Pressure-Related Creepage Discharge Characteristics for a 220-kV Superconducting Fault Current Limiter

Solid insulation materials are mainly used in superconducting magnet electrical applications. Such insulation must not only have the desired mechanical properties but also electrical properties under cryogenic conditions. Glassfiber-reinforced polymer (GFRP) needs to be studied with respect to its cryogenic insulation properties in relation to alternating current voltages with the current at maximum power (AC, Imp) (Kwang et al., 2007). A voltage lower than that at which dielectric breakdown occurs leads to creepage discharge, which causes the dielectric strength to decrease and results in electrical accidents; therefore, we need to study the properties of creepage discharge. In this paper, we present the results of experiments on the properties of creepage discharge inside GFRP with gaseous (GN2) and liquid (LN2) nitrogen (Bansal et al., 2008). The experimental results showed that the creepage discharge voltage increased with increasing creepage distance and pressure under LN2 and GN2 conditions (Hwang et al., 2012). In addition, the creepage discharge electric field value was confirmed by FEM analysis. We checked the safety factor through simulation to apply the outcome of these experiments to the design of electrical applications.