Protection of transmission lines in multi-terminal HVDC grids using travelling waves morphological gradient

Abstract This paper presents a new method for the protection of transmission lines in voltage source converter based multi-terminal HVDC grids. The fault generated travelling waves at the faulted line ends are filtered by series inductors. The filtered voltage waveform processed by morphological gradient accompanied by fault voltage drop is employed for fast single-end protection of HVDC lines. The proposed method is stable against external DC and AC faults, as well as faults at opposite pole and the breaker opening transients from the adjacent lines. Moreover, it does not require communications between the line ends, it is capable to detect and discriminate relatively high resistance faults, and uses relatively low sampling rate. The effectiveness of the proposed protection method is validated by simulation study on a four-terminal HVDC grid including modular multilevel voltage source converters.