UK Old Three phase UPS wasting electricity?

[jimbobbrad]

I'm hoping someone can sanity check or correct my thinking. I have a very old UPS, it's showing a power factor on the front display of 0.1

We put a clamp meter on the 3 incomers which all read 36 Amps. the 3 outgoing legs are showing 12, 6 and 4 Amps

That's 108 Amps in and 22 Amps out, I'm wasting 86 Amps?

86Amps is roughly 20kW x 24Hrs x 365Days x 35p/kWh = £61K

Am I really burning £61K?

My plan is to replace this relic with a modern smaller UPS but want to be able to confidently say to my boss that I'm spending £10K on a new UPS and will save £61K.

TIA

 

[James]

what sort of load are you expecting to be using?
36A at 400v 3phase is about 25kw
if the power factor is indeed 0.1 then that equates to 2.5kw of useful energy consumption

 

[jimbobbrad]

what sort of load are you expecting to be using?
36A at 400v 3phase is about 25kw
if the power factor is indeed 0.1 then that equates to 2.5kw of useful energy consumption

The 22 Amps on the output is my live load, this UPS has been installed and running for about 20 years. We're going to replace it with a new smaller one and the load will reduce slowly over the next few years as we decom kit.

I just wondered if I'm right that the current running cost of my 22 Amp load is really £60K and wasting lots of money using this relic of a UPS

 

[Lucien Nunes]

No, your calculation is flawed. Multiplying volts and amps gives you the 'apparent power' which does not take into account the power factor and is not what registers on your electricity meter. You pay for 'real power' which is apparent power x pf, which, if your displayed 0.1 is to be believed, is only a tenth of that amount. At very low pf (<0.25) it's likely that the waveforms are distorted and the measurements are significantly inaccurate anyway. So personally I would not infer anything much just from the figures you have quoted. In addition to the currents, you would need to know both the input and output pf to calculate the input and output real power and hence calculate the loss in the UPS.

In the absence of reliable figures, you can estimate the power loss quite well by how much heat the UPS gives off. All wasted power gets dissipated as heat and all electric heaters are equally efficient, so you can make a comparison with any heating appliance. E.g. If the unit has a cooling fan and it's blowing out as much heat as a fan heater on full, it's probably losing about 2kW. Or If the fans are stopped and it's just a big warm box, then if it's not as hot as the outside of a domestic oven in use, it's probably not losing more than 1kW. If it had really been dissipating 20kW, it would be like a commercial space heater blasting out a huge jet of hot air.