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    3 phase 3 wire measurement

    Dear all,

    I am trying to build 3 phase voltmeter that could measure L-L and L-N voltage during 3 phase 3 wire and 3 phase 4 wire connection. 3 phase 3 wire and 3 phase 4 wire connection are external connection.

    as we know in 3 phase 4 wire we will get neutral reference so we can get accurate reading for L-L and L-N.
    but in case of 3 phase 3 wire we dont have neutral reference .In this case it will be difficult to get gnd reference. I would like use both connection type in common circuit,

    I have seen one of the product where they using V-X-M-H IC , can some one suggest me functionality of this iC. i have attached schematic for reference.

    If any other suggestion with schematic will be appreciated. to differentiate 3 phase 3 wire and 3 phase 4 wireCadstar - Voltmeter.pdf

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    Re: 3 phase 3 wire measurement

    The schematic DOES have a neutral so the IC isn't creating a virtual one.

    With only three wires, your only option is to use Earth as a reference but that may not be reliable depending on where you are, or use one of the phases as reference and compare against the other two.

    Brian.
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    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.



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    Re: 3 phase 3 wire measurement

    The circuit will work on both 3 phase 3 wire and 3 phase 4 wire. when i tested the device i found with neutral i could get 1v difference and without neutral connected means 3 phase 3 wire. i could see difference of 3V.(Neutral connection removed)

    THe above attached circuit they using V-X-M-H IC i dont know to identify. its taking care of neutral absence.

    can you explain the circuit when 3 phase 3 wire without neutral connected.

    when neutral is not connected , unbalance voltage can be seen in neutral point due to (R,Y,B) what does V-X-M-H IC does as functionality.



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    Re: 3 phase 3 wire measurement

    Click image for larger version. 

Name:	nEUTRAL-1.jpg 
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    Here i have attached image for reference.

    In circuit: Here i would like use both Y and delta connection for measurement. when delta connected it should connected to virtual neutral . if virtual neutral connected if 3 phase voltage are balance i would get 0 volt across virtual gnd. if 3 phase are unbalance i would get differential voltage across virtual ground . how can i take care if i wanna use Y and delta connection in same circuit.

    How can i create virtual neutral for case 1.


    In circuit 2:: I have modified 1 st thread circuit . i found few more people using same ckt with V-X-M-H or TA1G . is any one could able to rectify any one of IC.it is SOT 353 package



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    Re: 3 phase 3 wire measurement

    Hi,

    I don´t know how this "VXMH" device works....

    But all you need to do is: make NEUTRAL = PIC_ADC_VREF / 2
    I don´t know what the ADC uses as reference voltage, thus I can´t give a value.

    With the DC shift of Neutral all the ADCs see just positive voltage. (This is important for the ADC to convert the values properly)
    The absolute value of the DC shift is not that imortant.
    All the rest can be done in software.

    In software: NEUTRAL_value = (R + Y + P) / 3
    I recommend to do heavy low pass filtering on NEUTRAL_value.

    R_phase to star_point voltage = ADC_R_value - NEUTRAL_value
    similar with the other phase signals.

    For delta voltages just calculate: ADC_R_value - ADC_Y_value.
    similar with the other phases. No need to care about NEUTRAL_value.

    All this works with and without NEUTRAL connection to the grid.
    But you need good isolation of system GND to EARTH. Best if you use a plastic box and battery powered.

    Klaus
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    Re: 3 phase 3 wire measurement

    There are few question which are running out of mind
    I wanted to use star and delta connection as common. When i use star i will get proper neutral reference. so it wont be difficult to read the analog voltage with reference to neutral line

    when i use delta connection there wont be neutral i will be using virtual ground it will be difficult to measure R,y,B

    as you said in case of delta connection
    NEUTRAL_value = (R + Y + B) / 3
    this r,y,b is converted value from ADC_value?? or Adc value need to take.

    R_phase to star_point voltage = ADC_R_value - NEUTRAL_value
    IN delta connection there will be no neutral connection?? How can create it? or what will be Rphase value here


    you have any recommend circuit to make it work.


    https://datasheets.maximintegrated.c...ds/78M6631.pdf

    http://ww1.microchip.com/downloads/e...S20005216B.pdf

    https://www.digikey.com/reference-de...ing-for-ac/833

    https://www.analog.com/en/products/a...-evaluationkit

    https://www.analog.com/media/en/tech...ts/ADE7880.pdf

    In above i have tested with ADE7880/ http://www.autex.spb.su/ad/ADE7752B.pdf

    There is no issue with star connection but facing when delta connected .
    In software , when delta connected how calculation i need to do??
    how MCU will know weather star connection or delta connection??
    or Weather i need to use above formula itself weather it will work?? do you have suggestion



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    Re: 3 phase 3 wire measurement

    Hi,

    All your questions are already answered in post#5.

    *******
    You can not choose between star and delta connection.
    If you wamt to choose then you need 6 wires, which you don't have.

    You just have 4 wires...
    Thus you need to connect the three phase wires....
    And the only option is whether you connect the star point or not.

    --> If you don't agree with the above, then please draw your two connection schemes.

    ********
    as you said in case of delta connection
    NEUTRAL_value = (R + Y + B) / 3
    this r,y,b is converted value from ADC_value?? or Adc value need to take.
    No, I wrote:
    In software: NEUTRAL_value = (R + Y + P) / 3
    I recommend to do heavy low pass filtering on NEUTRAL_value.
    In software you never have analog values, thus, it's clear that they are ADC values.
    ****
    IN delta connection there will be no neutral connection?? How can create it? or what will be Rphase value here
    Use the math above.
    ****
    you have any recommend circuit to make it work.
    What circuit?
    You just need to generate
    NEUTRAL = PIC_ADC_VREF / 2
    --> use two resitors. You may add a buffer, but no need to.

