© BIS 2005

B U R E A U O F I N D I A N S T A N D A R D SMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

IS : 5621 - 1980(Reaffirmed 2004)

Edition 2.2(1987-01)

Price Group 6

Indian StandardSPECIFICATION FOR

HOLLOW INSULATORS FOR USE IN ELECTRICAL EQUIPMENT

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

UDC 621.315.62-46 : 621.315.612

IS : 5621 - 1980

© BIS 2005

BUREAU OF INDIAN STANDARDS

This publication is protected under the Indian Copyright Act (XIV of 1957) andreproduction in whole or in part by any means except with written permission of thepublisher shall be deemed to be an infringement of copyright under the said Act.

Indian StandardSPECIFICATION FOR

HOLLOW INSULATORS FOR USE IN ELECTRICAL EQUIPMENT

( First Revision )

Electrical Insulators and Accessories Sectional Committee, ETDC 3

Chairman RepresentingSHRI L. C. JAIN Central Electricity Authority, New Delhi

MembersDIRECTOR (TRANSMISSION) ( Alternate I to

Shri L. C. Jain )DEPUTY DIRECTOR (SUBSTATION) ( Alternate II to

Shri L. C. Jain )SHRI B. C. BANERJEE All India Pottery Manufacturers’ Association,

CalcuttaSHRI N. K. GUHA ( Alternate )

SHRI CHANDER PARKASH Bengal Potteries Ltd, CalcuttaSHRI S. C. SEN ( Alternate )

SHRI D. S. CHABHAL Directorate General of Technical Development,New Delhi

SHRI R. T. CHARI Tag Corporation, MadrasSHRI A. GURUPATHAM ( Alternate )

SHRI K. S. CHELLAPPAN Tamil Nadu Electricity Board, MadrasSHRI N. R. SANKARAN ( Alternate )

SHRI A. K. CHOPRA Punjab State Electricity Board, PatialaSHRI NIRVAIR SINGH ( Alternate )

SHRI A. N. DEB Damodar Valley Corporation, CalcuttaSHRI A. C. BOSE ( Alternate )

DIRECTOR OF RESEARCH (T & D) Maharashtra State Electricity Board, BombayD I R E C T O R (TRACTION AND

INSTALLATION)Research, Designs and Standards Organization

(Ministry of Railways), LucknowJOINT DIRECTOR STANDARDS

(TI) ( Alternate )SHRI H. M. S. LINGAIAH Karnataka Electricity Board, BangaloreSHRI G. S. MAHAGAONKAR Mysore Porcelains Ltd, BangaloreSHRI S. K. MUKHERJEE National Test House, Calcutta

SHRI U. S. VERMA ( Alternate )DR G. M. PHADKE Indian Electrical Manufacturers’ Association,

BombaySHRI P. RAMACHANDRAN ( Alternate )

( Continued on page 2 )

IS : 5621 - 1980

2

( Continued from page 1 )

Members RepresentingSHRI J. M. PRANJPAY Directorate General of Posts and Telegraphs,

New DelhiSHRI T. L. BHATIA ( Alternate )

SHRI P. S. RAMAN NGEF Limited, BangaloreSHRI E. P. WILFRED ( Alternate )

SHRI R. SUBBA RAO Bharat Heavy Electricals Ltd, BhopalSHRI 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 )SHRI R. D. SHETH Electro Metal Industries, Bombay

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,

KhurjaSHRI T. B. L. SRIVASTAVA ( Alternate )

SHRI L. VENKATESUBBU Seshasayee Industries Ltd, Vadalur South ArcotDistrict

SHRI R. V. ACHUTHAN ( Alternate )SHRI S. P. SACHDEV,

Director (Elec tech)Director General, ISI ( Ex-officio Member )

SecretariesSHRI R. K. MONGA

Deputy Director (Elec tech), ISISHRI R. S. SARMA

Assistant Director (Elec tech), ISI

Panel for Dimensions of Bushings, ETDC 3 : P3

ConvenerSHRI V. SRINIVASAN W. S. Insulators of India Ltd, Madras

MembersSHRI K. N. JAYARAM Mysore Porcelains Ltd, BangaloreSHRI S. V. MANERIKAR Crompton Greaves Ltd, BombaySHRI 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, BomabySHRI P. RAMACHANDRAN Transformers & Electricals Kerala Ltd, Angamally

