An

Industrial Training Report

On

NTPC Faridabad

Submitted in Partial Fulfillment of the

Requirements for the Degree of

Bachelor of Technology

In

Electrical Engineering

By

PAWAN AGRAWAL

Roll No. 1104320028

Department of Electrical Engineering

Bundelkhand Institute of Engineering & Technology

(An Autonomous Institute)

Jhansi (U.P.) India - 284128

i

ACKNOWLEDGMENT

I am very grateful to all those who helped me towards its smooth and efficient

completion & under whose guidance this summer training was conducted successfully. I

feel highly indebted to all the senior NTPC officials who extended me a constructive

help in the technical field.

I feel especially thankful to

Mr. K.K. Sharma (Sr. Manager-Chemistry)

Mrs. Prachi (Electrical Maintenance)

Mr. N.N. Mishra (AGM- O&M)

Mr. Manoj Agarwal (DGM-Mechanical Maintenance)

Mr. Jimmy Joseph (S.S. - C&I)

Mr. D.C. Tiwari (S.S. - Operation & Fuel handling)

I gratefully acknowledge all the engineers/staff who gave us their valuable time,

encouragement & constructive criticism for familiarising us with all technical aspects of

the power plant.

PAWAN AGRAWAL

B.Tech Final year

Electrical Engineering

Roll no. 1104320028

ii

CONTENTS

Cover Page i

Acknowledgement ii

Certificate iii

Contents iv

List of Figures vi

List of Tables vii

1. About The Company 1

2. Introduction to NTPC Faridabad 3

2.1 Location 3

2.2 Major Milestones 3

2.3 Installed capacity 4

2.4 Production Inputs 4

2.5 Requirements 4

2.6 Anti-Salient Features 4

3. Basic Working of the Plant 5

4. Fuels 6

4.1 Natural Gas 6

4.2 Naphtha 7

5. Mechanical Systems 8

5.1 Gas Turbine 8

5.2 WHRSG 10

5.3 Steam Turbine 12

6. Switchyard 15

6.1 Circuit Breaker 15

6.2 Lightening Arrester 15

6.3 Earthing Switch 16

6.4 Bus Bar 17

6.5 Capacitor Voltage Transformer 17

6.6 Wave Trap 18

iv

6.7 PLCC 18

6.8 Current Transformer 19

6.9 Isolator 19

7. Generator 20

7.1 Main Components 20

7.2 Excitation system 21

7.3 Generator protection 21

7.4 Generator cooling system 22

7.5 Cooling specifications of turbo-generators 22

8. Transformers 23

8.1 Transformer accessories 23

8.2 Cooling of transformers 24

8.3 Main transformers 25

9. DC system 26

9.1 Requirement of DC system 26

9.2 Description of battery 26

9.2 Battery Charger 27

10. Switchgear 27

10.1 L.T. switchgear 27

10.2 H.T. switchgear 27

10.3 Variable Frequency Drive 28

10.4 Two channel arrangement for synchronous motor 29

11. Conclusion 30

References 31

V

LIST OF FIGURES Page No.

Fig 1.1 NTPC generation growth 2

Fig 1.2 NTPC in power sector 2

Fig 2.1 Plant Overview 3

Fig 2.2 Plant Layout 4

Fig 3.1 Combined Cycle Power Generation 5

Fig 4.1 Pipelines of gas source 6

Fig 4.2 Naphtha Specifications 7

Fig 5.1 Working of WHRSG 11

Fig 6.1 Lightening Arrester 16

Fig 6.2 Capacitor Voltage Transformer 17

Fig 6.3 Wave Trap 18

Fig 6.4 Current Transformer 19

Fig 6.5 Isolators 19

Fig 8.1 Three-Phase Transformers 25

Fig 10.1 Electrical scheme of VFD 28

Fig 10.2 Two channel arrangement of synchronous motor 29

vi

LIST OF TABLES Page No.

Table 5.1 Gas Turbine Specifications 9

Table 5.2 Gas Turbine Generator Specifications 9

Table 5.3 WHRSG Specifications 12

Table 5.4 Specifications of HP Turbine 13

Table 5.5 Specifications of LP Turbine 13

Table 5.6 Steam Turbine Generator Specifications 14

Table 6.1 Specifications of earthing switch 17

Table 7.1 Generator Specifications 21

vii

1. ABOUT THE COMPANY

Corporate Vision:

“A world class integrated power major, powering India’s growth, with increasing global

presence”

Core Values: (BE COMMITTED)

B-Business Ethics

E- Environmentally & Economically Sustainable

C-Customer Focus

O-Organizational Pride

M-Mutual Respect & Trust

M-Motivating Self & Others

I-Innovation & Speed

T-Total Quality For Excellence

T-Transparent & Respected Organization

E-Enterprising

D-Devoted

NTPC Limited is the largest thermal power generating company of India. A public

sector company, it was incorporated in the year 1975 to accelerate power development

in the country as a wholly owned company of the Government of India. At present,

Government of India holds 89.5% of the total equity shares of the company and the

balance 10.5% is held by FIIs, Domestic Banks, Public and others. Within a span of 31

years, NTPC has emerged as a truly national power company, with power generating

facilities in all the major regions of the country. NTPC’s core business is engineering,

construction and operation of power generating plants. It also provides consultancy in

the area of power plant constructions and power generation to companies in India and

abroad.

1

As on date the installed capacity of NTPC is 43,582 MW through its 17 coal based

(31,445 MW), 7 gas based (3,955 MW), 3 Hydro based (1,328 MW) and 7 Joint Venture

Projects (5,754 MW).

