iii ii project

8/6/2019 III II Project

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STUDYOF RELAY TECHNOLOGY AND TESTING

The Project report submitted in partial fulfillment of therequirements for the Award of the Degree of

BACHELOR OF TECHNOLOGY

In

ELECTRICAL AND ELECTRONICS ENGINEERING

SUBMITTED

By

M.P.PRASANNA KUMAR 06U41A0227

M.PRASAD KUMAR 07U45A0203

V.SAGAR 06U41A0237

S.REVATHI 06U41A0236

G.J.S.P.R.JYOTHSHNA RANI 06U41A0216

B.NAVEEN 06U41A0224

Under The Esteemed Guidance of

Mr.M.SAI SESHA

DEPARTMENT OF

ELECTRICAL AND ELECTRONIC ENGINEERING

DADI INSTITUTE OF ENGINEERING AND TECHNOLOGY

ANAKAPALLE, J.N.T.UNIVERSITY, KAKINADA

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CERTIFICATE

This is to certify that the Project entitled


is a bonifide work done by

M.P.PRASANNA KUMARpursuing his B.Tech in

DADI INSTITUTE OF ENGINEERING AND

TECHNOLOGYANAKAPALLE.

J.N.T.UNIVERSITY, KAKINADA


Date: External Guide

Place: Mr.B.Srinivasa Reddy

Senior manager (Electrical) Visakhapatnam Steel Plant

CERTIFICATE

This is to certify that this project work entitled

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is a bonifide work of

M.P.PRASANNA KUMAR M.PRASAD KUMAR

V.SAGAR, S.REVATHI, G.J.S.P.R.JYOTHSHNA RANI, B.NAVEEN

DADI INSTITUTE OF ENGINEERING AND TECHNOLOGY

ANAKAPALLE.


UNDER THE GUIDANCE OF

Mr.M.SAI SESHA

Associate Prof. (Electrical Dept.)

DADI INSTITUTE OF ENGINEERING & TECHNOLOGY

HEAD OF THE DEPARTMENT INTERNAL GUIDE

Mr.K.V.L.NARAYANA. M.SAI SESHA.

Date:

Place:

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ACKNOWLEDGEMENT

We humbly express our sincere profound sense of gratitude for

Mr.B.JAGAN MOHAN RAO, Principal for giving us an

opportunity to take up the project work in a prestigious organization

like Visakhapatnam Steel Plant.

It is needed a great privilege to express our deep sense of

gratitude and in debt ness to our distinguished Head of the Dept.

Mr. K.V.L.NARAYANA, Associate Prof. for his scholarly

inspiration, valuable guidance and immerse help. Our Sincere thanks

to Mr. B.SRINIVAS REDDY, Senior Manager (Electrical) that he

has extended us for the successful completion of this endeavor. It is

proud to privilege to have the opportunity of guidance from a great

personality like him.

Last but not the least; we would like to convey our thanks to

Mr. M.SAI SESHA, Associate Prof. for the kind guidance to do this

project in this prestigious organization with his vast knowledge

Radiance in Electrical Field of Stream.

CONTENTS

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1. Introduction

6

2. Introduction to Visakhapatnam Steel Plant

9

3. Introduction to Protective Relaying

12

4. Important Terms and Fault Characteristics 20

5. Requirements of Protective Relaying 21

6. Types of Electromechanical Relay 26

7. Static Relays 33

8. Latest Era in Relays -Numerical Relays 37

9. Testing of Relays and Procedures 39

10. Suggestions for the forthcoming batches 47

11. Conclusion 49

12. References

50

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INTRODUCTION

In a power system consisting of generator, transformer,

transmission and distribution circuits, it is inevitable that sooner

or later some failure will occur somewhere in the system, it must

be quickly detected and disconnected from the system. There aretwo principal reasons for it. Firstly if the fault is not cleared

quickly it may cause unnecessary interruption of service to the

customers secondly rapid disconnection of the faulted apparatus

limits the amount of damage to it and prevents effects of fault

from spreading into the system. The capital investment involved

in a power system for the generation, transmission and

distribution of electrical power is so great that proper precautions

must be taken to ensure that the equipment not only operates as

nearly as possible to peak efficiency but also that it is protected

from accidents.

The purpose of protective relays and protective relaying

system is to operate the correct the circuit breakers so as to

disconnect only the fault equipment from system as quickly as

possible, thus minimizing the trouble and damage caused by

faults when they occur. The modern power system is very

complex and even though protective equipments from 4% to 5%

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of the total cost involved in the System, they play a very

important role in the system design for good quality of reliable

supply. The protective relays do not eliminate the possibility of

faults on the system, rather their action starts only after the fault

has occurred on the system. It would be ideal if protection could

anticipate and prevent faults but this is impossible except where

the original cause of fault creates some effects which can operate

a protective relay. A protective relay is device that detects the

fault and initiates the operation of the circuit breaker to isolate

the defective element from the rest of the system. The relay

detects the abnormal conditions in the electrical circuits by

constantly measuring the electrical quantities which are different

under normal and fault conditions.

The electrical quantities which may change under faultconditions are voltage, current, frequency and phase angle.

Through the changes in one or more of these quantities the faults

signal their presence, type and location to the protective relays.

