standards / manuals / guidelines for small hydro development - AHEC

Section –3Selection of Power Transformer1.0 GeneralPower transformers function is to convert electric power from one voltage level toanother. In hydroelectric plants, step up transformer perform the task of delivering powerproduced by the generators to the transmission system. Most of these transformers areunit connected i.e. directly connected to generators with or without a generator breaker.These power transformers are generator transformers. Power transformers are liquidimmersed. Power transformers are located outside preferably in the switchyard /ortransformer deck in powerhouse. These guidelines are for generators/power transformersused in SHP for outdoor switching i.e. 11 kV to 220 kV.1.1 Relevant national and international standards in this connection are as follows:IS: 2026 (Part 1 to 4) - Specifications for Power TransformerIS: 2099 - Bushings for alternating voltage above 1000VIS: 3639 - Fittings and accessories for power transformerIEC: 60076 (Part 1 to 5) - Specifications for Power TransformerCBI & P - Manual on transformer (oil immersed)(Publication No. 295-2007)IS: 11802.0 Generator TransformersPower transformer which step up the power produced by hydroelectric generating units(0.415 to 11 kV) to a level which matches the sub transmission/transmission systemvoltage (typically 12 kV to 245 kV class) for range of power houses under considerationsare 2 winding oil immersed transformers.Three Phase Versus Single Phase TransformerThree phase generator transformers should be used unless transport limitations or otherspecial reasons require use of single-phase transformer because of the following reasons.a) Higher efficiency than three single-phase units of equivalent capacity.b) Smaller space requirements and reduction in weight and dimensions.c) Lower installed cost.d) Lower probability of failure when properly protected by surge arrestors, thermaldevices and oil cooling and preservation system.3-1