480/277 WYE service to 120/240 Single phase

[gporter85]

I have customer that recently had a new service dropped into an old storage building to facilitate a 35KW AC Solar PV system on top. The system has an SMA STP15000 and STP20000. He has never had power before and has only used it for storage. Now he wants to get some outlets and lights for welders and such. I told him about the service being 480/277 and he didn't mind the idea of a transformer. The only thing is he said he would more than likely never need 3 phase power. I figured 480 delta to 240 delta would work. I am wondering if i connect the A and C phase to a single phase panel and just leave the High leg out. Then i would get 3 phase to single phase. Is there another way? Is what I am thinking kosher?

 

[augie47]

Unless you already have the three phase transformer, why not simply use a single phase 480-240/120 transformer ?

 

[kwired]

Is there existing 277 lighting?

Have you calculated the load you need to supply?

Depending on capacity of current supply - you will only be using two of the three supply leads - so you have some limitation in regards to the total kVA you can use vs total kVA the service can deliver. Same goes for a 240/120 delta if you do not use the high leg you essentially still only are drawing from two of the three supply legs. If you put in a 208/120 system you can balance across all three phases easier - but you also have 208 volts instead of 240 - so take that into consideration for your equipment.

If there is significant enough load but you still want 240 volts - you could balance three single phase transformers across all three supply legs.


If there is no existing load at all - see what it will take to get the POCO to change supply voltage if you have no need for the 480/277. They may charge something, but customer owned transformers are not free either - plus you are not billed for any idle current or have to deal with heat from the transformer.

 

[ggunn]

If there is no existing load at all - see what it will take to get the POCO to change supply voltage if you have no need for the 480/277. They may charge something, but customer owned transformers are not free either - plus you are not billed for any idle current or have to deal with heat from the transformer.

He has two SMA Tripower inverters interconnected with the service at 480/277.

 

[kwired]

He has two SMA Tripower inverters interconnected with the service at 480/277.

Thanks, did not realize that, but since I am not familiar with that kind of equipment those model numbers flew right over my head as to what they may have meant.

That said OP needs to look at size of this service and figure out what kind of load he needs to supply when making decisions. Based only on the 35kW he mentions for the solar unit that is around 42 amps per line. To supply a 240 volts via a single phase transformer he can supply about 84 amps @ 240 volts if max primary current is 42 (about 20 kW), but his actual service could be higher capacity.

 

[jaggedben]

Thanks, did not realize that, but since I am not familiar with that kind of equipment those model numbers flew right over my head as to what they may have meant.

Although I'm somewhat familiar with the model numbers, if I weren't I still would have assumed that if the service was put in for the PV inverters then the PV inverters need that voltage and phasing. You can usually make that assumption about PV inverters, except that most single phase inverters can do both 208V and 240V.

 

[ggunn]

Although I'm somewhat familiar with the model numbers, if I weren't I still would have assumed that if the service was put in for the PV inverters then the PV inverters need that voltage and phasing. You can usually make that assumption about PV inverters, except that most single phase inverters can do both 208V and 240V.

Many can do 277 as well.

 

[electrofelon]

Many can do 277 as well.

That would be interesting, I wonder why one would connect that way. Would one of those be grounded?

 

[Joethemechanic]

Running just some lights, and a couple of welders, and he'll probably never use 3 phase. The guy is kidding himself. if he had a 480/277 3 ph building he'd never wantto go back

 

[ggunn]

That would be interesting, I wonder why one would connect that way. Would one of those be grounded?

Some single phase inverters will interconnect at 277V so they can connect phase to neutral on 480/277. The AC side connects to neutral, which is grounded, but they may or may not be grounded on the DC side.

 

[Carultch]

Some single phase inverters will interconnect at 277V so they can connect phase to neutral on 480/277. The AC side connects to neutral, which is grounded, but they may or may not be grounded on the DC side.

