In recent years, global installation of RTV coated insulators has been accelerating. This trend has been driven by the need for countermeasures in severely polluted areas where polymer insulators are unsuitable due to deterioration in a short time, as well as by user demands for higher reliability than offered by polymer insulators.

In 2021, CIGRE Working Group B2.69 compiled international application records and evaluation methods, resulting in the publication of TB 837. In response, IEC PT 63432 was launched in February 2022 with the aim of establishing technical specifications (including test methods and acceptance criteria) for RTV coated insulators, and activities are currently underway. Based on practical field experience in Japan and elsewhere, current specifications may not sufficiently cover all required performance characteristics.

Field Experience

Table 1 summarizes selected field application of RTV coated insulators where there have been no reported issues since 1999.

Key findings from field experience, laboratory testing, and published papers can be summarized as follows:

1. RTV coated insulators enhance pollution performance, reduces visible corona discharge caused by pollution, and mitigates associated noise.
2. There is a record of use for up to 25 years. Signs of deterioration in the coating have been observed.
3. Resistance to arcing and partial discharge varies depending on the RTV material　used.
4. The degradation rate of RTV coated insulators differs depending on the substrate material, such as ceramic or glass.
5. The performance of RTV coatings is influenced by factors including the coated area, adhesion condition, and uniformity of coating thickness.
6. RTV coating is more sensitive to jet washing compared to polymeric insulators.

Although data accumulation and related investigations are ongoing, findings indicate that high quality RTV coated insulators can be achieved by selecting the appropriate material and coating application process.

Plan to attend the upcoming 2025 INMR WORLD CONGRESS in Panama. Yasushi Okawa, Manager of the High Voltage Laboratory at NGK Insulators in Japan, will discuss limitations of the existing 2000h accelerated ageing test and propose improvements to better simulate actual environments, including desert and industrial areas with high non-soluble deposit density. He will also propose a nitric acid immersion test to assess material resistance under severe pollution and partial discharge conditions as well as recommend enhanced specifications and test methods to assure long-term performance.