Al-Nileain University

Department of Electrical Engineering

The Graduate College

Generators Protection of Haggling Power Plant

Station

A thesis Submitted for Partial Fulfillment of the

Requirement for the master Degree in Electrical

Engineering

Prepared by:

Mohammed NourUlhudaAhammed

Supervisor:

Dr. Abdelrahim Ate

August 2018

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ةـــــــــالآي

:قال تعالى

(وَقُمِ اعْمَهُواْ فَسَيَرَى انهّهُ عَمَهَكُمْ وَرَسوُنُهُ وَانْمُؤْمِنُونَ)

105

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Dedication

This thesis is dedicated to :The sake of Allah , my creator and my

Master .

My great teacher and messenger , Mohammed (May Allah bless and

grant him ), who taught us the purpose of life.

My homeland Sudan .

Al neelainuniversity : my second magnificent home: My great

parents and my wives, I have to thank my parents for their love

and support

throughout my life .

Thanks you both for Dr.Alategiving me strength to reach for the stars

and chase

My dreams.

My beloved brothers and sisters .

My friends who encourage and support me , All the people in my life

who touch my heart , I dedicate this research .

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Acknowledgment

In the Name of Allah . The Most Merciful , the most

compassionate all praise be to Allah , the Lord of the worlds : and

prayers be upon Mohamed His servant and messenger .

We would like to express our gratitude for everyone helped us

duringthe graduation project .

Starting with endless thanks for our supervisor Dr .Altewho

never stop encouraging us to do a great job .

Providing our group with valuable information and advice to be

better each time , Thanks for the continuous support and kind

communication witch had a great effect regarding to feel interesting

about what we are working on.

Also , we would like to say many thanks our neelain for their

endless support and their huge effort in contacting and providing us

with all what WE need for our graduation project . Also , we would

like to thank teachers that help us very much specially elate .

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Abstract:

The Problem Statement an electrical generator can be subjected

either internal faults or external faults or both, hence any fault occurred in

the power system should be cleared in the power from the generator as

soon as possible otherwise it may create permanent damage in the

generator , the number and variety of fault occur in the generator are huge.

That is why generator is protected with several protection schemes so in

this thesis are working to protect the expensive equipment. The object of

this project is to design generators protection of flegglig power plant by

using ETAP program. so as an electrical generator can be subjected either

internal faults or external faults or both, hence any fault occurred in the

power system should be cleared in the power from the generator as soon

as possible otherwise it may create permanent damage in the generator ,

the number and variety of fault occur in the aenerator are huge. That is

why generator is protected with several protection schemes. In this thesis

the one line diagram of Hegglig generation grid was simulated by using

ETAP program and we run load flow analysis to calculate the steady state

current (Is) and to choose suitable current transformers (CTs) ratio

connected with relays. After that we run short circuit analysis in all system

to calculate the short circuit current and determine the size of protection

devices. Then we used these values to calculate the value of T.M.S (Time

Multiplier Setting), or time operation and pick up current of protective

relays that used to protect the system. Finally we run star protective device

coordination in ETAP and test the protection device coordination. The

objectives of this study are: Study the protection techniques as a general.

Design optimum generators protection methods of Hegglig power plant

substation by using ETAP program. The Methodology A one line diagram

of Hegglig generation grid was simulated by using ETAP program and we

run load flow analysis to calculate the steady state current (Is) and to

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choose suitable current transformers (CTs) ratio connected with relays.

After that in this thesis run short circuit analysis in all system to calculate

the short circuit current and determine the size of protection devices.

The Result is summarized in four chapters, in chapter one is about

background of generator protection, thesis problems and objectives when

chapter two is studied general of the generator while chapter three is

discussed protection and faults that occur in the generator so that chapter

four is the case study in the system model by using ETAP and chapter five

is given the thesis conclusion and recommendations. We may say that the

objective of this project successfully achieved.

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مستخلص

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Table of Contents

CHAPTER ONE: INTRODUCTION

Dedication 2

Acknowledgement 3

Abstract English 4

Abstract Arabic 6

Table of Contents 8

List of Table 10

List of Figures 11

1.1 Background of Generator Protection 13

1.2 Objective 13

1.3 Problem Statement 13

1.4 Methodology 14

1.5 Thesis layout 14

CHAPTER TWO:ELECTRIC NETWORK SUPPLIES

2.1 History of generators 16

2.2 Generator working 18

2.3 Fleming's Right hand Rule 21

2.4 Types of Generator 23

2.5 Types and construction of rotors 24

2.5.1 Squirrel-Cage Rotor 25

2.5.2 Wound Rotor 26

2.5.3 Salient Pole Rotors 26

2.5.4 Cylindrical Rotors 27

2.5.5 Electrical 27

2.5.6 Uses for a Generator 27

2.5.7 Generators for Business, Commercial and Contractors 28

CHAPTER THREE: GENERATOR PROTECTION

3.1 Introduction 31

3.2 Internal Faults 31

3.3 Stator Windings Faults 31

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3.4 Stator Differential protection for generators 32

3.5 Modified differential protection 33

3.6 Biased circulating current protection (percentage

differential relay protection)

33

3.7 Self-balance protection system 34

3.8 Stator ground fault protection 35

3.9 Stator inter turn fault protection 36

3.10 Stator over heating protection 37

3.11 Protection of Generator Rotor Earth Fault 38

3.12 Under/Over Frequency Protection 40

3.13 Under/ Voltage Protection \ Over 41

3.14 Under voltage protection 42

3.15 Protection of the Generator Due to Unbalance Loading 42

3.16 Over current fault of a generator 43

3.17 Alternator Prime Mover failure fault or reverse power

fault

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CHAPTER FOUR: PROPOSED PROTECTION TECHNIQUES

THROUGH DIFFERENT CASES

4.1 The System Model 46

4.2 The system data are shown below 48

4.3 System Analysis 49

4.4 Protection system coordination test 52

4.4.1 Protect the fault that occur near the generator 53

4.4.2 Sequence-of-Operation Event Summary Report 54

CHAPTER FIVE: CONCLUSION & RECOMMUNDATOINS

5.1 Conclusion 56

5.2 Recommendation 56

5.3 Result 57

5.4 References 58

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List of Tables

Table (4.1) Bus input Data 48

Table (4.2) 2-Winding Transformer Grounding Input Data

Grounding

48

Table (4.3) Synchronous Generator Input Data 49

Table (4.4) This data shows suitable coefficient value of the current

transformer in each point of the system model

50

Table (4.5) The slope of the time/current curve sets is determined by

the constant α and β as follow

52

Table (4.6) Symmetrical 3-phase Fault at Bus395 54

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List of figures

Figure (2.1) Represent Generator Construction 21

Figure (2.2) Represent Generator Operation 23

Figure (2.3) Represent Fleming's Right hand Rule 24

Figure (2.4) Represent salient pole rotor 23

Figure (2.5) Represent cylindrical rotor 24

Figure (2.6) Represent Squirrel Cage rotor 25

Figure (2.7) Represent wound rotor 26

Figure (2.8) Represent cylindrical rotor 27

Figure (3.1) Differential protection for generators 32

Figure (3.2) Modified differential protection for generators 33

Figure (3.3) Biased circulating current protection for generators 34

Figure (3.4) self-biasing protection of the stator windings 35

Figure (3.5) Inter turn protection of the stator winding 37

Figure (3.6) protection against unbalance loading 43

Figure (4.1) One line diagram of Hegglig power plant

generation station

46

Figure (4.2) Testing System of Protection 54

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CHAPTER ONE

INTRODUCTION

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INTRODUCTION

1.1 Background of Generator Protection

Under Electrical Protection a generator is subjected to electrical traces

imposed on the insulation of the machine, mechanical forces acting on the

various parts of the machine, and temperature rises. These are the main

factors which make protection necessary for the generator or alternator.

