3 Phase Battery System

[redtruck]

Hello,

I am looking to install several battery systems on a 600a delta high leg 3 phase service. This means this service has 120/240 with a 208v high leg.

The panels within this site I am looking to back up are only 120/240 and do not contain the high leg, they are not 3 phase(although there are 3 phase panels on site).

My initial thinking is to install several individual residential 120/240 systems and a battery or 2 to each panel.
My concerns are that these systems are designed for a proper 120/240 single or split phase service.
Would there be issues with tying them into this service? Each of these panels that will be backed up have 3 wires and a ground-120/240, they each get 2 phase conductors from 2 of the 3 phases in this building's service.
Is this truly the same as a split phase 120/240? I would think that those 2 phases are 120 degrees out of sync(being from a 3 phase service) where a standard split phase has 2 conductors 180 degrees out of sync.
There will also be solar on site here(say several powerwalls with mods and MCI's on the roof)I am worried that powerwall(or any resi ESS system) will not output PV with the correct sine wave configuration.

So far I have reached out to several manufacturers trying to find a solution, the response I've gotten from each so far has been something along the lines of "this should work" or "this could work"

Has anyone done this with success?

Thank you

 

[jaggedben]

...
Would there be issues with tying them into this service?

Potentially but not necessarily. The systems will connect and generally work as expected. The potential issues have to do with phase power imbalance on the utility side. It may make a difference whether the delta is open or closed and how much current the high-leg is capable of carrying and expected to carry. Many high leg systems expect only a small load on the high-leg and so ignoring the high leg is not consequential, but some are designed for much larger three phase loads and the utility may be unhappy if you backfeed only one phase.

Is this truly the same as a split phase 120/240?

On the phase with the neutral, yes.

I would think that those 2 phases are 120 degrees out of sync(being from a 3 phase service) where a standard split phase has 2 conductors 180 degrees out of sync.

No, the 120V waves are 180 degrees apart. This is a difference between high-leg systems and wye systems.

 

[jaggedben]

Has anyone done this with success?

Yes. But you should submit the utility interconnection application and get approval before building. Also I've struggled a bit with utilities enforcing all their requirements for three phase services (such as disconnecting means, etc.) that they may not enforce in single phase resi services.

 

[Hv&Lv]

Yes. But you should submit the utility interconnection application and get approval before building.

This is the best advice here.

When someone connects to our system without the interconnect agreement and we find it and cut them loose, they get upset because they didn’t check with us first.

 

[kwired]

I am not well educated on what is all out there in the PV world. But if your inverters need a 120/240 three wire connection, the only place they can connect to this system is on the phase with the midpoint neutral.

Another consideration might be exactly what the transformer arrangement is. Can be common to have open delta systems here or even a larger 120/240 transformer and smaller transformer(s) for the rest of the delta. All this can depend on what kind of loading the bank was originally set up for.

If it is all three same sized transformers they likely intended it to supply a significant amount of three phase load. Such system would likely be best off to be connected to inverters that are capable of straight 240 and no neutral and connected equally across the delta. From my understanding those are not necessarily common or may not even be made at all on any mass production level.

I think I have read of others doing such a system with 480 volt inverter systems and using a step down transformer between the inverter and the grid.

 

[redtruck]

Potentially but not necessarily. The systems will connect and generally work as expected. The potential issues have to do with phase power imbalance on the utility side. It may make a difference whether the delta is open or closed and how much current the high-leg is capable of carrying and expected to carry. Many high leg systems expect only a small load on the high-leg and so ignoring the high leg is not consequential, but some are designed for much larger three phase loads and the utility may be unhappy if you backfeed only one phase.



On the phase with the neutral, yes.



No, the 120V waves are 180 degrees apart. This is a difference between high-leg systems and wye systems.

Thank you for this information.

 

[ggunn]

I am not well educated on what is all out there in the PV world. But if your inverters need a 120/240 three wire connection, the only place they can connect to this system is on the phase with the midpoint neutral.

There are some jurisdictions where connection to the B (high leg) phase by PV systems is not allowed. It seems likely to me that in those locations battery systems would also be required to not touch the B phase.

 

[kwired]

There are some jurisdictions where connection to the B (high leg) phase by PV systems is not allowed. It seems likely to me that in those locations battery systems would also be required to not touch the B phase.

Because of smaller high leg transformer being fairly common?

Around here there is a lot of full delta high leg systems that supply a fair amount of three phase load, particularly on farms and some light industrial applications.

Most open delta is either specifically for a limited load application or in older business districts where most customers are single phase with the occasional customer with limited three phase loads - particularly air conditioners. They often have one or two transformer banks that feed the entire block in those situations.

Again I don't have any real experience with PV for the most part. But if one my farm customers that has 240 high leg full delta supplying their grain storage site wanted to install some PV that interacts with grid on that site, sure seems it would be convenient to have equipment that basically is 240 volt three phase three wire to feed into the delta system. But sounds like most of what is commonly available has a neutral connection that must be utilized for it to work properly and wouldn't be able to be connected to the high leg

 

[ggunn]

Because of smaller high leg transformer being fairly common?

Around here there is a lot of full delta high leg systems that supply a fair amount of three phase load, particularly on farms and some light industrial applications.

Most open delta is either specifically for a limited load application or in older business districts where most customers are single phase with the occasional customer with limited three phase loads - particularly air conditioners. They often have one or two transformer banks that feed the entire block in those situations.

Again I don't have any real experience with PV for the most part. But if one my farm customers that has 240 high leg full delta supplying their grain storage site wanted to install some PV that interacts with grid on that site, sure seems it would be convenient to have equipment that basically is 240 volt three phase three wire to feed into the delta system. But sounds like most of what is commonly available has a neutral connection that must be utilized for it to work properly and wouldn't be able to be connected to the high leg

You could run a 480/277V inverter through a 240V delta (no neutral) primary 480/277V wye secondary transformer to connect to all three phases.