Infrared Technology & Maintenance
Electrical maintenance is a subject almost as broad and diverse as the opinions of those who sell it, perform it, and depend upon it to keep the lights on. The definition of maintenance has changed over time due to changing manufacturer’s recommendations, ideas from self-promoting industry groups, the influence of service providers, and the constraints of access to perform what we commonly call preventive maintenance.
Webster’s defines “preventive” as “something that prevents” and “maintenance” as “the act of maintaining, the upkeep of property or equipment.”
Dictionary.com defines “preventive maintenance” as “To bring down a machine for inspection or test purposes.”
A common ironic form of preventive maintenance goes like this. Actions are performed upon a machine at regularly scheduled intervals to ensure that the system remains in an unusable state. This so-called preventive maintenance is all too often performed by field servoids who don’t know what they’re doing; such maintenance often induces problems or otherwise results in the equipment remaining unusable for an indeterminate amount of time.
Ouch, that hurts. Fact is, there is often a difference between what we believe is being done and what is actually being done to mission critical electrical infrastructure. Over the years, our attitudes have changed in part as the mission of our facilities has become more directly related to the success of our businesses and the balance sheet.
The figure (see figure 1) shows the progression of our attitudes toward maintenance. No maintenance certainly reduces downtime until a cascading failure occurs due to lack of attention. Reactive maintenance is the product of no maintenance, “Don’t fix it if it ain’t broke,” and is no longer part of the mission-critical lexicon.
Preventive maintenance is the application of manufacturer’s recommendations and industry best practices. The word preventive is subject to tempering (or tampering) in this case. Most comprehensive “preventive maintenance” programs do not preclude a failure. They do, however, improve the odds of discovering and correcting a deteriorating condition in order to prevent an impending failure.
Proactive maintenance is the application of best practices taking full advantage of technology. One such technology, which has changed the way we maintain electrical infrastructure, was the discovery of infrared energy. In 1800, Sir William Herschel was engaged in building telescopes when he wondered if the different colors of light that passed through a prism had different temperatures. He devised an experiment to support his hypothesis and confirmed that the temperatures of the color spectrum of light did indeed increase from violet to red. He further noted the temperature increased further just beyond the red spectrum (infrared).
As the mission of facilities changed, so did approaches to maintenance. Not maintaining systems or simply reacting to failures are no longer options as preventive maintenance morphs into a more proactive posture.
What technology could be more proactive then thermal imaging? Developed for the U.S. military in the late ’50s and early ’60s by Texas Instruments & Hughes Aircraft, the first IR instruments were used primarily to detect the presence of opposing forces at night or under smoky battlefield conditions. It wasn’t long before other uses were developed.
The use of thermal imaging to detect abnormal heat in electrical gear has long been standard accepted best practice. A qualified operator with the right equipment stands in front of energized electrical switch gear with all shields removed and the gear under full normal building load. The resulting IR scan will reveal an image of the heat associated with load. A trained thermographer must interpret the image as normal or abnormal.
Should the operator detect an abnormal level or pattern of heat on cable terminations, buss joints, or other such connections, a still IR image of the problem area would be taken. This IR image is mounted in the report adjacent to a black-and-white control photograph of the same joint or area for identification purposes. A narrative describes what the thermographer believes the problem to be (loose connection, overload, etc.). Theoretically, this procedure is done annually prior to maintenance shut down windows so that identified problems may be addressed.
Pretty simple, really, except for the hazard of arc flash. No longer may the thermographer stand in harm’s way without full protection of PPE (personal protective equipment) commensurate with the class of hazard identified at the point in the system being scanned (see figure 2). NFPA 70E and OSHA requires that arc-flash hazard labels be affixed to all access points in electrical gear and that any person working in the vicinity with the covers or doors open while the gear is energized be appropriately attired, including the thermographer. The cost of IR scans has gone up and productivity has gone down.
We all know that given a challenge a solution will appear, and this topic is no exception. The view port is one such idea because standing in front of open gear under normal or full load is dangerous. Installing a window so the interior can be observed and thermally imaged without opening the door is logical (see figure 3). Logical yes; practical no.
In practice, each effort to install such windows has problems:
The best quality crystal cuts IR energy somewhat and degrades over time
The best quality crystal is also the most delicate
Not all bus or cable connections are viewable through these ports due to the realities of construction
- Mesh windows allow some exposure to arc flash
On-board thermal monitoring is emerging as a better solution (see figure 4). Sensors are mounted adjacent to critical bus and cable connections and interfaced to an EPMS or BMS via a converter. The ability to measure and log the difference between ambient temperature and the target (Delta T) 24 hours a day and trend those measurements provides early warning of a deteriorating electrical connection. These devices are especially useful in places where the traditional IR scan is not safe or practical (medium- and high-voltage transformers, switches, gear where substandard clearance might place the thermographer in harm’s way, breaker stabs inside a cell, etc.)
Get the picture? No one IR technology is a complete preventive maintenance solution by itself. The best approach is a combination of IR technologies, which makes the most sense for the installation.
Here are some questions for you to consider.
Are you performing annual thermographic scans?
Is the gear being scanned at normal facility or full load?
Are you able to scan all the necessary connections?
How are the people scanning your mission critical electrical infrastructure qualified?
Are the people performing the scan and your staff observing NFPA 70E requirements?
What would an arc flash event cost your company in terms of downtime, lost production etc.?
- Have you evaluated all available IR technologies?
Yes the definition of maintenance is subjective to a degree and our mission has changed. The challenge is to provide comprehensive pro-active maintenance while not impacting the facility’s mission. In this case, technology can be a boon or a seductive alternative to common sense. What’s in your maintenance master plan?