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मानक
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in order to promote transparency and accountability in the working of every public authority,
and whereas the attached publication of the Bureau of Indian Standards is of particular interest
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education and knowledge, the attached public safety standard is made available to promote the
timely dissemination of this information in an accurate manner to the public.
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“The Right to Information, The Right to Live”
“Step Out From the Old to the New”
Mazdoor Kisan Shakti Sangathan
Jawaharlal Nehru
IS 3842-10 (1976): Application Guide for Electrical Relays
for ac Systems, Part X: Relays for Transverse Differential
Protection [ETD 35: Power Systems Relays]
“!ान $ एक न' भारत का +नम-ण”
Satyanarayan Gangaram Pitroda
“Invent a New India Using Knowledge”
“!ान एक ऐसा खजाना > जो कभी च0राया नहB जा सकता ह”
है”
ह
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“Knowledge is such a treasure which cannot be stolen”
IS: 3842(PartX)-1976
Indian Standard
( Reaffirmed 2001 )
APPLICATION GUIDE FOR
ELECTRICAL RELAYS FOR AC SYSTEMS
PART X
RELAYS FOR TRANSVERSE
PROTECTION
DIFFERENTIAL
( Third Reprint OCTOBER 1992 )
UTX 621.316.925.2
@ Coplright1976
BUREA?
OF
INDIAN
STANDARDS
MANAK BHAVAN, 9 BAHADUR SHAH ZWAK
MARG
NEWDELHIllMXY2
Doceder 1976
c
.
IS : 3842( Part X ) - 1976
Indian Standard
APPLICATION GUIDE FOR
ELECTRI~AL~RELAY~ FOR AC SYSTEMS
PART X
RELAYS FOR TRANSVERSE
PROTECTION
DIFFERENTIAL
Relays Sectional Committee, ETDC 35
Chairman
DR T. S. M. RAO
Representing
University of Roorkee, Roorkee
Members
Tamil Nadu Electricity Board, Madras
&RI N. S. S. AROKIASWAMY
SHRI T. V. SUBRAMANIAM
(\ Alternatr )
Maharashtra State Electricity Board, Bombay
SHRI M. M. BANDRE
Directorate
General
of Supplies and Disposals
SHRI G. R. BHATIA
( Inspection Wing), New Delhi
DEPUTY
DIRECTOR
STANDARDS Railway Board, New Delhi
( TI ), RDSO, LUCKNOW
ASSISTANT DIRECTOR STANDARDS( RELAYS ). ( Alternate )
Central Electricity Authority, New Delhi
DIRECTOR ( CIP )
Universal Electrics Limited, 24 Parganas
SHRI A. K. GHOSE
SHRI C. GHOSE ( Alternate )
National Test House, Calcutta
SHRI B. P. GHOSH
SHRI S. GOVINDAPPA
Karnataka Electricity Board, Bangalore
Haryana State Electricity Board, Chandigarh
SHRI B. R. GUPTA
SHRIJ. C. JUNE~A ( Alternate)
Larsen & Toubro Limited, Bombay
SHRI I. C. JOSEPH
Bombay Electric Supply & Transport Undertaking,
SHRI A. D. LIMAY~
Bombay
SHRI A. M. KELKAR ( Alterna/e)
SHR~MATA PRASAD
U.P. State Electricity Board, Lucknow
SHRI N. NATH
English Electric Co of IndiaLtd, Madras
SIIRI J. S. NECI
Jyoti Limited, Vadodara
SHRI V. B. DESAI ( Alternate )
SHRI S. T. PATEL
ASEA Electric India Pvt Ltd, Bombay
SHRI V. RAGHUPATI( Alternate )
SHR~ V. RADHAKRISHNAN
Bharat Heavy Electricals Ltd, Bhopal
.
SHRI M. R. NANDESHWAR( Alternate )
( Continued on page 2 )
@ Copvright 1976
BUREAU
OF INDLW STANDARDS
This publication is protected under the Indian Copyright Act (XIV
of 1957) and
reproduction in whole or in part by any means except with written permission of the
publisher shall be deemed to be an infringement of copyright under the said Act.
