Use thermography to diagnose electrical problems
In brief:
- Without an electrical preventive maintenance program, management takes on a greater risk of serious electrical failure, and the resulting consequences.
- Adding thermographic surveys to a maintenance program can bring significant cost savings to the plant’s operation. But there is more to it than simply purchasing an imager.
- With a properly implemented program, the documentation serves a higher purpose and helps to justify the funding of the program.
I was recently called to a medium-sized manufacturing plant to discuss providing infrared services during the construction of a new addition. While there, I asked the plant manager and his facility engineer about the predictive maintenance program for their switchgear and the possibility of providing thermographic services. The engineer stated they already had a program in place. The plant had purchased a small IR imager and used it to find “hot spots.” Thermography of electrical switchgear involves imaging the electrical components while they are in an energized or “live” state. They employed a two-person team to walk around the plant looking at switchgear. While both were trained electricians, neither was a certified thermographer. Whenever they found a “hot spot” they fixed it immediately by tightening any loose connections. He stated they could also immediately verify their repairs by using the imager and watching the temperature of the connection drop to a “normal” operating range. The engineer was quite happy with this system, stating it was efficient and no time was wasted by needless reports or sending another worker to fix the problem at a later date. The problem was found and solved on the spot.
What could be the problem with that? The most serious problem is that such a method is in violation of OSHA standards and NFPA 70E: Electrical Safety in the Workplace and NFPA 70B: Recommended Practice for Electrical Equipment Maintenance. If anything, such as an arc flash, were to happen during the survey, the plant would be immediately subject to substantial fines, not to mention damage to equipment, loss of production, and the serious injuries or loss of life of plant workers. This plant’s procedures were cobbled together in the belief that these time-saving shortcuts will also save money. The costs associated with a single accident would likely wipe out all the savings associated with previous shortcuts.
There were no pre-planned routes for them to follow; no images of anomalies found that were saved for future reference; no reports generated, documenting the anomalies found during the survey, and no method of tracking problem areas or their repairs and the costs associated with same. And, of course, because they were making repairs “on the fly,” there were no energized work permits. At least there was one positive note: the employees on the IR team performed their tasks in the appropriate PPE.
Safety first
Safety is always our the priority. While we all hear a constant stream of criticism against bureaucracy in general, and OSHA in particular, we need to remember one thing: every standard, law, regulation, or guideline is put into place because someone has been injured or killed by an event the rule is designed to prevent. When dealing with electrical hazards and worker safety, OSHA references NFPA 70E and 70B. Informative Annex J of NFPA 70E describes the process of determining if an energized work permit is required. No energized work permit is required for systems of less than 50 V. The next step is determining if there will be live components exposed. The answer is “yes” because a thermographic survey requires that components be energized and exposed for viewing. And next is the crucial part. What type of work will be performed? Any planned physical contact such as making or tightening connections or removing or replacing components while the system is energized requires an energized work permit. A thermographic survey does not require any physical contact with the exposed energized parts and therefore does not require an energized work permit. Any problems found during the thermographic survey will need an energized work permit if the repairs are to be made while the system is live.
While an energized work permit is not needed for a thermographic survey, repairs are not performed while the thermographic survey is taking place. An energized work permit is issued for each individual item that needs repairs or other work. In other words, it is not a "blanket" permit — for example, “All distribution panels in Maintenance Corridor A” is not a proper listing. The request gives a description and location of the circuit or equipment, along with what work is being done and a justification as to why the work is being conducted while the system is energized. The individuals doing the actual work must describe the procedures they will use and the safe work practices to be employed. Filling out the permit leads the personnel through shock-hazard and arc-flash analysis. It forces them to determine the various safety boundaries and plan methods of restricting the access of unqualified personnel from the work area.
There must be documented evidence of a job briefing, which includes a discussion of any job-related hazards and how they will be mitigated. The approval for the work permit comes from the plant’s general manager and is also signed by the safety manager, as well as the maintenance manager and the person doing the work. While this may seem tedious to some, it helps to ensure not only worker safety, but management awareness and support of the work being performed. This factor can also address a morale issue. In most cases, the maintenance department and its workers are invisible to plant operations until something important breaks. If nothing seems to break, the tendency is not to credit proper and continuous maintenance but rather to believe “that’s how things are supposed to be.” The requests for work permits allow management to see that well-planned and safely executed ongoing maintenance is responsible for the efficient operations of the plant. In this case, visibility is the key to a well-run and properly funded predictive maintenance program.
