Electrical power generator for a gas turbine engine

An electrical power generation system (100) for an aircraft gas turbine engine (10). The system comprises an alternating current electrical generator (110) having a rotor (114) comprising a plurality of electromagnetic rotor windings (118) and a stator (124) comprising a plurality of electrical stator windings (126). The rotor (114) is mechanically coupled to a shaft (36) of the gas turbine engine (10) by a transmission system (129). The electrical generator (110) further includes an electrical output frequency controller (130), a torque sensor arrangement configured to determine a torque imposed on the transmission system (129) by the generator (110) and a controller (112) configured to operate the electrical power generation system in first mode and second modes. In the first mode, the frequency of the electrical power output of the electrical generator (110) is controlled by the electrical output frequency controller (130) to lie within predetermined limits, and a reduced idle signal is provided to a gas turbine engine controller (132). In the second mode, the frequency of the electrical power output of the electrical generator (132) is not controlled by the electrical output frequency controller (130) and an increased idle signal is provided to the gas turbine engine controller (132). The electrical generator controller (112) is configured to operate the electrical power generation system (100) in the first mode when the torque is below a predetermined limit, and in the second mode when the torque is above a predetermined limit.