVA transformer and Q is fed
from 6.6KV switchgear (UT side) through another 2000 KVA transformer.
Emergency diesel generators, one each, are connected to these class III buses
to restore supply in 30 to 60 sec.
There is a tie between two main buses P and Q. This tie is connected via two
breakers in series to take care of the eventually of failure class III supply to the
affected Bus.
Class II Power
Class-II Bus-S and Bus-T are kept constantly charged by two power generator
sets to convert 250 V DC to 415 V AC. As the motor of MG set is driven by 250V
DC from class-I power batteries, the class-II is also uninterrupted power supply.
Class-II may also be tied to class-III if any MG set becomes unavailable. This
condition calls continuous DG set running. Potential loss on any class-III or any
class-II buses initiate emergency transfer i.e. all DG's start to charge any dead
bus. The batteries can feed class II loads for about 30 minutes mean while class
III power supply must be restored.
Class I Power
The class I power supply system consists of two main buses U and V each is fed
from 500 KW ACVR, which is fed from class III buses P and Q respectively. Each
bus has a 2200 AH battery bank connected to it. The normal supply is from
class III system through ACVRs and the battery bank.
Battery bank has 2250 AH, discharge capacity for 30 minutes with the end of
discharge voltage of 204 volts.

21. ~ 18 ~
Control Power Supply System
Class I: Control Power Supply
250V DC control power supply consist of two DC Battery banks which supplies
power to one bus each. In normal condition the battery bank is kept charge by
Class III Power Supply through ACVR. When Class III supply fails this battery
bank supplies the power.
Control power supply is used for auto tripping circuit, auto closing circuit and
test circuit. This has been separated from Class–I Power Supply System keeping
in view all time, availability and reliability.
Class II: Control power Supply (415V AC)
Inverters have been used to convert DC to AC. There are four Invertors out of
these, three operate continuously and the 4th
remains as standby operating at
no load.
Source of supply to DC Motors are as below:
1. Bus-U (250V DC) CL-1 Power Supply Bus for INV-1
2. Bus-V (250V DC) CL-1 Power Supply Bus for INV-2
3. Bus-W (250V DC CL-1) Control Supply Bus for INV-3
4. Bus-X (250V DC CL-1) Control Supply Bus for INV-4
This shows four buses. Either bus may be tied to standby Bus-X when any
inverter trips. 240V AC is also derived from 415V AC (Inverter Output).
240V AC buses are called cells. There are eleven cells. Three cells for 240V AC
& remaining seven cells for 48V DC. 48V DC is used for logic circuits. 48V DC is
obtained by stepping down voltage from 240 AC to 48V DC and then by
rectifying.

22. ~ 19 ~
Automatic Transfer Scheme
6.6 KV Bus-D and Bus-E are fed by UT while Bus-F and Bus-G are fed by SUT. In
case either incoming breaker trips on protection, potential on corresponding
buses will be lost and loads may trip on under voltage. To avoid this both bus
sections have been provided with a CB to close within 80 ms. This avoids
tripping of Reactor on less than two PCP trip. This scheme is known as Auto
transfer.
Emergency Transfer Scheme
When potential is lost on either Bus-P or Bus-Q or Bus-S or Bus-T or any ACVR
trip all 3 DG start automatically DG-1 synchronizes on auto to Bus-P & DG-2 to
BU-Q. This is called - EMTR. This scheme operates for three conditions:
1. Class-III under voltage
2. Class-II under voltage
3. ACVR failure
It is used to restore class –III supply and to maintain class –II supply.
Power Line Communication
Apart from other modes of communication like telephone system, wireless
etc., communication can also be established through the transmission line,
which is known as Power Line Carrier Communication (PLCC). This system
provides direct and independent communication between main plant and
other substations and load dispatch center of U.P. State Electricity Board
(UPSEB) grid. This will be exclusively used for communication in relation to
Power System Operation and control. The carrier communication system is
coupled to the 220KV power lines through coupling Capacitor Voltage
Transformers (C.V.T’S).

23. ~ 20 ~
Diesel Generator Set
Technical Specification
Rated continuous output - 1450 kW
Overload capacity for 8 hrs. - 1650 kW
Overload capacity for 2 hrs. - 1750 kW
The DG set are capable of parallel operation of Class IV Power Supply.
Whenever there is a loss of Class IV Supply, the DG set is set into action which
restores the power within one minute. Hence it is also called short interruption
supply. The DG set is grounded through Neutral Grounding Resistor (NGR) of
0.5 ohms to limit the grounding current to 480 A.
Diesel Engine
Technical Specification
1. Rating - 2600 BHP
2. RPM - 1000rpm
3. No. of strokes - 4 stoke
4. Power factor - 0.8 lag
5. Engine cylinder - 16 cylinders
6. Excitation - Static Excitation
7. Pole - 6 Pole
8. Excitation voltage - 58.5 V
9. Excitation current - 326 A
10. Connection - star, 3 phase
The diesel engine is started by air motor. For cooling, oil and heavy water are
used. Speed is controlled by the governing system.
In the generator, lap wound type of stator winding is used. The field winding of
generator is excited by 48 V D.C. voltage through the slip ring. The rotor is
rotated and an E.M.F is produced in the stator winding. If the generator
generates 60% of the voltage then the field winding is excited by generated
voltage.

