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

Abstract

The novel method based on optimal overcurrent relay settings and coordination for effective substation relays in interconnected power systems was designed and developed. In this paper, the 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) of the power network were computed and determined. The maximum fault current of the interconnected power grids was considered. The network MVA short circuit was considered with both positive and negative sequence impedance of the feeder. The power system parameters like X/R ratio, current transformer (CT) ratio, transmission line length, positive & zero-sequence resistances, positive & zero-sequence inductances, full load current, line capacity, CT ratio for outgoing feeders, grid frequency, and real power were also considered and deployed in the power network. To ensure safety, reliable, and rapid operation of overcurrent relays, settings such as pickup value, time setting multiplier (TMS) of 0.05sec, and overcurrent relay (OCR) characteristics were carefully considered. The selection and determination of OCR characteristics were taken into account by calculating the fault current levels of each fault location percentage based on feeder impedance, turn CT ratio, and pickup values. The results proved that the OCRs coordination interval time to fastest clear faults was between 0.0927 sec-0.062 sec, 0.0949 sec-0.0720 sec, and 0.0764 sec-0.0661 sec for extremely, very, and standard inverse relays, respectively.