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

Abstract

The issue of DC transmission and distribution systems is increasing due to the increase in DC supply and demand. The fu-ture 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 equip-ment 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 com-bined model of a resistance-type superconducting element and a me-chanical DC circuit breaker. In detail, it limits the initial fault cur-rent by quenching the resistive superconducting element. Also, it creates an artificial zero-crossing through the LC divergence oscil-lation 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 el-ement 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.