All Photos: INMR ©
Silicone housing on bushing exposed to coastal pollution in New Zealand. Pollution accumulated on porcelain removed from same site (right).
winds. The most dangerous wind direction (associated with the four most severe pollution events and leading to the highest currents) has an angle of between 0 and 20° to the shore. This is due to a wall of sand that protects the site from the perpendicular (90°) direction. The description of the pollution event at the Kelso Test Station on South Africa’s Indian Ocean coast is slightly different. During the pre-
pollution phase at Kelso, salt comes in not only from the sea but also from the land since wind direction is almost parallel to the coast. Another practical application of leakage current data would be to convert it into pollution flashover performance curves. This approach was tested by applying STRI’s IST program (discussed in Part 1 of this article) to 10 uniquely different insulators at Eskom’s Koeberg
Insulator Pollution Test Station (KIPTS) on the Atlantic coast near Cape Town. Results proved quite reasonable in predicting outage rate compared to actual experience, i.e. number of blown fuses), (see Table 1). Results of such field station testing can be used practically well beyond simply assigning a ‘pass/fail’ grade to each insulator tested. For example, they can help estimate the pollution flashover performance of a complete overhead line located in the same area and equipped with these same insulators (geometry and material).
Photo: INMR ©
These days, however, many power supply companies are looking for simple and robust systems for pollution monitoring and warning in place of complicated ‘researchtype’ systems for measuring leakage current. This is because uprating/ upgrading existing overhead lines requires accurate evaluation of pollution levels.
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Wind direction is an important variable in understanding pollution deposition events.
INMR® Q2 2012
INMR Issue 96.indd 88
modErn pollution monitoring principlEs allow BEttEr sElEction
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