240/120, 3 phase, 4 wire, Delta, phase B high leg

[So Cal]

It is a small (8.6kW) commercial job in Los Angeles. I had planned to use 3 - 120/240 inverters and connect inverter 1 to phase A & B, inverter 2 to B & C and inverter 3 to C & A. However it was recomended to me that since B phase is a "stinger" I should connect only to A & B phases. I was told that pase B only comes into play for motor loads and that the other 2 phases carry the majority of the building electrical use. Is this correct? Will the main electrical meter register properly if only 2 phases are back fed?

 

[GoldDigger]

The high leg is different only with respect to ground. The phase to phase voltages are still 240V on all combinations.
You should check with the inverter manufacturer to see whether it can be used with a three phase delta configuration without a neutral and can withstand a voltage to ground greater than 120V.


Tapatalk...

 

[Smart $]

The high leg is different only with respect to ground. The phase to phase voltages are still 240V on all combinations.
...

A 1? inverter connected across an open delta will see ~ two times the service impedance compared to one connected parallel to a service winding.

 

[augie47]

A 1? inverter connected across an open delta will see ~ two times the service impedance compared to one connected parallel to a service winding.

resulting in what ?

 

[Smart $]

resulting in what ?

More work for the inverter.

 

[ggunn]

It is a small (8.6kW) commercial job in Los Angeles. I had planned to use 3 - 120/240 inverters and connect inverter 1 to phase A & B, inverter 2 to B & C and inverter 3 to C & A. However it was recomended to me that since B phase is a "stinger" I should connect only to A & B phases. I was told that pase B only comes into play for motor loads and that the other 2 phases carry the majority of the building electrical use. Is this correct? Will the main electrical meter register properly if only 2 phases are back fed?

The SMA manual spells out how to make this connection. The inverter which is phase to phase between A and C touches the neutral but the other two do not. I believe that transformerless inverters need to have a neutral for voltage reference and thus cannot be interconnected this way, so check on that if that's what you have.

 

[ggunn]

A 1? inverter connected across an open delta will see ~ two times the service impedance compared to one connected parallel to a service winding.

Is there an open delta with a high leg? I can envision how it might look but I have never seen one.

 

[Smart $]

Is there an open delta with a high leg? I can envision how it might look but I have never seen one.

Yep, assuming a 4-wire system. Nominal voltages are the same as a "closed" delta.

 

[Smart $]

The SMA manual spells out how to make this connection. The inverter which is phase to phase between A and C touches the neutral but the other two do not. I believe that transformerless inverters need to have a neutral for voltage reference and thus cannot be interconnected this way, so check on that if that's what you have.

He didn't mention a model, but you are correct if the inverter is 120/240 3-wire. I'm not familiar enough with SMA models to say they have a straight 240V 2-wire model.

 

[ggunn]

He didn't mention a model, but you are correct if the inverter is 120/240 3-wire. I'm not familiar enough with SMA models to say they have a straight 240V 2-wire model.

It's not a model but a setting; there is a jumper to move if the inverter will not touch the neutral, but as I said, I don't believe the TL models have that option.

 

[BillK-AZ]

I have run into this type of service several times in Arizona. APS recommends connecting the inverters to only the A and C legs for two reasons:

1. Most of the loads will be single phase and connected to legs A and C
2. There is less regulation of the voltage between leg A and leg C

The customer can pay the utility to close the delta by installing another transformer.

 

[GoldDigger]

I have run into this type of service several times in Arizona. APS recommends connecting the inverters to only the A and C legs for two reasons:

1. Most of the loads will be single phase and connected to legs A and C
2. There is less regulation of the voltage between leg A and leg C

The customer can pay the utility to close the delta by installing another transformer.

Your first point, primarily single phase loads, has two consequences:
1. The inverter output is more likely to be delivered to local loads, reducing the amount of backfeed APS has to accomodate.
2. The center tapped pot is sized much larger than the single high leg pot.
Just adding a second identical pot to close the delta would only double the power handling capability for that phase wire. Making the original single pot comparable in size to the 120/240 pot would have a larger effect.

 

[So Cal]

The inverters are Powerone 3.0 transformerless. They are configureable for 208 3 phase, 120/120 split phase, or 277 3 phase.

 

[GoldDigger]

The inverters are Powerone 3.0 transformerless. They are configureable for 208 3 phase, 120/120 split phase, or 277 3 phase.

Since 240 is not equal to either 208 or 277 and there will be no center tap when connecting to the high leg, it sounds like you have the choice of connecting entirely A to C or using a buck or boost transformer on the AB and BC connections.

 

[ggunn]

The inverters are Powerone 3.0 transformerless. They are configureable for 208 3 phase, 120/120 split phase, or 277 3 phase.

It appears to me from looking at the data sheet that that inverter won't work for you the way you describe. It doesn't connect 2 wire (phase to phase with no neutral) to 240V, which is what you need (for two of the three inverters) to connect to all three phases of a 240V with a high leg. It can only connect 208V 2 wire (phase to phase with no neutral), 240V 3 wire split (phase to phase with a neutral), or 277V two wire (phase to neutral). I think you are stuck with putting all three of them phase to phase with a neutral on the A and C phases and not touching the high leg.

 

[GoldDigger]

Since 240 is not equal to either 208 or 277 and there will be no center tap when connecting to the high leg, it sounds like you have the choice of connecting entirely A to C or using a buck or boost transformer on the AB and BC connections.

Just wanted to add that anything like connecting with a 208-277 boost transformer to the neutral to high leg connection would actually increase the current in the center tapped pot, so it would not be particularly advantageous compared to connecting directly to that pot with 120/240 3-wire.

 

[jaggedben]

The inverters are Powerone 3.0 transformerless. They are configureable for 208 3 phase, 120/120 split phase, or 277 3 phase.

To concur with ggunn...
You ain't gonna be able to connect those to the B phase. I was told in person by a Power-One engineer that they require the neutral reference. This was a general question applied to all their products. But don't take my word for it, ask Power-One.

Fronius will work, or so I was told by them. I'll take ggunn's word for it on SMA.

Do you know for sure that it's an open delta?