Introduction to the Delta Wye Transformer Part 6b

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Introduction to the Delta Wye Transformer Connection Part 6b.
In this part, we're going to continue our discussion on the voltage phasor diagram for the Delta Transformer connection. And by the end of this part 6 tutorial. Not this one but the part 6 section, we'll have a greater understanding what this illustration means – how it's drawn and what it represents. We often find this illustration in transformer nameplates as well as engineering drawings. So we want to have a very strong understanding of this connection.

So in part 6a, we setup our voltage phasors and we defined V_AG, V_BG, and V_CG. We also said that there is a difference between between V_AG vs V_AB or V_A. And that is the key to undersanding voltage phasor for the delta connection.

So let's jump right into it.

V_AB which is the voltage across line A and line B on the delta side. Is equal to the Phase A voltage which is the voltage across winding A. That is also equal to V_AG minus V_BG. Which makes sense right? A_AG is here which is the voltage across line A and ground. And V_BG is here which is the voltage across line B to ground.

So the voltage across line A and line B is essentially equal to the voltage across line A and ground minus the voltage across line B to ground. Make sense right?

Okay so let's evaluate this equation. So I've set something up already. This should look very similar to the examples that we've been doing in the previous tutorial. The first thing that we're going to do is that we're going to define our phasor values.

I'm going to choose a value for V_AG of 2400V at 0 degrees. V_BG is again 2400V at 240 degrees. And V_CG is equal to 2400V at 120 degrees. Now if you haven't caught on already, this is a balanced set of 3 phase voltages. And if you're still confused, you can click on this link here where you can find a video on balanced power systems. Okay so I'm going to call this phasor V_AG – because that's how I defined it right? So V_AG is at 0 degrees and 0 degrees is my reference line. V_BG is this phasor here. And V_CG is this phasor here. And, if you're having a hard time understanding this setup, just click on this link and go to the balanced power system video tutorial.

So this right here, is an ABC phase rotation. Now we said in our equation, that the line-to-line voltage across line A and line B which is essentially the voltage across our phase A winding for the delta connection is equal to V_AG minus V_BG. So here is V_AG right here. We're going to perform the head-to-tail method and substract V_AG minus V_BG.

Okay so now that we have a visual representation, if we were to relate V_AG to V_AB what would we have to do? We'll we would have to shift V_AG by 30 degrees – in the counter clock wise direction. And then, we would have to multiply it or stretch it by the 1.73 or the square root of three so it lines up with V_AB.

So we take V_AG – now we have to shift V_AG by 30 degrees in the counter clock wise direction. And then we have to multiply it or stretch it by 1.73 so it overlaps V_AB. Which means that V_AB is equal to the square root of three times V_AG rotated by 30 degrees. So this equal there. You see that?

So why are we doing this? Let's step back and understand exactly what's going on here and why we're doing this. We want to understand the relationship between V_AG and V_AB. Because that's what's going to help us understand the voltage phasor diagram for the delta wye transformer connection. 

Is that making sense? If it is, then comment on below. If it's not, then tell me how I can improve these videos. Now if you haven't already go ahead and click on the link on your bottom hand of your corner of your screen.

In the next part – part 6c – we'll go ahead and complete our phasor diagram and show the relationship between these voltages here vs. these voltages there.

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