Creating a Neutral

[renosteinke]

Since forums have somewhat different audiences, I'm posting this question in a few different places. I'm looking for advice and experienced comments.

I have a major 'heavy industry' faciiltiy that has all manner of power quality issues. It is my belief that these issues are the result of combining frequency drives, induction heating equipment, and HID lighting with an ungrounded 480 delta service.

For example: one lamp ballast with a high-impedence fault to ground caused weeks of poor welds on the line ... until the problem was 'solved,' mainly by accident.

I'd like to completely separate the lighting from the plant power. I'm thinking of installing 480 delta- 480/277 Wye transformers, grounding to the building steel.

The place has approximately 700 fixtures, of the 400w metal halide type.

Naturally, there are other plans afoot .... changing to T5's, moving/ adding lights, even the change to 277 will make less expensive ballasts available.

Any thoughts?

 

[pfalcon]

Even 1:1 transformers provide a lot of noise immunity.

 

[Cow]

I think there are rebates and tax incentives available to switch from metal halides to flourescent that make it pretty cost effective. If you can combine that with motion sensors and other ways to automate the lighting that'll save even more money yet.

Just an idea...

 

[templdl]

I'm intrigued with the ungrounded delta. I have found that it is most beneficial when there is a continuous manufacturing process that if the system were to be shut down in any part would cause a catastrophic event costing thousands of dollars in lost production as well as the possibility of machinery damage. An ungrounded delta should be monitored by a qualified person who understands the implications of the possibility of a L-G fault in said system and the importance of having a GF indicator system.
I am also intrigued with how well the AFDs do when applied with an ungrounded system.
Also, I have never considered what happens to the harmonics either.
Have you considered a Zig-Zag transformer to derive a neutral? A Zig Zag Grounding Transformer is often used as a ground source on the delta side of a transformer or as a ground path for an ungrounded ?Y.? A few of the most common benefits of a Zig Zag Grounding Transformer include the following:
1) Allows the connection of neutral to phase loads.
2) Hinders the probability of transient over voltages in the scenario of re-striking ground faults.
3)Allows ground fault currents a path during line to ground faults.
4) Maintains near ground potential or system neutral with a low impendence path to ground.

It may be worth the money to have a study done by a PE in order to assure that what ever money that would be spent will provide a solution to your issue. I personally am not a parts replacer, that is keep on replacing parts until you happen upon the solution. If what ever you decide to do doesn't solve the problem what next?
Again, I would strongly suggest that you get someone to identify the problem and direct your effort to the solution that is recommended. Whether or whether not you like the answer considering the size of the facility I certainly would like to be responsible for wasting a boat load of money by taking a calculated guess on my own. You may want to review these sights:
grounding transformers can be used to create a neutral;
http://www.postglover.com/Literature/GT210-08_Zigzag_Trans.pdf
How To Ground A Delta System;
http://www.aeusp.com/fundamentals/dsfdh.asp
Zig-Zag Transformers;
http://www.geindustrial.com/Newsletter/ZigZag_Transformers.pdf
Grounding Transformers;
http://www.pacificcresttrans.com/resource-center/15/Grounding-Transformers.html
This should be enough enfo for you to get an idea about the use of a zig-zag trasformer,
This may not end up to be a soluition to your problem but the Zig-Zag trasnformer as you can see is a useful way to derive a neutral.

 

[mike_kilroy]

have you checked with ur power company? will they come in and change u from delta to wye xfmr on your building? might be worth investigating.

adding delta -wye iso xfmrs and grounding the wye neutral certainly will reduce noise coming and going (this cancels all odd harmonics) and provide the Low Z hold down that probably would reduce afd damage you probably are experiencing (a lot of afd drive mfgrs spec ground Y source as a requirement, altho a lot of people don't realize this - got read the small print in manuals sometimes). they design the electronics for 480v but not 2kv or 10kv from line to ground and so pcbs tend to arc over and blow up, or exceed input diode pack PIV ratings if u have spike issues.

we have designed and supplied 3ph 480v 50kjoule low cost TVS units for troublesome machines that have had past experience with spike damage with good success; u might consider googlng large power low cost TVS devices - might help too.