With the SMA Sunny Tripower family, the inverters actively connect from phase to neutral on ALL THREE PHASES. The USA version of this family of inverters does not work with anything other than 277/480 Volts. During normal operation, there should be no significant current on the neutral. And if there ever is any serious current on the neutral, the inverter will shut off. This family of inverters has no grounded ("neutral") conductor on the DC side. Positive and negative are both normally ungrounded.

 

[Carultch]

Unless you already have the three phase transformer, why not simply use a single phase 480-240/120 transformer ?

Concerns of current imbalance among the phases perhaps? Is there a component that can distribute an individual single phase load uniformly onto all three phases of a three phase source?

If it is insignificant compared to other loads on the service premises, this shouldn't be an issue. Load currents are imbalanced all the time, and statistically add up to a nearly balanced load by the time it is seen by any serious utility equipment. Utilities do often require that PV sources be balanced, but seldom require that loads be balanced. A 480V to 120/240 single phase transformer, or mini power zone should do exactly what is needed.

 

[gporter85]

Concerns of current imbalance among the phases perhaps? Is there a component that can distribute an individual single phase load uniformly onto all three phases of a three phase source?

If it is insignificant compared to other loads on the service premises, this shouldn't be an issue. Load currents are imbalanced all the time, and statistically add up to a nearly balanced load by the time it is seen by any serious utility equipment. Utilities do often require that PV sources be balanced, but seldom require that loads be balanced. A 480V to 120/240 single phase transformer, or mini power zone should do exactly what is needed.

That first line was my exact question. I am pretty sure there isn't. I am sure i can find a decent 480v delta- 240delta 30KVA transformer for under $2,000. The utility is Pacific Gas and Electric and i guaranty they would want closer to $20,000 drop a second transformer for single phase 240.

I found a 240v 3 phase panel made by eaton with a 100 amp main for $250. I am just going to propose a 240 delta sub that way he has 240 and 120 and if he ever needs the 3 phase it is available.

I didn't see any 480v to 120/240 single phase transformers larger than 5kva. Could I land 3 (1 on each phase) on a breaker panel with 3 breakers?? nah 3 phase would probably be cheaper and definately easier.


Thanks for all the answers and suggestions. Everything was very helpful.

 

[gporter85]

Thanks, did not realize that, but since I am not familiar with that kind of equipment those model numbers flew right over my head as to what they may have meant.

That said OP needs to look at size of this service and figure out what kind of load he needs to supply when making decisions. Based only on the 35kW he mentions for the solar unit that is around 42 amps per line. To supply a 240 volts via a single phase transformer he can supply about 84 amps @ 240 volts if max primary current is 42 (about 20 kW), but his actual service could be higher capacity.

The service is a 100 amp 480/277 I think 100 amps 240 delta should be sufficient. The guy literally has only parked tractors in this structure and ran a 3/4 conduit from a nearby house that has 1 plug on the front corner of the building. And it has been like that for 20 years. I would think his max load would be 40 amps 240 single phase only when he is welding with the lights on and playing a radio. It is hard to tell what he might do with it in the next 20 years.

 

[kwired]

The service is a 100 amp 480/277 I think 100 amps 240 delta should be sufficient. The guy literally has only parked tractors in this structure and ran a 3/4 conduit from a nearby house that has 1 plug on the front corner of the building. And it has been like that for 20 years. I would think his max load would be 40 amps 240 single phase only when he is welding with the lights on and playing a radio. It is hard to tell what he might do with it in the next 20 years.

I wasn't all that sure what you were up to when you mentioned adding welders and other stuff - but sounds like more of an occasional use building with pretty limited load. Unless it is known load will increase in fairly near future, maybe just go with a 10 or 15 kVA single phase transformer - won't really be all that expensive. Can install 277 volt lighting to keep lighting load off the transformer. Depending on welder(s) some may even be usable on 277 or 480 volts - less transformer is needed if going that route.

 

[ggunn]

The service is a 100 amp 480/277 I think 100 amps 240 delta should be sufficient.

He doesn't have any 120V loads or 240V single phase loads that need a neutral?

 

[PVfarmer]

The service is a 100 amp 480/277.

