Protection Coordination for Assembly HVDC Breakers for HVDC Multiterminal Grids Using Wavelet Transform

A major challenge in a multiterminal high-voltage direct current (MT-HVdc) system is the detection and subsequent removal of dc faults, i.e., line-line or line-ground faults. This technology is crucial to make emerging MT-HVdc systems reliable and stable. Current detection solutions are either too sensitive to load variations causing false positives or are too slow to detect faults before the equipment is damaged. This paper proposes a framework and case examples for fault detection based on features derived from the wavelet transform of the grid current. The algorithm is intended to control new high-speed dc breakers (such as assembly HVdc breaker) for improved fault protection. This paper customizes the detection strategy to specific fault frequencies using multiresolution analysis, whose magnitudes are significant in the vicinity of the fault, and are attenuated at remote grid terminals. A model of a three-terminal MT-HVdc system is developed in power systems computer aided design/electromagnetic transients including dc. The results have been post processed in matrix laboratory and simulation results verify the effectiveness of the proposed solution for preventing dc faults on an HVdc system.