Today our hydro power company released a statement: “We’ve heard from many customers asking why clocks skipped a few minutes this morning. This was due to our system balancing to match customer demand following a period of high frequency overnight. We want to reassure this wasn’t a result of system/equipment related issues.”
When I checked around the house my alarm , microwave and oven clocks were all 8-10 minutes ahead but my PC and Keurig coffee maker were fine. How can this system balancing change what time some clocks are displaying and why does it only affect certain devices?
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There is a secret way to keep track of time when you’re plugged into the wall: count the alternating current’s cycles. If you’re in North America, the power at your outlet bounces back and forth between somewhere around -170 volts and +170 volts 60 times per second. That is, you’ll measure the +170 volt peak 60 times in a second. (or the negative peak if you want). In other parts of the world it’s 50 Hz and the voltage may be higher.
This makes for a cheap way to measure time without needing a calibrated clock inside the appliance. Count the cycles instead.
Of course, one quirk of the power grid is that it’s not exactly 60 Hz. The reason it’s 60 Hz is that the generators at the power company spin at 3600 rpm, as close to exactly as possible, but when load goes up and down the rotation speed can slow down or speed up. The goal is balance and the power company is known to intentionally adjust the speeds to make up for known slacks throughout the day because they know appliances do this timing thing.
The power company is acknowledging they did some work to their equipment, and it was spinning faster than usual for a longer time than usual. So clocks that count the rotations of the generators as a timing source have been screwed up as a result. Deal.
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