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है”ह”ह

IS 9678 (1980): Methods of measuring temperature rise ofelectrical equipment [ETD 1: Basic ElectrotechnicalStandards]

Is t 9678- 19s0

Indian Standard(~ed 1987)

( Reaffirmed 1999)

&fBTHODS OF MEASURING TEMPERATURE-RISEOF ELECTRICAL EQUIPMENT

( First Reprint APRIL 1992)

UDc 622.31 :621.317 .39[536.5]

@CO&mg& 1981

BUREAU OF INDIAN STANDARDS&fANAK BHAVAN, 9 BAHADIJR SHAH ZAFAR MARG

N8WDELH111LXXZ

Gr 2 @ii1981

IS : 9678 - 1980

Indian Standard METHODS OF MEASURING TEMPERATURE-RISE

OF ELECTRICAL EQUIPMENT

Electrotechnical Standards Sectional Committee; ETDC 1

Chainnan RCptWltiltg SH~I J. S. ZAVERI Bharat Bijlee Ltd, Bombay

Members SH~I V. K. BATRA

SHFKI T. L. BEATIA

SHRI J. M. NEOQY ( AJhwuzfs ) SHRI V. S. BHATIA

Nati;ozii Physical Laboratory ( CSIR), New

Indian Posts and Telegraphs Department ( Ministry of Communications ), New Delhi

BRIQ N. DAYAL COL K. V. KUDVA ( Ahnatr )

DIRECTOR STANDARDS ( ELECTRICAL )

D~EOTOB ( TED )

Low Voltage Switchgear and Controlgear Sectional Committee, ETDC 57, IS1

Ministry of Defence ( DC1 )

Research, Designs & Standards Organization, Lucknow

Central Electricity Authority ( Department of Power ) ( Ministry of Energy ), New Delhi

DEPUTY D~ECTOB ( TED ) ‘~ltcmuta ) S-1 M. L. Do~+~RE Power Cables Sectional Committee. ETDC 59.

ISI SERI R. D. JAIN Conducton and Accessories for Overhead Lines

SEBI S. K. KASIJWAL Sectional Committee, ETDC 66, IS1

Bharat Heavy Electricals Ltd, Bhopal SH~I P~AKASE SIN& ( Alternate )

SHF.I S. K. MTJKHEKJ~ZE National Test House, Calcutta SH~I B. MUKEOPADHYAY ( Alternate )

SEBI D. V. NARKE Srtm N. NATE

Transformers Sectional Committee, ETDC 16, IS1

SRRI H. M. PA1 Relays Sectional Committee, ETDC 35, IS1 High Voltage Switchgear and Controlgear

SHSI D. N. PURANDARE Sectional Committee, ETDC 58, IS1

Electrical Wiring Accessories Sectional Com-

SEBI S. G. RAMAOEANDRA

SERI V. L. SAS~RY

mittee, ETDC 44, IS1 Rotatin

ET d Machinery Sectional Committee,

C 15, IS1 Electronics and Radar Development Ettabliih-

Srxn~ K. V. BEAT ( Altmzatc ) m&t ( Ministry of Defence ), Bangalore

( Continued on pcrgs 2

0 afiyright 1981 BUREAU OF INDIAN STANDARDS

‘IX publication is protected under the Indian CopyIight Act ( XIV of 1957) and

reproduction in whole or in part by any means except with written permission of the publiiha shall be deemed to be an infringement of copyright under the said Act.

IS I 9678 - 1980

( Continuedfrom p~gr 1 )

iuembers R9prescnting

DE S. M. Slnr Institution of Engineers ( India ), Calcutta DB H. V. K. UDUPA Secondary Cells and Batteries Sectional Com-

mittee, ETDC Ii, IS1 S-1 H. n’. V~KOS~ RAO Central Electrochemical Raearch Institute

Smx Y. MAIUDEVA IY~ ( Alternate) ( CSIR ), Karaikudi

+%a%~ M. P. WAGE Indian Electrical Manufacturers’ Association,

S~BI S. D. M~GDXEKAR ( Ahmate) Bombay

SEBI s. P. SAOEDXV, Director General, IS1 ( Ex-&io Member ) Director ( Elec tech j ( SecWqy )

2

I81!#678-1986

Indian Standard METHODSOFMEASURINGTEMPERATURE-RISE

OFELE~TRI~ALBQUIPMI~NT

0. FOREWORD

0.1 This Indian Standard was adopted~ by the Indian Standards Institution on 18 December 1980, after the draft finalized by the Electrotechnical Standards Sectional Committee had been approved by the Electrotechnical Division Council.

