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schematic

simulate this circuit – Schematic created using CircuitLab

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My question is, because the delta primary in this case is connected A-C, rather than A-B, does this effect the direction of the 30 degree phase shift? I have read that if the primary is connected A-B then the primary phase is leading, and if it is connected A-C the primary phase is then lagging the secondary by 30 degrees. Can somebody please shed some light on this for me? I would like to know exactly what is shifting, leading or lagging, and why. Thank you !

nmorris
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    Can you draw phasor diagrams - maybe that is your real question? – Andy aka Jul 10 '16 at 15:44
  • See if [this question](http://electronics.stackexchange.com/questions/244697/what-are-the-pros-cons-on-the-30-degree-voltage-phase-shift-between-the-primary/244704#244704), my answer and the link in my comment to the OP help. – Transistor Jul 10 '16 at 15:51
  • @Andy My real question is the one I posted. Phasor diagrams are not a strong point of mine, I'm fairly new to this and need all the help I can get. – nmorris Jul 10 '16 at 16:02
  • @transistor Thank you for the reply and the reply to my last question as well. It is helping, but I am still unclear if it works the same way weather A is connected to coil B or C? or If that matters? Thanks again! – nmorris Jul 10 '16 at 16:04
  • As Andy says, draw the phasor diagram and post it up. You can draw a rough-one with the arrow symbol on the built-in schematic editor. Double-click the elements to change the properties such as the colour. See you at the interview. ;^) – Transistor Jul 10 '16 at 16:15
  • It might be helpful to forget about "phase shift", and think in terms of what voltage does each primary winding see. For example, the PH A primary winding sees Va-Vc. If you list the voltage and phase of Va, Vb, and Vc, you should be able to quickly figure out all the rest from writing the corresponding equation. – AndyW Jul 10 '16 at 16:59
  • Please check out possible duplicate:http://electronics.stackexchange.com/questions/191232/why-does-a-delta-wye-transformer-make-30-degrees-phase-shift?rq=1 –  Jul 10 '16 at 18:04
  • Ok I will try drawing the phasor diagram here. I have been watching all the videos, and as far as I can tell they all use the ABC sequence. Am I correct in saying my configuration has a ACB sequence? – nmorris Jul 10 '16 at 18:17
  • Very rough, but I'm hoping what I've drawn is correct? – nmorris Jul 10 '16 at 19:00
  • @transistor did you mean post it up here or as a new question? – nmorris Jul 10 '16 at 22:24
  • Keep everything together. See my answer. – Transistor Jul 10 '16 at 22:54
  • The given diagram is incomplete; we need to know the position of the dots of each winding in order to provide the only correct answer. Otherwise, people will assume a position for them, as Transistor did in his answer, which can be false depending on the actual position of the dots. – alejnavab May 16 '20 at 07:03

1 Answers1

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You'll be in trouble at the interview. Read on ...

schematic

simulate this circuit – Schematic created using CircuitLab

Figure 1. A delta-wye (delta-star) transformer connection and phasor diagrams.

  • Figure 1 shows a standard delta-wye 3-phase transformer connection. The useful aspect of showing it wired this way is that it is very easy to see that each of XFMR1 primary and secondary pairs must be in phase as they are on the same core.
  • Figure 1(i) shows the primary and secondary phasors. Note that we join the phasors wherever they are electrically connected. The secondaries are smaller (representing a step-down in voltage) for clarity and haven't been connected yet. Note that 'a' is in-phase with 'A', etc.
  • When we wye-connect the secondaries we join the secondary phasors at the neutral point. This is shown in Figure 1(ii). Note that the phase-neutral voltages are in still phase with the primaries.
  • Figure 1(iii) shows the phase to phase phasors in black. Note that these are 30° out of phase with the phasors in Figure 1(i). This is the phase-shift you will be interrogated on.

Draw the diagram a few times, then do it from memory. Show by trigonometry that the shift is actually 30°. Then explain it to a friend. If you can do that you should be ready for the interview.

Transistor
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    I hope it helps. Wait a day or two before accepting an answer so that you don't discourage better answers. – Transistor Jul 10 '16 at 23:22