As technological advancements help us get more done in less time, and at a reduced cost, are we taking full advantage of these improvements?
One common misconception is that the resistance within the connection point has to be very high in order to cause heating.
As an instructor of IRT, I often have students in Level One courses who complain about the size and weight of their cameras. That all ceases after I show photos of older equipment, such as this Inframetrics 740 rig from back in the early 80's (Figure 1). Believe it or not, this was once considered man-portable.
Well thank goodness for technology. Today's cameras are smaller, are less expensive, and have increased portability compared to what we lugged around in the "old days." Almost every camera on the market today has onboard memory, which is a far cry from the Polaroid camera attachment days, and even a huge improvement over carrying a video recorder attached to your imager. As these technological advancements help us get more done in less time, and at a reduced cost, are we taking full advantage of these improvements? As a service provider, my personal experience has been that as inspection costs decrease, the savings aren't passed on to increase the number of assets within the scope or the frequency of inspection. The opposite is often true, with the scope of an inspection decreasing, leaving "small" equipment out in the cold while switchgear equipment and large distribution devices remain on inspection lists.
Obviously facility switchgear equipment is quite critical; it's the heart of the electrical distribution system. Industrial equipment requires its operating voltage in order to perform, hence the inspection of distribution devices that feed process equipment. But why leave off the circuits feeding the process control or Human-Machine Interface (HMI) devices like touch screens and control panels? If the switchboard feeder breaker for your conveyor line never goes down, but the Programmable Logic Controller (PLC, seen in Figure 2) controlling it fails catastrophically due to a heat-related failure in its distribution path, what has been saved?
Almost anyone with knowledge of IRT as applicable to electrical apparatus inspections understands how we find anomalies. Increased contact resistance in an electrical connection causes heating that increases at the square of the applied current. For this reason, the NFPA-70B (Recommended Practice for Electrical Equipment Maintenance) suggests a minimum of 40% load on a circuit at the time of IRT inspection for optimum results. One common misconception is that the resistance within the connection point has to be very high in order to cause heating. In the example in Figure 3, the electrical resistance between the failed component and the new replacement component is 2.2 micro-ohms. Not exactly what we would normally consider "high," but significant nonetheless.
Another common misconception is that lower-power devices don't carry enough current to be susceptible to heat-related failure. While abnormal heating is a product of current squared times the resistance (I2R), and electrical devices are rated according to their ability to accommodate the flow of current, lower-current-rated devices can also experience heat related failure. Notice the following example in Figure 4.
We're looking at what appears to be 14AWG control wire, which is rated for between 25 and 35 amps, depending upon the particular application. In the thermal image you will notice that the conductor is only showing abnormal heat at the connection point, not on the entire conductor, which would appear to indicate that the conductor itself is not overloaded, and that the heat present is due only to the high resistance connection point. Note the apparent temperature of the anomaly by comparing the color to the temperature scale. An apparent load of significantly less than 30 amps is producing nearly 300 °F. Also important to note is that the control circuit was for an industrial boiler, and if it had failed the boiler would shut down, halting the process of this facility. Another example appears in Figure 5.
The white tape on the large conductor in the center of the image indicates that this is a neutral. We expect that a neutral conductor in a panel should carry some amount of current. If operating correctly, though, this amount of current should be a fraction of what is being carried by the phase conductors. Notice the temperature scale on the thermal image. The point of saturation is on the wire insulation (which has a high emissivity and therefore should give a relatively accurate temperature) and indicates an apparent temperature of greater than 200°F. THHN wire is rated at 90°C (194°F), so we're looking at the potential for thermal damage here.
Notice the wire colors on the breakers. This is a 208VAC panel, which is often overlooked in the inspection process. You might also notice that the panel components are completely exposed. Surface scanning is an excellent pre-inspection process, but it isn't a substitute for fully exposing a panel. If this panel had not been completely exposed, this anomaly wouldn't have been revealed until catastrophic failure occurred. Let's assume for a moment that this panel feeds an office space in a manufacturing facility, and within this office space is the computer that monitors a critical process. What happens in the event of a failure in this panel? Assigning criticality of an asset based on nothing more than its voltage or current rating might have led to the panel in this example having never been inspected.