Even when properly used, a machine in its perfect running condition does

not only maintain its specified rated performance for many years, but it does

also repeatedly withstand certain excess of over load. Hence, preventive

measures must be taken against overloads and abnormal conditions of the

machine so that it can serve safely.

Despite of sound, efficient design, construction, operation, and

preventive means of protection, the risk of that fault cannot be completely

eliminated from any machine. The devices used in generator protection,

ensure the fault, made dead as quickly as possible. The generator protection

is of both discriminative and non-discriminative type. Great care is to be

taken in coordinating the systems used and the settings adopted, so that the

sensitive, selective and discriminative generator protection scheme is

achieved.

1.2 Problem Statement

An electrical generator can be subjected either internal faults or external

faults or both, hence any fault occurred in the power system should be

cleared in the power from the generator as soon as possible otherwise it may

create permanent damage in the generator , the number and variety of fault

occur in the generator are huge. That is why generator is protected with

several protection schemesSoin this thesis are working to protect the

expensive equipment.

1.3 Objectives

The objectives of this study are:

1- Study the protection techniques as a general.

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2- Design optimum generators protection methods of Hegglig power plant

substation by using ETAP program.

3- Analysis the overall performance of the proposed methods through

simulation results.

1.4 Methodology

A one line diagram of Hegglig generation grid was simulated by using

ETAP program and we run load flow analysis to calculate the steady state

current (Is) and to choose suitable current transformers (CTs) ratio

connected with relays.

After that in this thesis run short circuit analysis in all system to

calculate the short circuit current and determine the size of protection

devices.

in this thesis used these values to calculate the value of T.M.S (Time

Multiplier Setting), or time operation and pick up current of protective

relays that used to protect the system.

Finally we run star protective device coordination in ETAP and test the

protection device coordination.

1.5 Thesis layout

The thesis is summarized in five chapters, in chapter one is about

background of generator protection, thesis problems and objectives when

chapter two is studied general of the generator while chapter three is

discussed protection and faults that occur in the generator so that chapter

four is the case study in the system model by using ETAP and chapter five

is given the thesis conclusion and recommendations.

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CHAPTER TWO

ELECTRIC NETWORK SUPPLIES

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Electric Network Supplies

In electricity generation, a generator is a device that converts

mechanical energy to electrical energy for use in an external circuit. The

source of mechanical energy may vary widely from a hand crank to an

internal combustion engine. Generators provide nearly all of the power for

electric power grids.

The reverse conversion of electrical energy into mechanical energy is

done by an electric motor, and motors and generators have many

similarities. Many motors can be mechanically driven to generate electricity

and frequently make acceptable generators.

2.1 History of generators

As its name suggests, a generator generates electricity. Michael

Faraday‟s discovery of electromagnetic induction demonstrated a way to

construct a simple generator, but there was little need for such a device until

commercial technologies that used electricity, such as lights, appeared. The

earliest commercial uses of electricity, such as telegraphy, arc, and metal

electroplating used batteries as their power source. This was a very

expensive way of generating electricity.

In the 1860s and 1870s many inventors sought ways of using Faraday‟s

induction principle to generate electricity mechanically. Two kinds of

generators emerged. The first type was a generator of direct current (DC)

electricity. The second type was a generator of alternating current (AC)

electricity. In truth, a DC generator could generate AC current, but it

contains a simple device called a commutator to turn AC into DC.

A commutator reroutes the flow of electrons inside the DC generator, so

that the energy that appears at the output is a pulsing direct flow. An AC

generator does not need a commutator and generates AC directly.

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One of the most important inventors of generators was German Werner

von Siemens, who designed improved DC generators and called them

dynamos. An even better generator was introduced by French

ZénobeThéophileGramme in 1867, which produced substantially higher

voltages than previous attempts. In 1871 he demonstrated a working model,

and with Hippolyta Fontaine began manufacturing them. Gramme‟s

dynamos

generated AC current and were widely used in arc lighting systems. In 1872,

however, von Siemens reemerged and invented what is essentially the

modern type of dynamo, referred to as the drum armature type of machine,

which was a more efficient design.

AC and DC generators were both used from the 1870s on. For

example, AC generators were used in a type of outdoor arc lighting known

as the Jablochkoff Candle. However, in the late 1870s when Thomas Edison

devised his highly successful electric lighting system, he used DC

generators. A major reason for this choice was that Edison wanted to use

electric power both for lighting (for which AC was fine) and for running

electric motors. At the time, there was no good AC electric motor available,

so DC was the only option. In 1882 Edison installed DC generators at the

Pearl Street station facilities in New York City, one of the earliest

commercial power generating plants.

As electric lighting and centrally distributed power began to achieve

commercial success in the 1880s, inventors began looking for ways to

distribute central-station power over longer distances.

Edison‟s DC system was poorly adapted to this, because he had

chosen to use 120-volt bulbs and motors. A much higher voltage would

have been easier to transmit down long wires, because at a low voltage

much energy is lost as heat. Edison stations, such as that at Pearl Street,

could be no more than about a mile from the customer. AC offered an

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alternative: a way to generate at a low voltage, “step up” the voltage for

transmission using a simple device called a transformer, and then “step

down” the voltage at the customer premises. The only remaining problem,

though, was the lack of a suitable AC motor design.

Nikola Tesla, a Serbian immigrant to the United States, devised an

improved AC generator as well as a practical AC motor. Tesla‟s system

used polyphase AC, in which the generator generated several different AC

flows that were combined or superimposed onto one another to create a

single polyphase AC output, with the component currents “out of phase”

with one another. The Tesla motor, introduced in 1887, was designed so that

the peaks of this polyphase current supplied power at just the right moment

in the rotation of the motor, and the resulting induction motor as he called it,

ran smoothly. With a practical AC motor and generator in hand, along with

transformers to raise and lower voltage, Tesla‟s system could be used by

power companies to create ever-larger networks of power distribution using

massive power plants, such as the Niagara Falls hydroelectric plant built in

the 1890s. Larger power systems helped lower costs, which stimulated

demand for electricity, especially in homes.

