Wrong voltage on 167 KVA bank. 2

[baaman]

3- 167 KVA transformers, they are hooked up wye-wye. 14.4 Ø to grd. This goes to a reda pump. They want 2500 volts Ø to Ø on the secondary. We have 2500 volts c to b, 1445 a to b,1445 a to c. 1445 Ø to grd. on a,b,and c. The 3 phases were all hot, polarity was the same. H2 was grounded. Anyone with any ideas on what I can look at next. Thank you, Bob.

 

[waross]

The wrong end of "A" phase is connected to the wye point.
Your phase angles are probably 60 deg, 60 deg, and 240 deg.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[baaman]

Would you explain in more detail? Thank you, Bob

 

[rcw retired EE]

Phase A transfomrer is connected reverse polarity from the other two.

Draw the wye vector diagram and then flip the A phase voltage 180 degrees and you will see what happens.

Assume the high side voltage vectors are:
A-G 8.3 kV @ 0 degrees
B-G 8.3 kV @ -120 degrees
C-G 8.3 kV @ -240 degrees
A-B = 14.4 kv @ +30 degrees
B-C = 14.4 kv @ -90 degrees
C-A = 14.4 kv @ +210 degrees

Low voltage on a wye- wye has no phase shift, voltages should be (asuming 14.4-2500V ratio):

A-G 1445 V @ 0 degrees
B-G 1445 V @ -120 degrees
C-G 1445 V @ -240 degrees
A-B = 2500 V @ +30 degrees
B-C = 2500 V @ -90 degrees
C-A = 2500 V @ +210 degrees


But if A transformer is connected backwards, it will be 180 degrees out and low side voltages become:

A-G 1445 V @ -180 degrees
B-G 1445 V @ -120 degrees
C-G 1445 V @ -240 degrees
A-B = 1445 V @ +60 degrees
B-C = 2500 V @ -90 degrees
C-A = 1445 V @ +120 degrees

 

[baaman]

Thanks for the help, I had to stay in today. Tomorrow I will go out and see what we can do. I will let you know. Bob

 

[baaman]

When I went back they had the transformers changed out. The transformers they took down, I could not find. On the dock, with other transformers. Thank you for all the help. Bob