1. INTRODUCTION

An electrical power system consists of generators,

transformers, transmission and distribution lines, etc. Short

circuits and other abnormal conditions often occur on a power

system. The heavy currents associated with short circuits is likely

to cause damage to equipment if suitable protective relays and

circuit breakers are not provided for the protection of each

section of the power system, if fault occurs in an element of

power system, an automatic protective device is needed to

isolate the faulty element as quickly as possible to keep the

healthy section of the system in normal condition. The fault must

be cleared in a fraction of second. If a short circuit persists on a

system for a longer period it, it may cause damage to some

important sections of the system. A heavy short circuit may

cause a fire. It may spread in a system and may damage a part

of it. The system voltage may reduce to a low level and

individual generators in different power stations may lose

synchronism. Thus, an unlearned heavy short circuit may cause

the total failure of the system.

A protective scheme includes circuit breakers and

protective relays to isolate the faulty section of the system from

healthy sections. A circuit breaker can disconnect the faulty

element of the system when it is called upon to do so by the

issue a command to the circuit breaker to disconnect the faulty

element. It is a device, which senses abnormal conditions on a

power system by constantly monitoring electrical quantities of

the system, which differ under normal and abnormal conditions.

The basic electrical quantities which are likely to change during

abnormal conditions are current, voltage, phase angle and

frequency. Protective relays utilize one or more of these

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quantities to detect abnormal conditions on a power system. A

protective relay does not anticipate or prevent the occurrence of

fault; rather it takes action only after fault has occurred. The cost

of the protective equipment generally works out to be about 5%

of total cost of the system.

1.1 NATURE AND CAUSES OF FAULTS:

Faults are caused either by insulation failure or by

conducting path failures. The failure of insulation results in short

circuits, which are very harmful as they may damage some

equipments of the power system. Most of the faults on the

transmission and distribution lines are caused by over voltages

due to lightening or switching surges causes flash over on the

surface of insulators resulting in short circuits. Some times

insulators get punctured or break. Sometimes, certain foreign

particles, such as fine cement dust or root industrial areas or salt

in costal areas or any dirt in general accumulates on the surface

of string and pin insulators. This reduces their insulation strength

and causes flashovers. Short circuits are lines.

Birds may also cause faults on overhead lines if their

bodies touch one of the phases and the earth wire. If the

conductors are broken, there is a failure of conducting path and

the conductor becomes open circuited. If the broken conductor

falls to the ground it leads in a short circuit. Joint failures on

cables or overhead lines are also a cause of failure of the

conducting path. The opening of one or two of the three phases

makes the system unbalanced. Unbalanced currents flowing in

rotating machines set up harmonics, there by heating the

machines in short period of time. Therefore unbalancing of the

lines is not allowed in the normal operation of the power

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systems. Other causes of faults on over head lines are direct

lightening strokes, aircrafts, snakes, ice and snow loading,

storms and earthquakes, creepers etc.

1.2. Types of Faults

Two broad classifications of faults are

(1)Symmetrical faults

(2)Un symmetrical faults

1.2.1. Symmetrical Faults:

A three phase fault is called a symmetrical type of fault.

The fault which gives rise to symmetrical fault currents ( that is

equal currents with 120 displacement ) is called a symmetrical

fault. In a three phase fault, all the three phases are short

circuited. There may be two situations, all the three phases may

be short circuited to the ground or they may be short circuited

with out involving the ground. A three phase circuit is generally

treated as a standard fault to determine the system fault level.

The following assumptions are made in this type of fault

calculation.

The e.m.f.s of all generators are 110 per unit. This

means that the system voltage is at nominal value

and the system is operating on no load at the time

of fault. When desirable the load current can be

taken in to account by the super position.

Shunt elements in the transformer model that

account for magnetizing current and core loss are

neglected.

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Shunt capacitor of the transmission line are

neglected.

The sub-transient reactance of the generators is

generally used in calculations. H

1.2.2 Unsymmetrical faults:

Single phase to ground, two phase to ground, phase to

phase short circuits, single phase open circuit and two phase

open circuit are unsymmetrical types of faults.

1.2.2.1 Single phase to ground (L-G) fault:

A short circuit between any one of the phase conductors

and Earth is called a single phase to ground fault. It may be due

to the failure of the insulation between a phase conductor and

earth, or due to phase conductor breaking and falling to the

ground.

1.2.2.2 Two phase to ground (2L-G) fault:

A short circuit between any two phases and earth is called

two phase to ground fault.

1.2.2.3 Phase to Phase (L-L) Fault:

A short circuit between any two phases is called a phase to

phase fault.

1.2.2.4 Open circuited Phases:

This type of fault is caused by breaking of conducting path.

Such fault occurs when one or more phase conductor’s break or

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a cable joint on a overhead lines fails. Such situations may also

arise when circuit breakers or isolators open but fail to close one

or more phases. During the opening of one of the two phases,

unbalanced currents flow in the system, there by heating

rotating machines. Protective schemes must be provided to deal

with such abnormal conditions.

Winding faults:

All types of faults discussed above also occur on the

alternator, motor and transformer winding. In addition to these

type of faults there is one or more type of fault, namely the short

circuiting of turns which occurs on machine windings

1.3 Effects of faults:

1. The most dangerous type of fault is a short circuit as it

may have the following effects on a power system, if it

remains uncleared. Heavy short circuit current may cause

damage to equipment or any other element of the system

due to over heating or mechanical forces set up due to

heavy currents.

2. Arcs associated with short circuits may cause fire hazards.

Such fires resulting from arcing may destroy the faulty

element of the system. There is also possibility of fire

spreading to other parts of the system if fault is not

isolated quickly.

3. There may be reduction in the supply voltage of the

healthy feeders, resulting in the loss of industrial loads.

4. Short circuits may cause the unbalancing of supply voltage

and currents, thereby heating rotating machines.

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5. There may be loss of system stability. Individual generators

in a power station may lose synchronism, resulting in a

complete shutdown of the system. Loss of stability of the

interconnected systems may also result.

6. The above faults may cause an interruption of supply to

consumers, thereby causing a loss of revenue.

High grade, high speed, reliable protective devices are

essential requirements of a power system to minimize the effects

of a faults and other abnormalities.

1.4. Fault Statistics:

For the design and application of protective scheme, it is

very useful to have an idea of the frequency of occurrence of

fault on various elements of a power system. The following table

gives an approximate idea of fault statistics.

Percentage Distribution of faults in various elements of a

power system.

