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Quadrature Booster or Phase shifting TX

  1. Apr 23, 2015 #1
    Hi, Does anyone know about these? Specifically I'm trying to figure out changing the tap on the Delta effects the series voltage:

    425px-Qb-3ph.svg.png
    source wiki: http://en.wikipedia.org/wiki/Quadrature_booster

    Any vector diagram or word explanations will help. Also, what size diameter coils must be used on the series transformer? I would imagine really huge if it's seriesed with a transmission line?

    Thanks
     
  2. jcsd
  3. Apr 23, 2015 #2

    jim hardy

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    Draw your phasor triangle.
    Then think back to eighth grade geometry.
    In an equilateral triangle, the bisector of any angle is perpendicular to and bisects the opposite side.


    Phase B's real current is perpendicular to phase AC's voltage, and so on around the three vertices.
    There's the 90 degrees.
    Observe that's how they connected the transformers.

    So they "tweak" the apparent phase difference between ends of the line.

    i never saw one of those transformers in real life. From the picture at WIKI , the insulators are what you'd expect.
    Maybe someone here has been inside one.
     
  4. Apr 24, 2015 #3
    Actually come to think of it I don't know if I ever found out, or just meant to find out how a Delta to Wye shifts by 30o, because I certainly can't remember now. (If you wanted to explain that a bit too that'd be brilliant)
    Ok, from what you said "
    In an equilateral triangle, the bisector of any angle is perpendicular to and bisects the opposite side.
    Phase B's real current is perpendicular to phase AC's voltage, and so on around the three vertices.
    There's the 90 degrees."
    I assume you chose Phase B just as an example phase from what you described I imagine it'd look something like this:
    123.png
    Sorry but I haven't used vector diagrams in ages, I perhaps understand (remember) less than you might (should) expect (sorry), do you think you could elaborate on the picture a bit, because I wasn't comfortable enough to label it myself, I was thinking the outside equilateral sides were the Delta phase voltage angles, but were the verticies? The series transformer on the side bucking the existing phase voltages?
    I still haven't gotten past the mental block between where I am and understanding it.
    Thanks
     
    Last edited: Apr 24, 2015
  5. Apr 24, 2015 #4

    jim hardy

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    three phase is easier than it looks. Tutorials are everywhere.
    i suspect you're past this one, but it looks like a decent refresher
    http://www.electronics-tutorials.ws/accircuits/phasors.html
    acp50.gif

    From one at https://mysite.du.edu/~jcalvert/tech/threeph.htm
    not recommending it, just this image showed up early in the search

    wyedelta.gif

    o would be neutral
    a b and c the three terminals

    Assuming unity power factor
    the current in line b is in phase with Vob
    which is perpendicular to Vca
    and so forth

    so a voltage that's in or 180° out of phase with Ib gets added to Vca
    is what they're up to. Bear in mind that's a small voltage compared to system voltage, for what they're doing is controlling voltage drop across a wire.

    i'm not a power systems guy, have only worked around some. So i'll hope a genuine one helps us with the power flow calcs, it'd save some stumbling.
     
  6. Apr 24, 2015 #5
    H'mm, almost there. I don't like the idea of talking about current's too.
    So would it also be fair to say the voltage pulled off the 'AC' line voltage (does not stand for Alternating Current here lol), is just perpendicular to VOB?
    [Anyway the current in VOB is in-phase with the VOB at unity isn't it?]

    I'm not entirely sure what you meant by "tweeking the apparent phase differences of the ends of the line"? But wouldn't the net result just be that the magnitude of VOB would be greater?

    Interesting, thanks for the explanation so far!
     
  7. Apr 24, 2015 #6

    jim hardy

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    Sure.
    Remember this thing is part of a power system.

    Its purpose is to control the current through a line connecting two locations.
    The voltage drop along the line is small compared to the voltage on the line itself.

    I was working it in my head last night.
    Think single phase for a minute:
    Current through the line is
    (Voltage between its ends)/Zline
    They are adding to the term (Voltage between its ends) a small voltage at 90 degrees.
    Their intent is to force current sharing between that and some other line connecting the two places.
    So Vob is pretty well fixed by the power system
    What they added is a small voltage in phase with VOB.
    If i understand this thing, those windings in series with the line aren't current measuring CT's they're voltage adding transformers.
    By adding a voltage out of phase they shift the phase of term (Voltage between its ends) . Hence the current through it.



    That's what wiki says they're up to.
     
    Last edited: Apr 24, 2015
  8. Apr 24, 2015 #7
    Ok, so if you want more current down B phase, you add a small voltage 90 degrees to B. So when they take Vca off the Delta, and add it to Vb you're adding a 90 deg out of phase voltage and that causes more current to flow down B phase?

    You're explanation should be added to the wiki page.
     
  9. Apr 25, 2015 #8

    jim hardy

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    You'd probably do all three phases so as to shift current from one whole transmission line to another, or to route power around a region.

    Have you seen this page? The power grid is a huge interconnected dynamic system with power flowing every which way.
    Watch it in motion.
     
  10. Apr 25, 2015 #9
    Yeah, but I meant just in the realm of keeping with your Phase B observation/example.

    Which page are you talking about? This thread?
    Yeah from what little exposure I have had to power system diagrams they do seem chaotic on first glance lol
     
  11. Apr 25, 2015 #10

    jim hardy

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    oops this graphic of US grid.. it's like watching a mobile swing in the breeze

    http://fnetpublic.utk.edu/gradientmap.html [Broken]

    cdgradgen.php?1429977001978.png
     
    Last edited by a moderator: May 7, 2017
  12. Apr 25, 2015 #11
    Ah that's cool, yeah I've been meaning to look into the 'droop characteristic' of how busses balance themselves by changing the frequency slightly or something, all I remember hearing is that the characteristic means that nothing needs to be controlled, it does it inherently. *I am aware that statement is probably conflating different aspects, and is wrong lol*

    So just for my final piece of mind, was I correct in my understanding of a single phase examination (of B phase)
    'if you want more current down B phase, you add a small voltage 90 degrees out of phase to B. So when they take Vca off the Delta, and add it to Vb you're adding a 90 deg out of phase voltage and that causes more current to flow down B phase line?'

    Cheers!
     
    Last edited by a moderator: May 7, 2017
  13. Apr 25, 2015 #12

    jim hardy

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    Absolutely !

    maybe more current, maybe less, depending on the phase difference between the substations at the two ends of the line.
    Observe they have flexibility to add it 90 deg leading or 90 degree lagging, depending on bus transformer tap ..

    it's a control system....needs to be symmetric
     
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