0.2 The safe and reliable operation of an electrical equipment is achieved by ensuring amongst other things that under normal conditions of operation, the steady state temperature of the equipment is maintained within limits for which the electrical insulation is designed. This factor ultimately decides the safe current (rated current) which can pass through the equipment without the temperature of the insulation exceeding the safe limits.

0.3 Indian Standards on the various electrical equipment specify the permissible limits of temperature-rise of the parts of equipment and the precise method to ensure that the temperature is within the safe limits. This standard has been brought out with a view to provide detailed guidelines on the methodology to be adopted while carrying out the temperature-rise test. This would also avoid the necessity of repeating the details of test method in individual standards.

0.4 While this standard covers all the three recognized methods, the choice of a particular method depends on several factors, individual specifications hence would stipulate the most appropriate method(s) for the equipment under test as well as guidelines on the application of the limits of temperature-rise specified for the same.

0.5 While employing the methods described in this specification, it is emphasized that the precautions mentioned therein shall be adhered to in view of the accuracy desired as well as the safety of the measuring device. Additional precaution shall have to be observed as indicated in indivi- dual specifications, depending on the specific nature of the equipment.

0.6 It is not intended to imply that measurements by more than one method shall he required for a single check of the temperature and the

3

IS : 9678 - 1980

results obtained by one method are to be used as a check against those by another. However, if the.purchaser wishes to have readings taken by more than one method, it shall be noted that the methods are reliable and accurate in the order given below:

a) Embedded temperature detector method,

b) Resistance method, and

c) Thermometer method.

0.7 This standard does not provide guidelines on the method of measuring the ambient temperature which are covered separately in IS : 3599-1966*.

0.8 This standard shall be read in conjunction with IS : 9677-19807.

0.9 For the purpose of deciding whether a particular requirement of this standard is complied with, -the final value, observed or calculated, expressing the result of a test, shall be rounded offin accordance with IS : 2-1960:. The number of significant places retained in the rounded off value should be the same as that of the specified value in this standard.

1. SCOPE

1.1 This standard specifies the methods ofmeasurement of temperature- rise in electrical equipment. . This standard also specifies the different precautions to be observed while adopting these methods.

2. METHODS OF MEASUREMENT OF TEMPERATURES

2.0 General-The following three methods of determining the temperature of windings and other parts are recognized:

a) Thermometer method,

b) Resistance method, and

c) Embedded temperature detector ( E.T.D. ) method. N~rs 1 -‘The term thermometrr also includes non-embedded thermocouples

and resistance-thermometers, provided they are applied to the points accessible to the usual bulb-thermomctcrs.

- *Method of measurement of cooling medium temperature for electrical apparattls. TGuide for limits of temperature-rise of the windings of electrical eqrtipment when

tested by different methods. :;li~rlcs for rounding off rumerical valoes (re&d).

4

ISt9678-1980

Norm 2 -~Reristaace method is also known = self-resistance method.

NOTE 3 --Embedded temperature detectora are resistance thermometera or tkermocoupla built into the part of the electrical equipment during construction at points which are inacceuible after completion.

2.1 Thermometer Method

21.1 Three types of thermometers are normally employed, namely, bulb thermometer containing mercury or alcohol and resistance thermometers.

2.1.2 When bulb, thermometers are employed in places where there is strong varying or moving magnetic field, alcohol thermometers should be used in preference to mercury thermometers.

21.3 When a thermometer is used to measure ‘the temperature of a surface, such as that of a coil, the bulb shall be surrounded by a single wrapping of tin-foil having a thickness of not less than 0.095 mm. The foil shall be turned up at the end to form a complete covering for the bulb and shall then be secured in contact with the surface under test. The exposed part of the wrapped bulb shall be completely covered with a pad of heat-insulating material without unduly shielding the test surface from normal cooling.

