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Current transformer self-capacitance Re: Re: [TCML] Measuring secondary current



For future reference, the self-capacitance of a current transformer secondary isn't possible to measure using an LCR meter (I got 7uF), but this page (http://www.g3ynh.info/zdocs/magnetics/appendix/Toroid_selfC.html) suggests it can be estimated with the formula CL(pF) = 0.90 + 78.1 / N (for an FT50-61 core, but I can't imagine it varies that much).

Or just C=1pF for > 15 turns, C < 5pF for < 15 turns.



On Sun, 2 Sep 2012, Antonio Carlos M. de Queiroz wrote:

On 1/9/2012 12:14, Andreas Hahn wrote:
Thanks. I was actually going off a post to TCML ages ago which recommended 300 turns on the toroid, evidently for a different purpose!

Is there a reference for CT construction you can point me to? Certainly I can follow your directions approximately (say, 25 turns on the toroid, a 100nF capacitor, 470 ohm resistor), but I would be doing so without knowing how any of those values interact or affect the final measurement.
I wrote this:
http://www.coe.ufrj.br/~acmq/tesla/current.pdf

Antonio Carlos M. de Queiroz
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