Diagnosis of Interturn Short-Circuit of SRM Based on Ratio of Current Components

Abstract

Inter-turn short-circuit is a common fault mode of switched reluctance motors (SRM) that causes changes in the parameters of the motor that can cause vibrations and noise. In this paper a diagnosis method is proposed to detect short circuit fault. Firstly, the model of a phase winding with inter-turn short-circuit is built and the fault characteristics are analyzed. Under normal condition, the sinusoidal components of phase currents are mostly a positive sequence with minimum distortion. The frequency signature of the motor is extracted by Fourier analysis when operating in normal conditions. When a fault condition occurs, symmetry of the phase currents is broken and both negative and zero sequence component of the phase currents appear. According to the asymmetry, an index, the ratio of negative to positive sequence component of the phase currents, is defined to identify whether the motor is working normally. The proposal is verified by simulations and experiments on a three-phase 12/8 structure SRM under different mechanical operating conditions. In normal condition, the fault index is about 0.02; in 12.5% fault condition, the fault index rises to about 0.07; in 25% fault condition, the fault index rises to about 0.08. According to the experimental results, fault index is robust because it is not influenced by the following parameters: turn on angle, turn off angle, rotor speed, load torque, etc.