The facilities guy helped us find a more sophisticated power line monitor, and we installed it in the lab. The first day we could easily see the problem: Just after lunch time, as all the engineers and technicians all over the plant came back from lunch and powered up their test benches and the equipment under test; the power factor began to swing far over toward the inductive side. Our earlier voltage-only tests didn’t see the roughly 30 percent voltage drop that all the power supplies in the radar felt. And when the power got far enough out of spec, the signals that energize the contactors would drop and turn off the radar.
But knowing what the problem was didn't explain why it was happening so suddenly, nor how to fix it. Yet now that we knew the essence of the problem, it only took a bit more investigation to solve the next levels. Our powerful, jet-engine-like cooling fan also ran on 400Hz, and we were one of the first labs to switch to those from the original old clunky 60Hz air conditioner units with the poor air flow. And these fans were gradually being added to other labs too, including some of the ones that also reported similar problems.
So, when all the engineers and technicians came back from lunch, it wasn't just the already-inductive loads on their radar equipment drawing on those 400Hz generators; it was also that sudden surge of the cooling fans spooling up that tipped the power factor beyond any previously anticipated limits.
But how to fix it? Well, that turned out to be the easy part. During my conversation with the facilities engineer, he had proudly showed me the new solid state, 3-phase, 400Hz inverters that were being installed to replace the 40-year-old motor generators. The “power factor correcting” inverters that is. Facilities sped up the installation of the inverters and looked at ways to break up our 400Hz distribution network to minimize the inductive effects of the transmission lines, too. In the meantime, for a few weeks, we adjusted our schedule to take a leisurely, slow, late lunch; and came back after the power rush had subsided.
This entry was submitted by John Shepley and edited by Rob Spiegel.
John Shepley is an electrical engineer with a broad experience base. In addition to 11 years of experience in the defense industry, he has worked as a management consultant, a project and business manager for a wireless dot-com, and is a part owner of a wholesale nursery where he designs and builds alternative energy solutions for power and heating. He currently is working in Italy on driverless subway projects.
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