Protection of multi‐terminal remote DC microgrids with overhead lines against temporary and permanent faults

Abstract

Multi-terminal low-voltage DC (MT-LVDC) remote microgrids are subjected to faults with low current magnitudes. Although such faults do not disturb microgrid steady-state operation, their continuous existence can lead to permanent (prm) power losses and personnel hazard. Yet, given that faults are often temporary (tmp) on overhead lines, instantaneous de-energisation of the entire microgrid upon fault detection can result in prolonged loss of infeed, i.e. loss of load. This study proposes a centralised protection scheme to achieve tmp-fault resilient MT-LVDC microgrids. The proposed approach is comprised of local intelligent electronic devices (IEDs) at each terminal and a central IED at one of the MT-LVDC microgrid terminals. Low-bandwidth communication is utilised between local and central IEDs. Local IEDs are equipped with overcurrent function to take fast protective action under faults with high current magnitudes. On the other hand, the central IED consists of two passive oscillators and DC choppers. The passive oscillators facilitate the detection and identification of tmp and prm faults with low current magnitudes. DC choppers are used for online pole voltage rebalancing upon tmp fault clearance. Testing the centralised protection scheme on a ± 750 V , TN-S grounded, MT-LVDC microgrid reveals that the approach is fast, sensitive, selective and resilient under various conditions.