IS 2026-1 (2011): Power transformers, Part 1: General

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2 > 0 B Bhart hari N ti atakam Knowledge is such a treasure which cannot be stolen Invent a New India Using Knowledge IS 2026-1 (2011): Power transformers, Part 1: General [ETD16: Transformers] BIS 2011B 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 MARGNEW DELHI 110002 December2011 Price Group 10IS 2026 (Part 1) : 2011 Hkkjrh; ekudikWoj V kalQkeZjHkkx 1 lkekU; nwljk iqujh{ Indian StandardPOWER TRANSFORMERS PART 1 General ( Second Revision )ICS Power Transformers Sectional Committee, ETD 16 FOREWORDThis Indian Standard (Part 1) (Second Revision) was adopted by the Bureau of Indian Standards, after the draftfinalized by the Power Transformers Sectional Committee had been approved by the Electrotechnical standard was first published in 1962 and covered naturally cooled oil-immersed transformers. With subsequentamendments forced cooled transformers were included, use of synthetic liquids as cooling medium was permittedand requirements for aluminium windings were revision was undertaken with a view to bringing it in line with the revision of IEC 76 : 1967 Powertransformers.}

3 This revision has been based on IEC 60076-1 : 2000 Power transformers Part 1: General , issued by theInternational Electrotechnical Commission with following temperature of ambient air and cooling medium oil is as per Indian Environment and tests are requirements for Power transformers are covered in eight parts. Other parts in the series are:Part 2 Temperature-risePart 3 Insulation levels and dielectric testsPart 4 Terminal markings, tappings and connectionsPart 5 Ability to withstand short circuitPart 7 Loading guide for oil-immersed Power transformersPart 8 Application guidePart 10 Determination of sound levelsThis standard shall be read in conjunction with the following standard: IS transformers:(Part 2) : 2010 Temperature-rise (first revision)(Part 3) : 2009 Insulation levels, dielectric tests and external clearances in air (third revision)(Part 4) : 1977 Terminal markings, tappings and connectioins(Part 5) : 2011 Ability to withstand short circuit (first revision)5553 : 1989 Reactors(All parts)6600 : 1972 Guide for loading of oil immersed transformers9001 : 2000 Quality management systems Requirements11171 : 1985 Specification for dry-type Power tansformers13964.

4 1994 Methods of measurement of transformer and reactor sound levelsIn addition assistance has also been derived from following IEC Standards:IEC StandardTitle60137 : 2008 Insulated bushings for alternating voltages above 1 000 V60815 : 1986 Guide for the selection of insulators in respect of polluted conditions60310 : 2004 Railway applications Traction transformers and inductors on board rolling stock60068-3-3 : 1991 Environmental testing Part 3: Guidance, seismic test methods for equipmentFor 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 or analysis , shall be rounded off in accordance with IS 2 : 1960 Rules for Rounding off numerical values (revised) . The number of significant places retained in the rounded offvalue should be the same as that of the specified value in this standard. 1IS 2026 (Part 1) : 2011 Indian StandardPOWER TRANSFORMERS PART 1 General ( Second Revision )1 SCOPEThis standard (Part 1) applies to three-phase and single-phase Power transformers (including auto-transformers) with the exception of certain categoriesof small and special transformers such as;a)single-phase transformers with rated powerless than 1 kVA and three-phase transformersless than 5 kVA;b) instrument transformers;c)transformers for static convertors;d) traction transformers mounted on rollingstock;e)starting transformers;f)testing transformers.

5 Andg) welding Indian Standards do not exist for such categoriesof transformers, this part of IS 2026 may still beapplicable either as a whole or in those categories of Power transformers and reactorswhich have their own Indian Standards, this part isapplicable only to the extent in which it is specificallycalled up by cross reference in the other Such standards exist for dry-type tranformers (seeIS 11171) and for reactors in General (see IS 5553). For tractiontransformers and reactors and for stastic convertor transformers, standards are under several places in this Part it is specified orrecommended that an agreement shall be reachedconcerning alternative or additional technicalsolutions or procedures. Such agreement is to be madebetween the manufacturer and the purchaser. Thematters should preferably be raised at an early stageand the agreements included in the Service Normal Service ConditionsThis standard gives detailed requirements fortransformers for use under the following conditions:a)Altitude A height above sea-level notexceeding 1 000 m (3 300 ft).