Having detected the fault the relay operates to close the trip

circuit of breaker. This results in the opening of breaker and

disconnection of faulty circuit. The relay circuit connections can

be divided into three parts viz..,

First part is primary winding of a current transformer

(C.T) which is connected in series with the line to be

protected.

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Second part consists of secondary winding of C.T. and the

relay operating coil.

Third part is tripping circuit which may be either A.C or

D.C. It consists of a source supply, the trip coil of the circuit

breaker and the relay stationary contacts. When a short circuit

occurs at a certain point on the transmission line the current

flowing in line increases to an enormous value. This result in a

heavy current flow through the relay coil, causing the relay to

operate by closing its contacts. This in turn closes the trip circuit

of the breaker, making the circuit breaker open and isolating the

faulty section from the rest of the system. In this way the relay

ensures the safety of the circuit equipment from damage and

normal working of the healthy portion of the system. The

demand for electrical power is increasing at a very fast rate.This necessitates the installation of transmission lines reaching

to all the areas of the state. When large bulk of power is to be

transmitted at very long distances, the efficiency should be

high. It requires extra high voltage and ultra high voltage

transmission lines to be erected. These transmission lines are

required to be protected by comprehensive and quite

complicated protective schemes. So that the power interruption

is reduced to minimum, with regard to both the time of

interruption and the area affected by power interruption. The

protective scheme must operate fast and selectively before the

power system becomes unstable.

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Our project is dedicated for discussion of different

protective schemes i.e. by the usage of Relays and mainly on

distance protection of transmission lines of power system.

Before going into the details of the Project Theme Line lets

know about the Overview of Steel Plant.

OVER VIEW OF VISAKHAPATNAM STEEL PLANT

BRIEF DESCRIPTION:

Visakhapatnam Steel plant is located on the coast of Bay of

Bengal, 16 km to the South West of Visakhapatnam. The

decision of the Government of India to set up an Integrated

Steel Plant at Visakhapatnam was announced by the Prime

Minister Smt. Indira Gandhi in Parliament on 17th April 1970.

The formal inauguration was done on 20th January 1971 by

the then Prime Minister. The Government of India and USSR

signed an agreement in 1979 in setting up the 3.4 million tones

integrated Steel plant at Vizag.

The project was estimated to cost Rs.3897.28 corers

based on 1981 prices but the cost has increased substantially

over the sanctioned cost and finally the project is estimated to

cast Rs.5822.17 corers as per 1987. Vizag Steel, also known

as Visakhapatnam Steel Plant, is a steel company based in the

outskirts ofVisakhapatnam, India. Its vision - Infrastructuring

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India. Vizag Steel bagged the first prize in Energy

Conservation constituted by Government, consecutively for

the last 2 years primarily due to its focus on energy

conservation, cost reduction and waste utilization. Vizag Steel

Plant today is among the lowest cost steel producers in the

world. The Visakhapatnam Steel Plant has been awarded the

Safety Innovation Award - 2006 by the Institution of

Engineers for its "outstanding contributions in the field and

adoption of the best and the most innovative safety practices".

The plant was awarded the Prime Minister's trophy for the best

steel plant in the country, for the year 02-03. VSP added

another feather to its cap by bagging six Government of India,

Vishwakarma Rashtriya Puraskar (VRP) Awards at national

level out of total number of 28 awards announced by Ministry

Of Labour, Government of India.

PRODUCT MI:

VSP produces angles, channels, bars, wire rods and billets for

re-rolling. The Plant produces Pig Iron, 1.44 million tones per

annum of granulated slag and there are also normal by-

products from coke-oven and coal chemical plant.

PLANT FACILITIES:

VSP has these major production facilities.

1. Three coke-ovens Batteries.

2. Two Sinter machines of 312 m square area.

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3. Two Blast Furnace of 3200 m cube use full volume.

4. Steel Melt shop with three L D converters of 150 tons.

5. Light & Medium Merchant mill of 7, 10,000 tones per year.

6. Wire Rod Mill of 850000 tons per year.

7. Medium Merchant & Structural Mill of 850000 tons.

MODERN TECHNOLOGY:

VSP is the most sophisticated and modern integrated steelplant it contains selective crushing of coal.

1. 7metres tall coke-ovens.

2. Dry quenching of coke.

3. On ground blending of sinter base mix.

4. 100% continuous casting of liquid steel.

5. Hot metal de-sulphurisation.

6. Computerization for process control. And many more

Integrated systems are being used in this plant.

POWER SUPPLY:

The plant has in plant power generation from a power plant

having three turbo generators of 60 MW and one 67.5 MW

generators totally supplying 247.5 MW power supply. And an

inclusion of Auxiliary Unit constitutes the plant with an Extra

of 40 MW (2 x 20 MW) resulting the total power supply to

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287.5 MW in total. The plant is estimated to cost about Rs.

8755 crores based on prices as on 1994.

