Transformer Compatibility

[Mian Usama]

The main service panel is connected to a low-voltage high-leg Delta transformer, with measured voltages as follows:

L1–L2: 240 V

L2–L3: 240 V

L3–L1: 240 V

L1–N: 120 V

L2–N: 208 V

L3–N: 120 V

We have 2 × 60 kVA inverters that operate at 480 V. My understanding is that we would need a 150 kVA step-up transformer with primary Delta 240 V and secondary Wye 480/277 V.

Question: Is it also feasible to install a 208 V Delta transformer at the primary

 

[jaggedben]

...

Question: Is it also feasible to install a 208 V Delta transformer at the primary

No, you don't have 208 on three phases. There is no delta at that voltage.

You have a high-leg delta service and I strongly recommend you file the utility interconnection application early. They may want you to backfeed only the split phase of this service, rather than all three phases. Or they may not want you to backfeed this service.

(Is this installation in the USA?)

 

[jim dungar]

Are you asking about installing two different transformers?

 

[Mian Usama]

Yes, In Texas

No, you don't have 208 on three phases. There is no delta at that voltage.

You have a high-leg delta service and I strongly recommend you file the utility interconnection application early. They may want you to backfeed only the split phase of this service, rather than all three phases. Or they may not want you to backfeed this service.

(Is this installation in the USA?)

 

[ggunn]

Yes, In Texas

Where in Texas? I have done several systems like this in Texas; what jaggedben says is spot on. I have encountered all three situations with Texas POCOs. Ask them or read their published interconnection guidelines (if they have any) before you go any further with the design and planning of your system; they will tell you whether your 120kW should connect to all three phases, just the A and C phases, or not at all. Obviously, if they restrict you to A and C you will have to change inverters.

But assuming the POCO allows you to connect three phase, your 480V to 240V 3P transformer configuration is correct. The 208V transformer question is a bit of a non sequitur; you cannot use it instead of a 480/277V:240V wye:delta.