Nowadays, the wind energy is one of the fastest growing renewable energies in the world. The increasing presence of wind farms with electronic controls pose several issues for the protective relaying systems. The issues with conventional protection relays when applied to wind farm protection is due to the fact that short circuit currents from wind farm, especially those based on type III and type IV, are fundamentally different from short-circuit currents of synchronous generators. This paper investigates the performance of a typical differential protection scheme for a 110kV power transformer which connects a DFIG wind farm to the grid. The simulation results show that wind farm short circuit current might cause incorrect relay operation.