Off-line estimation of abnormal field voltage occurrence condition at asynchronization for synchronous generator with brushless system

This paper presents a practical method to estimate the abnormal field voltage occurrence condition (AFVOC) at asynchronization for synchronous generator (SG) with a brushless excitation having a diode rectifier circuit in the rotational part of the SG. A simulation model to calculate the field transient current at asynchronization to the power bus system is shown. The AFVOC is estimated by simulating the field current at asynchronization and searching the condition (i.e., armature voltage and its phase differences) when the field current becomes negative. The proposed method is implemented on a 10kVA salient-type lamination-pole SG with pseudo external diode rectifier circuit connected to the field winding terminals. With simulation and experimental results, the validity of the proposed method is verified.