High leg delta?

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Tony S

Tony S

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A friend has asked me about this. A UK company has asked if he could install a supply to a US made machine with corner grounded 480V high leg delta, very unusual for the UK.

Having thought about it I can’t think of any reason why a 433/480V ΔY transformer can’t be used. There is no need for a neutral at the machine. The 480V star point will be grounded. Any thing I'm missing?

I’ve had dealings with EU companies that would not warrant machines unless the supply was 380/220V, again an oddball voltage for the UK. (It falls at the lower end of 400/230V -6% +10%. The plant had two distribution systems, normal power was at 433V alongside 380V for the machines.
 
Tony S said:
A friend has asked me about this. A UK company has asked if he could install a supply to a US made machine with corner grounded 480V high leg delta, very unusual for the UK.

Having thought about it I can’t think of any reason why a 433/480V ΔY transformer can’t be used. There is no need for a neutral at the machine. The 480V star point will be grounded. Any thing I'm missing?

I’ve had dealings with EU companies that would not warrant machines unless the supply was 380/220V, again an oddball voltage for the UK. (It falls at the lower end of 400/230V -6% +10%. The plant had two distribution systems, normal power was at 433V alongside 380V for the machines.
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If you use the Y secondary you are thinking of, it will be 277 volts to ground, no big deal, your machine still sees 480 volts between the conductors it is utilizing.

But no it can't be high leg and corner ground delta at same time.

Corner ground is exactly what the name says - one corner of the delta is grounded, the other two corners will be 480 volts to ground on such system. You still must run a separate grounding conductor to bond non current carrying components - so you are running 4 wire circuits either way you do it.

High leg delta has the mid point of one side of the delta grounded. It will have 240 volts to ground on the two adjacent corners and 416 volts to ground on the opposite corner (called the hi-leg).
 
Is the equipment rated for use at 50Hz with 480V? If not then the motor's voltage should be reduced to approximately (50/60)x480V=400V in order to prevent the current in the motor windings from increasing above the design value, and also to prevent the motor's magnetic components from saturating. But 430V should be acceptable.
Does the the equipment need a lower voltage like 200 to 240V for any control circuitry and that's why a high-leg delta would be mentioned? Or can it run with only the 3 outer legs of a delta or wye (using its own transformer if necessary)?
 
I concur with Kwire, you don't want to use corner grounded. Most drives will not tolerate for that very long.

I would suggest that you use a 3Φ Wye autotransformer. Smaller, less cost, more efficient. can have several taps for adjustment to site conditions.
System remains a wye.

Many machines designed for a world market, will come with the autotransformer built in.

MTW Ω
 
Sorry about my confusion with corner grounded and high leg, they’re not systems we use this side of the pond. (I’ve never come across them.)

In conclusion 480V Y connected shouldn’t cause problems, or will it?
 
Tony S said:
Sorry about my confusion with corner grounded and high leg, they’re not systems we use this side of the pond. (I’ve never come across them.)

In conclusion 480V Y connected shouldn’t cause problems, or will it?
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But, as Synchro mentioned, the 50Hz might.
 
MTW said:
I concur with Kwire, you don't want to use corner grounded. Most drives will not tolerate for that very long.

I would suggest that you use a 3Φ Wye autotransformer. Smaller, less cost, more efficient. can have several taps for adjustment to site conditions.
System remains a wye.

Many machines designed for a world market, will come with the autotransformer built in.

MTW Ω
Click to expand...
Drives that don't like corner ground likely don't like high leg delta either. On board surge protection is usually designed for 277 nominal to ground, and you have one leg that is 416.
 
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