# Current transformer DC offset Voltage

Discussion in 'General Electronics Chat' started by cmurugan-design, Mar 31, 2015.

1. ### cmurugan-design Thread Starter New Member

Nov 15, 2012
1
0
How to test CT dc offset voltage? Pls advice the circuit configuration to test th CT.
Primary current : 150A
Turns ratio : 1: 2500,
Toroidal version

2. ### crutschow Expert

Mar 14, 2008
13,488
3,372
A current transformer is is an AC only device. It has no DC offset.

3. ### DickCappels Moderator

Aug 21, 2008
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669
How to test the output voltage of a current transformer? If it is a passive current transformer, merely pass short length of wire through the aperture and connect the ends (this makes a shorted turn -there should be no other input to the transformer), load the transformer with the designated shunt and measure the DC offset voltage. (If it is not zero, then per crutschow, something is probably wrong.)

If your current transformer includes active circuitry, make sure the transformer is turned on and proceed as above.

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4. ### Hypatia's Protege Distinguished Member

Mar 1, 2015
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The principal effect of dc offset on a current transformer's performance (accuracy, if you will) owes to the magnetic properties of its core material (Spec. 'saturability').
While precise profiling of the core requires proper impedance analysis, you may determine its parameters (as regards a specific application) via coralation of the output (i.e. secondary EMF) to primary excitation comprised of a fixed (AC) component 'riding' various test levels of DC 'bias' (offset)...

Best regards
HP

5. ### #12 Expert

Nov 30, 2010
16,673
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Suggestion #4

Place the volt meter leads on the wires exiting the current transformer.
Adjust the voltage range lower and lower until you realize current transformers don't produce any DC voltage.

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6. ### Hypatia's Protege Distinguished Member

Mar 1, 2015
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Indeed not! Howbeit a DC 'bias' on the primary may effect the transformation parameters (à la saturable reactors)...

Best regards
HP

7. ### #12 Expert

Nov 30, 2010
16,673
7,320
Oh! I get it...
Somebody is talking about intentionally applying a DC current to the transformer that was not intended to have any DC current.
That was not obvious to me.