Does power factor fluctuation affect my UPS?

Question

I have noticed that my UPS is showing a power factor of 0.7 during the day and 0.55 at night. I did some online research and found that this is caused by load imbalance, and a low power factor means that the UPS is inefficient. My concern is that this low power factor may cause harm to my UPS in the future. I also wanted to know if there is any reason other than load imbalance that is making my UPS power factor low.

Answer 1

In general UPSs are rated based on Wh and VA.

The Wh rating relates to the amount of energy that is stored in the batteries, and can be provided on mains failure.

The VA rating indicates the maximum current that can be provided at a given output voltage by the UPS. It is related to the current limits of the output stages (generally in turn tied to I2R heating).

PF is defined as the ratio between apparent power (VA) and real power (W), so as PF goes down, the real power that can be delivered from a given UPS (which has a fixed VA rating) goes down.

For example, if a UPS is rated for 1KVA and the load has a PF of 0.5, then the maximum real power than can be supplied is 500W.

Low PF is therefore not an inherent risk to a well designed UPS, but it will reduce the real power that can be delivered.

Answer 2

One cause of low power factor is loads that don't have adequate power factor correction. If it's worse at night, then that might be large numbers of cheap LED lamps.

You'd need to check the UPS maker's documentation to see what power factors it can handle. As colintd notes, you may have a much reduced maximum true power output at low power factors.