Siemens DTU3005-B Especificaciones descargar pdf (Pagina 30)

Reactive Power Power in an AC circuit is made up of three parts; true power,

reactive power, and apparent power. We have already discussed

true power. Reactive power is measured in volt-amps reactive

(VAR). Reactive power represents the energy alternately stored

and returned to the system by capacitors and/or inductors.

Although reactive power does not produce useful work, it still

needs to be generated and distributed to provide sufficient true

power to enable electrical processes to run.

Apparent Power Not all power in an AC circuit is reactive. We know that reactive

power does not produce work; however, when a motor rotates

work is produced. Inductive loads, such as motors, have some

amount of resistance. Apparent power represents a load which

includes reactive power (inductance) and true power

(resistance). Apparent power is the vector sum of true power,

which represents a purely resistive load, and reactive power,

which represents a purely reactive load. A vector diagram can

be used to show this relationship. The unit of measurement for

apparent power is volt amps (VA). Larger values can be stated in

kilovolt amps (kVA) or megavolt amps (MVA).

Power Factor Power factor (PF) is the ratio of true power (PT) to apparent

power (PA), or a measurement of how much power is

consumed and how much power is returned to the source.

Power factor is equal to the cosine of the angle theta in the

above diagram. Power factor can be calculated with the

following formulas.

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Siemens DTU3005-B Especificaciones Pagina 30