Transformer Types of Transformer Tappings Transformer and Bushings
Transformer Types of Transformer Tappings Transformer and Bushings BUSHINGS OLTC PRESENTED BY PROF. VG PATEL
TRANSFORMER ENCYCLOPAEDIA Types of Transformer Bushings Monday, September 20, 2021 VG PATEL 2
TRANSFORMER ENCYCLOPAEDIA Type of Transformer Bushings used for power transformers Bushing comprises a central conductor surrounded by graded insulation. A bushing is necessary when a conductor is taken out through metallic tank or a wall. Simple porcelain insulator bushing can be used up to 20 k. V class. Such a bushing consists of a single porcelain housing through which a single central conductor passes. Oil filled bushing is used for 33 k. V applications. For making the bushing compact, synthetic resin bonded condenser bushings (S. R. B. P. condenser bushing) is used for 33 k. V and 66 k. V applications. For 132 k. V and above oil impregnated paper condenser bushing is used. (O. I. P. condenser bushings). Monday, September 20, 2021 PROF. V. G. PATEL 3
TRANSFORMER ENCYCLOPAEDIA Type of Transformer Bushings Monday, September 20, 2021 PROF. V. G. PATEL 4
TRANSFORMER ENCYCLOPAEDIA Type of Transformer Bushings Monday, September 20, 2021 PROF. V. G. PATEL 5
TRANSFORMER ENCYCLOPAEDIA Type of Transformer Bushings Monday, September 20, 2021 PROF. V. G. PATEL 6
TRANSFORMER ENCYCLOPAEDIA Type of Transformer Bushings 3 different type of Bushings • Solid • Oil filled • Condenser Bushings • Synthetic Resin Bonded Paper Condenser • Oil impregnated paper condenser • Cast resin Monday, September 20, 2021 PROF. V. G. PATEL 7
TRANSFORMER ENCYCLOPAEDIA Type of Transformer Bushings condenser bushing: The condenser bushing consists of a central conductor surrounded by alternate layers of insulating paper and tin foil. The capacitor formed by alternate layers of tin foil and paper insulation results in uniform electric stress distribution between conductor surface and the earthed flange. The bushing core is coated with suitable resign. The assembly is enclosed in hollow porcelain and is provided with support flange and top hood. The porcelain is filled with dielectric oil. One end of the bushing goes into transformer tank. The other end is in the outside air. In some cases there is a provision to mount current transformers on the bushing. Monday, September 20, 2021 PROF. V. G. PATEL 8
TRANSFORMER ENCYCLOPAEDIA Type of Transformer Bushings Constructional Details of OIP Condenser Bushing: The bushing is built up around a center tube on which the condenser body is wound. The upper porcelain, lower porcelain and fastening flange are held between the end plates by the center tube and sealing, is accomplished by oil-resistant rubber gaskets in grooves. The annular space between the condenser body and the porcelain is filled with transformer oil and a gas-filled expansion space is left at the top. The oil level can be checked by means of a dip-stick in the oil filling hole. The outer conducting layer of the condenser body is connected to an insulated test tap on the flange. During operation the test tap is automatically earthed and protected by a screw on cap. Monday, September 20, 2021 PROF. V. G. PATEL 9
TRANSFORMER ENCYCLOPAEDIA Type of Transformer Bushings Constructional Details of OIP Condenser Bushing: contd… The lower end-plate is enclosed by an epoxy resin insulated aluminium shield. The inner terminal is attached to the center tube by means of a through-going resilient pin which becomes locked when the outer terminal is screwed on. The pin ensures effective electrical contact between the inner and outer terminals. The inner terminal can be chosen for connection to leads either by brazing or crimping. The outer terminal is available in aluminium or copper alloy and can be supplemented by terminal plates of corresponding material. The upper porcelain is made in one piece of high quality electrical porcelain. The fixing flange is manufactured of corrosion resistant aluminium alloy and is available in straight or, for some types, also inclined designs, the latter giving the bushing an inclination of 150. Monday, September 20, 2021 PROF. V. G. PATEL 10
TRANSFORMER ENCYCLOPAEDIA Type of Transformer Bushings Constructional Details of OIP Condenser Bushing: contd… The flange as well as the other metal parts on the exterior side of the bushing are protected by painting with two-component primer and a grey-blue finishing cost of paint. The bushings are delivered oil-filled and ready for use. They can be stored in any position in warm dry storage. If the bushing is mounted with an inclination of more than 450 from the vertical, special measures may have to be taken to ensure sufficient filling of oil in the bushing. Monday, September 20, 2021 PROF. V. G. PATEL 11
TRANSFORMER ENCYCLOPAEDIA Type of Transformer Bushings Important tests on HV Bushings: High voltage bushings are subjected to the following type tests: - Measurement of D. C. resistance between terminals of conductor. - Temperature rise test (with one end placed in hot-oil corresponding to the transformers oil temperature). - Short-circuit test for one second: A current of the order of 25 times normal rated current is passed through the conductor for one second. The test is followed by dielectric test. Monday, September 20, 2021 PROF. V. G. PATEL 12
TRANSFORMER ENCYCLOPAEDIA Type of Transformer Bushings - Dielectric test: These include the one minute power frequency voltage withstand test (dry): One minute power frequency voltage withstand test (wet) for outdoor bushings only. Switching impulse voltage withstand test; Lightning impulse voltage withstand tests. - Partial Discharge Test. The routine tests on the bushing include - Measurement of Insulation Resistance - Measurement of resistance - Power frequency voltage withstand test for one minute. After installing the bushing on the transformer, the tests are conducted on the complete transformer. Monday, September 20, 2021 PROF. V. G. PATEL 13
TRANSFORMER ENCYCLOPAEDIA Type of Transformer Bushings Technical Particulars of HV transformer Bushing: - Rated voltage - Impulse withstand test level - Rated current - Rated short-circuit current and duration - Oil-impregnated condenser body of high-voltage insulation paper - Great adaptability-available with or without space for current transformers, with straight or, for some types, also inclined flanges, alternative connection details, normal or anti-fog porcelain in brown or light grey colour. - Free from partial discharges in the insulation. - Thermal stability-withstands system voltage to earth for unlimited time. - Equipped with test tap for tan measurement and measurement of partial discharges in the transformer. - Maintenance free and non-susceptible to ageing. - Hermetically sealed with own oil system. - The technical data fulfill the requirements for insulation according to the following standards: IEC, IS, ANSI, BS, DIN. Monday, September 20, 2021 14 PROF. V. G. PATEL
TRANSFORMER ENCYCLOPAEDIA OPEN FORUM Monday, September 20, 2021 15
TRANSFORMER ENCYCLOPAEDIA THANQ Monday, September 20, 2021 16
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