Excessive current into capacitive voltage divider / corona sensor
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Fredrick
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Fri Jun 20 2008, 04:25PM
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Registered Member #1339
Joined: Wed Feb 20 2008, 04:43PM
Location:
Posts: 9
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I am testing an old Biddle corona detector to 50KVAC and am getting some strange results. The input C (C1) is 0.003uF and the tap cap (C2) is about 1.25uF for a 400:1 nominal ratio. The low cap goes to ground via a 25mH choke (this is the corona signal tap)
I'm getting almost 5mA at 4KV 60Hz yet the measured C is correct at 3000pF. The DC 50KV hi-pot was ok, no pops or fireworks and no current. I have about 20K ohms in series to limit the fault current and damp possible oscillations..
What the heck is going on here ?
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GeordieBoy
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Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
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The 5mA of AC current flowing at 4kV/60Hz is consistent with what you would expect through a 3nF capacitor with AC voltage applied. (It's reactance at 60Hz is around 884k.)
BTW If a 3nF capacitor breaks down with 50kV across it, there will probably be more of a loud bang than a polite pop!
-Richie,
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