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Power Quality Logger
Methods of Logging
35
Calculation of THD in Measuring Function P
THD – Measuring Function P
Function P does not measure harmonic values.
Voltages:
1
2
1
2
V
VV
THDV
RMS
−
=
V
RMS
: RMS value of total signal
V
1
: RMS value of the fundamental
Currents:
1
2
1
2
I
II
THDI
RMS
−
=
I
RMS
: RMS value of the total signal.
I
1
: RMS value of the fundamental.
Note
THDI for currents < 5% of IE (measuring range) can have additional
uncertainties, or can be suppressed.
Harmonics up to 50th order are taken into account.
Flicker
Flicker is the visual impression of unsteadiness in a light source whose
luminance or spectral distribution changes over time. Flicker is logged in
accordance with the IEC 61000-4-15 standard. The short-term (st) flicker Pst
t
is logged over a default standard interval of 10 minutes, and is used to
calculate the long-term (lt) flicker Plt (by taking the sliding average of 12
short-term values). The interval value can be changed as needed in PQ Log.