Project

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
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abnormal conditions are current, voltage, phase angle and
frequency. Protective relays utilize one or more of these
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
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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
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
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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.
 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:
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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 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
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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.
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.
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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
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
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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 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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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:
1. Time graded system
2. Current graded system
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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.
 Taking an example of radial feeder
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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
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T = K1I2
- K3VI
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:
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• In this relay the operating torque is obtained by the
directional element and the restraining torque due to the
voltage element
T =K3VI K2V2
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:
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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:
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
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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.
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,.
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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
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:
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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.
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:
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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.
Types of auto reclosing schemes:
1. Based on phase:
A) Three phase auto reclosing.
B) Single phase auto reclosing
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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.
Each distance scheme is fed from independent CT secondary
cores.
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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:
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
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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:
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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
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.
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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
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
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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
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.
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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
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
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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.
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
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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.
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
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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
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.
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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
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
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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
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
36

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
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
37

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.
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).
38

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.
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:
39

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
NEUTRAL IMPEDANCE OHMIC SETTING:
1. Calculate the required Ohmic setting form the following
Formula Required Ohmic setting
KD KZ K1
40

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
5.3. SPECIMAN CALCULATION FOR THE RELAY SETTING
FOR “PYTS” DISTANCE PROTECTION SCHEME:
1 Length of the protected line 97.88KM
41

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
10 Line angle 79.22
11 Line charging MVAR 13.58
12 Secondary circuit data ----------------
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
42

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
Time setting adopted is 40mS
Position of PSB selector switch P is B position i.e., Power swing
blocking of all zones.
MEASURING UNIT
43

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
Time settings
Time setting Zone-1 inst
Zone-2 t22 0.3s
44

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
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
9 Line constants/phase/circuit
A Positive sequence R1 7.45
B Positive sequence X1 39.11
C Positive sequence Z1 39.82
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
45

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
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
46

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
(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
47

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 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 =1/3{Z0/Z1 -1} × (K1+K2) =3.78
K4=3 K5=0.7 K6=0.08
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
As K15=1 no zone extension
I) Time setting zone-1 inst
Zone-2 0.3s
Zone-3 0.6
48

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.
6.0. EXPERIMENTATION AND RESULTS
PROCEDURE FOR DYNAMIC TESTING OF IMPEDANCE
RELAYS WITH ZFB KIT AND CALCULATION OF
PERCENTAGE POTENTIAL FOR THE LINE SELECTED:
49

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.
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.
50

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)
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
51

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
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
52

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:-
Impedance value on the kit 2x relay setting/CT ratio of the kit
53

% 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%
54

% 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/p
hase
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
12.758
Ω 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
11 B-C 65
12 C-A 65
13 Zone-3 27.11Ω 5/1 38.6 38
55

A-N 600ms
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
Where Z1 = relay ohmic reach
N = CT ratio on the ZFB kit, K = earth fault compensation factor
calculated earlier
%POTENTIAL CALCULATION:
56

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
N
E
CT RATIO PHASE TO PHASE PHASETO NEUTRAL
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
57

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
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
58

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.
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.
59

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
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
F Positive sequence Z0 134.04
10 Susceptance Yc/2
11 Line angle 79.22
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
60

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
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
61

Rated closing voltage: 220V D.C
Rated opening voltage: 220V D.C
Rated gas pressure: 6Kg /Cm2
(at 200
C)
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
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.
62

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
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
800 800 800 800 800
63

current A
Rated
secondary
current
1 1 1 1 1
Output VA --- ----- 50 --- ---
Accuracy
class
PS PS 0.5 PS PS
Turns ratio -- 2/1600 -- 2/1600 ---
Resistance of
CT at7500
C
3 3 ---- 3 3
KVP(V) 1000 1000 -- 1000 1000
64

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.
66

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