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Comment by Animats | Hacker News Reader

This problem is similar to what electric utilities call "load takeup". After a power outage, when power is turned back on, there are many loads that draw more power at startup.

The shortest term effects are power supplies recharging their capacitors and incandescent bulbs warming up. That's over within a second.

Then it's the motors, which have 2x-3x their running load when starting as they bring their rotating mass up to speed. That extra load lasts for tens of seconds.

If power has been off for more than a few minutes, everything in heating and cooling which normally cycles on and off will want to start. That high load lasts for minutes.

Bringing up a power grid is thus done by sections, not all at once.

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If you're subject to peak load billing it's also a good idea to bring your loads online in sections, too. My family owns a small grocery store. I was taught the process for "booting-up" the store after a power outage. It basically amounted to a one-by-one startup of the refrigeration compressors, waiting between each for them to come up to operating pressure and stabilize their current demand.

An insightful share. You might be interested to know that startup current is called 'inrush current'. For a Direct On Line (DOL) start, (no soft starters or variable speed drives) electrical engineers usually model it as 6x normal full load current.

Other electrical devices such as transformers and long overhead power lines also exhibit inrush when they are energised.

I live in a somewhat rural area and we got bit hard by this last winter.

Our road used to have a handful of houses on it but now has around 85 (a mix of smaller lots around an acre and larger farming parcels). Power infrastructure to our street hasn't been updated recently and it just barely keeps up.

We had a few days that didn't get above freezing (very unusual here). Power was out for about 6 hours after a limb fell on a line. The power company was actually pretty quick to fix it, but the power went out 3 more times in pretty quick succession.

Apparently a breaker kept blowing as every house regained power and all the various compressors surged on. The solution at the time was for them to jam in a larger breaker. I hope they came back pretty quickly to undo that "fix" but we still haven't had any infrastructure updates to increase capacity.

"The solution at the time was for them to jam in a larger breaker"

I've seen some cowboy sh!t in my time but jeez, that's rough.

That’s “it can’t keep tripping if I jam in a penny instead” level of engineering from the utility! Wow!

Good thing none of your houses burnt down.

It'd have likely been the equipment in the street. That said, in Winter, you can overload this a bit. After all the failure mode would be the wires getting so hot they begin to melt. If you know they're covered in ice, or are currently being rained on in near-freezing air temperatures, you can push more current than they'd be able to at 2pm on a hot summer's day.

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