Anybody out there ever connected a PV system to a 240 V OPEN Delta with a high leg three phase service? When we sold the job they told us the service was going to be a 208/120 Wye service. I'm guessing they switched this to the 240 Delta High Leg because it's a senior home and they have some elevator motors that would work better with the 240 three phase. Customer wants multiple string inverters because it's new construction with three separate services and they want to be able to move inverters around in the future if they find the PV system is producing too much on one service and not enough on the other. I've done 240 CLOSED Delta interconnections before but never an Open Delta. String inverters that can connect to a 240 Delta high leg service are very slim pickings. Was looking at the Fronius Symo 12.0-2 208-240 as they will connect to a 240 Closed Delta High Leg but Fronius is telling me the Symos won't work on an Open Delta. Short of asking the utility to provide a closed delta service instead of the open delta I'm not sure what else to do. Could possibly connect single phase inverters but these can only connect to the two lower legs (avoiding the high leg) which would create a large unbalanced backfeed. Wondering if anyone has run into this type of interconnection before and what type of inverters were used for the interconnection. Thanks in advance!
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240V Open Delta PV connection?
- Thread starter SunFish
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jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
Ask the utility. Ultimately they are both the ones who know what the transformer can handle and also the ones who have to approve it.
The backfeed doesn't necessarily have to be balanced. If the load isn't normally balanced - i.e. if there's little three phase load and thus little current on the high leg - then it may not matter if you only back-feed the other legs. An open delta is if anything less likely to have a large three phase load, or they probably would have built a closed delta. Thus putting a large backfeed on the high-leg is perhaps running a higher risk than just backfeeding only the other legs.
I did one high-leg delta which for all I know was an open delta. The customer was no longer using any three phase loads, and at the time I knew less about balancing considerations, and I just backfed the split phase meter and the project sailed through. I don't recommend that approach, but the point is that if I had assumed that I had to have a balanced backfed on the service then I would have either torpedoed the project for no good reason or else created a lot of trouble and expense to no one's benefit. So just ask enough questions up front to confirm that what the customer wants will not get you in trouble.
The backfeed doesn't necessarily have to be balanced. If the load isn't normally balanced - i.e. if there's little three phase load and thus little current on the high leg - then it may not matter if you only back-feed the other legs. An open delta is if anything less likely to have a large three phase load, or they probably would have built a closed delta. Thus putting a large backfeed on the high-leg is perhaps running a higher risk than just backfeeding only the other legs.
I did one high-leg delta which for all I know was an open delta. The customer was no longer using any three phase loads, and at the time I knew less about balancing considerations, and I just backfed the split phase meter and the project sailed through. I don't recommend that approach, but the point is that if I had assumed that I had to have a balanced backfed on the service then I would have either torpedoed the project for no good reason or else created a lot of trouble and expense to no one's benefit. So just ask enough questions up front to confirm that what the customer wants will not get you in trouble.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
Anybody out there ever connected a PV system to a 240 V OPEN Delta with a high leg three phase service? When we sold the job they told us the service was going to be a 208/120 Wye service. I'm guessing they switched this to the 240 Delta High Leg because it's a senior home and they have some elevator motors that would work better with the 240 three phase. Customer wants multiple string inverters because it's new construction with three separate services and they want to be able to move inverters around in the future if they find the PV system is producing too much on one service and not enough on the other. I've done 240 CLOSED Delta interconnections before but never an Open Delta. String inverters that can connect to a 240 Delta high leg service are very slim pickings. Was looking at the Fronius Symo 12.0-2 208-240 as they will connect to a 240 Closed Delta High Leg but Fronius is telling me the Symos won't work on an Open Delta. Short of asking the utility to provide a closed delta service instead of the open delta I'm not sure what else to do. Could possibly connect single phase inverters but these can only connect to the two lower legs (avoiding the high leg) which would create a large unbalanced backfeed. Wondering if anyone has run into this type of interconnection before and what type of inverters were used for the interconnection. Thanks in advance!
I have done several of these. As jaggedben says, you should check with the AHJ before proceeding, but many times with a service like that when the PV system is relatively small they will want you just to connect to the A and C phases as if it were a 240V single (split) phase service. A three phase inverter which requires a neutral often won't play well with a high leg service.
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