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BRIEF CONTENTS

Chapter 1 Introduction

Chapter 2 Brief History Of Electric Power

Chapter 3 Electric Power System

Chapter 4 Generation Of Electric Energy

Chapter 5 Energy Supply And Consumption In Pakistan

Chapter 6 Potential Available For Power Generation

Chapter 7 Power Transmission

Chapter 8 Power Distribution

Chapter 9 Three Phase Power System

Chapter 10 Star – Delta Connections

Chapter 11 Power Transformer

Chapter 12 Auto Transformer

Chapter 13 132/220 KV Switchyard

Chapter 14 Earthing

Chapter 15 Protection Relays & Protection System Of Hydel Power Plant

Chapter 16 Turbines & Generators

Chapter 17 50/230V D.C Batteries

Chapter 18 Auxiliary And Emergency Supply System

Chapter 19 Fire Protection System

TABLE OF CONTENTS

Chapter 1 Introduction ........................................................................................................................................... 1

1.1 electric charge ........................................................................................................................................ 1

1.2 electric field ............................................................................................................................................ 1

1.3 electric potential .................................................................................................................................... 1

1.4 electric current ....................................................................................................................................... 1

1.5 electromagnets ...................................................................................................................................... 1

1.6 electric power ........................................................................................................................................ 1

1.7 electronics .............................................................................................................................................. 1

1.8 Generation ............................................................................................................................................. 2

1.9 Transmission system .............................................................................................................................. 2

1.10 Load ...................................................................................................................................................... 2

Chapter 2 BRIEF HISTORY OF ELECTRIC POWER ............................................................................................ 2

2.1 Early 1880’s ............................................................................................................................................ 2

Chapter 3 ELECTRICAL POWER SYSTEM ........................................................................................................ 3

3.1 STEPS OF TYPICAL POWER SYSTEM ............................................................................................................... 3

Chapter 4 GENEARATION OF ELECTRICAL ENERGY ........................................................................................ 4

4.1 TYPES OF GENERATION STATIONS ................................................................................................................ 4

4.2 GENERATION SOURCES IN PAKISTAN ............................................................................................................ 5

Chapter 5 ENERGY SUPPLY & CONSUMPTION IN PAKISTAN .......................................................................... 5

Chapter 6 POTENTIAL AVAILABLE FOR POWER GENERATION ........................................................................ 6

6.1 MULTIPURPOSE PROJECT .............................................................................................................................. 6

6.2 HYDEL POTENTIAL ......................................................................................................................................... 6

6.2.1 Run of River Projects Feasibility Studies in Hand ................................................................................... 6

6.2.2 PAKISTAN’S TOTAL HYDROPOWER POTENTIAL ..................................................................................... 7

6.3 COAL POTENTIAL ........................................................................................................................................... 7

6.3.1 COAL RESOURCES OF PAKISTAN: ............................................................................................................ 8

6.3.2 COAL RESOURCES IN SINDH ................................................................................................................... 8

6.3.3 COAL RESOURCES IN BALOCHISTAN ....................................................................................................... 9

6.3.4 COAL RESOURCES IN PUNJAB ................................................................................................................. 9

6.3.5 COAL RESOURCES IN KPK ........................................................................................................................ 9

6.3.6 COAL RESOURCES IN AJK ...................................................................................................................... 10

6.3.7 FUTURE COAL BASED POWER PROJECTS .............................................................................................. 10

Chapter 7 POWER TRANSMISSION ............................................................................................................. 11

Chapter 8 POWER DISTRIBUTION ............................................................................................................... 12

8.1 FEEDERS ....................................................................................................................................................... 13

8.2 DISTRIBUTORS ............................................................................................................................................. 13

8.3 SERVICE ........................................................................................................................................................ 13

8.4 UTILITY ......................................................................................................................................................... 14

Chapter 9 THREE PHASE POWER SYSTEM ................................................................................................... 14

9.1 THREE-PHASE SUPPLY ................................................................................................................................. 15

9.2 BALANCED 3-PHASE SYSTEM ....................................................................................................................... 16

9.3 ADVANTAGES OF 3-PHASE POWER SYSTEM ............................................................................................... 16

9.4 THREE PHASE TRANSMISSION LINES ........................................................................................................... 16

Chapter 10 STAR-DELTA CONNECTIONS ..................................................................................................... 17

Chapter 11 POWER TRANSFORMER ........................................................................................................... 18

11.1 TRANSFORMERS ........................................................................................................................................ 18

