By Jim Seffrin, Infraspection Institute
Despite the important role they play in facilities, electric motors often tend to be out of sight and out of mind—until they fail. Infrared thermography can be a cost-effective diagnostic tool for detecting problems within these systems.
Many infrared (IR) inspection programs focus on motor control circuits, but overlook the actual motors. Infrared inspections of a motor’s bearings and stator should be performed monthly by an experienced, certified IR thermographer that thoroughly understands the theory and operation of electric motors.
Here are the basic steps for performing this type of inspection:
1. Inspect motor casing for localized hotspots that may be indicative of short circuits within motor windings.
2. Qualitatively compare individual motors to similar motors under similar load.
3. When possible, qualitatively compare inboard and outboard bearings for each motor. If a large Delta T is present, it may be indicative of misalignment or a rotor balance problem. If both bearings are hot, the bearings may be worn or improperly lubricated.
4. Additionally, a thermographic inspection of the electrical connections within the motor junction box should be performed annually. This may be done in conjunction with a regularly scheduled IR inspection of the facility’s electrical system.
Because no complicated analysis is required, infrared inspections typically can be performed rapidly and at a fraction of the cost of other types of motor testing. Infrared can also detect evidence of misalignment at lower thresholds than those detectable by vibration analysis and motor-current signature analysis. MT
Words to the Wise: Stick to Facts
When used as a preventive/predictive maintenance tool, infrared (IR) thermography can detect and document evidence of thermal patterns and temperatures across the surface of an object. The presence of inexplicable thermal anomalies or exceptions is often indicative of incipient failures within inspected systems and structures. Because thermography alone can’t determine the cause of an exception, other diagnostic tools must be employed.
Some thermographers, however, provide opinions as to the cause of exceptions without the benefit of confirming test information. Such opinions are frequently accompanied by elaborate recommendations for repair. When those observations/recommendations are incorrect, they can cause repair efforts to be misdirected.
Unless a thermographer has performed, or has access to, confirming tests, it’s unwise to provide opinions regarding the cause of exceptions and offer suggestions for repair. Lacking confirming test data, a prudent thermographer should make only one recommendation: “Investigate and take appropriate action.”
This simple recommendation can be applied to any thermographic inspection and serves to avoid unnecessary liability by eliminating guesses and sticking to facts.
Jim Seffrin, a practicing thermographer with 30+ years of experience in the field, was appointed to the position of Director of Infraspection Institute, Burlington, NJ, in 2000. This article is based on one of his “Tip of the Week” posts on IRINFO.org. For more information on infrared applications, as well details on upcoming training and certification opportunities, email firstname.lastname@example.org or visit infraspection.com.