Comparison of rotor electrical fault indices owing to inter‐turn short circuit and unbalanced resistance in doubly‐fed induction generator

Abstract

Doubly-fed induction generator (DFIG) is the dominant technology in the wind energy market. Rotor inter-turn short-circuits (RITSCs) and unbalanced rotor resistance (URR) are the main types of rotor electrical asymmetries in DFIG. The URR has already been considered as an electrical fault or asymmetry in the rotor of DFIG. Although the RITSC introduces URR into the rotor circuit its consequences are not similar due to the structure of the machine and presence of current controllers in the DFIG system. In this study, both RITSC and URR are proposed and compared, and the detection of these faults was performed using appropriate indices in the stator current, reactive power, and rotor modulating voltage signals, which are available in the control system of the DFIG. Furthermore, it is supposed that the discrimination between these two types of faults is feasible by utilising proper fault indices at various operating regions of the wind turbine. The performance of the defined fault indices, for different fault severities, is verified using an experimental setup with the DFIG operating under several conditions such as different power injection into the grid and different rotor speeds, including sub-synchronous and super-synchronous operation.