Operation Characteristics of a Mechanical DC Circuit Breaker With a Resistive Superconducting Element for High-Reliability HVDC Applications

The issue of DC transmission and distribution systems is increasing due to the increase in DC supply and demand. The future MTDC (Multi-Terminal HVDC) system is becoming a big issue beyond the general PTP (Point to Point) HVDC system. We live in an era where the super grid is gradually expanding. However, the protection device is required to protect the grid conversion equipment from fault currents during line transients to progress from the HVDC stage to the MTDC stage in PTP. The DC fault current, about ten times higher than AC, occurs at a very high speed because of the lack of zero-crossings. We propose a resistive-mechanical DC circuit breaker with a resistive superconducting element is a combined model of a resistance-type superconducting element and a mechanical DC circuit breaker. In detail, it limits the initial fault current by quenching the resistive superconducting element. Also, it creates an artificial zero-crossing through the LC divergence oscillation circuit of the mechanical DC circuit breaker to perform safe fault protection. In this paper, the fault protection of the resistive-mechanical DC circuit breaker with a resistive superconducting element was tested to confirm the current limiting rate of the initial fault current, the artificial zero-crossing, and the total cutoff time. As a result, the initial fault current was limited by about 17.3% by quenching the resistive-superconducting element.