Using IR to diagnose motor issues

Temperature data can be key to optimizing motor and drive performance, uptime.

By Sat Sandhu, Fluke

Infrared cameras, also called thermal imagers, are useful for troubleshooting motor problems as well as for monitoring motor condition for preventative maintenance in power generation, manufacturing, and commercial plants.

Thermal images of motors reveal their operating condition as indicated by surface temperature. Such condition monitoring is important as a way to avert many unexpected motor malfunctions in systems that are critical to manufacturing. The onset of motor failures can often be detected by a variety of techniques, including vibration, ultrasound and thermal imaging.

Thermal imaging specifically enables you to:

  • Inspect while the equipment is running
  • Verify repairs have been done properly
  • Inspect faster and from a safer distance
  • Improve repair efficiency and reduce costs

To get started in building heat profiles of your motors, it is a best practice to capture good quality infrared images when the motors are running under normal operating conditions. That gives you baseline measurements of the temperature of components. An infrared camera can capture temperatures of all the critical components:  motor, shaft coupling, motor and shaft bearings, and the gearbox.

When you are working with low electrical loads, the indications of a problem may be subtle. Thus a minimum of 40% of design load is recommended (National Fire Protection Association NFPA 70B), and the higher the load, the better. When inspecting in low load situations, be sure to note all possible problems, even if they reflect only a small temperature difference. As a load increases, the temperature will increase too and if a problem exists, expect greater temperature differences at higher loads.

All motors should list the normal operating temperature on the nameplate. Abnormal temperatures, which will show up on a thermal imaging inspection, can be an indication of:

Inadequate cooling because of insufficient air flow. Clearing this issue may only require minor cleaning on the air intake grills.

Power quality issues such as unbalanced voltage or overload or harmonics. All of these will cause excessive heat dissipation.  

Impending bearing failure. An overheating bearing is an indication of an impending bearing failure. Bearing condition degrade for a number of reasons:

  • Heavier than anticipated loading
  • Inadequate or incorrect lubrication
  • Ineffective sealing
  • Shaft misalignment
  • Incorrect fit

Insulation failure. With failing insulation of the motor windings the overall motor temperature increases this overheating causes failures and reduces insulation time

Shaft misalignment. Most misalignment cases are a combination of parallel and angular misalignment (see image)

Creating regular inspection routes that include thermal images of all critical motor/drive combinations and tracking to those baseline images will help you determine whether a hotspot is unusual or not, and help you verify if the repairs were successful.

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