One of the most important methods in the field of anti islanding protection of wind turbine is rate of change of frequency (ROCOF). When a self-excitation induction generator is islanded, voltage and frequency will vary and in most cases, exceed from legal range that can be detected by voltage relays, frequency relays and ROCOF relays. In this paper ROCOF relay performance in case of induction generator is studied. However there are some condition called non detection zone that cause voltage and frequency remain in allowed interval and islanding situation doesn't recognized which leads to problems in power system. Performance of a ROCOF relay and its non-detection zone for an induction generator analyzed. A 0.66Mw, 690V induction generator and ROCOF relay were simulated in MATLAB/SIMULINK and characteristic curves of ROCOF relay obtained.