South P.O.SHRI KURIAKOSE ANTONY ( Alternate )

SHRI P. S. RAMAN NGEF Limited, BangaloreDR U. S. SINGH High Tension Insulator Factory, Ranchi

SHRI A. D. DUA ( Alternate )

IS : 5621 - 1980

3

Indian StandardSPECIFICATION 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 IndianStandards Institution on 29 October 1980, after the draft finalized by theElectrical Insulators and Accessories Sectional Committee had beenapproved by the Electrotechnical Division Council.0.2 The object of this standard is to prescribe methods of test and accep-tance criteria for hollow insulators for use in electrical equipment. Thisstandard does not specify impulse voltage or power frequency voltagetype tests as the withstand voltages are not characteristics of the hollowinsulator itself, but of the apparatus of which it ultimately forms a part.0.3 This standard was first issued in 1970 and covered the requirementsof large hollow porcelains only. This revision has been undertaken forinclusion of the requirements of small hollow insulators in this standard.0.4 In the preparation of this standard, assistance has been derived fromIEC Publication 233 (1974) ‘Tests of hollow insulators for use in electricalequipment’ issued by the International Electrotechnical Commission.0.5 This edition 2.2 incorporates Amendment No. 1 (July 1983) andAmendment No. 2 (January 1987). Side bar indicates modification of thetext as the result of incorporation of the amendments.0.6 For the purpose of deciding whether a particular requirement of thisstandard is complied with, the final value, observed or calculated,expressing the result of a test, shall be rounded off in accordance withIS : 2-1960*. The number of significant places retained in the roundedoff 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 appliesbefore any metal fittings are attached to them. These components arecollectively referred to in this standard as hollow insulators. They areintended for use in electrical equipment operating on alternatingcurrent at a frequency not greater than 100 Hz or direct current.

*Rules for rounding off numerical values ( revised ).

IS : 5621 - 1980

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1.1.1 A hollow insulator consists of a single insulating element or ofseveral parts permanently joined together.

NOTE 1 — The hollow insulators covered by this standard consist of hollow bodies, openfrom end to end with or without sheds, intended for use in electrical equipment suchas of the following types:

NOTE 2 — Hollow insulators are characterized by their shape and the dimensions givenon 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 manu-factured 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 thespecification. These are intended to prove the general qualities anddesign of a given type of hollow insulator.

2.3 Acceptance Tests — Tests carried out on samples taken from alot for the purpose of acceptance of the lot.

2.4 Routine Tests — Tests carried out on each hollow insulator tocheck 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 thefollowing type tests:

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

a) Instrument transformers,b) Lightning arresters,c) Capacitors,d) Bushings,e) Cable sealing ends,f) Circuit-breakers, andg) Cable sealing boxes.

a) Visual inspection (3.2),b) Electrical routine test (3.3),c) Verification of dimensions (3.4),d) Porosity test (3.5), ande) Temperature cycle test (3.6).

IS : 5621 - 1980

5

tests listed above. Although the scope of this standard is limited to hollow insulatorsbefore the metal fittings are attached, these special tests may have to be done after theattachment of the metal fittings. Attention is drawn to the risk that excessive loads inthese special tests may adversely affect the performance of insulators in service. Ingeneral, 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, testcertificate giving the results of type tests, made on not less than three hollowinsulator, identical in all essential details with those to be supplied, are regarded asevidence of compliance.NOTE 3 — Type tests shall be made and certified by the manufacturer or by an agreedindependent authority.NOTE 4 — Type tests shall be made on the hollow insulator that has passed theroutine tests.

