An Air Pocket - John Dunn, Consultant, Ambertec, P.E., P.C.

You have this high voltage assembly and you're really proud of it. The output is 50 kV (50,000 volts) and you've provided it with triple that voltage rating worth of high voltage dielectric material. Your insulating material is thick enough to be rated for 150 kV. That three-to-one safety factor should be just fine.

The assembly runs for a month or so and suddenly there is a total internal failure. The 50 kV of high voltage has managed to penetrate and break down the 150 kV worth of insulation.

Now you ask: "Why??????"

The problem may be that there was a trapped air pocket either in the insulating dielectric material or within some component. If so, then corona can occur in there and the resulting energy discharges can damage the surrounding material(s) so that corona starts happening in that area too.

 

The effect can propogate, sometimes very slowly. A track of damaged material starts forming causing more corona causing more material damage and so forth until there is no longer enough undamaged material left to support the high voltage.

You can easily wear down 150 kV worth of dielectric with only 50 kV of high voltage (just to cite some reasonable numbers) and have your systrem smithereen itself.

 

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[John Dunn]

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