Performance of ROCOF protection in microgrid

Accompanying the fast development of DG system and more DGs connecting to the distribution system, some new problems appear in protection technique area about grid-connected DG system, among which islanding is a typical and major one. Unplanned islanding will bring many problems to the grid: It threatens the life safety of power line maintaining staff and consumers; influence normal operation of equipment in the islanding system as well as reclosing action. This paper investigates the performance of rate of change of frequency (ROCOF) as used in embedded generation islanding detection of DFIG wind turbines. The impedance measurement based inter-lock algorithm was proposed to prevent the ROCOF from false tripping during a non-islanding situation. The simulation results show that the proposed inter-lock function can effectively distinguish the islanding and non-islanding situations.