When a gas-turbine generator is started-up, its rotor must be accelerated by external means to about 60% of the rated speed before the start-up process becomes self-sustaining,in other word before the turbine can generate sufficient power to continue process independently. The energy required for this purpose can be provided for instance by a static frequency converter (SFC).
generator circuit breakers GCB also contain the switching functions required for SFC starting within its enclosure. The output of the SFC (voltage of variable amplitude and frequency) is fed to the generator terminals via the starting switch that is designed for the voltage, current
and current duration occurring during the SFC start-up period of the gas turbine. Its rated voltage is chosen according to the rated voltage of the SFC which in general is considerably lower than the generator rated voltage.
The typical layout of a gas turbine power plant is depicted in Figure.
MT:Main transformer, UT:Unit transformer , SS:Starting switch, SFC: Static frequency converter, AUX:Unit auxiliaries.