Figure (2-1) Represent Generator Construction

2.2 Generator working

In the case when the coil is rotating in anticlock-wise direction without

commutator. As the coil assumes successive positions in the field, the flux

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linked with it changes. Hence, an e.m.f is induced in it which is proportional

to the rate of change of flux linkages (e=-N dΦ/dt). When the plane of the

coil is at right angles to lines of flux then flux linked with the coil is

maximum but rate of change of flux linkages is minimum.

It is so because in this position, the coil sides do not cut or shear the flux,

rather they slide along them i.e. they move parallel to them. Hence, there is

no induced e.m.f in the coil. Generally this no e.m.f is taken as the starting

position i.e. zero degrees position. The angle of rotation or time will be

measured from this position.

As the coil continues rotating further, the rate of change of flux

linkages (and hence induced e.m.f in it) increases till the coil rotates 90°

from its starting position. Here the coil plane is vertical (see in fig) i.e.

parallel to the lines of flux. As seen, the flux linked with the coil is

minimum but rate of change of flux linkages is maximum. Hence, maximum

e.m.f is induced in the coil when in this position. In the next quarter

revolution i.e. from 90° to 180°, the flux linked with the coil gradually

increases but the rate of change of flux linkages decreases. Hence, induced

e.m.f decreases gradually till it becomes zero.

So, in this thesis find that in the first half revolution of the coil, no

e.m.f is induced in it at 0°, maximum when the coil is at 90° position anno

e.m.f when coil is at 180°.The direction of this induced e.m.f can be found

by applying Fleming's Right hand rule.

In the next half revolution i.e. from 180° to 360°, the variations in the

magnitude of e.m.f are similar to those in the first half revolution. Its value

is maximum when coil is at 270° and minimum when the coil is at

360°position.But it will be found that th direction of induced current is

reverse of the previous direction of flow.

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Therefore, in this thesis find that the current which we obtain from such

a simple generator reverses its direction after every half revolution. Such a

current undergoing periodic reversals is known as alternating current. It

should be noted that alternating current not only reverses its direction, it

does not even keep its magnitude constant while flowing in any one

direction. The two half- cycles may be called positive and negative half-

cycles respectively.

Now see when the coil is rotating with commutator. In this case the slip

rings are replaced by split rings.

The split rings are made out of a conducting cylinder which is cut into

two halves or segments insulated from each other by a thin sheet of mica or

some other insulating material (you can see in fig). As before, the coil ends

are joined to these segments on which rest the carbon or copper brushes.

In case of split rings, the positions of the segments of split rings have

also reversed when the current induced in the coil reverses i.e when the

current direction reverses the brushes also comes in contact with reverse

segments as that of positive half-cycle.

Hence, this current is unidirectional. It should be noted that the

position of the brushes is so arranged that the changeover of segments from

one brush to other takes place when the plane of the rotating coil is at right

angles to the plane of the lines of flux. It is so because in that position, the

induced e.m.f in the coil is zero.

You can observe this in two cases by pausing the waveform. Another

important point is that now the current induced in the coil is alternating as

before. It is only due to the rectifying action of the split-rings (also called

commutator) that it becomes unidirectional in the external circuit.

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Figure (2.2) Represent Generator Operation

2.3 Fleming's Right hand Rule

Fleming's right hand rule (for generators) shows the direction of

induced current flow when a conductor moves in a magnetic field.

Figure (2.3) represent Fleming's Right hand Rule

The right hand is held with the thumb, first finger and second finger

mutually at right angles, as shown in the diagram.

• The Thumb represents the direction of Motion of the conductor.

• The First finger represents the direction of the Field.

• The Second finger represents the direction of the induced or

generated Current (in the classical direction, from positive to

negative).

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Electromagnetic generators fall into one of two broad categories, dynamos

and alternators.

• Dynamos generate direct current, usually with voltage or current

fluctuations, usually through the use of a commutator

• Alternators generate alternating current, which may be rectified by

another (external or directly incorporated) system.

A dynamo is an electrical generator that produces direct current with

the use of a commutator. Dynamos were the first electrical generators

capable of delivering power for industry, and the foundation upon which

many other later electric-power conversion devices were based, including

the electrical motor, the alternating-current alternator, and the rotary

converter. Today, the simpler alternator dominates large scale power

generation, for efficiency, reliability and cost reasons. A dynamo has the

disadvantages of a mechanical commutator. Also, converting alternating to

direct current using power rectification devices (vacuum tube or more

recently solid state) is effective and usually economical.

An alternator is an electrical generator that converts mechanical

energy to electrical energy in the form of alternator current for reasons of

cost and simplicity, most alternator use a rotating magnetic field with

stationary armature Occasionally, a linear alternator or a rotating armature

with a stationary magnetic field is used. In principle, any ac electrical

generator can be called an alternator, but usually the term refers to small

rotating machines driven by automotive and other internal combustion

engines. An alternator that uses a permanent magnetic for its magnetic field

is called a magneto. Alternators in power station driven by steam turbines

are called turbo-alternators. Large 50 or 60 Hz three alternators in power

plants generate most of the world's electric power, which is distributed by

electric power grid.

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2.4 Types of Generator

Alternators or synchronous generators can be classified in many ways

depending upon their application and design. According to application these

machines are classified as:

1. Automotive type - used in modern automobile.

2. Diesel electric locomotive type - used in diesel electric multiple unit.

3. Marine type - used in marine.

4. Brush less type - used in electrical power generation plant as main

source of power.

5. Radio alternators - used for low brand radio frequency transmission.

These ac generators can be divided in many ways but we will discuss

now two main types of alternator categorized according to their

design. These are:

1.Salient pole type it is used as low and medium speed alternator. It has a

large number of projecting poles having their cores bolted or dovetailed

onto a heavy magnetic wheel of cast iron or steel of good magnetic

quality. Such generators are characterized by their large diameters and

short axial lengths. These generator are look like big wheel. These are

mainly used for low speed turbine such as in hydra power plant.

Figure (2.4) Represent salient pole rotor

2.Smooth cylindrical type it is used for steam turbine driven alternator. The

rotor of this generator rotates in very high speed. The rotor consists of a

smooth solid forged steel cylinder having a number of slots milled out at

intervals along the outer periphery for accommodation of field coils.

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These rotors are designed mostly for 2 pole or 4 pole turbo generator

running at 36000 rpm or 1800 rpm respectively.

Cylindrical rotor cross sectional view

Figure (2.5) Represent cylindrical rotor

Mechanical

• Rotor: The rotating part of an electrical machine

• Stator: The stationary part of an electrical machine

The rotor is a moving component of an electromagnetic system in the

electric motor , electric generator or alternator. Its rotation is due to the

interaction between the windings and magnetic fields which produces a

torque around the rotor's axis.

