SW Efficiency/ PWM Angle Adjustment [RE-wrenches]

[Jeffrey Wolfe, Global Resources]

Hi Sharkey,

These ideas are not too "flash", as they exist now.  Many large facilities 
use capacitor banks to correct power factor. Some use smaller capacitors at 
devices, however, this is less common as these devices also "eat" any 
signals placed on the power line (common for synchronized clocks, etc.) 
This is important as large users get charged a significant fee for power 
factor outside the specified range. (usually must be better than .85 or .9, 
depending on the utility).

As I understand it, the old Trace UPV inverters are capacitor based. (As 
David Blittersdorf recounted recently, he had to increase the caps to make 
his work with more PV).

So it's not actually the PV that makes the pF correction, it's the caps 
that change it. The place I get confused on is whether or not the actually 
saves energy. It does save capacity on the distribution lines, as unity pF 
results in the lowest VARs on the lines, and lines are sized on VARs, not 
kW. I also think it makes rotating generators work more efficiently, which 
does save energy, but I'm not sure on this one. (I'm ducking...)

I also think Home Power (The magazine of Homemade Power Factor) had an 
article on how power factor affects battery based off-grid systems. Of 
course, I'm having trouble recalling the conclusions... (just 'cause it's 
Friday PM. No other reason.)

Jeff


On Friday, September 07, 2001 1:04 PM, Mr. Sharkey 
[SMTP:sharkey at eugeneweb.com] wrote:
>
> 	Eric;
>
> 	At this point, there are no inverters (that I know of) that correct for
> power factor beyond what the designers would consider "normal" and
> necessary for the inverter to react properly with the utility power to
> backfeed the system. It's an interesting concept that a grid-tied 
inverter
> might be capable of correcting the entire building's electrical service 
to
> unity, therefore making the building's consumption (or production) look
> like a pure resistive load (supply) to the utility. At this point, it's
> only a concept. It would probably take a lot of PV's and a really big
> intertied inverter to correct for the amount of reactance in a typical
> utility service load. That doesn't stop me from thinking about the
> possibility.
>
> 	Earlier this year, at the Oregon Country Fair, I had this discussion 
with
> some of the Wrenches in attendance, and we thought it was a pretty flash
> idea at the time. Even just loading the AC line with capacitors would go
> some way towards improving the efficiency with, *or without* an intertied
> inverter in the system. I'd think utilities would be very interested in 
the
> possibility of subscribers being able to correct for PF losses in their
> distribution system. Maybe this is another tendril of the net metering 
vine
> that can crack the wall of utility resistance to intertied systems. A
> premium price paid for independently-produced, unity PF electricity! 
Yay!!
>
> 	Extending the concept even farther: What if, instead of 
transformer-based
> inverters, we could develop capacitor-driven inverters? They would, by 
the
> laws of physics, be on the right side of the PF correction fence. This
> might be a better topic for HP's "The Wizard Speaks" column. Again, 
thought
> process need have no boundaries. Generally, it's been proven, if we as
> humans can think it up, (eventually) it becomes reality.
>
> 	-S
>
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