Positive sequence additional impedance based pilot protection for active distribution networks

The access of high penetration distributed generation (DG) seriously affects the reliability of traditional overcurrent protection in active distribution networks (ADNs). Therefore, this paper pro-poses a pilot protection method based on positive sequence additional impedance (PSAI). The PSAI is calculated by positive sequence phasors on the both ends of the protected feeder. When an internal fault occurs, the amplitude of the PSAI is close to the transition resistance which is a relatively small value, while that is theoretically infinitely great when an external fault occurs. Because the PSAI depends only on the faulty type and transition resistance, the proposed method is independent of the power source characteristics. The PSCAD simulation results prove that the method is immune to time synchronization error, has a stronger ability to withstand transition resistance than traditional current differential protection, and can not only adapt to the high penetration of DG, but also has high sensitivity even if DG exits. Finally, protection prototypes with proposed method and 5G communication function are developed. The real time digital simulation closed-loop test results indicate that the protection prototypes can correctly identify internal and external faults with an accuracy of 100 %.