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 ).
3
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
4
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.
6
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
mm
TEMPERATURE DIFFERENCE tºC FOR THICKNESS ≤23 (2) 60 55 50 45 40 35
23< ≤26 (3)
26< ≤32 (4)
32< ≤36 (5)
36< ≤43 (6)
55 55 50 45 40 35
50 50 50 45 40 35
45 45 45 45 40 35
40 40 40 40 40 35
43< (7) 35 35 35 35 35 35
Subject to agreement between the manufacturer and the purchaser. D2L>2 000 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 millimetres, of the largest circle which can be inscribed in the outline of a section through the axis of the hollow insulator ( see Fig. 1 ). NOTE — The temperature differences in Table 1 apply to insulators of parallel or tapered internal shape which allow free access of water to the interior on immersion. Insulators are considered not to offer free access of water if the smallest internal diameter is less than 0.25 times the largest internal diameter. In such cases, the value of t shall be agreed between the manufacturer and the purchaser.
3.6.4 Alternative Test for Large Hollow Insulators 3.6.4.1 For hollow insulators having a height greater than 1 200 mm, the following method of test may, by agreement between the manufacturer and 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 by any convenient means (circulation of heated air or water, infra red 8
IS : 5621 - 1980 radiation, etc) to a value tºC higher than that of the cold water which is later used to spray it with artificial rain. This temperature shall be maintained for 15 minutes.
FIG. 1 ILLUSTRATION FOR THICKNESS 3.6.4.3 The hollow insulator shall then be immediately sprayed with artificial rain at an intensity of about 3 mm per minute and this spraying shall continue for 15 minutes. 3.6.4.4 This heating and cooling cycle shall be performed three times in succession. The temperature difference t is given in Table 2 as a function of the wall thickness as defined above. TABLE 2 TEMPERATURE DIFFERENCE FOR TEMPERATURE CYCLE TEST ON LARGE HOLLOW INSULATORS TEMPERATURE DIFFERENCE tºC
THICKNESS (1)
(2)
≤30
70
>30
50
3.6.5 The volume of water contained in the baths for tests above shall be sufficiently great for the immersion of the insulator not to cause a variation of more than ± 5ºC in the temperature of the water. 3.6.6 After the three cycles, the hollow insulator shall show no cracks or damage to the glaze or other faults causing a deterioration in its electrical or mechanical properties. 3.6.7 The absence, of such deterioration is considered verified if the hollow insulator passes the electrical routine test described in 3.3. 9
IS : 5621 - 1980 3.6.8 A hollow insulator which has successfully passed the temperature cycle test may be supplied with the rest of the lot for normal service. 4. Clause deleted
APPENDIX 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 lot and in order to ensure the randomness of selection, procedures given in 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 the first stage shall be in accordance with col 1 and 3 of Table 3. Each of the selected hollow insulators shall be tested for the acceptance tests. If a hollow insulator fails in any one of the acceptance tests, it shall be termed as defective. The lot shall be declared as accepted if the number of defectives found in the sample is less than or equal to the acceptance number ( see col 5 ) and shall be rejected if it is greater than or equal to the rejection number ( see col 6 ). In case the number of defectives lies between the acceptance number and rejection number, the second sample of the same size shall be chosen at random and tested. If the number of defectives found in the combined samples is greater than or equal to the rejection number, the lot shall be rejected; otherwise the lot shall be accepted. TABLE 3 LOT SIZE (1) 2 to 100 101 to 300 301 to 500 501 and above
SCALE OF SAMPLING AND PERMISSIBLE NUMBER OF DEFECTIVES STAGE SAMPLE CUMULATIVE ACCEPTANCE REJECTION SIZE SAMPLE SIZE NUMBER NUMBER (2) (3) (4) (5) (6) First 2 2 0 2 Second 2 4 1 2 First 3 3 0 2 Second 3 6 1 2 First 5 5 0 2 Second 5 10 1 2 First 8 8 0 2 Second 8 16 1 2
*Methods for random sampling.
10
IS : 5621 - 1980
APPENDIX B ( Clause 3.4.3 ) TOLERANCES AND PERMISSIBLE LIMITS OF CERTAIN DIMENSIONAL CHARACTERISTICS OF HOLLOW INSULATORS B-1. GENERAL B-1.1 The general tolerance formula on dimensions is given in 3.4.2 of this standard. However, this formula may not be applicable to dimensions like diameter of upper and lower ends, wall thickness and ground portion and also does not cover 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. The tolerances and permissible limits for these dimensional 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 hollow insulators shall be as specified in Table 4 and Fig. 2. TABLE 4
TOLERANCES ON DIAMETER OF UPPER AND LOWER ENDS
NOMINAL DIAMETER ( D, d & ) (1) mm 0 to 50 Above 50 and up to 75 ,, 75 ,, 100 ,, 100 ,, 125 ,, 125 ,, 150 ,, 150 ,, 175 ,, 175 ,, 200 ,, 200 ,, 250 ,, 250 ,, 300 ,, 300 ,, 350 ,, 350 ,, 400 ,, 400 ,, 500 ,, 500 ,, 600 ,, 600 ,, 700 ,, 700 ,, 800 ,, 800 ,, 900 ,, 900 ,, 1 000 ,, 1 000
TOLERANCE (2) mm ± 2.0 ± 2.5 ± 3.0 ± 3.5 ± 4.0 ± 4.5 ± 5.0 ± 5.5 ± 6.0 ± 7.0 ± 8.0 ± 9.0 ± 11.0 ± 13.0 ± 15.0 ± 17.0 ± 19.0 ± 2 percent
NOTE — The general tolerances given in 3.4.2 of this standard shall be applicable unless tolerances given in this table are indicated on the drawing.
