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IS : 2099 1986I ndian St andard

SPECIFICATION FORBUSHINGS FOR ALTERNATING VOLTAGESABOVE 1000 VOLTS

( Second RevisionSecond Reprint DECEMBER 1991

UDC 6213156260275

( Reaffirmed 1998

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15:2099-1986Indian Standard

SPECIFICATION FORBUSHINGS FOR ALTERNATING VOLTAGESABOVE 1 000 VOLTS(Second Revision)

Electrical Insulators and Accessories Sectional Committee, ETDC 3Chairman

Smu V. D. ANANDMembers

RepresentingCentral Electricity Authority, New Delhi

DIRPCFORTRANSMIWON ( Alternate I toShri V. D. Anancl)DIRECTOR SUB-STATION( Alternate II toShri V. D. Anand )

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IS : 2099 - 1986Continuedrom page 1 )

Members RepresenlirtgSmu SYED KHADER MO~UDDIN Kamataka State Electricity Board, BangaloreSHRI R. RANGASWAMY Alternate )RI R. V. NADKARNI Maharashtra State Electricity Board, BombaySmu S. P. AMIDWAR ( Alrertrare )SHRI D. S. NELSON Tamil Nadu Electricity Board, MadrasSHRI N. R. SANKARAN Afrernure )SHRI P. L. NENE Madhya Pradesh Electricity Board, J abalpurSHRXS. Z. HCJ SSAIN Alternate )DR 0. M. PHADKE Indi~om~~3rical Manufacturers Association,

SHRI P. RAMACH~NDRAN Alternate )SHIUV. B. RAM MOHAN Central Power Research Institute, BangaloreSHRI K. N. SRINIVASAN( Alternure )SHRI N. RAMAKRISHNAN W. S. InsuIators of India Ltd, MadrasSHRI R. C. VANCW~ESWARAN Alternate )SXRI K. H. GURURAIA RAO NGEF Limited, BangaloreSHRI C. S. WARAD ( Alternate )Sm S. C. SEN Bengal Potteries Ltd. CalcuttaSHRI D. K . MAZUMDAR ( Akernuie )SHRI R. D. SHETH Electra Metal Industries, BombaySIXRISURENDRASINGH Government Pottery Development Centre,KhurjaSHRI T. B. L. SRIVASTAVA Alternate )

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IS : 2099 1986

Ind ian StandardSPECIFICATION FORBUSHINGS FOR ALTERNATING VOLTAGESABOVE 1000 VOLTSSecond Revi si on )0 FOREWORD

0.1 This Indian Standard ( Second Revision ) was adopted by the IndianStandards lnstitution on 28 April 198$ after the draft finalized by theElectrical Insulators and Accessories Sectronal Committee had been approv-ed by the Electtotechnical Division Council.

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Is:--19%0.5 The dimensions of the porcelain bushings and their related parts havebeen covered separately as follows:

a) Porcelain transformer bushings for normal and lightly pollutedatmospheres in Section 1 of each IS : 3347 ( Part 1 ) to ( Part 7 )*,b) Porcelain transformer bushings for heavily polluted atmospheres inIS : 8603-1977t,c) oil impregnated paper insulated condenser bushings - IS under

preparation, andd) Ceramic bushings for terminals in IS : 103141982:.0.6 In the preparation of this standard, assistance has been derived fromIEC publication 137 ( 1984& Bushings for alternating voltages above 1000 V(t&f edi t i on ) , issued by the International Electrotechnical Commission0.7 For the purpose of deciding whether a particular requirement of thisstandard is complied with, the final value, observed or calculated, expressingthe 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

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Is:~2099-l9lKNorx3- Moreover, this standard is not applicable to insulating structures similarto bushings which are used as support insulators inside metal enclosed switchgear.Norx4- If a bushing, due to its design or use, cannot be tested separately underthe conditions specified in this standard, the teat procedure is to be agreed uponbetween the purchaser and the manufacturer.

2. TERMINOLOGY2.0 For the purpose of this standard, the following definitions shall apply.2.1 Bushing - A structure carrying one or several conductors through apartition such as a wall or tank, and insulating it or them therefrom,incorporating the means of attachment ( Lange or other fixing device ) tothe partition.

