Is 5621 Spec for Hollow Insulators

IS : 5621 - 1980 (Reaffirmed 2004)

Edition 2.2 (1987-01)

Indian Standard SPECIFICATION FOR HOLLOW INSULATORS FOR USE IN ELECTRICAL EQUIPMENT

( First Revision ) (Incorporating Amendment Nos. 1 & 2)

UDC

621.315.62-46 : 621.315.612

© BIS 2005 BUREAU

OF

INDIAN

STANDARDS

MANAK BHAVAN , 9 BAHADUR SHAH ZAFAR MARG NEW DELHI 110002

Price Group 6

IS : 5621 - 1980

Indian Standard SPECIFICATION FOR HOLLOW INSULATORS FOR USE IN ELECTRICAL EQUIPMENT

( First Revision ) Electrical Insulators and Accessories Sectional Committee, ETDC 3 Chairman Representing Central Electricity Authority, New Delhi SHRI L. C. JAIN Members DIRECTOR (TRANSMISSION) ( Alternate I to Shri L. C. Jain ) DEPUTY DIRECTOR (SUBSTATION) ( Alternate II to Shri L. C. Jain ) All India Pottery Manufacturers’ Association, SHRI B. C. BANERJEE Calcutta SHRI N. K. GUHA ( Alternate ) Bengal Potteries Ltd, Calcutta SHRI CHANDER PARKASH SHRI S. C. SEN ( Alternate ) SHRI D. S. CHABHAL Directorate General of Technical Development, New Delhi Tag Corporation, Madras SHRI R. T. CHARI SHRI A. GURUPATHAM ( Alternate ) Tamil Nadu Electricity Board, Madras SHRI K. S. CHELLAPPAN SHRI N. R. SANKARAN ( Alternate ) Punjab State Electricity Board, Patiala SHRI A. K. CHOPRA SHRI NIRVAIR SINGH ( Alternate ) Damodar Valley Corporation, Calcutta SHRI A. N. DEB SHRI A. C. BOSE ( Alternate ) DIRECTOR OF RESEARCH (T & D) Maharashtra State Electricity Board, Bombay D I R E C T O R (TRACTION AND Research, Designs and Standards Organization (Ministry of Railways), Lucknow INSTALLATION) JOINT DIRECTOR STANDARDS (TI) ( Alternate ) Karnataka Electricity Board, Bangalore SHRI H. M. S. LINGAIAH Mysore Porcelains Ltd, Bangalore SHRI G. S. MAHAGAONKAR National Test House, Calcutta SHRI S. K. MUKHERJEE SHRI U. S. VERMA ( Alternate ) Indian Electrical Manufacturers’ Association, DR G. M. PHADKE Bombay SHRI P. RAMACHANDRAN ( Alternate ) ( Continued on page 2 ) © BIS 2005 BUREAU OF INDIAN 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 : 5621 - 1980 ( Continued from page 1 ) Members SHRI J. M. PRANJPAY

Representing Directorate General of Posts New Delhi

and

Telegraphs,

SHRI T. L. BHATIA ( Alternate ) SHRI P. S. RAMAN NGEF Limited, Bangalore SHRI E. P. WILFRED ( Alternate ) SHRI R. SUBBA RAO Bharat Heavy Electricals Ltd, Bhopal SHRI M. L. MITTAL ( Alternate I ) SHRI D. N. NAIDU ( Alternate II ) SHRI M. SANKARALINGAM Directorate General of Supplies & Disposals, New Delhi DEPUTY DIRECTOR OF INSPECTION ( Alternate ) SHRI P. K. SAXENA Rural Electrification Corporation Ltd, New Delhi SHRI G. L. DUA ( Alternate ) SHRI N. S. SEETHURAMON W. S. Insulators of India Ltd, Madras SHRI V. SRINIVASAN ( Alternate ) Electro Metal Industries, Bombay SHRI R. D. SHETH SHRI V. VENUGOPALAN ( Alternate ) DR U. S. SINGH High Tension Insulator Factory, Ranchi SHRI A. D. DUA ( Alternate ) SHRI SURENDRA SINGH U.P. Government Pottery Development Centre, Khurja SHRI T. B. L. SRIVASTAVA ( Alternate ) SHRI L. VENKATESUBBU Seshasayee Industries Ltd, Vadalur South Arcot District SHRI R. V. ACHUTHAN ( Alternate ) SHRI S. P. SACHDEV, Director General, ISI ( Ex-officio Member ) Director (Elec tech) Secretaries SHRI R. K. MONGA Deputy Director (Elec tech), ISI SHRI R. S. SARMA Assistant Director (Elec tech), ISI