Element % Of total faults

Overhead lines 50

Underground cable 9

Transformers 10

Generators 7

6

Switch gears 12

Ct’s, pt’s, relays & control

equipment

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Table1.0

Frequency of occurrence of different types of faults on a overhead lines:

Type of fault Fault symbol % of total fault

Line to ground L-G 85%

Line to Line L-L 8%

Double line to

ground

2L-G 5%

Three phase 3-Ǿ 2%

Table1.1

1.5. Zones of protection:

The power system contains generators, transformers, bus

bars, transmission lines, distribution lines etc,. There is a

separate protective scheme for each piece of equipment or

element of the power system, such as generator protection,

transmission line protection, bus bar protection. A protective

zone covers one or at the most two elements of the power

system. The protective zones are planned in such a way that the

entire power system is collectively covered by them, and thus,

no part of the system is left unprotected. The various protective

zones of a typical power system are as shown in fig 1.1. Adjacent

protective zones must overlap each other, failing which a fault on

the boundary of the zone may not lay in any of the zones, and

hence no circuit breaker would trip. Thus, the overlapping

between the adjacent zones is un-avoidable. If a fault occurs in

the overlapping zone in the properly protected scheme, more

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circuit breakers than the minimum necessary to isolate the fault

element of the system would trip. A relatively low extent of

overlap reduces the probability of faults in this region and

consequently, tripping of too many breakers does not occur

frequently.

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Fig 1.0 ZONES OF PROTECTION

2. LITERATURE SURVEY

2.1 FUNCTIONAL REQUIREMENT OF THE RELAY

Reliability: the ability of the relay to perform correctly when

needed and to avoid unnecessary operation

Speed: Minimum fault time and equipment damage.

Selectivity: The relay must be able to discriminate (select)

between those conditions for which prompt operation is required

and those for which no operation, or time delayed operation is

required.

Sensitivity: The relaying equipment must be sufficiently

sensitive so that it operates reliably when required under the

actual conditions that produce last operating tendency.

Economics: Maximum protection at minimum cost and it must

be less than 1% of the equipment cost

Simplicity: Minimum equipment and circuitry

2.2 Types of feeder protections:

1. Over current protection

2. Distance protection

3. Pilot relaying protection

2.2.1 Types of over current feeder protections:

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1. Time graded system

2. Current graded system

3. Time-current graded system

2.2.1.1 TIME GRADED SYSTEM:

The selectivity is based on the time of operation of the relays.

The relays used are simple over current relays. The time of

operation of the relay at various locations is so adjusted that the

relay farthest from the source will have minimum time of

operation and as it is approached towards the source the

operating time increase.

Taking an example of 6.6KV system:

2.2.1.2 CURRENT GRADING SYSTEM:

This type grading is done on a system where the fault current

varies appreciably with the location of the fault.

This means as we go towards the source the fault current

increases. With this if the relay are set to pick at a

progressively higher current towards the source. The accuracy

of the relay under transient conditions is likely to suffer;

current grading alone can not be done.

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Taking an example of radial feeder

2.2.1.3 TIME CURRENT GRADED SYSTEM:

This type of grading is achieved with the help of inverse time

over current relay and the most widely used in IDMT relay. t2

= t1 + t where t is the time step between successive relays

2.2.2 TYPE OF DISTANCE PROTECTIONS

1. Impedance relay protection

2. Reactance relay protection

3. Mho relay protection

PRINCIPLES OF DISTANCE RELAYS: Distance relays

compares the currents and voltages at the relaying point with

the current providing the operating torque and the voltage

provides the restraining torque.

T = K1I2 + K2V2 + K3VI + K

2.2.2.1 Impedance relay: Restraining torque developed

by voltage coil, operating torque by current coil therefore voltage

restrained over current relay

T = K1I2 K2V2

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When operating torque is greater than the restraining

torque relay is operated

K1I2 K2V2 V2/I2= K1/K2 Z < K1/K2

The above equation shows circle characteristics:

Impedance circle

2.2.2.2 Reactance relay:

In this relay the operating torque is obtained by current

and the restraining torque is due to a current-voltage

directional element. This means a reactance relay is an

over current relay with the directional restraint. The

directional element is so designed that its maximum

torque angle is 900

T = K1I2 - K3VI

T = K1I2 - K3VI

T = K1I2 - K3VI

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For the operation of the relay

K1I > K3VI

VI / I2 < K1/K3

Z < K1/K3 or X= K1/K3

This means that the resistance component of the impedance has

no effect on the operation of the relay. It responds only to the

reactance component of the impedance.

Characteristics of reactance relay:

2.2.2.3 MHO RELAY PROTECTION:

In this relay the operating torque is obtained by the

directional element and the restraining torque due to the

voltage element

T =K3VI K2V2

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For the relay operation-

K3VI > K2V2

(K3/K2) V2 / VI

Z < (K3/K2)

This characteristic when drawn on an impedance diagram

it is a circle passing through origin.

2.3 FEEDER PROTECTION:

1. The protection scheme is divided in three zones

2. Zone-1: protects 80% of total line

3. Zone-2: protects total line + 30% to 50% of the

adjoining line

4 .Zone-3: protects total line + 120% of the adjoining line

Three zone scheme:

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2.4. MAIN FEATURES IN DISTANCE SCHEME:

1. Starters

2. Measuring units

3. Timers

4. Auxiliary relays

2.4.1. Starters:

The starting relay (or starter) initiates the distance scheme

in the event of a fault within the required reach, other functions

of the starter are,

a) Starting of timer relay for second and third zones

b) Starting of measuring elements

Measuring units for phases and earth faults can be either

directional or non-directional.

2.4.2. Measuring units:

It can measure the line impedance, when the line

impedance falls below the setting value relay operates.

Phase fault units: these measuring units are fed with line to

line voltages and difference between line currents (Ia – Ib). They

measure the positive sequence impedance from the relay

location to the fault point.

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Earth fault units: These measuring units utilize line to neutral

voltage (VAN, VBN, VCN). And phase currents (Ia, Ib, Ic). In order to

make these units measure the positive sequence impedance

correctly, a zero sequence current compensation is to be

provided which is obtained by:

KN = (Z0 – Z1) / 3Z1. In the current circuit (1+KN)IA will be fed

from above measurement

2.4.3. Timers:

Timer relays when initiated by the starter provide the time

lag required for the zones.

2.4.4. Auxiliary relays:

Distance scheme comprises of several auxiliary relays,

which perform functions such as flag indications, tripping,

signaling, alarm etc,.

2.5. ADDITIONAL FEATURES IN DISTANCE

SCHEMES:

1. Power swing blocking relay

2. VT fuse failure relay

3. Switch on to fault relay

4. Fault locator

5. Auto-reclosing scheme

6. Carrier communication scheme

2.5.1. Power swing blocking:

Power swing occurs during system disturbance i.e. Major

load changes or dip in voltage due to delayed clearance. The

rate of change of impedance is slow in power swing condition

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and fast in fault condition. The PSB relays use this difference to

block the tripping during swings.