21.4 When a thermometer is used to measure the temperature of a resistor, the bulb shall not be wrapped with tin-foil.

2.1.5 For the purpose of determining the temperature of windings by the thermometer method, reference shall be made to the following standards regarding accuracy of instruments, further precautions in use if any, etc:

a) IS : 2gO6- 1964 ‘ Methods of temperature measurement by electrical resistance thermometers ‘;

b) IS : 4825-l 968 ‘ Laboratory and reference thermometers ‘; and

c) IS : 8787-1977 ‘ Principles of design, construction and use of liquid-in-glass thermometers ‘.

2.2 Resistance Method

2.2.1 In this method the temperature-rise of the windings is determined by the increase in the resistance of the windings.

5

X8:9678-1980

2.2.2 D&&nation of Ttmpcrature-R&e of Co#wr Windings from Increase in Resistance - The final temperature of the winding ( t; ) at the end of the test and hence the temperature-rise ( ts - ta ) may be obtained from the ratio of the resistance by the formula:

te+ 235 Rn tl+ 235 =-%-

wht?re

ta = temperature in degrees centigrade of the winding at the end of the test,

R s = resistance of the winding at,the end of the test, tI = temperature in degrees centigrade of the winding ( cold)

the moment of the initial. resistance measurement, and

RI = initial resistance of the winding ( cold).

For practical purposes, the following simplified formula may be found convenient:

4 - to = Ra-RI Rl (235+t,)+t, -t*

where

ta = temperature ( “C ) of cooling medium at the end of the test.

When the temperature of a winding is to be determined by resistance, the temperature of the winding before the test, measured by thermometer, shall be practically that of the coolitig medium.

NOTE 1 - For materials other than copper, replace’ the figure 235 in the above formulae with the reciprocal of the temperature coefficient of resistance at 0% for the material.

NOTE 2 -The simplified formula is based on the assumption that every 0.4 percent increase in resistance amounts to 1°C rise in temperature. Strictly speaking, such aq assumption is correct only, if the cold resistance &is measured approxi- mately at + 16°C. However, the inaccuracy will not be much as long as the corresponding’temperature lies within + 10°C and + 40°C.

2.2.3 Unlike the other methods, the method depending on self- resistance measures the average temperature-rise of the whole winding as contrasted with the temperature at the surface or other isolated point.

2.3 Embedded Temperature Detector ( E.T.D. ) Method

2.3.1 This method employs requisite number of detectors suitably distributed in the part of the electrical equipment built into it while I construction. All reasonable efforts, consistent with safety shall be made

G

Is : 9678 - 1966

to place the detectors at the various points at which the highest temperatures are likely to occur in such a manner that they are effectively protected from contact with the cooling medium.

2.3.2 The exact location of the detectors and their number shall be as dictated by the size and specific details of the e uipment or part under measurement. Specific guidelines on these sh & be as specified in the relevant standards.

2.23 ‘Ilrermocou~le as Embedded Detector

23.3.1 The two conductors between which the thermoelectric effect is produced shall be soldered or welded at both the hot and the cold

junctions.

2.3.3.2 When applied to the surface of the live conductors, the hot junction is covered with insulation, and shall be wrapped with tin-foil as described for bulb thermometers. The thermocouple circuit should be earthed to minimize the possibility of capacity currents.

2.3.3.3 The protecting pad of heat insulating material specified in 23.3.2 shall be employed whether the junction is insulated or not.

23.3.4 The cold junction shall be immersed in oil, preferably contained in a vacuum flask; the temperature of which is measured by means of a thermometer.

23.3.5 When the thermocouple is used to measure the temperature of a resistor, both the tin-foil wrapping and the pad shall be omitted.

23.3.6 For the puposes of determining the temperature of windin using thermocouple as embedded detector, reference shall also be ma B e to IS: 7356-1974* regarding selection of the proper thermocouple, accuracy desired, etc.

23.4 Resistance Thermometer as Embed&d Detector

2.3.4.1 The precautions applicable for thermocouples are generally applicable for resistance thermometers also. Special, precautions to be observed, if any, shall be as indicated in the relevant standards (see &o 21.5 ).

‘Soon for themlocouples.

7

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