NTPC’s share on 31 Mar 2007 in the total installed capacity of the country was 20.18%

and it contributed 28.50% of the total power generation of the country during 2006-07.

Fig 1.1 NTPC Generation Growth

Fig 1.2 NTPC in power sector

2

2. INTRODUCTION TO NTPC FARIDABAD

2.1 Location

Located near village Mujedi & Neemka in Faridabad district of Haryana State.

2.2 Major Milestones

Ever since then honorable Prime Minister Sh. I.K. Gujral laid down the foundation

stone on 03rd august 1997.

First two units of 138MW were commissioned on 21st Jan 2000 and 22nd March, 2000

and one unit of 156MW was commissioned on 16th July 2001 by Haryana Vidyut

Prasaran Nigam.

Faridabad project was taken over by NTPC from HVPN on 13th Feb, 2002.

It is the only power plant in this country to supply its entire power to a state i.e.

Haryana rather than to the national grid.

Fig 2.1 Plant Overview

2.3 Installed Capacity

Stage I (GT) = 2 X 138 MW

Stage II (ST) = 1 X 156 MW

3

2.4 Production Inputs

Water Source:

Rampur Distributaries of Gurgaon Canal

Fuel:

1. Natural Gas (Main Fuel)

(To be piped from HVJ pipeline by GAIL)

2. Naphtha (Alternate Fuel)

3. High Speed Diesel

2.5 Requirements

Gas – average 1.58 mcmd at 68.5% PLF & 2.30 mcmd at 100% PLF

Natural Gas 6.79 KG/Sec., Naphtha 6.58 KG/Sec

Water – 700 tones/ hr / unit

2.6 Anti-Salient Features

1. Cost of Generation: Rs. 2.05 / Kwh

2. Mode of Operation: Base Load

3. Rated Output: 135 MVA for GTG & 191.6 MVA for STG

4. Rated Terminal Vol.: 10.5 KV for GTG & 15.75 KV FOR STG

5. Rated Speed: 3000 rpm

6. Type of Cooling: Air Cooled

7. Black start facility: 3.5 MW Diesel Generator Set: 2000 rpm

8. 1kw power = 1975kcal of fuel

Fig 2.2 Plant Layout

4

3. BASIC WORKING OF THE PLANT

(Combined Cycle Power Generation)

1. The fuel is fed in the two turbines.

2. The fuel is burnt in the gas turbines to release the flue gases at high pressure and

temperature. These gases rotate the turbine shaft.

3. The shaft of the turbine is linked to the shaft of the gas turbine generator which leads

to the production of energy at the two generators.

4. The flue gases produced are passed through waste heat recovery steam generators

where it passes from super-heaters, evaporators, economizers and condensate

preheated.

5. Water present and flowing in the above devices absorb heat from the hot flue gases

and get converted in to high pressure and low pressure steam.

6. The high pressure steam generated in the WHRSG is passed to the steam turbine and

the low pressure steam to LP turbine.

7. The steam available at the outlet of HP turbine and LP turbine generated in the

WHRSG are supplied to the LP turbine.

8. In the step 6 & 7 the steam supplied to the HP and LP turbines rotates the respective

turbine.

9. These rotors are connected to the rotor of the steam turbine generators by rigid

coupling. Therefore due to the rotation of the turbine rotor of the steam turbine

generators by rigid coupling. Therefore due to rotation of the turbine rotor, the

generator turbine also rotates thereby producing electricity at the generator.

Hence in 9 steps 432 MW of electricity is produced.

Fig 3.1 Combined Cycle Power Generation

5

4. FUELS

Gas turbines are capable of burning a range of fuels including Naphtha, crude oil and

natural gas. Selection of fuel depend upon several factors including availability of fuel,

fuel cost cleanliness of the fuel. Natural gas is an ideal fuel because it provides

efficiency and reliability with low operation and maintenance cost. Liquid fuels

particularly heavy oils; usually contain contaminants, which case corrosion and fouling

in gas turbine. Contaminants which cannot be removed from fuel, may leave deposits

in gas turbine, which reduces the performance and adds to the maintenance cost.

Duel fuel system is commonly used, enabling the gas turbine to burn up the fuels when

primary fuel sources are not available. Duel fuel system can be designed to fire both

fuels simultaneously.

4.1. Natural gas

Natural gas is an ideal fuel for se in gas turbine. It contains primarily Methane (CH4)

other gases are ethane (C2H6), Nitrogen (N2), Carbon dioxide (CO2) and Sulphur(S). It

has following advantages:

Clean burning.

Availability at lower cost.

Particularly free from solid residue.

High calorific value of Methane.

Low Sulphur content.

For FGPP, This gas comes from Bombay High through medium of pipelines and one

pipeline from Village Chhainsa (Faridabad).

Fig 4.1 Pipelines of gas source

6

4.2. Naphtha

FGPP works on natural gas but if there is shortage of natural gas then plant is to be run

on Naphtha. Naphtha as compared to natural gas has less calorific value but there is no

alternate fuel other than Naphtha. It is cheaper than any other fuel and the amount of

flue gases that comes out of the Naphtha can also be sent out to boiler to boil the water

for manufacturing of steam for running the steam turbine.

Naphtha is highly inflammable and highly explosive fuel. When it makes a mixture

with air, it forms a very highly dangerous explosive mixture. When the supply of

natural gas cuts off, the pipelines are filled with air. So while using Naphtha, it is

necessary to remove that air because it can make explosive mixture with Naphtha. So

for flushing this air a high-speed diesel (HSD) is sent to the pipeline, which removes

the air present. In this way HSD enters the combustion chamber and working

continues. This is the procedure for working of gas turbine when it has to feed on

Naphtha without stopping the while plant, which was previously feed on natural gas.

