lightning strike

[deetz]

Had a lightning strike our pole supplying our manufacturing facility. It took out alot of contactors, or so it would seem. It took out 2 fuses and a resistor, or arrestor, on the pole. So there was still some power coming in. If we would have shut off the main breakers for the facility sooner, would that have mitigated the effects to all the contactors? Also would surge suppressors on each machine have protected them somewhat? Maybe on the panels?

 

[IRstuff]

Contactors: maybe, depends on how big a gap is created when the contactors are opened, but YMMV. Note that a lightning strike travels miles in the atmosphere, so even a few inches would hardly be a barrier.

Surge suppressors: if you mean lightning arresters, then possibly. I don't think lightning does any math to determine that the proposed path to ground is the obviously the correct choice, so any alternate path might still get something.

Overall, I'd think you'd need a layered approach, i.e., multiple defenses, so that there are additional protections should one or more layers fail to contain the strike.

TTFN (ta ta for now)
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[deetz]

We have a redundant system for our Computer Room in the other building. I suppose you are right that I should do that with this building. Thanks.

 

[waross]

With two phases out, there may have been a back feed through single phase loads putting enough low voltage on the unpowered phases to burn out the contactor coils.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[deetz]

That may have been the case waross. It's like it took out some coils, and some contacts. There really doesn't seem to be any consistancy to what it took out. Also, another question, on some of the newer machines they have power surge protectors installed. Is there a way to tell if they need to be replaced?

 

[cranky108]

Note that lighting arresters do have limits, and beyond those limits, the extra energy will go somewhere. That maybe an explosive type of somewhere, depending on the mode. If they mode is a rapidly expanding gas, then an explosive response will happen.
That said, adding surge suppressors or lighting arresters, may not be a complete answer.

I recall the phone company, in older days, would put a lighting arrester in a metal box at the demark location. It seems our grounding system and there's seemed to have a number of high voltage events.

 

[deetz]

That would have been Ma Bell. Most people today would not know that reference.

 

[Sparweb]

With two phases out, there may have been a back feed through single phase loads putting enough low voltage on the unpowered phases to burn out the contactor coils.

Ha, that might explain what happened to my house a month ago. Power went out but actually there was about 50V still across the lines. The lights, TV, and computers went out, but the clock radios were still on. I threw the main breaker of my house, because 25V line to neutral can't be good for anything designed for 120.

I've been wondering what could have caused that. Maybe this is a clue, if we assume that upstream of the single-phase line on my road, only 2 of the 3 phases tripped on a distribution line. Users downstream of that with single-phase service might have power if they were on the line that didn't trip. But downstream users with 3-phase service would just have extremely imbalanced phases and some of their equipment could back-feed the other phases just a bit. If I'm downstream of them, then their imbalance feeding through their transformer, and to mine, would appear strange.

(Sorry for the hijack)

 

[FacEngrPE]

Phase monitoring relays may be useful for protecting equipment in this situation. There are a large number on the market, features vary, so read the literature before ordering. The most basic feature is detecting loss of phase on a 3 phase service. Some can detect backwards phase rotation, and other stuff. They can be added to equipment control, or can be set up to trip your service when shunt trip breakers are present.

Try this search

https://www.google.com/search?q=phase+monitor+relay