“These strains on the power grid actually cause shifts in the alternating current frequency. The power grid operates at a precise frequency (e.g., 60 Hz in North America). A deviation can be damaging to equipment like TVs, stereos, microwaves, stove electronics, dishwasher electronics, and life support equipment.”
The North American grids do indeed run at a carefully regulated 60 Hz frequency, but the reason that it’s so important is a bit subtle. (See below.)
First of all, devices that merely generate heat, including old-style incandescent light bulbs, don’t care about the frequency, but only the approximate voltage. (Don’t plug a 120 V device into a 240 v outlet!)
Lot’s of modern electronics doesn’t much care about the frequency either, as it’s converted from AC to DC internally to drive the actual functional devices. Some older electronics, with vacuum tubes, may use transformers for the conversion to generate higher voltages often needed by the tubes, but the transformers aren’t very sensitive to the precise frequency.
In general, there are lots of electrically powered devices that work at either 60 Hz (North America) or 50 Hz (Europe etc.). Many of those also work nicely in the 120-240 Volt range. But check the specs (e.g. the label) carefully!
Electric motors can be quite sensitive to the frequency depending on their exact design: their speed may be determined by the frequency. A 60 Hz motor with a 50 Hz supply might well run at 5/6 speed — and vice versa. For some applications this might not matter much. But in other cases it might matter a lot. It could even result in overheating the motor itself. Again, check the specs.
I won’t venture an opinion about life support equipment, but I think that recent versions of the other items mentioned in the quote at the top don’t much care about the *exact* frequency of their electric supply.
The REAL reason that power companies worry about the exact frequency of the electricity is is that the electric “grid”, as a whole, does not receive its electricity from just *one* generator. If it did, it wouldn’t matter that much (to most users) if it was 59.9 Hz or 61.1 Hz.
Rather, the whole point of the grid is that there are multiple generators supplying electricity to the grid, and if they are not supplying AC at almost exactly the same frequency, all hell can break loose.
In detail, AC electricity is described by a “sine wave” which goes up and down above zero and below zero on a periodic basis. If the two generators aren’t in sync (”in phase”) then they are fighting each other, the worst case being 180 degrees out of sync. In that case no net power is delivered to the user, it’s sort of a “short circuit”, and the generators get destroyed (or at least severely damaged).
So when a generator is brought “on line” to the grid, it has to be synchronized (and phased) to the running grid before being connected. This can be done by adjusting its speed a bit via the turbine speed, for example.)
Now when you have a grid, the load at different parts of the grid will be different. These loads will be shared by the generators supplying the grid, but since the grid is made out of real wires (typically aluminum) which have resistance, the load will not be shared equally. Instead will depend on distances to the generators (among other things). This can mean that the nearer generator is supplying much of the load. If that generator is being overloaded, it will slow down. If it slows down, the frequency of the AC it produces will decrease. This can lead to trouble, or even disaster.
The reason is that if you have two different AC sources at different frequencies they cannot REMAIN in sync. (Visualize the sine waves.) What happens is that power starts flowing from one to the other, which, depending on the exact situation may stabilize things (if the other slows down?) or may run away, causing damage. To avoid such damage, monitoring mechanisms are typically set up to automatically disconnect the too-slow generator from the grid. Of course this can propagate, if other generators then become overloaded due to the capacity loss. But it’s better than a whole bunch of destroyed generators.
This is the main reason why the frequency of AC is carefully monitored and regulated.
P.S. Even the Northeast Blackout of Aug 2003, that affected 55 million people, took only 2 hours to 4 days to recover from. Although 256 power plants went offline, if there had been severe damage, it would have taken many months to repair. (And probably resulted in far more deaths than the almost 100 who did die.)
You gave a well explained understanding of AC current. Thanks!