Overcurrent relays coordination : comparison characteristics standar inverse, very inverse and extremly inverse

Abstract

This study discussed the coordination of working time of Over Current Relay (OCR) incoming and OCR feeders on a substation with a 60 MVA transformer, 150/20 kV which supplies 4 feeders. OCR working time coordination was done to compare the performance of OCR using 3 time characteristics : standard inverse (SI), very inverse (VI) and extremely inverse (EI). OCR feeder 1 (OCR F1) was chosen to coordinate work time with OCR incoming because feeder 1 (F1) is the longest (6.10 km) between the 4 feeders so that it has the largest impedance. Phase to phase short-circuit current was calculated at a distance of 0% (bus 20 kV), 1%, 25%, 50%, 75% and 100% length of feeder 1. The short-circuit current was used to calculate the time multiplier setting (tms) also working time (tOCR) OCR incoming and OCR feeder 1 with time characteristics SI, VI and EI. From the comparison analysis of OCR incoming and OCR feeder working time coordination, it was proven that the time characteristics of SI had the best performance by considering OCR feeder working speed and OCR incoming work speed as back up.