On the measurement of the dielectric strength of silicone elastomers

Critical reading of IEC 60243-1 shows that the standard does not give recommendations for the measurement of the dielectric strength of elastomeric materials (e.g. of silicone rubber). Specific recommendations for molded materials are provided in chapter 4.1.6 of the standard for thermosets and thermoplastics only. In the absence of specific recommendations for elastomeric materials often the procedure according to chapter 4.1.6 is used for elastomers as well. The specific electrical strength of 1 mm-plate shaped silicone elastomer specimens is measured to be 20 ... 40 kV/mm depending on the electrode arrangement. It is found that even major material modifications (extenders, degree of crosslinking etc.) do not lead to substantial changes of the specific electrical strength. Thus, the suitability of the method for silicone elastomers is limited. In contrary, the specific electrical strength of silicone elastomers was found to be higher than 100 kV/mm if measured with cast-in electrodes. Selected parameters were found to have a distinct influence in the specific dielectric strength. Since the application of embedded specimens requires high preparative effort for some elastomers the use of cast-in plate shaped specimens is desirable. Comprehensive investigation shows that a suitable electrode arrangement in combination with a suitable embedding material results in a specific electrical strength in the range of that of specimens with cast-in electrodes and allows a better investigation of material modifications. The findings will be part of the ongoing revision work of IEC 60243-1.