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Tagged: 15KV, 25 kv, Primary Metering, Window CT
Just wondering if anyone else has seen failures like this or a heads up to anyone installing some primary metering in the future.
MN Power has had several failures of both 15 and 25 kv installs of window style CTs. Most all of the failures are the same. After 4-6 years of being installed the CT fails and shorts to ground on its mounts. All the CTs are a window CT with a tub pressed in the window. Also all installs are where the CTs are mounted Vertically/Cantilever, thus far only one failure of a horizontal mounted setup. Root cause we believe is water is getting in between the CT and the pressed in insulation sleeve and over enough freeze/thaw cycles cause the tube to crack. We have more CTs like this installed in 5 kv style applications with no failures but I believe part of that is due to in a 2400 volt to ground scenario even if the tube fails they are unable to arc to ground.
An example of a CT with a design like this would be an ABB KOT style CT. I know others make something of similar design. When installing CTs like this my suggestion would be to look for a single molded piece type design of CT.
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