APC 7752 under frequency violation

[Anonymous user]

Hello, today I had a problem with the ATS AP7752 

Source A is connected to  UPS 1 

Source B is connected to  UPS 2 

frequency deviation is set at 2 Hz 

Preferred source is set to none

voltage transfer range is set to medium

The two UPS are connected to the commercial AC and they switch to a generator if a power outage occurs, the problem happen when the UPS switch to commercial AC again after the power outage, the ATS drops the load and show 0 A in the display, to solve this I had to press the front panel button to switch the preferred source as you can see in the last picture.

Any idea what could be the problem?

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[Terry_Kennedy_apc]

I don't have any good ideas for this. The only thing I can think of is that since the transfer switch will only change sources if the other source is "better", both UPSs switching back to AC power at the same time may cause the ATS to decide that neither source is good. If these are APC UPSs (and even if they aren't, but offer a similar option), you could try setting the "delay returning to utility power" to different lengths of time on the two UPSs. If one returns immediately and the ATS doesn't like that, it will stay/switch to the UPS that is still on batteries. By the time that second UPS then switches back to AC power, the first UPS should be supplying power that the ATS is happy with. I think the ATS will try to avoid switching sources more often than 30 seconds, so a 0-second delay on one UPS and a 60-second delay on the other might do the trick.

BTW, the log you posted seems to be from 10+ years ago. If that is because the time is not set on the ATS, you probably want to configure it to use an NTP server (or at least manually set the date / time) - it will make it a lot easier to correlate items in the event log with timestamps from other equipment. 

[BillP]

Hello,

When you walked over to the ATS, the output LED was off? This should typically never happen but I have seen it before - where the ATS needs manual intervention to turn the output back on. I have seen it in situations like what Terry described where both sources are potentially bad at the same time.

It would be helpful to see the full logs/configuration, if you could share event.txt, data.txt, and config.ini files from the AP7752. Instructions here on downloading those -> http://www.apc.com/support/index?page=content&country=ITB〈=en&locale=en_US&id=FA156131 

[Anonymous user]

The LED was on and the display showed zero amperes. I'll get the ;logs as soon as possible, thank you.

[Anonymous user · Accepted solution]

Nice idea Terry, thank you