Naphtha before entering the pipelines undergoes filtration various times so that there

should not be any impurity in that when it enters the combustion chamber. The main

difference between Naphtha and Natural gas is that, natural gas enters the combustion

chamber in the form of gas but Naphtha enters in form of liquid spray. Then it is

compressed in it and due to high compression it burns and leaves very highly

pressurized flue gases, which in turn is used to rotate the gas turbine. This entire

process of using the Naphtha as a fuel is known as Naphtha firing.

Fig 4.2 Naphtha specification

7

5. MECHANICAL SYSTEMS

The main generating unit consists of three main equipments in the plant. They are:

1. Gas Turbine

2. Waste Heat Recovery Steam Generator

3. Steam Turbine

5.1. Gas Turbine

It is a single shaft (with line compressive unit). It is a 50 Hz; 135MW machine which

runs on natural gas could also be operated on the liquid Naphtha. The gas turbine is

very heavy, industrial type, within line compressor multistage flow type. The

combustion chamber is of annular type.

According to the flow of the air compressor is placed first, combustion chamber is next

to it and turbine at the end of gas turbine. Two bearings are placed to support the shaft

of the machine, these turbines are provided at the compressor starting end, and other

are placed at the turbine end. The shaft of the unit is provided with the blades in the

turbine region.

5.1.1. Basic parts of the Gas Turbine:

1. Compressor: Is a fuel stage axial type. It is provided with a variable inlet guide

system to enable efficient operation. Filters are provided at the top of the

compressor to filter any unwanted material from entering the turbine. In the

compressor region there are 16 stages of blade, one set of blade, one set of blade

on shaft and other set of fixed blade comes alternatively.

2. Combustion chamber: There are two chambers in the gas turbine, one on each side

of the shaft, connected vertically and parallel to each other. The combustion

chambers are cylindrical in shape and attached to the unit in between the

compressor and turbine.

3. Turbine: It is provided at the end of the gas turbine unit. It consists of four stages

of blades it also has the gearing to support the shaft at its end.

Exhaust of the turbine is connected to the bypass stake which is further connected

to WHRSG. The bypass is take is provided with two gates namely diverter

damper and gelatin gates.

5.1.2. Working of the gas turbine:

During the start-up of generator, it act as motor. The generator is given supply and

compressor start working. The function of the compressor is to provide air at the high

pressure to combustion chamber, once air is supplied to the combustion fuel is

ignited. 8

Due to the burning of the fuel flue gases are released at high pressure and

temperature and thermal expansion of the gases rotates the turbine blades that are

connected to the shaft back supply to the generator is then stopped. Fuel supply is

slowly increased till the optimum speed (3000 rpm) is attained. Fuel supply is kept

constant. The fuel gases after rotating the turbine can be directed to the WHRSG sing

diverter damper and gelatin gate.

5.1.3. Gas Turbine Specifications:

manufacture SEIMENS(Germany); model-V 94.2

capacity 137.76 MW

compressor 16 stage

turbine 4 stages

burner Hybrid dual fuel

combustors SILO type

Air intake filters Pulse cleaning(576 in numbers)

By pass take Vertical 70 m in height

Ambient temperature 27 deg c

Ambient pressure 1013 Mbar

Table 5.1 Gas Turbine Specifications

5.1.4. Gas turbine generator specifications:

Relative humidity 60%

Voltage rating 10.5 kv

Power factor 0.85 lagging

KVA 170.12 MVA

Excitation current 833 Amp

Excitation voltage 410 V

Insulation type Class F micalastic

Connection type AA

Table 5.2 Gas turbine generator specifications

9

5.2. Waste Heat Recovery Steam Generator

The waste heat generator are unfired, heat recovery type design to accept the maximum

exhaust temperature along with flue gas flow from the turbine. It is a natural circulation

dual unit. All heat transfer surface are of fin type. The feed control system is located in

between the economizer and drain to eliminate the possibility of streaming in the

economizer and to enable operation with zero approach point thereby increasing in the

efficiency of the combine cycle plant. A condensate preheated is added to low

temperature zone of WHRB. There are two types of steam produced in this unit (H.P &

L.P).

5.2.1. Basic Parts of WHRSG:

1. Condensate Preheater: it is present at the end of WHRSG. It is added to lower

the temperature of flue gases in addition to increase the thermal efficiency of the

plant. It is consist of spiral fined tubes welded to the top and bottom headers. There

are maximum rows per module.

2. Economizers: There are three different types of economizers. These are:

a) L.P economizer: these tubes act as the economizer of the L.P steam; these are

spiral fined tubes welded to the top and bottom headers and have fully drainable

design.

b) H.P economizer: these tube act as economizer for H.P steam, they also have

spiral fined tubes welded to the top bottom headers and have fully drainable

design.

3. Evaporator: These are of two types:

a) L.P evaporator: these tubes act as evaporator for the L.P. steam; these are

connected to the L.P. drum and are spiral finned tubes.

b) H.P evaporator: these tubes act as evaporator for H.P. steam, these are

connected to H.P. drum and are placed closure to the turbine exhaust then the

L.P. evaporator. These are also spiral fined tubes welded to the top and bottom

headers are connected to the H.P. steam drum.

4. Superheater:

a) L.P. super heater: these tubes act as super heater for the L.P Steam. These are

the fourth heat transfer surface in the direction of the gas flow. These are

consisting of finned tubes, welded to the top and bottom headers and have

maximum of two rows per module. These are designed for single gas flow on tube

side and have fully drainable design. b) H.P. super heater 1&2: these tubes act as superheated for the H.P. Steam. These

are the first heat transfer surface in the direction of gas flow. These consist of multi

pass flow on the side and single flow on the gas side.

