Modeling and harmonic analysis of a permanent magnet synchronous machine with turn-to-turn fault

This paper presents analytical models of a permanent magnet synchronous machine with a turn-to-turn fault, both in the stationary and in the synchronously-rotating reference frame. The models are used to investigate how a turn-to-turn fault impacts the harmonic content of the machine. These models can thus be a powerful tool in order to identify a specific behavior caused by the fault, which can be further utilized for fault detection and/or condition monitoring applications. It is shown that, due to the fault condition, the amplitude of the harmonics in the back-EMF changes compared with the pre-fault conditions; the amplitude change is dependent on the number or short-circuited turns in the winding. If a reduced number of short-circuited turns are considered (as typically the case at the beginning of the fault and as considered in this paper), the harmonic amplitude change is comparatively small and therefore difficult to detect. It is shown that a more powerful indication of the turn-to-turn fault is to monitor the current harmonic content in the rotating reference frame, where new harmonics are introduced due to the unbalance caused by the turn-to-turn fault.