Schaffner Group
User and Installation Manual
Ecosine FS42842
39/43
I. International standard EN 61000-3-12
This standard applies to equipment intended to be connected to low-voltage systems interfacing with the
public supply at the low-voltage level. It does not apply to equipment intended to be connected only to
private low-voltage systems interfacing with the public supply only at the medium- or high-voltage level.
23.4 Definitions
Total harmonic distortion
(THD)
Ratio of the r.m.s. value of the harmonics (harmonic currents
I
n
of the
order n) to the r.m.s. value of the fundamental:
Partial weighted harmonic
distortion (PWHD)
Ratio of the r.m.s. value of a selected group of higher order harmonics
(in this International Standard beginning from the fourteenth harmonic),
weighted with the harmonic order
n
, to the r.m.s. value of the
fundamental:
Reference fundamental
current (I
1
)
r.m.s. value of the fundamental component of the rated line current
I
equ
of the equipment. The reference fundamental current
I
1
, shall be either
measured, or calculated as follows:
Total harmonic current
(THC)
The total r.m.s. value of the harmonic current components of orders 2 to
40:
Point of common coupling
(PCC)
The point in the public system which is closest to the customer
concerned, and to which other customers are, or may be, connected.
Short circuit power (S
sc
)
Value of the three-phase short-circuit power calculated from the nominal
interphase system voltage
U
nominal
and the line impedance
Z
of the
system at the PCC:
where
Z
is the system impedance at the power frequency.
Rated apparent power of the
equipment (S
equ
)
Value calculated from the rated line current
I
equ
of the piece of
equipment stated by:
Short circuit ratio (R
sce
)
Characteristic value of a piece of equipment defined as follows: