Decentralized Coordination of Load Shedding and Plant Protection Considering High Share of RESs

This paper estimates the average Rate of Change of Frequency (ROCOF) following islanding and/or cascading event/s using inflection points of frequency profile. Moreover, a frequency collapse barrier scheme is set up by tuning the frequency set points of Load Shedding (LS) relays as a dynamic variable using voltage drop data coordinated with plant protection scheme. A frequency anti stalling scheme is developed to interrupt more load feeders in case of frequency stall between consecutive set points. This time-based approach adjusts the time delay of the relay stages to disconnect the feeders with more voltage drop first, in order to bring the frequency back to the permissible range before the tolerable time period of plant protection relays is over. The load curtailment is stopped to avoid over LS, if the proposed algorithm recognizes that the frequency reaches the safe region in time based on estimated average ROCOF. Tripping of feeders, which inject active or reactive power to the grid due to penetration of dispersed generations into the load feeders is also prevented by considering the power flow direction of feeders.