Detection of Rotor Inter-turn Short Circuit Fault in Doubly-fed Induction Generator using FEM Simulation

Doubly fed induction generators (DFIGs) are negatively affected by the inter-turn short-circuit fault of rotor windings, so for continuous and safe operation of the wind turbine, it is important to examine the DFIGs. For this purpose, a finite element method (FEM) based model has been designed to check the behavior of the generator under normal and inter turn short circuit fault condition in the rotor windings. In this paper, a fieldcircuit coupled model of machine was designed using ANSYS Maxwell 2D. The circuit is modeled by a small elements mesh. Three phase AC current source is provided to the rotor windings and the excitations on rotor winding side are set in the external circuit. The stator and rotor slot number are 72/60 and number of turns per phase for stator and rotor are 228/100. The outer diameter of stator is 520mm and the inner diameter is 350mm. The outer diameter of rotor is 346.6mm and the inner diameter is 110mm. Different rotor inter turn short circuit fault conditions are accomplished by reducing the number of turns in rotor slot. Based on the simulation, it was found that phase difference and positive and negative sequence of current analysis were effective methods to diagnosis the rotor inter turn short circuit fault. During the normal operation, all the three phases are equally distributed and are 120° degrees apart and start to distracted from 120° degree when inter turn short circuit happened. Under normal condition, the negative sequence of current is low. However, as the fault degree enlarges, negative sequence of current becomes larger, thus ratio of negative to positive sequence of current also increases. The simulation results illustrate that the analysis done in this paper is quite appropriate as desired, also proposed technique is advanced in wind turbines.