11.1.1 INDUCTION ......................................................................................................................................... 18

11.2 POWER TRANSFORMERS ........................................................................................................................... 19

Chapter 12 AUTO TRANSFORMER .............................................................................................................. 20

12.1 CUIRCUIT DIAGRAM OF AUTO TRANSFORMER ........................................................................................ 20

12.2 As a result .................................................................................................................................................. 20

12.3 USE OF AUTO TRANSFORMER ................................................................................................................... 21

Chapter 13 132/220 KV SWITCHYARD ........................................................................................................ 21

Chapter 14 EARTHING ................................................................................................................................ 22

14.1 CONCEPT OF EARTHING SYSTEM .............................................................................................................. 22

14.2WHAT IS EARTHING .................................................................................................................................... 22

14.3 GOOD EARTHING MEANS: ......................................................................................................................... 23

14.4 QUALITIES .................................................................................................................................................. 23

14.5 PURPOSE.................................................................................................................................................... 23

Chapter 15 PROTECTION RELAYS & PROTECTION SYSTEM OF HYDEL POWER PLANT ................................... 23

Chapter 16 AUXILIARY AND EMERGENCY SUPPLY SYSTEM .......................................................................... 25

16.1 GENERAL REQUIREMENTS ........................................................................................................................ 25

Chapter 17 FIRE PROTECTION SYSTEM ....................................................................................................... 26

17.1 FIRE PROTECTION SYSTEM ........................................................................................................................ 26

17.2 OVER SPEED PROTECTION SYSTEM ........................................................................................................... 26

17.3 OVER TEMPERATURE PROTECTION SYSTEM............................................................................................. 26

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LIST OF FIGURES

Figure 1. Components of a Power System ................................................................................. 2

Figure 2. Typical Power System. ............................................................................................ 3

Figure 3. Typical Power Distribution System ............................................................................ 13

Figure 4. Elements of a Distribution System .......................................................................... 14

Figure 5. Three-phase supply .................................................................................................. 15

Figure 6. Three Phase Transmission Lines ................................................................................ 17

Figure 7. (a) Mesh connected network ............................................................................. 17

(b) Delta-connected network. .............................................................................. 17

Figure 8. (a) T-connected network. .................................................................................... 17

(b) Star-connected network. ................................................................................ 18

Figure 9. induction law in Transformer .................................................................................... 19

Figure 10. An example of a power transformer used in electric power system........................ 20

Figure 11. Auto vs Isolation Transformer ................................................................................. 20

Figure 12. Concept of Earthing ................................................................................................ 22

Figure 13. Typical single –line ac connection of a protective relay with its de trip schematic .. 25

LIST OF TABLES

Table 1 - Primary Energy Mix by Country 2003-04 .................................................................. 5

Table: 2 – Energy Supply in Pakistan 2003-04 ............................................................................ 5

Table 3 – Energy Consumption in Pakistan 2003-04 .................................................................. 5

Table 4 – Future Multipurpose projects in Pakistan 2003-04 ..................................................... 6

Table 5 - Hydel Projects under Feasibilty in Pakistan 2003-04 ................................................... 7

Table 6 – Total Hydro Power Potential in Pakistan 2003-04 ....................................................... 7

Table 7 – Coal Resources in Sindh 2003-04 ................................................................................ 8

Table 8 – Coal Resources in Balochistan 2003-04 ...................................................................... 9

Table 9 – Coal Resources in Punjab 2003-04 .............................................................................. 9

Table 10 – Coal Resources in KPK 2003-04 ............................................................................... 9

Table 11 – Coal Resources in AJK 2003-04 ............................................................................... 10

Table 12 – Future Coal Based Power Projects 2003-04 ............................................................ 10

1

Introduction

Electricity is the set of physical phenomena associated with the presence and flow of electric charge. Electricity gives a wide variety of well-known effects, such as lightning, static electricity, electromagnetic induction and electric current. In addition, electricity permits the creation and reception of electromagnetic radiation such as radio waves.

In electricity, charges produce electromagnetic fields which act on other charges. Electricity occurs due to several types of physics:

electric charge: a property of some subatomic particles, which determines their electromagnetic interactions. Electrically charged matter is influenced by, and produces, electromagnetic fields.

electric field (see electrostatics): an especially simple type of electromagnetic field produced by an electric charge even when it is not moving (i.e., there is no electric current). The electric field produces a force on other charges in its vicinity.

electric potential: the capacity of an electric field to do work on an electric charge, typically measured in volts.

electric current: a movement or flow of electrically charged particles, typically measured in amperes.

electromagnets: Moving charges produce a magnetic field. Electric currents generate magnetic fields, and changing magnetic fields generate electric currents.

