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Introduction to the Delta Wye Transformer Connection – Part 6c

In this part, we're going to continue our discussion on the voltage phasor diagram for the delta connection – and kind of explain what this means.

Okay, so in Part 6b, we concluded that VAB which is this voltage phasor here. That is equal to VAG which is this voltage phasor here – rotated by 30 degrees and then multiplied by the square root of 3. That's going to equal VAB.

So let me write that down here – so VAB – square root of 3 times VAB – rotated by 30 degrees.

I'm going to extend that concept to evaluate VBC and VCA. And that's going to look something like this. So this phasor here – is negative VCG. And this phasor here is VBC. So what we're saying – is we take VBG. We rotate it by 30 degrees in the counter clock wise direction and then if we multiply by the square root of 3 – that's going to equal VBC.

Similarly, we're going to do the same thing with VCA. So here is VCA – here is negative *VCG*. We take *VCG* – rotate it by 30 degrees in the counter clock wise direction and then multiply by the square root of 3 to equal VCA which is this phasor here. So now we have the line-to-ground voltages as well as the line-to-line voltages represented in our phasor diagram.

So let's zoom out here and verify this. So remember, VAB is the voltage across these two lines – line A and line B. VBC is the voltage across line B and line C. VCA is the voltage across line C and line A.

VAG is the voltage across line A and ground. VBG is the voltage across line B and ground. And VC is the voltage across line C and ground.

Now notice that in part 6a – we said that line-to-line voltages across line A and line B is equal to phase A voltage. Now if you're having a hard time recalling this, just click on this link here and it'll go to the video exactly where we talked about it.

Now, let's just label this is in our phasor diagram. Now remember, VAB is equal to V phase A. VBC is equal to V phase B. And VCA is equal to V phase C.

Now that we've drawn this – we're at a point where we can actually talk about this type of a phasor diagram – we find it in transformer name plates as well as engineer drawings.

But before we get to here – if you haven't already, go ahead and click on the button on the bottom right corner of this screen – there's a scribe button – click on that and subscribe to this channel if you haven't already.

Okay so – let me just clarify one thing. We said that this is VAB or V phase A – which is the voltage across line A to B. Which is the same voltage across phase A winding. Now since we've represented this side as the polarity side of our winding – we're going to represent that polarity side by putting a dot here. For this phasor – this side is the polarity side. This is for phase A winding. And we're doing this just to get a visual understanding.

I'm going to remove some things that we don't really need. To make this process as simple as possible.

Okay so this is what we do – this is where the magic comes from. I'm going to explain this in a little while but just bear with me and watch what I do to change this phasor diagram to something like this.

Alright so this is what we have –before I explain how this works, let's just move it to the left hand side so we have a comparison.

Okay so first of all – this phasor diagram right here is what referred to as the "open form" phasor diagram. And this right here is referred to as "closed form"

So you might ask – well what the difference those two and that's what we're going to cover. Okay so now we're at this point where we're going to continue this discussion in part 6d. Now if you like these videos and if you found this videos to be useful, please click the button on the bottom right corner of the screen – there is a button called subscribe. You want to subscribe to get the latest video tutorials on power system protection, automation, and controls.

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