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apparent power (S)

If a power consists of an active component and a reactive component, it is referred to as apparent power. The active part, the active power or effective power is the power converted in the consumer, the reactive power, on the other hand, is the power transferred to a reactance, an inductance or capacitance. Both powers are at an angle of 90 degrees to each other in the power vector diagram and form the apparent power as a geometric addition. All three power parameters are related to each other via the power factor.

The apparent power is given in volt-amperes( VA) and indicates how much voltage is applied to a consumer and how much current flows into it. It is critical to the design and loading of high and low voltage power systems, transformers, lines and switchgear.

Relationships between active, apparent and reactive power

Relationships between active, apparent and reactive power

In apparent power, there is a phase shift between the current flowing into the load and the voltage applied to it, which can be determined from the resistive component and that of the reactance. It can assume the two extremes of zero degrees and ninety degrees. At zero degrees phase shift, the current is in phase with the voltage, which means that it is a pure ohmic resistance and therefore an active power, at ninety degrees phase shift between current and voltage it is a pure reactance and therefore a reactive power. All values in between are to be attributed to apparent power.

Power vector diagram with active, reactive and apparent power

Power vector diagram with active, reactive and apparent power

Examples of apparent power are the power of highly inductive or capacitive loads such as AC motors or loudspeakers.

Informations:
Englisch: apparent power - S
Updated at: 28.04.2009
#Words: 271
Links: power (P), active, reactive power (Q), reactance, vector
Translations: DE
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