240vac, 2 pole system design question

[JoeWay314]

I have an industrial customer who wants to provide 480vac, 3 phase power to a system i am providing. this system is a large assembly platform and they want 15 individual drops on this platform to have a 240vac, single phase, 15 amp circuit to power assembly torque devices (fancy electric screwdriver). I was thinking of using a standard try type transformer to convert power and then use 2 pole breakers in a standard 3 phase, 240 volt distribution panel. anything I am missing? I had a local reputable vendor no-quote this with no explanation? the assembly torque tools are from UK, and only come as 240vac.

 

[ptonsparky]

Single Phase step down to 240/120 ?
Single phase panel.

 

[JoeWay314]

I have an industrial customer who wants to provide 480vac, 3 phase power to a system i am providing. this system is a large assembly platform and they want 15 individual drops on this platform to have a 240vac, single phase, 15 amp circuit to power assembly torque devices (fancy electric screwdriver). I was thinking of using a standard try type transformer to convert power and then use 2 pole breakers in a standard 3 phase, 240 volt distribution panel. anything I am missing? I had a local reputable vendor no-quote this with no explanation? the assembly torque tools are from UK, and only come as 240vac.

 

[JoeWay314]

Single Phase step down to 240/120 ?
Single phase panel.

Tom, since i have a total of 50kva i was going to use a 3 phase approach and just balance the secondary loads, such that they are not all on 2 phases of the secondary on the xfmr. A, B, C. breakers on A-B, B-C, A-C. in this way, the transformer is not overload on just 2 phases.

 

[winnie]

1) It is very unlikely that the torque screwdrivers require the full 15A for an extended period of time, so the 50kVA transformer is probably very oversized.
2) Make sure that the screwdrivers can handle 240V L-L, and are not intended for 240V L-N.
3) Make sure that the screwdrivers can handle 60Hz rather than 50 Hz.
4) Think about grounding your step down transformer; most 240V transformers will be _delta_.
5) What ever you select, make sure your breakers are rated correctly. Many 2 pole 240V breakers are intended for use on 120/240V single phase systems, and are 'slash rated' for 240V line-line 120V line-ground. Using these breakers on a 3 phase 240V delta secondary is a mis-application because the L-G voltage on some of the legs will exceed 120V.

-Jonathan

 

[JoeWay314]

1) It is very unlikely that the torque screwdrivers require the full 15A for an extended period of time, so the 50kVA transformer is probably very oversized.
2) Make sure that the screwdrivers can handle 240V L-L, and are not intended for 240V L-N.
3) Make sure that the screwdrivers can handle 60Hz rather than 50 Hz.
4) Think about grounding your step down transformer; most 240V transformers will be _delta_.
5) What ever you select, make sure your breakers are rated correctly. Many 2 pole 240V breakers are intended for use on 120/240V single phase systems, and are 'slash rated' for 240V line-line 120V line-ground. Using these breakers on a 3 phase 240V delta secondary is a mis-application because the L-G voltage on some of the legs will exceed 120V.

-Jonathan

Jonathan, Excellent points. Manual says 15amp service, you are correct. not only is the screwdriver not going to be 100% duty cycle, each station will not be used at the exact same time. what would be acceptable for sizing? 240vac Line to line, manual says 50/60hz input power. panel will either be square D, or Siemens. I will make sure to check breaker ratings. Thank you for the great insights.

 

[Jraef]

5) What ever you select, make sure your breakers are rated correctly. Many 2 pole 240V breakers are intended for use on 120/240V single phase systems, and are 'slash rated' for 240V line-line 120V line-ground. Using these breakers on a 3 phase 240V delta secondary is a mis-application because the L-G voltage on some of the legs will exceed 120V.

What you want to make sure of with your panel / breaker vendor is that the breakers are "straight 240V rated". Many 2 pole breakers are what's called "slash rated", meaning 120/240V, which CANNOT be used on a 240V delta 3 phase system, because the L-G reference could be higher than 120V (that's what the "slash" is all about). Straight 240V rated breakers are often more expensive and larger (in some brands).

 

[tortuga]

I'd look at using a 220Y127 transformer or if you don't have any use for a 120V leg they do sell a 240Y139, though many are labeled 'drive isolation' which I am not sure what that means if your not isolating a VFD with it.
If you need 240V L-N they do make a 416Y240 which is closest to 400Y230 50HZ what they use in the UK.
Pre 230V harmonization some parts of Europe (Spain I think) were on a 220Y127 they just did not use the 127 for anything, other areas still use 230V ungrounded, so I'd imagine any equipment manufacturer over there would not make equipment that depended L-N vs L-L, it would probably be a violaiotn of some IEC spec to make 230V equipment that depended on a grounded neutral.