2.5 Types and construction of rotors

Induction (asynchronous) motors, generators and alternators

(synchronous) have an electromagnetic system consisting of a stator and

rotor.

There are two designs for the rotor in an induction motor: squirrel

cage and wound. In generators and alternators, the rotor designs are salient

pole or cylindrical

2.5.1 Squirrel-Cage Rotor

The squirrel cage rotor consists of laminated steel in the core with

evenly space bars of copper or aluminum placed axially around the

periphery, permanently shorted at the ends by the end rings. This simple and

rugged construction makes it the favorite for most applications. The

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assembly has a twist: the bars are slanted, or skewed, to reduce magnetic

hum and slot harmonics and to reduce the tendency of locking. Housed in

the stator, the rotor and stator teeth can lock when they are in equal number

and the magnets position themselves equally apart, opposing rotation in both

directions. Bearings at each end mount the rotor in its housing, with one end

of the shaft protruding to allow the attachment of the load. In some motors,

there is an extension at the non-driving end for speed sensors or other

electronic controls. The generated torque forces motion through the rotor to

the load.

Figure (2.6) represent Squirrel - Cage rotor

2.5.2 Wound Rotor

The rotor is a cylindrical core made of steel lamination with slots to

hold the wires for its 3-phase windings which are evenly spaced at 120

electrical degrees apart and connected in a 'Y' configuration. The rotor

winding terminals are brought out and attached to the three slips rings with

brushes, on the shaft of the rotor. Brushes on the slip rings allow for external

three-phase resistors to be connected in series to the rotor windings for

providing speed control. The external resistances become a part of the rotor

circuit to produce a large torque when starting the motor. As the motor

speeds up, the resistances can be reduced to zero.

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Figure (2.7) represent wound rotor

2.5.3 Salient Pole Rotors

The rotor is a large magnet with poles constructed of steel lamination

projecting out of the rotor‟s core. The poles are supplied by direct current or

magnetized by permanent magnets. The armature with a three-phase

winding is attached to three slip rings with brushes riding on them and

mounted on the shaft.

The field winding is wound on the rotor which produces the magnetic

field and the armature winding is on the stator where voltage is induced.

Direct current (DC), from an external exciter or from a diode bridge

mounted on the rotor shaft, produces a magnetic field and energizes the

rotating field windings and alternating current energizes the armature

windings simultaneously

2.5.4 Cylindrical Rotors

The cylindrical shaped rotor is made of a solid steel shaft with slots

running along the outside length of the cylinder for holding the field

windings of the rotor which are laminated copper bars inserted into the slots

and is secured by wedges. The slots are insulated from the windings and are

held at the end of the rotor by slip rings. An external direct current (DC)

source is connected to the concentrically mounted slip rings with brushes

running along the rings. The brushes make electrical contact with the

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rotating slip rings. DC current is also supplied through brushless excitation

from a rectifier mounted on the machine shaft that converts alternating

current to direct current.

Figure (2.8) represent cylindrical rotor

The stator is the stationary part of a rotary system, found in electric

generators, electric motors, sirens, or biological rotors. The main use of a

stator is to keep the field aligned. The stator is the stationary part of a rotary

system, found in electric generators, electric motors, sirens, or biological

rotors. The main use of a stator is to keep the field aligned.

2.5.5 Electrical Rotors

• Armature: The power-producing component of an electrical machine. In

a generator, alternator, or dynamo the armature windings generate the

electric current. The armature can be on either the rotor or the stator.

• Field: The magnetic field component of an electrical machine. The

magnetic field of the dynamo or alternator can be provided by either

electromagnets or permanent magnets mounted on either the rotor or the

stator.

2.5.6 Uses for a Generator

Portable Electric Generators for Outdoor Recreational Activities

With portable generators, camping has become more convenient and safe.

The conveniences of modern living like having a refrigerator for safe

storage of food and perishables and having a coffee maker to brew your

29

favorite drink in the morning are now possible to enjoy at a rustic campsite,

thanks to a portable generator. With a portable generator, you can bring

along and use appliances like an electric fan and microwave oven while in

the woods. You can also protect yourself and your family even better with

low voltage lights powered by a compact electric generator.

2.5.7 Generators for Business, Commercial and Contractors

This is particularly important for contractors and workers working on

construction sites without available electricity. With portable generators,

construction workers would be able to operate their tools, including spray

gun systems and roofing guns. Of course, they‟ll also have lighting to work

indoors and during the night. Small entrepreneurs would also be wise to

invest in a generator, especially if their business would be affected by a mid

or long-term power outage. For example, markets, butcher shops, and

restaurants could suffer from tremendous loss during a power outage as the

perishables stored in refrigerators and freezers may become spoiled. The

same goes for companies that provide Internet-based services, as a power

outage can affect their operations even if power is out for only a few hours.

Backup electricity source is also essential healthcare providers like small

clinics and hospitals.

Generators for Backyard Use: Aside from providing backup power

during outages, a generator can also offer auxiliary electricity for home

improvement projects. Portable generators can give backup power for

electric powered equipment like saws and drills. These generators can also

be used for sanders and grinders as well as work lights and fans. Hence,

there is no need to string extension cords out of the back door. Portable

generators offer an alternative source of energy for home improvement

projects so you can complete the tasks in a shorter amount of time. Backup

Generators for Extreme Weather Conditions: A backup generator is a good

investment for people who live in areas where severe climate or weather

conditions are a threat.

30

For instance, a generator is a must have for an individual who lives in

an extremely cold climate where a power failure could be lethal, as heaters

and home furnace won‟t be able to run. With a portable or standby

generator, families would be able to use these heat-producing appliances

even during a power outage. Families who reside in coastal areas, where

storms and tornadoes frequently occur, should invest in a generator. Power

outages are often caused by storms. Hence, a generator can provide backup

energy during emergency situations. Having a backup generator would also

enable families living in storm-ravaged areas to monitor the latest news and

weather updates, since they would have access to information through

television and radio.

Comfort, Convenience for Family Members: Perhaps the most

compelling reason why people invest in generators is the motivation to

provide comfort and convenience to their loved ones, especially their

children or elderly parents. It is no secret that power outages can be very

stressful. By investing in a generator families would be able to avoid any

unnecessary inconveniences.

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CHAPTER THREE

GENERATOR PROTECTION

32

GENERATOR PROTECTION

3.1 Introduction

Generator protection and control are interdependent problems. A

generator has to be protected not only from electrical faults (stator and

rotor faults) and mechanical problems (e.g. Related to turbine, boilers

etc.), but it also has to be protected from adverse system interaction arising

if generator going on out of step with the rest of system, loss of field

winding etc. Under certain situations like internal faults, the generator has

to be quickly isolated (shut down), while problems like loss of field

problem requires an „alarm‟ to alert the operator. Following is a

descriptive list of internal faults and abnormal operating conditions.

