41/62 Device handbook SINEAX AM2000, 173 849, 04/2015
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.
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
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. 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.
