A new fast-acting backup protection strategy for embedded MVDC links in future distribution networks

Hunter, Lewis C. and Booth, Campbell D. and Egea Alvarez, Agusti and Dyśko, Adam and Finney, Stephen J. and Junyent-Ferré, Adrià (2020) A new fast-acting backup protection strategy for embedded MVDC links in future distribution networks. IEEE Transactions on Power Delivery. ISSN 0885-8977

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    Abstract

    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