Characteristics of a synchronous motor with current-compounded self excitation

It is common practice with synchronous motors to use some form of excitation control to ensure either constant power factor or constant reactive power at all normal loads. The use of a static current-compounded self-excitation circuit for this purpose is explained in the paper. Measurements showing the accuracy of control and the stability limit during steady-state operation are presented, and these are compared with corresponding results for constant excitation. The transient characteristics of the controlled motor are discussed, and the transient stability and the response to a sudden load change are investigated. Reasonably accurate agreement is obtained between measurements and theoretical predictions made from a simple study of an idealised excitation circuit. The possibility of this form of excitation giving rise to sustained rotor oscillations is mentioned, and a possible cure is advanced.