2.5.2. VT fuse failure relay:

The distance relay being voltage restraint over current

relays, loss of voltage de to main PT failure or in advertent

removal of fuse will cause the relay. They fuse failure relay will

sense such condition by the presence of residual voltage without

residual current and blocks the relay.

2.5.3. Switch onto fault:

When the line is switched on to a close by fault, the

voltage at the relaying point will be zero. Backup zone will

normally clear faults of this type. The voltage applied to the relay

is low and this condition occurring simultaneously with the

operation of starter will cause instantaneous trip by SOTF relay.

This SOTF feature will be effective only for about 1-2 seconds

after the line is charged.

2.5.4. Fault locator:

It measures the distance between the relay location and

fault location in terms of Z in ohms, length in KM or percentage

of line length.

The measurement is initiated by trip signal from distance relays.

2.5.5. Auto reclosing scheme:

This scheme comes into action after the clearance of fault.

It will automatically close the breaker after the fault is cleared.

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TYPES OF FAULTS:

1. Transient faults:

These are cleared by the immediate tripping of circuit

breakers and do not recur when the line is reenergized.

2. Semi Permanent faults:

These require a time interval to disappear before a line is

charged again.

3. Permanent faults: These are to be located and repaired

before line is to be charged.

About 80-90% of the faults occurring are transient in

nature. Hence the automatic reclosure of the breaker will result

in the line being successfully re-energized, thereby

1. Decreasing outage time

2. Improving reliability

3. Improving system stability

4. Reduces fault damage and maintenance time

DEAD TIME: The time between the auto reclosing scheme

being energized and the 1st reclosure of the circuit breaker. This

normally set 1sec.

RECLAIM TIME: The time between 1st and 2nd reclosure. The

reclaim time will in the range of 10-30 sec, depending on the

breaker opening and closing mechanisms.

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Types of auto reclosing schemes:

1. Based on phase:

A) Three phase auto reclosing.

B) Single phase auto reclosing

2. Case on attempts of re closing:

A) Single shot auto reclosing

B) Multi shot auto reclosing

3. Depending on speed:

A) High speed auto reclosing scheme

B) Low speed or delayed auto reclosing scheme

2.5.6. Carrier communication scheme:

The instantaneous zone-1 of the protective scheme at each

end of the protected line is set to cover 80% of the line and

hence faults in the balance 20% of the line is cleared in zone-2

time, which is undesirable. The 100% of the line can be

protected instantaneous by interconnection the distance relays

are each end of the by a signaling channel.

3.0 Norms of protection adopted for transmission

lines in A.P systems:

220 KV lines: two distance schemes

Main-I: Switched schemes fed from bus PT

Main-II: Non-switched schemes fed from bus CVT

A provision is generally made for changeover of voltage

supply for the distance schemes from the bus PT to CVT and vice

versa.

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Each distance scheme is fed from independent CT secondary

cores.

400 KV Lines: Two distance schemes

Main-I: Switched or numerical distance schemes

Main-II: Non switched or numerical distance schemes

3.1 Switched scheme: In the switched scheme, only one

measuring unit will be used for all types of faults. This single

measuring unit is switched to the correct fault loop impedance

by switching in the respective voltages and currents by the

starter. The reach of measuring element gets extended to zone-2

and zone-3 after the elapse of corresponding timings through

zone extension process.

3.2 Non-switched scheme: In this scheme there will be 6

starters, 3 for phase faults and 3 for ground faults. There will be

independent measuring units for both phase and earth faults for

each phase, for all three zones, totaling to 18 units. This scheme

is faster and more accurate but costly

3.3. TYPES OF DISTANCE PROTECTION SCHEMES

Q MHO: Types in Q-Mho

Zone-1 and 2 shaped partially cross polarized directional line.

Zone-3 offset lines (adjustable to offset circular mho)

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Zone-1 and 2 ground faults: quadrilateral with partially crass

polarized directional line.

Zone-1 and 2 phase faults: shaped partially cross polarized mho

with partially directional mho with partially cross polarized

directional line

Zone-3 ground faults: offset quadrilateral

Zone-3 phase faults: off set circular mho

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3.4. PYTS:

22

It has three under impedance starters and a single mho

measuring unit. One under impedance unit for power swing

blocking

SETTING RANGE: 0.05to 40 0hms, with starters having range of

20 to 70 ohms.

It has an uncompensated U/I starter, which has become a

problem due to load encroachment for long lines

4.0 LINE PROTECTION WITH STATIC RELAYS:

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Static relays can be effectively used for the line protection

because these relays are reliable, cheap when compared to

electromagnetic relays.

Following are the advantages of Static relays:

1. Low burden on current and voltage transformers. And less

burden on the D.C auxiliary supply.

2. Absence of mechanical inertia and bouncing contacts, high

resistance to shock and vibration.

3. Very fast operation and long life.

4. Low maintenance owing to the absence of moving parts and

bearing friction.

5. Quick reset action and to overshoot.

6. Ease of providing amplification enables greater sensitivity.

7. Unconventional characteristics are possible-the basic building

blocks of semiconductor circuitry permits greater degree of

sophistication in shaping of operating characteristics, enabling

the practical utilization of relays with operating characteristics

more closely approaching the ideal requirement.

8. The low energy levels required in the measuring circuits

permits miniaturization of relay modules.

4.1 STATIC DISTANACE PROTECTION SCHEME TYPE

(QUADRA MHO RELAY)

4.1.1 SHPM Relay:

It already indicated that the 220KV lines are to be

protected by two sets of relays. One as Main-1 having non-

switched scheme and another switched scheme,

In this chapter a non–switched SHPM relay by M/S GEC

Alsthom, Chennai, and supplied to various Electric Utilities and

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whose function is found to be very much satisfactory for the past

15 years is discussed. This relay is connected to 220kV RTPP

Anantapur feeder at Rayalaseema Thermal Power Project. The

adopted setting and test results obtained from RTPP are studied

and incorporated in this work.

The QUADRAMHO relay is a microprocessor based static

distance protection specially designed for comprehensive high

speed distance protection for HV and EHV transmission lines.

Three zones of protection are included, each employing separate

measuring elements, one each for three phase-to-phase and

three phase to earth faults per zone. Thus a total of 18 elements

are provided, there by increasing the reliability of protection.

The relay is suitable for both three poles and single and

three pole tripping of the circuit breaker. Either bus bar or line

voltage transformers may be used as these can be either

capacitor VT’s. CT requirements are moderate as the relay is

highly tolerant to saturated current transformers.

