Backup Time of UPS

Switch off the mains and measure it.

What do the original commissioning records say?

Er, wouldn't it depend upon the condition and state-of-charge of the batteries at the moment of mains disconnect? Are these batteries new or what?

And, are you powering both circuits at the same time?

...and is this 30min backup time governed by a pre-programmed timer within the UPS?

The second.

First up, If the 30min is due to software settings in the UPSs, they will both go offline at 30 mins.

Your first load is 5kVA X 0.8 = 4kW

Your second load is 5kVA X 1 = 5kW

Now that the values are the same, you should be able to work out which will drain first.

Regards,
Sapper

With voltage level of 220V

The second load will draw 5kW real power (I=22.72A)

The first load will draw 4kW real power (I=18.18A) + 3kVAr reactive load (I=13.63A) with the same magnitude of 22.72A.

My question is: does the 13.63 A of reactive load give different result compare to 4.54 A difference of the real power?

Well, it does rather depend on the resistance of the downstream cable:

• Are all the connections tight?
• Is it correctly sized?

Has the experiment been carried out yet?

Thank you all for the comments, but maybe I have to rephrase my question.

The rating of the UPS is 10kW/12.5kVA 30 minutes of backup time, that is equal to 6.25 kVAh.

Can I say that, with 5 kVA load, regardless of the pf, the backup time should be 1 hour and 15 minutes?

I think this paper should clear up any confusion.