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Electrical Testing

Tip of the Week: Test and Measurement

Here are some of the conditions to monitor and measure to help boost motor system reliability.

When added to the measuring done during scheduled preventive maintenance (PM) activities, monitoring can significantly boost motor system reliability. But what should you monitor?

The single biggest enemy of motors is, you guessed it, heat. Typically, a critical motor will be ordered with a temperature sensor in the windings. This can help prevent catastrophic motor damage if you can connect the sensor to a system that can send notifications to specific people for action when a high-level threshold is crossed.

But what about bearing temperatures? Monitor bearings also, adding sensors for that purpose; consult with a motor shop before finalizing your plans.

Poor ventilation can result in excess motor temperature, and so can excessively rapid restarting. But if you’ve taken care of these issues, voltage imbalance can defeat your efforts. Put something in place to prevent excess restarts.

If your plant doesn’t have a power monitoring system capable of monitoring specific loads, you can do the next best thing for that critical motor. Assuming we’re talking about a 480V motor, purchase a separate voltmeter or power monitor that can do the following:

  • Read voltage on each of the three phases.
  • Calculate voltage imbalance.
  • Alarm and alert when specific conditions are met.

Those conditions should include phase loss, ground loss, overvoltage, undervoltage, and voltage imbalance. If you can also get low power factor and excess harmonics, that’s even better. Mainly, voltage imbalance is what you really want to detect.

Any critical motor should have vibration monitoring. Evaluate your situation to determine if automatic action (e.g., motor shutdown) should be part of the protection plan or if notification is sufficient.

Don’t fall into the trap of thinking that monitoring makes measuring unnecessary. Monitoring is a way of catching condition changes between PMs. You also will need to PM the monitoring systems.



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