Important features of the relay:

1)3 zone distance relay with 18 non measuring units

2) Different characteristics to suit all lengths and fault levels.

3) Fast operating times over a wide range of fault conditions.

4) Digital synchronous polarizing for close up three phase faults.

5) Micro processed scheme logic with a range of built in schemes

selected option switches.

6) Continuous monitoring and on demand periodic self testing.

7) Built in power swing blocking

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8) Built in voltage transformer supervision

9) Full range of test features for commissioning and routine

testing interfacing enables automatic field test equipment to be

used when required.

Two models of the relay are available.

1) Zone-1 and 2 shaped partially cross-polarized mho with

partially cross-polarized directional line.Zone-3 offset lens

(adjustable to off set circular mho)

2) Zone-1 and 2 ground faults: shaped partially cross-polarized

mho partially crossed polarized directional line.

Zone-3 ground faults:-Off set quadrilateral

Zone-3 phase faults: - Off ser circular Mho.

The block of the relay and the external connection to the

modules are shown in the operation even under noisy condition

harmonically distorted wave forms commonly encountered in

power distribution systems.

The characteristic shapes of the relay ate shown in the

enclosed figures. For long lines the lens shaped zone-3

characteristic can be set to avoid the problems of load

impedance encroaching into the characteristic. For short line

applications involving strong feed of power in feed, the version

with quadrilateral ground fault characteristic for all three zones

can be specified, ensuring adequate tolerance to arcing and

tower footing resistance .The reactance line of the quadrilateral

characteristic automatically tilts to compensate for any pre fault

power flow to avoid over reach or under reach problems

associated with the resistance characteristics having fixed

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inclination. Synchronous polarization is provided on zone-1&2 to

allow correct response to forward and reverse three phase close

up faults.

4.1.1.1 LEVEL DETECTORS:

To avoid mal operation when a transmission line is de-

energized, phase current level detectors are provided. They have

a fast operating and reset timings and are connected so as to

lock comparator operation. In addition, pole dead signals are

generated by current and voltage level detectors which cause

the comparators to reset.

4.1.1.2 SINGLE POLE TRIPPING:

Following a single pole to ground fault and a single pole

trip, the out pit of the ground fault comparator is blocked by

resetting of the relevant phase current level detector and

comparator is forced to reset by the relevant pole dead signal

thus the comparator resets correctly even though the presents of

residual current due to load and sound phases cross-polarizing

may appear as impedance with in the mho characteristic.

4.1.1.3. PHASE SELECTION:

Two variable based neutral current level detectors are

provided. The “High set” when operated, blocking the phase-

phase comparators thus preventing a 3-pole trip under heavy

ground faults. The biasing of the high set prevents is operation

for most 2-phase to ground faults allowing the phase-phase

elements to give the fastest possible 3-pole trip.

The ’low set ‘when not operated blocks the ground faults

elements. The biasing ensures that the ground faults elements

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are blocked for 2 phase ground faults with high fault resistance.

The ground faults elements are also blocked for phase-phase or

3-phase faults even with considerable neutral spill current

caused, for example by current transformer mismatch.

4.2 SCHEME LOGIC:

QUADRA MHO is equipped with integral micro processor

based scheme logic which provides 5 schemes as standard

selected by a pair of push button option switches X and Y on the

front panel of the relay. The standard schemes are:

1) Basic 3-zone distance scheme incorporating

a) Variable time delayed zone-2 and 3 tripping.

b) Switch on to fault logic to provide instantaneous tripping of

close up solid 3 phase faults occurring on line energization

c) Voltage transformer supervision logic.

d) Power swing blocking logic

e) Block to auto recluse logic

f) Voltage memory for synchronous polarizing.

g) Control of out put contacts.

h) Logic to control various internal relay functions.

This scheme is included in all others schemes

2) Permissive under reach scheme. Signal aided trip is sealed in

until the zone -2 is resets to allow the time for possible breaker

failure protection operation in event of a breaker failure for a

fault near the remote end of the line.

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3) Permissive over reach scheme incorporating current reversal

guard feature with variable pick up and drop of time settings.

Also includes ‘echo’ feature for rapid clearance of faults near the

remote end of the line when the remote breaker is open.

4) Blocking scheme-using reverse looking zone-3 elements with

variable aided trip delay timer and current reversal guard feature

with variable time setting.

A guard feature for low-in feed through faults is also

incorporated. An optically coupled isolator is used as a ‘channel

in service’ input which, if not energized caused the blocking

scheme to revert the basics scheme.

5) Zone-1 extension scheme: This does not require signaling

channel. The extension of zone-1 controlled by an input from the

auto recluse equipment via,. An optically coupled isolator, each

scheme also provides a choice of 3 –pole tripping or single and 3-

pole tripping. Visual indicators of faulted phases and zones etc.,

are given by 9 latched light emitting diodes, which are rest by a

push button on the front of the module or at the next trip.

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Figure 3.1: Zone 1, 2 and 3 Quadrilateral earth faults

4.3 PYTS Relay:

The PYTS is a fast and accurate switched distance relay

scheme. This employs the mho principle of measurement. It

provides phase and earth fault protection and can be applied

economically to a short or medium length over head

transmission and distribution lines. The scheme is a practical

alternative to directional over current protection in power

systems but with a multiplicity of in feeds which make grading

difficult. Its realistic choice for protection where pilot wires

cannot be used and as backup protection on EHV system

Complete 3-phase 3 zone distance protection is provided,

using a mho characteristic. Residual current compensation is

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included to ensure that the relay measure correctly under earth

fault condition.

Features:

1. Minimum Operating lime 2Omsc for zone I protection.

2. Mho characteristic with full cross polarization ensures

maximum tolerance of arc resistance on the type PYTS

3. Accurate measurement for source/line impedance ratios up

to 100/i.

4. Static circuitry through out imposes low VA burden on

current transformer and voltage transformer.

5. Provision for single or 3-phase fault.

6. A switch on to fault facility which provides an

instantaneous trip if the line is energized on the 3-phase

fault.

7. A relay characteristic angle setting of 30-85 degrees.

8. LED indications with rest.

9. Modular plug in construction with built in test points

permits easy maintenance.

10. Compact construction saves panel saves.

11. This scheme provides faster fault clearance time at both

ends of the protected line for any faults, occurring on the

line.

12. With the signaling channel in service and zone faults

beyond the normal zone reach of the measuring element

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are cleared quickly by means of a trip signal received from

the remote and zone measuring unit.

