Voltage Transformers 2

[Nice77]

Hello All, I need to create template drawings for various voltage transformer connections....ie: Delta, Wye for 2 VT and 3VT for 3 phase, 4 wire system.

I'm kinda stuck on the 2 VT connections.
1) When you have 2 VT's, are they always Delta?
2) If there is an open-delta system, is there such a thing as closed delta?
3) In the attached drawing, it shows 2 sets of VT's. The top VT isn't grounded on the B phase, but the bottom one is. When do you know which connection you need?


Thanks in advance

 

[waross]

1. Almost always.
2.Open delta > two transformers (In North America, but not in IEC land.)
Closed delta > three transformers.
3. Use the bottom connection when you want to "Live long and prosper."
An ungrounded PT secondary circuit may result in a dangerously high common mode voltage on the secondary due to capacitive coupling.

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

 

[Nice77]

Thanks a lot Waross!