Abstract
The isolated power system in Kinmen island, Taiwan has already implemented the special protection system (SPS) to prevent various critical contingencies occurred during the past decade. However, when one severe N-2 contingency occurred on July 26, 2013, the SPS was not properly armed its under-frequency load shedding (UFLS). After re-examining the transient recorded waveforms, it was observed that the system still has sufficient spinning reserve and the coordination between the under-frequency relay and the current SPS was not well considered. In this paper, the current SPS is further modified in order to avoid the occurrence of the excessive load shedding under similar N-2 contingencies. Extensive time-domain dynamical simulations are performed first to study the relationship between the amount of the load shedding and the frequency deviations under these extreme N-2 contingencies. Based on these simulation results, the remediation scheme of the SPS will be proposed by modifying the existing SPS design logic and the amount of load shedding. More comprehensive input triggered states are proposed for identifying these severe N-2 contingencies. Simulation verifications are performed to validate the effectiveness of the proposed remediation scheme.