Industrial coordination technique of overcurrent protection relays between sub-transmission 132/33 kV and distribution 33/11 kV networks: a two-stage particle swarm optimization method

An overcurrent relay (OCR) is a crucial and cost-effective protection device for radial power networks. Coordination between OCRs can be challenging, though, given the complexity in different voltage levels, especially between sub-transmission and distribution substations (STADSs), and the need for quicker and more dependable fault clearance. Relay coordination on IEEE-bus networks has been the main focus of previous research, while realistic STADSs that more closely mimic real-world situations have received less emphasis. This research proposes a two-stage particle swarm optimization (PSO) method to bridge this gap. It coordinates OCRs for the STADSs from 11 kV to 132 kV and is based on a symmetrical three-phase bolt fault on the feeder end as a worst case. The method effectively optimizes time multiplier settings (TMS) for all the OCRs to reduce overall operating time while preserving the necessary Coordination Time Interval (CTI). This method is insightful since it uses real STADS data and offers a practical assessment of industrial relay coordination capability. The proposed method reduced the overall relay operation time by almost 20% over the traditional method using DIgSILENT Power Factory simulations. These outcomes demonstrate the method's efficacy in improving protection stability, selectivity, and dependability in contemporary power systems.