Deformed power

The distortion power is a term used in electrical engineering and describes a specific form of reactive power, which is caused in two-way or three-phase systems by non-linear loads. In addition to the standard term used here are used in the literature as an alternative before the terms distortion power, harmonic reactive power or harmonics reactive power.

General

Power supply networks are almost always operated with a sinusoidal AC voltage. Therefore, in linear electrical components such as resistors or ohmic called reactances of the power also has a sinusoidal shape. Are current and voltage sinusoidal, there occurs no distortion power. This can only be more and if a non-sinusoidal current or a non-sinusoidal voltage are available. Electrical loads that produce distortion power can most of a sinusoidal voltage (indicated by the grid provided ) and a distorted current can be assumed.

The cause of the non-sinusoidal current and the distortion power are non-linear electrical components such as rectifiers in power supplies, inverters or magnetic components, show the magnetic saturation phenomena. These components cause distortion to non-sinusoidal alternating currents. The course of which may be represented by a Fourier series as a sum of the fundamental and harmonics. These harmonics of the current in combination with the sinusoidal supply voltage result in a fraction of the total reactive power.

The harmonics occur are almost always undesirable because they stress the network and can not do any work on the consumer. Also they are often the cause of electromagnetic interference. By the use of power factor correction filters the harmonic content can be reduced.

In addition to the distortion power shift reactive power can occur.

Calculation

Context of the various performance specifications

The real power is the power that is provided at a consumer is able to perform work, such as a rotational movement to a torque on the electric motor or the increase in temperature of an electric heater. Active power results in harmonic systems subject to only harmonic components of current and voltage that are proportional to each other. If the voltage does not have harmonic components, wear harmonics total of active power at nothing (see also under active current ).

Only the fundamental frequency of the current generated so with the ( fundamental of ) voltage active power and reactive power shift if necessary. Then occurs when the two oscillations are displaced in phase. The fundamental apparent power is the Pythagorean sum of active power and reactive power shift:

For apparent power comes as a third component to the distortion power of the harmonics. If the RMS value of the voltage, the rms value of the fundamental current, and so on are the rms values ​​of the harmonic currents, so the total current and the reactive current distortion can be as

Express and the distortion power as

The total reactive power - not explicitly shown in the figure - is derived from the shift of the reactive power and distortion power to

The total apparent power is given in the general case by

The figure shows the phasor diagram is shown with the pointers for the various services.

The sizes are measured, see RMS measurement, measurement of active power, reactive power measurement.

Related to the distortion

The harmonic content and harmonic content of a affected by harmonics size is a measure of the distortion and the amount of distortion reactive power in electrical systems. The THD is the ratio of the Pythagorean sum of the rms values ​​of the harmonic spectrum for the Pythagorean sum of the rms values ​​of the total spectrum including the basic oscillating component. The distortion power can be combined with the harmonic distortion

And the apparent power expressed by

As an alternative to the harmonic content of the fundamental content is sometimes called. Numerical data of this size are often not very helpful, as for example, the range = 0 ... 14% of the fundamental frequency content through the range 100 ... 99% is covered in view of the amount of distortion reactive power.

Examples

• For linear reactances as ideal capacitors or inductors occurs no distortion reactive power, but only the displacement power factor.
• If one switches to a resistive load resistance, such as a hot plate, a diode in series, the source of a sinusoidal alternating voltage can be taken in addition to a fundamental current and direct current and harmonic currents. At the source occurs in addition to the active power to reactive power and distortion. Quantitative conclusions due to the distortion factor are not possible because of the DC component in the apparent power.

• For the distortion power when using a dimmer, see also under apparent power.

Harmonic components at different loads

Different consumers and their harmonic distribution are listed without filtering when operated on sinusoidal alternating voltage in the following table. The harmonic currents are given relative to the fundamental component of the current. The harmonic components, the higher the current the higher the distortion power of the concerned consumer: It generally applies.

Effects

Especially in the consumer goods sector, it has come in recent years to an increase of consumers who have a grid side rectifier and thus produce distortion power. These include, for example, Energy saving lamps and power supplies for computers, chargers for batteries, monitors, TV sets, etc. remedy a power factor correction (PFC ), usually implemented as so-called active power factor correction filter.

Because the distortion power should be transmitted by the network, there is a greater load on the electrical supply system and disorders such as flicker. In contrast to the currents of the fundamental frequency, the currents of the divisible by three harmonics in the neutral conductor of a three- phase AC network do not cancel, but add up. This concerns in the conventional European power supply frequency of 50 Hz, in particular the third harmonic at 150 Hz, and the ninth harmonic at 450 Hz Thus, it may, especially when the neutral conductor is constructed with a significantly smaller cross -section than the external conductor, at an impermissibly high current load Neutral come.

The limits of the harmonic levels in percent relative to the nominal voltage in public low -voltage systems (230 V between phase and neutral) and in the medium-voltage network ( between any two phase conductors with 10 kV and 20 kV) are set to: