Performance of Phase Comparison Line Protection Under Inverter-Based Resources and Impact of the German Grid Code

This paper studies the impact of inverter-based resources (IBRs) on the performance of phase comparison (PC) pilot line protection. The PC protection compares the phase angle of currents entering the zone of protection to detect a fault within the zone. IBRs have different fault current phase angle characteristics compared to conventional synchronous generators (SGs). This may have a detrimental impact on the performance of customary phase comparison protection schemes designed based on the assumption of a SG dominated power system. This paper provides examples of PC misoperation due to full-size converter (FSC) wind turbine generator (WTG). The case studies include various PC schemes including negative-sequence and mixed excitation and shows their misoperation. In both cases, the cause of misoperation is a shift in the phase angle of zone currents causing the PC to mistakenly classify an internal fault as external. The paper further studies the effectiveness of the German grid code in resolving the misoperation issue.