SM. An AC electrical machine operated with a constant electromagnetic field.
synchronous machine (SM)
A synchronous machine is an ac electrical machine operated with a constant electromagnetic field. Its instantaneous speed of normal operation is exactly proportional to the frequency of its ac voltage. An SM with a round rotor has a uniform air gap, so that the reluctance does not depend on the flux position. Contrarily, the air gap of an SM with a salient-pole rotor varies circumferentially around the rotor, resulting in a non-uniform reluctance.