Barrier Effect on the Breakdown Characteristics of the Resistive-Type Superconducting Fault Current Limiters in the Quenching State

When a resistive-type superconducting fault current limiter (R-SFCL) was quenched, a lot of bubbles will appear which will decrease the insulation strength of the R-SFCL. An insulation barrier was proved to be an effective way to increase the insulation strength of the R-SFCL. The objective of this paper is to obtain the barrier effect on the DC breakdown characteristics of the R-SFCL in the quenching state. In the experiment, the dynamic breakdown characteristics of liquid nitrogen (LN<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>) in the R-SFCL model with and without insulation barrier were studied. The R-SFCL model includes a superconducting the coil and a stainless-steel cylinder. The stainless-steel cylinder was attached outside the superconducting coil to simulate a real R-SFCL. The stainless-steel cylinder was connected to high voltage and maintained at a predetermined voltage level. The superconducting coil is in series with a current source, which was controlled to quench the R-SFCL and induce the breakdown. Both of the 50% breakdown voltage and the time delay T<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</inf> were recorded. The results showed that an insulation barrier can improve the insulation strength of the R-SFCL in the quenching state. With the increase of the heat flux H<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</inf>, the breakdown time delay T<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</inf> decreased when there was an insulation barrier present. Also, with the increase of the heat flux H<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</inf>, the 50% breakdown voltage decreased. The research results in this article can guide the insulation design of a R-SFCL.