User manual
PQM-702, PQM-703 Operating Manual
72
In four-wire systems:
where I
a
, I
b
, I
c
are RMS currents for individual phases (line or phase), I
n
is the RMS current in
neutral conductor, U
a
, U
b
, U
c
are RMS phase-to-neutral voltages, and U
ab
, U
bc
, U
ca
are RMS phase-
to-phase voltages.
S
e
calculated in this manner includes both the power losses in the neutral conductor (in four-
wire networks) and the effect of unbalance.
5.3.6 Distortion power D
B
and effective apparent power S
eN
During the discussion on reactive power, it was mentioned that the distortion power according
to Budeanu cannot be used for large distortions of voltage and current and for the unbalance of
three-phase systems (a paradox of distortion power which is not a measure of actual distortion).
However, this power is often used by energy quality specialists and manufacturers of systems for
reactive power compensation.
It must be clearly said that this parameter has given relatively good results only in conditions of
slight distortion of voltage and current waveforms.
IEEE 1459-2000 standard lists this definition of power, however just like in case of Budeanu
reactive power, it has a non-removable defect and it is recommended to discard it entirely. Instead
of D
B
, another value was proposed to reflect total distortion power in a system in a better way – it is
called non-fundamental apparent power S
eN
. S
eN
power allows a quick estimation whether a load
works in conditions of small or large harmonic distortion; it is also a basis for estimating the static
values and active filters or compensators.
According to the definition (for 3-phase systems):
where:
Effective current and RMS voltage of the fundamental component (I
e1
and U
e1
respectively) are
calculated similarly to I
e
and U
e
but instead of RMS phase-to-neutral or phase-to-phase voltages,
the effective voltages of fundamental components are substituted.
In single-phase systems to calculate the distortion apparent power, a simpler formula may be
used:
where U
1
and I
1
are effective values of the fundamental components of phase-to-neutral voltage
and current.