HV INSULATOR PROTECTION
CharCoat IC is a unique room temperature vulcanized (RTV) silicone elastomer formulation specifically developed by CharCoat Passive Fire Protection, Mace Technologies and in collaboration with the Electric Power Research Group of the University of the Witwatersrand for the prevention of pollution flashover of high voltage outdoor insulation.
The exceptional hydrophobicity of CharCoat IC inhibits the formation of continuous moist conductive layers on insulator surfaces. This, in turn, limits the flow of leakage currents thus preventing the creation of dry bands and partial discharges – critical steps in the flashover process.
The superior performance of silicone rubber over other insulating materials in polluted environments is well proven. What makes silicone unique is the fact that, owing to the migration of low molecular weight silanes that exist within the elastomer, the water repellent properties are imparted to contaminants which accumulate on the surface.
The constant water-repellency exhibited by CharCoat IC coated insulators, even in the most severe environments, coupled with silicone’s inherent resistance to degradation by ultra-violet radiation, ozone and most chemicals, combined with the use of specialized fillers to combat power arc damage, enables the material to provide enhanced system reliability over a period of many years.
What Does This Mean?
When Insulators (or other surfaces) are coated correctly with CharCoat IC, there is no leakage of current, the CharCoat IC will repel pollutants due to its superb hydrophobicity (hydrophobicity is the physical property of a molecule (known as a hydrophobe) that is seemingly repelled from a mass of water. ) and the insulator will perform at its maximum capacity! CharCoat IC, with good maintenance will continue to repel pollutants up to and over 20 years.
- BS2918 – Dielectric Strength
- IEC 93 – Surface Resistivity
- IEC 93 – Volume Resistivity
- IEC 60273 – Hydrophobicity
- ASTM D 495-99 – Arc Resistance
- ASTM D 2303-97 – Tracking and Erosion
- CPRI REC Sprc. – Hydrophobicity Recovery
By the early 1990’s the superior performance of silicone rubber in polluted areas had been well demonstrated and many overhead lines were being re-insulated with composite long rods. Substations, however, remained a problem. This prompted the formulation of CharCoat IC in 1991 as a joint development project with a view to significantly reducing maintenance costs and eliminating contamination flashover.
CharCoat IC is extremely hydrophobic displaying a water droplet contact angle greater than 100 degrees. Moreover, the coating has a quick hydrophobicity recovery rate and, by the migration of low molecular weight silanes present in the material, readily transfers its hydrophobic characteristics to any covering contaminating layer.
For improved performance, and a controlled cure at room temperature, CharCoat IC is a two- part material, i.e. a small volume of IC catalyst is poured into the coating before application. Unlike those materials utilising an oxime cross-linking agent, CharCoat IC‘s curing system has the benefits of not requiring any atmospheric moisture for vulcanisation to take place, the cure rate is independent of humidity, no by-products are released on curing and there is practically no shrinkage (<0,1% versus 0,5% to 1% for oxime systems). The shelf life is also much longer than single-part rubbers.
Although the coating does have some adhesion to porcelain and glass, the application of CharCoat IC Primer, which is supplied with all coating purchased, is recommended to provide a strong permanent bond to all ceramic, glass and resin materials. If a separate primer is not used, the bonding agent must be included in the coating. This, of course, replaces some of the silicone and thus adversely affects the material performance and longevity. It is our philosophy that primer be applied only at the interface between the insulator and the coating where it is needed and leave the rubber layer itself free of unnecessary materials.