ungrounded wye primary

[danlhanson]

Can anyone give me the pros and cons of an ungrounded wye primary / grounded delta secondary. Currently their is grounded wye primary, we are looking to reefed and considering going with an ungrounded wye primary.

 

[PHovnanian]

Pros: An ungrounded Wye primary prevents the transformer bank from backfeeding an open phase on its source side.

Cons: Poor voltage regulation, particularly for unbalanced bank loads.

If you must use such a configuration to serve three phase loads, it is best to use the wye-delta bank to serve three phase loads only and provide a separate single phase transformer for things like lighting and outlets if these represent asignificant part of the connected load.

 

[danlhanson]

Cons: Poor voltage regulation. How will I see this, can you provide examples. the primary load on transformers will be vfds, soft starters, and starters for motors.