Optimizing Silicone Rubber Housing Materials for HV Composite Insulators

Coatings, Insulators

Composite insulators have achieved a high level of technical maturity based on accumulated service experience and applications across all voltage classes. But to ensure reliable long-term operation, there remains the need to ensure optimization of an insulator’s materials and components, such as the end fittings, the FRP core rod and the housing material. There is also the need to optimize design of the various interfaces. At the same time, electrical, mechanical and other material properties must also be optimized, such as ease of processing during manufacture or to allow for special designs for certain unique environmental conditions.

Indeed, there is now a trend toward more tailor-made solutions that is pushing further development of polymeric housing materials as well as new insulator and string designs. This trend has been triggered by strategic decisions in the power sector, such as the move to ultra-high voltages (> 800 kV), expansion of HVDC transmission and more compact line designs to promote greater public acceptance.

Fig. 1: Cross-section of HTV with crack formation after 100h, 260h and 600h storage in nitric acid and tensile test.

There are also more demanding material requirements being found in some utility specifications. For example, there was a need to further develop the insulator housing material to yield a customized nitric acid resistant, high temperature curing (HTV) silicone rubber. In this case, the utility customer specification required that a cut insulator section be stored for 100h at 30°C in 1 molar nitric acid. The material would pass the test if after a further drying period of 12h at 80°C no crack formation was observed on the housing’s surface. This special requirement had been included in the specification following an incident of failure of a composite insulator. That failure was found to have been initiated by housing degradation, crack formation and exposure of the FRP core due to strong corona discharge activity. The strong corona was itself the result improper field grading combined with generation of nitric acid under specific service conditions that saw low levels of precipitation over a year.
Apart from all the above trends, maintaining the quality of composite insulators to ensure satisfactory long-term performance is yet another important industry trend, especially since composite insulators have moved from being regarded as exclusive and expensive to now seen as cost-optimized commodities.

These various trends are also reflected in on-going refinement of existing test methods to verify sufficient quality of composite insulators as well as in development of new test methods aimed at transferring service experiences into the design stage of composite insulators.

Attend the 2022 INMR WORLD CONGRESS in Berlin where materials specialist, Dr. Christiane Baer of Pfisterer will review current trends and their impact on development of new formulations of HTV silicone rubber. She will also provide specific examples of evaluation and development of silicone rubber formulations with respect to new and emerging market requirements.