No, this isn’t the first line of a bad joke. Thermographers, like vampires, have a serious aversion to the sun. Thermographers won’t burst in to flame and become a pile of ash, but the effects of the sun can make outdoor inspections extremely challenging. Ask any thermographer who has attempted to inspect a substation or a building in bright, glaring sunlight.
One of the most detrimental aspects of performing infrared inspections in bright sunlight is solar loading. Solar loading occurs when a surface is warmed by solar energy and is a year round concern, even on cloudy days. Solar reflections can also be a big hurdle to overcome when performing outdoor inspections. Electrical equipment especially, contains a large amount of metals of various types, most of which are reflective, which increases the difficulty level of performing an inspection in sunshine exponentially.
I recently performed a multi-day inspection of outdoor electrical equipment, and we got a late start on the first day. By the time we reached the third sub-station (on a long list of sub-stations), the temperature was approaching 80° F and there wasn’t a cloud in the sky. Attempting to inspect overhead switches and connections was nearly impossible at this point. Every piece of metal I could see appeared hot, making anomalies very tough to detect. When everything you image is both reflecting sunlight and is warmed by solar energy, it becomes very difficult to identify anomalies and potential problems.
The best available solution was to re-group and re-evaluate our plan of attack. We were able to shift items on our route and spent the rest of the day inspecting metal-clad components that were not in direct sunlight. We re-scheduled the substations for early the following morning. If this is not possible, and you absolutely have to perform your inspection during the day, in bright sunlight, narrow your span and work slowly and carefully. It is possible to detect potential problems, but it will be difficult.
By starting our inspection well before sunrise the next morning, we were able to complete our task with confidence that we wouldn’t miss potential problems. Without the sun beating down on everything, we were able to easily spot anomalies that did not appear to have a large ΔT (but were anomalies nonetheless), and that we would have probably missed the day before.
Starting our inspection at 0500 enabled us to view the sub-stations as the load was starting to increase for the day. If we went too early, there wouldn’t have been much load on the electrical system, resulting in a less effective inspection. This is definitely a factor to keep in mind. NFPA 70B recommends at least a 40% load when inspecting electrical equipment (for more information on NFPA 70B, please see: http://www.thesnellgroup.com/Content/infrared-tip-outdoor-electrical-inspection-considerations.aspx ). This is the minimum requirement; greater loads are desirable if possible. If loads are high enough at night, by all means, go ahead and perform your inspection at night. This may be possible in some locations.
Some clients may not want to have their employees up and ready to meet you at such early hours, but if you explain to them the reasons why inspecting outdoor equipment in bright sunlight is not recommended, they may make an accommodation for you.
When performing IR inspections of outdoor equipment or buildings, timing is crucial. Early morning, before sunrise, is by far the best time of day for an inspection. The sun has not warmed up the surfaces yet, and for electrical systems, the load is starting to increase as people wake up and start their day. For those of us who are not “morning people,” getting up so early isn’t pleasant, but the payoff is definitely worth it. Just like the fabled vampires, thermographers can do some of their best work in the dark of the night. Time your inspections for optimum conditions, and you’ll get the most out them.