Summary
Medium-voltage DC (MVDC) distribution systems are increasingly recognized as a practical solution for upgrading heavily loaded MVAC feeders, particularly where DER integration, efficiency demands, and limited space for new line construction hinder expansion. Retrofitting existing AC overhead lines allows a three-phase feeder to be converted into a bipolar MVDC line with a dedicated neutral conductor. This approach is particularly suitable for South Korea, where MVAC feeders have a dedicated neutral conductor and spare crossarm positions at the poles. While this approach reduces infrastructure costs, it introduces new challenges for protection and post-fault restoration due to limited availability of the DC circuit breakers
Read more Read less(DCCBs) and the necessity for fast clearing times.
This paper proposes a restoration strategy for a pair of MVDC feeders sharing a single twopole hybrid DCCB. The method relies entirely on measurements available at the relay location and does not require communication links. Three key detection functions are integrated: (1) pole-fault identification using deviation-based current criteria, (2) arc-extinction detection using the low-frequency component of the isolated pole voltage combined with a lowmagnitude test current injection, and (3) detection of unintended neutral conductor earthing through grounding-current monitoring, with a 5 A threshold derived from touch-voltage safety considerations.
The proposed strategy is validated through EMT simulations under a range of fault scenarios involving single- and double-pole faults on a 40 km bipolar MVDC feeder. For pole-to-ground faults, fault extinction is detected within approximately 160 ms and service is restored within 260 ms when the neutral conductor remains healthy. For pole-to-pole faults, selective isolation of faulted conductors enables restoration within 170 ms. The results demonstrate that selective reclosing and rapid service recovery is achievable even under constrained breaker configurations. The proposed method provides a practical path toward improving reliability in early-stage
MVDC distribution grids and can be extended to multi-terminal architectures and implemented in real-time in future work.
Additional informations
| Publication type | Session Materials |
|---|---|
| Reference | B4_11727_2026 |
| Publication year | |
| Publisher | CIGRE |
| Country | Korea, Republic of (South Korea) |
| Study committees | |
| File size | 876 KB |
| Price for non member | 30 € |
| Price for member | 30 € |
Authors
KIM Seul-Ki - Korea Electrotechnology Research Institute; JEON Jinhong - Korea Electrotechnology Research Institute; HWANG Jihui - Korea Electrotechnology Research Institute
Keywords
