Inverter-Embedded DFIG Rotor Winding Insulation Testing for Wind Energy Applications

Failure in the rotor winding insulation of doubly-fed induction generators (DFIG) is common due to the harsh environment and operating stresses. However, testing rotor insulation is difficult and costly due to the limited accessibility of wind generators as they are installed at remote locations inside the nacelle. Therefore, remote and automated insulation testing can help improve the reliability and reduce maintenance cost of wind generators. In this paper, a new approach for testing the integrity of rotor winding insulation for DFIGs is proposed. The main idea is to use the rotor-side inverter to perform off-line insulation testing whenever the wind generator is stopped. New test methods for off-line 1) partial discharge (PD) detection based on impulse voltage excitation and 2) capacitance (C) and dissipation factor (DF) testing based on common mode voltage excitation are proposed. Testing on a 6.3 kW wound rotor induction machine is given to verify the effectiveness of the proposed rotor insulation test method.