Certified
Figure 1. Engaging a trained and certified thermographer can prevent possible errors and mistakes during imaging and interpreting data. (Source: Stockton Infrared)
I never use the word “camera” when referring to an infrared imager. A “camera” is a consumer item which can be bought at any big-box store. Cameras employ “point-and-shoot” technology and are simple and easy to use. While modern imagers come in a form factor very similar to cameras, that is where the similarities end. It may be true that almost anyone can pick up an imager up and record an image, will it be a useful image? A common misconception with thermography is that infrared imagers measure the temperature of an object. They do not. Every object in nature emits varying amounts of infrared radiation. The amount of radiation emitted will be influenced by object temperature, surface condition, target shape, and viewing angle. This is called emissivity. Human skin emits infrared radiation at a very high level, while shiny metals such as copper emit very little. An object can also reflect the infrared energy from its surroundings. This is called reflectivity. Emissivity and reflectivity are linked. Objects with high emissivity have low reflectivity, and vice versa. The thermographer must enter the correct emittance of an object into the imager in order to get an accurate temperature. Other variables that must be considered include ambient air temperature, humidity, and distance to the target. So the imager can be used to show qualitative thermal differences in an object. In other words, the trained thermographer is able to detect thermal patterns in an object and determine when an anomaly exists. Remember reflectivity? A lot of electrical equipment is metal and is highly reflective of infrared radiation. The component being imaged can even reflect the thermographer’s own body heat and an inexperienced or untrained thermographer can mistake that reading as the temperature of the component. And detecting a hot spot isn’t the only issue. Is the increased heat due to a loose connection? Or is the circuit overloaded? These separate anomalies have their own characteristics, and a trained thermographer can tell the difference without first sticking a screwdriver into an energized panel to check for connection tightness (Figure 1). And some types of breakers are designed to operate at a particular temperature, which may be elevated compared to the other types of breakers in the same panel.
Paragraph 11.17.1 of NFPA 70B states, “Infrared inspections of electrical systems are beneficial to reduce the number of costly and catastrophic equipment failures and unscheduled plant shutdowns.” The use of thermography to perform surveys of electrical equipment is not only validated by NFPA 70B, but it is also recommended. It is also recommended that the personnel conducting thermographic surveys be “qualified and trained personnel who have an understanding of infrared technology.” Engaging a trained and certified thermographer can prevent possible errors and mistakes during imaging and interpreting data (Figure 2). It is highly recommended that a level-III certified thermographer take part in the design, implementation, and oversight of the plant’s IR predictive maintenance program. Level II should be considered the minimum level of certification for an individual imaging electrical equipment. A Level-II certified thermographer is qualified to interpret and evaluate the results of imaging with respect to applicable codes, procedures, and specifications, as well as properly calibrate imaging equipment. Many applications of IR thermography are qualitative in nature, and Level-I thermographers are able to perform those tasks. However, the imaging of electrical equipment involves the more advanced knowledge and experience of a Level-II thermographer in order to record accurate quantitative data. Utilizing properly trained personnel reduces liability while increasing the credibility of the program.
Figure 2. In the image to the left, the emissivity is placed at a very low setting to show how the imager interprets the input variables. At right, te same image is shown with the emissivity set to 0.99. Notice the change in temperature. Without all variables being known and taken into account, the exact temperature will not be known. But the image is still qualitative and an experienced thermographer is able to interpret the image for useful information without the temperature reading. The breaker at “A” is rated for 15 A and is currently loaded at 9.7 A (65% of capacity). The breaker at “B” is rated for 20 A and is currently loaded at 7.6 A (38% of capacity). The infrared condition of the wire tells the story. No amount of tightening will change the condition of the fuse. The loading on Circuit "A" is above optimum
Measure to manage
The key to any successful program is proper documentation. Documentation is not done for its own sake. With a properly implemented program, the documentation serves a higher purpose and helps to justify the funding of the program. The documentation is the basis for all of the metrics that allow management to make the important decisions concerning the plant. If maintenance is simply wandering around tightening loose connections without recording or documenting anything, what does management know or learn about the condition of the plant? They may only know the cost of paying the maintenance worker and the monthly amount spent of basic repair parts. Without documentation or a report of some kind, how will anyone see a trend or know if there is a bigger problem that needs to be solved? Are the same connections loose each time? Let’s say that, over the course of a year, the plant replaces five breakers a month on average. Those repairs may go unnoticed if not documented and tied to other maintenance reports. The repairs could mean nothing if each replacement was for a different piece of equipment. But what if each replacement was for the same piece of equipment? Now we know the problem is much bigger than a bad breaker. And remember, thermography allows the maintenance team to see the early signs of developing problems. The problems can then be fixed before they halt production and cause unscheduled shutdowns; or they can be monitored until the next scheduled shutdown.
