delta service

[dumitruN]

I have a 400A 120/240V delta service in a building. It feeds 3 phase and single phase panels in the building.
I will bring a new 1200A, 120/208V and I wand to feed the existing panels from the new switchgear.
Whant kind of transformer do I need to feed the old panels?
Thank you.

 

[davidbeach]

A 208V delta-240V delta.

 

[dumitruN]

Thank you

 

[dumitruN]

Can you elaborate why is the primary a delta since I have a Y from the street?
Thank you.

 

[davidbeach]

A grounded wye-delta would create any number of problems, and may be prohibited by the utility. An ungrounded wye-delta might work, but could also leave you with voltage balance problems. if you are feeding a load serving transformer, a delta winding on the source side is almost always the best connection. The only way to get the right voltages to reconnect the existing equipment is with a delta on the load side, so delta-delta it is.

 

[dumitruN]

Thank you very much

 

[dumitruN]

With the new service I will have a Y system the existing delta in the building will be part of it. The power company is not involved inside the building. Phase by phase from the new Y to the existing delta you still think it will be created an imbalance?
Another question will be: can a buck-boost transformer be used?
Thank you.

 

[rbulsara]

A key factor will be what is the ratio of 3 phase 240V loads to 120V single phase loads?.

Yes, boost transformers (auto transfromer)can also be used to boost 3 phase 208V to 3 phase 240V. I would also separate 120V loads from the delta service and re-feed them from new 208Y/120V service.

There can be a few options, I would suggest you hire a consulting engineer and review options along with costs.

Rafiq Bulsara

http://www.srengineersct.com