Using thermal imaging to troubleshoot motors and drives
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. Infrared images reveal a motor’s heat signature and that can tell you a lot about its condition. Indeed the condition of motors can play an important role in keeping plants up and running and keeping operating costs down.
What to scan?
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.
What to look for?
All motors should list the normal operating temperature 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. As the motor gets hotter inside, it also gets hotter outside. If a motor is overheating, the windings will rapidly deteriorate. In fact, every increase of 10 °C on a motor’s windings above its designed operating temperature cuts the life of its windings’ insulation by 50 percent, 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.
There are three primary causes of abnormal thermal patterns:
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.