It may take a little longer, but opening a single set of switchgear, or just a few buckets on one MCC at a time, not only reduces the effects ofconvective cooling, it is also safer as there is less energized exposed in the room at one instant. |
I’ve been a thermographer for a good while now –about 10 years. When I first picked up a thermal imager gasoline was under $2.00 USD per gallon, Arnold was campaigning to be Governor of California, and Ben Affleck was dating Jennifer Lopez (still having nightmares about Gigli, by the way, but I digress). We didn’t have Facebook, Twitter, iPhones or mobile hotspots back then. Man, how did we survive, huh?
When I first started inspecting electrical equipment with infrared, there was another phenomenon going on that has stuck around with some people; uncovering multitudes of panels and other devices, hours ahead of the actual thermal scan. I started my career in thermography with a company that had an impressive presence in commercial office properties. The process at the time was to send a crew ahead of the thermographer to take off panel covers, and the thermographer would follow behind, usually starting his route an hour or longer after the crew started to uncover everything. At that time, it was a rather widely accepted and used practice, not just in commercial applications. I can’t tell you how many times I went to industrial locations back in the early days and arrived to find that the in-house electricians had gone ahead of me and opened everything they wanted inspected before I showed up. Now, the upside was that, as the thermographer, I didn’t have to stand around and wait for equipment to be opened for me, I could just cook along and scan stuff. It felt like a good idea since we were able to maximize our time actually inspecting quipment. But, just like anything else, there was also a downside. Oh my, the downside.
Convective cooling, my friends. When we uncover a device, we expose it to the effects of convective cooling. In normal operation, the device cover prohibits air movement within the device. Once it’s uncovered though air movement cross the components increases and the potential exists for cooling to occur. Imagine how much cooling could occur if you uncovered a circuit breaker panel in a computer room, and the cooler air was able to move unimpeded across the breakers, buss, and lugs for four hours before you looked at it with your camera. Yeah, there might be problems that you could see immediately after uncovering it that would cool within a few hours of exposure. Heck, even a few minutes of exposure can be enough in some cases to distort data.
The old conventional wisdom should be dropped, and electrical devices should remain covered until just before they’re to be inspected. Although this may add some time to the inspection process, you may be able to discover lower-grade anomalies because you’re reducing convective cooling as much as is possible.
So, do it the new way; open, scan and re-cover!