Adaptive overcurrent relay coordination design for energy distribution networks

The fundamental task of protection relays in an electric distribution system is to detect faults and their types, and to generate the necessary tripping signal. The main objective is to isolate the faulty section from the rest of the system, preventing power loss in the unaffected areas. Achieving all these tasks emphasizes the importance of proper protection relay coordination that contributes to system reliability and reduces losses caused by faults. However, even if the parameters of the protection relays in an existing distribution network are set correctly, various factors such as operational changes, planned configuration modifications, restructuring of the distribution system, additions of Distributed Energy Resources (DERs) and generators to the system, fluctuations in energy demand during different seasons, and the impact of wind and ice loads can lead to situations of incorrect operation. To overcome such situations, numerous studies have been conducted in the literature on adaptive protection. These studies primarily aim to enhance the reliability, selectivity, and speed of protection actions in the presence of uncertainties, faults, and changes in the power system. For this purpose, new protection algorithms are being developed using methods such as artificial intelligence, machine learning, and fuzzy logic, which can adjust decision-making processes based on the changing conditions of the system. While these studies often use IEEE 14-bus power systems, there are limited studies that utilize real field data. Additionally, research has been carried out on various communication protocols and strategies for real-time data exchange between protection relays and other devices. In all these studies, one of the aspects that require examination concerning adaptive protection and relay coordination is the anomalies encountered in traditional distribution networks. One prominent anomaly is the operation of ring-shaped networks as two parallel radial feeders by opening them from a specific point. This situation is frequently encountered in locations where personnel are hesitant to make incorrect maneuvers in a ring network. In other words, a radial network is operated as two parallel feeders since it is partially simpler than a ring network. In such a scenario, the power flow direction and short-circuit impedance of the network will vary depending on the point where the ring network is opened. Therefore, recalculations of power flow direction and network short-circuit impedance are necessary based on the new network topology, which requires updating the relay settings. A similar situation can be encountered in a ring network during maintenance. When a ring network is opened for maintenance purposes, if a fault occurs in the system during that time, there may be issues with relay coordination since it was not designed for a ring network. This could lead to incorrect tripping or failure to timely trip the fault current. To prevent such situations, it is crucial to adapt the protection relays to the instant and changing structure of the system and enable them to detect and implement the necessary parameter changes in response to any modification in the system. Conventional protection systems may fall short in handling such scenarios, leading to a shift towards adaptive (change-responsive) protection systems. Adaptive protection systems can adjust the protection settings based on the state of the protected zone using multiple setting groups they possess. Thus, adaptive protection systems can adapt to different operating conditions, minimizing the possibility of incorrect operation compared to conventional protection systems. As a result, electric distribution companies and self-generating facilities are increasingly adopting adaptive protection systems instead of conventional ones due to their superior selectivity and reliability. In this specific study, the impact of power supply from different sources to a ring-structured distribution network was investigated using field data. Fault analyses were performed on all buses for three scenarios: grid supply, generator supply, and grid+generator supply. Tripping times were calculated for each scenario. Additionally, changes in relay tripping times when the ring network is opened from a certain point were examined. The results revealed significant changes in relay tripping times when the power source changes or when the ring network is opened from a specific point. Therefore, for every change in the power system, either in terms of the source or the connection, re-coordination of the relays and readjustment of the relay parameters based on the current situation become essential for power system stability. Keywords: Adaptive protection, Relay coordination, Selectivity in power systems 2023, 68 pages