By Colin PlastowMachinery and Equipment Maintenance Test and Measurement
Electric motors are the backbone of industry. Alone, they account for 70% of the electricity consumed by industry. An integral part of optimizing motor performance and minimizing downtime is having th...
Electric motors are the backbone of industry. Alone, they account for 70% of the electricity consumed by industry. An integral part of optimizing motor performance and minimizing downtime is having the ability to capture information on a motor’s temperature profile.
A tried and true tool used by technicians in understanding temperature variations within a piece of equipment is an infrared thermometer. While accurate and extremely useful in specific situations, these instruments have limitations, since they can only capture temperature at a single point.
Thermal imaging using infrared technology, on the other hand, can capture thousands of points at once, for all of the critical components -for example, the motor, shaft coupling, motor and shaft bearings, and the gearbox -to create a more comprehensive temperature profile in a much shorter space of time. This allows technicians to identify and analyze potential problems more safely and effectively, without having to make physical contact with the equipment.
An Ounce Of Prevention
Given the speed, efficiency and safety of thermal imaging devices, it is not surprising to see that they are playing an increasingly important role in preventive maintenance programs today. Preventive maintenance is especially important in industrial environments, since any system failure could lead to lost production time and revenues -and ultimately affect a company’s bottom line.
With the ability to accurately capture and assess all aspects of a motor’s surface temperature conditions, it is easier to avert many unexpected motor malfunctions in systems that are critical to manufacturing, commercial and institutional processes.
Regularly scheduled infrared inspections of electric motors can help to identify motors that are starting to overheat and reveal whether a motor is running hotter than a similar motor doing a similar job. This capability not only improves uptime, but also helps to reduce the cost of repairs significantly.
One thing to keep in mind is that an infrared camera can’t see the inside of the motor, but as heat is generated inside the motor, it will find its way to the outside, generally by conduction. In other words, as the motor gets hotter inside, it also gets hotter outside and the thermal patterns on the exterior surface are usually a good indicator of internal temperatures.
Know the normal operating temperature
When working with a thermal imager, an important first step is to check motors when they are running under normal operating conditions. Each motor has a maximum operating temperature that usually appears on its nameplate and represents the maximum allowable rise in temperature of the motor above ambient. Most motors are designed to operate in ambient temperatures that do not exceed 40C. Generally speaking, each 10C rise above its rated temperature cuts a motor’s life in half.
It is usually best to create an inspection route that includes all critical motor/ drive combinations. Then, save a thermal image of each one on a computer. This will provide baseline images that can be used for comparison with subsequent images captured later at regular intervals. This helps determine if any thermal images are unusual or not, and can also help you verify if any repairs that were made were successful.
Overheating of motors can be a result of a number of issues. Here are some of the common problems and possible actions that can be taken to analyze and/or remedy specific causes of overheating:
• Inadequate airflow: If a brief shutdown will not affect the plant process, shut off the motor long enough to perform minor cleaning on the air intake grills, then schedule a thorough motor cleaning during the next planned plant shutdown.
• Unbalanced voltage or an overload: This is often caused by a high-resistance connection in the switchgear, disconnect or motor connection box. It usually can be pinpointed during a thermographic inspection and confirmed using a multi-meter, clamp meter or a power quality analyzer.
• Impending bearing failure: When the thermal images indicate a bearing is overheating, lubricate the bearing or generate a maintenance order as soon as possible. When in doubt, having an expert perform a vibration analysis can help to determine the best course of action.
• Insulation failure: If possible, de-rate the motor in accordance with NEMA standards. Generate a work order to replace it as soon as possible.
• Shaft misalignment: In most cases, vibration analysis will confirm a misaligned coupling. If a shutdown is possible, misalignment can be corrected using the dial indicators of laser-alignment devices.
Whenever you discover a problem using a thermal imager, make sure you use the associated software to document your findings in a report that includes a thermal image and a digital image of the equipment. This is the best way to communicate the problems you found and the suggested repairs.
The ROI question
One additional aspect to consider when deciding about repairs is gaining an understanding of the return on investment (ROI). In order to determine this, you should perform an analysis based on the cost of the specific motor, the average amount of time a line is down from a motor failure, the labour required to change it out, etc.
Of course, productivity losses from downtime vary from industry to industry. For example, lost production from a papermaking machine can be as much as $3,000 per hour, while in the steel casting industry losses can be as high as $1,000 per minute.
As a critical component of any industrial operation, it is important to ensure that motors are running at peak efficiency at all times. Using thermal imaging to perform routine checks can play an important role in making sure that your operations stay up and running, and avoiding costly repairs. If and when repairs are needed, an accurate analysis of the problem will go a long way towards helping you determine next steps, and maximize the return on investment.
Colin Plastow has been with Fluke Electronics Canada since 1987 in various support and product management positions and currently is industrial product manager. He may be reached by e-mail at firstname.lastname@example.org.
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