What does the Hz/CPS of the AC electricity have to do with balancing demand/supply on the power grid?,(reply>), @jigpu Power generation equipment is governed to maintain the frequency. If a device shifts out of synchronisation with the grid you have an effect called pole slip. Run a search on pole slip. Lots of "interesting" pictures to be seen. I had two big diesel generators pole slip on me some years ago. Fortunately the protection system was fast enough to prevent damage. When I say big they were driven by 60 Litre V16 engines.,(reply>), I wonder how many devices are still in use that are dependent on mains frequency reference...like some old AC clocks?,(reply>), Actually it is connected. If the demand is lower than supply, the generators are not so loaded and start to increase RPM slightly, which in turn makes higher frequency of the output voltage. If the demand is higher than supply, the generators are slightly overloaded and slow down slightly, again lowering the frequency.,(reply>), +Stephen Tack Not a lot. I think it was inserted as an educational thing.,(reply>), @Pavel Sovička   And I guess it makes sense that an AC generator would stay phase locked. Thanks.﻿