3.2 Internal Faults

1. Phase and /or ground faults in the stator and associated protection zone

2. Ground faults in the rotor (field winding)

3.3 Abnormal Operating Conditions

1. Loss of field.

2. Overload.

3. Overvoltage.

4. Under and over frequency

5. Unbalanced Operation e.g. single phasing.

6. Loss motoring i.e. loss of prime mover.

7. Loss of synchronization (out of step).

8. Sub synchronous oscillation.

3.4Stator Windings Faults

Stator winding faults: These types of faults occur due to the insulation

breakdown of the Stator coils. Different types of stator windings faults are:

1. Phase to earth fault

2. Phase to phase fault

3. Intertern fault

33

Phase to earth fault are limited by resistance of the neutral

grounding resistor. There are fewer chances for the occurrence of the

phase to phase and Interturn faults. The insulation between the two phases

is at least twice as thick as the insulation between one coil and the iron

core, so phase to phase fault is less likely to occur. Inter turn fault occurs

due the incoming current surges with steep wave front.

3.5 Stator Differential Protection for Generators

Differential protection is used for Protection of the generator against

phase to earth and phase to phase fault. Differential Protection is based on

the circulating current principle.

Figure (3.1): Differential protection for generators

In this type of protection scheme currents at two ends of the

protection system are compared. Under normal conditions, currents at two

ends will be same. But when the Fault occurs, current at one end will be

different from the current at the end and this difference of current is made

to flow through relay operating coils. The relays then closes its contacts

and makes the circuit breaker to trip, thus isolate the faulty section. This

type of protection is called the merz price circulating current system.

34

3.5 Modified Differential Protection

In modified differential protection setting of the Earth faults can be

reduced without any effect on the stability.

Figure (3.2): Modified differential protection for generators

In this method two relays are used for the phase to phase fault and

one relay is used for the protection of earth fault. In this method the two

relays and the balancing resistance are connected in star and the phase

fault relay is connected between the star point and the Neutral pilot wire.

The star connected circuit is symmetrical in terms of impedance. So

when the fault current occurs due to the phase to phase fault, it cancels at

the star point Due to the equal impedance. Thus it is possible with this

scheme to operate with the Sensitive earth fault relays. Thus this scheme

provides protection to the greater Percentage of the stator winding.

3.6 Biased Circulating Current Protection (percentage

differential relay protection)

With the differential protection relaying, the CTs at both end of the

stator windings must be same. If there is any difference in the accuracy of

the CTs the mal-operation of the relay will occurs. To overcome this

35

difficulty, biased circulating current protection is used. In this protection

system we can automatically increase the relay setting in Proportion to the

fault current. By suitable proportioning of the ratio of the relay Restraining

coil to the relay operating coil any biased can be achieved.

Figure (3.3) Biased circulating current protection for generators

Under normal operating condition current in secondary of the line

CTs will be same as the current in the secondary of the CTs at the neutral

end. Hence there are balanced current flows in the restraining coils and no

current flows in the operating coil. If there is any phase to phase or phase

to earth fault occurs then it causes the differences in the Secondary current

of the two CTs. Thus the current flows through the operating coil and

Make the circuit breaker to trip.

3.7 Self balance protection system

This type of protection is employed for earth fault and also for the

phase to phase fault.

36

Figure (3.4): self-biasing protection of the stator windings

In this type of protection two cables are required which is connected

to the two ends of the each phase. These two cables are passed through the

circular aperture of the ring type CTs.

Under normal conditions the current flowing in the two leads of the

cable will be in the same direction and no magnetization occurs in the ring

type CTs. When the earth fault occurs in any phase the fault current occurs

only once through the CTs and thus magnetic flux induced, this induces

the emf in the relay circuit causes the circuit breaker to trip.

This is very sensitive type earth fault protection but it also have some

limitations:

a) A different design of the cable lead is required in this scheme.

b) Large electromagnetic forces are develop in the CT ring under the

condition of heavy short circuit.

3.8 Stator Ground Fault Protection

The method of grounding effect the degree of protection which is

employed by the differential protection. High impedance reduces the fault

current and thus it is very difficult to detect the high impedance faults. So

37

the differential protection does not work for the high impedance

grounding. The separate relay to the ground neutral provides the sensitive

protection. But ground relay can also detect the fault beyond the generator,

it the time co-ordination is necessary to overcome this difficulty.

3.9 Stator Inter Turn Fault Protection

Differential protection for stator does not provide protection against

the inter-turn faults on the same phase winding of the stator. The reason is

that the current produced by the turn to turn fault flows in the local circuit

between the turns involved and thus it does not create any difference

between the current entering and leaving the windings at its two ends

where the CTs are mounted.

The coils of the modern turbo generator are single- turn, so there is

no need to provide inter –turn fault protection for the turbo generator. But

the inter turn protection is necessary for the multi turn generator like hydro

electric generator. Sometimes stator windings are duplicated to carry

heavy current. In this case stator winding have two different paths. In this

type of protection primaries of the CTs are inserted in the parallel paths

and secondary‟s are inter connected. Under the normal condition current

flowing through the two parallel paths of the stator winding will be same

and no current flowing through the relay operating coil. Under the inter

turn fault, current flowing through the two parallel path will be different

and this difference in current flowing through the operating coil and thus

causes the circuit breaker to trip and disconnect the faulty section. This

type of protection is very sensitive. The coils of the modern turbo

generator are single- turn, so there is no need to provide inter –turn fault

protection for the turbo generator. But the inter turn protection is necessary

for the multi turn generator like hydro electric generator. Sometimes stator.

Windings are duplicated to carry heavy current. In this case stator

winding have two different paths. In this type of protection primaries of

38

the CTs are inserted in the parallel paths and secondary‟s are inter

connected. Under the normal condition current flowing through the two

parallel paths of the stator winding will be same and no current flowing

through the relay operating coil. Under the inter turn fault, current flowing

through the two parallel path will be different and this difference in current

flowing through the operating coil and thus causes the circuit breaker to

trip and disconnect the faulty section.

This type of protection is very sensitive.

Figure (3.5) Inter turn protection of the stator winding

3.10 Stator Over Heating Protection

Stator over heating is caused due to the overloads and failure in

cooling system. It is very difficult to detect the overheating due to the short

circuiting of the lamination before any serious damage is caused.

Temperature rise depend upon I^2Rt and also on the cooling. Over current

relays cannot detect the winding temperature because electrical protection

cannot detect the failure of the cooling system. So to protect the stator

against overheating, embed resistance temperature detector or

39

thermocouples are used in the slots below the stator coils. These detectors

are located on the different places in the windings so that to detect the

temperature throughout the stator. Detectors which provide the indication

of temperature change are arranged to operate the temperature relay to

sound an alarm.

