What is an AC voltage source

Alternating current and alternating voltage

Tesla is the end-user of alternating current and three-phase current. Both quickly found global use. Without this discovery by Tesla, which made it possible to transmit electrical power over many hundreds of kilometers, there would be no such thing as a matter of course for electricity today, with its enormously versatile applications.

In the case of alternating current and alternating voltage, one speaks of electrical quantities that are specified in the units amperes (A) and volts (V), the values ​​of which repeat themselves regularly over time (t). Alternating current is an electrical current that periodically changes its polarity (direction) and value (current strength). The same applies to the alternating voltage.
There are several types of alternating current. Pure alternating quantities are the square wave voltage, the sawtooth voltage, the triangle voltage and the sinusoidal voltage (wave) or a mixture of all of these variants.
In electrical engineering, AC voltages with a sinusoidal curve are mainly used. The sinusoidal curve has the lowest losses and distortions. Therefore, the following descriptions of the alternating current and the alternating voltage are explained using the sinusoidal curve shape.
Alternating voltage is generated by generators in power plants. A red in the generator rotates 360 degrees. This creates a voltage with alternating polarity, i.e. a sinusoidal curve.
The most important alternating voltage is 230 volts from our power grid. It has a frequency of 50 Hz. That is 50 revolutions per second of a rotor in the generator.

Characteristic values ​​of the sinusoidal voltage

  • Instantaneous value and amplitude
  • Period and frequency

Instantaneous value and amplitude


Since an alternating voltage never has a constant voltage value, electrical alternating quantities whose time dependency is to be shown are referred to as instantaneous values ​​(instantaneous values). These instantaneous values ​​are indicated by a lower case letter (formula symbol).
Maximum or peak values ​​of the amplitude of sinusoidal, time-dependent alternating quantities are indicated by a roof over the symbol. Examples would be the voltage û (pronounced: u-roof) and the current î (pronounced: i-roof).
If the peak value is known, the instantaneous value can be calculated at any angle of rotation λ (= 0 ° ... 360 °).

Period and frequency


The positive and negative half-waves of an oscillation are called the period. The time required to run through the period is the period duration Τ. The period Τ is specified in seconds.
The frequency indicates the number of periods that are passed through in one second. The frequency is given in Hertz (Hz).
The frequency is the reciprocal of the period duration. This means that the shorter the period, the greater the frequency.



Characteristic values ​​of a sine curve

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