WYE vs DELTA machine

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Ponchik

Ponchik

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Location
CA
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Electronologist
I am on project that needed a step up transformer 240 to 480 for a piece of machinery that is laser cutter. The building has 240V DELTA, so a transformer was reverse fed to get 480V DELTA. After everything was hooked up the manufacturer technician checked voltage between the legs and ground and it showed up as odd voltages and said the "machine will not work properly even though we only need 480V for operation and said that the transformer should be a Delta to Wye not a delta to delta.

My question: If the machine does not use ground as a reference or for operation why does it matter if the 480 is Delta or Wye?

Edit to add: Can a transformer be reverse fed with Delta 240 to get 480 Wye system?



Thank you
 
At least two factors at play here:


1. The machine, like all VFDs, may have surge suppression elements wired from each line to ground rather than just between lines. This protects the equipment against an induced voltage that affects all the ungrounded lines equally and would not trigger a line to line suppressor.
Either ungrounded or corner grounded risks blowing those elements up.

2. Insulation, relays, switches and other components within the machine may not be rated for 480 to ground or at least not for the 960 to ground that might occur with some restriking arc faults.

3. The NEC will not allow ungrounded operation without some sort of ground fault detector, not to shut the system down but to alert you to fix the fault before a second fault occurs that will draw fault current.
 
OK I need help with this.

The system is as pictured. It seems to me it is not the correct set up. I don't feel comfortable about the grounding.

Screen Shot 2017-09-13 at 8.26.52 PM.jpg
 
ActionDave said:
Don't feel comfortable in what way? Because right now you don't have any grounding on the 480V secondary or because you need to corner ground it to get a ground?
Click to expand...

That there is no grounding on the 480 side and I think the machine needs a delta to wye step up transformer instead of D-D.
 
edward said:
That there is no grounding on the 480 side and I think the machine needs a delta to wye step up transformer instead of D-D.
Click to expand...

Your right, you either need a corner ground or ground detectors. The reason the technician got weird voltage to ground reading is because you don't have a solid ground reference, might as well put one lead on the hot and the other lead on your lunch box. Depending on the electronics on the machine it may want a wye.

It's not hard to get a wye secondary step up transformer, and not cost prohibitive, you just usually need to order one whereas you can go out and by a step down transformer that day.
 
ActionDave said:
Your right, you either need a corner ground or ground detectors. The reason the technician got weird voltage to ground reading is because you don't have a solid ground reference, might as well put one lead on the hot and the other lead on your lunch box. Depending on the electronics on the machine it may want a wye.

It's not hard to get a wye secondary step up transformer, and not cost prohibitive, you just usually need to order one whereas you can go out and by a step down transformer that day.
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To corner ground a delta does a specific leg gets connected to the ground or any leg?

Tomorrow I will find out if the machine needs a wye or not.

Thanks
 
edward said:
To corner ground a delta does a specific leg gets connected to the ground or any leg?

Tomorrow I will find out if the machine needs a wye or not.

Thanks
Click to expand...

I believe B is customary but I'm not aware of any rules that say that. Once you ground it you treat it just like a grounded neutral and make sure you don't have any overcurrent protection on it.

There is only one corner ground in my sphere and it's a utility supplied 480V service on an irrigation system, so I understand them but don't work on them often. Every time my shop has needed to step up voltage we ordered a delta/wye step up transformer.
 
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