Panel for Dimensions of Bushings, ETDC 3 : P3 Convener SHRI V. SRINIVASAN W. S. Insulators of India Ltd, Madras Members SHRI K. N. JAYARAM Mysore Porcelains Ltd, Bangalore SHRI S. V. MANERIKAR Crompton Greaves Ltd, Bombay SHRI M. L. MITTAL Bharat Heavy Electricals Ltd, Bhopal SHRI S. P. SINGH ( Alternate I ) SHRI B. KRISHNAMURTHY ( Alternate II ) SHRI R. G. PRADHANANI Bharat Bijlee Ltd, Bomaby SHRI P. RAMACHANDRAN Transformers & Electricals Kerala Ltd, Angamally South P.O. SHRI KURIAKOSE ANTONY ( Alternate ) SHRI P. S. RAMAN NGEF Limited, Bangalore DR U. S. SINGH High Tension Insulator Factory, Ranchi SHRI A. D. DUA ( Alternate )

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IS : 5621 - 1980

Indian Standard SPECIFICATION FOR HOLLOW INSULATORS FOR USE IN ELECTRICAL EQUIPMENT

( First Revision ) 0. F O R E W O R D 0.1 This Indian Standard (First Revision) was adopted by the Indian Standards Institution on 29 October 1980, after the draft finalized by the Electrical Insulators and Accessories Sectional Committee had been approved by the Electrotechnical Division Council. 0.2 The object of this standard is to prescribe methods of test and acceptance criteria for hollow insulators for use in electrical equipment. This standard does not specify impulse voltage or power frequency voltage type tests as the withstand voltages are not characteristics of the hollow insulator itself, but of the apparatus of which it ultimately forms a part. 0.3 This standard was first issued in 1970 and covered the requirements of large hollow porcelains only. This revision has been undertaken for inclusion of the requirements of small hollow insulators in this standard. 0.4 In the preparation of this standard, assistance has been derived from IEC Publication 233 (1974) ‘Tests of hollow insulators for use in electrical equipment’ issued by the International Electrotechnical Commission. 0.5 This edition 2.2 incorporates Amendment No. 1 (July 1983) and Amendment No. 2 (January 1987). Side bar indicates modification of the text as the result of incorporation of the amendments. 0.6 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 off in 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 covers the requirements of insulating shrouds, weather shields and containers made of ceramic material and applies before any metal fittings are attached to them. These components are collectively referred to in this standard as hollow insulators. They are intended for use in electrical equipment operating on alternating current at a frequency not greater than 100 Hz or direct current. *Rules for rounding off numerical values ( revised ).

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IS : 5621 - 1980 1.1.1 A hollow insulator consists of a single insulating element or of several parts permanently joined together. NOTE 1 — The hollow insulators covered by this standard consist of hollow bodies, open from end to end with or without sheds, intended for use in electrical equipment such as of the following types: a) b) c) d) e) f) g)

Instrument transformers, Lightning arresters, Capacitors, Bushings, Cable sealing ends, Circuit-breakers, and Cable sealing boxes.

NOTE 2 — Hollow insulators are characterized by their shape and the dimensions given on the relevant drawings.

