Abstract: The problem of detecting low frequency faults is solved in a VSCF control system which is operated in a start mode to start an engine (18) using a brushless synchronous generator operating as a motor (12). The motor (12) receives power through a feeder (52) from a converter (36) which is coupled through an additional feeder (44) to a source (42) of AC power. During normal, non-fault conditions, the sum of the input currents to the converter (36) and the sum of the output currents from the converter (36) must each be zero. When a fault condition exists, then one or both of these currents will be non-zero, depending upon the location of the fault. A single current sensor (56) is used to sense feeder faults by positioning the sensor to read the current through the converter input feeder (44). As long as no feeder to ground fault condition exists, then the current sensor (44) senses zero current. If a non-zero current is sensed, then it is assumed that a fault condition exists.

Abstract: Prior starting/generating systems which operate a generator as a motor to start a prime mover have been inefficient since motive power was delivered to the prime mover through hydrostatic trim and differential components of a constant speed drive interposed between the prime mover and the generator. In order to overcome this problem, means are provided between the prime mover and the generator for bypassing these components of the constant speed drive when operating in a starting mode so that motive power is transferred directly to the prime mover. This, coupled with the fact that the generator is operated as a motor responsive to generator speed and/or generator power factor, increases the efficiency of the system when in the starting mode.