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Enhancing Insulator Pollution Performance and Longevity with RTV Coating
Combining hydrophobicity and durability for reliable grid performance in harsh environments.
Key Takeaways
Background
Environmental pollution has always been a critical factor in the specification of electrical grid insulators. Thanks to their hydrophobicity, composite insulators have exceptional pollution performance, which led to an increase in their use in the 1990s and 2000s. Up to this point, porcelain and glass were widely used in harsh environments, but they required regular washing to combat surface contamination, which was costly.
However, it soon became clear that while composite insulators have superior pollution performance, porcelain and glass have a much longer lifespan, and so utilities began searching for a way to combine the pollution performance of composite insulators with the strength and longevity of porcelain and glass.
Room Temperature Vulcanized (RTV) Coating
Engineers began developing RTV in the 1960s, though the first widespread implementation wasn’t carried out until the late 1980s. In its infancy, the adoption of RTV was low, but over the years, the technology has been further refined, building an impressive history that demonstrates strong performance and longevity.
RTV silicone is a liquid polymer that vulcanizes when exposed to moisture in air [2]. Vulcanization is a chemical process that forms crosslinks between individual polymer chains, as a result of which the material can become more elastic or rigid depending on the crosslink density created. Liquid RTV silicone is coated on insulators to achieve a thickness level of a few hundred µm. The coating enhances surface hydrophobicity, suppressing leakage currents and increasing flashover resistance under contamination.
When compared to the cost of greasing and washing porcelain and glass insulators, RTV coating is a more cost-efficient method. The graph below shows the cost comparison of all three.
Uses of RTV Coating for Insulators
RTV coating is suitable for both line and substation application and can be applied both during manufacture and in-situ. The primary application of RTV coating is for deployment in heavy, very heavy, and extreme pollution conditions.
Performance
Enhanced Electrical Performance
RTV coatings significantly improve the flashover voltage of insulators. Studies have shown that fully coated insulators can achieve flashover voltages up to 97.47 kV, compared to 83.4 kV for uncoated insulators, marking a 16.9% improvement. Even partial coatings yield a 10.79% increase. Under polluted conditions, RTV coatings maintain higher flashover voltages, with increases of up to 15.5% observed, depending on the severity of contamination. [3]
Hydrophobicity and Pollution Resistance
The hydrophobic nature of RTV coatings prevents the formation of a continuous water film on insulator surfaces, thereby reducing surface conductivity and the likelihood of flashovers. This feature is maintained over time due to the migration of low molecular weight siloxanes to the surface, which helps encapsulate contaminants and restore hydrophobicity even after exposure to pollutants.
RTV Ageing
Ageing and life expectancy of a coating are heavily influenced by coating type, application and environmental conditions. Ageing is characterised by reduced hydrophobicity, peeling and fading of the coating. According to CIGRE, the following conditions may lead to premature ageing of RTV coating:
- Low-quality coating, inadequate coating material, or inadequate coating thickness and uniformity
- Environmental extremes
- Prolonged presence of corona and leakage current
- Extreme contamination could impede hydrophobicity transfer
- Inadequate insulator design with Unified Specified Creepage Distance (USCD) much lower than required
RTV Inspection Schedule
Inspection of RTV-coated insulators is necessary to ensure continued optimal performance and hydrophobicity. An example of a maintenance schedule for insulators in a harsh environment can be seen below.
| Inspection Type | Frequency |
| Ground Inspection | Every three months |
| Ground inspection for hotspots | Monthly |
| Nighttime ground inspection and hotspot identification | Annually |
| Climbing inspection, including inspection of RTV coating | Every four years |
| Thermal scanning | Every three years, or as the need arises |
| Preventative/predictive maintenance and failure investigation | During outage period |
| Pollution and hydrophobicity measurements to update pollution maps | During outage period |
| Line inspection using drones | Annually |
End of Life of RTV Coating
The functional end-of-life of RTV is marked by an irreversible loss of hydrophobicity, often due to corona or environmental degradation. Testing methods like salt fog or accelerated weathering give insights into performance, but they cannot reliably predict lifespan. At the end of life, RTV recoating is feasible to restore functionality, but the ultimate cost must be evaluated.
Conclusion
RTV coatings have emerged as a practical and efficient solution to the challenges of environmental pollution on electrical insulators. By combining the hydrophobic properties of composite insulators with the mechanical strength and durability of porcelain and glass, RTV technology bridges performance and lifetime gaps. While its long-term success depends on proper insulator design, application, environmental conditions, and consistent maintenance, RTV coatings offer utilities a reliable way to enhance system reliability and reduce operational costs in polluted environments.
*The information provided in this content is for informational purposes only and should not be considered professional advice. We make no warranties or guarantees, express or implied, and are not responsible for any losses or damages resulting from your use of this information.