What about voltage levels? Among the common criteria used to determine criticality of electrical apparatus for inspection is the voltage class or rating of the device. Again, abnormal heating in an electrical connection is a product of current, not voltage. The voltage level of the device has no bearing on the potential for a heat-related failure. Take a look at Figure 6.
These images are from a 24 volt power supply. The temperature scale beside the thermal image indicates an apparent temperature of approximately 40.5°C (105°F), compared to an apparent 37°C (98°F) on an adjacent connection point. Had this particular device not been deemed critical due to other factors, and its importance gauged solely on the voltage level, this anomaly might not have been found until it failed.
Control panels offer an excellent opportunity to maximize the benefit of thermography as a predictive technology, but sadly they are often overlooked. Contained within a typical control panel are transformers, fuse blocks, circuit breakers, and a host of other electrical devices that are inspected in their larger forms inside of larger apparatus. The control transformer inside a control panel operates exactly the same as the larger ones we inspect as part of the utility equipment. Just because they are smaller versions of what we normally would consider critical devices doesn't mean they should be inspected at a reduced frequency. In Figure 7 you will note that even "small" components like those mounted on DIN rail can have sufficient I2R in their connection points to experience heat-related failures.
The 20 amp circuit breakers inside a control panel have the same potential for failure as the 400 amp ones in a distribution switchboard. Does the 20 amp circuit breaker cost less to replace? Sure it does, but what impact on the overall process of the facility does it have? Can we expect that a circuit breaker couldn't experience the same degree of abnormal heating because it's in a 120VAC panel as opposed to a 480VAC distribution board? See Figure 8. We have what appears to be a 20 amp circuit breaker in a 208Y/120VAC panel with a high temperature anomaly. What if this circuit breaker is the one feeding the production server in an office space? Sweating the small stuff yet?
Service main switches are routinely inspected, but what about the 20 amp service disconnect for the control panel (as shown in Figure 9)? Downtime is downtime, no matter the cause.
The anomaly in Figure 10 was found inside a control panel at a textile facility in Alabama. As my escort walked me past this control panel on our way to another device, I asked if we were going to inspect it. The answer I received was "if we have time after the important stuff." Upon the discovery of this item, my escort decided to take time to look at the other 19 control panels identical to this one, each one of which was responsible for the operation of finishing machines at the end of their process. Had this control panel failed, one half of the finishing process would have ground to a halt. Subsequent inspection of the remaining control panels in this production area yielded two additional discoveries. They're sweating the small stuff now!
As reliability professionals within a facility, your input to the routes and frequencies of asset inspections is crucial in bringing about a change. The assessment of criticality for any asset within a particular route needs to consider the impact of failure of devices previously believed to be unimportant due to its voltage class or current rating.
As a service provider for client companies, your task is to educate your customers on the importance of including these "small" devices in their inspection. Often a service provider only sees their customers once or twice a year, and they're almost always pushed to get as much out of their annual visit as they can and to cut time out of the inspection process to stay competitive in their pricing. It's often an uphill battle to make changes; we know that from the history of IR thermography itself. But it can happen, and you can make it happen if you start sweating the small stuff.
Dave Sirmans joined The Snell Group in the fall of 2008 as Operations Manager for the company. Here he is responsible for managing and coordinating The Snell Group's field service operations and overseeing the company's team of technicians that offer infrared thermography, motor circuit analysis, and ultrasound testing services at various locations throughout the United States. Prior to joining The Snell Group, Dave worked in reliability as lead engineer in an electrical testing company. www.thesnellgroup.com
Roy Huff, SMRP, CMRP, is New Product Development Manager and Instructor with The Snell Group and partner in the inspections services company specializing in auditing, mentoring, and consulting services for a broad range of industries. With a professional background in reliability engineering, Roy's strengths in management and program development have been a tremendous asset to The Snell Group. Before that, Roy spent twelve years as an Equipment Reliability Engineer with Allied Signal Aerospace. www.thesnellgroup.com