This paper investigates the impact of doubly fed induction generator (DFIG) based variable speed wind turbine on system frequency control. It is shown that DFIG has the capability to contribute short term frequency support following loss of generation. Simulation studies have been carried out on a reduced model of transmission power grid of Chittagong region in Bangladesh that combines hydro, gas and wind type generations. The dynamic simulations have been performed in professional software package PSS/E. Simulation results presented demonstrates the capability DFIG based wind farm to support system frequency during network contingencies.