13. Signifying that the fault is internal to the protected line.

14. The trip signal can be arranged by means of selection link

either to initiate tripping, provided that the local starters

have operated or extended the reach of the measuring

element from zone I to a pre determined amount beyond

the end of the line by means of instantaneous control

enable unit I.C.E

Operation:

These relays use block comparators to produce the well

established and proved mho measuring characteristics. It uses

fully cross polarized directional mho measuring element which

switched to the correct phase by staring elements phase

selection is performed by static phase starter elements S1, S2

and S3, The neutral over current element S4 is fixed to provide

remote indication of earth faults and to control zone extinction

facility for earth faults only when required.

It is also used to over ride the power swing - blocking unit

under earth fault conditions when used in conjunction with

impedance starter elements. A voltage V is derived from the

defaulted phase or phases and a voltage VPOL is taken from a

combination of faulted and healthy phases depending on the

polarizing characteristic chosen.

A signal is proportional to the fault current is provide by

transactors T5, T6, T7 and T8 which eliminate the effects of dc

transactor, T8 provides zero sequence current compensation the

measuring unit characteristic is produced by phase comparator

32

circuit which receives the signal V-IZ and VPOL. A switching

network selects b a switching networks according the fault

detected by the appropriate starting element an output from the

phase comparator is fed into an integrator and then to a level

detector to initiate a trip circuit

5.0. Calculation of mho unit settings

The positive sequence impedance and zero sequence

impedance for the protected line is usually given in the form

33

R+JX from which the magnitude and angle of the impedance can

be calculated.

Z= Ω/KM

Ф=tan-1(X/R)

The equivalent secondary line impedance is obtained by the

following formulae.

Secondary impedance primary impedance (CT ratio/VT ratio)

Secondary line impedance is used for all relay reach settings and

calculations.

Relay Ohmic setting required reach in KM Secondary

Ohms/KM

5.1. Percentage potential Calculation

Z1 (primary) = 39.87Ω

Z2 ( secondary) = Z1 (primary) *( CT ratio / VT ratio )

= 39.87 * (800 /1 ) * ( 110 / 220000 )

= 15.948Ω

5.2. Settings:-

Zone 1 = 80% of secondary line impedance

0.8 * 15.948 = 12.758Ω

Time setting required is 0.1 sec. and it need not be set as it is

inherent.

34

Zone 2 = Total length of the protected line + 20% of the line

impedance of largest line from station 2 .

= 1.3 times Z2

= 1.3 * 15.948 = 20.73Ω

Time setting required = 300 msec

Zone 3 = 1.7 times of Z2

= 1.7 * 15.948 = 27. 1116Ω

Time setting required = 600 msec.

5.2.1. ZONE- 1 OHMIC SETTING:

1) Calculate the required zone1 Ohmic reach (normally 80-85% of

the line section to be protected).

2) Set to the required fault angle (ФL).

3) Select the range doubling switch KD, and plug tapping KZ for

phases A, B and C, such that KD KZ is nearest to, but greater

than the required ohmic reach.

NOTE: switch KD should always be set at 1 whenever possible

and should only set at 2 when required reach exceeds the

maximum. KZ tapping or at 0.1 where extremely low zone1

impedance setting are required

4) Divide the required zone1 Ohmic reach by KD KZ.

5) Set the potentiometer K1, in phases A, B and C to the result

obtained in (4) above.

35

6) Check the KD KZ K1 equals the required zone1 reach in

secondary ohms (Z1).

.ZONE-1 EXTENSION OHMIC SETTING:

1. Calculate the required zone1 extension reach in secondary

ohms (normally 120% of the first line section to be protected).

2. Set the zone1 extension potentiometer KC according to the

following formulae:

KC

5.2..2. ZONE-2 OHMIC SETTING:

1. Calculate the required zone2 reach in secondary ohms,

(normally first line section plus 50% of the second line section

to be protected).

2. Set the zone2 potentiometer K2, according to the following

formulae.

K2

5.2.3. ZONE - 3 OHMIC SETTING:

1. Calculate the required zone3 reach in secondary ohms.

2. Set the zone3 potentiometer K3, according to the following

formula.

K3

36

NEUTRAL IMPEDANCE OHMIC SETTING:

1. Calculate the required Ohmic setting form the following

Formula Required Ohmic setting

KD KZ K1

Where Z0 Zero sequence impedance of protected line

Z1 Positive sequence impedance of the protected line.

2. Choose a KZN tapping such that KD KZN is nearest to but

greater than the required ohmic setting.

3. Set the KIN potentiometer, according to the following

formula

KIN

37

5.3. SPECIMAN CALCULATION FOR THE RELAY SETTING

FOR “PYTS” DISTANCE PROTECTION SCHEME:

1 Length of the protected line 97.88KM

2 Length of the shortest adjacent line

section

------------

3 Length of the adjacent long lie ------------

4 Conductor size(A) line conductor

(B)earth conductor

61/3.18mmACSR

7/9mm

5 Z0/Z1 3.366

6 CT ratio 800/1

7 PT ratio 220KV/110KV

8 CT ratio/PT ratio 0.4

9 Line constant/ Phase /circuit ------------------

A Positive sequence Resistance R1 7.45

B Positive sequence Reactance X1 39.11

C Positive sequence Impedance Z1 39.87

D Zero Sequence Resistance R0 25.93

E Zero Sequence Reactance X0 131.51

F Zero Sequence Impedance Z0 134.04

1

0

Line angle 79.22

1

1

Line charging MVAR 13.58

1

2

Secondary circuit data ----------------

38

A Line Impedance ZL 15.948

B Distance steps zone-1 reach Z1 12.758

C Line Impedance Z2 20.73

D Line Impedance Z3 27.1116

E Starter reach phase fault

Earth fault

63.0

35.22

5.4. RELAY SETTING CALCULATIONS FOR 220 KV

RTPP ANANTAPUR FEEDER AT RTPP END WITH

“PYTS” SCHEME

1) IMPEDENCE STARTING UNIT

These units have variable impedance setting at rated voltage

given by the formula

Z=K/IN(ohms)

The range of k is 20-70 ohms

Z=K for 1A relay

Starter reach is selected as 63ohms.ie,. ZA, ZB and ZC

Neutral starter current =0.2A fixed

2) POWER SWING BLOCK ING UNIT

The setting of the power swing relay should be

approximately 30% more than the

Starter set impedance

Starter set impedance=63Ω there fore PCB impedance is

63X1.3=81.9ohms

But the value adopted is 70Ω

39

Time setting adopted is 40mS

Position of PSB selector switch P is B position i.e., Power swing

blocking of all zones.

