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LF: Re: Current Transformers (off topic, but expertise probably here)

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Subject: LF: Re: Current Transformers (off topic, but expertise probably here)
From: "Vernall" <[email protected]>
Date: Thu, 15 Sep 2005 07:48:19 +1200
Delivery-date: Wed, 14 Sep 2005 20:49:23 +0100
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Andy G4JNT,

Having a "bend" in the transfer characteristic that changes with level certainly means some non-linearity. If you look at spectra (in the frequency domain) instead of RMS level (in the time domain), you may observe what harmonics grow as the level is increased (assuming things get worse with drive level). That would be one way to evaluate nonlinearity, but as you want to use it for measurements then it would be irritating to need to correct for self-distortion in the probe. One possible explanation is that magnetostriction dynamically modulates the (micro) air gaps between EI laminations?

Current transformers I have seen are invariably of toroidal construction. That suggests that leakage reactance is part of the quality of making a good current transformer, but leakage is "linear" and that alone would not explain why you have a "bend" in the transfer characteristic using an EI core. A toroidal core would seem to be less prone to magnetostriction affects?

Have you got a toroidal transformer to try? There is no need to strip off turns as it is fairly easy to arrange a 1 turn primary when the toroid has a decent internal diameter ;-)

73, Bob ZL2CA



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