Inter-Turn Short Circuit Fault and High Resistance Connection in Stator of Doubly-Fed Induction Generators

Doubly-fed induction generators (DFIG) have been widely used in wind turbines installed in the last decades. These generators are prone to some faults that could deteriorate their performance and even lead to their outage from the network. Stator inter-turn short-circuits (SITSC) and high resistance connections (HRC) in the stator are two major types of faults that cause electrical asymmetry in the stator circuit. Yet, SITSC are more noticeable and require immediate scrutiny. Hence, if an HRC can be distinguished from a SITSC fault, the immediate outage of the WT can be avoided in the case of an HRC. In this paper, both types of faults are studied and compared, being their detection performed using appropriate fault indices obtained from the stator current, rotor current, and rotor modulating voltage signals, all available in the control system of the DFIG. Several fault severity indices are proposed for a better evaluation of the fault extension, and the discrimination between SITSC and HRC is discussed. The performance of the defined fault indices is verified using a magnetic equivalent circuit model of the DFIG and an experimental setup with the DFIG running at several operating conditions.