Protection strategy for multi-terminal DC networks with fault current blocking capability of converters

Abstract

High voltage dc networks are a promising technology to flexibly transmit power over long distances. However, dc grid protection is still a major challenge. DC fault clearance can be mainly achieved with three devices. These are ac circuit breakers (ACCBs), dc circuit breakers (DCCBs) and converters with fault current blocking (FB) capability. In spite of their great operational advantages, FB converters have attracted less attention than ACCBs or DCCBs in dc protection research. To bridge this gap, this paper investigates a protection strategy for a multi-terminal dc (MTDC) network equipped with FB converters and fast dc disconnectors. A novel minimum opening protection approach fully based on local data is proposed. Digital simulations are carried out using PSCAD/EMTDC. Simulation results show that only the two fast dc disconnectors placed in a faulty link operate following a dc fault. These results have verified proposed ideas for the protection of MTDC networks.

Power‐system level classification of voltage‐source HVDC converter stations based upon DC fault handling capabilities

“…Pole rebalancing involves either external equipment in form of a dynamic breaking system or can be added to the converter station design in the form of a path for zero sequence currents and an associated controller [92]. In the case of converters with fault blocking capability, the approach to deal with pole-to-ground faults does not result in the need for an additional type to differentiate its capabilities compared to those available with pole-to-pole faults [93].…”

Nonunit Distance Protection Algorithm for Multiterminal MMC-HVdc Systems Using DC Capacitor Resonance Frequency

“…Derivative-based protection algorithms present good selectivity but may be challenging for higher fault resistances associated with noise, and also require high sampling frequencies, accurate measurements, compensation of filter delays and thresholds difficult to define. Similar noise-related issues might be present in methods based on second-order derivatives and the current comparison rate of change, such as [22], [23], although these methods require less pre-defined thresholds. Differential protection techniques are intrinsically selective but require a dedicated communication link and the time delay required to ensure reliable operation may become prohibitive in large systems.…”

Multi‐vendor interoperability in HVDC grid protection: State‐of‐the‐art and challenges ahead

“…The fault clearing speed of such a strategy is limited by the opening speed of ACCBs and the decay constant of the fault current once the ACCBs have opened. FBCs, such as FB-MMCs [45,47,93], alternate arm converters (AACs) [86] and hybrid MMCs [95] are used to quickly limit fault current. Furthermore, HSSes with a low counter-voltage capability [45] or low-rated DCCBs [86,93] in terms of speed and energy capability can be used to improve fault clearing speed.…”

“…In high-impedance grounded HVDC systems, dedicated pole rebalancing devices may be required to rebalance the pole voltages following a pole-to-ground fault for fast restoration. An exception is a non-selective protection strategy using FBCs, which can discharge both poles through the fault path before fault clearing [47,48]. Two main solutions for pole rebalancing, dynamic braking systems (DBSes) and AC-side grounding schemes permitting a zero sequence current, such as pole rebalancing reactors (PPR) and zig-zag transformers, have been studied in non-selective and fully selective protection strategies [26,49,50].…”