MEASURING UNIT

As the line angle is 79.22degrees the max torque angle of the

relay is selected as 800

Zone -1 Ohmic reach=line Ohmic valueX0.8=12.784, say12.8

Therefore KD KZ K1 =12.8

Select Kz =20 and KD=1 so K1=0.64

Zone-2 setting = Impedance value on secondary side is 20.73

Zone-2 potentiometer setting=20.73/12.8=1.619=K2

Zone -3 =impedance value on secondary=27.1116

Zone-3 potentiometer setting =27.1116/12.8=2.11=K3

Zone -1extension Kc =1 Zone 1 extension is nil

NEURAL IMPEDENCE SETTING KZN required Ohmic setting

(1/3)(Z0/Z1)-1) KD KZ K1 1/3(134.04/39.82)-1 12.8 10.09

So select KZN 10

KIN required Ohmic setting/KD KzN 10/1 10) 1

40

Time settings

Time setting Zone-1 inst

Zone-2 t22 0.3s

Zone-3 t23 0.6 s

Starter set up zone-4 1.4s

5.5. SPECIMEN CALCULATION FOR THE RELAY SETTING FOR “SHPM” DISTANCE

PROTECTION SCHEME

1 Length of the protected line 97.88KM

2 Length of the shortest adjacent line

section

-----

3 Length of the adjacent long line -----

4 Conductor size (A) line conductor

(B) earth conductor

61/3.18mm ACSR

7/9mm

5 Z0/Z1 3.366

6 CT ratio 800/1

7 PT ratio 220Kv/110v

8 CT ratio/PT ratio 0.4

9 Line constants/phase/circuit

A Positive sequence R1 7.45

B Positive sequence X1 39.11

C Positive sequence Z1 39.82

41

D zero sequence R0 25.93

E zero sequence X0 131.51

F zero sequence Z0 134.04

10 Susceptance Yc/2

11 Line angle 79.22

12 Line charging MVAR 13.58

13 Secondary circuit data

14 Line impedance Zl 15.93

A Distance steps zone-1 reach Z1 12.77

B Line impedance Z2 20.64

C Line impedance Z3 27.36

D Starter reach phase faults

Earth faults

00

00

E Relay characteristic angle phase &

neutral

800

15 Zone-3 reverse reach 1.25 ohms

16 Z0/Z1 3.366

17 Aspect ratio 0.41

5.5.1. SETTINGS ON THE RELAY

A) Zone-1 ohmic reach=80% of the length of the

line .15.93×0.8=12.8Ohms

42

B) Select K1+K2=4.8 K1=4, K2=0.8

K1 values on the relay 0 to 4 in steps 1

K2 values on the relay 0 to 0.8 in steps 0.2

Z phase 4.8/1=4.8

C) Divide the zone-1 reach by Zph to obtain the zone-1

multiplying factor

(K11+K12+K13)K14=12.8/4.8=2.66

Select K11=2.0 K12 =0.6 K13=0.06 K14 =1

K11 values are 1 to 9 and infinity,K12 values are 0 to 0.9

step 0.1 K13 value is 0 to 0.008 insteps of 0.002 K14 value is 1 or

5.

D) Zone-2 Ohmic reach as selected from the table is 20.73 ohms

(50% of the next line section) divide the required Z2 multiplying

factor

(K21+K22 + K23)K 24 i.e., 20.73/4.8=4.318 say 4.32

K21=4.0 K22 =0.3 Values of K21 on the relay 1 to 9 insteps 1

K23 =0.02 Values of K22 on the relay 0 to 0.9 insteps 0.1

K24 =1 Values of K23 on the relay 0 to 0.08 insteps 0.02

Values of K24 on the relay 1 to 5

E) Zone-3 ohmic reach (forward) =27.1116 ohms

Divide the required Z3 reach by Zph to obtain the Z3 multiplying

factor

43

(K31+K32 + K33)K34 = 27.1116/4.8=5.64

K31= 5 K32=0.7 K33=0.04 K34 = 1.0

Values of K31 on the relay 1 to 9 insteps 1

Values of K 32on the relay 0 to0.9 insteps 0.1

Values of K33 on the relay 0 or 0.08 insteps 0.02

Values of K34 on the relay 1 to 5

F) Zone-3 ohmic reach (reverse) =1.25 ohms

Divide the required Z3 reach by Zph to obtain the Z3 multiplying

factor

(K35+K36)K33×K37 = 1.25/4.8 =0.26

(K35=1.0 K36=0.0 K37=0.25

Values of K35 on the relay 1 to 9 insteps 1

Values of K36 on the relay 0 to 0.9 insteps 0.1

Values of K37 on the relay 0.25, 0.5 or 1.0

G) Neutral impedance setting: Zn

K4+K5+K 6 =1/3Z0/Z1 -1 × (K1+K2) =3.78

K4=3 K5=0.7 K6=0.08

Values of K4 on the relay 0 to 5 insteps 1

Values of K5 on relay 0 to 0.9 insteps 0.1

Values of K6 on relay 0 to 0.08 insteps 0.02

H) Zone-1 extension ohmic reach divide the required the Z1x

reach by Z1 to obtain the Z1x multiplying factor K15=one

44

As K15=1 no zone extension

I) Time setting zone-1 inst

Zone-2 0.3s

Zone-3 0.6

K) Power swing blocking relay (Zone-6 forward):1.3×Zone

forward=1.3×27.36=35.6 set automatically with zone-3 setting

l) Power swing blocking relay (Zone-6’reverse)=zone-3 reverse+

0.3 zone-3 forward.1.2+0.3×27.36=9.4 ohms set automatically

with zone-3 setting.

45

6.0. EXPERIMENTATION AND RESULTS

PROCEDURE FOR DYNAMIC TESTING OF IMPEDANCE

RELAYS WITH ZFB KIT AND CALCULATION OF PERCENTAGE

POTENTIAL FOR THE LINE SELECTED:

In testing of high speed distance relays it is

important to apply simulated fault condition suddenly, other wise

the behavior of the relay in service may be different from its

behavior in test. Checking the characteristic by reducing the

voltage or increasing the current until the relay operation is not

realistic, as the voltage and current change instantaneously in

magnitude and phase angle when a fault occurs in service. This

causes transient mechanical electrical and magnetic conditions

in the relay which may cause to over reach unless its operation

times exceed 4 cycles during which time the transient conditions

would disappear.

6.1. The test kit comprises of

supply unit

control unit

fault impedance unit

External current transformer

6.1.1. Supply Unit: The supply unit will supply potential

supply and polarizing voltage to the Relay .On the supply unit a

fault selector switch is provided to select the desired fault.

46

This unit comprises the following major components, three

single phase transformers ( T 1, T 2, T3 ) ratio 420, 400, 380 / 110,

63.5 volts connected delta / star to form a 3-phase transformer

bank.

