Grainger, Power System analysis book, Example 2.9

[Redskinsdb21]

Does anyone have this book..I am trying to see why the low-voltage side current lags by 30 degrees? the problem doesnt say the system is + or - sequence...dont you have to know this in this case?

 

[DK PE]

I think ANSI standard for transformer connection is to have high side lead low side. I think this is reference but you should check. Look harder in Grainger/Stevenson as I think it mentions it. I'll look tonight if you don't find.

IEEE Standard Terminal Markings and Connections for Distribution and Power Transformers,
IEEE Std. C57.12.70-2000.

 

[Redskinsdb21]

In grainger, pages 64-71 discusses phase shift between delta-y xfmrs....but is contradictory or I am just missing something. In figure 2.14 it says Vll y side leads Vll delta side by 30 with y being high side of a y-delta xfmr. Then page 68 it says when stepping up...in a delta-y or y -delta..."advance + seq voltages by 30" and " ****** (minus) - seq voltages by 30"...why does stepping up matter? Fig. 2.14 goes by whether its + or - seq?

 

[DK PE]

I only have a copy of Stevenson handy (predecessor of Grainger/Stevenson)... It states " The American standard of designating terminals H1 and X1 on Y-Delta transfomers requires that the positive-sequence voltage drop from H1 to neutral lead p-sequence voltage drop from X1 to neutral by 30 degrees, regardless whether Y or delta winding is on the high-tension side". Note this is a standard not some fundemental law of physics and may not be followed in all cases. Grainger text should state something similar.

So without Grainger in front of me to look at and just reading your post...

--> Vll y side leads Vll delta side by 30 with y being high side of a y-delta xfmr. -- this make sense as voltage on high side leads 30 degrees

--> page 68 it says when stepping up...in a delta-y or y -delta..."advance + seq voltages by 30 -- so when stepping up the high side leads by 30 which in this case is secondary

Add'l quick edit: You should take a look in Wildi assuming you have it as he has a little more detail.

 

[Redskinsdb21]

I have Wildi and I find no more details on this ....all the wildi books does is tell me in a d-y Xfmr, line voltages on y side secondary lead line voltages on delta primary side by 30 degrees. It doesnt say whether or not if its + or - sequence, which I think will affect it.

 

[DK PE]

I have Wildi and I find no more details on this ....all the wildi books does is tell me in a d-y Xfmr, line voltages on y side secondary lead line voltages on delta primary side by 30 degrees. It doesnt say whether or not if its + or - sequence, which I think will affect it.

I don't think Wildi says that...in fact for the D-Y transformer you mentioned, the y connected seconday would only lead if it was a step up transformer (see above high side leads low side). If it is step down then not true. What Wildi states in my copy (6th ed) under polarity marking of 3-phase txfms - very end of chap 12 ..." If the primary and sec. winding are connected in EITHER Y-Delta or Delta-Y, there is a 30 phase shift between pri and secondary. The internal connections are always made such that the voltage on the HIGH side ALWAYS lead the voltages of similarly marked terminals on low side..."