The conductor may form an integral part of the bushing or be drawnthrough.2.2 Liquid Filled Bushing - A bushing in which the space between the insidesurface of the insulating envelope and the solid major insulation is filledwith oil or another insulating liquid.

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IS:2099-19862.13 Indoor Bushing - A bushing, both ends of which are intended to be inambient air but not exposed to external atmospheric conditions.

NOTII - In indoor installations, moisture condensation on the surface of thebushing is to be prevented, if necessary by ventilation or heating.NOTE 2 - This definition includes bushings operating in air at temperatures aboveambient, such as occurs with air-insulated ducting.

2.14 Outdoor Bushing - A bushing, both ends of which are intended tobe in ambient air and exposed to external atmospheric conditions.2.15 Outdoor-Indoor Bushing - A bushing, both ends of which are intendedto be in ambient air. One end is intended to be exposed to external atmos-pheric conditions and the other end is intended not to be so exposed ( seealso notes under 2.13 ).2.16 Indoor-Immersed Bushing - A bushing, one end of which is intendedto be in ambient air but not exposed to external atmospheric conditions andthe other end to be immersed in an insulating medium other than ambientair ( for example, oil or gas ) ( see also notes under 2.13 ).2.17 Outdoor-Immersed Bushing - A bushing, one end of which is intended

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IS : 2099 - 1986maximum temperatures of ambient air and immersion media in accordancewith 6.4.2.23 Rated Dynamic Cnrreut ( Zd - The peak value of current which thebushing shall withstand mechanically.2.24 Temperature Rise - The difference between the measured temperatureof the hottest spot of the metal parts of the bushing which are in contactwith insulating material and ahe ambient air temperature ( see 8 ).2.25 Rated Frequency - The frequency by, which the bushing is designated.2.26 Rated Density of Insulating Gas - The density assigned by the supplierat which the bushing is intended to be operated in service.2.27 Minimum Operating Density of Insulating Gas - The density assignedby the supplier below which the rated values of insulating level no longerapply.2.28 Maximum Operating Pressure - The maximum permissible pressurewhen the bushing is in operation carrying nominal current at the highesttemperature given in 6.4.

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IS : 2099 - 19864. GENERAL REQUIREMENTS4.1 The porcelain (ceramic ) components ( see 11.1.1) shall comply witthe requirements laid down i n IS : 5621-1980*.4.2 The design of the bushing shall be such that stresses due to expansionand contraction in any part of the bushing shall not lead to deterioration.4.3 Cement used in the construction of a bushing shall not cause fractureby expansion or loosening by contraction. Cement thickness shall be asmall and even as practicable.4.4 The surface finish for ferrous parts shall be hot-dip galvanizing according to IS : 4759..1984t or zinc plating according to IS : 1573-1970: ocadmium plating with chromate passivation Cd8Cr according to IS : 15719688 or any other surface finish subject to agreement between the manufacturer and the purchaser.4.5 The surface finish for non-ferrous parts shall be electrotinning accordingto IS : 1359-1977~~subject to agreement between the manufacturer and thpurchaser.

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IS:2w9-1986NATE 2 -IN of the bushing need not necessarily be identical to the rated current

the complete apparatus. It may be hiiher or lower, depending on how the actuoperating conditions devlate from the standard test conditions for the bushing. Tgeneral rule for the permissible operating current should be that the temperatulimits should be in accordance with 8.NOTE3 - Bushings for transformers selected with I N not less than 120 percent rated current of the transformer are considered to k able to withstand the overloaconditions according to IS : 6600-1972. without furl ler clarification or tests.

5.3 Rated Thermal Short Time Current Ith ) - Unless otherwise statedthe standard value of Iln shall be 25 times IN, tth being 1 second. For bushings Witk fN greater than or equal to 4 000 A, h shall always be 100 kAftn shall always be 2 seconds for transformer bushings.5.4 Rated Dynamic Current Id ) - The standard value of Id shall have aamplitude of the first peak of 25 times the values of I :h acccrding to 5.3.5.5 Minimum Withstand Valaes of Cantilever Load - Unless otherwisspecified, the bushings shall withstand the following cantilever test load fo60 s, applied to the midpoint of the terminal or terminals, perpendicular the bushing axis:

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Is:20 @-1986b) 30 percent of the test values when the bushing is installed at anyangle exceeding 30 from the vertical.

