tertiary windings 1

[tintin75]

I just wanted to know why the manufacturer (on the B phase tertiary winding) has swapped the start and finish of the winding (compared with A and C) apologies if the question hasn't been phrased well but when I asked those more knowledgable than myself I was given the reply 'sometimes they do it that way' thankyou
oh more info I think it was a 150MVA Ynd if that helps

 

[tintin75]

when I say start and finish I think I might be talking about an 'inner' and 'outer' I hope that makes more sense.cheers

 

[waross]

It probably had to do with the way the coils were wound physically. If one coil of a delta is swapped electrically, and one connection left open the open circuit voltage will be 200% of rated voltage. When this connection is closed, BANG.
The primary should also be swapped.
respectfully

 

[prc]

This is done by transformer manufacturers for easiness of delta connection or rather to reduce the lead length in forming delta inside. To explain further normal winding terminations will be a1-a2,b1-b2,c1-c2with 1 at top and 2 at bottom.In tertiary esp with idle tertiary with one or none terminals brought out case, middle phase tertiary winding alone will be wound anticlockwise so as to get b2 at top and b1 at bottom.As delta connections require connections between a2-b1, b2-c1 and c2-a1(to get dy1 connection) we can see the easiness in connection .Please draw the windings and see.Of course then the windings of three phases will not be interchangeable.

 

[tintin75]

thankyou waross and prc. regards tintin75