A New Fast-Acting Backup Protection Strategy for Embedded MVDC Links in Future Distribution Networks

Abstract

1 -This paper presents a new fast-acting backup protection strategy for future hybrid ac-dc distribution networks. By examining the impedance measured by a distance protection relay measuring from the "ac-side" of the network, a unique characteristic is established for faults occurring on the "dc-side" of an embedded medium-voltage dc (MVDC) link, interconnecting two 33 kV distribution network sections. Based on the identified impedance characteristic, appropriate settings are developed and deployed on a verified software model of a commercially available distance protection relay. To remain stable for ac-side faults, it is found that the tripping logic of the device must be altered to provide correct time grading between standard, ac, protection zones and the fast-acting dc region, which can identify faults on the dc system within 40 ms. An additional confirmatory check is also employed to reduce the likelihood of mal-operation. Trials on a test system derived from an actual distribution network, which employs distance protection, are shown to provide stable operation for both ac-side and dc-side pole-pole and pole-pole-ground faults.

Review of MVDC Applications, Technologies, and Future Prospects

“…The fault propagation from one AC system through a DC link has been highlighted as a concern in the literature [189]. However, it has been suggested that existing AC protection systems can be updated for MVDC protection [190]. Damping the oscillations between multiterminal DC grids with AC connections is also being investigated in the literature [189,191].…”

Continuous Time Simulation and System Level Control Model of a Modern MVDC Distribution Grid including SST and MMC Based AFE

“…In [13], a DC fault ride-through method for MVDC distribution systems is presented. The problem of the partial discharge on the DC cables from an experimental point of view is studied in [14], while a backup protection strategy for embedded MVDC links is presented in [15].…”

“…Voltage sources must be connected through an arrangement of controlled current sources that reflect the dynamics due to cabling resistance RDCBUS and coupling inductors LDCBUS. This allows generating a PCC voltage that is equivalent to the mean value of all N primary side voltages of all N parallel connected SSTs as in (14), it also allows current sharing in between the cells, reflecting on what is drawn from the load side, as given in (15). The final current share in between the parallel connected modules is given by (16).…”

Backup protection with accelerating strategy based on fault control of modular multilevel converters in medium‐voltage direct current distribution network

“…In [11], local backup protection based on the cooperation of breakers and switches is proposed, where breakers trip the faulty sub‐grid first and then switches isolate the faulty line in the sub‐grid according to the DC voltage. Reference [12] utilizes distance protection on the AC side of converters to provide remote backup for DC faults, but the selectivity is reduced when multiple DC lines are connected to the converter. Travelling‐wave‐based backup protection is proposed in [13], the protection will fail if the travelling wave is not captured because of the short feeders.…”