IS : 3842 ( Part X ) - 1976
( Continuedfrom page 1 )
Reprtscnting
Members
Directt:;te
SHRI K. N. RAMASWAMY
SHRI R. K. GUPTA (Ahnate
General of Technical
)
Development,
New
Hindustan Steel Ltd, Ranchi
SHRI T. C. RAJAGOPALAN( Alfernatc )
Tata Merlin & Gcrin Ltd, Bombay
DR B. RAMESH RAO
SHRI C. P. RAMA RAO ( Alternate )
Hindustan Brown Boveri Ltd, Bombay
SHRIU. V. RAO
SHRI V. BALAXIBRAMANIAN( Ahnate )
Tata Hydra-Electric Power Supply Co Ltd, Bombay
SHRI A. M. SAW-41
SHXI V. S. DORAI ( Alfcrnatc)
National Physioal Laboratory ( CSIR ), New Delhi
DR Y. V. SOW.YAJULU
SHRI P. SURAYANARAYANA( Alternate )
Engineers India Limited, New Delhi
SHRI G. N. THADANI
SHRI H. K. KAUL ( Altern& )
Director General, IS1 ( Ex-O#&I Member )
SHRI S. P. SACHlXV,
Director ( Elec tech )
SHBJ P. RANGASWA~XY
Scnetaty
SHKI VIJAI
Deputy Director ( Elec tech ), IS1
2
16 : 3842 ( Part X ) - 1976
Indian Standard
APPLICATION GUIDE FOR
ELECTRICAL RELAYS FOR AC SYSTEMS
PART X
RELAYS FOR TRANSVERSE
PROTECTION
0.
DIFFERENTIAL
F-OREWORD
0.1 This Indian Standard ( Part X ) was adopted by the Indian Standards
Institution on 27 July 1976, after the draft finalized by the Relays
Sectional Committee had been approved by the Electrotechnical Division
Council.
0.2 Modern power systems are designed to provide uninterrupted electrical
supply, yet the possibility of failure cannot be ruled out. The protective
relays stand watch and in the event of failures, short circuits or abnormal
operating conditions help de-energise the unhealthy section of the power
system and restrain interference with the remainder of it and thus limit
damage to equipment and ensure safoty of personnel.
They are also used
to indicate the type and location of failure so as to assess the effectiveness of
the protective schemes.
0.3 The features
following:
which
the protective
relays
should
possess are
the
a) Reliability, that is, to ensure correct action even after long periods
of inactivity and also to offer repeated operation under severe
conditions;
b) Selectivity, that is, to ensure that only the unhealthy part of the
system is disconnected;
c) Sensitivity, that is, detection of short-circuit or abnormal operating conditions;
d) Speed to prevent and minimise damage and risk of instability of
rotating plant; and
e) Stability, that is, the ability to operate only under those conditions that call for its operation and to remain either passive or
~biased against operation under all other conditions.
0.4 Transverse differential protection system falls in the clas$ of unit
protection and is generally applied for circuits of a parallel group. This
protection system compares the currents at the same ends of two or more
3
IS : 3842 ( Part X ) - 1976
parallel circuits
and relies on the principle that load and throughfault
current divide equally between the circuits of a parallel group and any
difference is au indication of an internal fault.
0.4.1 Transvcrsc dilrcrcncjal protection
is extensively used for parallel
feeder protection on I’ccdcrs of moderate length, even up to 132 kV, where
economic and/or physic;11 factors preclude the application
of pilot wire,
This protection system is also some
power line carrier or distance schemes.
times applied for interturn fault ‘protection of large alternator sets provided
with two windings per phase.
0.4.2 Lo@tudinal
differential schemes applied to single circuit in which
the comparison of currents is at the opposite ends of the same circ’uit are
not covcrcd by this application guide.
0.5 It is emphasized that this guide has been prepare4
to assist in appliThis guide deals only
cation rather than to specify the relay to be used.
with the general principles of scheme5 and does not deal with the selection
The actual circuit conditions perhaps may be
of any particular scheme.
dilTercnt from those given in this guide.
assistance
has been
0.6 In the preparation
of this guide, considerable
derived from several published books and technical papers and from manufacturers’ trade literature.
0.7 This guide, is one of the series of application
guides for electrical
The other guides in this series are the following:
relays’ f’or ac systems.
