Wind farms are currently built in the North Sea in the Netherlands. The grid connecting the off-shore wind farm to the main-land distribution grid must be protected against short-circuits and other electrical disturbances. In this project is studied if electrical protection of a grid is suitable for grids connecting renewable energy sources to the transmission grid. The research question is as follows: Does the distance protection function of a protection relay respond correctly to all faults in a wind farm electrical grid? The research question is tried to be answered through simulations and tests. Faults are simulated, and a part of the grid is tested in a real protection relay. The results of these tests show that the protection relay does not always react as expected. Results are analyzed to explain these unexpected results. A situation with a three-phase fault and a situation with a two-phase to ground fault caught the attention. These two unexpected results are analyzed with calculations to explain the behavior and find the cause. The calculations give more insight, but no single solution has been found. Recommendations are given to reduce the change of undesired behavior of the protection relay.