3.1.2 Acceptance Tests — The acceptance tests shall comprise of thefollowing:

3.1.2.1 The acceptance tests are made on a small number of hollowinsulators selected from the lot after passing the routine tests. Therecommended sampling scheme shall be as given in Appendix A.3.1.3 Routine Tests — The following shall be carried out as routinetests on every hollow insulator:

NOTE — In special cases, the verification of certain dimensions should be a routinetest. 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 tosatisfactory performance in service. The colour shall be as specified onthe drawing, but small variations in colour shall be permitted andshall 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 ahollow insulator shall be permitted on the parts visible in service, if:

a) Verification of dimensions (3.4),b) Porosity test (3.5), andc) Temperature cycle test (3.6).

a) Visual inspection (3.2),b) Electrical routine test (3.3), andc) Verification of important dimensions (3.4) ( see Note ).

a) their total surface area is less than: mm2,

b) the area of a single glaze fault is less than: mm2

100 D . L1 000---------------+

50 D . L10 000------------------+

IS : 5621 - 1980

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where

3.2.4 The total area of glaze fault permitted by the formula given abovemay not be acceptable if the faults are concentrated in groups whichunduly affect the appearance. In such cases, high resistance coating maybe applied to the insulator to restore its appearance. The coated hollowinsulators 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 ofordering or on the drawing that glaze faults on the surfaces not visiblein service shall be in accordance with special requirements or,alternatively, that the above requirements for external surfaces shallapply also to internal surfaces. In the latter case, D shall be taken asthe greatest inside diameter of the hollow insulator (expressed inmillimetres).3.3 Electrical Routine Test3.3.1 This test is intended to verify the soundness of the wall of the hollowinsulator by means of a voltage applied between internal and externalelectrodes.3.3.2 The internal electrode shall be one of the following types:

Water, filling the hollow insulator, bottom end of which has beenclosed;

orA conductor applied to the internal profile.

3.3.3 The external electrode may consist of ribbons of damp cloth orany other conductor (chains, wires, etc) placed on the external wall asconsidered necessary and particularly at any joints made duringmanufacture.3.3.4 An alternating voltage with a frequency in the range of 15 Hz to100 Hz shall be applied between the internal and external electrodes.Its value shall be equal to 1.5 kV rms per millimetre of wall thicknessof 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 notalways be applicable because of flashover. In such cases, the highestpracticable 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 afterfiring, for example, when it is manufactured solely by extrusion, the electrical routinetest may be eliminated by agreement between the manufacturer and the purchaser.

D = greatest external diameter over the sheds, andL = height of the hollow insulator (each expressed in millimetres).

IS : 5621 - 1980

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3.4 Verification of Dimensions3.4.1 The dimensions shall conform with the values indicated on thedrawing.3.4.2 Unless otherwise specified, the tolerance on each dimension shallbe:

± (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 300d 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 beconsidered 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 statedabove will apply.

3.4.3 The tolerances on diameter of upper and lowest ends, wallthickness and ground portion are given in Appendix B. Thepermissible limits of out of roundness of inside and outside diameters(also known as ovality), camber, tilt of shed and sand band, lean andparallelism of ground surfaces and finish are also given in Appendix B.3.5 Porosity Test3.5.1 Verification of the absence of porosity shall be carried out:

3.5.2 The pieces used for the porosity test shall be representative of thebatch of hollow insulators and their minimum dimensions shallapproximate to the thickness defined in Table 1.3.5.3 The test pieces shall be broken into fragments which shall beimmersed in a 1 percent alcohol solution of fuchsin (1 g fuchsin in 100 gmethylated spirit). The solution shall be maintained at a pressure not lessthan 15 × 106 N/m2 during a time such that the product of the testduration in hours and the test pressure in newtons per square metre isnot 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 shallnot reveal any dye penetration. Penetration into small cracks formedduring the initial breaking of the test specimen shall be neglected.

a) on control blocks of the same ceramic composition as the hollowinsulator, fired adjacent to it, in the position considered by themanufacturer to be the region of minimum temperature;

b) or by agreement between manufacturer and purchaser on piecesof representative thickness cut from the hollow insulator duringgrinding; and

c) or on pieces from a hollow insulator of the same batch rejectedfor other reasons or broken during test.

IS : 5621 - 1980

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3.6 Temperature Cycle Test

3.6.1 The hollow insulator initially at ambient temperature shall bequickly immersed, without being placed in an intermediate container,in a water-bath maintained at a temperature tºC above that of the coldwater and shall remain submerged for a period of 15 + 0.7 m minuteswith a maximum of 30 minutes ( m being the mass of the hollowinsulator in kilograms ). It shall then be withdrawn and quicklyimmersed in the bath of cold water where it shall remain submergedfor the same number of minutes.3.6.2 This heating and cooling cycle shall be performed three times insuccession. The time taken to transfer from one bath to another shall beas short as possible.3.6.3 The temperature difference t is given in Table 1 as a function of thedimensions of the hollow insulator. This temperature difference may bemarked on the drawing.

