AVR (boost/trim) differences between UPS models

[marting]

Hi all,

We have various models of APC UPSes deployed at one of our sites and I'm seeing an interesting difference in the performance of the Automatic Voltage Regulation functionality between different line-interactive UPS models.

Last night - due to an increase in voltage from the utility, we had multiple UPSes kick into AVR mode (Event message: "UPS: Compensating for a high input voltage.").

While in this state:

• On a Smart-UPS 750, the output voltage dropped to ~ 110 - 112.5V
• On a Smart-UPS 3000 X, the output voltage stayed at 119.9 - 120V the whole time

Looking at the event logs on the UPSes, it doesn't look like either of them kicked over to battery so I'm assuming the AVR feature is trimming the voltage.

Question: both of these UPSes list AVR as a feature but the performance is significantly different.  Is there a way to tell from spec sheets, etc. what level of AVR exists on any given UPS model?

[Teken]

Generally speaking, the AVR is defined by upper and lower voltage limit defined under the Configuration -> Power Settings. The *Sensitivity* that is chosen from (Normal, Reduced, Low) will define when the UPS will transfer to battery power - I have appended a screen shot from the users manual.

[joc112]

Were you able to figure out why you saw these differences in AVR performance? Also, did that event message show up on your smartconnect.apc.com dashboard or are you monitoring differently?

[Teken]

As stated in 2024 the AVR circuit is defined in the power settings where the user has a limited range to choose from.

Depending upon model and firmware in place the upper and lower voltage transfer range is defined by the Local Power Quality setting.

Some units have the option to define the output voltage from 110, 120, 125 VAC. If this specific option is present it would offer tighter output voltage.

Other factors that affect the output voltage is Green Mode if available to enable / disable.

Other important considerations as it relates to both AVR / Battery only voltage output are design topology, component tolerance, age of system, firmware, and user defined selections.

A double conversion topology UPS will almost always have a tighter AC output vs a Line Interactive system. 

Lastly, the AVR output is physically defined by the transformer and where it’s tapped on the windings to buck / boost.

Questions Ask . . . 👍 

[marting]

I was not able to figure out why the UPSes were behaving differently.  They were both line-interactive (not double online conversion) models so - in theory - behavior should be similar.

I got the alerts via the DCE software, but the alerts should show up in the UPS log as well.

My understanding of the lower/upper voltage tolerance settings is that the UPS will actually kick over to battery if the voltage is outside the specified range; those settings are usually significantly off from the nominal/desired voltage.