Use Thermal Imagers To Identify Motor Trouble

Making and cataloguing thermal images part of your regular preventive maintenance routine will help determine when and what motor components are varying from their baseline.

Making and cataloguing thermal images part of your regular preventive maintenance routine will help determine when and what motor components are varying from their baseline.

Infrared cameras, also called thermal imagers, can be important tools for troubleshooting motor problems, as well as for monitoring motor conditions for preventive maintenance. Infrared images reveal a motor’s heat signature, which can tell you a lot about its condition. The condition of motors, in turn, can play an important role in keeping plants up and running and their operating costs down.

According to experts at Fluke Corp., Everett, WA, here are some tips for scanning motors and drives with thermal imagers:

Build motor heat-signature profiles.
Capture good quality infrared images when the motors are running under normal operating conditions. That gives you baseline measurements of component temperatures. Make infrared images of all of the critical components, including motor, shaft coupling, motor and shaft bearings, and the gearbox. Note that when working with low electrical loads, the indications of a problem can be subtle. As a load increases, the temperature will increase. If a problem exists, expect greater temperature differences at higher loads.

Note nameplate information and hot spots.
A motor’s normal operating temperature should be listed on the nameplate. An infrared camera cannot see the inside of the motor, but the exterior surface temperature is an indicator of the internal temperature. If a motor is overheating, the windings will rapidly deteriorate. Every 50-deg. F increase in a motor’s windings, above the designed operating temperature, cuts the winding life by 50%, even if the overheating is only temporary. If a temperature reading in the middle of a motor housing comes up abnormally high, an IR image of the motor can tell you where the high temperature is coming from, i.e., windings, bearings, or coupling. If a coupling is running warm it is an indicator of misalignment.

Know the three primary causes of abnormal thermal patterns.

• High-resistance contact surface, either a connection or a switch contact, often appears warmest at the spot of high resistance.
• Load imbalances can appear equally warm throughout the phase or part of the circuit that is undersized/overloaded. Harmonic imbalances create a similar pattern. If the entire conductor is warm, it could be undersized or overloaded. Check the rating and the actual load to determine the cause.
• Failed components typically look cooler than those that are functioning normally. The most common example is probably a blown fuse. In a motor circuit, this can result in a single-phase condition and the possibility of costly damage to the motor.

Create regular inspection routes and compare images.
It is a best practice to create a regular inspection regimen that includes making thermal images of all critical motor/drive combinations. Ideally, these images are made under identical operating conditions to have apples-to-apples comparisons. Comparing current state images with baseline images can help you determine whether a hotspot is unusual and also help you verify if any repairs undertaken were successful. A thermal imager can easily transfer images into software for cataloguing. Sharing can be invaluable in this effort. MT

For more information on thermal-imaging best practices, visit fluke.com.