6. OPERATING CONDITIONSG.l Temporary Overvoltages - In normal operation the maximum phase-to-earth voltage of the system should not exceed UN divided by q/

Bushings shall be able to operate at phase-to-earth voltage equal to Ufor bushings of which UN is equal to or less than 145 kV and a7 UNfor bushings of which UN is equal to or above 245 kV for periods noexceeding 8 hours in any 24 hours and of which the total period does noexceed 125 hours per year.

For systems in which overvoltages in excess of this may occur, it maybe advisable to choose a bushing with a higher UN. In such cases themanufacturers advice should be sought.6.2 Angle of Mounting - Unless otherwise stated, it shall be assumed thatbushings according to 2.13,2.14,2.15 and 2.18 are designed for mountingat any angle of inclination and that bushings according to 2.16 and 2.17are designed for mounting at any angle of inclination not exceeding 30

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IS : 2099 - 1986adequacy of the increased arcing. distance by actual tests at any altitudelower than that of operation. In such a case the manufacturer may demons-trate by any other means that the arcing distance is adequate.6.3.5 For general guidance, the amount by which the insulation level onwhich the arcing distance 1s based, should be increased is 1.0 percent foreach 100 metres in excess of 1 000 metres above sea evel.

Example :Altitude of installation =28OOmIncrease in insulation level = (28-10) x 1.0= 18 percent

Preferably, the next higher standard insulation level should be selected.6.4 Temperature of Ambient Au and Immersion Media - Unlessstated, shall be assumed bushings are for operationtemperatures ( degree Celsius not exceeding following limits:

a) Ambient MaximumMaximum daily 40CMaximum mean 32CMinimum

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IS : 2099 - 1986b) For medium polluted atmospheres 20 mm/kVc) For heavily polluted atmospheres 25 mm/kVd) For very heavily polluted atmospheres 31 mm/kV7.1.1 The value of creepage distance in the rain shadow at an angle ofprecipitation of 90 to the bushing axis should generally not exceed 50 per-cent of the total creepage distance.NOTE The definition for the various pollution classes is under consideration.

8. TEMPERATURE LIMITS8.1 The temperature limits commonly used under usual operating condi-tions of maximum daily mean ambient air temperature according to 6.4shall be as given below:

a) 120C for resin bonded and resin impregnated paper, andb) 105C for oil impregnated paper.

8.2 Consequently, the temperature rise above ambient air temperature ofthe hottest spot of metal parts shall not exceed the values given below:a) 80C where in contact with resin bonded and resin impregnatedpaper, andb) 65C where in contact with oil impregnated paper.NOTE1 - In case of other insulating materials, the temperature limits shall be asagreed between the purchaser and the manufacturer.

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I 3:2099-19NOTE I A lower aximum value of test tap capacitance with respect to earthmay be agreed between the manufacturer and the purchaser.NOTE 2 - At the request of the purchaser, the manufacturer should indicate thevalues of dielectric dissipation factor for the insulating material of the tap at frequen-cies used for partial discharge measurement on transformers.NOTE 3 - The bushing shall not incorporate substantial capacitances to earth whichmay divert the partial discharge current and so give rise to incorrect or misleadingpartial discharge measurements on the transformer.

RATEDVOLTAQB(UN)kV(=)

TABLE L STANDARD INSULATION LEVELS(Clu~ses 9.1, 11.1.2,11.1.2.1 and 11.13.3)D~~Lrmmmm POWER FREQ~NCY S~ITCHINGIMPULSIMPULSE WITH- WITHSTAND VOLT- WlTrtpTANlJOLT-STANDVOLTAGE AQE,DRYANDWET AC&DRY AND WETl-2/50kV(peak) kV(rma) 25012 500 (Lsk.V ( peak

(2) (3) (4)4060 2 -

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~15:2099-1986g) Rated current, 1~ ( see 2.21 );h) Type of insulating gas and minimum operating density, if applicable;j) Mass, if above 100 kg; andk) Maximum angle of mounting.NOTE It may be di5cult to include all the above markings on smaller bushings.In this case, marking of 10.1 (a) and (b) shall be mandatory; other markll may beagreed between the manufacturer and the purchaser.