5. Steam drum: these are the two drums placed at the top of WHSRG, these are:

10

a) L.P. Drum: these drum store the L.P steam produced during the flow of

water in the L.P. evaporator. It is small in the size than the H.P drum and has a

blow of cork at its top to avoid blasting at high steam pressure.

b) H.P. Drum: this drum store the H.P steam produced during the flow of water

through H.P. super heater. It also has a blow cork for safety purposes.

5.2.2 Working of the WHRSG:

The boiler feed pumps feed the water to the HP & LP economizers, where the

temperature of the water rises close to the saturation temperature after flowing to the

economizers the water is passed to the steam drums through feed control system, then

water is taken to the bottom header of the evaporator through the downpipes, here

water gets converted into a mixture of steam and water. The mixture is carried to the

tubes through rigor pipes. In the drum mixture is passed through centrifugal separators,

where water is passed for recirculation through the down pipes. In the super heater

steam gets superheated, to control the temperature of steam it is passed through spray

type de-superheated is provided between HP economizer 1&2. This steam at the outlet

of the super heater is carried to the steam turbine through feed pipes.

Fig 5.1 Working of WHRSG

11

5.2.3. WHRSG Specifications:

Table 5.3 WHRSG Specifications

5.3. Steam turbine

The plant is provided with one steam turbine generating unit. The turbine is a 3000 rpm

condensing set without any extraction for feed heating. It is a 160 MW, 50 Hz two

cylinder condensing type turbines. The first cylinder (H.P) is a single flow type 25

reactions stages and the second cylinder (L.P) is a double flow with 7 reaction stages. It

is provide with two main and two LP stop and control valves. The H.P and L.P sections

have individual turbine rotors, which are connected to each other, and the generator

with rigid couplings.

5.3.1. Basic parts of Steam Turbine:

1. H.P. Turbine: It is a single flow type turbine, with horizontal split casing and

double shell. The provision of steam inlet temperature and high pressure to admission

section is subjected only to low temperature and pressure and pressure effective at the

exhaust of the turbine. The high pressure turbine is provided with two main stop and

control valves to check and regulate the entry of the steam in to casing.

12

S.No. Parameter HP System LP

System

1. Design Pressure (bar) 83 9

2. working pressure (bar) 63 5.5

3. Steam temperature (deg.

C)

488 207

4. Steam flow (T/hr) 162.67 39.1

5. Total heating surface,

Superheater (m2)

8980 584

6. Total heating surface,

water tubes (m2)

55910 23859

2. L.P. Turbine: it is a three cell design and has a double flow system for max

efficiency. The inner casing caries the first row of stationary blades and is supported on

the outer casing so as to allow for thermal expansion. The middle casing rest on four

girders, independent of the outer casing. The LP turbine is provided with two control

valves.

3. Bearing: The HP rotor is supported on two bearings, a combined journal bearing

close to the coupling with LP rotor. The LP journal bearing at its end. The bearing pedestals are anchored to the foundation and are fixed in position.

5.3.2. Working of steam turbine:

The HP steam is fed to the HP section of the steam turbine. The steam passes through

the stop and control valves of the HP turbine and enters the inner casing. On entering

the inner casing the steam after leaving the HP turbine gets converted into LP steam.

This LP steam produced at the WHRSG is passed into the inlet of the double flow LP

turbine. On entering the steam once again expands and due to the combined effect of

HP&LP rotors, the generator rotor also rotated and electricity is produced. The two

outlet of the LP turbine are connected to the condenser where water and steam mixture

are connected into water for further use in the WHRSG.

5.3.2. Specifications of HP Turbine:

TYPE Single flow

No. of stages 25 reaction stages

Total H.P main steam pressure 76.4 bar

HP main steam temp. 528 deg c

HPT exhaust pressure 5.1 bar

HPT exhaust temp. 175 deg

Table 5.4 Specifications of HP Turbine

5.3.3. Specifications of LP Turbine:

Type Double flow

No. Of stages 7 reaction stages

Total LP steam flow 46 T/hr

LP main steam pressure 4.38 bar

Table 5.5 Specifications of LP Turbine

13

5.3.5. Steam turbine specification:

manufacturer BHEL(haridwar, India)

type 2 cylinder condensing turbine

capacity 156.07MW

Maximum terminal outputs 160 MW

Main steam pressure 76.4 and 4.38 bar

Condenser vacuum -0.92 bar

speed 3000 rpm

Steam turbine generator 160000 W/188230 VA

Stator current 6900 amp

coolant air

insulation Class F

Power factor 0.85 lag

Excitation system Brush less excitation

Rotor voltage 432 V

Rotor current 797 amp

Table 5.6 Steam turbine specification

14

1

6. SWITCHYARD

The switch yard is the place from where the electricity is send outside. We know that

electrical energy can’t be stored like cells, so what we generate should be consumed

instantaneously. But as the load is not constant, therefore we generate electricity

according to need i.e. the generation depends upon load. It has both outdoor and indoor

equipments.

6.1 Outdoor Equipments

Bus Bar

Circuit Breaker

Lightening Arrester

Earth Switch

Capacitor Voltage Transformer

Wave Trap

PLCC

Current Transformer

Isolators

Potential Transformer

6.2 Indoor Equipments

Relays

Control Panels

6.1.1 Bus Bar

There are three buses viz. two main buses (bus 1 and bus 2) and one transfer bus. The

two main buses are further divided into two sections thus giving us a total of five buses.

