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EE - Voltage and frequency

 Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in which electric power is delivered to businesses and residences, and it is the form of electrical energy that consumers typically use when they plug kitchen appliances, televisions, fans and electric lamps into a wall socket. The usual waveform of alternating current in most electric power circuits is a sine wave, whose positive half-period corresponds with positive direction of the current and vice versa.

The standard voltage and frequency of alternating current (AC) electricity used in homes varies from country to country throughout the world. Typically, either 120-volt AC or 240-volt AC is used. Also, most countries use 50Hz (50 Hertz or 50 cycles per second) as the AC frequency. Only a handful use 60Hz.



The type of electricity delivered to homes and businesses was initially direct current (DC) but then changed to alternating current (AC) electricity. AC frequencies varied considerably, according to equipment used. For example, electric generators at Niagara Falls put out 25Hz power.

Early in the history of electricity, Thomas Edison`s General Electric Company was distributing DC electricity at 110 volts in the United States.

Then Nikola Tesla devised a system of three phase AC electricity at 240 volts. Three-phase meant that three alternating currents 120° out of phase were combined in order to even out the great variations in voltage occurring in AC electricity. He had calculated that 60 cycles per second or 60Hz was the most effective frequency. Tesla later compromised to reduce the voltage to 120 volts for safety reasons.

With the backing of the Westinghouse Company, Tesla`s AC system became the standard in the United States. Westinghouse chose 60 Hz because the arc light carbons that were popular at that time worked better at 60 Hz than at 50 Hz.

Meanwhile, the German company AEG started generating electricity and became a virtual monopoly in Europe. They decided to use 50Hz instead of 60Hz to better fit their metric standards, but they stayed with 120V.

Europe stayed at 120V AC until the 1950s, just after World War II. They then switched over to 230V for better efficiency in electric transmission.

The United States also considered converting to 220V for home use but felt it would be too costly, due to all the 120V electric appliances people had. A compromise was made in the U.S. in that 240V would come into the house where it would be split to 120V to power most appliances.

Certain household appliances such as the electric stove and electric clothes dryer would be powered at 240V. The same is true in Canada.

For various reasons, Brazil and Japan have multiple standards.

In Brazil, most states use between 110V and 127V AC electricity. But many hotels use 220V. In the capital Brasilia and in the northeast of the country, they mainly use 220-240V. All operate at 60 Hz.

In Japan, they use the same voltage everywhere, but the frequency differs from region to region.

Eastern Japan, which includes Tokyo, uses 50Hz. In 1895, Japan purchased 50 Hz electric generators for Tokyo from the German company AEG. This was the same as what was done in Europe. In 1896, the American company General Electric provided 60Hz generators to cities in western Japan, which includes Osaka and Kyoto. It is unfortunate that they did not coordinate their efforts. Having different voltages and frequencies within the country not only must be confusing for the people but also can result in extra costs for appliances and adapters.