Jonathan Freedman rewt at eghetto.ca
Sun Dec 18 21:55:04 AST 2005

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>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>The amplitude (height) of the wave is changing all the time, as the load
.oO>on the system as a whole changes.
.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>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>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.
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