This work reports the deposition onto high voltage insulators and correlation to atmospheric corrosivity measurement. This work includes corrosion studies at 15 sites in New Zealand (1,816 tests) for in excess of 12 months, and co-operative research in South Africa. In addition, to confirm the relevance and transportability of this proposed model, a review of the published international data on deposition rates on insulators was conducted. It was noted that the deposition rate of airborne pollutants onto a surface is dependent upon the true surface area facing the wind and the aerodynamic properties of the surface. Such is the effect that surfaces with minimal exposure to the wind such as horizontal plates, have been shown to be poor collectors of deposits while vertical plates are more efficient, followed by high voltage glass insulators, the ISO9223 salt candle, and the largest collector is the Direct Dust Deposit Gauge. This study found that the ISO9223 wet salt candle and the average annual deposition rate on the High Voltage Glass insulator bottom surface (unenergized) provided relatively similar deposition results. The deposition onto insulator surfaces may be a more relevant method as it replicates deposition on large surfaces. This Equivalent Salt Dry Deposition (ESDD) method for HV insulators is an all inclusive measure of the airborne pollutants deposition rate and converts the total deposited material into a single value equivalent to that of salt, even though the deposit may consist of sulphur, marine salts, nitrates, and other conductive pollutants. The measured deposition rate on the sheltered insulator bottoms at 85 sites around the world predicted 87% of the ISO corrosivity categories (based on zinc corrosion) for these sites. Results from equatorial Asia appear to be non-compliant and warrant further investigation. The ESDD values are now being quoted from around the world, by electrical engineers who use the recently revised CIGRE methodology, to determine the probability of arc-over (shorting to earth) of high voltage cables due to pollution build-up on insulators. The implications from this research are significant, with the cost of atmospheric corrosivity studies becoming prohibitively expensive, this method converts technically valid surface deposition results from the electrical engineers from around the world (provided at no cost), to valid empirical corrosivity rates from often remote locations.
University of Newcastle Research Higher Degree Thesis