Transformer is used to supply the control unit at 100

volts or 63.5 volts as desired and is continuously rated at 12 Amp

secondary output. This transformer also has a further 115 V

secondary winding rated at 300 ma to give an auxiliary supply

to the fault contactor in the control unit transformer 2 and 3 are

used to supply quadrature of polarizing voltage to relay that

require such voltage in addition to the normal fault voltage.

These transformers are continuously rated at 1 Amp secondary

output fault selector switch is included to facilitate quick

selection of fault in the scheme.

When injecting into a neutral connected measuring

relay the fault voltage and current are supplied from transformer

T1 of main supply bank while the transformers T2 & T3 supply the

necessary quadrature voltage for the starting of relay in the

scheme. When injecting into a phase to phase connected

measuring relay the fault voltage and current are again supplied

from transformer T1

6.1.2. Control Unit: This unit comprises the following major

components.

This source impedance (L2), tapped to provide a

range of 0.5 to 24. This impedance used to control

the relay current and vary the source to line ( fault)

47

impedance ratio, in conjunction with the fault

impedance L1 and R1

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 to 110% this

permits a precise setting of voltage to be applied the

relay and allows the fault impedance to be matched

to the relay impedance setting. The fault contactor

is energized from 115 A.C.

Supply from the supply unit via bridge rectifier and push

button. Normally open contact of the fault contactor is brought

out to terminal to start an external timing device when required

the current reversing switch S3 is included to enable the current

supplied to the relay to be reversed and so check the relays are

measuring in the correct direction.

The control unit comprises source impedance tapped to provide

a range of 0.5 to 24 ohms. A tapped autotransformer in the unit

allows matching the kit with the line impedance and applying

correct potential to the relay under the faulty conditions. It also

provides for pre fault current to the relay under test. It also

provides a current reversing switch to supply current in reverse

direction while testing the relay for reverse reach.

6.1.3. Fault impedance Unit: This unit represents the

line impedance as seen by the relays under the fault conditions.

The impedance is made of choke (L1) and a resistance (R1) .The

choke has an ohmic reach of 0.5 to 24 ohms in 8 steps .The

resistance has 15 steps ranging from 0.2 to 10 ohms. By

providing a jumper between the selected tap on the reactance

and resistance taps the required line resistance along with the

48

power factor can be obtained .Connecting the kit and selection of

impedance and calculation of % potential and error in the relay

operation .The ZFB kit is to be connected as shown in the

drawing enclosed it .The kit is to be supplied with 400v supply

between RY&B phase with correct phase sequence. For correct

phase sequence is not maintained the kit will not work properly.

The testing of the relays involves choosing of correct fault

impedance on the kit for phase-to phase faults and phase to

neutral faults and for zones .The values to be tested are

indicated in the in the tabular form along with the fault

impedance values and impedance values and CT ratio of the

interposing transformer in the ZFB kit. After section of the

impedance on the kit the % potential for which the relay has to

operate is to be calculated and the relay tested.

P1-p/100 will give the percentage error. The error should not be

more than 5%.

The reactance and resistance taps chosen on the fault

impedance kit should be such that the resulting impedance

should gives the nearest value above that.

6.2. Calculation of percentage potential to test

the relay with ZFB kit (SHPM Relay)

%Potential for phase faults:-

49

Impedance value on the kit 2x relay setting/CT ratio of the kit

% potential for earth faults: - (1+K) relay setting /CT ratio of the

kit

Z for phase faults Zone-1 2×12.758/(5/2)=10.2 79.22

Zone-2 2×20.73/(5/2)=16.58 79.22

Zone-3 2×27.1116/(5/2)=21.68 79.22

Value selected on the impedance kit

R X Z θ

1 8 25 82

% potential for phase faults 1xrelay ohmic value/value on the kit

% potential for zone-1 phase faults 2x12.758/25x (5/2)

=40.82%

% potential for zone-2 phase faults 2x20.73/25x (5/2)

=66.33%

% potential for zone-3 phase faults 2x27.1116/25x (5)

=43.37%

% potential for zone-31 phase faults 2x1.2/25x (1) =9.6%

Earth fault compensation factor K=1/3(Z0/Z1)-1 =1/3(3.366-1)

=0.78

% potential for earth faults (1+K) x relay ohmic value/value on

the kit

% potential for zone-1 earth faults 1.78×12.758/25× (5/2)

=36.33%

50

% potential for zone-2 earth faults 1.78×20.73/25× (5/2)

=59.03%

% potential for zone-3 earth faults 1.78×27.1116/25× (5)

=38.6%

% potential for zone-31 earth faults 1.78×1.2/25×1 =8.54%

RESULTS:

Comparing of theoretical values with actual values

tested on the kit with the calculated and adopted settings

Name of the feeder: 220KV RTPP-ANANTAPUR AT RTPP END

Type of the relay SHPM

Sl.n

o

Zone/

phase

Relay

set

VALUE/

time

Tim

e of

Ope

rati

on

Value on ZFB kit The

oret

ical

valu

e

Test

valu

e

R X Z θ CTS

1 Zone-1

A-n

12.758Ω

int

1 8 25 82.5 5/2 36.3 36

2 B-N 36

3 C-N 36

4 A-B 40.8

2

40

5 B-C 40

6 C-A 40

7 Zone-2

N-N

20.73

300 ms

59.0

3

59

8 B-N 59

9 C-N 59

10 A-B 66.3

3

64

51

11 B-C 65

12 C-A 65

13 Zone-3

A-N

27.11Ω

600ms

5/1 38.6 38

14 B-N 38

15 C-N 38

16 A-B 43.3

7

42

17 B-C 43

18 C-A 42

19 Zone-31

A-N

Forward

1.2Ω

1 8.54 8

20 B-N 8

21 C-N 8

22 A-B 9.6 9

23 B-C 9

24 C-A 9

6.3. TESTING OF THE RELAY ON THE ZFB

IMPORTANCE RELAY KIT (PYTS Relay)

Fault impedance required on the kit 2Z1/N

Phase to phase faults =1Z1/N

Phase to earth faults = (1+K) Z1/N

52

Where Z1 = relay ohmic reach

N = CT ratio on the ZFB kit, K = earth fault compensation factor

calculated earlier

%POTENTIAL CALCULATION:

Phase to phase faults =2Z1/NZt

Phase to earth faults = (1+K)Z1/NZt

Where Zt= importance value selected on the kit .For phase to

phase faults CT ratio selected on the kit (5/2)

Z on the impedance kit for Zone-1 =2×12.8/ (5/2) =10.24

Zone-2 =2×20.73/ (5/2) =16.58

Zone-3 =2×27.1116/ (5/2) =21.68

Where Zt = impedance value selected on the kit. For phase to

earth faults

Earth fault compensation factor K=0.78, (1+K) =1.78

Z on the impedance kit for Zone-1 = 1.78×12.8/ (5/2) =9.11

Zone-2= 1.78×20.73/(5/2) =14.75

Zone-3= 1.78×27.1116/ (5/2) =19.3

Tap selected on the ZFB kit for selection of impedance

R X Z ANGLE

1 8 25 82.5

PERCENTAGE POTENTIAL CALCULATION:

