Teaching Phase Relations Determination using 2 pieces of paper (1 transparent) has anyone done this?

[BSEEDan23]

I'm tasked with visually explaining the connection change between an existing 30 degree lagging transformer to a new 330 degree lagging or (30 degree leading) transformer. Both transformers are Delta- Wye.

Instructions read: Draw and label the voltage vector diagram including the high and low side bushing designations of the new transformer on a transparent sheet of paper. On a second sheet of paper, draw to the same scale the voltage vector relationship for the existing system. Label this diagram with the required phase letter designations A B C and a b c. Place the transparent sheet of paper on top of the other and rotate it, or if necessary turn it over and rotate to match up the two drawings. Connect the new transformer as shown by the two drawings aligned on top of each other.

The text is a little unclear what it actually accomplished visually. Am I to draw the current transformer configuration on one sheet of paper. Both Delta high and Wye low connections then the same for the new transformer on a transparent sheet of paper and rotate them until what aligns?

The existing TR had a 30 deg lag and had:
H1=C phase x1 = c phase
H2= B phase x2 = b phase
H3 = A phase x3 = a phase

The new transformer has a 330 deg lag.

H1=A phase x1 = a phase
H2= B phase x2 = b phase
H3 = C phase x3 = c phase


I appreciate any help. Also I am not a teacher or anywhere close. I finished a transformer replacement project and am tasked to explain this to the new engineers.

 

[davidbeach]

faq238-1154.

 

[BSEEDan23]

I'm getting confused on the CCW and CW rotations. My existing transformer is CBA clockwise rotation correct? Bushing are H1=C,H2=B H3=A... when the new transformer configuration is superimposed I have H1=A , H2=B with H3=C. That would make the new transfomer ABC CCW rotation correct?

 

[unclebob]

The drawings show that rotation stays the same.

Just a question: Wye not choose a transformer with the same vector relationship?

 

[piterpol]

Hope this paper helps you.

 

[prc]

All these years, my understanding is to parallel a Dy1 (or Yd1 ) transformer to a Dy11 unit(or YD11) is to just interchange the external line connections( ie R&B or A&C) to outermost bushings (on both HV &LV sides) in one of the units. What benefit all these complications give?

 

[BSEEDan23]

Thanks for all the help guys. As a fairly new engineer I really appreciate all the input.

The project is complete and PRC is correct. A&C phase were swapped. I had confusion on the theory behind the change, but it has been cleared up with the documents posted. I was also able to figure out how to represent the configurations with 2 pieces of paper for teaching purposes.

The transformer replacement project is for a utility company. I believe they had a delta-wye 330 degree lag on hand and choose to use it in place of the previous 30 degree lagging transformer. This was all new to me so again I appreciate all the help.