Inverter-Embedded Detection of Rotor Winding Faults in Doubly Fed Induction Generators for Wind Energy Applications

Automated and remote testing of wind turbines is highly desirable since they are prone to failure with the harsh operating environment, and are difficult to test due to the remote location and limited accessibility. The turn insulation of the rotor winding is susceptible to failure due to operating stresses. Unlike turn faults in the stator, rotor turn faults do not cause immediate failure due to the low induced voltage in the shorted loop at low slip frequency, and therefore, are difficult to detect during operation. Although this fault progresses slowly, it must be detected to prevent performance degradation due to rotor asymmetry. In this article, a new concept for inverter-embedded testing of doubly fed induction generators (DFIG) used for wind energy applications is presented. The main idea is to inject test voltages into the DFIG rotor winding from the rotor side inverter whenever the wind turbine is stopped, to extract information on the rotor asymmetry. The proposed test concept is a simple off-line test that can be implemented in DFIGs without additional hardware to perform automated and sensitive detection of rotor faults. Experimental results show that faults in the rotor winding can be detected with higher sensitivity compared to on-line methods for improving the reliability of wind turbines.