Power industry has been emphasizing more importance on a distributed generation because there is new technology like Photovoltaic (PV), fuel cell, wind turbine, and power electronic use for advancement of the power system has been evolved so much which cannot be possible without distributed generation. The majority of small scale PV systems are domestic roof-top type installations and are generally single-phase systems. Rebates and concession schemes that were introduced by the government for installing small scale PV systems along with price reductions in PV panels are the main reasons for the increased number of grid-connected small scale PV systems in the power distribution grid. Hence Distributed Generation (DG) has become an inseparable part in power system and gained so much importance because of economic and environmental purpose. Islanding is a situation where a part of the distributed generation system containing a distributed generator gets electrically isolated from the remainder of the power system continues to energize the network where the situation has occurred. Thus it has become important that the portion where islanding has occurred must detect this situation immediately for safety purpose. If tripping doesn't occur in time, there can be a various and critical problem. Currently, in industry practice, we disconnect all distributed generators after islanding has occurred. Generally, a distributed generator should be disconnected within 0.1s to 0.3s after the loss of grid/main supply. This paper gives a simulation model to achieve this, each distributed generator must be supplied with an anti-islanding device which detects islanding like UOF and ROCOF relays.