3.11 Protection of Generator Rotor Earth Fault

The rotor of a generator is wound by field winding. Any single earth

fault occurring on the field winding or in the exciter circuit is not a big

problem for the machine. But if more than one earth fault occur, there may

be a chance of short circuiting between the faulty points on the winding.

This short circuited portion of the winding may cause unbalance magnetic

field and subsequently mechanical damage may occur in the bearing of the

machine due to unbalanced rotation. Hence it is always essential to detect

the earth fault occurred on the rotor field winding circuit and to rectify it

for normal operation of the machine.

There are various methods available for detecting rotor earth fault of

alternator or generator. But basic principle of all the methods is same and

that is closing a relay circuit through the earth fault path. There are mainly

three types of rotor earth fault protection scheme used for this purpose. 1.

Potentiometer method 2. AC injection method 3. DC injection method let

us discuss the methods one by one.

Potentiometer Method of Rotor Earth Fault Protection in Alternator

The scheme is very simple. Here, one resistor of suitable value is

connected across the field winding as well as exciter. The resistor is

centrally tapped and connected to the ground via a voltage sensitive relay.

As it is seen in the figure below, any earth fault in the field winding as

well as exciter circuit closes the relay circuit through earthed path. At the

same time the voltage appears across the relay due to potentiometer action

of the resistor.

40

This simple method of rotor earth fault protection of alternator has a

big disadvantage. This arrangement can only sense the earth fault occurred

in the any point except the center of the field winding.

From the circuit it is also clear that in the case of earth fault on the

centre of the field circuit will not cause any voltage to be appeared across

the relay. That means simple potentiometer methods of rotor earth fault

protection, is blind to the faults at the centre of the field winding. This

difficulty can be minimized by using another tap on the resistor

somewhere else from the centre of the resistor via a push button. If this

pushbutton is pressed, the centre tap is shift and the voltage will appear

across the relay even in the event of central arc fault occurs on the field

winding.

AC Injection Method of Rotor Earth Fault Protection in Alternator

Here, one voltage sensitive relay is connected at any point of the field and

exciter circuit. Other terminal of the voltage sensitive relay is connected to

the ground by a capacitor and secondary of one auxiliary transformer as

shown in the figure below.

Here, if any earth fault occurs in the field winding or in the exciter circuit,

the relay circuit gets closed via earthed path and hence secondary voltage

of the auxiliary transformer will appear across the voltage sensitive relay

and the relay will be operated. The main disadvantage of this system is,

there would always be a chance of leakage current through the capacitors

to the exciter and field circuit. This may cause unbalancing in magnetic

field and hence mechanical tresses in the machine bearings. Another

disadvantage of this scheme is that as there is different source of voltage

for operation of the relay, the protection of rotor is inactive when there is a

failure of supply in the AC circuit of the scheme.

41

DC Injection Method of Rotor Earth Fault Protection in Alternator

The drawback of leakage current of AC injection method can be

eliminated in DC Injection Method.

Here one terminal of DC voltage sensitive relay is connected with positive

terminal of the exciter and another terminal of the relay is connected with

the negative terminal of an external DC source. The external DC source is

obtained by an auxiliary transformer with bridge rectifier. Here the

positive terminal of bridge rectifier is grounded.

It is also seen from the figure below that at the event of any field

earth fault or exciter earth fault, the positive potential of the external DC

source will appear to the terminal of the relay which was connected to the

positive terminal of the exciter. In this way the rectifier output voltage

appears across the voltage relay and hence it is operated.

3.12 Under/Over Frequency Protection

Over frequency results from the excess generation and it can easily be

corrected by reduction in the power outputs with the help of the governor

or manual control.

Under frequency operation: Under frequency occurs due to the excess.

During an overload, generation capability of the generator increases and

reduction in frequency occurs. The power system survives only if we drop

the load so that the generator output becomes equal or greater than the

connected load. If the load increases the generation, then frequency will

drop and load need to shed down to create the balance between the

generator and the connected load. The rate at which frequency drops

depend on the time, amount of overload and also on the load and generator

variations as the frequency changes. Frequency decay occurs within the

seconds so we cannot correct it manually. Therefore automatic load

shedding facility needs to be applied.

42

These schemes drops load in steps as the frequency decays. Generally

Load shedding drops 20 to 50% of load in four to six frequency steps.

Load shedding scheme works by tripping the substation feeders to

decrease the system load. Generally automatic load shedding schemes are

designed to maintain the balance between the load connected and the

generator.

The present practice is to use the under frequency relays at various load

Points so as to drop the load in steps until the declined frequency return to

normal. Non-essential load is removed first when decline in frequency

occurs. The setting of the under frequency relays based on the most

probable condition occurs and also depend upon the worst case

possibilities.

During the overload conditions, load shedding must occur before the

operation of the under frequency relays. In other words load must be shed

before the generators are tripped.

3.13 Under/ Voltage Protection / Over

Over voltage occurs because of the increase in the speed of the prime

mover due to sudden loss in the load on the generator. Generator over

voltage does not occur in the turbo generator because the control

governors of the turbo generators are very sensitive to the speed variation.

But the over voltage protection is required for the hydro generator or gas

turbine generators. The over voltage protection is provided by two over

voltage relays have two units – one is the instantaneous relays which is set

to pick up at 130 to 150% of the rated voltage and another unit is IDMT

which is set to pick up at 110% of rated voltage. Over voltage may occur

due to the defective voltage regulator and also due to manual control

errors.

43

3.14 Under voltage protection

If more than one generators supply the load and due to some reason

one generator is suddenly trip, then another generators try to supply the

load. Each of these generators will experience a sudden increase in current

and thus decreases the terminal voltage. Automatic voltage regulator

connected to the system try to restore the voltage. And under voltage relay

type-27 is also used for the under voltage protection.

3.15 Protection of the Generator Due to Unbalance Loading

Due to fault there is an imbalance in the three phase stator currents

and due to these imbalance currents, double frequency currents are

induced in the rotor core. This causes the overheating of the rotor and thus

the rotor damage. Unbalanced stator currents also damage the stator.

Negative sequence filter provided with the over current relay is

used for the Protection against unbalance loading. From the theory of the

symmetrical components, we know that an unbalanced three phase

currents contain the negative sequence component. This negative phase

sequence current causes heating of the stator. The negative heating follows

the resistance law so it is proportional to the square of the current. The

heating time constant usually depend upon the cooling system used and is

equal to I²t=k where I is the negative sequence current and t is the current

duration in seconds and k is the constant usually lies between 3 and 20. Its

general practice to use negative current relays which matches with the

above heating characteristics of the generator. In this type of protection

three CTs are Connected to three phases and the output from the

secondary‟s of the CTs is fed to the coil of over current relay through

negative sequence filter.

Negative sequence circuit consists of the resistors and capacitors

and these are connected in such way that negative sequence currents flows

through the relay coil. The relay can be set to operate at any particular

44

value of the unbalance currents or the negative sequence component

current.