Z

O

CT RATIO PHASE TO PHASE PHASETO NEUTRAL

53

N

E

1 (5/2)=2.5 2×12.8/25×2.5=40.82 1.78×12.8/25×2.5=36.45

2 (5/2)=2.5 2×20.73/25×2.5=66.33 1.78×21.76/25×2.5=59.03

3 (5/1)=2.5 2×27.1116/25×2.5=43.37 1.768×28.16/25×5=38.6

6.4. TEST RESULTS OF PYTS RELAY

Name of the feeder: 220kv R.T.P.P.-ANANTAPUR

Type of the Relay : PYTS 104

S.n

o

Zone/

phase

Rel

ay

Set

Tim

e

(m

sec

Time of

operati

on

(m sec)

R X

ZLФ

CT

ratio

On

ZFB

Kit

%Reac

h

Theore

tical

Value

%Rea

ch

Practi

cal

value

1 Zone-

1

A-N

INS

T

72.8 1 8 25L

82.5

5/2 36.45 36

2 B-N 76.7 36

3 C-N 75.5 36

4 A-B 82.9 40.82 39

5 B-C 83.5 40

6 C-A 82.6 40

7 Zone-

2

A-N

300 372.6 5/2 59.03 62

8 B-N 384.1 60

9 C-N 377 61

54

10 A-B 380 66.33 66

11 B-C 379.3 66

12 C-A 379.8 66

13 Zone-

3

A-N

635.3 5/1 38.6 40

14 B-N 635.3 40

15 C-N 629.9 40

16 A-B 658.1 43.37 43

17 B-C 646.0 43

18 C-A 647.9 43

6.5. DISCUSSION OF RESULTS

The line data for 220KV Ananthapur line and the various settings

are,

Zone-1 - instantaneous tripping.

Zone -2 - 0.3sec

Zone-3 - 0.6 sec

Starter - 1.4sec

Power swing blocking unit setup For SHPM relay is 35.6 ohm.

55

For PYTS relay is 70 ohm.

Corresponding zone-1, zone-2, zone-3 settings were set on the

potentiometer.

With all the above setting the static relays which were adapted

for Anantapur 220 kV line is functioning properly.

1 Length of the protected line 97.88KM

2 Length of the shortest adjacent line

section

-----

3 Length of the adjacent long line -----

4 Conductor size (A) line conductor

(B) earth conductor

61/3.18mm ACSR

7/9mm

5 Z0/Z1 3.366

6 CT ratio 800/1

7 PT ratio 220Kv/110v

8 CT ratio/PT ratio 0.4

9 Line constants/phase/circuit

A Positive sequence R1 7.45

B Positive sequence X1 39.11

C Positive sequence Z1 39.82

D Positive sequence R0 25.93

E Positive sequence X0 131.51

56

F Positive sequence Z0 134.04

10 Susceptance Yc/2

11 Line angle 79.22

12 Line charging MVAR 13.58

13 Secondary circuit data

14 Line impedance Zl 15.948

A Distance steps zone-1 reach Z1 12.758

B Line impedance Z2 20.73

C Line impedance Z3 27.1116

D Starter reach phase faults

Earth faults

00

00

E Relay characteristic angle phase &

neutral

800

15 Zone-3 reverse reach 1.25 ohms

16 Z0/Z1 3.366

17 Aspect ratio 0.41

6.6.Name plate Details of SF6 circuit breaker.

Make: Cromprton greaves limited, Nasik, India.

Type : 200- SFM – 40A

57

Rated Lighting withstand voltage : 1050KVp

Rated short circuit breaking current : 40 KA

Rated operating pressure : 15 Kg /cm2

First pole to clear factor : 1.3

Rated duration of short circuit current: 40 KA-3 sec

Gas weight: 2 kg

SC no: 5145C

Year: 1993

Rated normal voltage: 245KV

Rated normal current : 2500A

Rated frequency: 50 Hz

Rated closing voltage: 220V D.C

Rated opening voltage: 220V D.C

Rated gas pressure: 6Kg /Cm2 (at 200C)

Rated voltage and frequency for auxiliary circuit : 415V, A.C, 50

Hz

Total weight with gas: 3900 Kg.

6.7. Name plate Details of voltage Transformer:

(PT’s)

Make : Transformer and Electrical kerala Limited,

Type :CPUEGLV

58

Frequency : 50Hz

Oil quantity : 200 L

Insulation level : 460 /1050 KV

Weight :1200Kg

Highest system voltage : 245KV

Method of connection: Between line and earth in an effectively

earthed neutral system.

No. of phases: 1

Type of T/ f - earthed

Maker sl.no: 730064-5

Year 1993.

Secondary

winding no

1 2

Measuring Protection

Output 500mvA 100VA

Accuracy class 0.5 /3P 3P

Primary Terminals A1 A2

Secondary

Terminals

1a1,1a2 2a1,2a2

Voltage factor 1.2 continuous 1.5 /30 sec

Voltage ratio 220 /1.732Kv/ 110/

1.1732V

220/1.732Kv/

110/1.732V

59

6.8. Name plate Details of Current Transformer:

Manufactured by WS Industries (India Ltd.,) Bangalore – India

Frequency: 50 Hz

Highest system voltage: 245 KV

Basic insulation Level : 460 /1050 Kv

Oil Weight: 360 Kg

Total weight: 1250Kg

Ratio: 800 /1-1-1-1-1

Core NO 1 2 3 4 5

Rated

primary

current A

800 800 800 800 800

Rated

secondary

current

1 1 1 1 1

Output VA --- ----- 50 --- ---

Accuracy

classPS PS 0.5 PS PS

Turns ratio -- 2/1600 -- 2/1600 ---

Resistance of

CT at7500C

3 3 ---- 3 3

KVP(V) 1000 1000 -- 1000 1000

60

61

62

BIBLIOGRAPHY

1. SUNIL.S.RAO.

Switch gear protection and power systems

Khanna publications, eleventh edition

2. CL WADHWA Electrical power system,

New age international, third edition.

3. BADRI RAM, DN VISWAKARMA ,

Power system protection and switch gear ,

TATA Mc GRAW HILL

4. IJ NAGARTH, DP KOTHARI,

Modern power system analysis

TATA Mc GRAW HILL.

5. Company manual for PYT,SHPM ralay setting by

GEC Alstom India ltd.

6. R.T.P.P. Electrical manual.

63