7.3 Auxiliary Power Supply in Powerhouse and at Da...
7.3.1 The plant service power should be supplied by two power sources，while the main power source should be connected to the generator voltage bus or unit branch line，and the standby power source may be connected to a bus of 35kV or below or to an outgoing line.
7.3.2 If the plant service transformer is installed indoor and used for distribution of 35kV or below，a drytype transformer should be adopted；if it is installed outdoor，an oil-immersed transformer may be adopted.The number of plant service transformers shall be determined according to the number of units and the characteristics of the hydropower station.The capacities of plant service transformers shall be selected according to the following provisions:
1 If one transformer is installed，its capacity shall conform to the maximum calculated load.
2 If two transformers are installed，when one of them is under overhaul or breaks down，the other one shall be able to bear the plant service power load under normal operation of the hydropower station or the maximum short-term load.
3 When the plant service power load is calculated，the load factor and grid loss rate shall be taken into account，and the self-starting load of electric motor shall be verified.(https://www.daowen.com)
7.3.3 Circuit breaker or fuses protection should be installed at the high voltage side of the plant service transformer.
7.3.4 The plant service power voltage shall be 380V/220V.
7.3.5 If two plant service transformers are installed，the bus for the plant service power should be a single bus or sectional single bus connection.
7.3.6 The dam site power supply may be provided by a dedicated transformer or by the plant service power directly.