Bus bars generally are of high conductive aluminum conforming to IS-5082 or copper of

adequate cross section .Bus bar located in air –insulated enclosures & segregated from

all other components .Bus bar is preferably cover with polyurethane.

6.1.2 Circuit Breaker

The code for circuit breaker is 52. An electric power system needs some form of

switchgear in order to operate it safely & efficiently under both normal and abnormal

conditions. Circuit breaker is an arrangement by which we can break the circuit or flow

of current. A circuit breaker in station serves the same purpose as switch but it has many

added and complex features. The basic construction of any circuit breaker requires the

separation of contact in an insulating fluid that servers two functions:

15

It extinguishes the arc drawn between the contacts when circuit breaker opens.

It provides adequate insulation between the contacts and from each contact to earth.

The insulating fluids commonly used in circuit breakers are:

Compressed air

Oil which produces hydrogen for arc excitation.

Vacuum

Sulphur hexafluoride (SF6 )

There are two makes of Circuit Breakers used at NTPC Faridabad switchyard:

i. SF6 Circuit Breaker – manufactured by ALSTOM

ii. Gas Circuit Breaker – manufactured by CGL

6.1.3 Lightening Arrester

These are provided to combat the effect of over voltages and surges caused due to

lighting strokes on the transmission lines. These are generally provided at the end near

the instrument which we want to protect. The lightening arrestors provide an easy path to

the surge current to the ground thereby not letting the Equipments to fail.It saves the

transformer and reactor from over voltage and over currents.

It has a round metal cap type structure on the top called CORONA RING, meant for

providing corona losses.

A meter is provided which indicates the surface leakage and internal grading current of

arrester.

Green – arrester is healthy

Red – arrester is defective

In case of red, we first de-energize the arrester and then do the operation.

Fig 6.1 Lightening Arrester

16

6.1.4 Air Break Earthing Switch

These are used to ground the circuit and to discharge the CB when CB is in off

condition.

The code of earthling switch is 5, 6, 7.The work of this equipment comes into picture

when we want to shut down the supply for maintenance purpose. This help to neutralize

the system from induced voltage from extra high voltage. This induced power is up to

2KV in case of 400 KV lines.

Table 6.1 Specifications of earthing switch

6.1.5 Capacitor Voltage Transformer (CVT)

The carrier current equipment can be connected via the capacitor of CVT. Thereby

there is no need of separate coupling capacitor. The reactor connected in series with

the burden is adjusted to such a value that at supply frequency it resonates with the

sum of two capacitors. This eliminates the error. CVT is attached at end of each

transmission, line and buses.

The CVT is used for line voltage measurements on loaded conditions. The basic

construction of a cvt is as follows. Each CVT consists of a coupling capacitor (CC)

which acts as a voltage driver and an Electro Magnetic Unit (EMU) which transforms

the high voltage to standard low voltage. Depending on the system voltage the CC

can be a single or a multi stack unit. 245 kV & 420kV CVTs no normally comprise

of 2 units.

Fig 6.2 Capacitor Voltage Transformer

17

Make Voltage Motor volt (ac) Control volt (dc)

S & S power 245 kV 415 volts 220 volts

The main points of difference between a CVT and a potential transformer (PT) is that in

a PT full line voltage is impressed upon the transformer while in cvt line voltage after

standard reduction is applied to the transformer.

It is used for three purposes:

Metering

Protection

PLCC

6.1.6 Wave Trap

It is used in PLCC system to trap frequency higher than 50 Hz. It is lightly inductive

having very less resistance. It is attached at each end of transmission line. It is of

cylindrical shape mounted on top of the transmission line.

Fig 6.3 Wave Trap

6.1.7 PLCC (Power Line Carrier Communication)

In addition to power supply transfer, transmission line is also used for communication

purpose. This is done by PLCC system. Here line conductors itself are used as channel

for carrying information between two end of line.

The PLCC system is used to trap the frequency higher than 50 Hz through high

inductance and low resistance along with a coupling capacitor. The main components of

PLCC are:-

Wave trap

Co-axial cable

CVT

PLCC cabinet

LMU ( Line matching Unit)

18

6.1.8 Current Transformer (CT)

These are used for stepping down AC current from higher value to lower value for

measurement, protection and control. Here N2 gas is used to prevent oil from moisture.

Its secondary winding has 5 cores.

Terminal 1,2,4,5 protection 3 Metering Turns ratio – 800/1

Fig 6.4 Current Transformer

6.1.9 Isolators

The isolators can be thought of switches that can either make or break the circuit at the

operator’s wish.

Sequence of operation while opening / closing a circuit:

While opening: open circuit breaker open isolator close earthing switch (if any)

While closing: ensure circuit breaker is open close isolator open earthing switch

close circuit breaker.

It is used as off line circuit breaker. It is normally used for purpose of isolating a certain

portion when required for maintenance. It operates at 2000 A.

In switchyard there are 3 types of isolators:

Line isolator

Transfer bus isolator

Bus isolator

Fig 6.5 Isolators

19

7. GENERATOR

The transformation of mechanical energy into electrical energy is carried out by the

generator. The generator also called the alternator is based upon the principle of

electromagnetic induction. The stator houses the armature windings and the rotor houses

the field windings. The alternator is a doubly excited system and the field is excited from

dc supply whereas the output received from the alternator is ac.

When the rotor is energised the flux lines emitted by it are cut by the stator windings

which induces an emf in them given by

E = 4.44 f Φ N

Where f frequency in Hz

Φ field strength in webers/m2

N speed of rotor in rpm

Turbo generators run at a very high speed hence the no. of poles are generally two or

four and have a cylindrical rotor construction with small diameter and long axial length.

7.1 Main components

The main components of a generator are the rotor and stator.

