Rockwell Automation 1426 PowerMonitor 5000 Unit - Manual (Page 75)

Rockwell Automation Publication 1426-UM001F-EN-P - November 2013 75
Power Quality Monitoring Chapter 5
Harmonic Analysis The PowerMonitor 5000 provides harmonic data to help you understand this
important element of power quality in your facility.
Setup
Only basic metering setup is required.
Operation - IEEE and IEC Total Harmonic Distortion
These total harmonic distortion calculation methods provide a summary
indication of the amount of distortion due to harmonics present in a system.
The standard IEEE definition of harmonic distortion is ‘Total Harmonic
Distortion (THD)’ and is computed for each voltage (V1, V2, V3, VN) and
current (I1, I2, I3, I4) channel as follows:
The standard IEC definition of harmonic distortion is the Distortion Index
(DIN) and is computed for each channel as follows:
Crest Factor
Crest factor is another measure of the amount of distortion present in a
waveform. It can also be used to express the dynamic range of a measurement
device. Crest Factor is the ratio of the peak to the RMS.
A pure sinusoid Crest Factor equals .
K-factor
K-factor measures additional heating in a power transformer due to harmonics in
the power signal. These harmonics cause additional heating due to increased core
losses that occur at higher frequencies.
THD
∞
Σ
n 2 =
H
n
( )2
H
1
------------------------- =
Where:
• H
n
= magnitude of the n
th
harmonic
(n
≤ 63)
• H
1
= magnitude of fundamental
DIN
∞
Σ
n 2 =
H
n
( )2
∞
Σ
n 1 =
H
n
( )2
---------------------
=
Where:
• H
n
= magnitude of the n
th
harmonic
(n
≤ 63)
• DIN is equivalent to IEC THD
Crest Factor Peak Value RMS Value
⁄
=
2