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- 2014 (2)
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- Rubber stress cone (2)
- Silicone rubbers (2)
- AC dielectric strength (1)
- Dielectric strength (1)
- Elongation at break (1)
- HV insulation (1)
- Optical transmittance (1)
- Silicone elastomer (1)
- Tensile strength (1)
- Thermal aging (1)
Optical methods and monitoring systems for the PD detection in GIS, GIL and oil-immersed type transformers have been demonstrated. Very recently these methods have been extended to the detection of PDs in solid insulation materials of cable accessories. This novel application in high-voltage (HV) cable terminations consists of integrated fiber-optic sensor which requires transparent insulation materials. Therefore, transparent silicone rubbers are considered as replacement material for currently used opaque elastomeric insulation material in stress cones of HV cable accessories. For this purpose a preliminary study on the long-term stability of two commercially available fully transparent silicone rubbers was performed. Accelerated thermal aging tests were carried out for 4 hours up to 100 hours at 200 °C under a normal air atmosphere and normal atmospheric pressure. The impact of thermal aging on the AC dielectric strength of the silicone samples was investigated and additionally the optical transmittance was determined using UV-Vis spectrophotometer. The investigation indicated that the dielectric strength value of the silicone samples was seriously reduced for long-term exposures to elevated temperatures. In addition, the UV-visible transmittance of thermally aged silicone samples was also decreased. The influence of these phenomena must be taken into account for the design of HV insulation materials, particularly under extremely high temperature operating conditions.
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 Eb 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 Eb 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 Eb 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.