There were several very unusual frequency events on the Eastern Interconnection this afternoon. They all happened within 15 minutes. My PSFM triggered several times. I graphed the data in DPLOT.

On the graph above you can see a huge drop in frequency beginning around 18:47 UTC (2:47 PM EDT). A large drop such as this is usually caused by a generator tripping off-line suddenly, however, a drop of 83 mHz (0.083 Hz) is pretty rare on the Eastern Interconnection. To get an estimation of the magnitude there is a value called beta with units of MW/mHz. Normally beta is around 28 or so mHz. On lightly loaded days it can be lower. But if we assume it’s around 25 today then that means a total loss of around 2000MW of generation.

Following the generator trip event the frequency got to around 59.927 Hz, which is to be expected for such a large generation loss. However in the following minutes the frequency shot up to 60.067 Hz, which is very rare. The system frequency rarely goes above 60.04, so this is an unusual occurrence. It’s probably due to the light load conditions today, but I don’t know for sure.

Because there were three rare events within 15 minutes today I thought it was worth sharing.