My first job out of college was working for the power company in southwest Virginia. It was a great first job. I was exposed to things that went bang and zap. (I still get a kick out of those, even at my age.) There, I learned almost every aspect of electrical engineering. I was assigned to the communications group that maintained the company's carrier relay, cable carrier, microwave, telephone, and VHF radio systems.
Mainly, it was office work, but I got to go out with the field service crew from time to time. The job had me knee deep in snow in a power station, under a greasy line truck fixing a VHF radio, and then 150 feet up a tower checking lightning sensors. A job like that is hard to disconnect from when you get home at the end of the day.
One day, I came home about 5:30 p.m., walked into my apartment, and turned on the lights in the dining room. Much to my surprise, they were visibly flickering. I pulled out my trusty multi-meter and plugged it into the wall outlet. The voltage was all over the place. In the two or three minutes that I measured it, I saw voltages as low as 80 volts and as high as 135 volts. It may not have been the most accurate meter, but I knew that the voltage was way out of spec.
Since I regularly worked with the operations center during the day, I had the number. I called the center and reported what I had found. Then suddenly, the flickering stopped. I thought the center had done something to alleviate the problem, but I found out the whole story a week later.
What happened was that there was an electric steel plant on the same feeder that eventually made its way through the substation to our apartment complex. The plant had recently been moved to our feeder, which was rather lightly loaded. It started its smelting process at about 3:30 p.m., and the transients that came back down the feeder were extraordinary. There is usually a variable-tapped transformer in the substation that adjusts to smooth out fluctuations in voltage for downstream customers. What happened was that the transients matched the frequency with which the transformer adjusted the voltage, causing it to oscillate wildly.
What made me think that the operations center had done something was that, between 5:30 p.m. and 6:00 p.m., almost like clockwork, lots of people came home and started making dinner, taking showers, and washing clothes. This is called load. Power companies see this load happening every day. When the load built up, the transformer settled down, its oscillations were damped, and my lights stopped flickering.
This entry was submitted by Dwight Bues and edited by Rob Spiegel.
Dwight Bues is a Georgia Tech computer engineer with 30 years of experience in computer hardware, software, and systems and interface design.
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