Dranetz PowerXplorer PX5, User Manual

Page: 60 / 286

3-18
Harmonic Options
Harmonic Options
Harmonic/
Interharmonic
data plots
The voltage and current harmonics and/or interharmonics for each phase channel can
be trended using the Options button. The properties specified under Harmonic Options
apply when harmonic/interharmonic data is viewed in either graph or list form.
Properties under Show Harmonics... pertain to both the graph and the list, and
determine how the harmonics and interharmonics are used.
If Show Harmonics... only is enabled, then only the actual harmonics are shown.
If Show Harmonics... and Interharmonics is enabled, the spectrum will include all
the (nominal) 5 Hz bins, which includes the actual interharmonics as well. On the
graph, the harmonics are shown in the channel color, while interharmonics are shown
in gray color. On the text, the harmonics are shown in boldface.
If Show Harmonics... calculated including adjacent interharmonics is enabled, the
interharmonics are not explicitly shown but the harmonic values include the adjacent
interharmonic values in their calculation, as specified by IEC 61000-4-7.
The IEC 61000-4-7 Standard specifies that the interharmonic bins adjacent to the
harmonic be included in the computation of that harmonic. For example, if there was a
3rd harmonic (150 Hz) of 10%, and the value of the 145 Hz bin was 1%, and the value
of the 155 Hz bin was 2%, then the value reported in the bin labelled “150 Hz” would
also include contributions from the 145 Hz and 155 Hz bins. This would give
10.2%, not 10%.
The following graphs illustrate harmonic computation as per IEC 61000-4-7 Standard.
Harmonic Computation for 50 Hz
Continued on next page
0.0%
0.5%
1.0%
1.5%
2.0%
2.5%
3.0%
… 130 135 140 145 150 155 160 165 170 175 180 185 190 195 200 205 210 215 220 …
3rd harmonic
+
2 adjacent
interharmonics
4th harmonic
+
2 adjacent
interharmonics
2 2 2
2 1 10
+ +
=
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