Transformer Chart for 240V 3PH?

[msilva94]

In my career, I have limited experience with residential work and electrical services outside of 480/277V and 208/120V systems. Specifically, I don’t have much hands-on experience with 240V applications, and even less with transformers that step down from 480V to 240V.

While there is no shortage of transformer charts online for stepping down from 480V to 208V—covering single-phase and three-phase systems, their KVA ratings, wire sizes, and more—information on 240V transformers seems scarce. For instance, I’ve been told that 30kVA is a common transformer size for 208V systems, but it doesn’t appear to be a standard offering for 240V systems. I’ve reached out to some colleagues, and it seems they’re also somewhat uncertain when it comes to 240V transformers.

Currently, I’m in a situation where I need a 480V to 240V transformer, but I’m struggling to find the typical standard sizes available. I’d appreciate any insights into standard 240V transformer sizes, applications, and offerings.

I posted in this General Forum, but please let me know if this belongs elsewhere.

 

[hillbilly1]

Low Voltage Dry-Type Webstore

General purpose dry-type transformers. 480, 208, 240, 600 volts and more. Outdoor enclosures, aluminum, copper windings. Custom dry-type transformers. In stock.

store.maddox.com

They have a chart that tells the standard sizes of delta transformers

 

[tortuga]

240V comes in 31 flavors, which one are you after? 3 phase delta?
the most common I see is
480 2 wire to single split phase 3 wire 120/240
480 3 wire to three phase hi-leg delta 4 wire
but I can think of at least 12 more types of 240V systems off the top of my head, 3 of which I have only ever seen in the state of PA.

 

[hillbilly1]

240V comes in 31 flavors, which one are you after? 3 phase delta?
the most common I see is
480 2 wire to single split phase 3 wire 120/240
480 3 wire to three phase hi-leg delta 4 wire
but I can think of at least 12 more types of 240V systems off the top of my head, 3 of which I have only ever seen in the state of PA.

The high leg delta can also be used as a corner ground three wire delta. XO is just not used.

 

[msilva94]

Low Voltage Dry-Type Webstore

General purpose dry-type transformers. 480, 208, 240, 600 volts and more. Outdoor enclosures, aluminum, copper windings. Custom dry-type transformers. In stock.

store.maddox.com

They have a chart that tells the standard sizes of delta transformers

I didn't find the chart in my quick gloss through, but man they have a TON of information.
This is a goldmine of information, and they have articles that keep us up to date with changes to the field. Thank you for this resource, into the bookmarks it goes!

 

[msilva94]

240V comes in 31 flavors, which one are you after? 3 phase delta?
the most common I see is
480 2 wire to single split phase 3 wire 120/240
480 3 wire to three phase hi-leg delta 4 wire
but I can think of at least 12 more types of 240V systems off the top of my head, 3 of which I have only ever seen in the state of PA.

I'm specifically looking for a 3-phase 240V Delta transformer, but more generally, I'm seeking any advice or resources similar to what hillbilly1 has shared—anything that could help me prepare for future electrical projects.

In my case, I have both 240V 3-phase and 1-phase devices. After some thought, I decided a 240V 3-phase panel with a 1-phase subpanel would be a good solution. However, when it came to sizing the transformer, I hit a roadblock.

For example, right now I need around 300A for my 3-phase 240V transformer (fingers crossed the client doesn’t keep adding more European equipment!).

I'm also hoping others in similar situations might find this discussion useful and can benefit from any input shared.

Thanks in advance!
P.S. - Also Tortuga, you've helped me out a lot in a couple of other forum questions I have, so thank you for today and thank you for then!

 

[jim dungar]

For example, right now I need around 300A for my 3-phase 240V transformer (fingers crossed the client doesn’t keep adding more European equipment!).

240V transformers come in the same standard sizes as 480V and 208V do.

You might want to consider building your own 'Open Delta' high leg 3Ph 4W transformer bank rather than buying a single custom transformer.

The formula for sizing the two transformers on this bank is:
Xmfr A = .58T + S
Xmfr B = .58T
Where T is the three phase load and S is the single phase load.

 

[msilva94]

240V transformers come in the same standard sizes as 480V and 208V do.

You might want to consider building your own 'Open Delta' high leg 3Ph 4W transformer bank rather than buying a single custom transformer.

The formula for sizing the two transformers on this bank is:
Xmfr A = .58T + S
Xmfr B = .58T
Where T is the three phase load and S is the single phase load.

Out of curiosity, why would this be better? In the equipment case, we're utilizing loads from saws and lathes and some scanners/imagers, wouldn't the voltage imbalance be a concern?

 

[Jraef]

240V transformers come in the same standard sizes as 480V and 208V do.

That’s my experience as well.

 

[Jraef]

Out of curiosity, why would this be better? In the equipment case, we're utilizing loads from saws and lathes and some scanners/imagers, wouldn't the voltage imbalance be a concern?

If you are planning on having a significant 120V single phase load on the 240V 3 phase system, the factory made 240D/120 high leg transformers often have limited capacity for the 120V aspect. Rolling your own allows you to design in whatever you need.

 

[jim dungar]

Out of curiosity, why would this be better? In the equipment case, we're utilizing loads from saws and lathes and some scanners/imagers, wouldn't the voltage imbalance be a concern?

Imbalance is not a concern if the transformers have been sized correctly. This is how most utilities provide 240/120V 3Ph 4W services.

 

[msilva94]

If you are planning on having a significant 120V single phase load on the 259V 3 phase system, the factory made 240D/120 high leg transformers often have limited capacity for the 120V aspect. Rolling your own allows you to design in whatever you need.

Good to know!
In my particular case, any 120V load off this particular setup would be for general convenience - the site has 208/120 available to handle most 120V loads.

That’s my experience as well.

That was my thought process as well, in the recent past I did a small design where I called out for a 30kVA XFMR (480 to 240), but a remark was made that such a XFMR doesn't exist for 240V.
I still let the design go out labeled with 30kVA, as the remark was made after the fact, but was afraid the contractor (or Permit office) was going to call me back cursing me out and calling me an idiot.

I have a lot to learn, thank god for this forum.