24. ~ 21 ~
Power Motor Generator Set
AC Machine
Rated terminal voltage - 425V
Rated continuous output at 0.8 pf - 325kVA
Over load rating for 30 min - 360kVA
Insulation class - F
Locked rotor current on the - 1250A
Base load of - 140kW
DC Motor
Rated normal terminal voltage - 258V
Maximum working terminal voltage - 300V
Minimum working terminal voltage - 200V
Rating - 290 kW
No load armature current - 60A
Full load speed - 1000rpm
Armature current at rated voltage - 1350 A
Pony Motor
Rating - 37 kW, 1000 rpm
Rated voltage - 415V, 50Hz
Current - 67 V

25. ~ 22 ~
Techo Generator
Output - 100V at 1000rpm
The motor generator set is meant for uninterrupted power supply (415V,
3phase, 50 Hz) to important auxiliaries. The D.C. motor of this MG set is
supplied from class-1-250V DC supply, 500kW ACVR from class 3 supply and
2200 AH, 250V DC batteries.
On loss of class IV supply, the class III system will also loose supply. DG set
starts and restores class III supply. During this period the 250V DC batteries will
continue to supply the MG set.
Starting
The PMG is started with the help of pony motor with resistance control on
Bus1. Initially the dc machine acts as a dc generator, when the terminal voltage
across the generator equals the supply voltage (250V DC), circuit 0breakers are
closed after which it acts as a dc motor. This in turn rotates the alternator.
Grounding
In order to reduce the ground fault, the machine is grounded through a neutral
grounding resistor of 0.4 ohm. This will restrict ground fault current to 600A or
less.

26. ~ 23 ~
SWITCHYARD

27. ~ 24 ~
Technical Specification
1. Type - Outdoor
2. Nominal Voltage - 220kV
3. Max. Operating voltage - 240kV
4. Basic impulse levels:-
a) For transformer winding - 950 kV (peak)
b) For other equipments - 1050kV
5. Three phase fault level - 10000 MVA
6. Short time current rating - 23.6 kA/sec
For all equipment
7. Minimum creep age distance- Total-5600 mm;
for insulation and Bushing- 2800mm.
8. Number of strain /Suspension/
Insulation /string - 254 X 140 fog type
9. Specified current rating for:
a) Main bus bar - 2000A
b) Bus coupler bay bus - 2000A
c) Bay bus of other element - 750A

28. ~ 25 ~
Switchyard Equipments
Circuit Breakers
There are 11 C.B used in switchyard. The circuit breakers are of air blast Type
Following C.B are used in switchyard as per follows:
CB No. USED
CB -1 Bus coupler
CB -2 Generated transformers - (Unit#1)
CB -3 Start up transformer - (Unit#1)
CB -4 One line - Moradabad
CB -5 SUT - (Unit#2)
CB -6 One line - Shimbholi
CB -7 One line - Khurja
CB -8 One line - Atrauli
CB -9 GT - (Unit#2)
CB -10 Transfer Bus
CB -11 One line - Harduaganj
There is a centralized compressed air system for feeding air to the circuit. A
ring main system with two feed points and in the piping to facilitates isolation
of any breaker circuit without disturbing air connection to the other circuits.

29. ~ 26 ~
Isolators
There are 44 isolators used in switchyard. The isolators are pneumatically
operated type and are capable of remote control from control room. These
isolators are worked only on off time condition. Grounding Switch is provided
on the line isolators. These grounding switches are mechanically interlocked
with the main isolators.
Lightening Arresters
Specifications:
Rating - 198 kV
Discharge current - 10 kA
Impulse spark over voltage - 550 kV peak
Switching surge spark over - 420/453 kV Power
Frequency spark over - 1.5 times rated Voltage
Reset Voltage - 205 kV
Lighting arrestors are provided on all five lines at their entry into switchyard
and also near the HV terminals of the power transformer. The arrestors are of
heavy-duty station type manufactured by M/s WS Insulators.