    ****
    In software , when delta connected how calculation i need to do??
    See post#5.

    ****
    how MCU will know weather star connection or delta connection??
    It can't know. And it doesn't need to.

    ****
    --> If you still have any doubts, then I recommend to use a simulation software. Post your simulation for further discussion.

    Klaus
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    Re: 3 phase 3 wire measurement

    Friendly reminder : If you are making your own neutral point (Y connection) better you connect your neutral to earth with a dumping impedance. In my region Y neutral - earth difference may vary 2-5V.
    Cake is a lie



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    Re: 3 phase 3 wire measurement

    Quote Originally Posted by Antor View Post
    Friendly reminder : If you are making your own neutral point (Y connection) better you connect your neutral to earth with a dumping impedance. In my region Y neutral - earth difference may vary 2-5V.
    Can you show with small circuit how can i do it??



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    Re: 3 phase 3 wire measurement

    Since I have no access to wikipedia I can't find the source. I can't exactly remember the reason I do this. But it might be for better measurement when there is unbalanced load or to avoid "a thing" if there is a fault on load side.

    [Moderator's note: Member requests readers to see his clarification, post #16.]
    Cake is a lie



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    Re: 3 phase 3 wire measurement

    Hi,

    Since I have no access to wikipedia I can't find the source.
    Nobody wrote about wikipedia... so what do you refer to?

    Klaus
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    Re: 3 phase 3 wire measurement

    Quote Originally Posted by nayakajit87 View Post
    in case of 3 phase 3 wire we dont have neutral reference
    Perhaps the 3 sources influence each other in such a way that you can detect. Possibilities:
    * zero crossings
    * voltage waveforms
    * Ampere waveforms
    * peaks versus troughs
    * Does a supply's peak influence the other two supplies?
    * sequence of Ampere peaks versus voltage peaks
    * Do readings change when you disconnect one supply?
    Etc.

    Simulation of the delta arrangement. Each source has two LED's in anti-parallel, to indicate presence of current and direction. An led lights only once per peak of a supply, yet the other two supplies are influenced when that happens.

    Click image for larger version. 

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    Re: 3 phase 3 wire measurement

    Hi,

    Especially with the picture of post#10 I get confused.

    * The picture shows the "load" side, usually inside a device, where you don't have access to the internal circuitry and thus are not able to measure anything inside.
    * The picture shows "currents" only, but you say you want to build a voltmeter.

    Please use a pencil and a paper and draw the situations you want to measure.
    All situations should include
    * the source side
    * the load side
    * your measurement device
    * the connections
    * information about the load (impedances)

    Klaus
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    Re: 3 phase 3 wire measurement

    Here i have attached for reference.
    i tried to trace IC label printed on using these website
    1) V-X-M-H http://www.s-manuals.com/smd/vx
    2)T-A-1-G http://www.s-manuals.com/smd/ta

    I am assuming in circuit using it.

    http://www.s-manuals.com/pdf/datashe...93_richtek.pdf

    http://www.s-manuals.com/pdf/datashe...vhc1g09_on.pdf



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    Re: 3 phase 3 wire measurement

    Hi,

    Instead of telling us what (and how) you want to measure .... you confuse with an even more uselss post...

    Maybe it´s my fault, but I can´t find any useful information in post#10.

    Klaus
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    Re: 3 phase 3 wire measurement

    There are transformers called "measurement transformers". When there is no Neutral line you may have to create your own neutral by connecting the seconder of the this measurement transformer as star (for some reasons Line-Line voltage measurements may not be enough). And measure the phase-neutral voltage. But the neutral of the star is not always 0 volt with respect to ground because of unbalanced loads.

    That's why you connect the new neutral to ground. But I can't remember why this grounding is done with an impedance. Nobody said wikipedia but me. The reason was explained on wikipedia but in my region we can't access to wikipedia now. That's an explanation of "why I can't refer to my source".

    Same thing done with Y connected generators and distribution transformers also. Its called "earthing impedance" but this is out of our case. This is about measurement transformer earthing impedance.
    Cake is a lie



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    Re: 3 phase 3 wire measurement

    From white papers (1):

    Resistance Grounding Systems are used in industrial electrical power distribution
    facilities to limit phase-to-ground fault currents. IEEE Standard 142-1991 states: “The
    reasons for limiting the current by resistance grounding may be one or more of the
    following:
    1. To reduce burning and melting effects in faulted electrical equipment, such as
    switchgear, transformers, cables, and rotating machines.
    2. To reduce mechanical stresses in circuits and apparatus carrying fault
    currents.
    3. To reduce electrical-shock hazards to personnel caused by stray ground fault
    currents in the ground return path.
    4. To reduce the arc blast or flash hazard to personnel who may have
    accidentally caused or who happen to be in close proximity to the ground
    fault.
    5. To reduce the momentary line-voltage dip occasioned by the occurrence and
    clearing of a ground fault.
    6. To secure control of the transient over-voltages while at the same time
    avoiding the shutdown of a facility circuit on the occurrence of the first ground
    fault (high-resistance grounding).”


    (1)
    IEEE Standard 141-1993, “Recommended Practice for Electrical Power Distribution for
    Industrial Plants” (Red Book)
    IEEE Standard 142-1991, “Recommended Practice for Grounding of Industrial and
    Commercial Power Systems” (Green Book)
    GE Publication GEI-72116, “High Resistance Pulsing Ground Detection System”
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