LAUSR

The medium-voltage direct current (MVDC) distribution grids have been given significant attention because of their wide applications in the grid integration of the renewable energy sources and in the improvement of the stability and quality of the grid. However, due to the absence of the natural zero current crossings and the high rate of the short-circuit current, the fault current interruption in the MVDC systems is more problematic than that in the ac systems. Several types of interruption schemes have been proposed, and the vacuum interrupter-based dc circuit breaker (DCCB) is a promising solution for the MVDC interruption. Because of its high arcing current, the dielectric strength of the vacuum interrupter after the current crossing point stays low, which makes the dielectric recovery strength a critical factor for the reliability of the interruption. To estimate the reliability of the MVDC interruption, an experimental circuit is designed to measure the dielectric recovery strength of the vacuum interrupter, and the main influence factors are investigated with the experiments conducted under different arcing currents, contacts, $di/{\Delta t}$ before the current zero, and arcing times. The analysis and comparison of the dielectric recovery strength under different conditions are presented. The safe recovery time under different interruption conditions is proposed.