10.1.1Bushings may also be marked with the IS1 Certification Mark.NOTE The use of the IS1 Certification Mark is governed by the provisions of theIndian Standards Institution ( Certification Marks ) Act and the Rules and Regula-tions made thereunder. The IS1 Mark on products covered by an Indian Standardconveys the assurance that they have been produced to comply with the requirementsof that standard under a well-defined dystem of inspection, testing and quality controlwhich is devised and supervised by IS1 and operated by the producer. IS1 marked

products are also continuously checked by IS1 for conformity to that standard as afurther safeguard. Details of conditions under which a licencc for the use of the IS1Certification Mark may be granted to manufacturers,or processors, may be obtainedfrom the Indian Standards Institution.11. TESTS

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l 3:24m-198611.1.5 The supplier shah provide the detailed type test certificate at therequest of the purchaser. The tests shall have been carried out on bushingsof a design that does not differ from that offered to the purchaser in anyway which may improve the features to be checked by a type test. Repett-tion of a type test IS only mandatory when speci&d in a particular contract.

11.2 Classification of Tests11.2.1Type Tests - The following shall constitute type tests (see Note 1below ):

a)W44e)f)l3)

Wet power frequency voltage withstand test ( see 11.3 ),Dry lightning impulse voltage withstand test ( see 11.4 ),Dry or wet switching impulse voltage withstand test ( see 11.5 ),Thermal stability test ( see 11.6 ),Temperature rise test ( see 11.7 ),Thermal short time current withstand test ( see 11.8 ),Dynamic current withstand test ( see 11.9 ),

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Is:2099-1986b>Cl4e)f)g)

Dry power frequency voltage withstand test ( see 11.13 ),Measurement of partial discharge quantity ( see 11.14 ),Tests of tap insulation ( see 11.15 ),Pressure test of gas filled and gas insulated bushings ( see 11.16 ),Tightness test on gas filled and gas insulated bushings ( see 11.17 )Pressure test on liquid filled and liquid insulated bushings ( s11.18 ), and

h) Tightness test at flange or other fixing device ( see 11.19 ).11.3 Wet Power Frequency Voltage Withstand Test

11.3.1 The test shall be applicable to outdoor, outdoor-indoor and oudoor-immersed bushings of which t;v is up to 245 kV. Duration of the teshall be 60 seconds.

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IS:2099-198611.4.4The time intervals between consecutive applications of the voltageshall be sufficient to avoid effects from the previous application of voltage.11.4.5 The bushing shall be considered to have passed the test if nopuncture occurs and if the number of flashovers at either polarity does notexceed two, except for transformer bushings for which not more than twoflashovers at positive polarity and one 5ashover at negative polarity shallbe permitted.

NOTE1 - Impulse voltage records are normally made.NOTE2 - By special agreement between the purchaser and the manufacturer, chopped wave impulse test may be carried out. In such cases, the method of the tesshould be agreed between the purchaser and the supplier.

11.5Dry or Wet Switchingmpulse Voltage Withatmd est11.5.1The test shall be applicable to bushings of UN equal to 420 kV.

11.5.1.1 A wet test only is applicable to outdoor, outdoor-indoor andoutdoor-immersed bushings of UN equal to 420 kV.

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IS : 2099 - 1986an organic material, intended for apparatus filled with an insulating mediumthe operating temperature of which is equal to or above 60C and of whicUN is greater than 245 kV for oil and resin impregnated paper bushingand equal to or greater than 145 kV for other types of bushings. For oimpregnated paper bushings having UN greater than 245 kV, the test canhowever, be omitted if it can be demonstrated that; based on the results ocomparative tests, the thermal stability of the bushmg is assured.

11.6.2 The ends of bushings which are intended for immersion in oil oanother liquid insulating medium shall be immersed in oil.11.6.3 The temperature of the oil shall be maintained at the operatingtemperature of the apparatus & 2C, except for transformer bushing wherthe oil temperature shall be 90 f 2C. This temperature shall be measured by means of thermometers immersed in oil about 3 cm below the surfacand about 30 cm from the bushing.11.6.4 The test voltage shall be equal ,to UN for bushings of which u,,,equal to or below 145 kV and O-7 UN for all other bushings.

