Photos: INMR ©
( left) Sampled disc prior to washing to establish ESDD level. Discs after washing still show evidence of embedded contamination that cannot be removed.
allows us to adjust lab tests in such a way that they better simulate what is really happening in service.”
Another element in this process of monitoring and reacting to pollution, he notes, is using test towers, such as the ones currently in operation in South Africa and nearby Namibia. These strain towers allow up to 9 test positions for different insulator designs, over and above the ones already installed on the line. An online monitoring system and weather station are also installed( as per CIGRE Guide 333) and together provide data at 10 minute intervals on leakage currents, wind speed and direction, humidity, solar radiation and precipitation.
Vosloo adds that the data being gathered and compiled by Watson also helps identify which substations are ideal for installation of sophisticated new Eskom-developed insulator pollution montoring apparatus( IPMA). This advanced equipment energizes naturally polluted test insulators every 10 minutes to measure resistance and also calculate ESDD. There is apparently also a leakage current recorder that identifies the worst performing insulator profiles at that location. All this, explains Vosloo, provides complete documentation on what is happening at the site from a pollution and climate perspective.
Finally, Vosloo points to the 765 kV Sterrekus Substation nearing completion north of Cape Town as a wonderful example of how pollution mapping using DDGs and reference strings has contributed toward Eskom’ s design process.“ The station’ s 31 mm / kV insulation was basically decided on as a direct result of the work Watson carries out,” he says.“ It may seem simple at first glance but ends up playing a significant role in the big picture.”
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Insulation levels at 765 kV Sterrekus Substation were determined in large part by local DDG and reference string measurements.
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