3.6.4 Alternative Test for Large Hollow Insulators3.6.4.1 For hollow insulators having a height greater than 1 200 mm, thefollowing method of test may, by agreement between the manufacturerand the purchaser, be used instead of the method of test described above.3.6.4.2 The temperature of the hollow insulator shall be raised slowly byany convenient means (circulation of heated air or water, infra red

TABLE 1 TEMPERATURE DIFFERENCE FOR TEMPERATURE CYCLE TEST

TEMPERATURE DIFFERENCE tºC FOR THICKNESS mm

D2L mm3 × 10–6 ≤23 23< ≤26 26< ≤32 32< ≤36 36< ≤43 43<(1) (2) (3) (4) (5) (6) (7)

D2L≤164 60 55 50 45 40 35164<D2L≤410 55 55 50 45 40 35410<D2L≤655 50 50 50 45 40 35655<D2L≤900 45 45 45 45 40 35900<D2L≤1 150 40 40 40 40 40 35

1 150<D2L≤2 000 35 35 35 35 35 35

D2L>2 000 Subject to agreement between the manufacturer and the purchaser.D = the greatest external diameter over the sheds of the hollow insulator, expressed

in millimetres.L = the height of the hollow insulator, expressed in millimetres.

= the greatest thickness of material defined as the diameter, expressed in milli-metres, of the largest circle which can be inscribed in the outline of a sectionthrough the axis of the hollow insulator ( see Fig. 1 ).

NOTE — The temperature differences in Table 1 apply to insulators of parallel or taperedinternal shape which allow free access of water to the interior on immersion. Insulatorsare considered not to offer free access of water if the smallest internal diameter is lessthan 0.25 times the largest internal diameter. In such cases, the value of t shall beagreed between the manufacturer and the purchaser.

IS : 5621 - 1980

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radiation, etc) to a value tºC higher than that of the cold water which islater used to spray it with artificial rain. This temperature shall bemaintained for 15 minutes.

3.6.4.3 The hollow insulator shall then be immediately sprayed withartificial rain at an intensity of about 3 mm per minute and thisspraying shall continue for 15 minutes.

3.6.4.4 This heating and cooling cycle shall be performed three timesin succession. The temperature difference t is given in Table 2 as afunction of the wall thickness as defined above.

3.6.5 The volume of water contained in the baths for tests above shallbe sufficiently great for the immersion of the insulator not to cause avariation of more than ± 5ºC in the temperature of the water.

3.6.6 After the three cycles, the hollow insulator shall show no cracksor damage to the glaze or other faults causing a deterioration in itselectrical or mechanical properties.

3.6.7 The absence, of such deterioration is considered verified if thehollow insulator passes the electrical routine test described in 3.3.

FIG. 1 ILLUSTRATION FOR THICKNESS

TABLE 2 TEMPERATURE DIFFERENCE FOR TEMPERATURECYCLE TEST ON LARGE HOLLOW INSULATORS

THICKNESS TEMPERATURE DIFFERENCE tºC

(1) (2)

≤30 70

>30 50

IS : 5621 - 1980

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3.6.8 A hollow insulator which has successfully passed the temperaturecycle test may be supplied with the rest of the lot for normal service.

4. Clause deleted

A P P E N D I X A( Clause 3.1.2 )

RECOMMENDED SAMPLING PROCEDURE FOR ACCEPTANCE PURPOSE

A-1 SELECTION OF SAMPLES

A-1.1 The hollow insulators shall be selected at random from the lotand in order to ensure the randomness of selection, procedures givenin IS : 4905-1968* shall be followed.

A-2. CRITERION FOR CONFORMITY

A-2.1 The number of hollow insulators to be selected at random in thefirst stage shall be in accordance with col 1 and 3 of Table 3. Each ofthe selected hollow insulators shall be tested for the acceptance tests.If a hollow insulator fails in any one of the acceptance tests, it shall betermed as defective. The lot shall be declared as accepted if thenumber of defectives found in the sample is less than or equal to theacceptance number ( see col 5 ) and shall be rejected if it is greater thanor equal to the rejection number ( see col 6 ). In case the number ofdefectives lies between the acceptance number and rejection number,the second sample of the same size shall be chosen at random andtested. If the number of defectives found in the combined samples isgreater than or equal to the rejection number, the lot shall be rejected;otherwise the lot shall be accepted.