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Is:m99-198611.7.2 Test Procedure

11.7.2.1 Bushings, one or both ends of which are mtended to beimmersed in oil or another liquid insulating medium, shall be appropriatelyimmersed in OX at ambient temperature except for transformer bushingswhere the oil shall be maintained at a temperature of 50 f 2C above theambient air. The level of the oil shall be maintained at least up to themounting flange of the bushing.11.7.2.2 The ends of bushings which are intended for immersion in a

gaseous insulating medium other than air at atmospheric pressure shahnormally be appropriately immersed in gas at minimum operating density,the gas being at ambient temperature at the beginning of the test.11.7.2.3 Gas insulated bushings shah be at ambient air temperature atthe beginning of the test.11.7.2.4 The test shall be carried out at IN + 2 percent, all parts ofthebushing being substantially at earth potential.11.7.2.5 Bushings with a conductor drawn into the central tube shallbe assembled with an appropriate conductor, the cross section of whichshall correspond with IN.

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Is:m-1986hottest spot may be determined as follows:

The maximum conductor temperature @Ms deduced by the relations1 and 2:

. . . ( 1 )

. . . (2)If the result M of the relation ( 2 ) is positive, the higher temperatureof the conductor is OM nd it is situated in any point of the conductorbetween the two extremities. If the result M is negative or zero, the highertemperature of the conductor is t12.The point of maximum conductor temperature lies at a distance LMfrom the cooler end given by:

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Is : 2099 - 198611.7.3.2 Temperature of ambient air - The ambient air temperatureshall be measured with lagged thermometers placed around the bushing atmid-height and at 1 to 2 m distance from it.

NOTE - A satisfactory degree of lagging s obtained by placing the thermometersin oil filled containers with a volume of approximately O-5 We.11.7.3.3 Temperatur e of the oil or gas - The temperature of the oil orgas shall be measured by means of thermometers placed 30 cm distant fromthe bushing and in the case of oil 3 cm below the surface of the oil.

11.8 Thermal Short Time Current Withstand Test11.8.1 Unless otherwise agreed between the purchaser and the manu-facturer, the ability of the bushing to withstand the standard value of Itisshall be demonstrated by the following calculation :

where8/ = final temperature of the conductor, in degree Celsius;00 = temperature of the conductor, in degree CeIsius, under conti-

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IS : 2099 - 1986

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Is:2099-1986pressure shall be applied inside the bushing and also inside the central tubeiii the case of a bushing with a hollow stem with a gasketted joint, at theterminal to be tested.11.10.4 The load shall be applied perpendicular to the axis of the bushingat the mid-point of the terminal for one minute. It shall be applied onlyto one terminal at a time. It is generally sufficient to apply the load onlyto the terminal which wili cause the highest stresses at the critical parts ofthe bushing in normal operation.

11.10.5 The bushing shall be considered to have passed the test if thereis no evidence of damage ( deformation, rupture or leakage ) and if it haswithstood a repetition of routine tests as given in 11.12 and 11.14 withoutsignificant change from previous test results.11.11 TigMness Test on Liquid Filled and Liquid Insulated Bashings

11.11.1 Either of two test methods given in 11.11.1.1 and 11.11.1.2 maybe used to check the requirement as given in 11.11.2.11,ll.l.l The bushing shall be mounted on a tank filled with oil,

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IS:2099-198611.13 Dry Power Frequency Voltage Withstand Test

11.13.1 The test shall be applicable to bushings of all types except gainsulated bushings.*~~~~~*~~l~~~~~~~~~~~~~~ k Wy$&cdV rt of a gas insulated apparatus of which the gas tUii is common to that of thushing provided the insulating envelope of the bushing has been subjected to aadequate electrical test ( for example, wall test of the porcelain ) before assembly.11.13.2 The test duration shall be one minute.11.13.3 The values of dry power frequency withstand voltage shall be agiven in Table 1.11.13.4 The bushing shall be considered to have pas&d the test if n

flashover or puncture occurs. If there is a puncture, the bushing shall bconsidered to have failed the test. If a flashover occurs, the test shall brepeated once only. If during the repetition of the test no flashover opuncture occurs, the bushings shall be considered to have passed the test.