INTRODUCTION TO PROTECTIVE RELAYING

About Protective Relaying:

Protective relaying is necessary with almost every electrical

plant, and no part of the power system is left unprotected. The

choice of protection depends upon several aspects such as type

and rating of the protected equipment, its importance, location,

probable abnormal conditions, cost etc. Between generators

and the final load points, there are several electrical equipment

and the machines of various ratings. Each need is certain

adequate protection. The protective relaying senses the

abnormal conditions in a part of the power system and gives an

alarm or isolates that part from the healthy system. The relays

are compact, self-contained devices which respond toabnormal condition. The relays distinguish between normal

and abnormal condition. Whenever an abnormal condition

develops, the relays close its contacts. There by the trip current

of the circuit breaker is closed. Current from the battery supply

flows in the trip coil of the circuit breaker opens and the faulty

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part is disconnected from the supply.The last thirty years have

seen enormous changes in relay technology. The

electromechanical relay in all of its different forms has been

replaced successively by static, digital and numerical relays,

each change bringing with it reductions and size and

improvements in functionality. At the same time, reliability

levels have been maintained or even improved and availability

significantly increased due to techniques not available with

older relay types. This represents a tremendous achievement

for all those involved in relay design and manufacture. The

entire process, occurrence of fault-operation of the relay-

opening of circuit breaker, removal of faulty part from the

system is automatic and fast.

Circuit breakers are switching devices which can interrupt

normal currents and fault currents. Besides relays and circuit

breakers, there are several other important components in the

protective relaying scheme. These include: protective current

transformers and voltage transformers, protective relays, time

delay relays, auxiliary relays, secondary circuits, trip circuits,auxiliaries and accessories etc. Each component is important

protective relaying is a team work of these components.

The functions of protective relaying include the following:

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To sound an alarm or to close the trip circuit of circuit-

breaker so as to disconnect a component during an abnormal

condition in the component, which include over-load, under-

voltage, temperature rise, unbalanced load, reverse power,

under-frequency, short circuits etc...

To disconnect the abnormally operating part so as to

prevent the subsequent faults.

Example: Over-load protection of a machine protects the

machine and prevents insulation failure.

To disconnect the faulty path quickly so as to minimize

the damage to the faulty part eg: if a machine is

disconnected immediately after a winding fault, only a

few coils may need replacement. If the fault is sustained,

entire winding may get damaged and machine may be

beyond repairs.

To localize the effect of fault by disconnecting the

faulty path, from the healthy part, causing least

disturbance to the healthy system.

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To disconnect the faulty part quickly so as to improve the

system stability, service continuity and system

performance. Transient stability can be improved by

means of improved protective relaying. Faults cant be

avoided completely .They can be minimized. Protective

relaying plays an important role in minimizing the faults

and also minimizing the damage in the event of faults.

IMPORTANT TERMS:

It is desirable to define and explain some important terms

much used in connection with relays.

1. PICK-UP CURRENT:

It is the minimum current in the relay coil at which the relay

starts to operate. So long as the current in the relay is less than

pick-up value, the relay does not operate and the breaker

controlled by it remains in the closed position. However, when

the relay coil current is equal to or greater than the pick-up

value, the relay operates to energize the trip coil which opensthe circuit breaker.

2. CURRENT SETTING:

It is often desirable to adjust the pick-up current to any

required value. This is known as current setting and is usually

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achieved by the use of tappings on the relay operating coil.

The taps are brought out of a plug bridge as shown in figure.

The plug bridge permits to alter the number of turns on the

relay coil. This changes the torque on disc and hence the time

of operation of the relay. The values assigned to each tap are

expressed in terms of percentage full-load rating of Current

Transformer with which the relay is associated and represents

the value above which the disc commences to rotate and

finally closes the trip circuit. Therefore, pick-up current=rated

secondary current of C.T.*current setting.

3. PLUG-SETTING MULTIPLIER(P.S.M.):

It is the ratio of fault current in relay coil to the pick-up current

i.e.., P.S.M= fault current in the relay coil / pick-up current.

= fault current in the relay coil / rated secondary

Current of C.T.*100

4. TIME SETTING MULTIPLIER:

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A relay is generally provided with control to adjust the time of

operation. The time setting dial is calibrated from 0 to 1 in

steps of 0.05sec as shown in figure. These figures are

multipliers to be used to convert the time derived from time

/P.S.M. curve into the actual operating time.

Thus if the time setting is the 0.1 and the time obtained from

the time/P.S.M curve is 3 seconds, then actual relay operating

time is 3*0.1=0.3sec. For instance, in an induction relay the

time of operation is controlled by adjusting the amount of

travel of the disc from its reset position to its pick up position.

This is achieved by the adjustment of the position of a

movable backstop which controls the travel of the disc and

thereby varies time in which the relay will close its contacts

for given values of fault current. A so-called time dial with an

evenly divided scale provides this adjustment. The time of

operation is calculated by multiplying the time setting

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multiplier with the time obtained from time /P.S.M. curve of

the relay.

FAULTS, CAUSES AND EFFECTS:

A fault in its electrical equipment is defined as a defect in its

electrical circuit due to which the flow of current is diverted

from the intended part. Faults are caused by breaking of

conductors or failure of insulation fault impedance is generally

low and fault currents are generally high. Fault currents being

excessive, they can damage not only the faulty equipment but

also the installation through which the fault current is fed.

For ex: if a fault occurs in a motor, the motor winding is

likely to get damaged. Further if the motor is not disconnected

quickly enough the excessive fault currents can cause damage

to the starting equipment, supply connections etc.

