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IS 11354 (1985): Guide for identification by hour numbersof the phase conductors of 3-phase electric systems [ETD 1:Basic Electrotechnical Standards]

IS: 11354 - 1985

Indian Standard GUIDE FOR

IDENTIFICATION BY HOUR NUMBERS OF THE PHASE CONDUCTORS OF 3-PHASE ELECTRIC SYSTEMS

Basic Electrotechnical Standards Sectional Committee, ETDC 1

Chairman SHRI S. G. RAMAoHANDRA

Representing

Rotating Machinery Sectional Committee, ETDC 15, IS1

Msmbns

SARI V. K. BATRA SHRI V. S. BHATIA

National Physical Laboratory ( CSIR ), New Delhi Low Voltage Switchgear &

Committee, ETDC 57, IS1 Controlgear Sectional

SRRI M. SESHADRI ( AIfernalc ) SHRIA. DASCWPTA Secondary Cells & Batteries Sectional Committee,

ETDC 11, IS1 SHRI B. MUEHOPADHYAY ( Alternate )

MAJ-GEN N. DAYAL DIREoTOR STANDARDS

Institution of Engineers ( India ), Calcutta

( ELEoTRICAL ) Research, Designs

Lucknow and Standards Organization,

JOINT DIREcToR STANDARDS ( ELECTRICAL )/S (Alternate )

DIRECTOR ( TED ) Central Electricity Authority, New Delhi DEPUTY DIRECTOR ( TED ) ( Alfernatc )

SRRI M. L. DONO~R-E Power Cables Sectional Committee, ETDC 59, IS1 SHRI M. M. HONAVAR ( Alternate )

SHRI A. N. GHOSH Electrical Appliances Sectional ETDC 43, IS1

Committee,

SHRI R. D. JAIN Conductors and Accessories for Overhead Lines

SHRI K. C. KAUL Sectional Committee, ETDC 60, IS1

Bharat Heavy Electricals Ltd, Bhopal SHRI PRAKASH SINCW ( Alternate )

SHRI A. S. LAKSHYANAN Solid Electrical Insulating Materials Sectional Committee, ETDC 63, IS1

SHRI B.A. GOVINDARAJ ( Alternate) SHRI KALYAN K. MONDAL National Electrical Code Sectional Committee,

SHRI B. C. NAIR ETDC 56, ISI

Industrial Process Measurement and Control Sectional Committee, ETDC 67, IS1

( Continued on page 2 )

@ Cojyright 1986

INDIAN STANDARDS INSTITUTION

This publication is protected under the In&n 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 : 11354 - 1985

( Continuedfrom page 1 )

Members Representing

SHRI N. NATI* Relay Sectional Committee, ETDC 35, IS1 SI~RI B. S. SIIAI~MA ( Alternate )

SHRI H. M. PAI High Voltage Switchgear and Controlgear Sectional Committee, ETDC 58, IS1

SIIRI V. B. DESAI ( Alternate ) SHRI S. PARAMESWARAN Central Power Research Institute, Bangalore

SHRI SUJATHA STJBEASH ( Alternate ) SHRI D. N. PURANDARE Electrical Wiring Accessories Sectional Committee,

ETDC 44. IS1 SRRI S. JHAVERI ( Alternate )

SHRI P. K. RAO Ministry of Defence ( DGI ) LT-COL AMARJIT SINGE ( Alternate )

SHRI C. R. VARIER Transformers Sectional Committee, ETDC 16, IS1 SHRI M. L. MITTAL ( Alternate I ) SHRI V. B. BHATIA ( Alternate II )

SHRI M. P. WAQH Indian Electrical Manufacturers Association, Bombay SHRI J. V. VAIDYA ( Alternate )

SRRI S. P. SACHDEV, Director General, IS1 ( Ex-oficio Member ) Director ( Elec tech ) ( Secretary )

2

IS:11354 - 1985

Indian Standard GUIDE FOR

IDENTIFICATION BY HOUR NUMBERS OF THE PHASE CONDUCTORS OF 3-PHASE ELECTRIC SYSTEMS

0. FOREWORD

0.1 This Indian Standard was adopted by the Indian Standards Institution on 18 October 1985, after the draft finalized by the Basic Electrotechnical Standards Sectional Committee had been approved by the Electrotechnical Division Council.

0.2 The object of this standard is to provide a uniform means of identification of conductors of 3-phase interconnected systems by the use of hour ( clock-face ) numbers, taking as a basis, the phase sequence, starting from an arbitrary origin of their applied voltages.

0.3 The hour numbers established as per the guidelines given in this standard are used in the following situations:

a) To establish the possibility, in a given station, of interconnecting groups of 3-phase conductors associated with networks already connected elsewhere;

b) To indicate clearly which conductors within those groups must; be connected together in order to effect the desired interconnection

c) In operation, and especially during system disturbances, to facilitate the recognition and the utilisation of the indications provided by the measuring and protective equipment allocated to the different phases.

0.4 The system of marking with hour numbers takes into account the shift in the phase-voltage vectors due to interposed power transformers and determined by the winding connection, but it disregards any shift resulting from the impedance of the conductors and of the transformer windings which will vary with the length and the connected load, and which plays no part in this system of conductor indentification. Thus, the same number accompanies a given conductor along its whole length and is subject to change only when the conductor system phases through a transformer. This change in hour number is constant for a given transformer and indicates the change in position of the voltage vectors introduced by the transformers at no load.

