Siemens 9810 Series, User Manual, Page: 146 / 218

Power quality
For a pure sinusoidal waveform, crest factor is equal to 1.414. The meter uses the
following equation to calculate crest factor:
C =
V
peak
V
RMS
C = Crest factor
V
peak
= Voltage peak
V
RMS
= Voltage RMS
Current crest factor
Crest factor is the ratio of peak to RMS current values.
For a pure sinusoidal waveform, crest factor is equal to 1.414. The meter uses the
following equation to calculate crest factor:
C
I
peak
I
RMS
= -------------
C = Crest factor
I
peak
= Current peak
I
RMS
= Current RMS
K-factor
K-factor relates the heating effect of a distorted current in a transformer to a
sinusoidal current with the same RMS magnitude — it describes a transformer’s
ability to serve non-linear loads without exceeding rated temperature rise limits.
The K-factor is equal to the sum of the squares of the harmonic currents multiplied
by the squares of the harmonic order. The meter uses the following equation to
calculate K-factor:
K =
h
(Ih x h )
2 2
n = 1
h
Ih
2
n = 1
∑
∑
Where
K
is the K-factor,
h
is the harmonic order and
Ih
is the true RMS current of
harmonic order
h
.
Harmonic content calculations
Harmonic content (H
C
) is equal to the RMS value of all the non-fundamental
harmonic components in one phase of the power system.
The meter uses the following equation to calculate H
C
:
HC = (H
2
)
2
+ (H
3
)
2
+ (H
4
)
2
...
THD% calculations
THD% is a quick measure of the total distortion present in a waveform and is the
ratio of harmonic content (H
C
) to the fundamental harmonic (H
1
).
By default, the meter uses the following equation to calculate THD%:
THD
H
C
H
1
-------- 100% =
x
146 7EN05-0390-00