Faults in certain important equipment can affect the

stability of the power system for ex: a fault in bus-zone of a

power station can cause tripping of all the generator units in

power station and can affect the stability of interconnected

systems. These are several causes of faults occurring in a

particular electrical plant. Faults can be minimized by

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improved system design improved quality of components,

better maintenance etc. however the faults cant be entirely

eliminated.

Equipment Cause of fault %of total faults

1.Overhead lines 1.Lightening strokes, 30-40

2.storms, earthquakes, icing3. Birds, trees, kites, airplanes etc.

4.Internal over voltages

30-40

2.Under ground

cables

1.Damage during digging

2. Insulation failure due to

temperature rise.

3.Failure of joints

8-10

3.Alternators 1.Stator faults

2.Rotor faults

3.Abnormal conditions

4.Faults in associated equipment

5.Faults in protective system

6-8

4.Transformers 1.Insulation failure

2.Faults in tap changer

3.Faults in protection circuit

4.Inadequate protection

5.Faults in bushing

6.Over loading, overprotection

10-12

5.Switchgear

and protection

1.Insulation failure

2.Mechanical defect

10-12

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3.Leakage of air/oil/gas

4.Inadequate rating

5.Lack of maintenance

METHODS OF BACK UP PROTECTION:

1. Relay Back-up:

Same breaker is used by both main and back-up protection,but the protective systems are different. Separate trip coils may

be provided for the same breaker.

2. Breaker Back-up:

Different breakers are provided for main and back up

Protection, both the breakers being in the same station.

3. Remote Back-up:

The main and back up protections provided at different

stations and are completely independent.

4. Centrally Co-ordinate Back-up:

The system having central control can be provided with

centrally controlled back-up. Central control continuous

supervises load flow and frequency in the system. The

information about load flow and frequency is assessed

continuously .If one of the components in any part of system

fails (ex: a fault on a transformer, in some system) the load

flow in the system is affected .The central coordinating station

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receives info about the abnormal condition through high

frequency carrier signals. Main protection is at various stations

and back up protection for all stations is at central control

center.

BASIC REQUIREMENTS OF PROTECTIVE

RELAYING:

A well design and efficient protective relaying should have

1. Speed2. Selectivity

3. Sensitivity

4. Reliability

5. Simplicity

Speed:

Protective relaying should disconnect a faulty element

as quickly as possible. This is desirable for many reasons,

principles among which are:

a) Improves power system stability

b) Decreases the amount of damage incurred

c) Lessens annoyance to electric power consumers and

decreases total outage time for power consumers

d) Decreases the likelihood of development of one type of

fault into other more severe type.

e) Permits use of rapid re closure of circuit-breakers to restore

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service to customers.

Selectivity:

It is the basic requirement of relay in which it should

be possible to select which part of the system is faulty and

which is not and should isolate the faulty part of the system

from the healthy one. Selectivity is achieved in two ways:

(i)Unit system of protection

(ii)Non-unit system of protection

Unit system of protection means the one in which if

the protection responds only to faults with in its own zone and

does not make any note of the conditions else where, e.g., the

differential protection of transformers and generators. Here,

the protection scheme will work only if the fault is in the

transformer or generator respectively. Non-unit system of

protection is one in which the selectivity is obtained by

grading the time or current settings of the relay at differentlocations, all of which may respond to a given fault. Any

failure occurring within a given zone will cause the opening of

all breakers within that zone. The various protective zones are

a) Generators or generator transformer unit

b) Transformers

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c) Bus bars

d) Transmission lines

e) Distribution circuits

Sensitivity:

It is the capability of the relaying to operate reliably

under the actual conditions that produce the least operating

tendency. There may be abnormalities in the normal operating

conditions or the faults for which the protection has been

designed. It is desirable to have the protection as sensitive as

possible in order that it shall operate for low values of

actuating quantity. However, a protection with high degree of

sensitivity is more complex and uses more equipment and

circuitry and therefore is more expensive.

Reliability:

Reliability means that the protective relaying must be

ready to function, reliable and correct in operation at all times

under any kind of fault and abnormal conditions of the power

system for which it has been designed.Simplicity:

Simplicity of construction and good quality of the relay,

correctness of design and illumination qualified maintenance

and supervision, etc. are the main factors which influence

protective relaying. As a rule, the simple the protective scheme

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and the lesser the number of relays, circuits and contacts it

contains, the greater will be its reliability.

Economy:

As with all good engineering designs, economics play a

major role. It is futile to achieve all important general

requirements together, so compromises become necessary. Too

much protection is as bad as too little and the relay engineer

must strike a sensible compromise with due regard to practical

situation.

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Relays and relay settings are not to be changed from what

is indicated on current issues of relay data sheets unless

authorized by regional or project personnel with the

proper responsibility.

TYPES OF ELECTROMECHANICAL RELAY

These relays were earliest forms of relay used for the

protection of power systems, and they date back nearly 100

years. They work on the principle of a mechanical force

causing operation of a relay contact in response to a stimulus.

