Detection of stator turn fault in induction motors using the extension of multiple reference frames theory

This paper analyses some methods that are used to detect the stator turn fault in induction motors, and points out that the negative sequence impedance is the recommended indicator of the stator turn fault detection when the inherent asymmetry of the motor, unbalance of the supply and variety of the load are taken into account. Furthermore, a novel approach to obtain the negative sequence impedance based on the extension of multiple reference frames theory (MRFT) is proposed. Since the supply fundamental frequency is not a constant and hard to be measured accurately, the conventional synchronous reference frame transform is not quite strict. To extend the synchronous reference frame transform matrix, this method uses the fundamental positive sequence components of three-phases voltage signals and their Hilbert transform to replace its elements. Negative sequence current can be acquired exactly through the new transform, and then the negative sequence impedance is also obtained precisely. The advantage of this method is avoiding the dependence of the supply frequency and making the detection more reliable. Experimental results demonstrate the validity and effectiveness of this method.