30. ~ 27 ~
Capacitive Voltage Transformer (CVT)
CVT’s are provided on all 3 phases of the 220 kV lines. These CVT's serve the
dual function viz. VT for the line protection and coupling capacitor for carrier
communication. Each main bus bar is provided with one set of electromagnetic
VT for the purpose of metering synchronizing and feeding other protection
circuit. One single phase cut is provided for synchronizing bus.
Current Transformer
Current transformers are used for measurement of large current flowing in a
power line of AC supply. It is connected in series with phase wire. It has
secondary winding and the conductor whose current is to measured acts as
primary. 5 core CT's are provided for each of the elements of the switchyard.
Carrier Communication
Carrier communication facilities are provided for communication between
NAPS control room and Grids substations connected to NAPS. Phase coupling
has been envisaged for single circuit lines. Wave traps are provided on phases
associated with the ‘’communication”. Wave traps block the high frequency
carrier waves due to its high impedance and pass the power frequency signal.
CVTs having high capacitance pass the carrier frequency for PLCC.
Synchronizing Arrangements & Remote Controls
The remote controls for the switchyard circuit are provided on the control
room of NAPS. Synchronizing facilities are available for synchronizing any
element to the line bus bars. Emergency and synchronizing control is done
from control room.
All isolators can also be controlled remotely from the central control room.
However the grounding switches have to be operated manually at the
switchyard.

31. ~ 28 ~
Motor Control Centre
The motor control Center (MCC) is an assembly of panel from where motor
starters for different motors in the station are grouped and controlled from
control room or field. The centralized system of motor control through MCC’s
in contrast with the distributed starter scheme affords the following
advantages:
a) Grouping of large number of motor starter used in the station makes
maintenance and operations easier.
b) Control cabling length and installation costs are reduced. This is
especially true where centralized control system is used - such as in
NAPS where most of the equipments are controlled from control room -
or from location near to the load. Motors below 90 kW capacity are fed
from the MCC of the associated class of the systems (Class IV, III or II).
Circuit diagram of Motor Control Centre (MCC)

32. ~ 29 ~
Electrical Protection System
The objective of a protection scheme is to keep the power system stable by
isolating only the components that are under fault, whilst leaving as much of
the network as possible still in operation.
Circuit Breakers
A circuit breaker is an automatically operated electrical switch designed to
protect an electrical circuit from damage caused by overload or short circuit.
Its basic function is to detect a fault condition and interrupt current
flow.
Circuit Breaker Specification

 Rated voltage
 Rated current
 Rated Frequency
 Rated making capacity
 Rated breaking capacity
 Short time current rating
 Insulation level
 Number of poles
Arc Formation
When a fault occurs, heavy current flows through the contacts of the circuit
breaker. At the instant, when the contacts begin to separate, the contact area
decreases rapidly and large fault current causes increased current density and
hence produces a rise in temperature. The heat produced in the medium
between contacts is sufficient to ionize the air or the oil. The ionized medium
acts as conductor and an arc is struck between the contacts.

33. ~ 30 ~
220 KV & 6.6 KV System
Both 220 KV and 6.6 KV system has air blast type circuit breakers. These
breakers employ a high pressure air blast as an arc quenching medium. The
contacts are opened in a flow of air blast established by the opening of blast
valve. The air blast cools the arc and sweeps away the arcing products to the
atmosphere. This rapidly increases the dielectric strength of the medium
between contacts and prevents from re-establishing the arc. Consequently, the
arc is extinguished and flow of current is interrupted.
6.6 KV breakers are indoor type with compressed air as medium for operating
and quenching the arc during the process of interruption. Operating air
pressure for ABCB is 16 kg/𝑐𝑚2
and for 220 kV air blast circuit breaker is 31.7
kg/𝑐𝑚2
.
415V System
Air circuit breakers are used in 415V system. These breakers are used in 415V
class IV (Bus J, K, L and M) and class II (BUS S and T). 415V breakers are used
for controlling motor loads from 90KW to 200KW. The breakers are
continuously rated for 1300A, 2000A and 3750A and symmetrical making
capacity of 50 kA.
250V DC System
DC circuit breakers employ high resistance method for arc extinction. Air circuit
breakers are used with arc splitters and arc chute to lengthen the arc.
The Switchgear for MG set, ACVR and supply breakers to power board is rated
for 2500A.The bus section breakers are rated for 1000A and feeder breakers
are rated for 630A. All 2500A breakers are electrically operated while 1000A
and 630A breakers are manual breakers.

34. ~ 31 ~
Protective Relays
 It is a protective device which detects abnormal condition in the power
system and initiates corrective action in order to bring the system to its
normal state.
 It processes the input mostly voltage and current from the system and
issues a trip signal when a fault is detected within its jurisdiction.
Functional Characteristics of Relays
Selectivity
Relay should select the faulty section and protect that section only and must
not disturb the healthy circuit.
Sensitivity
Relay should be able to detect the smallest fault and system abnormality.
Speed
Relay should have a proper speed of operation. It should clear the fault before
it damages the system.
Reliability
The protection should not fail to operate in the event of faults in the protected
zone.

