Patent ID: 6931856

Claim:
A method for operating an electrical generation system having a multi-spool gas turbine engine comprising at least first and second spools, the first spool including a first shaft, a first compressor mounted on the first shaft, a first turbine mounted on the first shaft, and a combustor operable to combust or react a mixture of fuel and compressed air from the first compressor to produce hot gases that are expanded in the first turbine to produce mechanical power to drive the first compressor, the second spool including a second shaft and at least a second turbine mounted on the second shaft, the second turbine arranged to receive gases exhausted from the first turbine and expand the gases to produce mechanical power, the second spool being rotatable independently of the first spool, the method comprising the steps of: providing a main generator coupled with one of the first and second spools so as to be driven thereby, the main generator operable to generate an alternating current; providing an auxiliary generator/motor coupled with the other of the first and second spools, the auxiliary generator/motor selectively operable in either a generation mode or a motor mode, the auxiliary generator/motor in the generation mode being operable to extract mechanical power from the spool to which the auxiliary generator/motor is coupled and generate an alternating electrical current for supply to the load, the auxiliary generator/motor in the motor mode being operable to receive electrical power from a source and convert the electrical power into mechanical power that is injected into the spool to which the auxiliary generator/motor is coupled; causing the auxiliary generator/motor to operate in a selected one of the generation and motor modes; and controlling operation of the auxiliary generator/motor in the selected mode so as to affect an operating condition of the gas turbine engine.