That's very interesting...just wondering if that's a "standard" service from PG&E or if they put that in to match the PV system size-wise.
I'm dealing with the same sort of thing here, (about to be installed) except it's three 20000TL inverters and the load is not small, it's 25kVA or so.
What's the transformer setup for the 100A service? Three 25kVAs or one 75kVA?

Pretty sure you don't want to, or even if it's possible, to connect Tripowers at 480V.
If you look at page 6 here, delta isn't recommended, and I can't figure out how a single leg of 480V would work, because the neutral has to "lead out", although I'm not 100% sure. More like 95%.

http://files.sma.de/dl/7418/STP24-US_MV_Trafo-TI-en-10.pdf

Since there won't be much use and the load is small, assuming the load is 120/240V (3 wire or split phase? going by "old barn" there) I *think* you'd want to get three 277V to 120/240 transformers, connected wye on the Tripower side and then...
You have some options on the load side. You could have the three single phase wired wye/Tripower side and 240V delta for loads, or...
So I guess I'm also going to ask is this kosher:
You said max load of 40A at 240V- that's 9.6kVA (call it 10).
So a reasonable solution would be three 5kVA xfmrs, each 277V to 120/240, then take L1 from each of the three, and L2 from each, wired to the (existing?) load panel, also with the neutral from each xfmr. (so keeping the building wiring as is? I'm assuming it's already wired with 2 legs of 120V to neutral, that make 240V when combined and grounded.)

That would balance the biggest part of the load between the three xfmrs, whereas if it was 240V delta, the welder would be wired to one point on the triangle.
But like someone said, that might not be enough "imbalance" to bother the Tripowers, much less the grid?

Maybe something like this (3 of them?)
http://www.temcoindustrialpower.com/products/Transformers_-_General/HT4067.html

 

[PVfarmer]

I wasn't all that sure what you were up to when you mentioned adding welders and other stuff - but sounds like more of an occasional use building with pretty limited load. Unless it is known load will increase in fairly near future, maybe just go with a 10 or 15 kVA single phase transformer - won't really be all that expensive. Can install 277 volt lighting to keep lighting load off the transformer. Depending on welder(s) some may even be usable on 277 or 480 volts - less transformer is needed if going that route.

So how much will that affect the overall balance of things? That's the part I'm a little confused on.

I can't paste from this, but check out page 29 if you want- any 277V lights would need to have their own circuit breakers if running directly off of the inverters, and I'm not sure you can actually get 480V from Tripower inverters.
http://files.sma.de/dl/21561/STP12-24TL-US-IA-en-16W.pdf

 

[PVfarmer]

I am sure i can find a decent 480v delta- 240delta 30KVA transformer for under $2,000.

I found a 240v 3 phase panel made by eaton with a 100 amp main for $250. I am just going to propose a 240 delta sub that way he has 240 and 120 and if he ever needs the 3 phase it is available.

I didn't see any 480v to 120/240 single phase transformers larger than 5kva. Could I land 3 (1 on each phase) on a breaker panel with 3 breakers??

Thanks for all the answers and suggestions. Everything was very helpful.

GE makes a "Tran Zone" 480 to 240V thing- I was checking that out, but I'm "pretty sure" you have to go 277V on the inverter side.
If you want 30 kVA, maybe you could use 3 of something like this?

Same here on the "thanks" part!

http://www.temcoindustrialpower.com/products/Transformers_-_General/HT4084.html

 

[PVfarmer]

wait a minute! before i get yelled at...

wait a minute! before i get yelled at...

That's very interesting...just wondering if that's a "standard" service from PG&E or if they put that in to match the PV system size-wise.
I'm dealing with the same sort of thing here, (about to be installed) except it's three 20000TL inverters and the load is not small, it's 25kVA or so.
What's the transformer setup for the 100A service? Three 25kVAs or one 75kVA?

I got my circuits crossed there, ha ha.
Three 25kVAs or one 3 phase 75kVA Is for 200A of 208/120V service-
for 100A of 480/277, you'd have, I think...three 1 phase 37.5kVAs or one 112.5kVA three phase?