In the examples to follow, we show how to use the Teledyne LeCroy MDA810 Motor Drive Analyzer to measure power delivered to two independent three-phase winding sets. We also show how to add and subtract the measurements to understand winding-set balance under static and dynamic operating conditions.
Figure 1 shows a short (200-millisecond) capture of signals: two voltages and two currents for each three-phase winding. The first winding set appears at left and the second winding set appears at right. The MDA is sampling at 10 MS/s using 2 MS of acquisition memory in this acquisition.
Calculating and Displaying Power Quantities
Figure 2 shows the same acquisition along with the Numerics table display of the mean power values and the Motor Drive Analysis summary dialog. The Numerics table displays the total mean three-phase power for all of the measured cycles for each of the two winding sets We set up the MDA to calculate these values for the fundamental frequency only. We have used the two-wattmeter method to calculate three-phase system power for each set of windings. Note that we use the AC (line) Input setup to calculate the power for one of the two sets of windings.
The total power for the six phases would be the sum of the Σabc and Σrst power values. This can be simply added manually, or parameter math can be used to add them automatically, as shown in Figure 3.
Understanding Motor Winding-Set Balance under Dynamic Operating Conditions
After taking a longer acquisition (5 seconds) of the same signals, we will now describe analysis of how well the winding sets share total power under dynamic operating conditions. Figure 4 displays the voltage and current signals for both winding sets on the left, and calculated waveforms on the right. The top-right grid shows the total three-phase power vs. time for each winding set (blue and dark green waveforms). The top middle-right grid (red waveform) shows the power vs. time waveforms of both winding sets added together (total motor drive power). The bottom middle-right (light green) waveform shows the difference in total three-phase power between each winding set. The bottom-right (orange) waveform shows the difference in power between each winding set as a ratio of the total power.
The Numerics table reveals that this difference is about 1 W on average, but it ranges from to 20 to 60% of the total power under light load and is only about 5 to 10% of the total power under heavier load (the exact values could be confirmed through zooming or use of cursors).
The Teledyne LeCroy Motor Drive Analyzer measures total three-phase power using a two-wattmeter method (four signals total) for each of two motor winding sets. Additional built-in math functions calculate the balance amongst the winding sets during a dynamic operating condition.