Dielectric Recovery of Ultrafast-Commutating Switches used for HVDC and Fault Current Limiting Applications

Abstract

This paper is devoted to numerical simulation of arcs in ultra-fast switches with an electrodynamic (Thomson) drive.Ultra-fast switches with Thomson drive mechanisms are used to generate the high arc voltage necessary for current commutation in hybrid HVDC circuit breakers (HVDC CB) / fault current limiters (FCL). To make such a hybrid circuit breaker / fault current limiter a practical solution, the dielectric recovery of the commutating switch is to be sufficiently fast to avoid the re-ignition of the switching gap as a consequence of the voltage build up during the current interruption and limitation process.In this study, the dielectric recovery characteristic of a prototype switch with air as insulation medium has been investigated. A finite element model with the use of moving mesh is created. Different arcs at three different contact speeds (5, 7 and 9 m/s) and different arc currents (200 A and 300 A) are simulated, then different voltage stresses with Rates of Rise of Recovery Voltage (RRRV) from 70 to 600 V/μs have been applied 50 μs after the simulated arc was extinguished to obtain the dielectric recovery curves. The Volume Flow Rate (VFR) in the switch, which is directly related to the contact speed, plays a crucial role in insulation recovery in the post-arc phase. The impact of contact opening speed and the transient recovery voltage parameters on the dielectric recovery of the prototype ultra-fast switch has been thoroughly discussed.