208 to 240 delta transformer

[SES]

Hi guys,

We are looking to install a 15kva transformer for a Solaredge 14.4kw 208 delta/Y inverter on 240v high leg service. I've never worked on 240v delta before and wanted to get your opinions on what would be best. I.e. 208 delta to 240 delta or 208Y to 240 delta. Thanks.

 

[Carultch]

Hi guys,

We are looking to install a 15kva transformer for a Solaredge 14.4kw 208 delta/Y inverter on 240v high leg service. I've never worked on 240v delta before and wanted to get your opinions on what would be best. I.e. 208 delta to 240 delta or 208Y to 240 delta. Thanks.

What does the inverter manual require?

 

[SES]

The inverter will run on 208 delta 3 wire or 4 wire wye plus pe

 

[GoldDigger]

With high leg delta service your transformer primary must either be delta or a wye with the center point left unconnected. But finding a 240Y/137 wye primary will not be easy.
For the inverter side you want a wye so that you can ground the center point. The inverter may not be happy with either corner grounded or ungrounded delta.

 

[jaggedben]

FWIW, I've installed 8.8kW of single phase inverters on the split phase of a high-leg delta, and had no problem at interconnection. That was a 100A service. Of course it's also no guarantee that your mileage won't vary.

If it's PG&E, you could try this: Submit the NEM for single phase, with a line diagram. When they kick it back because you don't have final building, call the contact and tell them you want the engineering review upfront to find out if your design will be approved, and you know the application will be pending until it's built. Be persistent.

Just a suggestion.

 

[SES]

With high leg delta service your transformer primary must either be delta or a wye with the center point left unconnected. But finding a 240Y/137 wye primary will not be easy.
For the inverter side you want a wye so that you can ground the center point. The inverter may not be happy with either corner grounded or ungrounded delta.

Thanks for the help GD. Looks like the 240 delta / 208y transformer is the way to go. One question, if the SE14.4 is an ungrounded TL what wound be the issue of connecting to delta? Just curious. Thanks.

 

[SES]

FWIW, I've installed 8.8kW of single phase inverters on the split phase of a high-leg delta, and had no problem at interconnection. That was a 100A service. Of course it's also no guarantee that your mileage won't vary.

If it's PG&E, you could try this: Submit the NEM for single phase, with a line diagram. When they kick it back because you don't have final building, call the contact and tell them you want the engineering review upfront to find out if your design will be approved, and you know the application will be pending until it's built. Be persistent.

Just a suggestion.

Thanks Ben. In the future we would think about using two single phase inverters but I doubt we will run into this service again.

 

[GoldDigger]

Thanks for the help GD. Looks like the 240 delta / 208y transformer is the way to go. One question, if the SE14.4 is an ungrounded TL what wound be the issue of connecting to delta? Just curious. Thanks.

Even "ungrounded" transformerless may not like an ungrounded delta (with potentially 480V to ground) or corner grounded delta (with 240V to ground max instead instead of 120 or 137).

 

[kwired]

Several possibilities can come up with the high leg system. First one is if it is an open delta system vs full delta system, then comes whether all the transformer components are all same size or not.

A system feeding primarily single phase load and limited amount of three phase load may have a small high leg coil compared to the main single phase coil. Sometimes I do see full delta but still with a larger 120/240 transformer then the two that connect to the high leg. These kinds of details could need closer looking at if significant amount of power in relation to transformer kVA is being fed back into the utility over all three phase conductors, but the source is not three equally sized coils.