*Methods for random sampling.

TABLE 3 SCALE OF SAMPLING AND PERMISSIBLENUMBER OF DEFECTIVES

LOT SIZE STAGE SAMPLESIZE

CUMULATIVE SAMPLE SIZE

ACCEPTANCE NUMBER

REJECTION NUMBER

(1) (2) (3) (4) (5) (6)2 to 100 First

Second22

24

01

22

101 to 300 FirstSecond

33

36

01

22

301 to 500 FirstSecond

55

510

01

22

501 and above FirstSecond

88

816

01

22

IS : 5621 - 1980

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A P P E N D I X B( Clause 3.4.3 )

TOLERANCES AND PERMISSIBLE LIMITS OF CERTAIN DIMENSIONAL CHARACTERISTICS OF HOLLOW

INSULATORSB-1. GENERAL

B-1.1 The general tolerance formula on dimensions is given in 3.4.2 ofthis standard. However, this formula may not be applicable todimensions like diameter of upper and lower ends, wall thickness andground portion and also does not cover permissible limits of out ofroundness of inside and outside diameters (also known as ovality),camber, tilt of shed and sand band, lean and parallelism of groundsurfaces and finish. The tolerances and permissible limits for thesedimensional characteristics are covered in B-2 to B-8.

B-2. TOLERANCES ON DIAMETER OF UPPER AND LOWER ENDS

B-2.1 Tolerances on diameter of upper and lower ends of hollowinsulators shall be as specified in Table 4 and Fig. 2.

TABLE 4 TOLERANCES ON DIAMETER OF UPPER AND LOWER ENDS

NOMINAL DIAMETER( D, d & )

TOLERANCE

(1) (2)mm mm

0 to 50 ± 2.0Above 50 and up to 75 ± 2.5

,, 75 ,, 100 ± 3.0,, 100 ,, 125 ± 3.5,, 125 ,, 150 ± 4.0,, 150 ,, 175 ± 4.5,, 175 ,, 200 ± 5.0,, 200 ,, 250 ± 5.5,, 250 ,, 300 ± 6.0,, 300 ,, 350 ± 7.0,, 350 ,, 400 ± 8.0,, 400 ,, 500 ± 9.0,, 500 ,, 600 ± 11.0,, 600 ,, 700 ± 13.0,, 700 ,, 800 ± 15.0,, 800 ,, 900 ± 17.0,, 900 ,, 1 000 ± 19.0,, 1 000 ± 2 percent

NOTE — The general tolerances given in 3.4.2 of this standard shall be applicableunless tolerances given in this table are indicated on the drawing.

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B-3. PERMISSIBLE LIMITS OF OUT-OF-ROUNDNESS OF INSIDE AND OUTSIDE DIAMETERS

B-3.1 Permissible limits on out-of-roundness of inside and outsidediameters [also known as ovality] shall be in accordance with Table 5and Fig. 3.

All dimensions in millimetres.

FIG. 2 TOLERANCE ON DIAMETER OF UPPER AND LOWER ENDS

FIG. 3 OUT-OF ROUNDNESS OF INSIDE AND OUTSIDE DIAMETERS ( a — b )

IS : 5621 - 1980

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.

B-4. CAMBER

B-4.1 The camber of a hollow insulator is defined as the maximumdistance between the theoretical, straight, axis A-A of the piece asshown on the drawing and the actual, deformed, axis of the insulator(locus of the centres of transverse cross sections).

B-4.1.1 One method of measuring the camber is as follows:

The hollow insulator is mounted so that it may be rotated about anaxis passing through the centres of the end faces or as close as possibleto these centres. The insulator is then rotated through a completerevolution and the distance from the outer surface of the wall to areference plane parallel to the axis of rotation is measured at variouspoints along the length of the piece. At each point, the differenceXmax- Xmin resulting from a rotation of 180º is determined.

The camber is then given by the maximum value of: ½ ( Xmax- Xmin ).

