190 Series III
Users Manual
64
Current Unbalance
Current Unbalance checks for the difference between current levels of the phases for 3-phase
systems. To calculate the unbalance value:
% unbalance = (maximum deviation from average / average of three phases) x 100 %
Tips:
•
Current unbalance should be <6 % and depends on load current and circuit capacity.
Excessive current unbalance can point to or cause drive rectifier problems that result in the
motor overheating. Current unbalance can be caused by voltage unbalance. For example,
1 % of voltage unbalance can result in 3 % to 4 % of current unbalance.
•
2
changes the readings that are displayed in the top of the screen to the peak-peak
values of each phase as well as the highest Crest Factor (ratio between peak and rms value)
of one of the phases.
Harmonics
Harmonics are periodic distortions of the voltage and current sine wave. Harmonics occur when
multiples of the fundamental waveform are superimposed over the fundamental. You can
consider the signal as a combination of various sine waves with different frequencies. The
contribution of each of these components to the full signal is shown as a bar. For example, a 5th
harmonic is 300 Hz (5 x 60) for 60 Hz systems or 250 Hz (5 x 50) for 50 Hz systems. The effect of
these harmonics is distortion of the voltage or current. The sum of all distortions from the 2
nd
harmonic to the 50
th
harmonic divided by the fundamental component is expressed as the Total
Harmonic Distortion (THD).
The readings in the top of the screen show the ac rms value of the signal, the fundamental (H1)
value, the frequency of the fundamental and the THD value.
To view the reading for the harmonic component:
1. Select
4
Harmonics
.
2. Push
2
Input
to select the channel for the harmonics display.
For Voltage and Current measurements, select A for the Voltage harmonics on Channel A
and select B for the Current harmonics on Channel B.
For Unbalance measurements, select A, B, or C to show the voltage or current harmonics for
the selected channel.
3. Push
h
to vertically zoom in on the harmonics display.
4. Push
3
Scale Options
to change the vertical scale.
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