An electromagnetic model for shaft voltages in synchronous generators

Shaft voltages were first observed over a century ago and subsequent work has been conducted on elimination, mitigation and interpretation of the phenomena. Whilst extensive efforts have been placed on modeling of shaft and bearing induced voltages in AC motors driven by variable frequency drives (VFD), similar efforts towards a model dedicated to generators are insubstantial. This paper presents an electromagnetic model dedicated to shaft voltages in a 2-pole synchronous generator. The model is analytically derived in order to improve current physical interpretations of shaft induced voltages in generators. Generalization of the model is established in order to accommodate all practical applications that necessitate shaft voltage prediction. A comparison with experimental shaft voltages indicates that the model yields an effective approximation of the real signal amplitude and harmonics. Additional investigations regarding the behavior of shaft voltages under varying machine complexities and operating conditions provides clarification of previous uncertainties regarding this phenomena.