Protection of Multi-Terminal HVDC Grids

Abstract

This thesis introduces four novel protection schemes for multi-terminal HVDC grids: primary protection, fault location identification, and breaker/relay failure backup protection schemes. The proposed single-ended primary protection scheme employs Hilbert-Huang Transform (HHT) to extract two instantaneous features from local voltage measurements, namely the instantaneous frequency and energy. Abrupt changes in these features during internal faults are detected as outliers. Simultaneous outliers in the extracted features correspond to internal faults, which offers a setting-less fault detection criterion; thus, eliminating the need for simulation-based and grid-specific thresholds. The proposed double-ended fault location identification scheme employs the setting-less outlier-based criterion to capture the arrival instants of the initial fault-induced backward traveling waves at both line terminals, based on which the fault location is identified with high precision.