Transformers in series for AC phase measurement

Discussion in 'General Electronics Chat' started by ToonooT, Dec 31, 2015.

  1. ToonooT

    Thread Starter New Member

    Aug 8, 2013
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    Hi all,

    I want to measure AC line voltage and frequency from a 3 phases ~400V generator (wind turbine application) and no neutral.
    In order to measure this I need to get this signal to let's say 0-3.3V and isolated from high voltage.

    The best solution for me is to measure between two phases with a transformer.
    So, I was looking for a transformer which can directly handle such voltage but it seems hard to find. By doing research on compenents I found this one :
    http://catalog.triadmagnetics.com/i...mount-split-pack-power-transformers/f10-110-1
    It can provide two 5V outputs output from 230V.
    My questions are :
    - Can I put 2 of this one in series to handle up to 460V ?
    - Do I need to equilibrate load between this 2 transformers ? (link all outputs in parallel so 4 outputs because of 2 outputs per transformer)
    - Do I need to install this solution between each phase to equilibrate the load ? For me, assuming the load will be very light, it's not necessary.

    Hope someone can help me
    Thanks and Happy new year !
     
  2. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
    2,831
    89
    For this i think, you should use less VA transformer or Current transformer
    by this convert to voltage divider 3.3V max.
    by this it can work.
     
  3. ToonooT

    Thread Starter New Member

    Aug 8, 2013
    11
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    Thanks for your answer but how can I measure Voltage with a Current transformer ?
    Is it not only to measure current ?
     
  4. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
    2,831
    89
    No current transformer are used to measure current only.
    potential transformer are used to measure voltage/emf

    Current transformer
     
  5. ToonooT

    Thread Starter New Member

    Aug 8, 2013
    11
    0
    By the way, I do not need to measure current...
    Can someone answer my 3 questions ?
     
  6. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    945
    A 100:1 voltage divider would not load down your generator, and would provide a 0 to 5 volt scaled reading of your generator voltage.
    A 2 Meg resistor in series with 20k resistor would be my suggestion
     
  7. ToonooT

    Thread Starter New Member

    Aug 8, 2013
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    Of course it will not load the generator but this solution is not isolated from power lines which can be dangerous.
    Also, I don't have a common voltage reference between generator and my device so for me, it's not a good approach.
     
  8. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    ANYTHING which generates 400 to 500 volts is dangerous, so having a current of 200 or so microamps flowing through a 2 Meg resistor to ground is not an increased risk in this respect.

    Ground is a common electrical condition with both your generator and your meter. Use it.
     
  9. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,388
    1,605
    Yes the series combo should work. Loading them the same is also a good idea to keep it all in balance.

    I would not worry about the load on the 3phase power, it should not notice the slight imbalance.

    Isolating the monitor from the HV as you are doing recommended.
     
    ToonooT likes this.
  10. BR-549

    Well-Known Member

    Sep 22, 2013
    1,995
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    They make "control transformers" that go directly across two 480 legs. They usually output 120 or 24 vac. I use to find them at 12 v, but that's been awhile.

    The output is proportional the the leg(line) voltage. Yours will be a little lower.

    You can measure the frequency and voltage across the <24 vac. Or knock that down to where you need it.

    One transformer per phase.
     
  11. ToonooT

    Thread Starter New Member

    Aug 8, 2013
    11
    0
    Ok thanks for your help.

    I think I will follow your advice Erniem, by putting 2x230V transformers in series between two 480 legs in order to get my 5V AC signal from power.
     
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