A travelling wave based primary and backup protection for MMC-MTDC transmission system using morphological un-decimated wavelet scheme

Abstract

The primary protection speed requirement for the HVDC grid is much faster as compared to the conventional HVAC grid. This research article proposes a travelling wave-based primary and backup protection scheme for the multi terminal HVDC transmission system using the morphological un-decimated wavelet decomposition signal processing technique. Depending on the polarity and arrival time information of the first incident travelling wave at both DC transmission line terminals, the fault is identified to be either in the internal zone, forward external zone, or backward external zone of the DC transmission line. Each DC transmission line is covered by its own internal zone as well as forward & backward external zone of its neighbouring line. The internal zone fault identification of the protection scheme sends the primary relay trip signals to associated hybrid DC circuit breakers. But if the primary protection relay fails, then the neighbouring DC substation protection system identifies the fault either in forward external or backward external zone. Then it sends a remote backup trip signal to the DC circuit breaker in the forward or backward external direction with a coordinated time delay.