Introduction to the Delta Wye transformer connection
Part 7
In this section, we’re going to look at how these transformer phase shifts are actually defined.
Throughout this series, I’ve been using this definition for this transformer connection.
This is a formal way of defining it
And this is an informal way of defining it.
So we’ll take a look at how to interpret these two things.
To really understanding the phase shift
For the Delta Wye transformer connection
we have to understand the quantities that we’re actually defining.
We’ll take a few moments to go over this very quickly.
VAG is the voltage measure across line A and ground.
VBG is the voltage measured across line B and ground. And
VCG is the voltage measured across line C and ground.
And you see that’s the High Voltage side of the Delta side of our transformer.
Similarly, we have voltages that are measured across each individual windings.
We have the HV winding and we have the LV winding here.
So winding A on the HV side –
V phase A measured the voltage across
the polarity side of winding A and the non-polarity side of winding A.
V phase B voltage measures the voltage across
the polarity side of winding B and the non-polarity side of winding B.
Same thing for V phase C on winding C.
Similarly, we’re measuring the voltage across
the polarity side of the LV winding a and the non-polarity side of the LV winding a.
Same thing with winding b and winding c.
Now line-to-line voltages are a little tricky.
So on the Delta side or the HV side,
the line to line voltage across line A and line B we’ve labeled that as VAB
which is also equal to the voltage across winding A or V phase A.
Now if you’re having a hard time understanding this,
just click on this link where we talked about this in the previous tutorials.
So the line to line voltage across line B and line C –
we’ve labled that as VBC which is also equal to voltage across winding B on the HV side.
which is also equal to voltage across winding B on the HV side.
And lastly, the voltage across line C and line A –
we’ve labeled that as VCA
and that is equal to the voltage across winding C.
Now the line-to-line voltage on the LV side is a bit more trickeier.
Because our transformer is connected
in Wye as you can see here – wye grounded
So the line-to-line voltage across line a and line b is equal
to voltage phase a times the square root of 3 and then shifted by 30 degrees.
Now if you’re having a hard time understanding that,
just click on this link here where we talked about it in the previous tutorials.
Similarly the line-to-line voltage across line b and line c,
we’ve labeled that as Vbc and
the line-to=line voltage across line c and line a,
we’ve labeled that as Vca.
Oka so now that we’ve talked about all of these quantities,
let’s introduce one more quantity.
You see that our low voltage side is correct in Wye correct?
The LV side is also grounded.
So all the none-polarity side are connected like that and they are all grounded.
Which means that we can also label this voltage –
which is measured across winding a –
as Vag because
the voltage measurement is across the polarity side of winding a and to ground
so Vag.
Similarly, we can take the voltage across winding b on the LV side and call it Vbg
– and lastly, do the same thing here – Vcg.
Okay there is one more thing we need to note about the voltage across
primary winding and the voltage across the secondary winding.
This will be covered in part 7b