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( Reaffirmed 2001 )

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IS : 3231 ( Part 3/Set 3 ) - 1987

I ndian St andardSPECIFICATION FOR

ELECTRICAL RELAYS FORPOWER SYSTEM PROJECTIONPART 3 REQUIREMENTS FOR PARTICULAR GROUP OFRELAYS

Section 3 Biased ( Percentage ) Differential RelaysRelays Sectional Committee, ETDC 35

Chairman Refmssnting*SHRI V. S. DORAI Tata Hydro-Electric Power Supply Co Ltd,BombayMembersSHRI R. D. BATRA Hindustan Steel Ltd, RanchiSH~ G. K. SARAN ( Alternate )SHRI R. C. BHATIA Delhi Electric Supply Undertaking, New Delhi

SHRI M. K. CHAUDHARY ( Alternuts )SHRI T. B. CHIKKOBA Tamil Nadu Electricity Board, MadrasSHRI V. V. SAMPATE ( Alternate )DEPUTY DIRECTOR ( PSI-II ) Railway Board, New DelhiDEPUTY DIRECTOR, S&T ( Alternate )DIRECTOR ( CIP ) Central Electricity Authority, New DelhiSHRI K. L. GARQ Directorate General of Supplies & Disposals( Inspection Wing ), New DelhiSHRI S. KRISHNA ( Alternate )

SHRI S. G. KARADKAR Bombay Electric Supply & Transport Under-taking, BombaySHRI M. A. KARIX ( Alternate )SHRI V. S. KAUSHIKKAR Larsen & Toubro Ltd. BombaySHRI DEVE~DER NATH ( Alternate )SERI G. K. MALAVIYA Universal Electrics Ltd, 24 ParganasSHRI C. GHOSH ( Alternate )SHRI B. C. MUKRERJ EE National Test House, CalcuttaSnar D. P. MUK RERJ EE ( Alternate )SHRI NACHHATTER SINQ~ Bharat Heavy Electricals Ltd, Bombay

SARI R. RA~ASUBBAIAH ( Altcrnnte I )SHRI S. G. DESHPANDE ( Alternate I I )

*Shri V. S. Dorai was Chairman for the meeting in which this standard wm fmalized.( Continued on page 2 )0 Copyright 1987

BUREAU OF INDIAN STANDARDSThis publication is protected under the fndian Copyright dct ( XIV of 1957 ) andreproduction in whole or in part by any meana except with written permission ot thepublisher shall be deemed to be an infringement of copyright under the said Act.

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IS : 3231 ( Part J /Set 3 ) - 1987( Continrredfrompugs1 )

Members RsprcssntingSHRI S. NATARAJ AN Easun Reyrolle Relays and Devices,Tamil NaduSHRI A. A. PAUL Tata Consulting Engineers, Bombay

SHW P. P. KARHADB ( AltenrateSHRI A. K. BAJ A University of Roorkee, RoorkeeSHRI R. RAMANUJ AN Aluminium Industries Ltd, TrivandrumSHRI B. NAEAYANAN ( Alternate )SHRI U. V. RAO Hindustan Brown Boveri L td, VadodaraSHRI P. U. BEAT ( Altcmafe )SHRI A. M. SAHNI Tata Hydro-Electric Power SuppIy CoBombay*SHRI V. S. DORAI (Alternate )DRM.T.S~NT _. . ASEA Ltd, Bangalore

Ltd,

Ltd,

SHRI B. S. PALKI ( Alternate 1SHRI B.S. SHARMA U. P. State Electricity Board, Lucknow

SHRI C. P. GUPTA ( Alternate)SHRI S. SIVASUBRA~IANIAN Directorate General of Technical Development,New Delhi&RI P. K. HALDAR ( Alternate )SUPERINTENDINO NOINEER Haryana State Electricity Board, ChandigarhSRRI HARNARINDER SINEW ( Alternate )SHRI S. I. SURI National PhysicalNew Delhi Laboratory ( CSIR ),SHRI S. C. GARQ ( Alternate )SHRI G. N. THADANI Engineers India Ltd, New Delhi

SHRI S. G. GOKHALE ( Altcrnate )DR K. K. THAKKAR J yoti Ltd, VadodaraDR B. K. DASWPTA ( Alternate)SHF.I K. VASUDEVAN English Electric Co of India L td, MadrasSHRI T. V. G. MENON ( Alterpate )

SHRI B. IS. VENRATESE Karnataka Electricity Board, BangaloreSHRI K. T. RAMASWAMY ,( Alternate )SHRI S. P. SACHDEV, Director General, BI S ( Ex-o&o Member )Director ( Elec tech ) Smrrtary

SHRI K. M. BHATIAJ oint Director ( Elec tech ), BIS

(Continued on baga 16 )*Ski V. 5. Dorai wils Chairman or the meeting n whichthis standard was finalized.

