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4 Steps to preventing motor failure

Motors, drives, pumps, compressors, Predictive maintenance

Motor control systems used in critical manufacturing processes are becoming increasingly complex, which makes it more challenging than ever to keep them at peak performance. Equipment failure is expensive, whether due to the cost of replacing parts or lost production.

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Because motor failure can cause mechanical and electrical issues, it is important to consider both when troubleshooting motors. Arming maintenance engineers and technicians with the right knowledge, prioritizing workloads, and running preventive maintenance can help avoid motor failures due to normal system operating stresses and reduce overall downtime costs. Here are four steps to preventing failures in motor drives and rotating components:

1. Capture initial asset condition data and specifications at installation

The first step in preventing motor failure is to capture critical information on the asset—including operating condition, machine specifications, and performance tolerance ranges—at installation. That way you will know how the asset is supposed to run, and as you conduct regular preventive checks, it will be easier to detect any variations from the original installation.
By following this process, you can catch potential issues with improper installation before they cause motor failure. All mechanical assets wear, but improper installation wears them down sooner. Proper installation lays the foundation for the asset’s life and can extend that life. Before getting the asset up and running, check for issues such as:
  • Soft foot: the mounting feet of a motor are uneven
  • Pipe strain: stresses and forces acting on the rest of the equipment transfer backward into the motor
  • Shaft voltage: exceeding the insulating capacity of the bearing grease causes flashover currents to the outer bearing

2. Establish a preventive maintenance schedule and stick to it

Once you have captured the initial asset condition data you can set up a regular preventive maintenance schedule to track the operating conditions of the motors in your facility. On each preventive maintenance you can compare your new measurements to the motor specifications and tolerances that were captured at installation and identify any anomalies. Add thermal imaging to your testing to capture the heat output of motors and assets. For example, the Fluke Ti480 PRO Infrared Camera captures minute temperature differences to indicate that a motor is running too hot or too cold so you can dig deeper to find the root cause.

Fluke Ti480 PRO Infrared Camera
Using a thermal imager, (like the Fluke Ti480 PRO Infrared Camera shown here) as part of your preventive maintenance program can help you catch motor issues early

Mechanical issues are likely to show up no matter what because time wears down most assets eventually. However, assets can last longer if you follow a regular preventive maintenance program to find and fix mechanical issues early, so you don’t have replace an entire asset or system before its time. Some common mechanical issues include:

  • Misalignment: the motor drive shaft is not in alignment with the load
  • Shaft imbalance: the center of a rotating part does not lie on the rotational axis
  • Shaft looseness: excessive clearance between rotating and stationary elements inside a motor
  • Bearing wear: surfaces sliding against each other without enough lubrication to keep them apart

Many breakdowns that arise from mechanical issues show up first as vibration. Incorporating a vibration sensor system, such as the Fluke 3563 Vibration Analysis Sensor,into your preventive maintenance schedule can help you catch many problems before they lead to motor failure.

3. Store and record individual measurements to establish a baseline

Save the measurements and thermal images taken during your preventive maintenance route and use them to create a baseline of your assets’ performance. Any change in the trend line of more than 10% to 20% should be investigated to identify the underlying factors. For some assets you may need to determine what the percent change in the trend line should be based on your system’s performance or the asset’s criticality.

Since variable frequency drives (VFD) take one wave shape and convert it to another, establishing a baseline for running motors will allow you to see when the output changes. Use a true-RMS multimeter and a motor drive analyzer like the MDA-550 Series III Motor Drive Analyzer to diagnose problems related to VFDs. The MDA 550 Series III offers guided test setups and automated drive measurements to simplify complex motor-drive troubleshooting and provide reliable, repeatable results. You’ll be able to quickly detect problems such as:

  • Reflections on drive output PWM signals: impedance mismatch between the source and load
  • Sigma current: stray currents circulating in a system
  • Operational overloads: a motor under excessive load

A portable oscilloscope such as the Fluke 120B Series Industrial ScopeMeter can validate wave shapes and help you decide how to repair a VFD. As with many other asset repairs, it’s more cost effective to catch and repair issues in the early stage than to run to failure and need to replace the whole asset or system.

4. Run a trend analysis

Once you’ve established the baseline, continue tracking and recording measurements regularly. You can use this information to create an archive as you go, which helps to create a trend analysis and makes it easier for others to identify a change in the condition of a motor over time.
A proper trend analysis can help you diagnose many power-quality-based problems such as:
  • Transient voltage: a sudden release of energy that causes electrical energy surges
  • Voltage and current imbalance: differences between the voltage magnitudes or phase angle
  • Harmonic distortion: unwanted additional sources of high-frequency AC voltage or current supplying energy to the motor windings
These issues should be validated with power quality loggers such as the Fluke 1732 and 1734 Three-Phase Power Measurement Loggers. Based on what you find, external intervention may be required to repair the problem.

Be proactive to avoid having to be reactive
Equipping your maintenance engineers and techs with the proper tools, knowledge, and data will enable them to identify signs of motor problems before they become serious. Following the four steps described above will help them catch issues before a motor fails, which will help you avoid the cost of asset replacement and downtime.
 
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