Figure(3.6) protection against unbalance loading

3.16 Over current fault of a generator

Causes of over current fault on a generator is the Partial breakdown

of internal winding insulation, Overload on the supply system. Overcurrent

protection for generator is unnecessary because of high internal impedance

of generator, Modern design concept of generator is to set high internal

impedance of generator. Thus if over current fault occurs, due to high

internal impedance generator can withstand short circuit for a while. It can

manually disconnect from the bus. False tripping on an generator by over

current protection relay is need to be considered as this might disconnect

generator from bus for some fault outside of plant. This will cause

interruption of continuous operation, so over current relay used must have

time delay.

3.17 Alternator Prime Mover failure fault or reverse power

fault

What is prime mover in generator -We know about prime mover.

It‟s the mechanical system that rotates the rotor in alternator or just in

simple word runs the alternator. Typical prime movers are diesel or gas

engines, steam turbine, wind tidal force, water flow static force in

45

hydroelectric plant with dam etc. Now that we understand about prime

mover, it is clearly understandable that any time a prime mover might fail

to keep the alternator running. The root causes are so simple like fuel flow

shut up in gas /diesel engine, inadequate water flow in hydroelectric plants

etc.

The effect of prime mover failure in an alternator– we can imagine

the situation, an alternator is coupled with prime mover running, and it is

directly connected to the grid or some parallel electrical bus supplying

power. When the prime mover fails, it is still connected to the live electric

bus. Then the alternator fails to supply power but starts receiving power

from live electric bus. This time the synchronous alternator takes power

acts as a synchronous motor and run the engines or turbine in uncontrolled

high speed. This is called reverse power.

Severity of reverse power: For gas turbine and any hydroelectric

system the turbine installed is capable of running in very high speeds, so

when high speed occurs due to reverse power, any technician can decouple

the circuit breaker. But for diesel/ engine system, the reverse power is so

dangerous, as the over speed limit of engines re nominal like 120% of

rated speed. As example our plant‟s Wasilla engines rated speed was 750

RPM, and its high speed limit was 840/880 RPM.

Remedy -A reverse power relay is recommended. But this relay

should have time delay to avoid false trip in case of short time system

disturbance, phase swinging and fluctuation in synchronization.

Thus when a reverse power problem occurs, the first thing is to

decouple the corresponding circuit breaker to disconnect the alternator

from live line. If it is stuck, then shut down the whole bus, if that too is not

possible then shut the whole power plant for engine based power plant

only.

46

CHAPTER FOUR

PROPOSED PROTECTION TECHNIQUES THROUGH

DIFFERENT CASES

47

Proposed Protection Techniques through different Cases

4.1 The System Model

Heggligpower plant generation station consists of 4 phases The system each

phase contains two generators.

- Phase four contains two generators and their capacity is 3.5MW one of

them in the case of standby.

- Phase three contains two generators and their capacity is 3.6MW one of

them in the case of standby.

- Phase two contains two generators and their capacity is 3.5MW one of

them in the case of standby.

- Phase one contains two generators and their capacity is 3.5MW one of

them in the case of standby.

The capacity of the station in completely within 14.1MW.

The station contains in six transformers.

Figure (4.1): One line diagram of Hegglig power plant generation station

In network operation, stability plays a major role in the energy saving of the

Higgling station. This network shows that any disturbances must be resolved

quickly to ensure the stability of the power system network. The protective

equipment must be chosen in a suitable manner that can be obtained by short

48

circuit analysis.

Through this network, we study the short circuit of the Heglig 14.1 MW

using the ETAP program. Short circuit analysis was performed based on the

standards of the American National Institute (ANSI) -38 and the

International Electrotechnical Commission (IEC) -60909 and IEC 61363-1.

Short circuit responses of the Heglig 14.1 MW were obtained for different

types of symmetric and asymmetric faults at different locations.

49

4.2 The system data are shown below:-

Table (4.1) Bus input Data

Bus initial Voltage

ID Type Nom kv Base kv Sub-sys %Mag Ang

Bus 3 SWNG 6.6 6.6 3 100 00 0.00

Bus 2 SWNG 6.6 6.6 3 100 00 0.00

Bus 1 SWNG 6.6 6.6 3 100 00 0.00

The table (4-1) represents Bus input Data, the table shows the Bus

identification Nominal voltage Base voltage, initial voltage and angle .

Table (4.2) 2-Winding Transformer Input Data of Grounding

Trans former Rating conn

ID MVA PrimKV Sec KV Type

T200 30.000 6.6 0.4 D/Y

T204 30.000 6.6 33 D/Y

The table (4-2) Shows the r-winding transformer connection identification,

rating in MVA, primary voltage, secondary voltage and connection type.

50

Table (4. 3) Transformer Input Data

Transformer Rating Z-Variation % Tap Setting Adjusted Phase shift

ID MVA Prim KV

Sec KV %Z X/R +5% % Tol Prim Sec %Z Type Angle

T211 30.000 311.000 110.000 10.00 23.70 0 0 0 0 10.0000 Std Post. Seq 30.000

T212 30.000 11.000 110.000 10.00 23.70 0 0 0 0 10.0000 Std Post. Seq 30.000

T213 100.000 11.000 110.000 12.00 34.10 0 0 0 0 10.0000 Std Post. Seq 30.000

T214 100.000 11.000 110.000 12.00 34.10 0 0 0 0 10.0000 Std Post. Seq 30.000

T215 60.000 11.000 110.000 11.00 34.10 0 0 0 0 10.0000 Std Post. Seq 30.000

T216 60.000 11.000 110.000 11.00 34.10 0 0 0 0 10.0000 Std Post. Seq 30.000

* The table (4.2) shows the transformer input Data. This table

represent the Rating ,primary voltage, secondary voltage ,Z-variation ,

Tap settings and phase shift and connection type.

4.3 System Analysis and Result

First:- In this thesis run the load flow study in the system model

analysis of the system under.

The purpose of current calculated in the steady state to choose the

suitable current transformer ratio to the current transformer and use

these values in equation to set the relay as shown below.

The figure (4-2) represent the one line diagram of Hegglig power

plant station load flow analysis to calculate the steady state current and

choose suitable current transformer ratio.

51

Table (4.4):- This data shows suitable coefficient value of the current transformer in

each point of the system model.

Bus-Bars Current Transformer

Bus4 1458.B A

Bus3 145.9 A

Bus2 3174 A

The table (4.4) shows the suitable coefficient value of current

transformer in each point of the system model and this value used to

choose suitable current transformer ratio in each point , whereas choose

values very important to set the protection device.

The figure (4.3) shows the current transformer CT editor in ETAP-7,

represent the rating of the current transformer ,use choose CT-5 as example.

Second:- we run short circuit analysis in all bus bars to calculate

short circuit faults in each data to calculate the value of short circuit to

52

choose the suitable capacity in each circuit breaker and to use this value

to set relay.

