Thermal imagers are excellent tools for troubleshooting motor issues and monitoring the motor condition for preventive maintenance for power generation, manufacturing, and commercial plants. Infrared images reveal a motor’s heat signature to tell you about its condition.
What to Scan?
In building your heat profiles, it is best to start capturing good quality infrared images when the motors are running under normal conditions. Doing so will give you baseline measurements of the temperature of components. Thermal imagers or infrared cameras can capture temperatures of all the crucial components: motor, shaft coupling, motor, shaft bearings, and gearbox.
However, working with loads can be more difficult as the indications of issues are subtler. Thus, a minimum of 40% design load is recommended (National Fire Protection Associate NFPA 70B), and it is better to have a higher load. When you are inspecting in low load situations, take note of all possible issues, be sure to note all possible problems, even if they reflect only a minimal temperature difference. When the load increases, the temperature rises too–and if a problem exists, assume larger temperature differences at higher loads.
What to Look For?
All motors should have the normal operating temperature listed on the nameplate. An infrared camera/thermal imager is unable to see inside the motor, but the exterior surface temperature is an indicator of internal temperature. When the motor is overheating, the windings rapidly deteriorates. As a matter of fact, every increase of 10°C on a motor windings’ designed operating temperature cuts the life of windings’ insulation by half even though the overheating is 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. If a coupling is warm, there may be a misalignment.
There are three primary causes of abnormal thermal patterns:
- High-resistance contact surface, either a connection or switch contact, usually appears warmest at the spot of high-resistance, cooling off the further away from the spot.
- Load imbalances, normal or out of specification, appear to be equally warm throughout the part of the circuit that is overloaded or undersized. Harmonic imbalance also creates the same pattern. If the entire conductor is warm or hot it may be undersized or overloaded. Check on the rating or the actual load to know the cause.
- Failed components may also appear cooler than normally functioning ones. The most common example is a blown fuse. While, in a motor circuit, this can result in a single phase condition and the possibility of costly damage to the motor.
Practicing regular inspection routes including thermal images of all critical motor and/or drive combinations as well as tracking baseline images will help you know if a hotspot is unusual or not. It will also help you verify if the repairs were a success.
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