Maintenance Methods For Three-Phase Asynchronous Motors

For three-phase asynchronous motors operating continuously, routine maintenance includes the following: visual inspection; verifying that the cooling fan is functioning correctly; checking for abnormal vibrations; ensuring the coupling connection is secure; confirming that the base mounting bolts are tight; checking for proper bearing operation (by listening for unusual sounds); and monitoring operating temperature (using an infrared thermometer).

Additionally, wire connections and switch contacts should be inspected periodically, and the operating current should be verified (using a clamp meter). Furthermore, wound-rotor motors require specific inspection of their carbon brushes and slip rings.

Terminal Identification
⑴ First, identify the two start and end terminals for each of the three-phase windings. Set a multimeter to the resistance range to perform measurements; terminals belonging to the same-phase winding will show continuity (zero resistance), whereas terminals belonging to different phases will show no continuity. By observing the multimeter readings, you can clearly distinguish which pair of terminals corresponds to the leads of a single-phase winding.
⑵ Next, identify the "like-named" terminals (terminals of the same polarity) across the different windings. Set an analog multimeter to its lowest DC current range. Connect the two terminals of any one phase winding to the multimeter's probes. Then, momentarily touch the two terminals of a *different* phase winding to the positive and negative terminals of a dry-cell battery, respectively. At the precise moment the battery connects to the winding, observe the multimeter's needle: if the needle deflects toward the positive side (i.e., swings clockwise), then the battery's positive terminal and the multimeter's black probe correspond to like-named terminals; conversely, if the needle deflects in the opposite direction, the polarity is reversed.