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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 carguy on Tuesday December 15 2015, @05:44AM
I'm the OP. I like the explanation of a neighbor with incorrect generator setup, except for one thing. The 16 VAC appeared almost immediately after the failure. As I remember it, the lights went out (including the LED bulb) and back on a couple of times quickly. This (I believe) is the utility's circuit breakers resetting a couple of times to see if the fault has gone away. After that the power was off for a few seconds and then the LED came on at the dim level.
So the 16 VAC was on the line almost immediately after the final cutoff. It was also on at our next door neighbors -- an elderly couple who were very pleased that I brought over a couple of spare LED bulbs. Saved them trying to get around by flashlight. They also had 16 VAC for a few hours, confirmed by volt meter. Don't know if they are on the same transformer as us or not--will have to check sometime.
How about this -- the utility circuit breaker actually was able to reconnect, but during the few seconds of the failure/overload a transformer winding partially shorted and the output voltage was greatly reduced. Could this do it?
There was another short power failure today, but this time I watched the LED bulb and it did not stay lit. So no repeat (yet).
(Score: 0) by Anonymous Coward on Tuesday December 15 2015, @06:30AM
What you have then is an old-fashioned soldering gun.
Not a lot of voltage across that 1 turn but, with essentially zero ohms limiting the current, it's gonna pull a whole bunch of current.
The transformer will self-destruct before long--if it doesn't blow a fuse first.
-- gewg_
(Score: 2) by LoRdTAW on Tuesday December 15 2015, @02:44PM
See my comment above: https://soylentnews.org/comments.pl?sid=11142&cid=276656#commentwrap [soylentnews.org]