Ageing phenomena such as chalking and cracking of hollow core composite insulator housings made from LSR material can greatly impact outdoor performance. In the case of those housings deemed only ‘slightly aged’, repair is both time efficient and economical. Normal outdoor insulation performance can be regained by removing the chalking layer in the silicone rubber housing and spraying RTV coatings onto the aged surface. Mirror glossiness, Shore hardness and hydrophobicity are all parameters that can help evaluate extent of ageing of LSR housings and determine which insulators can be repaired and which have aged beyond repair.
To repair an aged insulator, the first step is to use a grinder to remove the chalking layer and then clean the surface with an air spray gun. The second is to treat the surface with an RTV silicone coating to improve the degraded hydrophobicity.
As far as RTV coated insulators are concerned, removing the original coating is inefficient and hence the better choice is to recoat new RTV coatings directly over the original layer. Weather, surface condition and application methods all influence adhesion between the new and the original coating. Tests have shown that adhesion of RTV coatings is best when applied at ambient temperatures from 5°C to 45°C. High relative humidity will not affect adhesion whereas extremely low humidity can lead to coupling failure. Dust and moisture have a great negative impact on adhesion and therefore must be thoroughly eliminated. Spraying is believed to be the best method to apply RTV coatings and ideal air pressure, spraying distance and time are 0.6 MPa, 20 cm and 5 s respectively.