In electrical engineering, electricity is used for:

electric power where electric current is used to energise equipment;

electronics which deals with electrical circuits that involve active electrical

components such as vacuum tubes, transistors,diodes and integrated circuits, and associated passive interconnection technologies.

Electricity is the basic need for the economic development of any country. Electricity has

now become a necessity for all as it powers the machinery, the computers, the health-care

systems and the entertainment of modern society. Every power system has three major

components.which are as follows:

2

LoadT.L

Transmission Line

Generator

Distribution

Figure 1 Components of a Power System

Generation: source of power, ideally with a specified voltage and Frequency.

Transmission system: transmits power; ideally as a perfect conductor.

Load: consumes power; ideally with a constant resistive value.

BRIEF HISTORY OF ELECTRIC POWER Early 1880’s – Edison introduced Pearl Street dc system in Manhattan supplying 59

customers

1884 – Sprague produces practical dc motor

1885 – invention of transformer

Mid 1880’s – Westinghouse/Tesla introduce ac system

Late 1880’s – Tesla invents ac induction motor

1893 – First 3 phase transmission line operating at 2.3 kV

1896 – ac lines deliver electricity from hydro generation at Niagara Falls to Buffalo, 20

miles away

Early 1900’s – Private utilities supply all customers in area (city); recognized as a natural

monopoly; states step in to begin regulation

By 1920’s – Large interstate holding companies control most electricity systems

1935 – Congress passes Public Utility Holding Company Act to establish national

regulation, breaking up large interstate utilities

3

1935/6 – Rural Electrification Act brought electricity to rural areas

ELECTRICAL POWER SYSTEM How electrical power system works in various places is defined in the figure given

below:

Figure 2 Typical Power System.

STEPS OF TYPICAL POWER SYSTEM:

1) The generating station converts the energy of gas, oil, coal or nuclear fuel to electric

energy. The generator voltage is around 15-25 kV (12.5KV at Mangla Dam Generation).

2) The main transformer increases the voltage to 230-765 kV. (220-500KV in Pakistan). This

reduces the current and losses.

3) The high voltage transmission line transports the energy from the generating station to

the large loads, like towns. Example: Energy generated at Palo Verde is transported by a

500 kV line to the KYRENE substation at Phoenix.

4) The high voltage substation reduces the voltage to 500-220 / (220-132) kV. The substation

serves as a node point for several lines.

4

5) The sub-transmission lines (132 kV-11 kV) connect the high voltage substation to the local

distribution station.

6) The Distribution lines 11 kV distribute the energy along streets or underground. Each line

supplies several step-down transformers distributed along the line.

7) The distribution transformer reduces the voltage to 240 (1-phase) or 415V (3-phase)

which supplies the houses, shopping centers, etc.

GENEARATION OF ELECTRICAL ENERGY Electrical energy is generated at the power stations by synchronous generators. Typical

generation voltages vary from 3.3 to 33 kV depending upon the demand of the load.

TYPES OF GENERATION STATIONS:

1. Thermal Power Plant

Large plants (more than 500 MVA) carry constant load (base load plant).

Smaller plants loads are regulated but they operate continuously. Minimum down

time is 20-35 hours. Depending upon the situation of the fossil fuel availability, it

can be used as base load or peak load plant. But in Pakistan, it is used as peak load

plant.

2. Nuclear Power Plant

These plants carry constant load and are used as base loads plants.

3. Hydroelectric Plants

These plants are loaded to the maximum capacity, because of the low

operating cost. (Water is free)

4. Combined Steam and Gas-Turbine Power Plants

High efficiency plants for variable load.

5. Gas Turbine Power Plants

Peak load plants, high operating and low investment cost.

6. Renewable Energy Sources (Solar & Wind) Power Plants

Loaded to the maximum capacity when sun or wind power available.

