One operation circumstance in Dispersed Generation (DG) concepts, an island, is formed when one or more DGs and an aggregate of local loads are disconnected from the main grid and then, remain operational as an islanded entity. This condition of islanding is conventionally undesirable. Consequently, the customers will suffer the blackout. Recently, this blackout phenomenon has been eliminating by facilitating islanded operation. This paper presents a passive method in detecting islanding for DGs by measuring the negative-sequence impedance differences between islanded mode and grid-connected mode at the line frequency. Subsequently, the islanded entity is connected to a backup system by Solid State Transfer Switch (SSTS) in order to smoothly and quickly keep electricity available to customers.