The Research On Fault Characteristic Of The Stator Winding Inter-turn Short Circuit In Doubly Fed Induction Generators

In recent years renewable energy which is used to solve the problem of human survival has become a strategic choice because of energy crisis. In this context, wind power generation has expanded rapidly throughout the whole world. With wind power technology is emphasized more and more, large-scale wind turbines are and will be in operation. The Doubly Fed Induction Generator is the most epidemic model in wind power system. It is necessary to discover incipient faults as soon as possible to minimise maintenance costs and down time. Incipient faults may occur in the stator, rotor, bearings, air gap eccentricity etc. According to a survey, stator faults account for some30%-40%of all faults. The inter-turn short circuit fault in the stator winding is taken to be the essential fault and it can cause such as more heat and makes the local temperature higher than other place. In the end the local insulation becomes worse and brings a catastrophic fault, such as phase-to-earth and phase-to-phase fault. So the characteristics of a DFIG must be known for this fault condition in order to select the best way to diagnose the fault. In view of this, in the thesis characteristics of the Doubly Fed Induction Generator stator winding inter-turn short circuit fault are studied.First, this thesis erects the mathematical model for the Doubly Fed Induction Generator stator winding inter-turn short circuit fault based on multi-loop theory. The way of branch and loop selection is analyzed and the calculation of inductance parameters in mathematical models is also explained.Second, this thesis simulates inter-turn short circuit fault in varying degrees. The stator voltage, branch current and variation of line current under appropriate degree of fault are analyzed and harmonic analysis is introduced. The characteristics of the line current harmonics are given. The simulation results are basically consistent with the theoretical analysis.From the results of the simulation, the following conclusions can be obtained: The current of the fault phase is bigger than that of normal phase and inverse to fault percentage in DFIG. By harmonic analysis, fractional harmonic appears in the current of fault phase. when inter-turn short circuit fault occurred in the stator windings, it can be distinguished by phase current. So that phase current and fractional harmonic are suitable fault features to stator fault.