XFMR Single phase the 3 Phase

Zyb

Zyb

Member
Location
Maine
Occupation
Design Engineer
Hi,
I'm planning to buy a transformer, would the transformer (image below) work? and can you also verify my drawing. Thanks
  1. is there a single phase to three phase Y transformer?
  2. is my 20A fuse correct [(1.25 x 11,400) / (480 x 1.732)]?
  3. is the ground wire correct?
  4. on the 480V side how many conductors should be connected to the transformer?
  5. if there are two SE11400H-US inverter does this mean that 30kVA is enough?


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This might work (as in, inverter turns on and outputs power), but it's the wrong way to go about it.

If you have a three phase service you want a three phase inverter these days. If the smallest 480V Solaredge inverter (30kW) can't be justified then I would go with the 208V 10kW inverter and a 480 to 208wye transformer. (Probably with a delta primary.)

Interconnecting a single phase inverter to just one phase of a three-phase 480V service is not so likely to receive utility approval. The transformer you have specified also appears to have a high-leg secondary which is ... unnecessary.

If it's going to be larger than one 10kW inverter I strongly advise filing the interconnection application before you build this one.
 
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There are a lot of issues with what is shown.
  1. There is not a single phase to three phase transformer. You would need a rotary phase converter or something similar to turn a single phase system into a three phase system.
  2. You can put whatever size of fuse you want on the secondary of a transformer. You just have to size the conductors to match the fuse size. I would size the overcurrent protection at 125% of the rated current of your transformer secondary.
  3. No. You need to bond the center of your Y to the ground conductor, not just pass the ground conductor straight through.
  4. 4 wires plus the ground.
In addition, there is no such thing as a 240Y/120V electrical system. The vector math doesn't allow it. The transformer catalog looks to have an error as it calls out a delta primary and secondary, but also states there is a 480/277V secondary which would be a Y configuration. The transformer shown would be 240V, three phase delta on the primary and 480Y/277V on the secondary.
 
d0nut said:
In addition, there is no such thing as a 240Y/120V electrical system. The vector math doesn't allow it. The transformer catalog looks to have an error as it calls out a delta primary and secondary, but also states there is a 480/277V secondary which would be a Y configuration. The transformer shown would be 240V, three phase delta on the primary and 480Y/277V on the secondary.
Click to expand...
It's probably built for either high leg 120/240V delta systems or corner-grounded 240V delta systems.
 
I'm not that familiar with transformer, just want to verify if the line diagram below make sense? transformer specs at the bottom.
I'm choosing between 277V to 120/240V and 480V to 120/240V


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Very broadly speaking, it makes sense and probably would function, however I hasten to add that it seems like you ignored my reply in post #2. Three phase inverter(s) would be the normal approach here and the utility is not likely to approve an interconnection on a single phase. The single phase design is asking for trouble.
 
jaggedben said:
Very broadly speaking, it makes sense and probably would function, however I hasten to add that it seems like you ignored my reply in post #2. Three phase inverter(s) would be the normal approach here and the utility is not likely to approve an interconnection on a single phase. The single phase design is asking for trouble.
Click to expand...
Thank you, just want to finalize the design before going to the utility. crossing my fingers. this helps a lot.
 
I also recommend always planning for an interconnection at the opposite end of the busbar from the main supply. Otherwise, the 120% rule is demoted to a 100% rule. The 705.12 rules propagate all the way to the service point.
 
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