A Passive Technique for Detecting Islanding Using Voltage Sequence Component

Islanding is a well-known phenomenon in Distributed Generation (DG) in which the microgrid continues to provide power to an isolated load area even after it is disconnected from the utility grid. Fast detection of islanding is very important to maintain stability in voltage and frequency, restrict the disturbances within permissible limits, and prevent faults and cascade tripping in the grid. In case of delayed islanding detection, the system may have increased harmonics, distorted voltage profile during the transition, faults, and service interruption during critical loads. The main disadvantage of passive detection approaches is their large non-detection zone. Due to external signal injection at a common coupling point, active islanding reduces power quality and system performance. The suggested passive islanding detection approach is based on measuring the negative sequence voltage rate of change (ROCONSV) at the point of common connection (PCC). The negative sequence voltage is calculated using symmetrical component transformation and the derivative is then compared to predefined threshold values. Based on the system decision, the islanding trip signal is released for the circuit breaker at the microgrid. The proposed method is simple, reliable, and fast without the use of any external signal injection and power quality degradation.