7.1.1 Rotor

Body: The electrical rotor is the most difficult part of the generator to design. It is an

electromagnet and to give it the required strength of magnetic field a large current is

required to flow through it.

Rotor winding: Silver bearing copper is used for the winding with mica as the insulation

between conductors. Rotor has hollow conductors with slots to provide for circulation of

the cooling gas.

Rotor balancing: The rotor must then be completely tested for mechanical balance

which means that a check is made to see if it will run upto normal speed without

vibration.

7.1.2 Stator

Stator frame: It is the heaviest load to be transported. The major part is the stator core.

This comprises an inner frame and an outer frame. The outer frame is a rigid fabricated

structure of welded steel plate. In large generator the outer casing is done in two parts.

Stator core: it is the heaviest part and is built from a large no. of thin steel plates or

punching.

Stator windings: It is of lap type and employs direct water cooled bar type winding. The

stator winding bar is made from glass lapped elementary conductor and hollow

conductors. The main insulation is applied by means of mica tape which is wrapped and

is compounded with the help of a silicon epoxy compound.

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KVA Pf Stator

Voltage

(V)

Stator

Current

(A)

Rotor

Voltage

(V)

Rotor

Current

(A)

Rpm Hz Phase Coolant

247000 0.85 15750 9050 310 2600 3000 50 3 Water

(stator)&

hydrogen

(rotor)

Table 7.1 Generator Specifications

7.2 Excitation System

Static Excitation System-The generators in stage -1(U-1&U-2) have this excitation

system. Static excitation system has slip ring and carbon brush arrangement. It

consists of step down transformer, converter and AVR (automatic voltage regulator).

Brushless Excitation System –The generators in stage -2(U-3, U-4& &U- 5) have

this excitation system. It has two exciters, one is main exciter and other is pilot

exciter.

7.3 Generator Protection

Stator Protection- The neutral of star connected winding is connected to primary of

neutral grounding transformer, so that earth fault current is limited by over voltage

relay.

Differential Protection- In case of phase-to-phase fault generator is protected by

longitudinal differential relay.

Rotor Protection-Rotor winding may be damaged by earth faults or open circuits.

The field is biased by a dc voltage, which causes current to flow through the relay for

an earth fault anywhere on the field system.

Over Speed Protection –Mechanically over speed device that is usually in the form

of centrifugally operated rings mounted on the rotor shaft, which fly out and close the

stop valves if the speed of the set increase more than 10%.

Over Voltage Protection – It is provided with an over voltage relay. The relay is

usually induction pattern. The relay open the main circuit break and the field switch if

the over voltage persists.

Seal Oil System –is a possibility of this hydrogen to come out of gaps, which is very

hazardous. So, seal oil is used to seal the gaps so that hydrogen doesn’t come out.

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Lubrication Oil System –Turbine lubrication-oil system seeks to provide proper

lubrication of turbo generator bearings and operation of barring gear. Pumps are used

to circulate lubrication-oil inside the generator. The oil of the lubrication and the

governing system is cooled in the oil coolers. The cooling medium for these coolers is

circulating water.

7.4 Generator Cooling System

Turbogenerator is provided with an efficient cooling system to avoid excessive heating

and consequent wear and tear of its main components during operation. The two main

systems employed for cooling are water cooling system and hydrogen cooling system.

Hydrogen cooling system: Hydrogen is used as a cooling medium in large capacity

generator in view of the following feature of hydrogen. When hydrogen is used as a

coolant the temperature gradient between the surface to be cooled and the coolant is

greatly reduced. This is because of the high coefficient of heat transfer of hydrogen.The

cooling system mainly comprises of a gas control stand, a driver, hydrogen control panel,

gas purity measuring instrument and an indicating instrument, valves and the sealing

system. A great care should be taken so that no oxygen enters the cooling system

because hydrogen forms an explosive mixture with air. The purity of hydrogen be

maintained as high as 98%.to produce hydrogen in such large quantities a separate plant

called the hydrogen plant is also maintained.

Water cooling system: Turbo generators require water cooling arrangement. The stator

winding is cooled by circulation of demineralised water through hollow conductors. The

system is designed to maintain a constant rate of cooling water flow to the stator winding

at a nominal temperature of 40 deg Celsius.

7.5 Cooling Specifications of Turbo generators At FGPS

Stage-I:

Water as well as hydrogen cooling is present in stage-I turbo generators with following

specifications:

Rotor cooling: Hydrogen gas pressure: 3.5 Kg/cm2, Purity: 98%

Stator cooling: Water pressure: 3.5 Kg/cm2, Rate of flow of water: 130 m3/hr

Stage-II & III:

Only hydrogen cooling is used for both stator and rotor cooling.

Rotor cooling: Hydrogen gas pressure: 3.5 Kg/cm2, Purity: 98%

Stator cooling: Hydrogen gas pressure: 2.0 Kg/cm2, Purity: 98%

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8. TRANSFORMERS

The transformer is a device that transfers electrical energy from one electrical circuit to

another through the medium of magnetic field and without the change of frequency. It is

an electromagnetic energy conversion device, since the energy received by the primary is

first converted to magnetic and is then reconverted to electrical energy in the secondary.

Thus these windings are not connected electrically but coupled magnetically. Its

efficiency is in the range of 97 to 98 %.

8.1 Transformer accessories

Conservator: with the variation of temperature there is a corresponding variation in

the volume of oil due to expansion and contraction of oil caused by the temperature

change. To account for this, an expansion vessel called the conservator is connected

to the outside atmosphere through a dehydrating breather to keep the air in the

conservator dry. An oil gauge shows the level of oil in the conservator.

