Islanding Detection and Protection

Abstract

Islanding occurs when a portion of distributed system becomes electrically isolated from the rest of the power system yet continues to be energized by distributed generators. The DG interconnected to power distribution system must be able to detect islanding condition. The current requirement is to disconnect all distributed generators immediately as the island occurs. For this, each distributed generator must be equipped with an islanding detection device. In this thesis, a review of current practices and research work developed on distributed generation has been discussed and main focus is done on DG problem Islanding. 7-Bus system in which one is an Infinite Bus, two are Generator Buses and rest are Load Buses, has been simulated in DIgSILENT. Various parameters like Voltage, Frequency, Active Power and Reactive Power are detected in islanded mode, fault and load switching. If a line is disconnected due to any type of fault, then islanding condition arises. In this thesis, we have considered voltage threshold value of the voltage relay connected at the bus up to 95%. Some cases will be there when generator has to supply more than its capacity. In that case, Load Shedding has been done according to some priority level and that priority level has been followed according to the voltage threshold value of the bus voltage. It has been concluded that when islanding occurs then there is voltage dip and some transients in the bus occurs. The remedies taken to maintain the bus voltage and frequency are like Load Shedding as per priority and Transformer Switching.