6 B)Temperature of ambient air and coolingmedium A temperature of ambient air notbelow 5 C and not above +50 C. For water-cooled transformers, a temperature of coolingwater at the inlet not exceeding +30 limitations, with regard to cooling aregiven for;1) oil-immersed transformers in IS 2026(Part 2); and2) dry-type transformers in IS )Wave shape of supply voltage A supplyvoltage of which the wave shape isapproximately This requirement is normally not critical inpublic supply systems but may have to be consideredin installations with considerable convertor loading. Insuch cases there is a conventional rule that thedeformation shall neither exceed 5 percent totalharmonic content nor 1 percent even harmonic note the importance of current harmonics for loadloss and )Symmetry of three-phase supply voltage Forthree-phase transformers, a set of three-phasesupply voltages which are )Installation environment An environmentwith a pollution rate that does not requirespecial consideration regarding the externalinsulation of transformer bushings or of thetransformer environment not exposed to seismic disturbancewhich would otherwise require special considerationin the design.

7 (This is assumed to be the case when theground acceleration level ag is below 2 m/s). Provision for Unusual Service ConditionsAny unusual service conditions which may lead tospecial consideration in the design of a transformershall be stated in the enquiry and the order. These maybe factors such as high altitude, extreme high or lowtemperature, tropical humidity, seismic activity, severecontamination, unusual voltage or load current waveshapes and intermittent loading. They may also concern 2IS 2026 (Part 1) : 2011conditions for shipment, storage and installation, suchas weight or space limitations (see Annex B).Supplementary rules for rating and testing are givenin other publications for:a)temperature rise and cooling in high ambienttemperature or at high altitude: IS 2026(Part 2) for oil-immersed transformers, andIS 11171for dry-type transformers, andb) external insulation at high altitude.

8 IS 2026(Part 3) for oil-immersed transformers, andIS 11171 for dry-type REFERENCESThe standards given in Annex A are necessary adjunctsto this DEFINITIONSFor the purpose of this standard, the followingdefinitions shall Power Transformer A static piece of apparatuswith two or more windings which, by electromagneticinduction, transforms a system of alternating voltageand current into another system of voltage and currentusually of different values and at the same frequencyfor the purpose of transmitting electrical Auto-Transformer A transformer in which atleast two windings have a common Where there is a need to express that a transformer isnot auto-connected, use is made of terms such as separatewinding transformer, or double-wound Booster Transformer A transformer of whichone winding is intended to be connected in series witha circuit in order to alter its voltage and/or shift itsphase.

9 The other winding is an energizing Oil-Immersed Type Transformer A transformerof which the magnetic circuit and windings areimmersed in For the purpose of this part any insulating liquid,mineral oil or other product, is regarded as Dry-Type Transformer A transformer of whichthe magnetic circuit and windings are not immersed inan insulating Oil Preservation System The system in an oil-immersed transformer by which the thermal expansionof the oil is accommodated. Contact between the oil andexternal air may sometimes be diminished or Terminals and Neutral Terminal A conducting element intended forconnecting a winding to external Line Terminal A terminal intended forconnection to a line conductor of a Neutral Terminala)For three-phase transformers and three-phasebanks of single-phase transformers:The terminal or terminals connected to thecommon point (the neutral point) of a star-connected or zigzag connected )For single-phase transformers.

10 The terminal intended for connection to aneutral point of a Neutral Point The point of a symmetricalsystem of voltages which is normally at zero Corresponding Terminals Terminals ofdifferent windings of a transformer, marked with thesame letter or corresponding Winding The assembly of turns forming anelectrical circuit associated with one of the voltagesassigned to the For a three-phase transformer, the winding is thecombination of the phase windings (see ). Tapped Winding A winding in which theeffective number of turns can be changed in Phase Winding The assembly of turns formingone phase of a three-phase The term phase winding should not be used foridentifying the assembly of all coils on a specific High-Voltage Winding The winding havingthe highest rated Low-Voltage Winding The winding having thelowest rated For a booster transformer, the winding having thelower rated voltage may be that having the higher Intermediate-VoltageWinding A winding of amulti-winding transformer having a rated voltageintermediate between the highest and lowest windingrated voltages.