please correct me if im wrong, i am under the impression that resonance and power factor are the same thing when talking about transmformers and caps. the think im wondering is for example when achieving resonance on the out put of a Microwave oven transformer the caps are in series with the xfomer. but if i wanted PF correction on the primary side the cap would go in parralel. im not playing with a transformer, just wondering from what i have gathered on the net. can someone please clarify this? TY

 

Resonance is when an L and a C have the same impedance at the frequency of interest. Power factor is the difference between minimal current to do the job and current flowing in and out of a reactive component, but not doing any work. By adding a capacitor to an inductive load, you can seemingly resonate the circuit so that working current is recycled between the inductor and the capacitor and the current flowing from the power line is minimized. You can add a capacitor to change the power factor on the primary, but it eats the crap out of the relay contacts (or the triac) by allowing huge start currents. Don't do it. The power company doesn't charge for current that isn't doing any work, so there is nothing to gain on a household appliance except melted relays.

The output of the microwave transformer has nothing to do with either of these. It is a voltage doubler circuit where the current charges the capacitor through a diode on the first half cycle and shoves that charge and another equal charge through the magnetron on the second half cycle.

I've tried to respond at the intellectual level you used to ask the question, but someone else will be along quickly to explain this in exquisite detail, complete with mathematics and several corrections of my casual way of saying things.

 

<snip>. The power company doesn't charge for current that isn't doing any work, so there is nothing to gain on a household appliance except melted relays.

<snip>.

Although true for most residential usage, it is quit different for large capacity utility users.
Check this out.....http://lansing.apogee.net/foe/frbp.asp