Short circuit currents of DFIG based wind turbines

The share of wind energy is growing day by day and asynchronous machines like doubly fed induction generators are finding their place in the grid. These asynchronous generators under transient conditions like fault behave in a different manner than synchronous ones. In order to achieve fault ride through capabilities for such generators special protection scheme is needed. One of the solution technique is to use crowbar resistances on rotor winding to protect the rotor side converter. During a fault, the current profile of DFIG is different compared to a conventional generator. This paper focuses on the short circuit current profiles of DFIG for wind turbines. An analytical expression is described for an asymmetrical fault current which is slip and initial condition dependent. Crowbar protection scheme and its effect on short circuit characteristics has been discussed. A brief analysis on the effects of these fault currents on generator circuit breaker is considered. Simulation results compared with theoretical analysis is presented for verification.