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 transformer 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 multipled 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.
Simililarly, 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 couter 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 VCG 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 - on the High Voltage side.
Now that we’ve drawn this
we’re at a point were 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,
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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
This right here is the polarity side. And this right here is the polarity side.
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 bare 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
This 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.
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