Came across an old friend this afternoon, low frequency transients related to utility or facility power factor capacitor switching, controlled via a timer (rather than sensing voltage, current, or power factor)
Here’s the voltage waveform – this seems to be a very minor transient, hardly worth noticing.
Adding the current, we see a small ringing current related to the transient event. Oftentimes with more severe transients we see a large current swell.
The RMS voltage logs show a small but clear step increase in voltage at the time of the transient, clear sign of power factor correction capacitor switching.
Finally, here is a table of all such transients captured. Notice how each transient occurs at 7:03 am, on different mornings. This sort of “same time every day” incident is a clear indication that the capacitor bank is on a timer control.
Not a super serious issue, this time, but interesting to come across a timer based system. They seem to be increasingly rare as more sophisticated controllers are brought online each year.