Protection scheme for high-voltage direct-current transmission lines based on transient AC current

This study presents a new protection scheme for high-voltage direct-current (HVDC) transmission lines which only uses a specific frequency AC current (SFAC) at one of the line terminals during fault transients. The fluctuation characteristic of the root mean square (RMS) of SFAC is analysed under different fault conditions. The fluctuation in the RMS of SFAC during the transient period of internal and external faults is quite different. A fluctuation coefficient (FC) is proposed to measure the fluctuation. Fault types and the faulted line can be distinguished by calculating FC. A HVDC test system modelled in PSCAD/EMTDC is used to validate the proposed scheme considering different fault types, operation modes, sampling frequency and interference. Comprehensive test studies show that the performance of the proposed protection scheme is inspiring, and it is simpler and is of higher reliability compared with some traditional protections based on harmonic currents.