Schaffner Group
User and Installation Manual
Ecosine FS42842
37/43
23
Appendix I: International standards
The use of non-linear loads with six-pulse rectifiers has grown rapidly in recent years, to the point where
this type of load represents more than 50% of western world power system load. Harmonic currents and
the resulting voltage distortions can have devastating effects on power distribution systems and
connected equipment. Therefore, national and international standards for harmonic distortions (and
other Power Quality problems) are needed.
In the following, a brief overview of some important international standards/recommendations
are provided. For full details, please obtain the required standards directly from IEEE, IEC, and
other organizations.
23.1 Engineering recommendation G5/4-1 Definitions:
Non-linear load or equipment A load or equipment that draws a non-sinusoidal current when
energized by a sinusoidal voltage.
Aggregate load
Non-linear load equal to the sum of the individual non-linear equipment
ratings.
Fault level
A value expressed in MVA of the symmetrical short-circuit power at a
point in the supply system. It is defined as the product of the
symmetrical short-circuit current (I
sc
) and the nominal system voltage
(U
ph-ph
or U
ph-n
):
F
=
I
sc
U
ph
−
ph
3
=
I
sc
U
ph
−
n
3
Harmonic current (I
h
)
The RMS value of a harmonic current, of order
h
, expressed in
amperes.
Harmonic distortion
The cyclic departure of a waveform from the sinusoidal shape. This can
be described by the addition of one or more harmonics to the
fundamental.
Point of common coupling
(PCC)
The point in the public supply system, electrically nearest to a
customer’s installation, at which other customers’ loads are, or may be,
connected.
Total harmonic voltage
distortion (THD)
𝑻𝑯𝑫 =
√∑
𝑽
𝒉
𝟐
𝒉=𝟓𝟎
𝒉=𝟐
𝑽
𝟏
23.2 G5/4-1 planning levels for harmonic voltages:
