Electrical power generator for a gas turbine engine

An electrical power generation system for an aircraft gas turbine engine, the system comprising:

• a main electrical generator comprising a wound field electrical machine, the main generator having a rotor comprising a plurality of electrical rotor windings and a stator comprising a plurality of electrical stator windings, the rotor being mechanically coupled to a shaft of a gas turbine engine by a transmission arrangement, wherein the electrical power generation system comprises:
• an electrical output frequency controller configured to control the frequency of an electrical output of the main electrical generator within a predetermined range of frequencies;
• a torque sensor arrangement configured to determine a torque imposed on the transmission arrangement;
• and
• an engine controller configured to increase the rotational speed of the gas turbine engine in the event that the torque imposed on the transmission arrangement exceeds a predetermined torque limit, and to reduce the rotational speed of the gas turbine engine in the event that the torque imposed on the transmission arrangement is less than the predetermined torque limit,
• wherein the system is configured to operate in a first mode, in which the frequency of the electrical power output of the electrical machine is actively controlled by the electrical output frequency controller to lie within predetermined limits and the engine controller is configured to operate the gas turbine engine at a reduced idle speed, and in a second mode, in which the frequency of the electrical power output of the electrical machine is not actively controlled by the electrical output frequency controller and the engine controller is configured to operate the gas turbine engine at or above an increased idle speed;
• wherein the system is configured to operate in the first mode when the torque is below the predetermined torque limit, and in the second mode when the torque is above the predetermined torque limit.