UPS reporting problems with Phase Difference and Frequency

The log message

On battery power in response to frequency and phase difference

sounds like the UPS is monitoring the incoming supply for early warnings of impending failure, and one of these is  that it thinks the mains frequency / phase is not what it should be - that is to say in the 50Hz waveform, the timing of the zero crossings of successive cycles are not sufficiently repeatable.

Unless there really is a problem with the incoming mains, this is likely to be a mistake,  or locally generated interference from some nasty sizzling load that shares the supply where the suppresion has failed, or the addition of some big inverter generation locally, such as a solar panel farm or wind turbines.

Is the PFC equipment some modern fast electronic thing, or traditional banks of capacitors ? - the former may itself be a source of interference.


However, if nothing like that has been changed, it is also possible that the UPS has programmable detection sensitivity, and after the repair work it has been reset to some new levels that are a bit too keen.

The UPS makers data should tell you what the limits are, and if they are adjustable. With some actual numbers we may be able to decide if what is going in is serious or if it can be ignored without problems.

its traditional, with stages of capacitors switched in and out with contactors. 


The site is full of inverter drives, and we do have a grid tied PV array too, but its been in for a couple of years. 


The sensitivity can be changed on the UPS, I think ill just do that regardless and see how it goes. 


There is also a MEM surge protector on the dis board that the UPS is connected to, and thats showing its status as working.

On battery power in response to frequency and phase difference

I'd suggest checking the UPS manual to see if it suggests what the fancy words mean - but I suspect it could be triggered by something quite simple - perhaps such as a brief loss of one phase (one phase at 0Hz then doesn't match the others at 50Hz, likewise a constant 0V doesn't register the expected 120 degrees from the other two) - so could be a simple loose connection.


Or it could be distortion of, or noise on, the normal sine waveforms that fool the UPS's detection electronics to think that the peaks/troughs or zero-crossing points are occurring at unexpected times. Matching the time stamp of the log messages with what else might be going on at the time might provide some clues.


  - Andy.

thanks for that, helps it make sense to me. 


With the size of the place, its full of machinery that could cause a voltage sag, and I know in the past we have seen the effects of supplies being switched around on the HV network. 


As expected, nothing further has come from the IT department regarding the issue, so ill wait and see!


Thanks

We had this problem on a little UPS several years ago

The Grid is obliged to maintain frequency between 49.5 and 50.5Hz (although apparently it usually does much better than that)

The UPS supplier had set the allowable limits much tighter than the routine variation in frequency, so we had the same problem

We just widened the limits to the Grid's maximum spec and everything was OK

You could check the manuals but much PLC and IT equipment that I've worked with is designed to work over the full range of 50 to 60Hz (and a wide range of voltages) so IMHO I would expect that most up-to-date equipment should tolerate a reasonable frequency swing.

Hope this helps

Ian

thanks for your reply, if i ever get logs, or to see the settings, ill be sure to check that too!