Detection of rotor turn-to-turn faults in doubly-fed induction generators in wind energy plants by means of observers

The importance of condition monitoring and fault detection increases. This paper presents a state-space observer based condition monitoring algorithm for the detection of rotor turn-to-turn faults in doubly-fed induction generators. A reduced order time invariant machine model for asymmetrical internal parameters will be derived. The model is used for simulation of rotor turn-to-turn faults, which can cause phase to ground or phase to phase short circuits in the rotor. Furthermore a Luenberger observer will be designed using the reduced machine model. It can be used for detection and identification of rotor turn-to-turn faults by analyzing the different behavior of system and observer. Another advantage of the observer is its ability to reconstruct immeasurable internal states like the current in the short circuited turns of the turn-to-turn fault. Due to the fact that the induced fault current is speed dependent and becomes zero at synchronous speed, the reconstruction of the fault current can help to evaluate the danger of the short circuit current at the actual operating point of the generator and permits a limited operation until maintenance.