Impact of overspeed protection control on stability for islanded power system

Islanded power system can be formed by unexpected electric equipment failure or initiative breaking off of a main system avoiding a whole collapse. Unbalanced power between generation and load may cause an overspeed of the units and trigger the action of Overspeed Protection Controller (OPC) which is mainly designed for a load rejection condition. The mathematic model was built to simulate the islanded system stability with the effect of OPC. The simulation reproduced the power and frequency oscillation as the accidents. The results show a great impact of OPC on the stability of an islanded system. Modified OPC logic was proposed to avoid the oscillation and increase the stability.