Moisture Degradation of Cyanate Ester/S2 Glass Composite Insulation Systems

Abstract

The fusion devices currently being developed present several challenges for magnet designers. One challenge lies within the electrical insulation, which must be able to withstand extreme temperatures, large shear and compressive stresses, high operating voltages, and high levels of incident radiation. To address the need for better performing insulation systems, Composite Technology Development (CTD), Inc. has developed CTD-403, a cyanate ester resin with increased radiation resistance, ease of processing and fabrication, low moisture absorption characteristics, and high mechanical and electrical strength at cryogenic and elevated temperatures. The moisture absorption trends of CTD-403/S2 glass composite insulation were studied. The effects of humidity exposure on interlaminar shear strength (ILSS), compressive strength, dielectric strength, and glass transition temperature were also studied. The saturation level of the insulation was seen to increase with the relative humidity of the aging environment. Fickian behavior was seen at room temperatures below 97% relative humidity exposure. Non-Fickian behavior was seen at elevated temperatures. Saturation levels after 6 months exposure were seen to be below typical epoxy-based insulation systems, averaging 0.5% weight gain. Degradation of mechanical and electrical properties was seen with increased humidity exposure and moisture absorption. ILSS showed an average retention rate of 75% after 6 months exposure. The compressive strength showed no decrease after 6 months exposure at room temperature, and show retention rates greater than 90% at 75°C/79% RH. An average dielectric strength of 98.6 kV/mm was seen for all specimens at room temperature (above 90% retention) after 6 months exposure.

Keywords

cyanate ester CTD-403 electrical insulation fusion moisture degradation composite technology development Fickian Fick’s Law.

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