An Intelligent Model and Simulation of High Voltage and Medium Voltage Transmission Line Protection Scheme Using Time Overcurrent Relay Optimization Settings

Abstract

A new method for optimizing overcurrent relay (OCR) settings and coordination in interconnected power systems was developed. The method considers factors such as feeder impedance equivalences, phase-to-phase fault currents, current settings of 110kV incoming and 15kV outgoing feeders, and operating times for relay characteristics (standard, very, and extremely inverse of overcurrent relay). The maximum fault current of the interconnected power grids is also considered. Power system parameters like X/R ratio, current transformer ratio, transmission line length, resistances, inductances, full load current, line capacity, CT ratio for outgoing feeders, grid frequency, and real power are also considered. To ensure safety and rapid operation of overcurrent relays, settings such as pickup value, time setting multiplier (TMS), and OCR characteristics are carefully considered. The results show that the OCRs coordination interval time to fastest clear faults range from 0.0927 sec-0.062 sec to 0.0764 sec-0.0661 sec for extremely, very, and standard inverse relays, respectively.