What type of Transformer do I need? Does it exists?

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ExtremeSolar

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Merced, CA
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Solar Installer
Installing an 82kw solar system that operates on 3P 480V Y and need to go to an existing 400A main service that is 3P 240V Delta with a 208V high leg. Does anyone have any idea as to how I can make that happen and what the maximum output might look like?
 
So you need a 3Ø 480 volt to 3Ø, 4-wire, 240/120 volt Delta secondary transformer. Pretty common type.
 
infinity said:
So you need a 3Ø 480 volt to 3Ø, 4-wire, 240/120 volt Delta secondary transformer. Pretty common type.
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Disagree. The utility service is 240V, so the OP needs a transformer with a 240V primary.

The transformer would be a 240V delta primary, 480/277V wye secondary.

Probably something along the lines of https://www.hubbell.com/acmeelectri...istribution-Transformer/T3112K0074B/p/1655382

(Note: I am not recommending this particular product, simply as an example of the sort of transformer needed. Consideration needs to be made for environmental location, power rating, harmonics, etc.)

-Jon
 
winnie said:
Disagree. The utility service is 240V, so the OP needs a transformer with a 240V primary.

The transformer would be a 240V delta primary, 480/277V wye secondary.

Probably something along the lines of https://www.hubbell.com/acmeelectri...istribution-Transformer/T3112K0074B/p/1655382

(Note: I am not recommending this particular product, simply as an example of the sort of transformer needed. Consideration needs to be made for environmental location, power rating, harmonics, etc.)

-Jon
Click to expand...

Thank you very much, while I understand that you do not necessarily recommend the listed product, you would agree that it is the type of transformer needed, yes?
 
Doesn't he need to go from 480 to 240, the existing system is 240 why is it the other way around?
 
Inverters often require a wye configuration for their interface.
If you did have high-leg delta windings instead of the 240 3-wire delta that Jon mentioned, you shouldn't connect the center tap. Otherwise currents would flow through the grounded conductor if there are even slight mismatches between how "centered" that tap is on this transformer vs. the distribution transformer.
 
infinity said:
Doesn't he need to go from 480 to 240, the existing system is 240 why is it the other way around?
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Good question. Power is flowing from the PV system at 480V to the electrical service at 240V, so why do I suggest a 240V primary transformer?

The answer is that the 'primary' of a transformer is not defined by the direction of power flow, but rather by the side that is setting the operating voltage, and which generally gets energized first.

Line interactive power sources such as PV inverters sense the mains voltage and adjust their output to match. Lose the utility supply and the PV shuts down. Reduce the utility voltage and the PV system adjusts to match. This transformer will be energized from the utility service. The voltage adjustment taps will need to be on the 240V side to adjust if the utility service runs a bit high or low.

The 480V will be supplied from the secondary of this transformer to tell the PV system what to do. The PV system will match the secondary voltage, and then power will flow from the 480V side to the 240V side.

-Jon
 
ExtremeSolar said:
Thank you very much, while I understand that you do not necessarily recommend the listed product, you would agree that it is the type of transformer needed, yes?
Click to expand...

I was focusing on the coil arrangement and the voltages. No comment on things like winding material (Cu or Al) enclosure (indoor or outdoor) insulation (air cooled or oil immersed) capacity (nominal vs overload), etc. Just the 240V delta to 480/277V wye bit.

-Jon
 
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