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Operation
Methods of Measurement/Formulas 3
3-19
Harmonics and Interharmonics Parameters
Voltage and Current Harmonics and Interharmonics
Voltage and current harmonics are calculated based on a 10/12 cycle (200ms) averaging
interval. This interval contains exactly 2048 sample values. From these samples 1024
FFT bins (5Hz) are calculated.
The harmonics are then calculated using a gapless harmonic subgroup assessment.
The interharmonics are calculated using a gapless interharmonic centered subgroup
assessment.
Harmonics and interharmonics calculation as per IEC 61000-4-7:2002 section 5.6 (no
smoothing).
THD – (Total Harmonic Distortion)
The calculation utilizes the following formula: Voltage or current respectively.
1
40
2
2
V
V
THD
n
n
∑
=
=
n: order of the harmonic.
V
1
: rms value of the voltage fundamental.
Vn: rms value of the voltage harmonic with order n.
1
40
2
2
I
I
THD
n
n
∑
=
=
n: order of the harmonic.
I
1
: rms value of the current fundamental.
In: rms value of the current harmonic with order n.
TID
TID is the complete interharmonics contents of the signal. It is calculated as per EN
61000-4-7:1993 from all interharmonics spectral bins (absolute values) up to the
harmonic with order 40.
THD ind
THD ind is calculated according to the formula in the norm EN61000-4-7:1993. This
formula is no more part of the actual version of EN 61000-4-7 but has still importance for
applications in networks with inductive loads.
∑
=
=
40
2
2
1
1
n
n
ind
n
V
V
THD
n: Order of the harmonic.
V
1
: rms value of the voltage fundamental.
Vn: rms value of the voltage harmonic with order n.
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