sherwood@cbnewse.ATT.COM (charles.a.sherwood) (01/12/90)
Someone stated that they did not know of any equipment that caused a capacitive power factor. One of the engineers in our power supply group told me that switch mode power supplies have a capacitive factor of about .65 due to the low conduction angle. This would imply that any electronic equipment that uses a switch mode power supply would have a has a capacitive power factor. This would include PCs, computer terminals and maybe even your TV. How would an office building that has a few hundred terminals correct for this? Big inductors? chuck sherwood
logajan@ns.network.com (John Logajan) (01/12/90)
sherwood@cbnewse.ATT.COM (charles.a.sherwood) writes: >Someone stated that they did not know of any equipment that caused a capacitive >power factor. Way back in my tech school days, my instructor claimed that the power company used certain types of motors at various locations along the line to balance the inductive power factor with a capacitive power factor. I don't recall which type of motor appears capacitive. -- - John Logajan @ Network Systems; 7600 Boone Ave; Brooklyn Park, MN 55428 - logajan@ns.network.com, john@logajan.mn.org, 612-424-4888, Fax 424-2853
jeffw@midas.WR.TEK.COM (Jeff Winslow) (01/13/90)
In article <12525@cbnewse.ATT.COM> sherwood@cbnewse.ATT.COM (charles.a.sherwood) writes: >Someone stated that they did not know of any equipment that caused a capacitive >power factor. One of the engineers in our power supply group told me that >switch mode power supplies have a capacitive factor of about .65 due to the >low conduction angle. This would imply that any electronic equipment that uses >a switch mode power supply would have a has a capacitive power factor. Power factor in switchers is due to a fundamentally different phenomenon than in inductive loads. As you say, the low conduction angle translates into a much higher RMS input current that one would expect from the power consumed, hence P/VA deviates from unity. However in my experience it's a tossup whether the (fundamental of the) current leads or lags the voltage. It's true there would be a tendency to lead, since you're charging partially discharged capacitors, but usually there's enough impedance in series (EMI filters, etc.) that there is significant current conduction on both sides of the voltage peak. Most of that .65 figure is due to the small conduction angle, not phase shift. So all those PC's aren't going to help balance much of an inductive power factor. Phase shift or not, it's considered enough of a problem that there's a fair amount of research going into how to cheaply and reliably correct it. Jeff Winslow
sic@ritcsh.cs.rit.edu (Eric A. Neulight) (01/16/90)
In article <12525@cbnewse.ATT.COM> sherwood@cbnewse.ATT.COM (charles.a.sherwood) writes: >Someone stated that they did not know of any equipment that caused a capacitive >power factor. One of the engineers in our power supply group told me that >switch mode power supplies have a capacitive factor of about .65 due to the >low conduction angle. This would imply that any electronic equipment that uses >a switch mode power supply would have a has a capacitive power factor. Running a synchronous motor 'overexcited' (with high field current) will create a capacitive load, and it is adjustable. This is common practice in industry to balance the power factor. The motor runs hotter, but if rated current is not exceeded (they are made to handle it), not only do you get greater maximum torque, but it can be put to usefull work. I don't fancy trying to correct the power factor with a bank of switchers :-) ============================================================================== CLAIMER: Well -- I wrote it! Eric Alan Neulight "Nothing is Impossible -- Just Impractical." Electrical Engineering "For every Lock, there is a Key." Computer Science House "INSANITY is just a state of mine." Rochester Institute of Technology BITNET: EAN4762@RITVAX IP: sic@ritcsh.cs.rit.edu ==============================================================================