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IS : 3231 ( Part J /Set 3 ) - 1987

I ndian St andardSPECIFICATION FORELECTRICAL RELAYS FOR

POWER SYSTEM PROTECTIONPART 3 REQUIREMENTS FOR PARTICULAR GROUP OFRELAYS

Section 3 Biased ( Percentage ) Differential Relays

0. FOREWORD0.1 This Indian Standard ( Part 3/Set 3 ) was adopted by the IndianStandards Institution on 29 January 1987, after the draft finalized by theRelays Sectional Committee had been approved by the ElectrotechnicalDivision Council.0.2 This standard is one of the series of standards being brought out tocover requirements of protection relays. General introduction to this seriesis given in IS : 3231 ( Part 0 )-1986*.The standards published in the series so far are:IS: 3231 Specification for electrical relays power system protection:

(Part O)-1986(Part l/Set l)-1986(Part 1jSec 2)-1986(Part l/Set 3)-1986(Part 2/Set 1).1987(Part B/Set 2)-1987

General introduction and list of parts(jirst revision)General requirements; Section 1 Contact perfor-mance (jnt revision)General requirements; Section 2 Insulation tests(jrst revision)General requirements; Section 3 High frequencydisturbance test for static relays ( j i rst revi sion)Requirements for principal families; Section 1All-or-nothing relaysRequirements for principal families; Section 2General requirements for measuring relays

*Specification for electrical relays for power system protection: Part 0 General intro-duction and list of parts ( jrst revision ).3

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IS : 3231 ( Part 3/Set 3 ) - 1987(Part 3/Set l)-1987

(Part S/Set 2)-1987

(Part 3)Sec 3)-1987

Requirements for particular group of relays;Section 1 Non-specified time or independentspecified time measuring relaysRequirements for particular group of relays;Section 2 Dependent specified time measuringrelaysRequirements for particular group of relays;Section 3 Biased (percentage) differential relays.

0.3 According to classification on hierarchical basis [ see IS : 3231 (Part O)-1986* 1, this standard is a third level document.0.4 In preparing this standard, assistance has been drawn from thefollowing:

IEC Pub 255-l 3 (1980) Electric relays : Part 13 Biased ( percen-tage ) differential relays. Internationa! Electrotechnical Com-mission,

BS 142 : Section 4.1:1984 Electrical protection relays: Part 4Requirements for multi-input energizing quantity relays:Section 4.1 Specification for biased ( percentage ) differentialrelays. British Standards Institution.0.5 This standard ( Part 3/&c 3 ) should be read in conjunction withIS : 3231 ( Part P/Set 2 ) -1987-t to which a reference has been made, asthese relays constitute a particular sub-family (group) of measuring relayswith more than one input energizing quantity.

1. SCOPE1.1 This standard (Part 3/Set 3) specifies the performance requirements ofelectrically biased (percentage) differential relays and the parameterswhose values are to be declared by the manufacturer of such relays. It alsospecifies methods of presentation of the characteristics and performance ofthese relays.1.2 This standard applies to relays designed for the detection of faultsparticularly in ac generators, motors and transformers.1.3 This standard covers the majority of biased (percentage) differentialrelays and also, for example, those where the restraint percentage increasesas the through-current increases. For particular cases, supplementaryrequirements may be stated in lower level standards.

*Specification for electrical relays for power system protection: Part 0 Generalintroduction and list of parts (jirst evision 1.@pecification for electrical relays for power system protection: Part 2 Requirementsfor principsl families, Section 2 General requirements for measuring relays.

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I$ : 3231 ( Part 3/$ec 3 ) - 19871.4 This standard applies only to relays in a new condition.1.5 This standard does not apply to relays designed for busbar protection,nor does it apply to current differential (for example, pilot wire) relaysused for the protection of transmission lines.2. TERMINOLOGY2.0 For the purpose of this standard, the definitions given in IS : 1885(Part 9) -1986* and the following shall apply.2.1 Differential Relay - A relay which, by its design, is intended torespond to differential current.2.2 Biased (or Percentage) Differential Relay - A differential relayin which the designed response is modified by a restraint current.2.3 Differential Current - In a differential relay, a current which isthe phasor difference between specified incoming and outgoing currents.2.4 Restraint Current - In a differential relay, the combination of in-coming and outgoing currents, which restrains operation of the relay.2.5 Restraint Percentage - The ratio, expressed as a percentage, bet-ween the differential current and the restraint current(s) up to which therelay does not operate.

