[This is the second part of a series started in February. The first part is here.]
A few years ago I took a look at the AC power here at my house on an oscilloscope. I had done this when I first moved to Yerington, Nevada in 1999 and saw a sine wave with a few glitches here and there. Now I saw a strange waveform that was far from a sine wave. To make sure this wasn’t caused by some odd load in the house, I shut off all the power except for the scope, and the waveform was unchanged. I called my friend Wally in Sunnyvale, California and asked him to check his power, and he found essentially the same waveform. Here is a waveform I took recently, which is similar to what I saw a few years ago:
What has caused the change over the last ten years? My theory is that the amount of non-linear loads on the power grid has increased dramatically. These are almost always power supplies with capacitor-input filters which draw current only at the peak of the waveform, thus flattening the waveform. The large increase in the use of computers with their cheap switching power supplies as well as the program to replace incandescent light bulbs with CFL lighting is probably driving this. I saw this “flat-topping” effect on the power line waveform when I worked at Tandem Computers in the 1980s. The buildings were filled with multi-processor mainframe computers with multiple 1 KW switching power supplies. However, the waveform at my house in San Jose, in a residential neighborhood, was a sine wave. The waveform I see now is deranged in a more complicated way.