Neutral on a 120?240V High Leg Delta

[Carultch]

Heres the system overview as I have it so far.

2x SolarEdge Se33.3k inverters
218 Hanwa 315 QPro modules
Hooking up to a 240v High leg service

The question is in finding a legal interconnection betweeen the 480 wye output of the inverters and the 240v high leg service.

I tried getting a hold of the POCO to see if they would allow a connection to the AC phases and ignoring the B phase like has been suggested (and just using 1 phase inverters) but nobody at Rocky Mtn Power was able to give me an answer. The SolarEdge guys dont seem to know much about this service and they recommended trying the single phase route across the phases or just going all on the A and C phases. Again this depends on if the POCO approves...

We will have an EE look over everything before we submit the interconnetion application.

You'll need to get a transformer that is 277/480WYE (inverters) on one side, and 120/240 Delta on the other side (building grid). There is no way to connect the 33.3k inverters directly to any other grid than 277/480.

 

[Ctay005]

You'll need to get a transformer that is 277/480WYE (inverters) on one side, and 120/240 Delta on the other side (building grid). There is no way to connect the 33.3k inverters directly to any other grid than 277/480.

Does it matter which is the primary and which is the secondary? All of the transformers that Ive found have the 240 Delta as the primary and the 480 wye as the secondary. Could i reverse that without running into issues?

 

[Carultch]

Does it matter which is the primary and which is the secondary? All of the transformers that Ive found have the 240 Delta as the primary and the 480 wye as the secondary. Could i reverse that without running into issues?

Transformers are bi-directional by the default design. Sometimes they are built to operate better in one direction of operation than the other. You'll need to confirm with the manufacturer, to verify that there isn't an issue.

 

[Ctay005]

Transformers are bi-directional by the default design. Sometimes they are built to operate better in one direction of operation than the other. You'll need to confirm with the manufacturer, to verify that there isn't an issue.

So would something like https://www.hubbell-acmeelectric.com/p-12-208-480y277 work in this configuration? Not necessarily this exact model but this config?

 

[pv_n00b]

Heres the system overview as I have it so far.

2x SolarEdge Se33.3k inverters
218 Hanwa 315 QPro modules
Hooking up to a 240v High leg service

The question is in finding a legal interconnection betweeen the 480 wye output of the inverters and the 240v high leg service.

I tried getting a hold of the POCO to see if they would allow a connection to the AC phases and ignoring the B phase like has been suggested (and just using 1 phase inverters) but nobody at Rocky Mtn Power was able to give me an answer. The SolarEdge guys dont seem to know much about this service and they recommended trying the single phase route across the phases or just going all on the A and C phases. Again this depends on if the POCO approves...

We will have an EE look over everything before we submit the interconnetion application.

All you need is a 3ph 480/277V WYE/240V Delta transformer. Ignore the neutral from the utility, it's not used. You need to verify with the utility that you can back feed 66.6kW 3ph if the service is not obviously over 277A. This is the simplest solution.

 

[GoldDigger]

Does it matter which is the primary and which is the secondary? All of the transformers that Ive found have the 240 Delta as the primary and the 480 wye as the secondary. Could i reverse that without running into issues?

Since the magnetization current will be coming from the utility side, I would call that the transformer primary even though the power flow is in the opposite direction.
Since this is a power transformer rather than a control transformer I would expect the turn ratio to exactly match the nominal voltage ratio, so that will not be a factor for reverse power flow either.

 

[ggunn]

Since the magnetization current will be coming from the utility side, I would call that the transformer primary even though the power flow is in the opposite direction.
Since this is a power transformer rather than a control transformer I would expect the turn ratio to exactly match the nominal voltage ratio, so that will not be a factor for reverse power flow either.

FWIW, when I went through a similar process a few years ago, the transformer manufacturer (I don't remember which one we used) had different part numbers for the step up and step down versions of the same transformer kVA and voltage ratio, and they told me that they were not interchangeable.

 

[pv_n00b]

There are some small transformers with voltage regulation built in that are one way only.

There really is no reason that power can't flow either way with a symmetrical design. I have run into transformer manufacturers who say their transformers are set up for power to flow in one direction, but when pressed for why they have not been able to justify it, other than to say that's just how we sell them. I try to only work with transformer manufacturers who have experience with PV system transformers and that takes a lot of trouble out of it.

 

[ggunn]

There are some small transformers with voltage regulation built in that are one way only.

There really is no reason that power can't flow either way with a symmetrical design. I have run into transformer manufacturers who say their transformers are set up for power to flow in one direction, but when pressed for why they have not been able to justify it, other than to say that's just how we sell them. I try to only work with transformer manufacturers who have experience with PV system transformers and that takes a lot of trouble out of it.

Even if a transformer would work equally well in both directions it may only be listed to work in one direction, in which case you could have a problem at an inspection.

 

[GoldDigger]

Once again, the very important factor of inrush current is dependent on which coil supplies the magnetizing current, which is the side first energized, namely the POCO side. The inrush current is far from symmetrical in most transformer designs.

 

[electrofelon]

Actually, sometimes the POCO does care and they do not want you to land anything on the B phase.

:? I was agreeing with you. I meant that if the POCO doesn't care about having the load imbalanced. Yes I know and concur that, as a separate issue, they may not want backfeed on the B phase if its an open delta.

 

[Smart $]

Heres the system overview as I have it so far.

2x SolarEdge Se33.3k inverters
218 Hanwa 315 QPro modules
Hooking up to a 240v High leg service

The question is in finding a legal interconnection betweeen the 480 wye output of the inverters and the 240v high leg service.

I tried getting a hold of the POCO to see if they would allow a connection to the AC phases and ignoring the B phase like has been suggested (and just using 1 phase inverters) but nobody at Rocky Mtn Power was able to give me an answer. The SolarEdge guys dont seem to know much about this service and they recommended trying the single phase route across the phases or just going all on the A and C phases. Again this depends on if the POCO approves...

We will have an EE look over everything before we submit the interconnetion application.

If you go single phase with an inverter that does not require a neutral, you can balance with triplets configured as 240V delta. As noted earlier, verify service kVA per winding to determine if balancing (or intentional unbalancing) is desired.

 

[Garrison]

Does it matter which is the primary and which is the secondary? All of the transformers that Ive found have the 240 Delta as the primary and the 480 wye as the secondary. Could i reverse that without running into issues?

We are working on a project with the same service type and same inverter right now, and Dongan has specified 480Y/277 primary, 240 Delta secondary. Dongan is familiar with solar and would be a good manufacturer to consider. As others have mentioned, I don't think it really matters which side is primary and which is secondary as long as the manufacturer will stand behind your application when the inspector asks for supporting documentation.

Good luck.

 

[pv_n00b]

We will have an EE look over everything before we submit the interconnetion application.

If you are going to have an EE involved it's better to do it early, particularly if you are not familiar with the interconnection. Otherwise you may find you put in a lot of hours designing it incorrectly, the EE has to spend several hours reviewing to tell you it is incorrect, and you have to start over. Doing it correctly the first time with the EE is cheaper than going back and forth later to fix a design. You will also learn more.