NOTE - The definition of restraint percentage ignores an error, which may notbe negligible, due to the finite operating current required under zero restraint con-ditions. This may be taken into account when necessary.2.6 Through Current - In a differential relay, that portion of the totalincoming current which is also present in the outgoing current.3. STANDARD VALUES3.1 Input and Auxiliary Energizing Quantities and Frequency -The standard values of input and energizing quantity and of frequency arespecified in IS : 3231 ( Part P/Set 2 )-1987j-.3.2 Standard Reference Values of Influencing Quantities andFactors and Standard Values of Their Nominal and ExtremeRanges

3.2.1 Influencing Quantities and Factors - The standard reference condi-tions are specifiedin Table 1 of I S : 3231 (Part P/Set 2) -19871. I n addi-tion, the standard conditions given in Table 1 in this standard apply tobiased (percentage) differential relays.*Electrotechnical vocabulary : Part 9 Electrical relays (first revision ).jSpecification for electrical I clays for power system protection: Part 2 Rcquirrmentsfor principal families, Section 2 General requirements for measuring relays.

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IS : 3231 ( Part 3/Set 3 ) - 1987

TABLE 1 STANDARD REFERENCE CONDITIONS AND TEST TOLERANCESOF INFLUENCING QUANTITIES AND FACTORS( Clause 3.2.1 )

INFLUENCINO QUANTIPP OR FACTOR REFERENCE TEST TOLERANCESCONDITIONS(3)

r Input energizing currents [1 Restraint current < AS agreed between the manufacturer1 Differential current 1 and the userICharacteristic 1 Phase angle between input 0 f2and input Ienergizing { energizing quantities

quantities 1 Transient dc component Zero 5 percent of peak! in ac ( see Note ) ac value[ Setting value(s) where As agreed between the manufacturer1 ~.%Ye adjustments are and the user

Auxiliary r Transient dc component Zero 5 percent of peakenergizing { in ac ( see Note ) ac valuequantities 1NOTE - In the special case of relays in which polyphase measurements are

made on a single relay, the manufacturer shall define which of the input currentsshall be under reference conditions.

3.2.2 Limits of the Nominal Ran*Tes af Injluencing Quantities and Factors -The standard values are specified m Table 2 of IS : 3231 ( Part 2ISec 2 )-1987*. In addition, the standard values given in Table 2 of this standardshall apply to biased ( percentage ) differential relays.3.3 Characteristic Quantity(ies) and Setting Range(s) - There areno standard rated values of either characteristic quantity(ies) or settingrange(s). The values and the limits of setting range(s) shall be as agreedto between the manufacturer and the user.3.4 Restraint Percentage - There are no standard values of restraintpercentage. The setting values shall be as agreed to between the manufac-turer and the user.__~____~

*Specification for electrical relays for power system protection : Part 2 Requirementsfor principal families, Section 2 General requirements for measuring relays.6

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IS : 3231 ( Part 3/Set 3 ) - 1987

TABLE 2 STANDARD VALUES OF THE LIMITS OF THE NOMINALRANGES OF INFLUENCING QUANTITIES AND FACTORS( Clause 3.2.2 )

INFLTJENCINGQUANTITYOR FACTOR NOMINAL RANGE

ICharacteristic 1and input {energizingquantities fI:IIAuxiliary Ienergizing {quantities

(1)Reference input energizing quantityNon-reference input energizing quantityPhase angle between input energizingquantitiesFrequencyWaveformSteady-state dc component in acTransient dc component in acVoltage or current frequencyFrequencyWaveformac component in dc ( ripple )

Steady-state dc component in acTransient dc component in ac

(2)rI1 As agreed to between the< manufacturer and theI user

r As agreed to between thef manufacturer and theI user unless specifiedin this standard

0 to 12 percent of therated dc valuer As agreed to between thei

manufacturer and theI user unless specifiedin this standard

3.5 Resetting and Disengaging Ratios - There are no standard valuesof the resetting and disengaging ratios. The values shall be as agreed tobetween the manufacturer and the user.4. OPERATION AND ACCURACY4.1 Operation

4.1.1 Operating Characteristics - The manufacturer shall declare theoperating characteristics of the relay under reference conditions, theseincluding the reference setting of the differential circuit, and as the maxi-mum and minimum setting of the restraint circuits, when applicable.Minimum differential current shall be declared by the manufacturer.4.1.2 E$rcfive Range - The manufacturer shall declare the effectiverange of restraint current values [ see 6.7 of IS : 1885 ( Part 9 )-1986* 1.*Electrotechnical vocabulary : Part 9 Electrical relays (first revision).