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Is:m-1986The maximum permissible values of the partial dii quantity on descendvoltage with reference to the terminals shall ba agreed between the purchaser and

manufacturer except for resin bonded papa capacitance graded bushing for which ValuefThall be as follows :

= 1.05 UN/dr T5 u&\/j NOlbmetallii 10 to.18 10 to 16Metallic 10 to 16 10 to 15

Norx4- When as a substitute for the measurement of partial discharge quantthe radio intet%erence voltage, expressed in microvolts, is measured by means oradio. interference meter the permissible value, as well as the minimum measurabvalue, shag be agreed between the purchaser and the supplier.Nora 5 - The measurement may be carried out as a type test only on gas insula

bushings which are intended to be used as an integral part of a gas insulated appatus of which the gas filling is common to that of the bushing provided the insulatienvelope of the bushing has been subjected to an adequate electrical test ( example, wall teat of the porcelain ) before assembly.

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IS:2099-1986Test tap ( see 2.33 )Voltage tap ( see 2.34 )

At least 2 kV2 times the rated voltage of the voltagtap but-at least 2 kV

Before and after the power frequency voltage withstand test on voltagtaps, the capacitance with respect to earth shall. be measured at ratevoltage.11.15.2 After the pqer frequency voltage withstand test, the capacitancewith respect to earth shall be measured at O-5 kV at least on all test taps.11.15.3 After the power frequency voltage withstand test on test tapon transformer bushings, the capacitance with respect to earth and dielectric dissipation factor shall be measured at O-5 kV at least and the resulshall be in accordance with 9.3.

11.16 Pressure Test of Gas Filled and Gas Insulated Bushings11.16.1 The test shall be applicable only to gas filled and gas insulated

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IS:2099-1986It is advisable to carry out a preliminary tightness test on such com-ponents as is considered useful.

11.18 Pressure Test on Liquid Filled and Liquid Insulated Bushings - Thepressure test for leakage of internal filling is applicable only to bushingsdefined in 2.2 and 2.3 except for those bushings of which the liquid fillinghas a viscosity equal to or above 5 x 10 mz/s at 20C. Any one of thetwo alternative test procedures given in 11.18.1 and 11.18.2 may be used atthe choice of the supplier. *

NOTE - If the design of the bushing is such that the tests as specified below areimpracticable, the test procedure shall be subject to agreement between the purchaserand the manufacturer.11.18.1 Test with Oil or I nsulating L iquid at Ambient Temperature -The bushing complete as for normal service shall be filled to the normallevel with oil or insulating liquid of the quality specified by the manufac-turer. The bushings shall be placed in air at ambient temperature of notless than 10C. The temperature of the oil or insulating liquid shall beambient temperature.

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lS:2099-198611.19 Tightness Test at Flange or Other Fixing Device

11.19.1 The test shall be.applicable to all bushings of indoor-immersed,outdoor-immersed and completely immersed types, intended to be used an integral part of an apparatus, such as switchgear or transformer, wherthe bushings contribute to the sealing of the complete apparatus.11.19.2 The bushing shall be assembled as far as necessary for the tesThe end for immersion shall be mounted on a tank as for normal opera

tion. The tank shall be filled with air or any suitable gas at a gauge pressure of 1.5 f 0.1 bar and maintained for 15 minutes.11.19.3 The bushing shall be considered to have passed the test if theris no evidence of leakage.

NOTBThe test shall be a type test only in the case of bushii with gaskeof which the ha1 placing is not carried out, for example, the top tap gasket of drathrough conductor transformer bushings.The test may be omitted for transformer and circuit breaker bushingfitted with a one-piece metal flange, provided the flange has been subjecte

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I 3:2099-1986A-2. CORRECTION FACTORSA-2.1 When the atmospheric conditions in the neighbourhood of thebushing during the test differ from the reference conditions, adjustmentsshould be made to correct the test voltages by the application of air densitycorrection factor, ka, and humidity correction factor, kh, as given below[ see alro IS : 2071 ( Part 1 )-1974* ] for bushings for which the electrodeconfiguration of rod-plane gap is valid:ClaitseReference Test

*Correction of Test Vol tage

113 Wet power frequency voltagewithstand test11.411.5

Dry lightning impulse voltagewithstand testDry switching impulse voltagewithstand test

11.5 Wet switching impulse voltage

Multiply by kaMultiply by k,i/kh in the condi-tions indicated in A-2.2Multiply by k,i/kh n the conditions indicated in A-2.2Multiply by kd in the condi-

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IS:=-l986purchaser and the manufacturer. shall agree as to whether the test shall orshall not be continued.

