Short-circuit faults in high-speed PM machines with parallel strands and coils

Electrical machines for safety critical applications need to be able to withstand all possible short-circuits, including those between individual turns. In high-speed machines multiple parallel strands may be used to reduce AC losses in the winding, increasing the likelihood of a turn-level short-circuit. This paper considers the consequences of using parallel strands on the short-circuit losses. Additionally, the effect of using a PWM voltage supply is also considered. It is found that using multiple parallel strands reduces the local losses that occur during a short-circuit, but at the same time slightly increases the total losses. Also, local fault currents can be reduced better with a remedial terminal short-circuit when using parallel strands, suggesting a small safety benefit. The effect of supply voltage harmonics on the maximum short-circuit losses is found to be negligible.