Capability improvement of over/under frequency relays by using a hybrid islanding detection method for synchronous based DG units

The aim of this paper is increasing performance of over / under frequency relays using of both active and passive method to prevent islanding operation. The proposed active method is based on applying high value impedance load which can improve performance of ROCOF relays (passive method) in small power mismatches. In fact, proposed method is a supplement for over / under frequency protection (OFP/UFP). In addition, the performance of proposed method is evaluated under various disturbances. Results demonstrate that proposed method can be discriminated between islanding and non islanding situations.