NOTB~- ~sthedielectric routineteats (secllf3)ars intended to check theinternal insulation only, it tiperm&ibla practiceto- the-metal partsof the bushing during these tests.Nope 2 - A bushing is normally tested in an wt having sutWeut ckar-ante to surrounding earthed parts to avoid direct flashover tothem through theambient air or the immersion medium.Nom3 - Normally %ransformer bushings arc teated in vertical position; other

teat arrangements must be agreed between the purchaser and the supplier.Nom 4 - The angle of mounting 6f the bushing for the wet power frequency volt-age withstand test may be the subject df special agreement between the purchaser andthe supplier. In certain cases, it may be neassafy to extend the voltage range abovethat specified in 11.3.At the request of the purchaser, the supplier shall furnish any

information concerning the bushing necessary for determining the minimumclearances to earthed parts in the operating -arrangement.The purchaser may use the bushing for a simulation test to prove theadequacy of the operating arrangement.

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Is:m9 ar1986B-l.3 Liquid filled and liquid insulated bushings shall be filled to thenormal level with insulating liquid of the quality specified by the supplier.B-l.4 Gas filled and gas insulated bushings shall be filled with the type ofgas specified by the manufacturer and raised to the minimum operatingdensity of insulating gas. The density may be expressed as the pressure atthe reference temperature of 20C. If at the beginning of the test, thetemperature differs from 2OC, the pressure shall be adjusted to correspondwith the required density.

Bushings according to 2.16, 2.17 and 2.18 shall normally be immersedin an immersion medium which is as similar as possible to that used innormal operation except for the following:a) Bushing for which the immersion medium is gas, the immersionmedium may be replaced by oil for the dielectric routine tests, byagreement between the supplier and the purchaser.b) Bushings for which the immersion medium is neither oil nor gas,the immersion medium may be replaced by oil or gas for all dielec-tric and thermal tests by agreement between the supplier and thepurchaser.

B-l.5 The applicable atmospheric conditions for dielectric and thermaltests are given in IS : 2071 ( Part 1 )-1974*.

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Is:209 3-l B6should be drawn to any features (including tests) of the completeapparatus which may affect the design of the bushing.

b) Class~ification - The classification of bushings shall be as given in2.2 to 2.18.c) Ratings

i) Rated voltage ( UN ) ( see 2.19 );ii) Rated phase-to-earth voltage ( see 2.20 );iii) Standard insulation level ( see 9 );iv) Rated current ( Znr ( see 2.21 );v) Rated thermal current Ztn and rated duration fth, if deviatingfrom the values indicated in 5.3;

vi) Rated frequency ( see 2.25 );vii) Rated density of insulating gas ( see 2.26 ) ( relevant only tobushings according to 2.4 and 2.5 when the gas of the equip

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Is:2999-1986viii) Minimum operating density of insulating gas (see 2.27 ) ( rele-vant only to bushings according to 2.4 and 2.5 when the gas

of the equipment is in communication with that of thebushing );ix) Maximum operating pressure ( see 2.28 ) ( relevant only tobushings according to 2.4 and 2.5 when the gas of the equip-ment is in communication with that of the bushing );x) Angle of mounting ( see 6.2 );xi) Minimum specific creepage distance ( see 7 ) ( relevant only tobushings according to 2.14,2.15 and 2.17 ); and

xii) Unusual climatic conditions.e) Design

i) For bushings supplied without a conductor the diameter, type( cable, solid or hollow stem ), material and position of theconductor with which the bushing will be fitted in service;ii) Particular dimensional requirements, if any;

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AMENDMENT NO. 1 J ANUARY 1989IS : 2099 - 1986 SPECIFJ ?iTlON FOR BUSHINGS

FOR ALTERNATING VOLTAGES ABOVE1000 VOLTS( Second Revision )

Page 31, clause 11.7.2.4 - Stibstitute the following for the exist-ing clause :11.7.2.4 The test shall be carried out at fN + 2 percent, all parts ofthe bushings being substantially at earth potential.

(ETDC 3)

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AMENDMENT NO. 2 JANUARY 1993TO

IS 2099 : 1986 SPECIFICATION FOR BUSHINGS FORALTERNATING VOLTAGES ABOVE 1000 VOLTS

( Second Revision )(Page 29, clause 11.153, ast ine -Substitute 9.2for 9.3.

Reprography Unit, BIS, New Delhi, l