Operation of Over-Current Relays During Double-Phase Operation Mode of Power Distribution Systems

Power system reliability is one of the objectives of every electric utility. Statistical analyses of faults in power systems demonstrate that most of the faults are asymmetrical, most commonly, single-phase to ground. Despite conventional breakers, modern breakers are capable of disconnecting the faulted phase(s). Disconnection of the faulted phase(s) increases the reliability of the system. However, a disconnected faulty phase can cause different challenges for distribution system. These challenges for distribution systems adversely affect the operation of protective devices. In this research, the effects of operating the distribution system with a disconnected phase double-phase operation mode (DPOM)on operation of over-current relays are analyzed. A new method for setting the relays properly during DPOM is presented. In this method, two type of settings, called "prompt settings" and "optimum settings" are presented. The methodology evaluation results prove that the method is capable of re-coordinating the relays during DPOM.