2. TERMINOLOGY 2.0 For the purpose of this standard, the following definitions shall apply. 2.1 Lot — All the hollow insulators of the same type and design manufactured under similar conditions of production, offered for acceptance; a lot may consist of the whole or part of the quantity offered. 2.2 Type Tests — Tests carried out to prove conformity with the specification. These are intended to prove the general qualities and design of a given type of hollow insulator. 2.3 Acceptance Tests — Tests carried out on samples taken from a lot for the purpose of acceptance of the lot. 2.4 Routine Tests — Tests carried out on each hollow insulator to check requirements which are likely to vary during production. 3. TESTS 3.1 General 3.1.1 Type Tests — The hollow insulators shall be subjected to the following type tests: a) b) c) d) e)

Visual inspection (3.2), Electrical routine test (3.3), Verification of dimensions (3.4), Porosity test (3.5), and Temperature cycle test (3.6).

NOTE 1 — For certain applications, hollow insulators may have to be submitted to other tests, for example, internal pressure tests or bending tests. Such tests should always be the subject of agreement between the manufacturer and the purchaser and will generally be considered as additional tests and not replacements for the normal

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IS : 5621 - 1980 tests listed above. Although the scope of this standard is limited to hollow insulators before the metal fittings are attached, these special tests may have to be done after the attachment of the metal fittings. Attention is drawn to the risk that excessive loads in these special tests may adversely affect the performance of insulators in service. In general, routine test loads should not exceed 70 percent of the minimum failing load. NOTE 2 — Type tests are normally made once and unless otherwise agreed to, test certificate giving the results of type tests, made on not less than three hollow insulator, identical in all essential details with those to be supplied, are regarded as evidence of compliance. NOTE 3 — Type tests shall be made and certified by the manufacturer or by an agreed independent authority. NOTE 4 — Type tests shall be made on the hollow insulator that has passed the routine tests.

3.1.2 Acceptance Tests — The acceptance tests shall comprise of the following: a) Verification of dimensions (3.4), b) Porosity test (3.5), and c) Temperature cycle test (3.6). 3.1.2.1 The acceptance tests are made on a small number of hollow insulators selected from the lot after passing the routine tests. The recommended sampling scheme shall be as given in Appendix A. 3.1.3 Routine Tests — The following shall be carried out as routine tests on every hollow insulator: a) Visual inspection (3.2), b) Electrical routine test (3.3), and c) Verification of important dimensions (3.4) ( see Note ). NOTE — In special cases, the verification of certain dimensions should be a routine test. In such cases, the relevant drawing or the order should specify which. dimensions are to be verified as a routine test.

3.2 Visual Inspection 3.2.1 The glaze shall be smooth and free from any faults prejudicial to satisfactory performance in service. The colour shall be as specified on the drawing, but small variations in colour shall be permitted and shall not constitute cause for rejection. 3.2.2 Glazed and unglazed areas shall be in accordance with the drawing. 3.2.3 In general, glaze faults which affect only the appearance of a hollow insulator shall be permitted on the parts visible in service, if: D .L a) their total surface area is less than: 100 + --------------- mm2, 1 000 D .L b) the area of a single glaze fault is less than: 50 + ------------------ mm2 10 000 5

IS : 5621 - 1980 where D = greatest external diameter over the sheds, and L = height of the hollow insulator (each expressed in millimetres). 3.2.4 The total area of glaze fault permitted by the formula given above may not be acceptable if the faults are concentrated in groups which unduly affect the appearance. In such cases, high resistance coating may be applied to the insulator to restore its appearance. The coated hollow insulators may be accepted if it withstands the electrical routine test (3.3) satisfactorily. 3.2.5 For certain hollow insulators, it may be specified at the time of ordering or on the drawing that glaze faults on the surfaces not visible in service shall be in accordance with special requirements or, alternatively, that the above requirements for external surfaces shall apply also to internal surfaces. In the latter case, D shall be taken as the greatest inside diameter of the hollow insulator (expressed in millimetres). 3.3 Electrical Routine Test 3.3.1 This test is intended to verify the soundness of the wall of the hollow insulator by means of a voltage applied between internal and external electrodes. 3.3.2 The internal electrode shall be one of the following types: Water, filling the hollow insulator, bottom end of which has been closed; or A conductor applied to the internal profile. 3.3.3 The external electrode may consist of ribbons of damp cloth or any other conductor (chains, wires, etc) placed on the external wall as considered necessary and particularly at any joints made during manufacture. 3.3.4 An alternating voltage with a frequency in the range of 15 Hz to 100 Hz shall be applied between the internal and external electrodes. Its value shall be equal to 1.5 kV rms per millimetre of wall thickness of the hollow insulator at its thinnest point, with a minimum of 35 kV. This voltage shall be maintained for 5 minutes. 3.3.5 For small hollow insulators, the minimum voltage of 35 kV may not always be applicable because of flashover. In such cases, the highest practicable voltage shall be applied. 3.3.6 Any insulator which punctures during the test shall be eliminated. NOTE — When a hollow insulator does not contain any joints made before or after firing, for example, when it is manufactured solely by extrusion, the electrical routine test may be eliminated by agreement between the manufacturer and the purchaser.