The figure (4.4) shows short current circuit analysis of Khartoum north

power generation station to calculate of short circuit current and this

value very important to choose suitable protective device capacity.

We run the coefficients of equation as follows below to set the relays

this equation relates the values of steady state currents (Iss) and short circuit

(Isc) as follows below:

The relay current:

sc

f

II

C T R A T IO (1)

Where:

Isc = short circuit current

ss

s

II

C T R A T IO (2)

If = fault current of relay

Is = steady state current of relay Iss = steady state current

The pickup phase current=

s1 ,2 IC T R A T IO (3)

The pickup Ground current =

s0 ,3 IC T R A T IO

(4)

o p n + 10 .0 2o p

0 ,1 4 T .M .ST T 0 .0 4 m s

P S M 1

@ (5)

Where

TOPn = operation of the zone n

T.M.S = time multiple setting of relay

53

s

t ,= I 1 TI

*

(6)

t im eA = C o n stan t o f c u rre n t

t im eB = C o n stan t o f c u rre n t

Table (4.5):- The slope of the time/current curve sets is determined by

the constant α and β as follow:

The Table (4.5) shows the slope of the time current of the relay represent

standard measure, inverse, very inverse, extremely inverse.

Slope of time / current curve set Α Time Β Current

IEC Standard inverse 0.02 0.14

IEC Very inverse 1.0 13.5

IEC Extremely inverse 2.0 80

Therefore, all trip time calculations of over current relay were performed

according to above The International Electro-technical Commission (IEC)

standard formula.

4.4 Protection system coordination test

It was analyzed for simulation in electrical faults in three different positions

located at the station of Hegglig power plant .

The first location is the Generator (3.5MW) at bus bar4 near the

Generator H The second location is the Transformer (33KVA) as the

fault occur near the Transformer (T204)

system. Example when a fault occur in near the generator Hat bus bar 4

and the fault isn‟t line to ground and will be short circuit phase.

Note that the circuit breaker of the generator is tripped because the relay 1

gives the order to the circuit breaker and immediately feared to.

54

4.4.1 Protect the fault that occur near the generator

The figure (4.5) shows 3-phase fault sequence when fault occur near

the generator , and we notice that the circuit breaker near the generator

open quickly as much as possible to protect the generator we choose

fault near the generator H .

When fault occurs near the generator the simulation of the

three phase at the guarantor (Gen-H) at bus bar 4 we find

result as shown in finger 4.2 and the table 4.6 the circuit

breaker CB-H1 is tripped at the time 154 sec the relay 1 and

the fault current.

In this line program we run load flow study in thesis system model

analysis of the system under the purpose of current calculated in the

study state to choose the suitable current transform ratio to the

current transformer.

55

Figure (4.2) Testing System of Protection

4.4.2 Sequence-of-Operation Event Summary Report

Table (4.6):- Symmetrical 3-phase Fault at Bus395

Time(ms) ID if (KA) T1 (ms) T2 (ms) Condition

154 Relay1 3.054 154 OC1-51

204 CB-H 00 50 Tripped by relay1 Phase OC1-51

The table (4.6) shows sequence of operation of symmetrical 3-phase

fault at bus 4 , this table contains the fault current (IF) in KA ,firing time

and condition of sequence of operation.

When fault occurs near the transformer 204 and the fault is not line to

ground it is short circuit three phase.

Note that the circuit break of the transformer will immediately

disconnected very short time .

Result :

When fault occurs near the generator the simulation of the three

phase at the guarantor (Gen-H) at bus bar 4 we find result as shown in

finger 4.2 and the table 4.6 the circuit breaker CB-H1 is tripped at the

time 154 sec the relay 1 and the fault current.

56

CHAPTER FIVE

CONCLUSION ، RECOMMENDATIONS& Result

57

CONCLUSION ، RECOMMENDATIONS & Result

5.1 CONCLUSION

This project objective was to design generators protection of Hegglig

power plant by using ETAP program. so as an electrical generator can be

subjected either internal faults or external faults or both, hence any fault

occurred in the power system should be cleared in the power from the

generator as soon as possible otherwise it may create permanent damage in

the generator , the number and variety of fault occur in the generator are

huge. That is why generator is protected with several protection schemes.

In this thesis the one line diagram of Hegglig power plant generation

grid was simulated by using ETAP program and we run load flow analysis

to calculate the steady state current (Is) and to choose suitable current

transformers (CTs) ratio connected with relays. After that we run short

circuit analysis in all system to calculate the short circuit current and

determine the size of protection devices. Then we used these values to

calculate the value of T.M.S (Time Multiplier Setting), or time operation

and pick up current of protective relays that used to protect the system.

Finally we run star protective device coordination in ETAP and test the

protection device coordination.

The proposed methods were given good results which indicate that

the objectives of this study were successfully achieved.

5.2 RECOMMENDATIONS

1- In this thesis recommend that to protect the generators from any fault that

may occur due to external and internal faults.

2-Also we recommend to use suitable CT ratio with relays, and avoid the

current transformer from saturation.

3- In this thesis recommend to test the protection devices coordination to be

sure that the power system protection coordination well.

58

Result:

In this thesis run the load flow study in the system model analysis of

the system under.

The purpose of current calculated in the steady state to choose the

suitable current transformer ratio to the current transformer and use

these values in equation to set the relay as shown below.

The figure (4-2) represent the one line diagram of Hegglig power

plant station load flow analysis to calculate the steady state current

and choose suitable current transformer ratio.

The suitable coefficient value of current transformer in each point of

the system model and this value used to choose suitable current

transformer ratio in each point , whereas choose values very important

to set the protection device.

Bus-Bars Current Transformer

Bus4 1458.B A

Bus3 145.9 A

Bust2 3174 A

Bus4

Bus3 Bust2

Indicators of the stability number of minutes lost to thecurrent.Indicates the number of times a typical

power outage of a power outage occurs within a predetermined time period (unit measured in

number).

The equation: the average value of the frequency of power outages = the sum of

the wrong current / on the state of the current.

59

References

1. Raman deep kaurAujla "Generator stator protection over /under

voltage over/under frequency and unbalanced loading ", (May 5

2008)

2. Y.G.Paithankar and S.R.Bhide “Fundamentals of Power System

Protection” (2003).

3. The book reflects many years of experience of the authors in

teaching this subject matter to undergraduate electrical engineering

students.

4. The book, now in its second edition, continues to provide the

most relevant concepts and techniques in power

5. Laboratory setup for teaching and research in computer-based

power system protection, conference paper, Dec. 1995.

6. T.S. Sidhu M.S. Sachdev M.S. Sachdev View show abstract.

7. Development of power system protection laboratory through

senior design projects article, jun 2005 IEEE TO POWER SYST.

8. Mason, C. Russell. "The Art and Science of Protective Relaying"

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Engineers. 1991-02-25. Archived from the original on 2008-01-13.

Retrieved 2009-01-26.

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