They also vary the line frequency so that  in any 24 hour period there
are as close to 5184000 cycles as they can get (in the US on 60Hz AC
lines).  This is for the many clocks that still base their time on the
frequency of the line, and that loading during the day changes the
frequency slightly.

I suppose the matter is more complex than that, since they have to
synchronize the AC on many grids, but it's easier to adjust the
frequency when the load is lighter.

-Adam

Jim wrote:

>Rex wrote:
>
>     "Take note of your regrigerator at 2 in the
>      morning.  I will probably indicate that
>      your freq increases markedly in the wee
>      hours if you are on a bulb blower line."
>
>That means *most* of us in the US would see this - as
>we are all (*) tied to the same 'grid'.
>
>I suspect it that it seems to be running faster because of
>the higher line voltage at that time of night.
>
>
>(*) There are a few exceptions, such as Texas - who once upon a
>time was on it's own isolated grid and I think still is even
>now.
>
>Jim
>
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