The mechanical force is generated through current flow in one

or more windings on a magnetic core or cores, hence the term

ELECTROMECHANICAL RELAY. The principle

advantage of such relays is that they provide galvanic isolation

between the inputs and outputs in a simple, cheap and reliable

form therefore for simple on/off switching functions where

the output contacts have to carry substantial currents, they are

still use. They work on the following two main operating

principles:

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(1)Electromagnetic attraction

(2)Electromagnetic induction

ELECTROMAGNETIC ATTRACTION RELAYS:

Electromagnetic attraction relays operate by virtue of an

armature being attracted to the poles of an electromagnet or a

plunger being drawn into a solenoid. Such relays may be

actuated by d.c or a.c quantities. The principle advantage of

such relays is that they provide galvanic isolation between the

inputs and outputs in a simple, cheap and reliable form

therefore for simple on/off switching functions where the

output contacts have to carry substantial currents, they are still

used. The important types of electromagnetic attraction are:

Attracted armature type relay

Solenoid type relay

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Balanced beam type

ATTRACTED ARMATURE TYPE RELAY:

The figure shows the schematic arrangement of an attracted

armature type relay.

It consists of a laminated electromagnet M carrying a

coil C and a pivoted laminated armature. The armature is

balanced by a counter weight and carries a pair of spring

contact fingers at its free end. Under normal operating

conditions, the current through the relay coil increases

sufficiently and the relay armature is attracted upwards. The

contacts on the relay armature bridge a pair of stationary

contacts attached to the relay frame. This completes the trip

circuit which results in the opening of the circuit breaker and

therefore in the disconnection of the faulty circuit. The

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minimum current at which the relay armature is attracted to

close the trip circuit is called pickup current. It is a usual

practice to provide a number of tapings on the relay coil so that

the number of turns in use and hence the setting value at which

the relay operates can be varied.

SOLENOID TYPE RELAY:

Under normal operating conditions, the current through the

relay coil C is such that it holds the plunger by gravity or

spring in the position However, on the occurrence of a fault,

the current through the relay coil becomes more than the

pickup value, causing the plunger to be attracted to the

solenoid. The upward movement of the plunger closes the trip

circuit, thus opening the circuit breaker and disconnecting thefaulty circuit

BALANCED BEAM TYPE RELAY:

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It consists of an iron armature fastened to a balanced beam.

Under normal operating conditions, the current through the

relay coil is such that the beam is held in the horizontal

position by the spring. However when a fault occurs, the

current through the relay coil becomes greater than the pickup

value and the beam is attracted to close the trip circuit. This

cause the opening of the circuit breaker to isolate the faulty

circuit.

ELECTROMAGNETIC INDUCTION RELAYS:

Electromagnetic induction relays operate on the principle of

induction motor and widely used for protective relaying

purposes involving a.c. quantities. They are not used with D.C.

quantities owing to the principle of operation. An induction

relay essentially consists of a pivoted aluminum disc placed in

two alternating magnetic fields of the same frequency but

displaced in time and space. The torque is produced in the disc

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by the interaction of one of the magnetic fields with the

currents induced in the disc by the other.

The important types of structures are commonly used for

obtaining the phase difference in the fluxes and hence the

operating torque in induction relays:

(i) shaded-pole structure

(ii) Watt-hour meter or double winding structure

(iii) Induction cup structure.

SHADED-POLE STRUCTURE:

The general arrangement of shaded pole structure is shown in

figure. It consists of a pivoted aluminum disc free to rotate in

the air-gap of an electromagnet. One-half of each pole of the

magnet is surrounded by a copper band known as shading ring.

The alternating flux s in the shaded portion of the poles will,

owing to the reaction of current induced in the ring, lag behind

the flux u in the unshaded portion by angle . These two a.c.

fluxes differing in phase will produce the necessary torque to

rotate the disc.The driving torque T is given by

T s u sin

Assuming the fluxes s and u to be proportional to the

current I in the relay coil,

T I^2sin

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This shows that driving torque is proportional to the square of

current in the relay coil.

WATT-HOUR METER OR DOUBLE WINDING

STRUCTURE:

This structure gets its name from the fact that it is used in

Watt-hour meters. The general arrangements of this type of

relay are shown in figure. It consists of a pivoted aluminum

disc arranged to rotate freely between the poles of two

electromagnets the upper electromagnet carries two winding;

the primary and the secondary. The primary winding carries

the relay current I1 while the secondary winding is connected

to the winding of the lower magnet. The primary current

induces e.m.f in the secondary and so circulates a current I2 in

it. The flux 2 induced in the lower magnet by current in

secondary winding of the upper magnet will lag behind 1 by

an angle . The two fluxes 1 and 2 differing in phase by

will produce a driving torque on the disc proportional to 1

2sin.

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INDUCTION CUP STRUCTURE:

This figure shows the general arrangement of an induction cup

structure. It most closely resembles an induction motor; expect

that the rotor iron is stationary, only the rotor conductor

portion being free to rotate. The moving element is a hollow

cylindrical rotor which turns on its axis. The rotating field is

produced by to pairs of coils wound on four poles as shown.

The rotating field induces current in the cup to provide the

necessary torque. If 1 and 2 represent the fluxes produced

by the respective pairs of poles, then torque produced is

proportional to 1 2 sin where is the phase difference

between two fluxes. A control spring and the back stop for

closing of the contacts carried on an arm are attached to the

spindle of the cup to prevent the continuous rotation.

