Electric power

The physical size of power is energy per unit time and is referred to as electric power, if the energy delivered is related or electrical energy.

Sizes to power

Is actually converted electric power is the product of the electrical voltage and electrical current

Behaves the consumer as an ohmic resistance, one can also express the performance by

Are the magnitudes of voltage and current of the time dependent, and. Here are several performance criteria are to be distinguished:

  • Instantaneous value of the power or instantaneous power
  • Active power, the actual converted energy per time. It is expressed in watts ( symbol ' W).
  • Apparent power, also referred to as port value or connected load. It is measured in volt-amperes ( symbol 'VA ).
  • Reactive power, a generally undesirable and not useable energy per time. It is expressed in Var ( symbol 'var ).

If and sinusoidal alternating quantities are of the same frequency, then it is also sinusoidal, but with twice the frequency and a DC component. The variables are defined by averaging; for them there is no instantaneous values ​​.

The period duration or statistical operations a sufficiently long time ( mathematically strict: ) for periodic processes.

The apparent power is formed from the RMS values ​​and that these are the root mean square values ​​of voltage and current,

Apparent power is larger than the active power to consumers, the impressed voltage in the power at

  • A phase shift or
  • Distortion ( additional harmonics )

Cause. The difference is determined by the total reactive power


Sensing circuits and associated power meter are described in the active power and reactive power. Measuring instruments for apparent power are not common. However, there are multi-purpose transmitter which are also designed for this.

An effective value of the power does not exist according to the definition above. The " RMS power " is a formal size in audio technology, however, has nothing to do with the physical size " performance ".

Performance as a device identifier

To characterize the performance of a device ( electrical loads, power converter ), the rated power is used, which may differ significantly from the actual implementation performance. It is specified as an active power.

It is essential, what kind of performance is indicated on the nameplate. For engines the available mechanical power is given, for lamps, vacuum cleaners, or speakers, however, the absorbed power. For generators, like bicycle dynamos or alternators, the output electric power is specified.

Are difficult to interpret the performance data of audio amplifiers or speakers. In audio amplifiers which RMS power, music performance, RMS power or peak power ( PMPO ) is often given. The values ​​vary considerably, often have little practical relevance and usually prevent comparability.

In high-frequency or low-frequency speakers, the power refers often to the music performance of the entire frequency range - they endure these electric power never in continuous operation.