Gas-Free Relay Technology for DC Grids

Abstract:
As the demand for compact and reliable direct current (DC) relays grows with the expansion of renewable energy and the deployment of DC grid architectures, traditional arc-quenching methods using sealed gases such as hydrogen face limitations in miniaturization, cost, and long-term stability. This study presents a gas-free relay technology that eliminates the need for internal pressurization while ensuring safe interruption of high-voltage DC arcs. To address the technical challenge of arc extinction in confined environments without gas assistance, we developed a coupled magnetohydrodynamic simulation framework that models arc behavior under realistic spatial and electrical conditions. The simulation results—validated through high-speed imaging and waveform analysis—enabled a detailed understanding of arc dynamics, including the roles of magnetic flux density, enclosure geometry, and arc–wall interaction. Based on these insights, we propose an empirical arc length model that quantitatively predicts the minimum arc length required for successful interruption. The model incorporates key design parameters such as load voltage, current, magnetic flux density, and wall spacing, and reflects nonlinear effects such as magnetic compression and thermal confinement by enclosure walls. Experimental verification confirms that the model supports early-stage relay design by reducing reliance on trial-and-error prototyping. This technology, grounded in the simulation and modeling framework presented in this study, has been implemented in Omron’s G9KB and G9EK series, contributing to their ability to perform safe and reliable high-voltage DC switching.