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Induction cup structures are more efficient torque producers

than either shaded-pole or the watt-hour meter structures.

There fore this type of relay has very high speed and may have

an operating time less then 0.1second.

STATIC RELAYS

The term static implies that the relay has no moving parts.

This is not strictly the case for a static relay, as the output

contacts are still generally attracted armature relays. In a

protection relay, the term static refers to the absence of

moving parts to create the relay characteristic. Introduction of

static relays began in the early 1960s. Their design is based onthe use of analogue electronic devices instead of coils and

magnets to create the relay characteristic. Early versions used

discrete devices such as transistors and diodes in conjunction

with resistors, capacitors, inductors, etc., but advances in

electronics enabled the use of linear and digital integrated

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circuits in later versions for signal processing and

implementation of logic functions.

While basic circuits may be common to a number of

relays, the packaging was still essentially restricted to a single

protection function per case, while complex functions required

several cases of hardware suitably interconnected. User

programming was restricted to the basic functions of

adjustment of relay characteristic curves. They therefore can

be viewed in simple terms as an analogue electronic

replacement for electromechanical relays, with some additional

flexibility in settings and some saving in space requirements.

In some cases, relay burden is reduced, making for reduced

CT/VT output requirements. The term static relay refers to a

relay which incorporates solid state components like

transistors, diodes etc., for the measurement or comparison of

electrical quantities. The static network is so designed that it

gives an output signal in the tripping direction whenever a

threshold condition is reached.

The output signal in turn operates a trip device whichmay be electronic or electromagnetic. The need for the static

relays arose because of the requirement of fast and reliable

protective schemes for the modern power systems which is

growing both in complexity and fault levels. The scheme

should be fast so as to preserve dynamic stability of the system

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as the character and loading approach design limits. The

supply problem associated with the thermionic valves has been

solved with the use of semi-conductors. The transistors have

made it possible to achieve greater sensitivity and at the same

time excellent mechanical stability which is not possible with

the electro-mechanical relays. It is to be noted here that is

usually not economical to replace existing electro-mechanical

relays with their static counter parts just to reduce

maintenance. The protective relays, now -a-days, are being fed

by iron cored current transformer and hence excessive

saturation should be avoided to ensure high speed and

discriminative operation the static relays reduce the burden on

the current transformer .It is interesting to note that the static

relays have first been commercially manufactured for the

distance and differential protective schemes whereas the much

simpler over current relays have not been brought out.

The reason behind this that distance and differential

schemes are more amenable to mathematical analysis whereas

the over current characteristics are more of empirical nature.Therefore, a static over current relay cannot compete with the

conventional electro-mechanical relay. With the use of static

relays it has been possible to obtain many varied and complex

distance protection characteristics which are impossible to

obtain with the conventional electro-mechanical relays.

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Transistor relays are the most widely used static relays.

In fact static relays are generally mean Transistor relay. The

fact that a transistor can be used both as an amplifying device

and as a switching device makes this component suitable for

achieving any functional characteristics.

The transistor circuit can not only perform essential

functions of relay such as comparison of inputs, summation

and integrating them but they also provide necessary flexibility

to suit the various relay requirements the advantages of

transistor relays can be summarized as follows:

The power consumption is low and hence provides less

burden on C.Ts and P.Ts as compared to the

conventional electro mechanical relays.

The relays are fast in operation.

No moving parts, hence friction or contact troubles are

absent and as result minimum maintenance is required.

The relays have greater sensitivity as amplification of

signals can be obtain very easily.

The relay has a high reset pick-up ratio and the reset is

very quick

The use of printed circuits avoids wiring errors and

facilitates rationalization of batch production.

It is possible to obtain wide range of characteristics

approaching more or less to the ideal requirements.

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Transistor relays, however, have the following limitations:

1. The characteristics vary with temperature and ageing.

2. The reliability of the scheme depends upon a large

number of small components and their electrical

connections.

3. The relays have low short time over load capacity

compared with electromechanical relay.

NUMERICAL RELAYS

INTRODUCTION TO MICOM

MiCOM is a comprehensive solution capable of meeting all

electricity supply requirements. Central to the MiCOM

concept is flexibility. MiCOM provides the ability to define an

application solution and, through extensive communication

capabilities, to integrate it with power supply control system.

Additional Features for the P442 Relay Model:

Single pole tripping and auto-reclose.

Real Time Clock Synchronization - Time

synchronization is possible from the relay IRIG-B input.

Fiber optic converter for IEC60870-5/103

communication (optional).

16 Logic Inputs - For monitoring of the circuit breaker

and other plant status.

21 Output relay contacts - For tripping, alarming, status

indication and remote control.

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TESTING OF RELAYS BY ANNUAL INSPECTION

All relays shall be given an annual inspection. This inspection

should include the following:

1. A visual inspection should be made of all relays on a

terminal including the tripping auxiliaries and accessories.

Any draw out type relay should be withdrawn from its case

for a close-up examination. All other, including auxiliaries,

should at least have covers removed. Included in this visual

inspection should be a check for loose connections, broken

studs, burned insulation, and dirty contacts. Each relay

should be checked to be in agreement with its setting sheet.

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On some distance relays it may have been necessary to set

the taps on something other than specified values in order to

get proper calibration.