5

GENERATION SOURCES IN PAKISTAN:

The Energy mix in Pakistan and various other countries for the year 2003-04 is given

in Table 1.1:

Sources Pakistan India UK USA Canada

Oil 30.0% 35.0% 35.0% 40.0% 30.0%

Natural Gas 50.0 % 7.0% 35.0% 23.0% 27.0%

Coal 1.0 % 55.0% 16.0% 23.0% 24.0%

Other (Hydel, Nuclear, etc.) 19% 3.0% 14.0% 14.0% 19.0%

Table 1 - Primary Energy Mix by Country 2003-04

ENERGY SUPPLY & CONSUMPTION IN PAKISTAN Source wise primary energy supply in Pakistan in 2003-04 is indicated below:

Gas Hydel Coal Nuclear

15.8 % 50.8 % 30 % 0.2 % Oil

Table: 2 – Energy Supply in Pakistan 2003-04

Sector wise energy consumption, excluding fuels consumed in thermal power generation in the

Year 2004 is as follow:

Industry Transport Domestic Commercial Agriculture Other

Governments

38.3 % 32.0 % 21.7 % 3.2 % 2.5 % 2.3 %

Table 3 – Energy Consumption in Pakistan 2003-04

6

POTENTIAL AVAILABLE FOR POWER GENERATION God has blessed Pakistan with tremendous potentials available for power generation is:

Hydel Potential

Coal Potential

MULTIPURPOSE PROJECT:

Following table presents the multipurpose projects whose feasibility are

completed.

Name of Project Capacity (MW) Feasibility Status

Kalabagh 3600 Completed

Munda 740 Completed

Basha 4500 In Hand

Total 8840

Table 4 – Future Multipurpose projects in Pakistan 2003-04

HYDEL POTENTIAL:

Pakistan is a water rich country with a hydel potential of more than 50,000 MW but

unfortunately Pakistan’s energy market investment in hydel-power generation has been caught

up in confusion and paradoxes for more than decade and no significant progress has been

achieved so far.

To exploit Pakistan’s hydel resource productively, huge investments are necessary, which our

economy cannot afford except at the expense of social sector spending. Considering the

limitations and financial constraints of the public sector, the Government is trying to facilitate

private investors to promote hydel power generation in the country.

Run of River Projects Feasibility Studies in Hand

Following is the list of run of river Projects whose feasibility studies are in hand;

7

Name of Project Capacity (MW) Feasibility Status

Bunji 5400 In Hand “

Dasu 3700 “

Gabral 105 “

Keyel Khwar 130 “

Lawi 65 “

Spat Gah

Lower scheme

545 “

Chor Nullah

Lower scheme

386 “

Total 10331

Table 5 - Hydel Projects under Feasibilty in Pakistan 2003 -04

PAKISTAN’S TOTAL HYDROPOWER POTENTIAL :

Following is the total hydro power potential in Pakistan;

Station/Projects Capacity (MW)

Hydel Stations in Operation 6596

Under Implementations 1965

Feasibility Study Completed

i. Run Of River

ii. Multipurpose

1780

8840

Feasibility Studies in Hand 10331

Projects for Which Feasibility Studies are to be Carried Out 25000

Total 54511

Table 6 – Total Hydro Power Potential in Pakistan 2003 -04

COAL POTENTIAL:

Coal is global energy source in the true sense of the world. Coal contributes

approximately 38% to the total global primary energy demand. Share of coal in total electricity

production in different countries are:

China = 81%

USA = 56 %

8

UK = 58 %

Unfortunately, the share of coal in total electricity production in Pakistan is less than 1%.

Pakistan is a coal rich country, but unfortunately coal has not been developed for power

generation for more than three decades due to lack of infrastructure, insufficient financing and

absence of modern coal mining expertise. The Government has now determined to facilitate

private investors to promote investment in coal development and coal power generation.

Coal is a cheap indigenous resource and after the discovery of 175.5 billion tones of coal in Thar

area of Sind, Pakistan’s coal power potential has increased manifold. It is anticipated that if

properly exploited, Pakistan’s coal resources may generate more than 100,000 MW of electricity

for the next 30 years. Pakistan is now the 6th richest nation of the world in respect of coal

resources.

COAL RESOURCES OF PAKISTAN:

There are vast resources of coal i.e. 185,175 million tonnes in all four of Pakistan’s

provinces and in AJK

COAL RESOURCES IN SINDH:

Following are the coal resource is Sindh area.

Location Million Tonnes

Thar 175,506

Lakhra 1,328

Sondra – Jherruck 5,523

Meting – Jhimpir 473

Indus East 1,777

Badin 16

Total 184,623

Table 7 – Coal Resources in Sindh 2003-04

9

COAL RESOURCES IN BALOCHISTAN:

Following are the coal resources in Balochistan.

