Condition monitoring of wind turbine induction generators with rotor electrical asymmetry

This study investigates the condition monitoring of wind turbine wound rotor and doubly fed induction generators with rotor electrical asymmetries by analysis of stator current and total power spectra. The research is verified using experimental data measured on two different test rigs and numerical predictions obtained from a time-stepping electromagnetic model. A steady-state study of current and power spectra for healthy and faulty conditions is performed to identify fault-specific signal changes and consistent slip-dependent fault-indicators on both test rigs. To enable real-time fault frequency tracking, a set of concise analytical expressions, describing fault frequency variation with operating speed, were defined and validated by measurement. A variable speed study, representative of real wind turbine operations, of current and power frequency components for healthy and faulty conditions was then carried out on one test rig, which could simulate wind conditions. The current and power fault frequency tracking previously identified achieved reliable fault detection for two realistic wind turbine generator fault scenarios of differing severity. Conclusions are drawn on the relative merits of current and power signal analysis when used for wind turbine wound rotor induction machine fault detection and diagnosis.