Risk reduction in special protection systems by using an online method for transient instability prediction

Special protection systems (SPS) are designed to detect abnormal system conditions and initiate corrective action to mitigate the consequence of the abnormal conditions and provide acceptable system performance. Most of SPS are designed based on offline simulations. This may result in additional risk when system conditions differ from the offline simulations. To solve this problem, an online algorithm is proposed in this paper to predict transient instability based on the measurements of phasor measurement units (PMU). This algorithm is employed to design a generator rejection scheme (GRS) which acts according to the online instability prediction. The proposed GRS is implemented on a test system; WSCC 9-bus system. Also, the power plant instability risk is calculated with the old GRS decided based on offline simulations and with the proposed GRS. Comparison between the results of the risk assessment reveals the effect of the proposed GRS on risk reduction.