IS : 3638-1966
Application
guide for gas-operated
relays
Application guide for electrical relays for ac
IS : 384‘2 ( Part I )-1967
systems: Part I Overcurrent
relays for feeders and transformers
Application guide fdr electrical
relays for
IS : 3842 ( Part II )-1966
ac systems: Part II Overcurrent
relays for generators and motors
Application guide for electrical relays for
IS : 3842 ( Part III )-1966
ac systems: Part II!
Phase unbalance
relays including negative
phase sequence relay&
Application
IS : 3842 ( Part IV )-lo66
ac systems: Part IV Thermal relays
Application
IS : 3842 ( Part V )-1968
systems: Part V Distance protection
Application
IS : 3842 ( Part VI )-1972
ac systems: Part VI Power relays
guide for electrical
guide for electrical
relays
relays
for
relays for ac
guide for electCca1
relays for
Application guide for electrical
IS : 3842 ( Part VII )-1972
ac systems: Part VII Frequency relays
relays for
Application
guide for electrical
IS : 3842 ( Part XII )-1976
ac systems: Part XII Differential relays for transformers
relays for
4
IS : 3842 ( Part X) - 1976
1. SCOPE
1.1 This guide ( Part X ) deals with the application
IS : 3231-1965* for transverse differential systems.
of relays covered by
2. TERMINOLOGY
2;O For the purpose of this guide the definitions given in IS : 1885
( Part IX )-1966t and IS : 1885 ( Part X )-1968$ shall apply.
3. TRANSVERSE
DIFFERENTIAL
SYSTEMS
3.0 There are generally the following two types of relays available
transverse differential systems:
a) High impedance type circulating current’relays,
for the
and
b) Low impedance differential relays.
3.1 Parallel %eeder Protection
3.1.1 Transverse differential protection. for duplicate parallel feeders
comprises balancing of the currents of the two feeders at the same end, as
shown in Fig. 1 with cross connected current transformers and a high
impedance type measuring relay in the differential circuit across the equipotential lines. Under load or external throughfault conditions the current
is equally distributed between the two lines. As such the secondary
current circulates along the cross connected current transformers and the
connecting leads and the voltage across the relay is practically zero or too
small to drive enough current through the relay. Under internal fault
conditions, the balance of circulating current is upset in magnitude and,
depending on the source of in-feed, in direction as well. This unbalance in
current is monitored by a set of directional relays to distinguish between the
healthy feeder and the faulty feeder.
3.1.1.1 The throughfault stability of the scheme is ensured by giving a
voltage setting to the relay more than the voltage that would appear across
the relay if one set of current transformers completely saturate for a
throughfault.
Relays tuned to the system frequency are used to reject
harmonics which tend ’ to appear in current transformer spill currents
especially under heavy throughfault conditions when current transformer
saturation either partial or total is inevitable owing to the dc transients.
*Specification for electrical relays for power system protection.
tElectrotechnica1
vocabulary: Part IX Electrical relays.
$‘&@rpteQnical
vocsbulary: Part X Electrical power system protection,
5
IS : 3842( Part X ) - 1976
/
I
CURRENT
TRANSFORMER
,yUNGER
CURRENT
RELAYS
.i
~DIRECTIONAL
RELAYS
i
NORMALLY
CONTACT
OPEN
\
CLOSEDCONTACT
b
.-.. .z-t IAtJILILING
_ -”
r
1
1
FIG. 1 TYPICAL HIGH IMPEDANCESCHEMEFOR DUPLICATE
PARALLEL FEEDERS
3.1.2 Current balance relay is at times used for fast protection of
duplicate parallel feeders. The current balance relay compares the current
between the two feeders and when there is an abnormal change in the
division of current between the two circuits, which happens during a fault
in a feeder, the relay operates to trip the breaker associated with the faulty
line.
3.1.2.1 Such a relay has two operating elements actuated by currents
obtained from the two circuits. One element receives operating current
from one of the feeders and restraining current from the other. Vice-versa
is the case for the other element. Depending on which of the feeders has
6
c
IS : 3842 ( Part X ) - 1976
more current, the corresponding element operates to trip the associated
breaker.
The operation of the relay is dependent on its “ slope ” which is
the ratio between the operating current to the restraining current.