The camber way conveniently be measured in this way while thehollow insulator is being ground.

TABLE 5 PERMISSIBLE LIMITS OF OUT-OF-ROUNDNESSOF INSIDE AND OUTSIDE DIAMETER

( Clause B-3.1 )

NOMINAL DIAMETERD & d

OUT-OF-ROUNDNESS( a — b )

(1) (2)mm mm

0 to 50 ± 2.0Above 50 and up to 75 ± 2.5

,, 75 ,, 100 ± 3.0,, 100 ,, 125 ± 3.5,, 125 ,, 150 ± 4.0,, 150 ,, 175 ± 4.5,, 175 ,, 200 ± 5.0,, 200 ,, 250 ± 5.5,, 250 ,, 300 ± 6.0,, 300 ,, 350 ± 7.0,, 350 ,, 400 ± 8.0,, 400 ,, 500 ± 9.0,, 500 ,, 600 ± 11.0,, 600 ,, 700 ± 13.0,, 700 ,, 800 ± 15.0,, 800 ,, 900 ± 17.0,, 900 ,, 1 000 ± 19.0,, 1 000 ± 2 percent

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B-4.1.2 Alternatively, the camber may be checked by internal gauges:Since a hollow insulator may have a camber δ up to 0.8 percent ofits length, it follows ( see Fig. 4 ) that the angle between theperpendicular to the deformed axis and the end face after grinding maybe up to 0.032 radians. Thus, the sheds at the ends of the insulator maybe inclined at this angle and the distance H between the end shed andthe ground face of the insulator will vary round the periphery. Theminimum allowable dimension H may be shown on the drawing, takinginto account the dimensions of fittings which are to be attached to theinsulator. To verify the dimension H, Hmax and Hmin shall be measured.The position of the end shed complies with the drawing if the averagevalue of H, that is ½ Hmax + Hmin is within the general tolerances orany special tolerances on dimension H shown on the drawing. Inaddition, the inclination of the end shed shall not be such thatHmax – Hmin exceeds 0.032 D + 3 mm, where D is the nominaldiameter of the end shed, express in millimetres. Similar considera-tions apply to the length of sandglazing and to the height h of aflange at the end of an insulator where the face AB is not ground andthe end face is ground ( see Fig. 5 ).

B-4.2 Camber (δ in Fig. 4) — It shall not be greater than the valuespecified in Table 6 and Fig. 4.

FIG. 4 ILLUSTRATION FOR CAMBER

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B-4.3 The permissible value for the camber shall be subject to specialagreement between the manufacturer and the purchaser if the ratio ofheight to greatest inside diameter of hollow insulator is equal to orgreater than 6, or if the shape of the hollow insulator leads to a specialdifficulty.

B-4.4 A gauge rod of diameter A as shown in Fig. 6 shall be passedthrough the bore of the porcelain and rod should pass freely.

B-4.4.1 The diameter A shall be determined by the following relationin case when centering with the porcelain axis is required:

A = ( D – d ) – 2 δ

B-4.4.2 In case when centering is not required, diameter A shall bedetermined by the following relationship:

A = ( D – d ) – δwhere

A = diameter of gauge rod,

FIG. 5 ILLUSTRATION OF CAMBER IN CASE OF SANDGLAZING

FIG. 6 GAUGING ROD FOR CAMBER

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D = diameter of bore,δ = camber, andd = ± (0.04 d + 1.5) mm where d is equal to or less than 300 mm

( see also 3.4.2).

TABLE 6 CAMBER

( Clause B-4.2 )

NOMINAL HEIGHTL

CAMBER, δ

(1) (2) (3) (4)

