[nSLUG] UPS

Jason Kenney jason at ohm.ath.cx
Mon Dec 19 06:49:38 AST 2005


I'm just trying to justify spending 4+ years doing an engineering degree.

Every little bit helps.

On Sun, 18 Dec 2005, Jonathan Freedman wrote:

> You love physics, don't you.
>
> On Sun, 18 Dec 2005, Jason Kenney wrote:
>
> .oO>> I'm not going to pass myself off as an expert on electricity.
> .oO>> However I don't understand the above.  If a UPS produces
> .oO>> power that is dirtier than from the electrical company, then
> .oO>> why do we have them?
> .oO>
> .oO>There are two types of dirty too. I suspect people are probably not too
> .oO>familiar with the look of the wave coming off the line.
> .oO>
> .oO>The amplitude (height) of the wave is changing all the time, as the load
> .oO>on the system as a whole changes.
> .oO>
> .oO>In addition, the shape of the wave is far from a perfect sine. This is
> .oO>changing too, but less than the amplitude. (Although I suppose they are
> .oO>related - the amplitude of the frequencies components are changing
> .oO>relative to each other, which is what changes this shape).
> .oO>
> .oO>The only thing about the wave that can be even approximately called
> .oO>"perfect" is the frequency. The amount of variability of this is
> .oO>specificed by law I believe, and is very tightly limited (something like
> .oO>no more than .001% deviation over the course of a year).
> .oO>
> .oO>Frequency is important for time-sensitive applications. The others don't
> .oO>matter at all really. Things that take big AC are motors which don't care
> .oO>too much about the look of the wave. Lighting and heating don't care about
> .oO>either. Most other things are DC, so they just need a frequency/amplitude
> .oO>combo they can regulate.
> .oO>
> .oO>
> .oO>Jason
> .oO>
> .oO>
> .oO>
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