Breakdown strength and dielectric recovery in a high pressure supercritical nitrogen switch

Fast and repetitive switching in high-power circuits is a challenging task where the ultimate solutions still have to be found. We proposed a new approach. Supercritical fluids (SCFs) combine favorable properties of liquids - insulation strength, thermal behavior, and gases - self healing, high fluidity, and absence of vapor bubbles. That's why we start investigating the subject of plasma switches in SC media. First results indicate excellent switch recovery and very high insulation strength. We present the design of a SCF insulated switch (SC switch). Breakdown strength of the SCF is investigated and found to be high in comparison with most of the solid insulating media. The dielectric recovery inside the SC N₂ switch is tested under a repetitive 30 kV, 200 ns pulse voltage at repetition rate up to 5 kHz. The recovery breakdown voltage across the SC switch achieves 80 % within 200 μs. The current interruption capability of SC N₂ is investigated experimentally in a synthetic circuit generating a high-frequency arc of several hundreds of amperes and a transient recovery voltage of hundreds of volts. The results show that a SC N₂ switch with fixed electrodes and an inter-electrode distance of mm range can successfully interrupt this current at approximately 2 ms after arc initiation.

1 Introduction

SUPERCRITICAL fluids (SCFs), widely researched in chemistry, have recently drawn attention for their potential in the area of electrical switching, due to their combined advantages of liquids and gases. Plasma in SCFs is a quite new research area that covers fundamental researches and applications for a wide area: SC plasma chemistry, SC plasma power switches, and dense planet atmosphere, etc‥ Figure 1 gives an overview of the application fields of plasma in SCFs. Figure 1.

Application area of plasmas in supercritical fluids. The research area of interest in our work is high-lighted.