harry wrote:

Better to work the system on voltage fluctuations than frequency.
If the voltage drops, reduce the load by what ever means you decide
on. When it rises the cut off loads can be reconnected.
Much easier.

Yes, but much less effective.

There are a *lot* of places in this Country where voltage varies wildly
even under normal load conditions, and there are a *lot* of automatic
tap changers in substations and at the top of poles which try to
maintain the correct voltage. These would all have to be either adjusted
or overridden to do what you suggest. On the other hand, the frequency
is generally stable except under conditions of grid overload, and a
frequency drop is easily detected with very few false alarms.

If you plot mains frequency against time with enough resolution, you can
actually work out when popular TV programmes end by the frequency dip as
millions of kettles are turned on. You'd be hard pushed to do the same
by checking the Grid voltages.


--
Tciao for Now!

John.