Identification of the optimum protection co-ordination in medium voltage distribution system of Sri Lanka

Abstract

Majority of the faults in power network are transient and these faults can be cleared with proper installation of protective devices with appropriate protection settings. It is important to clear the faults as soon as possible by keeping the healthy network undisturbed while avoiding damages to lives and instruments. Monthly tripping summary of Medium Voltage feeders of Grid Substations of Ceylon Electricity Board revealed that some feeders getting disturbed abnormally. Further, it is observed that Auto Reclosers are installed in downstream of these 33 kV feeders to respond to the transient faults but they are not yielding expected results. Hence, applying most appropriate protection setting to these protective devices are very much required for the higher reliability of the Medium Voltage network. Two Medium Voltage feeders which were mostly disturbed were analyzed deeply and found that most of the feeder trippings are owing to Earth Fault Further, with installation of temporary Digital Disturbance Recorder, it was observed that most of the faults have lasted less than 100ms. Four scenarios were analyzed to identify the optimum way of installing Auto Reclosers and protection setting for this Medium Voltage network. An algorithm was defined to find the optimum protection settings for any Grid Substations.