Cryogenic Dielectric Testing Performed for the SMES-ETM Program
The operation of superconducting magnetic energy storage (SMES) systems such as the SMES-ETM requires charge and discharge of electrical energy to and from the SMES coil. These charge and discharge operations produce voltage stresses between the coil windings, as well as between the coil and the grounded cryostat and its accessories. Electrical insulation design for withstanding these electrical stresses typically have employed solid insulators, such as G-10 and Kapton, and the cryogen as liquid dielectrics. For a large scale SMES such as SMES-ETM, the insulation design requires consideration of the presence of mechanical stress, the large surface area and volume under electrical stress, the possibility of contamination in the cryogen, and the requirement of a long device lifetime. Experimental database of cryogenic dielectric breakdowns in all of these areas are either not sufficient for reliable design or are non-existing. A comprehensive testing program was thus undertaken in the SMES-ETM program to generate the required database. The tests produced data of dielectric breakdown of liquid helium in the temperature range covering the λ-transition region and data which include the effects on dielectric breakdown associated with large surface area/volume under electrical stress, mechanical stress, cryogen contamination and electrical stress aging of solid insulators. The testing and the analysis of test results are presented.
KeywordsLiquid Helium Breakdown Voltage Electrode Spacing Breakdown Strength Dielectric Breakdown
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