Rockwell Automation 1426 PowerMonitor 5000 Unit User Manual
Page 76
76
Rockwell Automation Publication 1426-UM001F-EN-P - November 2013
Chapter 5
Power Quality Monitoring
The increased losses are related to the square of the harmonic frequency.
Therefore, a slight harmonic content can significantly increase the heat rise in a
power transformer. The additional harmonic heating can cause a transformer to
exceed designed temperature limits even though the RMS current is less than the
transformer rating. The K-factor is used as justification to oversize a power
transformer to allow extra margin for harmonic losses or to select an appropriate
K-factor rated transformer. A K-factor rated transformer is the preferred choice
because it has known performance in the presence of harmonics.
The formula for K-factor is as follows:
Harmonic Magnitude and Angle (M6 model)
The PowerMonitor 5000 M6 model calculates the RMS magnitude and angle of
each individual harmonic. Results are calculated for harmonics DC to 63 for all
voltage and current channels. Each magnitude is expressed in rms volts or rms
amps. DC offset is always zero for current channels. Only directly-connected
voltage channels return non-zero DC offset values.
Angles are expressed in degrees, with zero degrees corresponding to the time
stamp of the metering results.
Harmonic Power (M6 model)
The PowerMonitor 5000 M6 model calculates the magnitudes of real, reactive,
and apparent power of each individual harmonic. Results are calculated for
harmonics DC to 63. L1, L2, L3, and total power values are returned for Wye and
split-phase wiring modes. Delta wiring modes return only total power values.
Each magnitude is expressed in kW, kVARs, or kVA.
Harmonic Analysis Results (M6 model)
The PowerMonitor 5000 M6 model returns results for IEEE and IEC THD,
crest factor and K-factor in the PowerQuality.RealTime_PowerQuality tab.
Table 13 - Harmonic Analysis Results
Tag Name
Units
Range
V1_Crest_Factor
0
…
9.999E15
V2_Crest_Factor
0
…
9.999E15
V3_Crest_Factor
0
…
9.999E15
V1_V2_Crest_Factor
0
…
9.999E15
V2_V3_Crest_Factor
0
…
9.999E15
V3_V1_Crest_Factor
0
…
9.999E15
K-Factor
∞
Σ
n
1
=
H
n
2
n
2
•
∞
Σ
n
1
=
H
n
(
)
2
----------------------------------------
=
Where:
•
H
n
= magnitude of the n
th
harmonic
(n
≤ 63).