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My question is why it is easier to correct an inductive power factor with a capacitor and not a capacitive power factor with a coil?

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  • \$\begingroup\$ As I understand it, both are equally easy, but large loads (those for which correcting the power factors matter) are large motors, with inductive power factor. \$\endgroup\$ – user2233709 Apr 11 '17 at 8:44
  • \$\begingroup\$ What do you mean by preferred? If you have a load to power, you're stuck with the power factor it has. You can't run you laptop instead of your fridge just because your laptop has a better power factor. Anyway, the best power factor (in terms of losses) is a purely resistive one, not inductive. \$\endgroup\$ – Dmitry Grigoryev Apr 11 '17 at 13:01
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It's just as easy both ways theoretically but consider "size" as the main practical limitation. A 10 uF non-polarized capacitor running on 230 V AC will have an impedance of 318 ohms at 50 Hz and you should be able to hold a couple of them in your hand (discharged of course) very easily. They will also be less than a dollar each.

The equivalent inductance is about 1 henry and will take a current of about 720 mA and, to avoid saturation problems will weigh more than a couple of kilogrammes and not that easily fit in your hand. Price probably about $10+.

But, the bottom line is that most pieces of equipment that cause non ideal power factors are motors and these are corrected by capacitors.

Why is inductive instead of capacitive power factor preferred?

It's not anyone's preference, it's practicality.

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    \$\begingroup\$ When I look around in my house, or office, the majority of things messing up the power factor are smps or capacitive droppers. I would guess that in industrial environments motors are the worst \$\endgroup\$ – PlasmaHH Apr 11 '17 at 8:59
  • \$\begingroup\$ @PlasmaHH Sure, most of the devices are. But most of the load (excluding heating, which tends to be resistive) is going to be in the motors in your AC unit, fridge, ceiling/standing fans etc. \$\endgroup\$ – Someone Somewhere Apr 11 '17 at 12:09
  • \$\begingroup\$ @PlasmaHH yes, in industrial environments, inductive loads prevail. \$\endgroup\$ – Andy aka Apr 11 '17 at 12:57
  • \$\begingroup\$ @SomeoneSomewhere: Hm, my fridge has like a 90W motor, same for the chest freezer, and the motors are definitely not running for most of the time. No ceiling fans, no AC, I think somewhere in the basement there mightbe a standing fan. The lawn mower and vacuum cleaner are probably the highest powered motors, but then again they run like once a week or so. I would be the majority of the ~400W average consumption in my house comes from multimedia network and generally technical equipment, all so small that they don't do any PFC. \$\endgroup\$ – PlasmaHH Apr 11 '17 at 13:21
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    \$\begingroup\$ SMPSUs are tricky to correct for externally because they aren't really either capactive or inductive. Instead they are harmonic generators. The best way to fix power factor problems from SMPUs is to redesign the SMPSUs themselves. \$\endgroup\$ – Peter Green Apr 11 '17 at 14:47

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