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#205510 - 02/28/12 05:55 AM Re: Creating a Neutral [Re: renosteinke]
twh Offline
Member
Registered: 03/11/04
Posts: 901
Loc: Regina, Sask.
What I have seen, the way to avoid problems with equipment in a large plant is to install isolation transformers for the electronic stuff and NOT ground those transformers. I didn't pay any attention to whether they were ordinary transformers or iron rich or iron poor. Aren't welders transformers, anyway? As you might tell from my previous comments, we can't bond to the building, so I have no experience with that.
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#205513 - 02/28/12 09:00 AM Re: Creating a Neutral [Re: twh]
LarryC Offline
Member
Registered: 07/05/04
Posts: 780
Loc: Winchester, NH, US
Quote:
As you might guess, there are power quality issues. One bad ballast, and the induction equipment starts making bad welds.


How does a bad ballast lead to bad welds?
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#205514 - 02/28/12 09:03 AM Re: Creating a Neutral [Re: renosteinke]
ampherder Offline
Member
Registered: 09/29/11
Posts: 19
Loc: VA
There is some good literature on the Schneider site.

You might start with

http://static.schneider-electric.us/assets/consultingengineer/appguidedocs/section6_0307.pdf
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#205518 - 02/28/12 12:43 PM Re: Creating a Neutral [Re: renosteinke]
renosteinke Offline
Cat Servant
Member
Registered: 01/22/05
Posts: 5316
Loc: Blue Collar Country
A bad ballast has the effect of 'grounding' one leg of the 'ungrounded' delta. If there's another incidental ground somewhere, you have a fault. If the fault is a high-impedence type of fault, you don't trip breakers or light up the pahse monitors ... but your line voltages swing all over the place. That, in turn, means that the electronics of the induction equipment don't work right.

For those unfamiliar with 'induction welding,' that is a process quite a bit different from anything you'll see in a workshop. There is no electrode, rod, or flux. Instead, steel is passed through a magnetic field that cycles very fast .... we're talking about thousands of cycles per second. This filed makes the metal withing it red-hot. The red-hot metal is then squeezed together, where it mixes with the other red-hot metal and forms a weld. This is how pipe is made (including EMT).

The induction welding equipment has no transformers; it relies upon very rapid switching of the AC supply to create both the high frequency and the higher voltages used. If your AC supply coming in is not a clean waveform, the electronics (SCR's and IGBT's most often) won't work right.

Of course, the opposite also applies: the induction equipment does introduce harmonics to the AC supply. Not as bad as a variable speed drive, but there is the effect.

Hence, my desire to isolate the lighting from the power.
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#205519 - 02/28/12 12:56 PM Re: Creating a Neutral [Re: ampherder]
renosteinke Offline
Cat Servant
Member
Registered: 01/22/05
Posts: 5316
Loc: Blue Collar Country
Perhaps a better link, that explains some of the issues I am facing, is:

http://www.iaei.org/magazine/2010/03/are-we-really-ungrounded/
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#205520 - 02/28/12 04:25 PM Re: Creating a Neutral [Re: renosteinke]
gfretwell Offline


Member
Registered: 07/20/04
Posts: 9038
Loc: Estero,Fl,usa
A corner ground won't work for you? You won't need any additional wire beyond the GEC.
This requires some awareness about what is going on but it is a fairly simple way to ground a delta where you are not using any line to neutral loads.

Another option might be to just add a 480 wye transformer for the loads that are not going to the welders. (maybe they expect an ungrounded source) I assume they already have a 120/240 or 120/208 transformer for the office loads.
_________________________
Greg Fretwell
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#205529 - 02/29/12 07:54 PM Re: Creating a Neutral [Re: renosteinke]
renosteinke Offline
Cat Servant
Member
Registered: 01/22/05
Posts: 5316
Loc: Blue Collar Country
Just had a visit today by a rather sceptical gent, rep of a major French/German maker of all manner of power related equipment.

End result? My description of the existing equipment is accurate, and the idea should work. Quote will follow.

A few matters that were clarified:

1) This is an instance where an 'ordinary' transformer will probably suffice. No real need for a "K" rating, since the lights are not the source of the 'harmonics.' Here it is important to recognize that there's more to 'power quality' than just harmonics; and,

2) Yup, they can make a lot of stuff that's not in the catalog. For example, the transformers I want in an unvented (though still Nema-1) case. That will be enough to keep the rather modest amount of conductive dust at bay.

Of course, now I need to dig deeper into the plant's distribution system. This is going to be an incremental project.
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#205549 - 03/02/12 11:37 PM Re: Creating a Neutral [Re: renosteinke]
pdh Offline
Member
Registered: 01/20/05
Posts: 354
Search "induction welding" on Youtube. Fun stuff.
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