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IS : 3231 ( Part J /See 3 ) - 19874.1.3 Muximum Through Current - The manufacturer shall declare themaximum through current up to which the relay produces no output. Therelay shall be able to withstand the sudden application and removal ofthrough current up to this value. This duration shall be declared by themanufacturer and shall be at least 100 ms.

NOTE - This maximum value is based on a test in which there is no inten-tional differential current, the incoming and outgoing ( through ) current shouldbe equal.4.1.4 Harmonic Restraint - For relays which have harmonic restraint,the manufacturer shall declare which of the harmonics have a restrainingeffect and explain how the harmonic restraint interacts with the funda-mental frequency restraint. The amount of each of these harmonics whichwill prevent operation of the relay shall be declared, the amount beingexpressed as a percentage of the differential current at the rated frequency.If different values are obtained under steady-state and dynamic conditionsthe highest value shall be stated.

4.2 Accuracy - For biased ( percentage ) differential relays, considera-tions of accuracy apply to the operating characteristics and to the operat-ing time under reference conditions. For these items, the manufacturershall declare the assigned errors in accordance with IS : 323 1 (Part 2/Set 2)-198i.4.2.1 Operating Characteristics - The accuracy of the operating charac-

teristics may be shown graphically by maximum and minimum lines, asin Fig. 1. Alternatively, the manufacturer may declare the restraintpercentage, with a plus or minus tolerance, over the effective range ofrestraint current.4.2.2 Operating Time - The accuracy of the operating times may beshown graphically as in Fig. 2, or it may be declared by the manufacturerfor a specific range ( normally 3 to 10 times ) of differential currents.

NOTE - Normally only a maximum operating time is specified.5. METHODS OF PRESENTING RELAY CHARACTERISTICSAND PERFORMANCE5.1 Operating Characteristics - When presenting the operatingcharacteristics of a relay, the manufacturer may use the average of incom-ing and outgoing currents as a restraint current.

*Specification for electrical relays for power system protection:Part 2 Requirementsfor principal families, Section 2 General requirements for measuring relays.

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IS : 3231 ( Part 3/Set 3) - 1387

NON-OPERATE ZONE

LIMITS OF ERRORUNDER REFERENCECONDITIONS

RESTRAINT CURRENT (FOR EXAMPLE ll)

NOTE - Setting value shall be stated.FIQ. 1 OPERATING CHARACTERISTIC UNDER REFERENCE CONDITIONS

5.1.1 Figure 1 shows the recommended method of presenting the opera-tion characteristics and associated limits. Differential current is shown onthe vertical axis and restraint current on the horizontal axis.NOTE 1 - Methods other than graphical may be used for the presentation ofthe operating characteristics.NOTE 2 - Where appropriate, the manufacturer should declare results both ona single and a three-phase basis.

5.2 Operating Time - Figure 2 shows the recommended method ofpresenting the operating time and associated limits over a range ofcurrents to be declared by the manufacturer ( see 4.2.2 ).5.2.1 The manufacturer shall declare the operating times of the relay

under reference conditions at three and ten times the operating value ofthe differential current at its minimum and maximum settings ( if any ).Where necessary, this shall be done on a three-phase basis.5.3 Harmonic Restraint - Figure 3 shows a recommended method ofpresenting in graphical form, the harmonic restraint characteristic of adifferential relay which uses only the harmonic frequency to restrain.Figure 4 shows a recommended method for a differential relay thatresponds to more than one harmonic frequency.

