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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Because many electric clocks have a genius way to keep time: they have a little motor to run the hands (not the genius part) that’s run pretty much straight from the power. Power from the electric company is almost always alternating current; in the US and Canada it’s at 60 Hz. A motor connected to that AC will ‘pulse’ 60 times a seconds; that’s fast enough that they don’t look like pulses. But it means that when the electric company runs fast (like 61 Hz), the clock will go fast, and when the electric company runs slow (like 59 Hz), the clock will run slow.
It’s genius because the power company will actually count how many pulses they put out during the day and will go a little faster or slower to catch up. This keeps the clocks running very acurately.
Your PC, on the other hand, just has a chip inside that keeps track of time, with a correction from the internet. There’s a US agency (and others) that will provide accurate times and the PC clock will keep up.
I don’t know the deal with your Keurig. If it’s on Wi-Fi, that’s why it’s accurate? Or maybe the Keurig company uses a better clock chip to track time?
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.
Many cheap clocks use the 60Hz frequency of mains AC as their clock tick (every sixty peaks they increment the clock 1 second). It sounds like they had some problems over night that increased this frequency above 60 Hz. This means that those clocks dependent upon the stable frequency actually ticked fast so they would be ahead of an actual clock.
Many clocks use GPS signals, radio broadcast time signals (q.v. [WWVB](https://en.wikipedia.org/wiki/WWVB)), or have their own oscillators. These would not have been affected by AC frequency since they do not rely upon it to count time.
In addition to what the others said not all power grids worldwide maintain frequency accurately enough to run clocks so when you design a product expected to be sold worldwide like Keurig it’s better not to rely on the power grid. Your Keurig coffee maker has a crystal oscillator that generates signal at a known frequency. As for the PC, virtually all PCs since 80s have a battery powered clock chip with its own a crystal oscillator.
thank you everyone for your replies! the fact that household clocks are using the electrical current to measure time is news to me and I learned a lot!
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