Location Million Tonnes

Sor - Range/Degari 50

Khostan/sharigh/Hanai/Ziarat 88

Mach 23

Duki 56

Total 217 Table 8 – Coal Resources in Balochistan 2003-04

COAL RESOURCES IN PUNJAB:

Following are coal resources in Punjab.

Location Million Tonnes

Salt - Range 213

Makarwal 22

Total 235

Table 9 – Coal Resources in Punjab 2003-04

COAL RESOURCES IN KPK:

Following are coal resources in NWFP

Location Million Tonnes

Cherat 9

Hungu 82

Total 91

Table 10 – Coal Resources in KPK 2003-04

10

COAL RESOURCES IN AJK:

Following is coal resource in AJK.

Location Million Tonnes

Kotli 9

Table 11 – Coal Resources in AJK 2003-04

FUTURE COAL BASED POWER PROJECTS:

Following is the list of coal based power project in Pakistan.

Projects Capacity ( MW )

Thar Coal 4200

Lakhra Coal 450

Sonda – Jherruk Coal 200

Ghotki 150

Total 5000

Table 12 – Future Coal Based Power Projects 2003-04

The electricity demand in the country is increasing day by day. The demand/supply

projections indicates that power shortage will appear from the year 2006, and will increase to

5500 MW in the year 2010 if no measures are taken to bring in new capacity.For Pakistan, the

cornerstone of self-reliance in power sector development is optimal utilization of hydel

resources.

11

Hydropower is cheaper, eternally available source of energy and a bounty of nature in contrast

to environmentally hazardous and non-renewable sources of energy. Pakistan is fortunate to be

endowed with economically exploitable hydropower potential of more than 50,000 MW.

There are vast resources of coal in Pakistan as well and coal is a cheap indigenous energy

resource. Pakistan’s coal resources may generate more than 100,000 MW of electricity for the

next 30 years.

The power requirements must be fulfilled by setting up new projects based on indigenous fuel

resources such as coal, hydel power, and renewable energies.

Development & utilization of indigenous available potential fuel resources will not only reduce

the cost of electricity but also strengthen the country’s economy and save precious foreign

exchange.

POWER TRANSMISSION The power stations are located quite far away from the load centers. Transmission

networks are required to:

Connect generating plants to consumption points

Create large power pools for increased reliability

The primary transmission voltages are 110, 132, 220 or 500 kV depending upon the distance and

amount of power to be transmitted. Secondary transmission is normally of the order of 66kV

(obsolete in Pakistan now) and 132 kV.

High voltage AC transmission offers:

Higher transmission capacity / Km

Lower line-voltage drop / Km

Lower transmission losses / MW transfer

Reduced right-of-way requirement / MW transfer

Lower capital and operating costs / MW transfer

The equipment used for power transmission system is

Transformers

Step-up transformer

12

Voltage Regulators

Phase Shifters

Step-down Transformers

Transmission Lines & Cables

Relays & Circuit Breakers

Disconnectors & Earthing Switches

Shunt & Series Reactors & Capacitors

Static VAR Compensators

Current Transformers & Potential Transformers

POWER DISTRIBUTION Power Distribution System receives electrical energy from the HV/MV levels at bulk

power delivery points and supplies energy to customers

At standard voltage levels

Single phase and/or three-phase

The voltages for primary distribution are 11, 6.6 or 3.3 kV depending upon the requirement of

bulk consumers and for secondary distribution the voltage level are 415/240V.

It is made up of the following main equipment:

Distribution transformers (DXF)

Feeder sections (including underground cables)

Switches, fuses, reclosures

Automatic load transfers

13

14

Bulk

Power

Point

33/11

DXF11/5

DXF

5/0.4/0.21

DXF

HV / MV

Network

33KV 15 KV 5 KV220V

Industrial

Customers

Residential

Customers

Commercia

l

& Municipal

Customers

Large

Industrial

Customers

Power Distribution

Figure 3. Typical Power Distribution System

A distribution system may further be classified into feeders, distributors and service mains.

1. FEEDERS:

Feeders are the conductors, which connect the substations to the areas fed

by those substations. Generally feeders are not tapped at any point for supply to

the consumers, therefore, current density remains constant throughout the length

of the feeder. Hence, it is designed mainly for constant current carrying density.

2. DISTRIBUTORS:

Distributors are the conductors from which load is tapped at different points

for supply to the consumers. The current density of a distributor does not remains

constant throughout its length. Distributors are designed mainly for voltage drop

in them. The voltage drop in a distributor should not exceed +- 5%.

3. SERVICE MAINS:

Service Mains are the conductors, which connect the distributor to the

consumer’s premises.

