Optimized Distance Protection Scheme for AC Transmission Lines Based on Phase Angle Difference of New Energy Equivalent Source

This paper discusses the adaptability of positive-sequence voltage polarized phase-comparison distance protection in renewable energy integration scenarios and proposes an optimization scheme. In the voltage plane, the analysis indicates that an increased phase angle difference between the internal electromotive force (EMF) of renewable energy sources and the positivesequence voltage measured by the protection device may lead to incorrect operation of the distance protection. Using the port equivalent method, the position of the internal EMF of renewable energy sources under different fault types is calculated and analyzed, leading to conclusions regarding the adaptability of distance protection. The study finds that the performance of distance protection remains largely unaffected during single-phase-to-ground faults and three-phase faults. However, for phase-to-phase faults when renewable energy sources only output active power, and for double-phase-to-ground faults with a grounding offset angle set to 30°, there is a risk of maloperation or failure to operate. Specifically, distance protection on the renewable energy side may fail to operate for internal faults and maloperate for external faults in the forward direction, while distance protection on the grid side may maloperate in the reverse direction. An optimization scheme for distance protection is proposed, which involves real-time adjustment of the polarization voltage angle based on the phase angle difference between the internal EMF of renewable energy sources and the positive-sequence voltage, along with a directional element. A renewable energy integration scenario is established based on the PSCAD simulation platform, and the correctness of the theoretical analysis and optimization scheme is verified through extensive fault simulations.