Sequence circuit-based modeling of a doubly fed induction wind generator for eccentricity diagnosis by split-phase current signature analysis
A wound-rotor three-phase induction generator with eccentric rotor and parallel connections in both stator and rotor can be represented by five equivalent sequence-circuits of virtually centered-rotor machines, as mathematically proved in previous papers. The five circuits allow the calculation of stator and rotor fault-related currents, in form of 2(p±1)-pole space vectors for 2p-pole machines. The formal calculation of fault-related currents is very useful to define fault indicators and tools for diagnosis, and in case of parallel-connected stators (like in many wind generators) the split-phase current signature analysis becomes viable. In fact, by reversing the equations linking split-phase current amplitudes and eccentricity degrees, original fault indicators are carried out in this paper. The new indicators are validated by simulations of a 1800kW wind induction generator with static, dynamic, and mixed faults in full-load conditions. The simulations are carried out by using a full FEA model of the motor, implemented by time-stepping FEM-circuit co-simulation software (Maxwell-Simplorer). A good match is obtained between theoretical calculations and simulations.