1. (a) With reference to the phasor diagram, state what is meant by the load angle of a synchronous motor. (b) What is the value of this angle when the motor runs on no-load? 2. (a) Sketch the curve of the power factor characteristic of a synchronous motor as the excitation current changes.
(b) (i) With reference to the curve in part (a), when the excitation is increasing initially state whether the power factor is leading or lagging.
(ii) Explain, with the help of a phasor diagram for one phase, briefly what happens as the excitation increases further.
3. Explain briefly with the aid of phasor diagrams, how the synchronous machine stator current can be varied if the load is constant.
4. (a) State and explain briefly the main methods of excitation of a synchronous induction motor.
(b) Identify which method of excitation is most commonly used in modern machines.