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IS a 3231 ( Part 3ISec 3 ) - 1987

A:F::

UPPER LIMIT OF TIMEF2

;DIFFERENTIAL CURRENT 5-

I ((,=il) f MULTIPLE OF SETTI I VALUE_ LIMITS OF EFFECTIVE H

RANGE

ING

FIG. 2 OPERATING TIME UNDER REFERENCE CONDITIONS

C OPERA1 E5f

IFfCURRENT AT RATEDFREQUENCYu IxF = CURRENT Af SPECIFIEDHARMONIC FREQUENCY

NON-OPERATE

NOTE - Setting value shall be stated.FIG. 3 HARMONIC RESTRAINT CHARACTERISTICSHOWIKO RESPONSE

TO A SINGLE HARMONIC FREQUENCY10

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IS : 3231 ( Part 3/Set 3 ) - 1987

I0 50 loo 150 200 250 300 w(t-k)FREQUENCY OF IXF

FIG. 4 HARMONICRESTRAINTCHARACTERISTICHOWING ESPONSETO DIFFERENTHARMONIC REQUENCIES6. THERMAL REQUIREMENTS6.1 The thermal requirements as specified in IS: 3231 (Part P/Set 2)-1987*shall be applicable. In addition, the following requirement applies tobiased ( percentage ) differential relays:

When a differential circuit has a lower thermal capability thanthe restraint circuit, the thermal capability shall be declared by themanufacturer.

7. MECHANICAL REQUIREMENTS7.1 The mechanical requirements as specified in IS : 3231 ( Part P/Set 2)-1987* shall be applicable.8. VALUES OF LIMITS OF OPERATIVE RANGE OF AUXILIARYENERGIZING QUANTITIES8.1 The values of limits of operative range of auxiliary energizingties shall be as specified in IS : 3231 ( Part P/Set 2 )-1987*.9. SHOCK AND VIBRATION

quanti-

9.1 The relevant provisions of IS : 3231 ( Part P/Set 2 )-1987* shall beapplicable.*Specification for electrical relays for power system protection: Part 2 Requirementsfor principal familirs, Section 2 General requirements for measuring relays.

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1s : 3231 ( Part a/SecP ) - 198710. CONTACT PERFORMANCE10.1 Requirements of IS : 3231 ( Part l/Set I )-1986* shall apply.11. RATED BURDEN11.1The rated burdens are specified in IS: 3231 ( Part P/Set 2 )-1987t. Inaddition, the following requirements apply to baised ( percentage ) diffe-rential relays:

a) If the differential circuit has a lower thermal capacity ( and,therefore, a lower rated value ) than the restraint circuits itshould be considered to have the same rated value as therestraint circuits for the purpose of making burden measurements;andb) The manufacturer shall declare the burden between each appro-

priate set of input terminals:1) with no differential current flowing; and2) with differential current equal to input current.

12. INSULATION12.1 The relevant provisions of IS : 3231 ( Part l/Set 2 )-19861 shall beapplicable.13. MARKINGS AND DATA13.1 The markings and data requirements shall be as specified in IS : 323 1( Part P/Set 2 )-1987t.14. HIGH-FREQUENCY DISTURBANCE TEST14.1 Where required for static relays, the requirements for the high-frequency disturbance test specified in IS : 3231 ( Part l/Set 3 )-19868shall be applicable.15. TESTS15.1 General

15.1.1 The classification of tests and the requirements for routine test-ing shall be in accordance with 12 of IS : 3231 ( Part P/Set 2 )-19877.*Specification for electrical relays for power system protection: Part 1 Generalrequirements, Section 1 Contact performance (Jirst revision ).tspecification for electrical relays for power system protection : Part 2 Requirementsfor principal families, Section 2 General requirements for measuring relays.SSpecification for electrical relays for power system protection: Part 1 Generalrequirements, Section 2 Insulation tests (Jirsl revision ).EjSpecification for electrical relays for power system protection : Part 1 Generalrequirements, Section 3 High frequency disturbance test for static relays (f;rsl reuisiorr ).

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IS : 3231 ( Part 3/&c 3 ) - 198715.1.2 Unless otherwise specified, the test methods shall be as givenin 15.2 to 15.5.

15.2 Tests Related to Accuracy and Operating Characteristics15.2.1 TestConditions

a) All influencing quantities and factors shall be at the referencevalues ( within the specified test tolerances ) unless otherwisestated in this standard;b) The auxiliary energizing quantities shall be at the rated value forall tests unless otherwise stated in this standard;c) The method of applying the input energizing quantity (for exam-ple, suddenly or gradually) shall be declared by the manufacturer

if not prescribed in this standard; andd) Timing tests shall be done with only one of the restraint windingsenergized over the range of values of differential current forwhich specified times are indicated by the manufacturer. Othertests with through current present may be agreed to between themanufacturer and the user.15.2.2 Test Ci rcuit s and M et hods for M easuri ng Rel ay Characteri st i cs - Thetest instructions in this clause are based on single-phase relays. Wherepolyphase relays are provided, they shall be tested with relevant combina-tions of phase currents and magnitudes of the test currents shall be asdeclared by the manufacturer.

