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Reactive power
Most of the loads consume a combination of ohmic and inductive current from the power system. Reactive
power arises by means of the inductive load. But the number of non-linear loads, such as RPM regulated
drives, rectifiers, thyristor-controlled systems or fluorescent lamps, is increasing. They cause non-
sinusoidal AC currents, which may be represented as a sum of harmonics. Thus, the reactive power to
transmit increases and leads to higher transmission losses und higher energy costs. This part of the
reactive power is called distortion reactive power.
Normally reactive power is unwanted, because there is no usable active component in it. Because the
transmission of reactive power over long distances is uneconomic, it makes sense to install compensation
systems close to the consumers. So, transmission capacities may be used better and losses and voltage
drops by means of harmonic currents can be avoided.
The reactive power may be divided in a fundamental and a distortion component. Only the fundamental
reactive power may be compensated directly by means of the classical capacitive method. The distortion
components have to be combated using inductors or active harmonic conditioners.
The load factor PF is the relation between active power P and apparent power S, including all possibly
existing harmonic parts. This factor is often called cosφ, which is only partly correct. The PF corresponds
to the cosφ only if there is no harmonic content present in the system. So, the cosφ represents the
relation between the active power P and the fundamental apparent power S(H1).
The tanφ is often used as a target quantity for the capacitive reactive power compensation. It
corresponds to the relation of the fundamental reactive power Q(H1) and the active power P.
Power factors
The power factor PF gives the relation
between active and apparent power. If
there are no harmonics present in the
system, it corresponds to the cosφ or
displacement power factor. The PF has a
range of -1...0...+1, where the sign gives
the direction of energy flow.
The load factor LF is a quantity derived
from the PF, which allows making a
statement about the load type. Only this
way it's possible to measure a range like
0.5 capacitive ... 1 ... 0.5 inductive in a
non-ambiguous way.
The reactive power factor QF gives the
relation between reactive and apparent
power.
P10 Rev A
Example from the perspective of an energy consumer
Device handbook LINAX PQ3000-PQ5000
P:
Active power
S:
Apparent power including harmonic
components
S1:
Fundamental apparent power
Q:
Total reactive power
Q(H1): Fundamental reactive power
D:
Distortion reactive power
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