Starter-Generator Systems

Several types of turbine powered aircraft are equipped with starter systems which utilize a prime mover having the dual function of engine starting and of supplying power to the aircraft's electrical system. Starter-generator units are basically compound-wound machines with compensating windings and interpoles, and are permanently coupled with the appropriate engine via a drive shaft and gear train. For starting purposes, the unit functions as a fully compounded motor, the shunt winding being supplied with current via a field changeover relay. When the engine reaches self-sustaining speed and the starter circuit is isolated from the power supply, the changeover relay is also automatically de-energized and its contacts connect the shunt-field winding to a voltage regulator. The relay contacts also permit DC to flow through the shunt winding to provide initial excitation of the field. Thus, the machine functions as a conventional DC generator.