2. b. A test trip should be made of all relay systems. All relay

elements which initiate some protective function should be

checked. This includes reclosing, carrier starting, or any

similar type function. After proving that tripping relays will

successfully trip the circuit breaker and that all reclosing

schemes work, continuity checks should be used, where

applicable, to complete the checkout of the circuit breaker

trip circuits.

TEST PROCEDURES

Tests to be performed during routine maintenance are

determined by the type of relay to be tested. The following

tests should be included for all electromechanical relays.

1. A visual inspection of the relay cover can reveal valuable

information. Any excessive dust, dirt, or. Metallic material

deposited on the cover should be noted and removed, thus

preventing such material from entering the relay when the

cover is removed. A cover glass which is fogged should be

cleaned. Fogging is in most cases a normal condition due to

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volatile materials being driven out of coils and insulating

materials, and is not an indication of a problem.

2. Mechanical adjustments and inspection should be made

according to instructions shown following:

(1) Check to see that all connections are tight. Several loose

connections could indicate excessive vibration which should

be corrected.

(2) All gaps should be checked that they are free of foreign

material. If foreign material is found in the relay, the case

gasket should be checked and replaced if necessary.

(3) All contact or armature gaps should be measured and

values compared with previous measurements. Large

variations in these measurements may indicate excessive wear,

and worn parts should be replaced. Also an adjusting screw

could have worked loose and must be tightened.

(4) All contacts except those not recommended for

maintenance should be burnished, and measured for alignment

and wipe.

(5) Since checking bearings or pivots usually involves

dismantling the relay, it is recommended that such a test be

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made only when the relay appears to be extremely dirty, or

when subsequent electrical tests indicate undue friction.

3. Electrical tests and adjustments should be made

according to the instructions shown following:

(1) Contact function.-Manually close or open the contacts, and

observe that they perform their required function; such as trip,

reclose, or block.

(2) Pickup.-Gradually apply current or voltage to see that

pickup is within limits. The current or voltage should be

applied gradually in order to yield data which can be compared

with previous or future tests and not be clouded by such effects

as transient overreach.

(3) Dropout or reset.-To test for excess friction, reduce current

until the relay drops out or resets. Should the relay be sluggish

in resetting or fail to reset, then the jewel bearing and pivot

should be examined. A four power magnification is adequate

for examining the pivot, and the jewel bearing can be

examined with the aid of a needle which will reveal any cracks

in it. If dirt is the problem, the jewel can be cleaned with an

orange stick and the pivot can be wiped clean with a soft, lint

free cloth. No lubricant should be used on either the jewel or

pivot.

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PORTABLE TEST KITS

Portable test equipment type ZFB for distance relays:

In testing high speed distance relays it is important to apply

simulated fault conditions suddenly, otherwise the behavior of

the relay in service may be different from its behavior in test.

Checking the relay characteristic by reducing the voltage or by

increasing the current until the relay operates is not realistic, asthe voltage and current change simultaneously in magnitude

and phase angle when a fault occurs in service.

Relay System

Variables

Factor Reducing Test

Interval

Factors lengthening Test

Interval

Type of RelaysComplex (distance,

differential),

Simple (hinged armature

plunger).

Age of Relays New installations with

little operating history.

Systems 20 years or olderwhere insulation aging,

etc., can be a problem

5-10 years old with a good

operating history

Environment Dusty area, contaminated

atmosphere, temperature

extremes.

Clean and/or air

conditioned area.

History and

Experience

Subjected to severe or

frequent faults. Often

required adjustmentswhen tested.

Subjected to moderate or

few faults.

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Current Rating Relays rated 5 amperes

which are called upon to

carry 7 or 8 amperes due

to load requirements.

Relays operated at or below

their 5 ampere rating

Control Voltage Relays operated in batterycircuit more than 5

percent above nominal

relay rated voltage of

nominal relay rated

voltage

Relays operated in batterycircuit within _+ 5 percent

Station Service Station service voltage

supplied is more than 5

percent above nominal

relay rated voltage.

Station service Voltage

supply operated within + 5

percent of

Table 1.- Criteria to determine possible alteration of the test period for relays

This causes transient mechanical, electrical and magnetic

conditions in the relay which may cause overreach unless its

operating time exceeds four cycles, during which the transient

conditions will have disappeared.

Description:

The test equipment is contained in three portable metal cases.

a. Supply unit

b. Control unit

c. Fault impedance unit plus external current transformer

Supply unit:

The unit comprises:

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1. Three single phase transformers (T1, T2 and T3) ratio

420,400,380/110, 63.5V connected Y/Y to form a three phase

transformer bank. Transformer is used to supply the control

unit at 100V or 63.5V as designed and is continuously rated

at 12A secondary output. This transformer also has a further

115V secondary winding rated at 300mA to give an auxiliary

supply to the fault contactor in the control unit. Transformers 2

and 3 are used nearly to supply quadrate or polarizing voltage

to relays that require such voltages in addition to the normal

fault voltage. These transformers are continuously rated at 1A

secondary.

