Field current signature analysis for fault detection in synchronous motors

Often encountered driving critical applications, synchronous machines (SM) require reliable condition monitoring systems. In this paper, the advantages of using the field winding current of a synchronous motor as an early indicator of machine faults are demonstrated. Analysis is carried out, both through simulation, via the use of finite element methods (FEM), and through experimentation, using a specially-designed synchronous machine which allows various fault conditions to be investigated such as eccentricities and short-circuits. It is established from the comparison of the spectra, between healthy and faulty field current data, that the field winding current is well suited for fault detection as well as discrimination among the common faults in SMs. Further, it is shown that field winding current is quite sensitive to any problem of the stator, permitting the detection of stator short-circuits at a very early stage. Thus, it is concluded that an improved condition monitoring and protection system for SMs may be achieved if the field current is effectively monitored.