3

1S :11354 l 1985

0.5 In the pre aration of this standard considerable assistance had beenEderived from t e IEC publication 152( 1963 ) Identification by hour

numbers of the phase conductors of 3-phase electric systems, issued bythe International Electrotechnical Commission ( IEC ).

1. SCOPE

1.1 This standard covers recommendations on identification of phaseconductors of 3-phase systems by the use of hour ( clock-face ) numbers.

2. BASIS OF THE NUMBERING

2.1 Each conductor of the network or group of networks receives anumerical index and the number chosen applies to all conductors of thesame phase.

Only conductors of the same number can be connected together.

2.2 An angle of phase difference of 30 electrical degrees is taken as a unitfor the purposes of the marking, this angle corresponding to the actualangle through which the hour hand of a clock travels in moving fromone hour to the next. (This system is already in use for indicating thephase shift introduced by the winding interconnections in powertransformers ).

Twelve hour numbers are possible, from 1 to 12, or if necessaryfrom Oto 11.

NOTE Quite clearly it is equivalent to write O [ that is zero phase difference)or 12 ( that is, 360 phase difference ). In general, it is immaterial if one writes eitherof these two numbers. There are cases, however, where one of them is to be pre-ferred, For example, the number 12 is necessary when the figure O or the letter Ohave already been given another meaning, as neutrai conductoti on the other hand,the figure O may be considered preferable when this risk of ambigui ty does notexist. In the remainder of this text the notation 12 (0) is used.

Thus, the three conductors forming a 3-phase group have indices differing fromeach other by four units ( equivalent to 120 electrical degrees ), for example4-8-12(0) or 3-7-11.

2.3 The lagging voltage conductor is indicated by the Iarger hournumber; thus, the voItage of a conductor numbered 8 attains its maxi-mum value 120 electrical degrees behind that of the conductornumbered 4.

2.4 The conductors connected to the terminals of the respective windingsof a power transformer, which are characterized by the same phaseletter must carry hour numbers which differ by an amount equal to thehour number of the transformer.

4

IS : 11354 - 1985

If the alphabetical sequence of the phase letters of the high-voltage terminals is the same as the phase sequence ( that is, if the terminals A, B and C are connected to conductors carrying numbers increasing by 4 and 4 ), the markings of the lower voltage conductors are obtained by adding the hour number of the transformer connection to the hour numbers of the high-voltage conductors.

Thus, if the terminals A, B and C of a star-delta connected transformer with an hour number 11 are connected respectively to con- ductors 12( 0 )-4-8 on the high-voltage side, the low-voltage coductors, connected to a, b and c will carry the numbers 11-3-7 ( the addition of 11 being equivalent to subtracting 1 ).

Conversely, if the alphabetical sequence of the phase letters of the high voltage terminals is opposite to the phase sequence ( that is if the terminals A, B and C are connected respectively to conductors carrying numbers decreasing by 4 and 4 ), the markings of the low-voltage termi- nals are obtained by subtracting the hour number of the transformer connection from the hour numbers of the high-voltage conductors.

Thus, if the terminals A, B and C of a star-delta connected transformer with the hour number 11 are connected to conductors 12( O)- 8 and 4 on the high-voltage side, the low-voltage conductors, connected to the terminals a, b and c will carry the numbers l-9-5 ( the subtraction of 11 being equivalent to the addition of 1 ).

These examples show that with a transformer with hour number 11 ( and it would be the same with a transformer with hour number 1 ) it is possible to connect a 4,8, 12( 0 ) system both to a 1, 5, 9 system and to a 3, 7, 11 system provided that in one of the two cases the sequence of the terminal in relation to the phase sequence is reversed.

2.5 The coherence of the hour numbers between all the interconnected networks, or between those which are to be interconnected in the future, is assured by giving the hour number 12( 0 ) to one of the conductors of all very-high-voltage networks in which the windings are star-connected.

NOTE - The latter assumption is based on the following considerations:

a) Generally, the windings of transformers connected to very-high-voltage systems are star-connected, and, if in the future, still higher voltages be used, the windings for those new voltages will also probably be star-connected. The direct couplings between all these systems are made or will then be made without any phase shift and, consequently, it is desirable to design them from the beginning with the same hour numbers. The hour numbers 4, 8, 12(O) have been chosen because they have been used from the beginning for these very-high-voltage systems in the countries which have already adopted identification by means of hour numbers.

b) If an existing coupling between these very-high-voltage systems has been made through a lower voltage system, it is always possible in practice to arrange a direct coupling that is one without phase shift, between the high-voltage system.

5

IS:l1354-1985

Hence, it is always possible in practice to use the hour numbers 4, 8, 12( 0 ) for the conductors of all very-high-voltages networks of voltage greater than approximately 100 kV. Naturally, the choice of the con- ductor 12( 0 ) for one of the systems requires all the systems already interconnected to be numbered one after the other. As to those which are not yet interconnected, it will be necessary, as the need arises, to interconnect them by connecting conductors of the same hour number together.

3. LOCATION OF HOUR NUMBERS

3.1 The hour numbers are in general not carried by the conductors themselves, but are conveniently placed in their neighbourhood.

3.2 It is also convenient to mark the measuring and protective devices with the hour numbers of the corresponding phases.

tt: ( Reaffirmed 2002 )