3.1.2.2 During single line operation, the current balance protection is
taken out by the semi-automatic
scheme stated in 3.1.3 (a).
As the
restraining current is zero during single line operation, the relay is provided
with a suitable minimum operating value to avoid unwanted operation.
3.1.2.3 In a parallel feeder system having a source at one end, current
balance relays are employed at the sending end only and corresponding
feeder at the receiving end is protected by directional relays. However, if
separate source is available at both ends, current balance relay can be
employed at either end.
3.1.3 When one feeder of a pair or multiple parallel feeders is taken out
of service either automatically or on fault or manually, the differential
protection is unbalanced and certain precautions are necessary to prevent
its operation by load or through fault currents to trip the healthy feeder.
These usually take the form of automatic cutouts which in general are of
two kinds:
a) The semi automatic scheme, which depends on circuit breaker
position and uses circuit breaker auxiliary switches; and
b) The fully automatic scheme, which depends on the absence of
current in one of the feeders and uses undercurrent cut-out
relays.
3.1.3.1 The method used in the semi automatic scheme is not entirely
satisfactory, because it does not provide for the condition where the circuit
breaker is open at one end and closed at the other end of one of the parallel
feeders. Since this feeder will not carry load, the protection of all the
feeders will be unstable at the end where the circuit breaker is closed. This
imposes responsibility on the human element both for cutting out the
protection and restoring it to service when the feeder is recommissioned.
3.1.3.2 The above limitation is overcome by the automatic method in
which undercurrent relays are used. The contacts of under current relays
are used either to short the differential relays in case of duplicate parallel
feeders when the corresponding feeder is taken out of service. As in this
scheme, closing of a feeder on fault may call for high breaking duty of
contacts of the under current relay, in many applications interposing
current transformers may be required so that the breaking duty of the under
current relay contacts is limited to a reasonable value.
3.1.3.3 Back-up protection on each feeder is required to take care of
single line operation or when transverse protection is taken out of service.
Back-up protection may consist of non-directional or directional relays with
time delay or distance protection.
7
IS : 3842 ( Part X ) - 1976
’
3.1.4 Need ,for Directional\Fcature- Directional relays are required in the
scheme to control the differential relays to distinguish the faulty and
healthy circuits.
Referring to Fig. 2 A at A, for the fault position shown,
there is hardly any difference between the two feeder currents until the
faulty line is cleared at B; the faulty line at A then carries more current than
the healthy line. As can be seen sequential tripping of faults at or near the
terminal sections is inherent in this type of protection.
Directional relays
are required at end B to select the faulty feeder.
3.1.4.1 In Fig. 2B, there are three circuits in parallel, and it can be
seen that in this case and in fact in all cases where there are more than two
circuits in parallel a magnitude difference exists at end B for the fault at
F; conditions at end A are the same as for the duplicate parallel feeder.
Therefore, at in-feed or sending ends where an internal fault cannot cause
a reversal of current directional feature can be omitted and at those ends
where such a reversal may take place, for example, both ends of interconnectors and the receiving ends of circuits connected only to loads,
directional relays are always necessary.
END A
END
B
END
B
%
2A TWO
END
PARALLEL
CIRCUITS
A
26 THREE
FIG. 2
NEED
PARALLEL
CIRCUITS
FORDIRECTIONUFBATUIU
18 : 3b42 ( Part X ) - 1976
3.2 Transverse Differential Protection of -Synchronous Machines
3.2.1 This scheme can be applied, as shown in Fig. 3 interturn
fault
protection of synchronous machines provided with two windings in parallel
per phase.
This scheme is based on high impedance
principle which has
and 3.1.1.1
and is applicable
both for starbeen explained
in 3.1.1
connected and delta connected synchronous machines.
For the application
of this protection, the ends of the parallel windings should be brought out
to external terminals for current transformer inclusion,
1 ( ONLY
ONE
PHASE
SHOWN
I
RELAY
STABILIZING
RESISTOR-
FIG. 3
TRANSVERSE DIFFERENTIAL PROTECTION OF
SYNCHRONT)USMACHINES
3.2.2 The scheme as shown’ in Fig. 4 can be applied to synchronous
machines the phase windings of which arc star connected
and have two
-windings in parallel in this case.