2. Fault selector switch is included to facilitate quick selection

of fault in the scheme. Having once connected the 3-phase

voltage and current leads to the relay scheme, anyone of the

measuring or starting relays in the scheme can quickly be

selected by the 6 position switches. This avoids possible

human error when changing connections from the relay in

the scheme to another.3. The selector switch connections are arranged such that

when injecting into a phase to neutral connecting measuring

relay the fault voltage and current are supplied from

transformer T1 of the main supply bank while T/Fs T2 and

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T3 supply the necessary quadrate voltage for the starting

relays in the scheme.

When injecting into a phase-phase connected measuring relay

the fault voltage and current are again supplied from

transformer T1 while additional voltage connection for the

starting relay is taken from transformer T3.

Control unit:

The unit comprises:

1. The source impedance (L2) tapped to provide a range of 0.5

to 24ohms. This impedance is used to control the relay current

and vary the source to line (fault) impedance ratio, in

conjunction with the fault impedance L1 and R1.

2. The voltage auto-transformer (T4) which is connected

across the line impedance via the fault contactor is tapped in

10% and 1% steps from 0-100%.

3. The load impedance which is connected in series with the

line impedance via the load push button, permits load current

to be passed the relay coils prior to the fault being applied.

The load resistance is fixed to give a current of approximately5A for phase to phase faults and 2A for phase to earth faults

4. The fault contactor is energies from the 115V ac supply

from the supply unit via the bridge rectifier and the push

button. The contactor is fitted with an economy resistance

when the coil is continuously rated.

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5. The current reversing switch is included to enable the

current supply to the relay to be reversed and so check that the

relays are measured in the correct direction.

FAULT IMPEDANCE RELAY:

This unit represents the line impedance as seen by the relays

under the fault condition. The impedance is made up from a

tapped choke L1and tapped resistance R1. The choke is the

type as used for the source impedance L2 and has ohmic range

of approximately 0.5ohm to 24ohms in 8 steps. The angle of

the choke varies approximately between 72 and 82

depending upon the ohmic tap. The resistance has 15 taps

giving an ohmic range of approximately 0.2 to 10ohms.

PERSONALITY DEVELOPMENT:

The outdoors provides an extremely powerful medium for

training students in new skills or helping them to improve old

ones, largely because outdoor learning is experimental in

nature .Our Industrial training certainly served the purpose. As

We all learn through experience. The basic idea behind our

training was to provide motivation and we were very much

benefited by it as it provided an encouraging physical and

psychological security framework for these experiences, as

well as theoretical and practical aids. Our training program

focused on teamwork and Interpersonal Skills Management

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and provided ample opportunity for us to understand its

importance and develop better relationships. It helped us to

appreciate the changes we will encounter later in life. The

training program also provided an insight to our behavior

patterns in different situations. These aspects helped us in

overcoming areas of concern or weakness and provide a

platform for all-round development of an individual

personality. Another aspect which this training brought to the

fore was safety. Safety has been the overriding concern in the

practical world. This is particularly true in the outdoor, where

the potential for danger is often higher.

SUGGESTIONS FOR OUR FORTHCOMING

BATCHES & MOTIVATION FOR THE

INDUSTRIAL TRAINING:

Try to attain permission from industries as early as

possible so that there will no tension at the last minute

Students should form themselves into groups and create

their own websites which would feature the lists of the

students, their resume, tour plans, the companies to be visited

and the benefits which the sponsors would get.

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Maintain dignity at the industries you visit so that our

juniors will also be benefited. It will also help to improve our

college name and fame.

Through this tour we got idea about industrial

environment and we can behave well in the industrial training

that will be in 4rth year-2nd Semester.

With these experiences we got knowledge about

communication, corporate culture & competitive world. More

of all I got the reason why I have to work hard in my B-Tech.

Through this tour I felt I lessen my fear to talk with

Corporate Workers and I improved my communication skills.

CONCLUSION

Lines or feeders can be protected by several methods. Each

method has some advantages and some limitations .The classes

of protective relays used for line protection.

Roughly in ascending order of cost and complexity are:

Instantaneous over current relay

Directional over current relay

Time over current relay

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Distance relay

Pilot(Pilot wire, power line carrier or microwave) relay

Graded time lag and graded over current protection is used

for single radial feeders where time lag can be permitted.

Differential protection is of unit type. It gives us fast relaying

pilot wire differential relaying used for short lengths. In

distance protection distance relaying is based on measurement

of impedance between relay location and fault point. It has

three types namely impedance type, reactance type, mho type.

The relay operates if the impedance is below the set value .In

distance protection if electro magnetic relays are replaced by

static relays then the operation will be more reliable. Because

in electro magnetic relays, the relay operates with moving coil

but in static relays the relay operates without moving coil.

In distance protection the operation will be more efficient by

Fast operation

Independent zones of operation

Current transformer supervision

Voltage transformer supervision

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REFERENCES

1. A Text book on Power System Engineering -

A.ChakrabarthiM.L.Soni

P.V.Gupta

U.S.Bhatnagar

2. Switch gear and protection - Sunil.S.Rao

3. Instruction Manuals - MRT I, Stage-I

4. Protective Relays Application Guide, 3rd edition.

ALSTOM T&D Protection and Control, 1987.

5. IEEE Transactions on Power Delivery, Vol. 16, No.2, pp.

238-246, April 2001.

iii ii project

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