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IS : 5621 - 1980 3.4 Verification of Dimensions 3.4.1 The dimensions shall conform with the values indicated on the drawing. 3.4.2 Unless otherwise specified, the tolerance on each dimension shall be: ± (0.04 d + 1.5) mm, where d is equal to or less than 300 ± (0.025 d + 6) mm, where d is greater than 300 d being the value expressed in millimetres, on the drawing for the dimension concerned. NOTE — If a minimum creepage distance is specified on the drawing, it should be considered as the minimum value to be obtained in measurements on the insulators. If the creepage distance is specified as a nominal value, the negative tolerance stated above will apply.

3.4.3 The tolerances on diameter of upper and lowest ends, wall thickness and ground portion are given in Appendix B. The permissible limits of out of roundness of inside and outside diameters (also known as ovality), camber, tilt of shed and sand band, lean and parallelism of ground surfaces and finish are also given in Appendix B. 3.5 Porosity Test 3.5.1 Verification of the absence of porosity shall be carried out: a) on control blocks of the same ceramic composition as the hollow insulator, fired adjacent to it, in the position considered by the manufacturer to be the region of minimum temperature; b) or by agreement between manufacturer and purchaser on pieces of representative thickness cut from the hollow insulator during grinding; and c) or on pieces from a hollow insulator of the same batch rejected for other reasons or broken during test. 3.5.2 The pieces used for the porosity test shall be representative of the batch of hollow insulators and their minimum dimensions shall approximate to the thickness defined in Table 1. 3.5.3 The test pieces shall be broken into fragments which shall be immersed in a 1 percent alcohol solution of fuchsin (1 g fuchsin in 100 g methylated spirit). The solution shall be maintained at a pressure not less than 15 × 106 N/m2 during a time such that the product of the test duration in hours and the test pressure in newtons per square metre is not less than 180 × 106. 3.5.4 The fragments shall then be removed from the solution, washed, dried and again broken. 3.5.5 Examination with the naked eye of the freshly broken surfaces shall not reveal any dye penetration. Penetration into small cracks formed during the initial breaking of the test specimen shall be neglected. 7

IS : 5621 - 1980 3.6 Temperature Cycle Test 3.6.1 The hollow insulator initially at ambient temperature shall be quickly immersed, without being placed in an intermediate container, in a water-bath maintained at a temperature tºC above that of the cold water and shall remain submerged for a period of 15 + 0.7 m minutes with a maximum of 30 minutes ( m being the mass of the hollow insulator in kilograms ). It shall then be withdrawn and quickly immersed in the bath of cold water where it shall remain submerged for the same number of minutes. 3.6.2 This heating and cooling cycle shall be performed three times in succession. The time taken to transfer from one bath to another shall be as short as possible. 3.6.3 The temperature difference t is given in Table 1 as a function of the dimensions of the hollow insulator. This temperature difference may be marked on the drawing. TABLE 1

TEMPERATURE DIFFERENCE FOR TEMPERATURE CYCLE TEST

D2L mm3 × 10–6 (1) D2L≤164 164