Salt Deposit Density Research Articles

Fundamental Characteristics of AC Flashover on Contaminated Insulators Covered with Ice

The fundamental characteristics of ac contaminated flashover on iced insulators were studied for the three icing states, i.e., glaze, hard rime and soft rime, which are observed most frequently in service conditions. The results showed that thawed snow with a relatively low salt concentration can produce a salt deposit density (SDD) high enough for flashover on an iced insulator. For the same concentration of contamination liquid, average values of SDD for icing states are 5 to 9 times higher than those for icing-free conditions. The results also showed that the minimum flashover stress of the soft rime condition is 20% lower than that of icing-free conditions. For this reason, we deduced that the number density of Na atoms in the discharge space at flashover tends to become highest under the soft rime conditions.

Wetting Processes on a Contaminated Insulator Surface

This paper presents the theoretical aspects and the experimental results of a study carried out at Ecole Polytechnique de Montrdal on wetting processes on a contaminated insulator surface. Four wetting processes for clean-fog test using the precontamination method are distinguished, namely, collision of water droplets with the insulator surface, condensation, the hygroscopic behavior of the surface deposit, and molecular diffusion. The effect of various parameters such as the equivalent salt deposit density (ESDD), humidity, temperature difference between the cohtaminated surface and the ambient air, and the density of the inert materials are identified for the last three wetting processes.

Natural Contamination test of Insulators at Noto Testing Station Near Japan Sea

This paper describes the results of investigation into the performance of various types of insulators energized with 200 kV ac and ±280 kV dc voltages and exposed to natural conditions by the seaside for about five years. DC voltage application had almost the same influence on the salt deposit density as ac voltage application. Salt deposit density and flashover characteristics of insulators were much affected by their types. Flashover voltage for dc is almost the same as that for ac in rms value.

Natural Pollution Test of Insulators Energized with DC High Voltage

Various types of insulators have been energized with ±250 kV dc voltage and exposed to natural conditions by the seaside continuously. Salt deposit density and flashover phenomenon of these insulators have been investigated extensively for about two years. According to the results obtained so far, the influence of dc voltage application on the salt deposit density was not so notable as expected, while the effect of insulator types on the voltage withstand strength was greater than anticipated.