FLUKE MDA-550/FPC User Manual for the Fluke MDA-550/FPC Motor Drive Analyzer with one-year Premium Care, 500 MHz, 4-channel

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190 Series III

Users Manual

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

harmonic to the 50

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

to vertically zoom in on the harmonics display.

4. Push 3 Scale Options to change the vertical scale.

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FLUKE MDA-550/FPC Motor Drive Analyzer with one-year Premium Care, 500 MHz, 4-channel