During normal operating conditions,
the
current flowing through current transformer is negligible since the voltages
generated in each parallel windings are equal.
In the event of a turn to
turn fault in one of the parallel branches of a phase, the current transformer
will carry a current I as given below:
Where
7
h = induced
x=
reactance
emf in the winding
of the winding
9
The prefix 1 and 2 refer to the
two parallel windings of a phase
IS : 3842 ( Part X ) - 1976
FIG. 4
TRANSVERSE I)IFFEKENTIAL PROTECTION OF SYNCHRONOUS
MACHINES CONNECTED IN STAR
3.2.2.1
The protection
will operate
if the unbalance
current
is more
than the operating current of the relay.
The difference Er - I$ varies
with the number ol‘sl~ortcd turns and if the resulting unbalance
current is
less than protection opcratin g current, t!le protection will not be responsive,
that is, it will have a blind zone.
3.2.2.2 The relay for this application
should be provided with 3rd
harmonic filter. to prevent its maloperation
due to the circulation of zero
sequence currents caused by asymmetry of emf in two branches.
4. SETTING
REQUIREMENTS
4.1 Parallel Feeder Protection - The effective setting of parallel feeder
protection,
as distinct from relay setting, depends on the distribution
of
fault current between
the healthy and faulty feeders and hence on the
Setting is defined in terms of the total fault current
position of the fault.
fed by all paths to the fault and is considered for an iq-feed at one end of
the feeder only.
A condition of fault in-feed at both ends of the feeder is
less onerous.
With this condition the high&t effective setting occurs for a
fault near the centre of the faulty feeder, faults at other points correspond to
lower effective settings although sequential tripping of the respective feeder
ends may be involved.
4.1.1 The under current relays for the automatic
scheme should have
their pick-up and drop-off within 10 percent of rated current transformer
secondary cutrent and these should be able to withstand the rated current
continuously.
When a fault occurs near the sending end busbars, current
is concentrated
in the faulted feeder, and healthy feeders may carry very
low currents.
Under these conditions
the under current
relays in the
healthy feeder must remain operated,
otherwise the differential
protection
10
IS : 3842 ( Part X ) - 1976
may be switched out of service.
Although the operating current may be as
low as possible, the reset current should be greater than the feeder charging current to prevent the relay remaining operated w’hen the circuitbreaker at far end opens. A sensitive relay is therefore required for this
application specially for the sending end. At the receiving end the requirements are less onerous since either load or fault current flows in both or
all feeders while they are in service.
The operating value of the relay
should be equivalent to the setting of parallel feeder protection, and the
relay should reset just above the value of charging current.
4.2 Transverse
Differential
Protection
of Synchronous
Machines The method of calculating the stabilising resistor in series with the r#ay for
high impedance protection and relay voltage setting for transverse differential protection of parallel feeders is given in Appendix A.
APPENDIX
A
( Clause 4.2 )
CALCULATION
A-l.
OF RELAY VOLTAGE
SETTING
OF STABILIZING
RESISTOR
AND
VALUE
CALCULATION
OF RELAY VOLTAGE
SETTING AND
VALUE OF STABILIZING
RESISTOR FOR A TYPICAL
HIGH IMPEDANCE
SCHEME
A-l.1 Consider a generator. rated at 125 MVA,
windings per phase. The sub-transient reactance
percent.
Full load current of the generator = J
Therefore, maximum throughfault
current from the machine
3 Ff
11 kV and having two
of the generator is 20
l”,‘~~s
= 6 600 A
6 600
=--33000A
0.2
Let the protective current transformer to which the high impedance
relay is connected have a ratio of 4 00015.
Current transformer equivalent of
33 000
x &
maximum throughfault current ( 4 ) = --2--11
=20*62A
IS : 3842 ( Part X ) - 1976
Voltage Setting ( VR ) - Maximum voltage that would appear
across the relay if one of the current transformers completely saturates is:
A-1.2
v, =
If ( R,,
+ 2 R, ) volts
where
current transformer secondary winding resistance, and
R CT
=
R,
= one way maximum lead resistance between the relay
and the current transformer.
