480v 3ph with 480v 1ph transformers

[gar]

201209-1044 EST

Starting with post #1.

I would not call a single wire a phase, but some do. It takes two wires to have a phase.

From the three wires of what I think is being described in post #1 we have most of a 3 phase wye source, two phases of the source. The one wire being called ground is not required to be grounded to analyze the circuit operation. This wire is the neutral of a balanced 3 phase wye, but as applied here is not really a neutral.

From this partial three phase wye you can easily obtain an open delta with two transformers. That is how my shop building is driven. This type of loading is all around me.

I believe in the first post is described three single phase transformers with their primaries connected in parallel, all connected across one 480 V phase of the source. Nothing wrong with this, if that is what the power company expects.

The transformer for my home is a single phase transformer connected to two wires of a three phase delta on the pole. Power distribution in my area is 3 phase delta, three wires on the pole. No neutral or ground for the primary distribution. However, it is probably driven by a 3 phase wye at the substation to provide a reference to earth.

As you go down the poles in my area you will find that different distribution transformers are on different phases to evenly distribute load back at the substation.

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[winnie]

Thats a clever idea Jon. Just to be clear, are you saying make the three phase service corner grounded, use the EGC as the grounded phase/conductor, and use 250.30(A)(1) exception 2?

Unfortunately no. I think I misread the OP and thought that there were 3 3/0 conductors available. I'd imagined 2 hiots and a grounded circuit conductor, but on rereading I don't think this is the case

IMHO what you describe could work if all 3 available conductors are large enough, but it is unlikely that an egc is big enough.

Jon

 

[electrofelon]

Unfortunately no. I think I misread the OP and thought that there were 3 3/0 conductors available. I'd imagined 2 hiots and a grounded circuit conductor, but on rereading I don't think this is the case

IMHO what you describe could work if all 3 available conductors are large enough, but it is unlikely that an egc is big enough.

Jon

Yeah that was my thought. I actually didn't mean to quote you after I realized/assumed the egc wouldn't be the right size, but the forum saves stuff sometimes.

 

[synchro]

A

Yeah that was my thought. I actually didn't mean to quote you after I realized/assumed the egc wouldn't be the right size, but the forum saves stuff sometimes.

An ECG would be very unlikely to be adequately size for balancing the three 50 kVA transformers across all phases, but it might still be worthwhile to check if it could be sufficient for the ~ 60A line current of a 50 kVA 480V 3-phase inverter.

 

[hillbilly1]

,Yup I tried the exact same thing once. They said a residential service could only be 120/240. There were only single phase lines, but if there were three phase, I don't know if they would give me a three phase 120/208 or 277/480 or not.

We wired a mansion in South Georgia many years ago that had a 480 volt service, this guy had more money than he knew what to do with. It was his hunting lodge just for him and his family. Full commercial kitchen in the basement, two 500 kw generators. 75 kva transformer in the closet on every floor.

 

[electrofelon]

A

An ECG would be very unlikely to be adequately size for balancing the three 50 kVA transformers across all phases, but it might still be worthwhile to check if it could be sufficient for the ~ 60A line current of a 50 kVA 480V 3-phase inverter.

Yeah that could work, there is nothing requiring the phases to all be the same size. It would certainly be quite a bastard red headed step child set up. Would still need an inverter that was ok with corner grounded.

 

[kwired]

[QUOTE="electrofelon, post: 2629709,Yup I tried the exact same thing once. They said a residential service could only be 120/240. There were only single phase lines, but if there were three phase, I don't know if they would give me a three phase 120/208 or 277/480 or not.

We wired a mansion in South Georgia many years ago that had a 480 volt service, this guy had more money than he knew what to do with. It was his hunting lodge just for him and his family. Full commercial kitchen in the basement, two 500 kw generators. 75 kva transformer in the closet on every floor.
[/QUOTE]
Anything I ever worked on that seemed like a mansion was nothing compared to some those owned by the wealthiest people.

I can see three phase being desired on anything much larger than what I have worked on. If the place is not served by municipal water there can be need for rather large well pump, not just for domestic water use which may not need too large of a pump, but if a large enough place could need a pretty large well for a fire pump application. Then you have HVAC, that is probably the major demand load. If the place has a pretty large footprint 480 does yield smaller feeders and less voltage drop even if a lot of the connected load is still 120/208-240.