Enhancement of Dielectric Strength of Cryogenic Gaseous Helium by Addition of Small Mol% Hydrogen
A valuable solution to the voltage rating limitation of gaseous helium (GHe) cooled HTS power devices is demonstrated through the use of cryogenic gaseous mixtures of small mol% of gaseous hydrogen (H 2 ) balanced with GHe. An 80% enhancement of the dielectric strength, both in dc and ac, is observed for the mixture with 4 mol% H 2 . The observed linear dependence of dielectric strength from varying the H 2 mol% suggests a significant potential for further enhancements by using mixtures with higher H 2 mol%. Partial discharge (PD) measurements were performed on a 1 m model cable to demonstrate the potential practical applications of GHe-H 2 mixtures for superconducting devices. The results of the PD measurements for model cable showed a 20-25% increase when the 4 mol% H 2 mixture was used. The demonstrated enhancements in the dielectric strength will provide additional design options to HTS power devices cooled with GHe mixtures.