Utility frequency
The utility frequency (American English) or mains frequency (British English) is the frequency at which alternating current (AC) is transmitted from a power plant to the end user.
In most parts of the Americas, it is typically 60 Hz, and in most parts of the rest of the world it is typically 50 Hz. Precise details are shown in the list of countries with mains power plugs, voltages and frequencies.
Places that use the 50 Hz frequency tend to use 220/230 voltage, and those that use 60 Hz tend to use 110/120 V.
Other utility frequencies are used. The countries Germany, Austria, and Switzerland use a traction power network for railways, distributing single-phase AC at 16.7 Hz. A frequency of 25 Hz was used for the German railway Mariazeller Bahn and some railway systems in New York and Pennsylvania (Amtrak) in the USA.
History
Early alternating-current generating schemes did not need to standardize the frequency, since most of the load was incandescent lighting which worked well at any frequency. Frequencies as low as 16.7 Hz and up to around 133 Hz were produced by alternating current generators in early systems. The frequency was a consequence of the operating speed and design of the generators. It was not until the invention of induction motors that a standard frequency was found to be useful. Electrical generators can only be interconnected to operate in parallel if they are of the same frequency and wave-shape. By standardizing the frequency used, generators in a geographic area can be interconnected, providing reliability and cost savings.