Assuming R,,
= 1 ohm and R, = 0.5 ohm,
VR = 20.62 ( 1 + 2 x OS5)
= 41.24 volts
A-l.3 Stabilizing Resistor - For the purpose of calculating the stabilizing resistor value, a voltage setting of 45 V will be assumed to give an
Total relay circuit impedance at 45 V with
adequate margin of stability.
a setting of 1 A ( 20 percent) on the relay is:
45
_=
1
Relay burden at 1 A is 1 VA.
(
45 ohms
Thus relay impedance at setting is :
:*:,2
= 1 ohm
and can, therefore, be neglected.
will be 45 ohms.
Thus the value of stabilizing resistor
A-2. CALCULATION
OF RELAY
VOLTAGE
SETTING
AND
VALUE
OF STABILIZING
.RESISTOR
FOR A TYPICAL
SCHEME OF TRANSVERSE
DIFFERENTIAL
PROTECTION
OF PARALLEL
FEEDERS
A-2S
Consider a typical 33 kV system having the following parameters:
Fault level at sending end
= 2 000 MVA
Length of the feeder
= 10km
Impedance per km
= 0.5 ohms
Secondary, winding resistance of main current
transformer ( R,, ) of ratio 500/5
= 0.5 ohms
One way lead resistance
Primary winding resistance of interposing current
transformer of ratio 5/l ( Rp )
= 0.5 ohms
= 0.05 ohms
12
c
IS : 3842 ( Part
X ) - 1976
Secondary winding resistance of interposing current
transformer
= D-25 ohms
NOTE - It is assumed that to limit the break rating of the associated under-current
relay contacts, interposing current transformer of ratio 5/l is used for the scheme.
A-2.1.1
Per unit impedance
of the parallel
feeder = 5 x 4 x &
=
Fault MVA at receiving
Fault current
2 000
=---=357MVA
1+4*59
end
per feeder
=43x33x2
Secondary current from 50015
current transformer
Secondary current
transformer
from 5/l
4.59
=
current
357 x 10:
3 130x
= 31.3
&
x 1
5
=3130A
=31*3
A
= 6.26A
A-2.1.2 For a throughfault,
assuming one of the interposing current
transformers get saturated, maximum
voltage that can develop across the
differential relay is:
Vr = Ir ( RB -i &xc >
where
Ii = fault current,
winding resistance of the interposing
transformer, and
RUc = impedance of the under current relay at Zf
RN = secondary
Then
Hence
current
Vr = 6.26 ( O-25 + 1.25 )
P 6.26 x 1.5 = 9.4
the relay setting voltage should be above 9.4, say 10 volts.
b2.2
Stabilizing
Resistor
- Assuming a setting of 40 percent ( 0*4A )
on the differential relay, the value of stabilizing resistor can be calculated
from the following:
0.9
= 19.4 ohms
Value of stabilizing resistor = g
- (0.4)s
( since the differential
relay burden is assumed to be 0.9 VA at setting).
NOTE- It is essetitial to check that:
(a ) The megnetising current drawn by the
dead lime current transformers under single line working, when the load current in
the healthy feeder may be about 1.5 times the normd.full lqad current, and the cbarging current of the feeder, when tpe remote end breaker w off, IS low enough to drop out
he under-current relays of the dead line, and ( b) Under single line working, during
an external fault condition, the magnetising current drawn by the dead line current
transformers is not high enough to pick-up the undercurrent relays of the dead line.
13
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$
BANGALORE 560058
Gangotri Complex, 5th Ftoor, Bhadbhada Road, T.T. Nagar.
BHOPAL 462303
Plot No. 82183, Lewis doad, BHUBANESHWAR
751b02
Kalai Kathir Building, 6/48-+,Avanasi
Road, COIMBATORE
641437
Quality Marking Centre, N.Hd IV1 N.I.T., FARIDABAD
121001
201001
Savitri Cbmplex. 116 G. T. Ro d, GHAZIABAD
5315 Ward No. 29, R.G. Bar 2 a Road, 5th By-lane,
GUWAHATI
781003
6-8-56C L. N. Gupta Marg, ( Nambally Station Road )
HYDERABAD
500001
R14 Yudhister Marg, C Scheme, JAIPUR 302005
llJ/418
331 dl 31
i
BOMBAY
Square.
89 65 28
22 39 71
Reprography Unit, BIS. New Delhi, India