How the excitation of synchronous motor effects the power factor presented to the load?
“With a synchronous motor, there are two possible sources of excitation: alternating current in the armature or direct current in the field winding. If the field current is just sufficient to supply the necessary mmf, no magnetizing-current component or reactive kilovolt-amperes are needed in the armature and the motor operates at unity power factor. If the field current is less, i.e., the motor is under excited, the deficit in mmf must be made up by the armature and the motor operates at a lagging power factor. If the field current is greater, i.e., the motor is overexcited, the excess mmf must be counterbalanced in the armature and a leading component of current is present; the motor then operates at a leading power factor. Because magnetizing current must be supplied to inductive loads such as transformers and induction motors, the ability of overexcited synchronous motors to supply lagging current is a highly desirable feature which may have considerable economic importance. In eff
