The following measurement examples demonstrate use of the Teledyne LeCroy MDA810 Motor Drive Analyzer to characterize a 480-V, three-phase, 1.5-hp AC induction motor drive. Examples will include measurement of drive input and output performance and efficiency when measured for a short time period under no-load and under loaded conditions, as well as dynamic analysis of the drive from a no-load startup to a steady-state load. The latter example shows how the MDA810 leverages its long acquisition time to gain a full understanding of the motor drive’s performance characteristics.
Input-Output Performance Analysis with No Load
To begin with, Figure 1 shows acquisition waveforms of the drive’s input and output signals.
The four waveforms on the upper left side of the screen capture are the AC inputs to the motor drive (acquired using the two-wattmeter method). The setup summary at bottom left shows that the input is configured for three-phase, three-wire, 2V2A. Channels 1 and 2 (yellow and magenta, respectively) are the input voltages, while channels 5 and 6 (white and lavender, respectively) are the input currents.
Shown at top right are the acquired waveforms present at the motor drive’s output. We have defined the waveforms in the setup summary at bottom left using the two-wattmeter method. Thus, the MDA810’s eight analog input channels afford viewing of inputs and outputs of a three-phase system.
In this example, the acquisition is relatively short as shown by the Timebase descriptor box at bottom right. The acquisition spans 500 ms and comprises 2.5 Mpoints. From a cursory glance, it appears to be a steady-state load. Below the waveform display grids is a numeric table of mean values (see inset above). The input voltage is 480 V and output voltage is 120 V, which is substantially less because the drive is running at a low speed with no load. From the currents, we can calculate the real, apparent, and reactive power; power factor; phase angle; and efficiency. The latter is very low, which one would expect with no load on the drive.
Plotting of Efficiency vs. Time
Among the MDA810’s powerful analysis capabilities is its ability to plot measurement results vs. time, time-correlated to the original acquisition data. In this fashion, the instrument makes it easy to spot dynamic changes in data and correlate them to other acquired signals. In Figure 2, the AC input signals appear at top left. Atop the right-side display grids, note the selection of the Efficiency tab to display the calculated sync signals derived from Channel 1. These sync signals indicate the period of time over which the various power values are measured, and these periods are different between the AC input and drive output. Shown in Figure 2 are two color-coded grids that show the power period for the AC input sync signal (center right) and drive output sync signal (bottom right). Viewing the sync signals serves to verify the power periods for input and output.