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
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    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
    13,056
    3,245
    A current transformer is is an AC only device. It has no DC offset.
     
  3. DickCappels

    Moderator

    Aug 21, 2008
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    634
    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)...

    Should this response fail to answer your question or appear a non-sequitur, please elaborate...:)

    Best regards
    HP
     
  5. #12

    Expert

    Nov 30, 2010
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    Suggestion #4

    Adjust your volt meter to, "DC".
    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!:D 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
    16,355
    6,852
    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. :(
     
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