Smart-UPS X 3000 was still compensating the power output after the voltage has gone back normal

[BillP]

My company owns  Smart-UPS X 3000.

One of the UPS showed an error "UPS: Compensating for a low input voltage.".

But after 20 minutes, it still shows that it has a poor input and was still compensating the power output. We looked at the input voltage and frequency. They are just normal and within the range between output upper limit and lower limit.

Is it by design? It stopped just after we manually perform UPS self-test. When would it stop automatically?

And for the option "Sensitivity", is it related?

[BillP]

Hi,

The UPS should have switched over automatically. Running the self-test or resetting the UPS was the proper solution. 

On 5/26/2016 10:33 PM, H said:

And for the option "Sensitivity", is it related?

For information on Sensitivity please review Knowledge Base document FA156514 "What are the different sensitivity settings of a Smart-UPS?"

[BillP]

Running the self-test or resetting the UPS was the proper solution. 

It sounds very odd to me that if this occurs at night or in holidays, the UPS will be in compensation mode for a long time.

[voidstar_apc]

If the input is still near the limits, the UPS will continue to compensate due to hysteresis.

[BillP]

Thanks! Is there any manual talking about this kind of hysteresis? i.e. the formula or decision tree for the UPS to judge whether it still needs to compensate? 

[voidstar_apc · Accepted solution]

I'm not sure where it's documented.

The idea is when the voltage is moving around the limit, the UPS designers want to avoid the UPS switching rapidly in and out of compensation. So say the upper limit is 260 V and there's 2V of hysteresis, it'll start compensating at 260 and will remain in compensation until voltage drops below 260-2 => 258V. You can determine the hysteresis amount experimentally using a variac.