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posted by martyb on Tuesday December 15 2015, @04:18AM   Printer-friendly
from the blackouts-and-brownouts dept.

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?


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  • (Score: 5, Informative) by LoRdTAW on Tuesday December 15 2015, @01:27PM

    by LoRdTAW (3755) on Tuesday December 15 2015, @01:27PM (#276638) Journal

    It's not always split phase. Some areas will feed you from a 120/208 3 phase Y using two of the three phases. Makes balancing a 3 phase high voltage feeder much easier. If the phases are labeled A, B and C, homes are connected A-B, B-C, C-A to achieve balance. The only downside is appliances expecting 240V will operate at slightly reduced power. But it usually isn't a problem.

    And don't expect everything to be uniform, power companies do weird stuff. I live in south Queens a my home is powered by 120/240 true split phase. If you look at the poles, there are three wires that feed every house on the block. But when you get to either corner, you can see that the three wires met up with four wires from a 3 phase setup. This is not kosher and the lines could never be connected. So the hot legs are actually isolated with insulators on each side of the block and only the neutrals are connected. So my block is the only block in the area with true 120/240 split phase fed from a single 100KVA pole transformer. Everyone else has 120/208 off of a 3 phase Y. Why? Who knows. Maybe it was originally supposed to be multiple 120/240 feeders and they canned the idea or upgraded and our block was forgotten.

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