Breather: it is provided to prevent the contamination of oil in the conservator by the

moisture present in the outside air entering the conservator. The outside air is drawn

into the conservator every time the transformer cools down which results in the

contraction of the volume occupied by the oil in the conservator. The breather

contains a desiccator usually Silica gel which has the property of absorbing moisture

from the air. After sometime silica gel gets saturated and then it changes it colour

from purple to pink indicating that it has become saturated and hence needs to be

replaced or regenerated.

Relief vent: In case of severe internal fault in the transformer, the pressure may be

built to a very high level which may result in the explosion in the tank. Hence to

avoid such condition a relief vent is provided with a bakelite diaphragm which breaks

beyond certain pressure and releases the pressure.

Bushings: they consist of concentric porcelain discs which are used for insulation

and bringing out the terminals of the windings from the tank.

Buchcholz relay: this is a protection scheme for the transformer to protect of against

anticipated faults. It is applicable to the oil immersed transformer and depends on the

fact that transformer breakdowns are always preceded by violent generation of gas

which might occur due to sparking or arcing.

Temperature indicators: transformers are provided with two temperature indicators

that indicate the temperature of the winding and that of the oil in the transformer for

an oil filled transformer.

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The temperature indicators are also protective in nature whereby the first create an

alarm and then trip the respective transformer in case the temperature of the

respective parts rises beyond a certain value.

Tap changers: these are also provided and are mounted on the transformer. In case

some kind of load fluctuations the taps can be changed or adjusted as per the need.

There are two types of tap changers: On load tap changer and off load tap changer.

8.2 Cooling Of Transformers

Heat is produced in the transformers due to the current flowing in the conductors of the

windings and on account of the eddy current in the core and also because of the

hysteresis loss. In small dry type transformers the heat is directly dissipated to the

atmosphere. In oil immersed systems oil serves as the medium for transferring the heat

produced. Because of the difference in the temperatures of the parts of the transformers

circulating currents are set. On account of these circulating currents hot oil is moved to

the cooler region namely the heat exchanger and the cooler oil is forced towards the hot

region. The heat exchangers generally consist of radiators with fins which might be

provided with forced or natural type air circulation for removal of heat.

The oil in oil immersed transformers may also be of forced or natural circulation type.

The oil used for cooling is silicone oil or a mixture of naphthalene and paraffin. When

forced oil circulation is used then pumps are used for the circulation of the oil. The oil

forced air forced type cooling is used in large transformers of very high KVA rating.

1. Simple Cooling

AN: Natural cooling by atmospheric circulation, without any special devices. The

transformer core and coils are open all round to the air. This method is confined to very

small units at a few kV at low voltages.

AB: In this case the cooling is improved by an air blast, directed by suitable trunking and

produced by a fan.

ON: The great majority of transformers are oil-immersed with natural cooling, i.e. the

heat developed in the cores and coils is passed to the oil and thence to the tank walls,

from which it is dissipated.

OB: In this method the cooling of an ON-type transformer is improved by air blast over

the outside of the tank.

OFN: The oil is circulated by pump to natural air coolers.

OFB: For large transformers artificial cooling may be used. The OFB method comprises

a forced circulation of the oil to a refrigerator, where it is cooled by air-blast.

OW: An oil-immersed transformer of this type is cooled by the circulation of water in

cooling tubes situated at the top of the tank but below oil-level.

OFW: Similar to OFB, except that the refrigerator employs water instead of air blast for

cooling the oil, which is circulated by pump from the transformer to the cooler.

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2. Mixed Cooling

ON/OB: As ON, but with alternative additional air-blast cooling. ON/OFN, ON/OFB,

ON/OFW, ON/OB/OFB, ON/OW/OFW.

A transformer may have two or three ratings when more than one method of cooling is

provided. For an ON/OB arrangement these ratings are approximately in the ratio 1/1.5;

for ON/OB/OFB in the ratio 1/1.5/2.

8.3 Main Transformers

i. Generator Transformer: This is a step up transformer. This supply gets its primary

supply from generator and its secondary supplies the switchyard from where it is

transmitted to grid. This transformer is oil cooled. The primary of this transformer is

connected in star. The secondary is connected in delta. These are two in number.

ii. Station Transformer: This transformer has almost the same rating as the generator

transformer. Its primary is connected in delta and secondary in star. It is a step down

transformer. These are 4 in number.

iii. Unit Auxiliary Transformer: This is a step down transformer. The primary receives

from generator and secondary supplies a 6.6 KV bus. This is oil cooled. These are 10

in number.

iv. Neutral Grounded Transformer: This is used to ground the excess voltage if

occurs in the secondary of UAT in spite of rated voltage.

Fig 8.1 3-Phase Transformers

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9. D.C SYSTEM

9.1 Requirement of DC System

There are some auxiliaries which need to run even when the ac supply fails such as seal

oil pumps, the scanner system, valve control, lights, etc. So we require the DC system.

All the circuit breakers in the power plant operate on DC. The DC system comprises of

batteries, chargers & control circuit to maintain a continuous supply for the DC feeders.

There are five units in unchahar power plant and in each unit separate battery rooms are

made from which we have 220V as well as 24V DC supply.

9.2 Description of battery:

Capacity = 220 V (1400 AH) / 24 V (400 AH)

Per unit cell = 2.2 V

Battery plate:

Positive terminal = PbO2

Negative terminal = Pb

Electrolyte = H2SO4

Reactions occurring in the battery:

i. At the time of charging:

At positive plate –

PbSO4 + SO4 + 2H2O PbO2 + 2H2O

At negative plate –

PbSO4 + H2 Pb + H2S

ii. At the time of Discharging:

At positive plate –

PbO2 + H2 + H2SO4 PbSO4 + 2 H2O

At negative plate –

Pb + SO4 PbSO4

9.3 Battery charger

Battery charger normally operates in two modes.

