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Our power went down yesterday afternoon (December 12). The utility posted a message on their 1-800 number with expected repair time (a few hours later), but no explanation except that ~2000 customers were affected in our suburban area (Northeast USA).
Here's the weird bit -- LED bulbs stayed on, at reduced brightness. I got out a meter and measured 16 VAC in the house. This was enough to make useful light from "dimmable" LED bulbs (happened to be GE brand). After it got dark, we could also see that incandescent bulbs were giving off a faint reddish glow.
16VAC was also enough to keep a Netgear home router/Wi-Fi box going, it must have a switcher in the wall wart that accepts a really wide input voltage range?
Called a friend on the other side of the country who is an EE (with hardware background). He didn't have a good explanation, but suggested that in the process of bringing the grid back up there might be some big voltage swings--recommended unplugging everything we could. Went out to dinner and all was restored when we got home (no damage).
He also told a story from a rural area (near CA-Nevada border) where there was a power failure that upset the normally-balanced split phase -- instead of ~120V on both sides of neutral, the power went to 80V on one side and 160V on the other side of neutral. Equipment on the high voltage side failed due to extended over-voltage, seems that surge suppressors won't deal with this much energy.
Anyone? How does the grid fail-soft?
(Score: 2) by LoRdTAW on Tuesday December 15 2015, @02:25PM
I'm surprised the circuit breakers don't blow. My only guess is there is enough impedance to prevent this but I still doubt that a ~6kW gas genset could ever back feed the grid without tripping one of its two 20 amp breakers. Though, I have heard of this happening. My guess was in those situations is the utility lines become isolated enough to prevent generator loading and just float. So if someone has their own little transformer and their high voltage feeder fuse blows, they can still backfeed the transformer and cause a floating high voltage potential on the primary.
(Score: 3, Interesting) by VLM on Tuesday December 15 2015, @04:22PM
If you try to power an entire neighborhood off a small generator, combined with trying to make the governor smoother by having a heavy flywheel, I've heard stories about the crankshaft of the generator shearing when the output is shorted either by a wiring error or back feeding foolishness. Usually cars can't be damaged by stalling them, but often enough you can damage a generator trying the same trick. 60 Hz is pretty slow and you can have quite a torque spike in the shaft before mechanical breakers open. Most backfeeding incidents end in a loud bang, sudden silence, then swearing about all the damage to the engine.
In practice there's two problems.
Linemen aren't complete idiots and know how to handle electricity, but after working 36 straight hours without a break after a hurricane because he likes overtime $$$ and he literally falls asleep on his feet and falls out of the bucket asleep to his death, then everything gets kinda smoothed over such that no one is to blame because he must have gotten shocked by a back feeding generator or WTF, causing a minor shock that scared the hell out of him so he lost his balance. Or just plain old lost his balance, how does an old timer lose his balance and fall to his death, must have been a GD backfeeder. A close second is after 36 straight hours of work literally spacing out and forgetting which side of the circuit is currently live. If I climbed a pole I'd have an interesting time not getting killed, but these guys know what they're doing and its not an issue.
The other problem is see first paragraph generators hooked up incorrectly generally don't operate for long, and as such are not a significant threat however people stupid enough to do something that stupid, will none the less perform all manner of other idiocy likely leading to death, fire, etc. Like run circuits between hot and ground, making massive ground loops by making multiple gnd-neutral connections, staple stranded extension cords to rafters instead of installing romex, make virtual 220 circuits by grabbing two opposing phase 110 circuit hot leads, wire their kitchen stove for 4-wire then hotwire a 3-wire cord/circuit onto it, all kinds of stupid stuff. Even non-electrical stupid stuff like run the generator in their basement or garage to prevent theft, run it in the rain unprotected, refill the gas tank while the generator is running, look for gas line leaks with a lit match, etc. Its a general denigration of "hold my beer and watch this" culture rather than specifically making fun of one practice of that culture.
(Score: 2) by LoRdTAW on Tuesday December 15 2015, @05:36PM
I've seen some pretty dumb stuff myself. The best is I worked with a guy who refilled a small coleman gas generator while running on a carnival job that was running a bouncy castle and cotton candy machine. The gas splashed and hit the hot cylinder head and I assume the exhaust pipe. The whole thing flashed, so his reaction was to whip the gas can around and throw it. Well that resulted in him splashing gas on his arm which caught fire and then heaved the gas can at a wood fence which went up in flames. My uncle was there with his ride truck and said he heard screams and saw a plume of black smoke coming from behind the bouncy castle along with people running away. Fire department came and put the fence out and the gas that was on the ground burnt itself out. Dumb dumb who filled the tank was treated for minor burns as he was at least smart enough to stop drop and roll to put his arm out before it was severely burned. We had to pay for the fence and the generator needed a new fuel tank. We then made him pay us back for the fence which wasn't much. That dude always caused all sorts of cartoonish calamities. Once he actually did the paint can on a board across two horses that gets turned into catapult after something heavy fell on it and splashed white paint all over the yard, equipment, two vans and himself.