15.2.2.1 Operat i ng characteri st i cs ( see Fig. 5 )- For differential relays,the tests are performed as follows:a)b)c)

With I, equal to zero, check the threshold value of the relay;With low values of I t , increase I a until relay operations;Increase I, to higher value. Again increase Id until relay operates;and

d) Repeat for a number of different 1% values up to the limit of theeffective range. Values shall be as declared by the manufacturer.

Frc. 5 TEST CIRCUITFOR OPERATINGCHARACTERISTICEST13

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IS t 3231 ( Part 3/Set 3 ) - 198715.2.2.2 Operat i ng t ime characteri sti cs ( see Fig. 6 ) - For differentialrelays, the tests are performed as follows:4b)44

Set current level with switch closed;Open the switch;Apply test current by closing switch, and measure operating time;If point-on-wave control is used, choose an angle which givesmaximum time. If this control is not available, take ten shots ata random closing angle; and

4 Repeat the test procedure for higher values of current.

FIG 6 TEST CIRCUIT FOR OPERATING TIME TEST15.2.2.3 Harmonic restrain t character istics ( see F ig. 7 ) - The following

test procedure may be used:Let Ir be the current at rated frequency and let I xB be the current atspecified harmonic frequency ( see Fig. 3 ):a) Set value of I,, to initial value,b) Increase Ir from zero until relay operates.

The reference condition of the phase relationship between IPand I xp shall be as declared by the manufacturer;c) Repeat at different values of IxE;d) Repeat (b) with different phase relationship between I = and 1.rplotting additional curves, if necessary; ande) Having found the values under steady-state conditions, the testshall be repeated under dynamic conditions by switching IF and

I Xp simultaneously from zero.The test shall be conducted with no transient dcin the funda-mental current. If necessary, increase Ixr until relay is blockedfrom operating.

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IS t 3231 ( Part 3,Sec 3 ) - 1987

FIG. 7 TEST CIRCUITFOR HARMONIC RESTRAINT TEST15.3 Thermal Tests - The tests for thermal requirements shall be per-formed in accordance with IS : 3231 ( Part B/Set 2 )-1987*.15.4 Performance with Through Current

15.4.1 When testing to determine the limiting value of through currentup to which the relay will not operate, the duration of application ofcurrent shall be declared by the manufacturer.15.4.2 For relays with more than two restraint circuits, the total currentshall be applied to one restraint circuit as an incoming current, and divi-ded approximately equally among the other restraint circuits, as outgoingcurrents. If one or more of the restraint windings are of minor importance,

the test procedure shall be declared by the manufacturer.15.5 Mechanical Tests - The tests for mechanical requirements shallbe carried out in accordance with 14 of IS : 3231 ( Part P/Set 2)-1987*.15.5.1 In addition to the test conditions specified in 14.1.1 of IS : 3231( Part P/Set 2 )-1987*, the following condition shall also be fulfilled fordifferential relays:

At values of the differential current of zero for the initial valueand three times the operating value for the final value. Unless other-wise agreed, the differential current shall be applied suddenly( seeFig. 6 ),

*Specification for electrical relays for power system protection: Part 2 Requirementsfor principal families, Section 2 General requirements for measuring relays.

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1s : 3231 ( Part 3/Set 3 ) - 1987[ Continned fram page 2 )

Panel for the Revision of IS : 3231-1965, ETDC 35/P9Convener

SHRI B. S. SHARBXA U. P. State Electricity Board, L ucknowMem hers

DR B. K. DASGUPTASHRI H. DE)IRECTOR ( CIP 1SHRI P. K.&TuR;

J yoti L td, VadodaraHindustan Brown Boveri Ltd, VadodaraCentral Electricity Authority, New DelhiLta Hydro-Electric Power Supply Co Ltd,a BombayI;nar T. V. G. M~N~N EI-___ -. ~-- -- iglish Electric Co of India Ltd, MadrasSasr A. A. PAUL Tata Consulting Engineers, BombaySHRI P. P. KARHADE ( dllernate )SHRI A. K . RAJ A University of Roorkee, RoorkeeDR M. T. SANT ASEA Ltd, BangaloreSEW J . V. VAIDYA Larsen & Toubro Ltd, Bombay

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