- Measurements overlap and relate in such a way that, taken in conjunction with one another, they can help you to troubleshoot the root cause of just about any motor problem.
- Electrical, insulation resistance, thermal, and vibration measurements are all pretty quick and easy to capture, using handheld tools, and they tell you a lot about system performance.
- Many factors go in to the decision whether to repair or replace a motor: cost of the repair, cost of the new motor, expected lifespan, availability of a new motor, and efficiency of the exiting motor.
Would it be fightin’ words to say that, most of the time, motors run just fine? Because really, as maintenance professionals, we have a good grasp of the expected performance of our mechanical systems. We’re checking them out for one reason or another on a somewhat regular basis. We’re more or less aware of the loads they’re running. And we’re paying attention to the lifecycle, either through that ticker in the back of our head or through a more formal maintenance management program.
So if it’s that easy, what keeps us employed? A lot of the time, it’s the changes to the system that monkey-wrench older components. And then, stuff just breaks. Contrary to the casual tone taken here, most of us take great pride in keep things up and running, and we really don’t like surprises, especially the kind that make our phones ring after hours.
Figure 1. Measurements can be saved and stored centrally for everyone on the team to access.
That’s where the importance of measurement comes in. If we’re doing all of those other parts of our job described above, such that we have a pretty good mental handle on the health of our mechanical equipment, then what’s left is the physical data that confirms what we think we know or surprises us with conditions we didn’t know were building.
Electrical, insulation resistance, thermal, and vibration measurements are all pretty quick and easy to capture, using handheld tools, and they tell you a lot about system performance. What’s especially interesting is that thermal, insulation, vibration, and electrical tests each provide information about different aspects of the system. The measurements overlap and relate in such a way that, taken in conjunction with one another, they can help you to troubleshoot the root cause of just about any motor problem.
Plus, the measurements can be saved and stored centrally for everyone on the team to access, enabling multiple different people, not just you, to respond to that late night call (Figure 1).
Never leave home without it
Figure 2. When dealing with operational equipment, start with a thermal inspection.
Never leave home without your common sense and safe electrical measurement knowledge. Where at all possible, shut it down and then lock out and tag out. Wireless meters now enable you to shut the system down, lock out, hook up a meter, close the panel door, re-engage, and start monitoring measurements. But not everything can be shut down.
If a situation arises that requires working it live, make sure to follow these essential safety practices. First, know the arc flash rating of your electrical environment. Second, be sure to wear appropriately rated personal protective equipment (PPE) for that environment. Third, use a test instrument that is safety rated for the environment. Fourth, use a meter to verify live or not live and then use the three-point test method to verify that your meter is working properly: Test a known live circuit; test the target circuit; and test the live circuit again.
Speaking of safety, when dealing with operational equipment, start with a thermal inspection (Figure 2). You will still need to wear PPE — reference NFPA 70E for the specific gear required for non-contact inspections — but it’s both less dangerous to be several feet away and the thermal picture view shows you at a glance what kind of heat signature the system is giving off (Figure 3). Is it normal? Compare to a similar system or to a previous image to make that determination. Differences in temperature will help you to build a quick list of what to measure first with your other measurement tools.
Figure 3. The thermal picture view shows you at a glance what kind of heat signature the system is giving off.
High temperatures in and of themselves don’t necessarily mean anything, but a component with a higher temperature than that of similar components, or a rise in temperature, are good indicators that something is amiss. For example, a coupling that is running warm could indicate misalignment. A motor’s heat signature will tell you a lot about its quality and condition. 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%, even if the overheating is only temporary.