Electronic – mains frequency accuracy worldwide


I like to build a device that needs long term time stability. In germany, one of the best simple clocks use the mains power frequency to obtain a time measure. While the frequency is allowed to change a little with the power net load, the errors are nullified over longer periods, usually over night. So in the long term, a mains driven clock is actually atomic clock driven and very precise.

This applies to the whole european power network I guess.

So I wonder how about other countrys worldwide? Would it be feasable to use mains frequency for timing issues after adjusting to a country's official frequency?

Best Answer

In Australia, the interconnected grid frequency is held to a nominal frequency of 50 Hz, to be within ± 0.15 Hz 99% of the time. The accumulated time error may not be more than five seconds.

Excerpt from the AEMO Frequency Report Reference Guide:

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The various Australian power utilities do a pretty good job of maintaining the target frequency and accumulated time error within the stated limits. AEMO publishes reports on this monthly - for the month of June 2013 the accumulated time error in Queensland varied between + 2.40 and -3.77 seconds.

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From this, we can conclude that the 50 Hz power system frequency is an OK clock signal - but only so long as your time-keeping device has uninterrupted access to the power grid!

Here is a list of conditions that may cause you to lose your mains power, and therefore your time reference:

  • Someone turns off the mains power switch to your device
  • A circuit breaker trips in your house
  • The power goes out on your street
  • A transient fault occurs on the distribution network - enough to result in a brief 200ms auto-reclosing cycle
  • A major fault occurs on the transmission network - the grid goes black in your area

You would almost certainly be better off finding some other way to keep time. A GPS time receiver (ref. "IRIG B") is common in applications where precise time keeping is required, such as power systems protection relaying.