14

Figure 4. Elements of a Distribution System

UTILITY RESTRUCTURING :

Driven by significant regional variations in electric rates

Goal of competition is to reduce rates through the introduction

of competition

Eventual goal is to allow consumers to choose their electricity

supplier

In Pakistan, WAPDA is also under the process of disintegration. Eight Distribution

companies (Disco) are being constituted: which are

LESCO

GEPCO

MEPCO

IESCO

FESCO

KESC

PESCO

THREE PHASE POWER SYSTEM:

15

THREE-PHASE SUPPLY:

A three-phase supply is generated when three coils are placed 120° apart and the

whole rotated in a uniform magnetic field as shown in Figure 19.2(a). The result is three

independent supplies of equal voltages which are each displaced by 120° from each other as

shown in Figure 19.2(b).

The convention adopted to identify each of the phase voltages is:

R-red, Y-yellow, and B-blue, as shown in Figure 19.2.

Figure 5. Three-phase supply

The phase-sequence is given by the sequence in which the conductors pass the point

initially taken by the red conductor. The national standard phase sequence is R, Y, B.

A three-phase a.c. supply is carried by three conductors, called ‘lines’ which are coloured red,

yellow and blue. The currents in these conductors are known as line currents (IL) and the

p.d.’s between them are known as line voltages (VL). A fourth conductor, called the neutral

(coloured black, and connected through protective devices to earth) is often used with a

three-phase supply.

If the three-phase windings shown in Figure 19.2 are kept independent then six wires are

needed to connect a supply source (such as a generator) to a load (such as motor). To reduce

the number of wires it is usual to interconnect the three phases. There are two ways in which

this can be done, these being:

A Astar connection, and

A delta, or mesh, connection.

Sources of three-phase supplies, i.e. alternators, are usually connected in star,

16

whereas three-phase transformer windings, motors and other loads may be connected

either in star or delta.

BALANCED 3-PHASE SYSTEM:

A balanced 3 phase () system has

three voltage sources with equal magnitude, but with an angle shift of 120

equal loads on each phase

equal impedance on the lines connecting the generators to the loads

Bulk power systems are almost exclusively 3

Single phase is used primarily only in low voltage, low power settings, such as residential and

some commercial

ADVANTAGES OF 3-PHASE POWER SYSTEM:

Can transmit more power for same amount of wire (twice as much as single phase)

Torque produced by 3 machines is constant

Three phase machines use less material for same power rating

Three phase machines start more easily than single phase machines

THREE PHASE TRANSMISSION LINES:

17

Figure 6. Three Phase Transmission Lines

STAR-DELTA CONNECTIONS:

The network shown in Figure (a) consisting of three mpedances ZA, ZB and ZC is said to be

p-connected. This network can be redrawn as shown in Figure (b), where the arrangement is

referred to as deltaconnected or mesh-connected.

Figure 7. (a) Mesh connected network,

(b) Delta-connected network.

The network shown in Figure 34.2(a), consisting of three impedances, Z1, Z2 and Z3, is said to be

T-connected. This network can be redrawn as shown in Figure 34.2(b), where the arrangement

is referred to as starconnected.

Figure 8 (a) T-connected network.

18

(b) Star-connected network.

POWER TRANSFORMER TRANSFORMERS:

A transformer is a static electrical device used in electric power systems to transfer

power between circuits through the use of electromagnetic induction. Transformers are devices

that transfer energy from one circuit to another by means of a common magnetic field. When

an alternating current flows in a conductor, a magnetic field exists around the conductor. If

another conductor is placed in the field created by the first conductor such that the flux lines

link the second conductor, then a voltage is induced into the second conductor. The use of a

magnetic field from one coil to induce a voltage into a second coil is the principle on which

transformer theory and application is based. Transformers range in size from thumbnail-sized

used in microphones to units weighing hundreds of tons interconnecting the power grid. A wide

range of transformer designs are used in electronic and electric power applications.

Transformers are essential for the transmission, distribution and utilization of electrical energy.

INDUCTION LAW:

The transformer is based on two principles:

An electric current can produce a magnetic field.

A changing magnetic field within a coil of wire induces a voltage across the ends of

the coil (electromagnetic induction).

19

Figure 9. induction law in Transformer

Referring to the figure here, current passing through the primary coil creates a magnetic field.