35. ~ 32 ~
Types of Relay
Instantaneous Over Current Relay
It is applied for phase fault protection of Motor feeders, Transformers feeders
etc.
Earth Fault Relay Type
It is basically an over current relay used for earth fault protection of motor
feeders and transformer feeder. It provides time delayed over current
protection.
Definite Time Over Current Relay
The relay is used for time grade over current protection for feeders and stalling
protection for motors.
Under Voltage Relay
If under voltage occurs below the set point of relay, it drops and DC relays
picks up to give trip signal for breaker.
Instantaneous Differential Relay
It is basically a 3 phase over current relay designed for more sensitive
application. The way the relay will be connected in the circuit gives it the name
differential. The relay is past action and sensitive. It is used for short circuit
protection for big motor generators.

36. ~ 33 ~
Fuse Failure Relay
It is used for detecting the failure or inadvertent removal of voltage
transformer, secondary fuses and prevention of incorrect tripping of circuit
breaker, for example - failure of PT secondary fuse in distance protection can
result in tripping of the feeder.
Directional Inverse Time Over Current Relay
Relays will operate for current flowing in either direction. Directional over
current relays operate only in one particular direction of power flow as
desired.
Transformer Differential Relay
It is used in phase to phase fault and ground fault protection of power
transformer.

37. ~ 34 ~
Trainee’s Training Experience at NAPS
My training experience at NAPS was quite fruitful and beneficial as it was
a golden opportunity for me to visit Narora Atomic Power Station from
inside which would not have been possible any other time as for security
reasons.
From Day One itself we were exposed to Industrial Working Procedures
like visiting the Electrical Workshop and seeing specially the gigantic
circuit breaker. Exploring various parts of it made me understand many of
its concepts better.
The experience we had at the field training was also very vibrant. Starting
from Turbine Building Visit to visiting individual component section gave
an actual feeling of how huge machineries are handled and maintained.
Although this was my first training at Power Station Industry and so this
training experience was more intriguing.
The Lectures started with Alternator, its specifications at NAPS, its
working, cooling, its capability curve and its protection. Watching the
huge 265 MVA generator amidst blatant noise was itself an experience.
Next we were introduced about the electrical protection practices at
NAPS where all types of protection schemes were given lecture on.
One of the best moments was visiting the switch yard. The best place to
clear all doubts one has is to visit the switch yard and understand it’s
working. To see installed CVTs, main busses, CTs, Lightening arrestors,
transformers at one place in service condition- what more one could ask
for as an Electrical Engineering student.

38. ~ 35 ~
Later in the field visits we visited PMG sets, DG sets, Battery Section etc. I
must admit it was my first experience here to see the inside of DC motor
and alternator. To see how the machines are wound and how actually slip
rings, commutator look like in actual and how it is different from book
diagrams gave a real glimpse of vastness of electrical engineering.
One of the major difference which I saw here and wasn’t in the another
Power Plant where the strictness and alertness of CISF security. I really
appreciate the way security is beefed up owing to its strategic
importance.
Not to leave the wonderful subsidized canteen which was a harbinger of
new energy whenever we were given short tea breaks.
All in all, my experience at NAPS was full of learning and understanding
Power System concepts and had its twists and turns which were beautiful
in their own way.
I just wished I had some pictures standing beside the humongous NDCT
Tower as a souvenir of what transpired in the one month training I
undertook.

39. ~ 36 ~
Conclusions
The nuclear power has come of age with comprehensive capabilities in all
aspects of nuclear power and is poised for a large expansion program.
The challenge is to pursue the three-stage program, develop and
commercially deploy technologies for utilization of thorium and ensure
the country’s long term energy security.
At present nuclear reactors has an increasingly important role to play in
the generation of electricity and in the other areas such as defense.
Needless to say, when pursuing such a program, it is paramount
importance that health and safety of the plant personnel and member of
the public are fully ensured.
The pressurized heavy water reactor, which will be the main source of the
nuclear power in India for present as well as future, have several safety
features. This Design provides redundancy in protective and safety
system and adopts the concept of defense in depth. The double
containment feature provides an added level of safety level.
Operation of nuclear power station is characterized by the strict
adherence to a set of prescribed limits and guidelines. The operation
personnel are carefully selected, trained and qualified. Environmental
releases and exposure of personnel are routinely monitored so as to
ensure that they are within stipulated limits. The regulation authorities
critically review the design and procedure for manufacture, construction
and operation, prior to issue of appropriate licenses. Experience with
Narora atomic power station has demonstrated that the pressurized
heavy water reactor system are capable of operation with high reliability
while ensuring safety of plant personnel and the surrounding population,
and with the with minimal impact on environment.