The information gathered by the thermographers is documented in a report. The reports are given to management with an analysis of the equipment imaged during the survey. The report will list which equipment was imaged and which equipment had anomalies, along with a classification of the anomaly. In the reports, it’s useful to include not only the numbers, but also a pie chart displaying the criticality of the various anomalies found. It displays system health at a glance. The report is also used to generate work tickets for the maintenance department. The individual work tickets are also used to request energized work permits, if repairs are to be made to an energized system. The maintenance department then makes the repairs and documents that work. The repair is verified and documented in either a follow-up or the next regularly scheduled thermographic survey. With the proper documentation feeding a database, management is able to track the overall health of the system at any given time. The system can be as low-tech as manually created spreadsheets, or you can utilize a CMMS/EAM system. The point is it allows managers to see trends or patterns in the plant’s equipment through the maintenance program. They are also better able to calculate costs for maintenance and see the value of the program.
Ideal IR/thermography
The ideal method is to have a dedicated predictive maintenance team. The team may perform thermographic surveys as their full-time jobs, or they may only perform them monthly. Having dedicated personnel, or at least using the same personnel each time, allows them to gain familiarity and expertise with not only the task, but with each other. This familiarity and experience builds competency and increases efficiency. The team may be as small as two personnel. One will open and close electrical panels, while the other images the equipment once it is exposed. Whoever is using the imager needs to be a trained and certified thermographer. While the use of electricians is not required, all members of the team must be qualified personnel. A qualified person is defined by NFPA 70B as someone “who has the skills and knowledge related to the construction and operation of the electrical equipment and installations and has received safety training on the hazards involved.”
Working around energized systems comes with inherent dangers, and possible emergencies and responses must be addressed. OSHA requires that capabilities for both CPR and first aid be provided for in some fashion when performing work on electrical systems over 50 V, as stated in OSHA General Industry Standards (29 CFR, Part 1910, subpart R). There is no further guidance on the matter, and having trained EMS personnel on standby at the plant would satisfy the requirement. However, that is not a practical solution. If an accident occurs, every second matters, and immediate help is necessary to save lives. From a practical standpoint all members of the team should be trained in first aid and certified in both CPR and the use of automated external defibrillators (AEDs), along with training in the proper release of individuals caught in a live circuit. While it would be easier to simply have one of the team members trained as a first responder, what happens if that individual is the one who is incapacitated in an accident?
Greater efficiency can be achieved using a team of four. In such a configuration, the first person is opening cabinets, the second is imaging the switchgear, and the third is recording anomalies and taking notes, while the final member is closing the cabinets which have already been imaged. While performing the thermographic survey, the team’s sole job is conducting the survey along a predetermined route. They image the switchgear along the route and record their findings, which are later documented in their report. The team does not attempt to fix any of the problems they find along their route — remember, they don't have energized work permits.
Survey routes are determined by the program manager and are dependent on the size of the plant and the systems involved. A small plant may have only one route and can be imaged in a day. Large plants or plants with several complex systems may have multiple routes. A basic route may only need to be surveyed once a year, while others may need quarterly surveys. In some cases it may be a good idea to have the critical components of the plant’s operation on one route, with other sections of the plant broken up into other routes. That critical route can then be surveyed as needed to provide a snapshot of system health to management. That critical route may get walked monthly or as otherwise directed, while the other routes get surveyed on separate schedules. The important part is having the preplanned route. Doing so allows for repeatable surveys, which allow for easy system comparisons between multiple surveys of the same route.
Conclusion
Without an electrical preventive maintenance program, management takes on a greater risk of serious electrical failure, and the resulting consequences. A well-run program will minimize costly breakdowns and unscheduled shutdowns, as well as reduce accidents, potentially saving lives. The program has the ability to identify problems at an early stage, before they become major problems that will require costly and more time-consuming solutions. Any predictive maintenance program requires the support of top management. The programs require investments in not only equipment, but proper training for the personnel involved, as well as the extra resources needed for proper administration. Adding thermographic surveys to a maintenance program can bring significant cost savings to the plant’s operation. But there is more to it than simply purchasing an imager. The program must be well-planned, administered, and in compliance just like every other aspect of the plant’s operation. Properly executed, the program will save money while saving lives.