Float charging: It is constant voltage mode and works as a trickle charger.

Boost charging: It is constant current mode and works as a quick charger.

Trickle Charger – It operates at 220V. It is used for continuous charging of the battery.

Full time battery is charged by the trickle charger and remains in float condition.

Quick charger – It is also known as Boost Charger. This is used at the time of

overhauling. It operates in two modes –

i. Constant current (CC) ii. Constant Voltage (CV)

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10. SWITCHGEAR

Switchgear is an electrical functional switch used for starting any drive and provide

protection to the drive during on load condition. It is of two types:-

Low tension switchgear (below 1000 V)

High tension switchgear (above 1000 V)

10.1 L.T Switchgear

OPERATING VOLTAGE- 415VOLT

The main components are:

Relays: the purpose of protective relaying system is to operate the circuit breaker so

as to disconnect only the faulty equipment from the system as quickly as possible thus

minimizing the trouble and damage caused by faults when they do occur. The general

relay used is BMR (Bi-Metallic Relay). It trips due to thermal overloading when

overcurrent passes through the bimetallic strips causes different expansions in

different parts as a result the BMR strip is bent.

Contactors: these are used on-load operations under normal conditions. Contactor is

a mechanical switching device capable of making carrying and breaking electric

current under normal circuit conditions including operating overload conditions

Isolators: These are disconnecting switches used for off-load operations. These are

operated manually. Before operation power is switched off. Isolators are kept in

closed position when the system components are in operation. During any

maintenance work isolators are kept open.

Fuses: It is a device used in circuit for protecting electrical equipments against

overload or short circuit. The fuse wire melts when an excessive current flows in the

circuit and thus isolates the faulty device from the supply circuit.

10.2 H.T. Switchgear OPERATING VOLTAGE - 6.6KV

For low voltage circuits fuses may be used to isolate the faulty circuit. For voltage higher

than 3.3 kV isolation is achieved by circuit breaker.

Requirement of circuit breaker:

After occurrence of fault the switchgears must isolate the faulty circuit as quickly

as possible i.e. keeping the delay to minimum.

It should not operate when an over current flows under healthy condition.

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Basic principal of operation of circuit breaker:

Circuit breaker consists of a fix contact and sliding contact into which moves a moving

contact. The end of moving contact it attached to a handle that can be manually operated

or may operate automatically with the help of mechanism that has a trip coil energized

by secondary of CT. Under normal condition the secondary of CT is not energized

sufficiently to trip the coil but under false condition the coil is energized fully to operate

the trip coil and the circuit breaker is operated.

MOCB (Minimum oil circuit breaker)

SF6 (Sulphur hexafluoride circuit breaker)

Here oil and SF6 are used to quench the arc.

Bus ducts:

These serve as interconnection between transformer and switchgear and are non-

segregated phase type. These are natural air cooled.

Bus coupler:

It acts as interconnection between the two buses. If the supply of one bus fails then the

bus coupler connects the two buses and charges the bus from the other bus.

Different relays used:

Motor protection system

Earth fault relay

Over load relay

Lock out relay

Check synchronizing relay

Differential protection relay

Auxiliary relay

10.3 Variable frequency drive:

Fig 10.1 Electrical scheme of VFD

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The panel in the figure is a variable frequency drive panel. Using variable frequency

drive voltage is compensated at low frequencies, the torque at low speeds is improved.

To obtain the voltage boost, we require a controlled converter as well as a controlled

inverter.

First the three phase supply from transformer is fed to the controlled rectifier which the

ac to dc. The advantage of using a controlled rectifier is that the average value of the

output can be controlled by varying the firing angle. Then its output is fed to the inverter

which is a type of load commutated inverter. Before passing it to the inverter a reactor is

also employed in between this reduces the ripples. The inverter then converts dc to ac

and the ac is fed to the synchronous motor. The speed of synchronous motor is fixed and

is given by 120 f / p. since the only thing variable in the expression is the frequency

which is directly proportional to the speed. Hence the inverter varies the frequency and

hence controls the speed of the motor. The controlled rectifier in the circuit is used for

voltage control while the load commutated inverter is used for frequency variation.

10.3.1 Advantages of Variable Frequency Drive:

1. Speed control is fine as the frequency is varied from 0.5Hz to 47.5 Hz.

2. Very low starting current as motor starts on reduced voltage.

3. Power consumption is low.

4. Motor life is improved

10.4 Two channel arrangement for synchronous motor:

The stator of the synchronous motor is given supply using two channels. Normally the

motor works on both channels but under some faulty conditions on any one of the

channels the other channel can continue working since the motor is required for

continuous operation

Fig 10.2 Two channel arrangement of synchronous motor

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11. CONCLUSION

On completion of my vocational training at NTPC Faridabad, I have come to know about

how the very necessity of our lives now a days i.e. how electricity is generated & what

all processes are needed to generate and run the plant on a 24x7 basis.

NTPC Faridabad is one the plants in India to be under highest load factor for the

maximum duration of time and that to operating at highest plant efficiencies. This plant

is an example in terms of working efficiency and management of resources to all other

thermal plants in our country. The operating pf of the NTPC as compared to the rest of

country is the highest with 95 % the highest since its inception.

The training gave me an opportunity to clear my concepts from practical point of view

with the availability of machinery of diverse ratings.

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REFERENCES

[1] N.T.P.C. magazines. [2] Google [3] Wikipedia [4] N.T.P.C. Websites.

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