The utility electric power signal is periodic or not? Our nationalgrid frequency is 50 hz and in some other places in world, it is 60 hz

If I observe this signal on oscilloscope, will I get an exact repeating pattern ??

  • $\begingroup$ I’m voting to close this question because it doesn't belong anywhere. $\endgroup$ Mar 17 at 17:51
  • $\begingroup$ 60Hz m ean 60 cyles er sec, so it is periodic. In periodic signal we look for frequencies. In oscilloscoe we will see reoeating patteren. $\endgroup$
    – Creator
    Mar 17 at 17:53

2 Answers 2


will I get an exact repeating pattern ??

No. You will get a repeating pattern but it's not exact. No physical signal can be "exactly" periodic. There will always be some amount of noise, frequency drift, amplitude drift, harmonics, etc.

In case of AC power some of this is intentional: power plants adjust amplitude and frequency by small amounts to match power generation and consumption.

This being said, for many applications its perfectly fine to assume the signal to be periodic. The deviations from being "ideally" periodic are often small enough that they can be neglected.


A fundamental of engineering practice is that you look for some way of taking the messy real world, and describing it in terms that are easy to solve mathematically.

Is utility electric power -- or any other physical signal, electrical or otherwise, designed by man -- strictly periodic?

No, no it is not.

Is utility electric power close enough to being strictly periodic that you can pretend that it is, and use that periodicity to solve problems?

Yes it is -- sometimes.

Typical utility power deviates from perfect periodicity several ways. Here's the ones that rise to the top of my mental list:

  1. The amplitude and harmonic content can vary depending -- mostly -- on the load. This can be slow variation, or it can be rapid as equipment is switched on and off.
  2. The frequency can vary. This is due to a complex interaction between the load, the generation equipment, and the way that the generation equipment is controlled.
  3. Loads can introduce unpredictable transients, such as 'spikes' in voltage. These happen when loads are switched in or out; they can also happen synchronously with the voltage waveform because of rectifiers or SCRs in the loads.

So, it's periodic -- kinda. You can treat it as periodic -- sometimes. You can treat it as periodic, with deviations from perfect periodicity treated separately -- sometimes. It's exceedingly rare that you'd have to throw the assumption of periodicity out the window, and just treat it as a random signal.

  • 1
    $\begingroup$ I will add to this that major public power grids are monitored and adjusted for long-term frequency accuracy. There have been cases where a power grid has "gotten behind" regarding the grid frequency due to load or other disturbance. This is measured and "made up," later by running slightly fast for some time. This maintains long-term grid frequency accuracy. $\endgroup$
    – gschro
    Mar 17 at 22:09

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