Electricity
Electric current

Alternating Current

Alternating Current

Alternating current (AC) is a type of electric current that is characterized by changing over time, either in intensity or direction, at regular intervals.

The voltage varies between the maximum and minimum values cyclically, the value of the voltage is positive half the time (half positive cycle or half positive period) and negative the other half. This means that half the time the current flows in one direction, the other half in the other direction. The most common form of undulation follows a sine-type trigonometric function, since it is the most efficient and practical way to produce electrical energy by means of alternators. However, there are certain applications in which other waveforms are used, such as square wave or triangular wave.

In general, the electric current is distributed as alternating current at 50 Hz (50 changes per second).

It is usual for photovoltaic solar energy installations to use a converter from direct current to alternating current so that the generated energy can be supplied to the grid.

Alternating current electricity distribution

In Europe, electricity is distributed in the form of sinusoidal alternating current at a constant frequency of 50 Hz.

The use of alternating current is consecuéncia of the following reasons:

  • Transportation (especially long distances) of high electrical powers is very efficient if carried out at high voltages, the latter being quite easily achieved with the use of transformers.
  • Alternators are constructively simpler and more efficient than dynamos.
  • In direct current it is not possible to exploit the advantages of a three-phase system. Almost all consumer electronic devices operate in direct current, but this can be achieved by means of alternating current by means of a simple rectifier.

On the other hand, it is possible to obtain alternating electric current from the direct current, generated in appropriate parameters of frequency, waveform and voltage by means of devices called inverters.

History of alternating current

In the industrial origins of the use of electricity in the nineteenth century was used direct current, which offers the advantage of being able to be stored in batteries, but with the arrival of alternating current by the scientist Nikola Tesla the world was revolutionized again. The efficiency of this new type of current allows drastically reducing energy losses over long distances thanks to the increase in electrical voltage. This feature allowed the high-voltage electric power transmission and the current dissipation losses drastically reducing low in the line and then the thickness of the conductor used for transport, compared to the Edison direct current.

The alternating current was extended thanks to the use of the transformer, which makes it possible to carry the potential difference (voltage) to very high levels (high voltage) and correspondingly the current to very low values, thus maintaining the power unaltered and then transmitting it to large distances and small losses, achieving considerable economies of scale.

In addition, alternating current electric motors are more reliable and efficient than direct current electric motors.

Currently in the world, alternating electric power is distributed in two frequencies, 50 Hz (Europe, Asia, Africa) and 60 Hz (America, part of Japan) and different voltages (see electrical standards in the world).

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Last review: May 9, 2018

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