IEEE Consultants' Network of Long Island

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??????"

Rise Times of Voltage Multipliers - John Dunn, Consultant, Ambertec, P.E., P.C.

A voltage multiplier does not achieve its full output voltage instantaneously upon the application of its AC input voltage. The half-wave doubler shown below and analyzed by the recursive differential equation method, illustrates the point.

The ratio of the two capacitors of this circuit, the ratio of C1 to C2 affects the DC output rise time, but there is always some rise time slowness. 

High Voltage Corona Test - John Dunn, Consultant, Ambertec, P.E., P.C.

High voltage capacitors can exhibit problems with corona at voltages well below their ostensible voltage ratings. The problem can be qualitative tested for as follows:     

 
The high voltage power supply feeding this circuit can be the Spellman Model 205B-20R whose datasheet  is available at http://www.spellmanhv.com/~/media/Files/Products/205B.ashx .

Dielectrophoresis - John Dunn, Consultant, Ambertec, P.E., P.C.

"Dipole moment" is a measure of the electrical polarity of a system of charges. Consider two molecules, one of ethyl alcohol and the other of di-methyl ether:  

 

High Voltage Ratings of Silicone Rubber - John Dunn, Consultant, Ambertec, P.E., P.C.

Sometimes, when we look way back in time, we find the most useful things. I refer to this application note:

 
I had the pleasure of meeting Jim Hawkins back in 1986. It was both an enjoyable and educational experience. His key point to me that day was from the CDS-2081 document that the volts per mil ratings of silicone rubber or RTV is not a constant as the thickness of the RTV is varied.