DrewE wrote:
The error is most likely caused by some noise on the power lines that the EMS is somehow interpreting as the incorrect frequency. The power supply from the electric grid is quite well regulated in terms of frequency, within 1 or 2 Hz at the very worst under normal conditions (instantaneously) and within a tiny fraction of a percent when averaged long-term. The long-term accuracy is due to the need to keep clocks that reference the power line from gaining or losing time on average: a 1% error there would mean their gaining or losing about fifteen minutes over the course of a day, which is clearly not acceptable.
The main problem you might see if the frequency were actually well out of specification are some clocks and timers running fast (or slow)--these days, that's mostly mechanical appliance timers, as digital electronics generally use a crystal oscillator or similar timebase independent of the line frequency. Synchronous AC motors will try to run at a different speed, but for most household devices that's not a concern as their actual speed is usually a result of mechanical loading rather than synchronous line frequency. It would take a quite large deviation to cause "real" problems that might damage things.
Most clocks now days do not depend of the line frequency for time keeping, heck even finding an new old fashioned synchronous motor driven clock is pretty difficult to impossible find now days. Most clocks are fully electronic driven with a crystal time base oscillator and only periodically "sample" the line frequency to snap the oscillator back into sync. Lots of battery powered clocks now days and much of the world uses their cellphones for time/alarm functions.
Induction motors do not care very much about frequency and are often marked 50Hz/60Hz which means they are designed to operate a bit below 50Hz to a bit above 60Hz and still operate efficiently and be operable anywhere in the world.
Much of the electronics world have moved over to switching power supplies which 100% ignore line frequency by rectifying and brute force filter the incoming AC line to DC then run the DC through a chopper at high frequency.. They too are also pretty much always will be rated 50Hz/60Hz which allows that power supply to be universally used anywhere in the world..
Line frequency from PoCos now days does indeed vary..
Here is a couple of snap shots from this morning..
Did see a 60.2 briefly but was not able to get a photo of that..
The frequency was changing consistently every second and I verified that on all three UPS units I have with that display while the same model were manufactured in different yrs.
Typically I will see a constant 59.9 or 60.1 for hrs on end, today, not so much.
While these examples are not +(-)1 Hz they do show that the grid frequency is not "rock stable".
I suspect however that the OPs EMS has a fault and will require replacement since it should tolerate enough frequency variation that comes from not only the POCO but a generator. Most generators will vary from 62Hz unloaded to 58Hz fully loaded.
