Abnormal conditions such as overload and generator tripping usually result in large excursion of power system frequency, voltage and other system variables. In this case, an effective method to prevent the electric power system from instability, frequency collapse and blackout is an under-frequency load shedding scheme. It is applied in order to maintain stability of the system, when the power system generation fails to supply the increase of load. Load shedding is a common technique to maintain the power system stability by curtailment of partial load in some part of the system. However, the load shedding techniques for an islanded distribution network should be treated differently from the transmission power system. A particular approach of under-frequency load shedding scheme is required for an islanded system which is known to be not as strong as the grid.