mm mm mm mm

0 to 50 1.0 1.0 1.5Above 50 and up to 70 1.2 1.2 1.5

,, 70 ,, 100 1.5 1.5 2.0,, 100 ,, 200 2.0 2.0 3.0,, 200 ,, 300 3.0 3.0 4.0,, 300 ,, 400 4.0 4.0 5.0,, 400 ,, 500 4.0 4.5 6.0,, 500 ,, 600 4.5 5.0 6.5,, 600 ,, 700 5.0 6.0 7.0,, 700 ,, 800 5.0 6.0 8.0,, 800 ,, 900 5.5 7.0 9.0,, 900 ,, 1 000 5.5 7.0 9.0,, 1 000 ,, 1 100 6.0 8.0 10.0,, 1 100 ,, 1 200 6.0 8.0 10.0,, 1 200 ,, 1 300 7.0 9.0 11.0,, 1 300 ,, 1 400 8.0 10.0 12.0,, 1 400 ,, 1 500 9.0 11.0 13.0,, 1 500 ,, 1 800 10.0 12.0 14.0,, 1 800 ,, 2 100 11.0 13.0 15.0,, 2 100 ,, 2 400 12.0 14.0 16.0,, 2 400 ,, 2 700 13.0 15.0 17.0,, 2 700 ,, 3 000 18.0,, 3 000 ,, 3 500 20.0,, 3 500 ,, 4 000 22.0,, 4 000 ,, 4 500 24.0,, 4 500 0.8 percent

*NOTE — Use B1 or B2 whichever is greater.

L

B1* or B2

--------------------------- 2≤ 2 L

B1* or B2

---------------------------- 3≤< 3 L

B1* or B2

--------------------------- 6≤<

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B-5. TOLERANCES ON WALL THICKNESS

B-5.1 Tolerances on wall thickness and differential of wall thickness [ aand ( t1 – t2 ) in Fig. 7 ] shall be in accordance with Table 7 and Fig. 7.

TABLE 7 TOLERANCES ON WALL THICKNESS

NOMINAL WALL THICKNESS TOLERANCES ON WALL THICKNESS (SEE NOTE 2 BELOW)

DIFFERENTIAL OF WALL THICKNESS, ( t1 – t2 )

(1) (2) (3)

mm mm mm

0 to 10 + a– 1.5

1.5

Above 10 and up to 15 + a– 2.0

2.0

,, 15 ,, 20 + a– 3.0

2.5

,, 20 ,, 25 + a– 3.5

3.0

,, 25 ,, 30 + a– 4.0

3.5

,, 30 ,, 40 + a– 4.5

4.0

,, 40 ,, 55 + a– 5.0

4.5

,, 55 ,, 70 + a– 6.0

5.0

NOTE 1 — These tolerances shall not be applied to ground wall.NOTE 2 — Plus side tolerance ‘a’ on all thickness shall be determined by followingequation:

x, y are diameter tolerances on diameter D and d respectively (Fig. 7).

FIG. 7 TOLERANCE OF WALL THICKNESS

a x y+2

------------=

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B-6. TILT OF SHED AND SAND BAND

B-6.1 Tilt of shed and sand band shown in Fig. 8 shall not be greater thanthe value specified in Table 8 and Fig. 8. These shall be determined bythe following relations:

B-6.2 Tilt of Clamping Part — The tilt of clamping part is givenin Fig. 9. The limit of tilt of clamping part shall have the same limitsas for tilt of shed and sand band.

Tilt of shed = h1 Max –h2 Minor h´1 Max –h´2 Min

Tilt of sand band = r1 Max –r2 Minor r´1 Max –r´2 Min

FIG. 8 TILT OF SHED AND SAND BAND

IS : 5621 - 1980

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B-7. TOLERANCES ON GROUND PORTION

B-7.1 Porcelain body may be ground within a tolerance whose minimumis indicated in Table 9, when specially requested by purchaser. Specialattention shall be drawn to the fact that grinding affects tolerances ofinter-relating portions as illustrated in B-7.2, B-7.3 and Fig. 10.

B-7.2 Tolerances r and s ( see Fig. 10A ) shall be determined by usingthe following equations:

where

NOTE — Tilt of clamping part — S1 Max –S2 Min or— S1 Max –S2 Min

FIG. 9 TILT OF CLAMPING PART

r =

s =

( a + b ) = X – H (Divide X – h into a and b properly.)

r and s = tolerances of R and S respectively but minimum 2 mm,

α and = tilts of R and S respectively,

X = general tolerance of H, and

h = required tolerances of H.

a α2---+

b β2---+

IS : 5621 - 1980

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TABLE 8 TILT OF SHED AND SAND BAND

( Clause B-6.1, Fig. 8 )

