Traveling Wave Protection for the AC Transmission Lines between MMC Stations and Renewable Energy Sources

Several MMC-HVDC systems with renewable energy sources connected have been constructed in the past decades. For the AC transmission lines between the MMC stations and the renewable energy sources, fault-ride-through strategies at both ends will lead to complicated fault characteristics. Specifically, the current amplitudes are restricted and the phase angles are controlled, the characteristics decrease the reliability and sensitivity of traditional relay protection. This paper proposes a differential protection based on the traveling wave theory, which focuses on the transmission lines and excludes the influence of the power sources outside the protected area. Criterion is constructed based on the integral value of the amplitude of the traveling wave differential current. The proposed protection is verified in a PSCAD simulation model. Test results prove that, compared with traditional current differential protection, the traveling wave differential protection has advantages in reliability, and the ability to withstand fault resistance.