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Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
I stumbled on this illustrative example:
It provides 7.5 volts at 53 amps for, presumably, the filament of a great big rectifier tube. The secondary is isolated for a working voltage of 7000 volts DC plus 7000 volts AC plus 400 volts at 5 MHz.
I'm guessing that it's meant to be used dry, but could hold off a lot more high voltage if immersed in oil. Filling the oil tank under vacuum would not add much -- there are no high potential differences within the primary or secondary coil, and not much in the space between them to trap air.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
I have several small isolation transformers for use in low voltage floating power supplies that can hold off up to about 3kV. The windings are encased in orange epoxy blocks into which laminate cores are secured with copper-plated straps.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Are these used by the power company, when they need remote instruments powered by the line thery're monitoring? or radio transmission? 7.5 volts at 53 amps must mean tube heating... it would be odd used any other way....
Registered Member #816
Joined: Sun Jun 03 2007, 07:29PM
Location:
Posts: 156
Kind of reminds me of something like a picture of an Austin ring transformer I seen, but for high current and low voltage. I guess low capacitance from secondary to primary or ground, must have needed such a large air space.
I agree you could make an oil filled version to obtain a much greater isolation voltage, maybe for powering some measuring sensors floating at some silly voltage above ground like on the output of a big voltage multiplier cascade.
Aside from its original purpose, I guess it’s one of those solution looking for a use thingies, unless you have some ideas.
Registered Member #3343
Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311
Yes, the first idea in my mind was a ground grid amplifier.
Them I remember the low capacitance transformers used to couple 60Hz voltage in the broadcast transmiting towers. The 60Hz voltage is to feed the red lights in the tower, airbone lights. The tower 5/8 wave lenght is fed with RF.
Im sure ha the construction is to provide high insulation, very low secondary capacitance.
Registered Member #193
Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022
Nice if you can get them. If I was trying to do that I'd probably get a motor, a low voltage generator and an insulating shaft to couple them together with.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Bored Chemist wrote ... Nice if you can get them. If I was trying to do that I'd probably get a motor, a low voltage generator and an insulating shaft to couple them together with.
That's another way to get the job done. Here's one amateur motor-generator project designed for high voltage isolation, so far used up to 11 kV.
The first follow-up post at shows a Faraday cage where human operator and instruments can work 750 kV above ground. Power comes from a three-story-high insulating shaft turned by a 5 HP motor.
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Low voltage transformers with high voltage isolation
