RE: Online/double-conversion UPS economy/high efficiency modes?

[Alex Rubenstein <alex () corp nac net>]

> > I'm looking at several brands of rackmount 3kva double-conversion
> > UPSes, such as Tripp Lite and Eaton Powerware. I'm specifically
> > looking for something that will work as a line-interactive UPS until
> > the power starts to misbehave and will then switch to
> > double-conversion mode until a while after the last power bump.

Not entirely the topic asked, but we have good experience doing this at the 500 kva module level. We are using the 
'eBoost' method from GE, which is more or less what you ask for. It keeps the inverter and rectifier alive and 
energized, but current flow is via the bypass static switch. 

We have used this for about a year or so now, and even including hurricane sandy craziness, have seen in excess of 98% 
usage of eBoost. When in that mode, system efficiency jumps from about 92% to 99.8% efficient. A huge savings per 500 
kva / 450 kw. 

450 kw * 24h * 30d * 7.8% increase in efficiency is 25,272 kw-hrs saved per month, or at $0.12/kw-hr is 
$3,032/month/450 kw of load. 

The point is that it works, works well, and is green. 

http://www.gedigitalenergy.com/products/brochures/PowerQuality/brochure-eBoost-GEA-D1050-GB.pdf

To this point:

> even if it can switch - you are still taking that risk of power issues that will
> jump your ups and hit your connected equipment anyways.

If the overall power system is designed correctly, this should never be an issue. We did pretty extensive testing on 
this.

I don't know if anyone does this at the very-small level. I know GE's smallest unit is 300 kva for eBoost.


"Question everything, assume nothing, discuss all, and resolve quickly."

-- Alex Rubenstein, AR97, K2AHR, alex () nac net, latency, Al Reuben --
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