The primary and secondary coils are wrapped around a core of very high magnetic permeability,

so that most of the magnetic flux passes through both the primary and secondary coils. Any

secondary winding connected load causes current

and voltage induction from primary to secondary circuits in indicated directions. POWER TRANSFORMERS

The term power transformer is used to refer to those transformers used in the generator and the distribution circuits, and these are usually rated at 500 KVA and above. Power systems typically consist of a large number of generation locations, distribution points, and interconnections within the system or with nearby systems, such as a neighboring utility. The complexity of the system leads to a variety of transmission and distribution voltages. Power transformers must be used at each of these points where there is a transition between voltage levels.

20

Figure 10. An example of a power transformer used in electric power system

AUTO TRANSFORMER Transformer that acts like an isolation transformer by changing

Voltage Levels

Current Levels

Impedance values

But does not isolate between the Primary and the Secondary

CUIRCUIT DIAGRAM OF AUTO TRANSFORMER:

Circuit diagram of auto transformer is as follow:

Figure 11. Auto vs Isolation Transformer

As a result:

21

Requires less copper

Lighter

I2R losses are less

More efficient

Lower leakage

Lower losses

Lower magnetizing current

Increase kVA rating

No galvanic Isolation

USE OF AUTO TRANSFORMER:

In power distribution lines to counteract line Z

Motor starting circuits

If there is an insulation breakdown between coils the supply voltage may be

imposed onto the low voltage load

It is recommended that the voltage reduction should only be by a maximum of

25%

132/220 KV SWITCHYARD Switchyard is basically switching scheme which may be termed as substation for

transmission while Planning and design of substations to be based on the following aspects:

Security of supply, extendibilty, maintainabilty and operational flexibility

Statutory safety requirements

Protection from direct lightening stroke

Switching scheme:-

765 kV Substation: Double bus double breaker

400 kV Substation: One and half breaker scheme/ double main and transfer bus bar

scheme

220 kV Substation: Double main and transfer scheme/ double main with breaker

by-pass scheme

22

132kV Substation: Main and transfer scheme.

EARTHING:

CONCEPT OF EARTHING SYSTEM:

All the people living or working in residential, commercial and industrial

installations, particularly the operators and personnel who are in close operation and contact

with electrical systems and machineries, should essentially be protected against possible

electrification. To achieve this protection, earthing system of an installation is defined,designed

and installed according to the standard requirements.

WHAT IS EARTHING:

The process of connecting metallic bodies of all the electrical apparatus and

equipment to huge mass of earth by a wire having negligible resistance is called Earthing. The

term earthing means connecting the neutral point of supply system or the non current carrying

parts of the electrical apparatus to the general mass of earth in such a manner that all times an

immediate discharge of electrical energy takes place without danger.

Figure 12. Concept of Earthing

1 OBJECTIVES OF THE EARTHING:

Provide an alternative path for the fault current to flow so that it will not

endanger the user

23

Ensure that all exposed conductive parts do not reach a dangerous potential

Maintain the voltage at any part of an electrical system at a known value so as

to prevent over current or excessive voltage on the appliances or equipment.

GOOD EARTHING MEANS:

Good Earthing must have low impedance enough to ensure that sufficient

current can flow through the safety device so that it disconnects the supply ( <0.4

sec ). Fault current is much more than the full load current of the circuit which melts

the fuse. Hence, the appliance is disconnected automatically from the supply

mains.

1 QUALITIES OF GOOD EARTHING:

Must be of low electrical resistance

Must be of good corrosion resistance

Must be able to dissipate high fault current repeatedly

1 PURPOSE OF EARTHING:

To save human life from danger of electrical shock or death by blowing a fuse

i.e. To provide an alternative path for the fault current to flow so that it will not

endanger the user

To protect buildings, machinery & appliances under fault conditions ie. To

ensure that all exposed conductive parts do not reach a dangerous potential.

To provide safe path to dissipate lightning and short circuit currents.

To provide stable platform for operation of sensitive electronic

equipments i.e. To maintain the voltage at any part of an electrical system at a

known value so as to prevent over current or excessive voltage on the

appliances or equipment .

To provide protection against static electricity from friction

PROTECTION RELAYS & PROTECTION SYSTEM OF HYDEL POWER

PLANT 1 WHAT IS A RELAY?

(IEEE) define a relay as an electric device that is designed to interpret input

condition in a prescribed manner and after specified condition are met to respond to cause

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contact operation .Relay are utilized in all as pacts of activity, the home ,communication ,

industry…..etc.

