Although wind power development is still mainly based on land sites, a number of large offshore wind farms have been developed, and there are significant plans for further offshore wind power development, This development produces a need for accurate models of all main components in a wind farm because simulations are widely used to predict what happens in case of faults and switching operations in the grid. The result of simulations can always be questioned, and depends on the accuracy of the component models used in the simulation program. Validation of simulations with reliable measurements performed in a real large wind farm makes it possible to verify and improve the simulations and to give more reliable results. DELTA has built a system for measuring fast transients synchronously in three different locations on a wind farm.