11
IS : 5621 - 1980 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 outside diameters [also known as ovality] shall be in accordance with Table 5 and 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 ) 12
IS : 5621 - 1980 .
TABLE 5
PERMISSIBLE LIMITS OF OUT-OF-ROUNDNESS OF INSIDE AND OUTSIDE DIAMETER ( Clause B-3.1 )
NOMINAL DIAMETER D&d (1) mm
OUT-OF-ROUNDNESS (a—b) (2) mm
0 to 50 Above 50 and up to 75 ,, 75 ,, 100 ,, 100 ,, 125 ,, 125 ,, 150 ,, 150 ,, 175 ,, 175 ,, 200 ,, 200 ,, 250 ,, 250 ,, 300 ,, 300 ,, 350 ,, 350 ,, 400 ,, 400 ,, 500 ,, 500 ,, 600 ,, 600 ,, 700 ,, 700 ,, 800 ,, 800 ,, 900 ,, 900 ,, 1 000 ,, 1 000
± 2.0 ± 2.5 ± 3.0 ± 3.5 ± 4.0 ± 4.5 ± 5.0 ± 5.5 ± 6.0 ± 7.0 ± 8.0 ± 9.0 ± 11.0 ± 13.0 ± 15.0 ± 17.0 ± 19.0 ± 2 percent
B-4. CAMBER B-4.1 The camber of a hollow insulator is defined as the maximum distance between the theoretical, straight, axis A-A of the piece as shown 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 an axis passing through the centres of the end faces or as close as possible to these centres. The insulator is then rotated through a complete revolution and the distance from the outer surface of the wall to a reference plane parallel to the axis of rotation is measured at various points along the length of the piece. At each point, the difference Xmax- 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 the hollow insulator is being ground. 13
IS : 5621 - 1980
FIG. 4 ILLUSTRATION FOR CAMBER 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 of its length, it follows ( see Fig. 4 ) that the angle between the perpendicular to the deformed axis and the end face after grinding may be up to 0.032 radians. Thus, the sheds at the ends of the insulator may be inclined at this angle and the distance H between the end shed and the ground face of the insulator will vary round the periphery. The minimum allowable dimension H may be shown on the drawing, taking into account the dimensions of fittings which are to be attached to the insulator. To verify the dimension H, Hmax and Hmin shall be measured. The position of the end shed complies with the drawing if the average value of H, that is ½ Hmax + Hmin is within the general tolerances or any special tolerances on dimension H shown on the drawing. In addition, the inclination of the end shed shall not be such that Hmax – Hmin exceeds 0.032 D + 3 mm, where D is the nominal diameter of the end shed, express in millimetres. Similar considerations apply to the length of sandglazing and to the height h of a flange at the end of an insulator where the face AB is not ground and the end face is ground ( see Fig. 5 ). B-4.2 Camber (δ in Fig. 4) — It shall not be greater than the value specified in Table 6 and Fig. 4. 14
IS : 5621 - 1980 B-4.3 The permissible value for the camber shall be subject to special agreement between the manufacturer and the purchaser if the ratio of height to greatest inside diameter of hollow insulator is equal to or greater than 6, or if the shape of the hollow insulator leads to a special difficulty. B-4.4 A gauge rod of diameter A as shown in Fig. 6 shall be passed through the bore of the porcelain and rod should pass freely. B-4.4.1 The diameter A shall be determined by the following relation in case when centering with the porcelain axis is required: A=(D–d)–2δ
FIG. 5
ILLUSTRATION OF CAMBER IN CASE OF SANDGLAZING
FIG. 6
GAUGING ROD FOR CAMBER
B-4.4.2 In case when centering is not required, diameter A shall be determined by the following relationship: A=(D–d)–δ where A = diameter of gauge rod, 15
IS : 5621 - 1980 D = diameter of bore, δ = camber, and d = ± (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 ) CAMBER, δ
NOMINAL HEIGHT L
L --------------------------- ≤ 2 * B 1 or B 2 (1) mm 0 Above 50 ,, 70 ,, 100 ,, 200 ,, 300 ,, 400 ,, 500 ,, 600 ,, 700 ,, 800 ,, 900 ,, 1 000 ,, 1 100 ,, 1 200 ,, 1 300 ,, 1 400 ,, 1 500 ,, 1 800 ,, 2 100 ,, 2 400 ,, 2 700 ,, 3 000 ,, 3 500 ,, 4 000 ,, 4 500
to and up to ,, ,, ,, ,, ,, ,, ,, ,, ,, ,, ,, ,, ,, ,, ,, ,, ,, ,, ,, ,, ,, ,, ,,
50 70 100 200 300 400 500 600 700 800 900 1 000 1 100 1 200 1 300 1 400 1 500 1 800 2 100 2 400 2 700 3 000 3 500 4 000 4 500
L L 2 < ---------------------------- ≤ 3 3 < --------------------------- ≤ 6 * * B 1 or B 2 B 1 or B 2
(2)
(3)
(4)
mm
mm
mm
1.0 1.2 1.5 2.0 3.0 4.0 4.0 4.5 5.0 5.0 5.5 5.5 6.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0
*NOTE — Use B1 or B2 whichever is greater.
