Dielectric strength behavior and mechanical properties of transparent silicone rubbers for HV cable accessories

Modern optical partial discharge (PD) detection system based on fiber-optic sensors for PD on-line health monitoring in high-voltage (HV) cable terminations necessarily requires optically transparent or translucent insulation materials. The optically compatible silicone rubbers are the key to facilitate such innovative technology. In this work, AC 50 Hz dielectric strength E_b and mechanical properties of three types of commercially available silicone rubbers have been investigated. The investigations revealed that the translucent silicone rubber has a good mechanical performance but its E_b value is considered too low. However it is sufficiently good for use as base material for rubber stress cones. Unfortunately, its optical transmittance is poor compared to optically clear transparent silicones. On the other hand, the mechanical properties of transparent silicone rubbers do not comply with those demanded from push-on stress cones. In particular, their elongation at break is considered too low for that application. However they provide the E_b values of about 28 kV/mm to 29 kV/mm at 0.5 mm thickness, which are higher than those of the translucent type. Moreover, it was found that the post-curing process does not provide a positive impact on the ultimate elongation of silicone rubbers.