What does AC Mean?

Alternating current (abbreviated AC according to abbreviationfinder) is called the electric current in which the magnitude and direction vary cyclically. The most commonly used alternating current waveform is that of a sinusoidal wave (figure), since a more efficient transmission of energy is achieved.

Other periodic wave forms, such as triangular or square, are used in certain applications. Used generically, AC refers to the way in which Electricity reaches homes and businesses. However, Audio and Radio signals transmitted by electrical cables are also examples of alternating current. In these uses, the most important purpose is usually the transmission and retrieval of the encoded (or modulated) information on the AC signal.


In the year 1882 the physicist, mathematician, inventor and engineer Nikola Tesla designed and built the first AC induction motor. Later, in 1885, the physicist William Stanley reused the principle of induction to transfer AC power between two electrically isolated circuits. The central idea was to wind a pair of coils on a common iron base, called an induction coil. In this way, what would be the precursor of the current Transformer was obtained.

The system used today was fundamentally devised by Nikola Tesla; alternating current distribution was commercialized by George Westinghouse. Others who contributed to the development and improvement of this system were Lucien Gaulard, John Gibbs and Oliver Shallenger between the years 1881 and 1889. Alternating current overcame the limitations that appeared when using Direct Current (DC), which is an inefficient system for large-scale energy distribution due to problems in power transmission, marketed aggressively by Thomas Edison in its day..

The first interurban transmission of alternating current occurred in 1891, near Telluride, Colorado, which was followed a few months later by another in Germany. Despite the noted advantages of AC over DC, Thomas Edison continued to strongly advocate the use of direct current, for which he held numerous patents.

In fact, he strongly attacked Nikola Tesla and George Westinghouse, promoters of alternating current, despite which it ended up being imposed. Thus, using alternating current, Charles Proteus Steinmetz, of General Electric, was able to solve many of the problems associated with the production and transmission of electricity, which finally caused the defeat of Edison in the battle of the currents, being his winner George Westinghouse, and to a lesser extent, Nikola Tesla.

Characteristics of alternating current

Alternating current has a series of particular characteristics that distinguish them from each other. The main ones are:

  1. a) the waveform
  2. b) the amplitude
  3. c) the frequency
  4. d) the phase(when there are two or more alternating currents superimposed on the same circuit, as is the typical case of the three-phase current of the public service)

Alternating vs. Direct Current

The reason for the wide use of alternating current is determined by its ease of transformation, a quality that direct current lacks. In the case of direct current, the voltage increase is achieved by connecting dynamos in series, which is not very practical, on the contrary, in alternating current there is a device: the transformer, which allows the voltage to be raised efficiently.

The electrical energy is given by the product of the Voltage, the Intensity and the time. Given that the section of the conductors of the electric energy transport lines depends on the Intensity, we can, by means of a Transformer, raise the Voltage to high values ​​(High tension), reducing the Current Intensity in the same proportion. With this, the same energy can be distributed over long distances with low current intensities and, therefore, with low losses due to the Joule Effect and other effects associated with the passage of current such as Hysteresis or Foucault Currents..

Once at the point of consumption or nearby, the voltage can be reduced again for industrial or domestic use in a comfortable and safe way.

Triphasic current

The three-phase generation of electrical energy is the most common form and the one that provides the most efficient use of the conductors. The use of three-phase electricity is common, mostly for use in industries where many of the machines work with motors for this voltage. The three-phase current is made up of a set of three wave forms, one out of phase with respect to the other by 120 degrees, according to the diagram shown in the figure.

Three-phase currents are generated by alternators with three coils or groups of coils, wound on three systems of equidistant pole pieces. The return of each of these circuits or phases is coupled at a point, called neutral, where the sum of the three currents, if the system is balanced, is zero, with which the transport can be carried out using only three cables.

This arrangement would be the so-called star connection, and there is also a triangle or delta connection in which the coils are coupled according to this geometric figure and the line wires start from the vertices.

Alternating current