Traditionally, preventive maintenance (PM) actions are scheduled to coincide with downtime, or downtime is schedule to perform them. This necessarily limits how often they can be performed.
The model is based on mechanical maintenance procedures, in no small part because the typical plant engineer is a mechanical engineer. You really do need downtime to measure the axial runout of a shaft, for example. But even that procedure is often unnecessary for routine maintenance because a vibration monitor or ultrasonic testing can tell you what you need to know. They can tell you about many mechanical conditions, also.
In the electrical world, downtime will probably always be necessary to properly maintain equipment such as circuit breakers. But many other types of testing don’t require downtime. They can be done more frequently, and, in many cases, done continually, with a monitoring system. The aforementioned vibration monitoring is one example. System power monitoring is another, and it should extend out to all critical equipment.
Previous PM models often instructed the tech to tighten all connections, which has the opposite effect of what’s intended. Plus, it can be dangerous. Performing a thermographic scan on all connections is more efficient and safer, plus it removes from the program unnecessary actions that introduce error.
Transformers, switchgear
Dry-type transformers traditionally get no downtime for maintenance, but they do get downtime once they fail due to overheating. They are not the best subject for a thermographic scan because the equipment cannot see internal temperatures. Installing temperature monitoring in every dry-type transformer beyond a certain size or that supplies a critical load is how you address surprise failures due to overheating.
If the transformer gets hotter than the alarm setpoint, you’ll know there’s a problem to investigate. That may not require downtime; you can check your power monitor to see if you have low power factor or some other issue that is making this transformer run hot. If this transformer isn’t being monitored by the power monitor, you can still use a portable power analyzer to see those issues. You can also measure the load current using an inductive current clamp (standalone or accessory for a DMM).
For liquid-filled transformers, there are standard tests that can be done without downtime. The dissolved gas analysis (DGA) is arguably the most useful of these, especially if overheating is the issue. That’s because when transformer is subjected to abnormal conditions such as excess heat, the transformer oil starts to decompose and the decomposition releases gases into the oil. Consider installing a DGA monitor on every liquid-filled transformer, thereby eliminating manual sample collection.
With switchgear, thermographic inspections are particularly useful for detecting issues without requiring downtime to do. If the camera also produces images using visible light, you can conduct a visual inspection without having to poke your head in there.
If something is blocking your direct line of sight, you can use an endoscopic camera. These cameras are underutilized in the typical maintenance department; insulation doesn’t fail only on the front facing side of a conductor and only in good light. You can have arc tracking or other evidence of an insulation puncture or other spot failure, but out of your line of sight. The endoscope allows you to see into an enclosure without sticking your head in there while doing handstands.
Motors
Motor data for maintenance has traditionally not included such things as the motor start time or the number of restarts and time between them. This information can be automatically collected and stored in the CMMS. You could also use PLC control to lock out the motor starter to enforce the wait between restarts, something that is preventive design rather than preventive maintenance.
For motor maintenance without downtime, insulation resistance monitors, vibration monitors, bearing temperature monitoring, and motor voltage monitors are all available. Motor voltage monitors are extremely effective protection for motors because (if the model you have incorporates a relay to interrupt supply power) your motor is protected against excess voltage, undervoltage, voltage imbalance, phase loss, and phase reversal.
Having a system that monitors and alarms for these conditions is hugely advantageous over relying on quarterly manual testing. Providing the actual protection so that you can solve the problem before having to replace the motor is even better.
These are just examples of how you can maintain equipment without needing downtime to do it. Much of the traditional PM is devoted to manual tests and inspections that can be replaced by other methods that don’t require downtime or even scheduling.
If you want to improve maintenance efficacy while simultaneously reducing the downtime needed to perform PMs, start by reviewing your PM procedures. Identify each task that requires downtime. What is the purpose of that task (why do we do it?) Is there a way to satisfy that purpose without incurring the downtime? For example, instead of measuring motor shaft runout every six months, stick a vibration monitor near the shaft and take this manual task off the PM.
Some maintenance tasks not requiring downtime should also be eliminated simply because they pose unnecessary risk. Power monitors, motor voltage monitors, and the like will not only eliminate risk to the people who would otherwise be making the measurements these monitors make, they will make the measurements continuously instead of quarterly.
