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Tuesday, December 15, 2009

Commentary on Death by Ignorance, and System Protection

There's a little tie-in commentary I want to make in regard to the previous post and all of the system protection stuff talked about in the last two tutorials.

Everything in a substation is protected by zones, so why in the world would the carnage depicted in the photos on the last post be so severe? Why didn't something detect the fault and clear it before it got so bad?

Well, my friends, what probably happened in that case and does happen in many others like it, is that technically there was never a fault. There was never a hard connection to the fatal arc from the generator-to-component chain that is watched by fuses and relays.

Part of the transmission of electricity involves a powerful electromagnetic field which literally rotates around energized equipment and power lines, out to a distance of several yards, though the strength of this field weakens quickly as the distance from the energized equipment increases.

You hear about people complaining about EMF exposure when living near power lines, so you can imagine the distances the fields can reach out to. And then you can imagine the fields you're immersed in when you're in a substation and fairly close to the big stuff. Induction potential is normally negated on the structures and fences at stations by the grounding straps which dissipate the potential immediately

If the induction potential is not dissipated by grounds (because some Darwin Award candidate removed them), any electromagnetic induction potential will look for a way out, and will create an arc when it finds it. Since it draws no actual fault current from the energized equipment, there is nothing for the relays to detect. It will just burn and burn and burn, either until (1) there's nothing left to burn, (2) the damage created by the arc grows so large that the arc can no longer jump the gap, (3) the arc reaches energized equipment where the relays can see it, (4) the damage causes a structural failure of some variety that indirectly creates a real fault, or (5) a power company guy observes the arc and takes action to de-energize the associated equipment.

So, as you might conclude, exposure to electricity by induction is far more hazardous than exposure to straight-up energized equipment. The energized stuff will pretty much kill you 99.999% of the time, though rare exceptions have been noted and made possible by quick fault clearing and only on relatively low voltages. But you've got no chance at all when you get whacked by undetectable and non-clearing induction current.

Just some things to think about.

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