Pilot Protection for Hybrid DC Transmission Line Based on Voltage Fault Component

Abstract

The boundary and fault-response characteristics are not consistent at the sending and receiving terminals of the multi-terminal hybrid DC power transmission system, so the traditional pilot protection of the HVDC line cannot be directly applied to multi-terminal hybrid DC systems. Therefore, a hybrid HVDC line pilot protection scheme based on voltage fault components is proposed. Cosine similarity is used to measure the difference between the calculated and the measured voltage fault component waveforms to judge forward and backward faults. Combined with the line-selection criterion constructed by using the current fault component, the internal and external faults can be identified effectively. A short window is used to extract the characteristic quantity to improve the protection speed. The protection doesn’t need data synchronization between two ends and doesn’t rely on double-end boundary-feature consistency, which is suitable for both double-terminal and multi-terminal systems. Simulation results show that the protection can quickly, sensitively and reliably identify the internal faults from external ones, and has good ability to withstand the fault resistance, which can be used as quick backup protection for DC power grids.