16
1.0 1.2 1.5 2.0 3.0 4.0 4.5 5.0 6.0 6.0 7.0 7.0 8.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 18.0 20.0 22.0 24.0 0.8 percent
1.5 1.5 2.0 3.0 4.0 5.0 6.0 6.5 7.0 8.0 9.0 9.0 10.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0 17.0
IS : 5621 - 1980 B-5. TOLERANCES ON WALL THICKNESS B-5.1 Tolerances on wall thickness and differential of wall thickness [ a and ( t1 – t2 ) in Fig. 7 ] shall be in accordance with Table 7 and Fig. 7. TABLE 7
TOLERANCES ON WALL THICKNESS
NOMINAL WALL THICKNESS
0 Above 10
DIFFERENTIAL OF WALL TOLERANCES ON WALL THICKNESS (SEE NOTE 2 BELOW) THICKNESS, ( t1 – t2 )
(1)
(2)
(3)
mm
mm
mm
+a – 1.5 +a – 2.0 +a – 3.0 +a – 3.5 +a – 4.0 +a – 4.5 +a – 5.0 +a – 6.0
1.5
to
10
and up to
15
,,
15
,,
20
,,
20
,,
25
,,
25
,,
30
,,
30
,,
40
,,
40
,,
55
,,
55
,,
70
2.0 2.5 3.0 3.5 4.0 4.5 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 following equation: x+y a = -----------2 x, y are diameter tolerances on diameter D and d respectively (Fig. 7).
FIG. 7
TOLERANCE OF WALL THICKNESS 17
IS : 5621 - 1980 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 than the value specified in Table 8 and Fig. 8. These shall be determined by the following relations: Tilt of shed
= h1 Max –h2 Min or h´1 Max –h´2 Min Tilt of sand band = r1 Max –r2 Min or r´1 Max –r´2 Min
FIG. 8
TILT OF SHED AND SAND BAND
B-6.2 Tilt of Clamping Part — The tilt of clamping part is given in Fig. 9. The limit of tilt of clamping part shall have the same limits as for tilt of shed and sand band. 18
IS : 5621 - 1980
NOTE — Tilt of clamping part — S1 Max –S2 Min or — S1 Max –S2 Min
FIG. 9
TILT OF CLAMPING PART
B-7. TOLERANCES ON GROUND PORTION B-7.1 Porcelain body may be ground within a tolerance whose minimum is indicated in Table 9, when specially requested by purchaser. Special attention shall be drawn to the fact that grinding affects tolerances of inter-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 using the following equations: α r = a + --2
β s = b + --2 ( a + b ) = X – H (Divide X – h into a and b properly.) where 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. 19
IS : 5621 - 1980 TABLE 8
TILT OF SHED AND SAND BAND ( Clause B-6.1, Fig. 8 )
NOMINAL SHED DIAMETER, , ´, D or D´
TILT OF SHED AND SAND BAND
(1)
(2)
mm
mm to
100
4.0
Above
100
0
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
0
TOLERANCE
(1)
(2)
mm
± mm 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
20
IS : 5621 - 1980
FIG. 10 TOLERANCES OF GROUND PORTION B-7.3 Tolerances a, b, r and s ( see Fig. 10B ) shall be determined by using the following equation: α r = ( ϒ 1 – a ) + --2
β s = ( ϒ 2 – b ) + --2 a+b≤ h where r and s α and ϒ1 and ϒ2 a and b h
= = = = =
tolerances of R and S respectively but minimum 2 mm, tilts of R and S respectively, general tolerances of A and B, tolerances of A and B respectively, required tolerances of H.
B-8. FINISH OF GROUND SURFACES B-8.1 Finish of ground surfaces shall be as specified in Table 10 and Fig. 10. 21
IS : 5621 - 1980 TABLE 10 FINISH OF GROUND SURFACE ( Clause B-8.1, Fig. 10 ) FINISH OF GROUND SURFACES
APPLICATION
Marking (1)
Surface Finish (2)
(3)
V
Roughness height 25 micron PVA Max
Oil-tight sealing portion and general purpose
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
B-8.2 Parallelism and lean of ground portions shall not be greater than the value specified in Table 11 and Fig. 11. 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
to
200
0.5
0.4
Above
200
0
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 subject so agreement between the manufacturers and the purchasers.
22
IS : 5621 - 1980
FIG. 11
PARALLELISM AND LEAN OF GROUND PORTIONS
23
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