High-Leg Delta-Stinger Leg Service - OCPD rating for AC compiner Panel- Solar Project

[UMirza]

Hi All,
I am looking for an advice and guidance in this particular project.
I am connecting 3 single phase solar inverters into a 3 phase ac combiner panel. Each inverter puts out 31.6A @ 240VAC. Service I am connecting to is 120/240 with 208V stinger leg.
My question is, how do i determine the size of OCPD to protect the ac combiner with solar inverters?

Typically, I would just take the total wattage and divide by service voltage and three phase correction factor (FLA) times that by 1.25 and I have my OCPD rating. In this case I am connecting to 240VAC service, would I consider that as three phase and follow the same calculation route as for three phase service?

Thanks

Usman

 

[GoldDigger]

Hi All,
I am looking for an advice and guidance in this particular project.
I am connecting 3 single phase solar inverters into a 3 phase ac combiner panel. Each inverter puts out 31.6A @ 240VAC. Service I am connecting to is 120/240 with 208V stinger leg.
My question is, how do i determine the size of OCPD to protect the ac combiner with solar inverters?

Typically, I would just take the total wattage and divide by service voltage and three phase correction factor (FLA) times that by 1.25 and I have my OCPD rating. In this case I am connecting to 240VAC service, would I consider that as three phase and follow the same calculation route as for three phase service?

Thanks

Usman

No. Since you are connecting only between the two lower legs, all of the current will flow only in those legs. The 3-phase OCPD will see line current in two of the three legs exactly equal to the inverter output current.
To get the OCPD current level, follow the same calculation as for split phase 120/240, since that is all you will be connecting to.

 

[ggunn]

No. Since you are connecting only between the two lower legs, all of the current will flow only in those legs. The 3-phase OCPD will see line current in two of the three legs exactly equal to the inverter output current.
To get the OCPD current level, follow the same calculation as for split phase 120/240, since that is all you will be connecting to.

Couldn't he also connect them phase to phase to all three phases A-B, B-C, C-A and eliminate the combiner?

 

[GoldDigger]

Couldn't he also connect them phase to phase to all three phases A-B, B-C, C-A and eliminate the combiner?

As long as the single phase inverters do not require a neutral reference or he constructs two of them using transformers.
Also they need to be able to accept a neutral reference that is pretty far from ground. Could be a design issue.

 

[Smart $]

As long as the single phase inverters do not require a neutral reference or he constructs two of them using transformers.
Also they need to be able to accept a neutral reference that is pretty far from ground. Could be a design issue.

Will need more info to determine if a neutral is necessary for the inverters to function... but assuming they are straight 240V single phase inverters, they should be able to be connected as ggunn suggests, i.e. in delta configuration.

 

[ggunn]

As long as the single phase inverters do not require a neutral reference or he constructs two of them using transformers.
Also they need to be able to accept a neutral reference that is pretty far from ground. Could be a design issue.

If they happen to be standard SMA's (SB8000, maybe?) they don't require a neutral.

 

[UMirza]

Thank You Guys. I appreciate the answers.
What I understood is, I am connecting a 3 phase ac combiner panel to service with 3 hot legs but all the current will be carried by 2 hot legs that will see 120/240VAC? hence, my calculations will be based on typical single phase interconnection?
Below is the single line that shows the details

I am using fronius inverters and they require neutral reference.

Thanks

usman

 

[jumper]

I moved this thread to the PV forum.

 

[BillK-AZ]

Thank You Guys. I appreciate the answers.
What I understood is, I am connecting a 3 phase ac combiner panel to service with 3 hot legs but all the current will be carried by 2 hot legs that will see 120/240VAC? hence, my calculations will be based on typical single phase interconnection?
Below is the single line that shows the details

I am using fronius inverters and they require neutral reference.
View attachment 8582
Thanks

usman

Fronius does not require the neutral, but you have to select the correct setup options the first time the inverter is powered up. See Commissioning in the User Manual. I do not understand why you state "but all the current will be carried by 2 hot legs". When all the inverters are operating at maximum the three phase currents will be equal. Your single phase 31.6A becomes about 54.8A, then apply the normal factors to select OCPD ratings, wire, etc.

 

[Smart $]

Thank You Guys. I appreciate the answers.
What I understood is, I am connecting a 3 phase ac combiner panel to service with 3 hot legs but all the current will be carried by 2 hot legs that will see 120/240VAC? hence, my calculations will be based on typical single phase interconnection?...

I agree with BillK-AZ's assessment.

Judging from the symbols used, whomever made that drawing has an IEC background. As such, they typically do not know US standard electrical supply systems. It appears you have a 240/120V 3? 4W system, often called a high-leg delta supply. When connected to Code (NEC), there will be...

120Vac A-N and C-N
240Vac A-B, B-C, and C-A
240V 3? A-B-C
~208Vac B-N

The last connection mentioned is rarely used for anything.

 

[UMirza]

I guess I should have flipped pages in the manual before calling for captain planet
Apprecaite the feedback.

Have a great long weekend!