The Infrared Inspections on Electric Panels without Removing Covers Cannot be Completed Correctly – And here’s why.
There has existed in the past a misunderstanding that Infra-red Thermography could be accomplished without the benefit of removing panel and/or front covers on electrical apparatus. This would be wonderful from the standpoint of logistics, manpower, and labour hours.
The basis behind this web page is to determine if the scans can be successful by leaving the various covers in place. Before and after images were collected on several different location cabinets to determine the results.
Infared cameras used in the performing of thermal image surveying in any application are not X-Ray devices that allow for “seeing” through solid surfaces and materials. We know that when temperature variations are visible to the camera on these types of scenarios, the actual problem area and source of the thermal energy is going to be exponentially higher at the source, and the camera is “seeing” only a portion of the total.
EXAMPLES TAKEN DURING INFRARED INSPECTIONS
The following examples were taken on different sites during actual component inspections. We will give the necessary details of each component and show both infrared images prior to removing the cover and after removing the cover.
Our first two examples explore the possibility of doing proper IR thermography in distribution board without removing the front cover to view the actual buss and load side terminals.
- 20 Amp Square D Single Pole Breaker.
- Loaded 5.2 amps.
- 6% THDC.
- High emissivity target on the dead front cover due to its painted surface (around .94).
- Lower emissivity target at the line lug, but geometry and cavity allowed for an improvement in emissivity for a more accurate measurement of the problem (around .89).
- .785 Millivolt drop across contact.
- 10-12 degree C difference between the breaker body and problem spot at the line side, as heat was conducted to the line lug and was more predominant there as opposed to the load side. This would be masked if the front cover was not removed.
- Controlled environment in a college hallway, no forces or natural convective cooling, ambient temperature around 20 degrees C, no background radiation.
As you can see in Figure #1 prior to the removal of the front cover, there is an obvious load on the suspect breaker 4th down on the right.
The observed temperature is around 30 degrees C and within the manufacturer’s operating specifications. The temperature on the front cover is closer to 23 degrees C and not an apparent concern, right? One may simply deduce this is only load created energy on the breaker and bypass it during an inspection.
Once the cover is removed, a far worse issue is revealed in Figure #2.
- The problem area is centered on the line side connection.
- The actual problem temperature at this light load was approximately 39 degrees C.
- This is an error of nearly 9 degrees C.
- If the cover had not been removed, this more than likely would have been bypassed.
- Any addition of loads would increase the problem temperature exponentially.
In today’s world, the mentality and “buzzword” is lean manufacturing and reduced maintenance costs. Competition throughout the industry demands that we must all do more with fewer resources. This should not mean that in the interest of cost savings, short-cuts should be taken that can cause misjudgements which may contribute to downtime or equipment failure.
In the examples above, there are no doubts that problems that existed on line side connections. Analysis, including voltage drop measurements, confirmed that due to resistance issues, thermal energy was being created and radiated. Although there was conduction noted on the breaker cases, it most likely would not be considered to be abnormal, deficient, or in failure stage.
The Square D I-Line panel is an excellent illustration of the types of critical temperature errors that may be realized while performing services if we do not safely take that necessary step of removing ALL covers to have the line of sight to the target. For one to identify and quantify an anomaly on the exterior of an electrical enclosure, the severity of the problem and the amount of thermal radiation needed internally to be visible to the camera would be exponentially higher and near catastrophic failure. In this case, one would not want to attempt to open the enclosure while it was energized, and a shutdown would be the prudent course of action to correct the deficiency.
To be accurate in our analysis and identification of anomalies directly relates to our credibility with our customers. For this to be accomplished, we must follow established procedures each and every time we apply the technology. This becomes a function of the application and discipline we are practicing, along with the fundamental knowledge of the equipment we are performing services on.
It is an elementary requirement and an industry-accepted standard that to effectively perform infrared services on energized electrical equipment, it must be under normal load and operating conditions. Normal, admittedly, is defined as having the covers and dead fronts installed. However, from a maintenance and service standpoint, accuracy and precision must be the focus of our objectives, and this can only be achieved by the safe removal, each and every time, of both panel and any internal shields. This is imperative to ensure that our preventive maintenance programs do not overlook potentially critical issues and cause customers to experience unscheduled outages and equipment damage.
This information was taken from here as it is an excellent depiction of how thermal imaging must be conducted under normal load with the covers removed.