When performing short-circuit investigations in power systems including wind power, valuable and accurate results can only be obtained by considering the real behaviour of wind turbines which is specified in national grid codes. This requires the consideration of the exact active and reactive current injections during the fault. In this master thesis an equivalent VSC-based wind turbine model for short-ciruit calculations at steady-state conditions is developed; it is based on the Thevenin equivalent where paramenters are adjusted by a routine in order to force the model to behave as required by the German grid code, which is considered as reference regarding the grid voltage support. The routine, including the adjustable wind turbine model, is implemented in DigSILENT PowerFactory using the DPL-Programming Language. The developed wind turbine model is validated by comparison with a valiadated dynamic model provided by Siemens Wind Power. The comparison in some significant cases proves that the routine accurately implements the injection of the desired active and reactive current components according to the German grid code. The wind turbine model is finally rescaled to obtain an aggregate wind farm model and used to perform short-circuit calculations in a real power system including wind power. The Danish transmission system is considered and a large offshore wind farm with VSC-based wind turbines is included in the investigation. Test results in significant study cases prove that the current contribution from the wind farm has been successfully implemented in a general way and, thus, initial project goals have been completely achieved.