Collection Tubes Adjustable Guys Collection Jars
Support Column 3m
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DDG installed early in the construction cycle of newly built 765 kV Sterrekus Substation provided input to dimension insulation at this site.
Photos: INMR ©
“ The information I gather helps design engineers select the creepage needed at substations and also allows us to better understand how pollution is affecting our lines.” insulation, such as CTs, VTs, autoreclosers, arresters and cable accessories.
Vosloo notes that while the use of DDGs first originated in England, Eskom perfected their application over the years beginning in the late 1970s and early 1980s.“ One of the keys to using them,” he explains,“ was being able to make sense of the data gathered. Once this was done, the information proved invaluable in developing the whole philosophy behind IEC 60815.”
The standard DDG used by Eskom is comprised of four vertical tubes, each with a large slot of standard dimension cut into its sides and arranged with proper identification to face all four directions on the compass. A removable cylindrical receptacle at the bottom of each tube then collects all wind blown deposits that enter these slots. Before removing containers for analysis, the sides of the DDG are typically sprayed with water to ensure that whatever particulate matter adheres to them is washed down into the appropriate container and included in the analysis.
Watson explains that among the advantages of the latest generation of DDGs used by Eskom is that they do not require an energy source, are relatively simple and cheap to install and are made from rugged plastic components. This makes them not only durable but also less likely a target for theft, as occurred in the past with earlier metallic versions.
He and Vosloo note that a DDG’ s efficiency in collecting dust is greatest for relatively coarse particles and correspondingly less for very fine particles that the air stream typically sweeps around the gauge. Nevertheless, they also point out that this same physical process is inherent in dust deposition on
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Receptacles facing different directions collect varying amounts of particulates, allowing prevailing wind direction and sources of pollution deposition to be identified.
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