A protective relay is defined as a relay whose function is to detect defective line or apparatus or

other power system condition of an abnormal or dangerous nature and to initiate appropriate

control circuit condition. Fuse are also used in protection and define as an over current

protective device with in a circuit opening fusible part that is heated and severed by the passage

of the over current thought it.

A primary objective of all power system is to maintain a very high level of condition of service,

and to minimize the outage times when intolerable conditions occur. Loss of power, dip of

voltage and over voltage will occur due to consequences of natural events, physical accident,

equipment failure a disoperation by human error.

Protection is the science, skill, and art of applying and setting and / or fuses to provide

maximum sensitivity to fault and undesirable condition.

1 TYPICAL POWER CIRCUIT BREAKER:

Protective relays provide the "brains" to same trouble ,but as low energy device

they are able to open and isolate the problem area of the power system . CBs and varions types

of circuit interrupters are used to provide the "muscle" for fault isolation .

Thus protective relays and interrupting devices are "team" . protective relays without CBs have

no basic value except for alarm. On the other hand , CBs without protective relays are only

energized or de energized manually.

1 TYPICAL RELAY & CB CONNECTION :

Usually protective relays are connected to power system through CT and/or VT.

The circuit can be represented by a typical "one-line'" ac schematic and dc trip circuit schematic

as shown in fig (1-9) . in normal operation and when CB(52) is closed , it is contact closes to

energize the CB trip coil 52T, which function to open breaker main contact and de energize the

connected circuit. The relay contacts are not designed to interrupt the CB trip coil current so an

auxiliary relay is used to "seal in" or by pass the protective relay. Then 52a will open to de

energize the breaker coil.

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Figure 13. Typical single –line ac connection of a protective relay with its de trip schematic

1 BASIC OBJECTIVES OF SYSTEM PROTECTION :

Protection does not mean prevention, but minimizing the duration of the trouble,

the five basic objectives are:

Reliability: assurance that the protection will perform correctly.

Selectivity: maximum continuity of service with minimum system disconnection.

Speed of operation: minimum fault duration and consequent equipment damage.

Simplicity: minimum protective equipment and associated circuitry to achieve the

protection objectives.

Economics: maximum protection at minimum total cost.

AUXILIARY AND EMERGENCY SUPPLY SYSTEM GENERAL REQUIREMENTS

The A.C and D.C auxiliary services panels equipped with circuit breakers for

incoming and outgoing circuits, protective devices, instruments, meters, C.T's

and auxiliary equipment to be used with 200 kVA pad mounted transformer.

The cubicle for auxiliary services panels shall consist of three separate portions

with partitions of insulating material for separating A.C., D.C. and D.C. emergency portions.

The panels shall be designed for indoor use and shall be mounted on the floor.

The panels shall be designed throughout to secure safety during operation inspection and

maintenance.The auxiliary panel shall consist of bus bars, three phase and neutral for A.C and

positive and negative for D.C. main and emergency supplies, appropriate connections, incoming

and outgoing circuit breakers, A.C. no voltage relay D.C. under voltage and battery earth fault

relays, instruments, meters, annunciators, cable glands and cable trays all mounted in a suitable

metal enclosure.The breakers,instruments and meters shall be flush mounted. The panel will be

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fed through LT underground cables which will be connected directly to the A.C. and D.C.

incoming circuit breakers terminations.

FIRE PROTECTION SYSTEM FIRE PROTECTION SYSTEM

The CO2 fire protection system for the gas turbine unites extinguishing the fire by

reducing the oxygen.

To reduce the oxygen content, a quantity of Co2 greater than 34% a compared by

volume is discharged in to the combustion chamber, when exposed to high

temperature.

OVER SPEED PROTECTION SYSTEM

Under normal operation the speed of the shaft is under the control of speed loop

or temperature loop.

The over speed protection system consists of a primary electronic system.

The primary electronic over speed protection system senses the turbine speed,

speed detection software and associated circuits.

Mechanical over speed protection system is a backup for electronic over speed

protection system failure.

OVER TEMPERATURE PROTECTION SYSTEM

The over temperature protection system protects the GT from possible damage

caused by over firing. It is a backup system which operates only after failure of the

speed and temperature over ride loops.

Control of turbine is done mainly by start up speed acceleration, synchronization

and temperature controls

Temperature, speed, vibration, flame and compressor operation limits over

temperature and over speed systems are provided as independent backup system

for temperature control and speed control systems.

Vibration detections and protection is activated by abnormal turning vibration

amplitude.

Flame Diction and protection system is activated if flame is not established during

start up or if it is lost during operation.

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