Application of Under-Frequency Relay (UFR) in Load Shedding Scheme for System Stability (A Case Study on PT. PLN Kendari)

A reliable electric power system must maintain its operation in stable conditions with the support of various protection system during normal operation or when a fault occurs. To minimize the frequency of blackouts in the system due to interference, transient conditions, or the increased load, this study simulated the load shedding scheme using under-frequency relays (UFR). The analysis was done in ETAP 12.6.0 software using the Transient Stability Analysis feature. In this simulation, discontinuation occurs in the CB (Circuit Breaker) generator which causes the generator to escape from the system in two conditions, namely Peak Load Time (PLT) and Off-Peak Load Time (OPLT). The study simulated scenarios where circuit breakers (CB) tripped due to a fault, which causing a power plant to be disconnected from the grid. The scenarios were simulated in two conditions, during the peak load and off-peak load. The results show that during the peak load, the simulated Load Shedding Scheme 1 to 3 was occurred on the frequency of 49.3918 Hz, 48.72 Hz, and 48.0195 Hz, respectively. The respective disconnected loads on Scheme 1 to 3 were 4.529 MW, 41.84MW, and 59,072 MW while the recovery times were 2.432 s, 0.081 s, and 0.626 s, respectively Meanwhile, in the off-peak load, the UFR tripped at the frequency of 49.3958 Hz, 48.5855 Hz, and 47.75 Hz, the disconnected loads were 3.652 MW, 30.627 MW, and 43.93 MW, and the recovery time were 2.934 s, 0.588 s, and 0.592 s for Load Shedding Scheme 1 to 3, respectively.