Wavelet-based protection strategy for DC faults in multi-terminal VSC HVDC systems

A new protection algorithm for DC line faults in multi-terminal high voltage DC (MTDC) systems is proposed in this study. A four-terminal MTDC model is used to investigate fault behaviour and detection using the simulation program PSCAD/EMTDC. The simulation results are post-processed using Matlab. The fault clearing must be done very rapidly, to limit the effect of the fault on neighbouring DC lines because of the rapid increase in DC current. However, before clearing the line, the fault location must be detected as soon as possible. A rapid fault location detection algorithm is therefore needed, preferably without communication. The protection algorithm proposed in this study uses wavelet analysis to detect the fault location based on local measurements. The protection algorithm consists of three independent fault criteria, of which two use wavelet analysis. The third criterion is based on a detection method in the time domain. The latter is an additional detection method independent of wavelet analysis. Using a two out of three selection criteria results in an increased reliability of the whole protection algorithm. The final objective is to implement a protection algorithm which allows to detect a DC fault within 1 ms without using communication between the participating converter stations.