NOMINAL SHED DIAMETER,, ´, D or D´

TILT OF SHED ANDSAND BAND

(1) (2)

mm mm

0 to 100 4.0

Above 100 and up to 200 5.0

,, 200 ,, 250 6.0

,, 250 ,, 300 7.0

,, 300 ,, 350 8.0

,, 350 ,, 400 8.0

,, 400 ,, 450 9.0

,, 450 ,, 500 10.0

,, 500 ,, 525 11.0

,, 525 ,, 550 12.0

,, 550 ,, 575 13.0

,, 575 ,, 600 14.0

,, 600 ,, 700 15.0

,, 700 ,, 800 16.0

,, 800 ,, 900 17.0

,, 900 ,, 1 000 18.0

,, 1 000 ,, 1 200 19.0

TABLE 9 TOLERANCES ON GROUND PORTION

( Clause B-7.1 )

NOMINAL DIMENSIONS TOLERANCE

(1) (2)

mm ± mm

0 to 100 0.2

Above 100 and up to 250 0.5

,, 250 ,, 500 1.0

,, 500 ,, 1 000 1.5

,, 1 000 ,, 2 500 2.0

,, 2 500 3.0

IS : 5621 - 1980

21

B-7.3 Tolerances a, b, r and s ( see Fig. 10B ) shall be determined byusing the following equation:

where

B-8. FINISH OF GROUND SURFACES

B-8.1 Finish of ground surfaces shall be as specified in Table 10 andFig. 10.

FIG. 10 TOLERANCES OF GROUND PORTION

r =

s =

a + b ≤ h

r and s = tolerances of R and S respectively but minimum 2 mm,α and = tilts of R and S respectively,

ϒ1 and ϒ2 = general tolerances of A and B,a and b = tolerances of A and B respectively,

h = required tolerances of H.

ϒ1 a –( ) α2---+

ϒ2 b –( ) β2---+

IS : 5621 - 1980

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B-8.2 Parallelism and lean of ground portions shall not be greater thanthe value specified in Table 11 and Fig. 11.

TABLE 10 FINISH OF GROUND SURFACE

( Clause B-8.1, Fig. 10 )

FINISH OF GROUND SURFACES APPLICATION

Marking Surface Finish(1) (2) (3)

V Roughness height 25 micron PVA Max Oil-tight sealing portion and generalpurpose

VV Roughness height 12 micron PVA, Max Specially air-tight sealing portion

Waviness height 25 micron PVA, Max

VVV Roughness height 3 micron Specially required portion

Waviness height 8 micron PVA, Max

TABLE 11 FINISH OF GROUND SURFACES

( Clause B-8.2, Fig. 11 )

NOMINAL HEIGHT, H LEAN, a PARALLELISM, b ( See Also Note )

(1) (2) (3)

mm mm mm

0 to 200 0.5 0.4

Above 200 and up to 300 0.8 0.4

,, 300 ,, 400 1.0 0.4

,, 400 ,, 500 1.3 0.4

,, 500 ,, 600 1.5 0.4

,, 600 ,, 700 1.8 0.4

,, 700 ,, 800 2.0 0.4

,, 800 ,, 900 2.3 0.4

,, 900 ,, 1 500 2.5 0.4

,, 1 500 ,, 2 800 3.0 0.4

,, 2 800 ,, 4.0 0.4

NOTE — When special parallelism value below 0.4 mm is required, it shall be subjectso agreement between the manufacturers and the purchasers.

IS : 5621 - 1980

23

FIG. 11 PARALLELISM AND LEAN OF GROUND PORTIONS

Bureau of Indian StandardsBIS is a statutory institution established under the Bureau of Indian Standards Act, 1986 to promoteharmonious development of the activities of standardization, marking and quality certification ofgoods and attending to connected matters in the country.

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Review of Indian StandardsAmendments are issued to standards as the need arises on the basis of comments. Standards are alsoreviewed periodically; a standard along with amendments is reaffirmed when such review indicatesthat no changes are needed; if the review indicates that changes are needed, it is taken up forrevision. Users of Indian Standards should ascertain that they are in possession of the latestamendments or edition by referring to the latest issue of ‘BIS Catalogue’ and ‘Standards : MonthlyAdditions’.This Indian Standard has been developed by Technical Committee : ETDC 3

Amendments Issued Since Publication

Amend No. Date of IssueAmd. No. 1 July 1983Amd. No. 2 January 1987

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