Evaluation of “open grid” protection strategy for a DC Network

Abstract

“Open Grid” protection strategy is proposed for protecting DC networks with converters that cannot block fault current and rely on DC circuit breakers. With this method, each DC circuit breaker (DC-CB), based on its own, local measurements (e.g. overcurrent, undervoltage) trips without discrimination. Using the same local measurements, the DC-CBs, discriminate “healthy” DC circuit(s) and re-close. This mainly aims to increase the speed of fault current interruption and reduce the duty of an individual DC-CB in blocking a fault. This paper develops the protection algorithms which can meet DC protection requirement with different fault types, locations and fault impedances. The analysis of the fault behaviour following the action of protection system in the event of a DC fault has also been given. Different DC fault characteristics have been described. Further validations of the robustness of the Open Grid via simulation models developed in PSCAD/EMTDC have been provided. Tests have shown that the Open Grid can successfully detect and discriminate DC faults in a meshed DC grid model.