Single Phase inverter to 3 phase OPEN Delta

[HoosierSparky]

We have an area of town that used to be citrus orchards and have 3 phase open delta (240/120) services to homes. 3 phase was used for irrigation pumps. The older homes have delta breakers for their A/C units in single phase panels. Updated services have 3 phase panels with the high-leg breaker spaces skipped, except for the A/C units.

I am seeing an uptick in PV being installed and they are using single phase inverters. EVERYTHING on my side of the service (homeowner side) is to code or better. I am concerned about the other side. I do not see issues with only a few single phase PV backfeeding a 3phase service. My issue is with a lot of these connecting creating an imbalance. Due to the type of inverters used, they are connecting 3-wire (2 hots, one neutral). Also, being open delta, the high-leg transformer is smaller.

I have pointed this out to the local POCO's that serve this area. For some reason, they had not considered this issue before, due to the low number of PV systems being installed there. That has now changed.

Am I overthinking this?

 

[kwired]

Many those homes probably would be served with single phase only today. If three phase was needed a VFD or phase converter would be used for the limited loads that do use three phase.

That said the high leg is probably derived with a smaller transformer than the main transformer is. Backfeeding this with balanced three phase might not be a great idea either because of the smaller high leg capacity.

Balancing of loads by the utility on the distribution side is not your problem and will need consideration whether they have these open delta systems or is all single phase secondaries.

Probably still want to have some discussion with POCO before selecting and installing equipment anyway.

 

[electrofelon]

I think you are overthinking this. If you are worried about imbalance, take a look at a single phase branch off a three phases distribution line. Those go on for 15 miles easy.

But even more important to note, the POCO probably connects these open Delta banks to different phases as they go along so it all averages out

 

[kwired]

I think you are overthinking this. If you are worried about imbalance, take a look at a single phase branch off a three phases distribution line. Those go on for 15 miles easy.

But even more important to note, the POCO probably connects these open Delta banks to different phases as they go along so it all averages out

Yes when all three phases are present POCO's will stagger the single phase loads and any that are known to have higher demand will be even more carefully considered which phase to connect to for better balancing. High leg pot on limited load open delta services probably can often be ignored to some extent as it is only carrying the third leg of that limited three phase load, everything else is on the 120/240 pot.

 

[HoosierSparky]

One of the POCO's has responded to me and "suggested" a fused disconnect in front of the PV meter be installed due to the higher fault current. I also caught a mistake on the 3 line where they were connecting A-B, not A-C at the panel. C leg at the meter is the stinger, B at the panel is the stinger.

 

[jaggedben]

I will just add that the utility is the one who would say what level of imbalance is too much.

I don't see why a fused disconnect for the PV would be a general need or what problem it would solve. Interrupting ratings would follow the same rules as any other connection, and there is no general reason that a circuit breaker shouldn't be adequate. What higher fault current are we talking about?

 

[Hv&Lv]

One of the POCO's has responded to me and "suggested" a fused disconnect in front of the PV meter be installed due to the higher fault current. I also caught a mistake on the 3 line where they were connecting A-B, not A-C at the panel. C leg at the meter is the stinger, B at the panel is the stinger.

So... what’s the problem again?
high leg is supposed to be on far right of meter and middle of panel.

or are you saying the drawing is wrong?

 

[kwired]

So... what’s the problem again?
high leg is supposed to be on far right of meter and middle of panel.

or are you saying the drawing is wrong?

I think something was found wrong in the drawing. Sounds like for simplicity high leg was drawn straight through though it actually crosses over to center leg after the meter.

People familiar enough with high leg systems probably don't think much about it and still connect to the proper locations even though it technically is drawn wrong.

 

[Hv&Lv]

I think something was found wrong in the drawing. Sounds like for simplicity high leg was drawn straight through though it actually crosses over to center leg after the meter.

People familiar enough with high leg systems probably don't think much about it and still connect to the proper locations even though it technically is drawn wrong.

very true.