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    EM field around Current Transformer

    Hi

    I am receiving input current in the range 0-50A, 50 Hz AC current. I have a 1000/1 CT. Nearby , I have Downstream electronics consisting of ADC and MCU for displaying the input current. The question is, can AC current produce sufficient EM field to damage ADC and MCU?

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    Re: EM field around Current Transformer

    Hi,

    impossible to answer.

    Generally: for every I/O that leaves/enters the PCB (or the device) you need to consider ESD protection and EMI/EMC filters.
    If you are not sure, then add one.
    If cost is a problem then ask the customer for EM field specification.

    Klaus
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    Re: EM field around Current Transformer

    For CT secondary , I do have a protection diodes in shunt along with the resistor. My question is can current in primary cause sufficient EM field to damage the electronics?



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    Re: EM field around Current Transformer

    You would have to provide the datasheet, or at the very least a good photo, of your current transformer.

    Most toroids contain the stray fields pretty good.
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    Re: EM field around Current Transformer

    Hi

    CT data sheet https://www.mouser.in/datasheet/2/192/CT07-1003158.pdf. Please advice for the precautions to be taken



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    Re: EM field around Current Transformer

    Wrong question. If at all, the field of the primary conductor would be the problem. The CT core can reduce but not increase the field.

    The induced voltage around a 50A 50Hz conductor is quite low.



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    Re: EM field around Current Transformer

    Hi FvM

    The datasheet says that secondary inductance is around 8H. Will it not create EM field?



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    Re: EM field around Current Transformer

    secondary inductance is around 8H. Will it not create EM field?
    no, not if it has a low value R across it completing the circuit. The mag field cannot dmage your ckt - only a high fault current giving a high voltage on the CT output - or if the burden R goes Hi-Z or open circuit...



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    Re: EM field around Current Transformer

    Hi,

    Current causes magnetic field. In a CT the primary is just one winding, thus the magnetic field will not higher than without CT. But in the CT the magnetic field is concentrated in it's core. And the magnetic field in the core causes current in the secondary of the CT. This current again causes the magnetic field within the core to be compensated. It becomes reduced, but not completely to zero.
    The magnetic field outside the core will cause about no current in the secondary.

    Klaus
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    Re: EM field around Current Transformer

    I got my ADC damaged in two boards after injecting currents (after approx ten iterations). The ADC is about 100mm distance from the primary wire. Input currents were in the order 0-10A, 50 Hz AC.



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    Re: EM field around Current Transformer

    Most likely the unclamped CT sensor output voltage has been routed to the ADC. Please show a schematic.


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    Re: EM field around Current Transformer

    Hi,

    I agree with FvM.
    Wrong usage / wrong circuit.

    Show your schematic.
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    Re: EM field around Current Transformer

    Perhaps the OP doesn't know the CT must be terminated with a suitable resistor 1000:1 CT 50A thru middle => 50mA on 10 ohm this is 500mV and 0.025VA

    if you have 10k input impedance - rather than a low ohm burden resistor - the volts will be 500V ...!



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    Re: EM field around Current Transformer

    No, It is 2 ohms burden. It works for a while and then suddenly everything fails.



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    Re: EM field around Current Transformer

    faulty soldering or component or connection when moved.... ?

    - - - Updated - - -

    put some big diodes ( 10A10 ) in inverse parallel across CT LV terminals this will limit the V to 600mV peak



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    Re: EM field around Current Transformer

    Hi

    It's still the same:
    Either schematic or PCB layout problem.

    Klaus
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    Re: EM field around Current Transformer

    cracked 2 ohm SMT resistor ... ?



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    Re: EM field around Current Transformer

    Some discovery from my side, but I need confirmation. I have transformer based current injection kit, which shares the same distribution board,from where I tap 230V to power my board ( through AC-DC converter). I am guessing that some form of inrush lifting neutral voltage might have caused my board to fail. Is it possible?

    Anycase, the schematics is provided below, TVS diode used is SMBJ5V0CA ( input current range 1-50A, output of CT 2mV-100mV RMS, 2 Ohm in shunt)

    Click image for larger version. 

Name:	CT_schematic.png 
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ID:	152602



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    Re: EM field around Current Transformer

    try some 100nF 250Vac caps to earth on each line ...

    - - - Updated - - -

    what is FB1 & 2 ..?



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    Re: EM field around Current Transformer

    Hi,

    You make the thread (and to get a solution) unnecessary lengthy.
    It seems you donīt want to get a solution ... why else do you give the requested informations slowly piece by piece?

    This little snippet of schematic is not useful. --> show the complete circuit of the signal chain from CT to ADC including PCB layout. With all connections involved.

    Klaus
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