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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 sjames on Tuesday December 15 2015, @06:15PM
It can be a lot of things depending on the exact setup of the neighborhood wiring. If the power company loses the neutral, suddenly fairly simple circuits effectively become comp[lex and somewhat unpredictable. Much moreso if it's a neighborhood that has a 120/208 wye setup. For example, two lights on seperate phases are suddenly effectively connected in series across the phases instead. Turn one off, both go off. But just to confuse matters, the (disconnected) neutral is bonded to ground, so if one light is off, the other is now powered by 208v but with a high value parallel resistor and capacitor connected in series. Who knows what voltage drop it might see? (it depends on the weather, soil composition, solar activity, etc). Your TV might end up in series with the neighbor's dryer.