Electrical Systems

Thermography's role in motor monitoring

You don't need a highly trained expert toting expensive equipment to perform thermographic analysis anymore.

By Bill Gray, CMRP

Most maintenance professionals recognize that infrared thermography is a powerful predictive maintenance (PdM) tool because it detects problems in nearly any kind of mechanical or electrical equipment. Until recently, however, only highly trained experts toting expensive equipment could perform thermographic analysis.

Until three years ago, the only such analyses at our facility were done by a consulting firm that inspected our switchgear annually. The inspectors usually found hotspots for us to eliminate. Afterward, however, it was cost-prohibitive to remobilize the consultant to verify our repair was successful.

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Our mill runs continuously, and we can’t afford unscheduled shutdowns. We wanted to inspect switchgear more than once a year. We wanted to monitor other equipment before and after repairs. We wanted to establish baselines when we installed new equipment.

We purchased an affordable thermal imager when the technology became economical. After completing a training course and passing a rigorous exam, I qualified as the plant’s first Level I Thermographer, an achievement that gave us the ability to conduct ad hoc thermal inspections. Two additional training courses showed us the finer points of applying thermography to mechanical and electrical systems.

After having used the thermal imager for three years now, we’re using the experience we’ve gained to develop a formal motor condition-monitoring reliability maintenance program.

Thermal imaging today

We still use contract thermography to monitor switchgear annually because we lack the resources to survey 5,000 pieces of equipment in only a week. Nevertheless, our infrared (IR) camera has proven its worth from the first day we used it. For example, of the items the outside thermographer identified as a problem, post-repair images revealed that about 30% of our repairs were either unsuccessful or had made things worse. Now, however, we know enough to keep working until a repair is satisfactory and more likely to avoid unexpected failure.

Because infrared imagers can monitor temperature buildup in an array of critical process systems, we use our instrument to detect underperforming heat exchangers as well as dysfunctional pumps, gearboxes, bearings and motors.

Motor monitoring today

We’re especially interested in a more effective use of thermography to troubleshoot problems in our mill’s 3,000 motors. Most are heavy-duty, ranging in size from sub-hp to 1,000-hp units. It’s important for us to detect overheating because hot windings deteriorate rapidly. In fact, every increase of 10°C on a motor’s windings above its design operating temperature cuts the insulation life by 50%, even if the overheating is only temporary.

We think it’s important to be able to collect the heat signatures from the whole population of motors at the plant. On a paper machine, a five-hp unit on a pump supplying a coating or additive can be just as critical as a 1,000-hp motor. A failed pump motor can ruin a batch of paper or shut down the machine.

A motor’s heat signature tells much about its quality and condition. We perform vibration analysis as well as thermography on our most critical motors. If vibration analysis uncovers a problem, it’s likely that a thermal image will help pinpoint what’s wrong.

The motivation for establishing regular routes for motor inspections derived from using thermography on motors only on an “exceptional occurrence” basis. In other words, if someone notices that a motor seems hot, I investigate to find a root cause. If vibration data suggests a bad bearing or imbalance, we confirm the diagnosis by camera. In addition, I often spot-check motors with a sweep of the IR camera as I walk past them. More than once, the thermograph identified a clogged cooling fan or some other problem.

We keep thermographic records of motors that have given us problems. This allows us to make sure the corrective action we took was successful. Motors that are a chronic problem are subjected to root cause analysis.

The picture that saved the day

A fan pump is the device that supplies paper stock to the head box, the first piece of hardware in a paper machine. The motor driving our fan pump is large and was running warm. If the pump went down, the paper machine would be dead in the water.

The IR image indicated a motor housing temperature of 284°F, hot enough to fry an egg. The image also showed that the heat was coming from the windings. We needed to install a new motor and send the hot one to be repaired. We deemed the replacement mandatory, so this wasn’t a planned outage. I monitored the motor closely for about a week until the replacement arrived and we shut the machine down. The outcome was better than it might have been if we had waited for a scheduled shutdown. And it was clearly better than letting it run, destroying the motor with no replacement on hand.

A formal motor-monitoring program

While our mill doesn’t yet have a formal motor-monitoring program, we are actively building one. In fact, we’ve just added a new position in our equipment reliability group to cover the electrical and instrumentation side of reliability. The new hire will monitor motors and perform current-phase analysis, a technology we haven’t used before. That data will be correlated with vibration analysis data. The new electrical technician ultimately will assume responsibility for using thermography on electrical devices.

Adding this position allows me to concentrate on my specialty: mechanical devices. Freed from doing thermography on electrical equipment, I’ll concentrate on shafts, couplings, gearboxes and other mechanical components. When the formal motor-monitoring program is in place, I expect that we’ll improve our track record, especially on our most critical and costly motors.

Vibration analysis and thermography are predictive technologies that prolong the life of large motors, as they already do for our problem motors. Current-phase analysis also will help prolong motor life, and it will offer additional insight into why some motors have chronic problems.

One additional element in our plans will help greatly in implementing a motor-monitoring program. We’re currently bringing online a new condition-based monitoring and asset management system (the MAINTelligence suite from Design Maintenance Systems Inc., or DMSI).

Bar coding our production assets allows us to use a handheld instrument to identify the piece of equipment before doing a series of diagnostic and condition-monitoring checks. In the case of a motor, we might perform a visual inspection first. Then, we check the temperature in the middle of the motor housing using an IR spot thermometer

Windings that are going bad show up as a high temperature and the DMSI program trends each motor’s temperature. If the temperature exceeds an alarm limit, we use the IR camera to capture a thermal image to determine precisely which component is overheating (windings, bearings or coupling). A hot coupling is an indicator of misalignment.

Also, we capture a vibration signature. The bar code system and software can link this collected data to the specific asset and flag any reading that is out of bounds. One strategic goal we seek is to have the program initiate a work order automatically in response to a trend that vibration analysis or the IR thermometer uncovered. Related information, such as oil analysis reports, are uploaded from the lab directly into the software. The monitoring and management system will tie thermographic images and reports to specific assets, and link them to work orders.

Soon, our reliability team will be able to apply the most appropriate predictive technology to each piece of equipment in the plant. Our new software system will put all the analysis data into one picture to permit us to deal with problem motors most effectively and prolong the lives of critical ones. Such goals seem possible because the objective of everyone at the mill, where unplanned work stoppages can ruin an entire batch of specialty paper, is to eliminate unscheduled downtime. I hope it’s evident that we work daily to reach that goal by steadily improving the ways we do PdM.

Bill Gray, CMRP, is A Maintenance Reliability Specialist and Level 1 Thermographer in Rhinelander, Wis. Contact him at 715-369-4484.