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EEVblog 1482 - Mains Capacitor Zener Regulator Circuit

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ticktok:
Thanks Golden_labels.. Yes, but this cap is included in the circuit for practical reasons, and even though the losses are negligible, this minute amount would be offsetting a naturally inductive grid right? Everyone is a winner when capacitors are used as load droppers in these grid connected domestic appliances? Dave seemed to suggest that there would be some sort of cost that is passed on to the generators, so I am a bit confused.

Kleinstein:
For this application wasting a little power is not a problem - it is a heater after all and supposed to convert electricity to heat.  So heat lost in the electronics is not even really lost.

golden_labels:

--- Quote from: ticktok on June 26, 2022, 04:09:01 am ---this minute amount would be offsetting a naturally inductive grid right?
--- End quote ---
No. The current still goes back and forth along the wire. Just in this case to the inductive load elsewhere in the grid.

Power factor must be corrected at the spot where it is needed. Between the load and the device used for power correction, whether it is a capacitor, an inductor or an active power correction circuit, the losses are still present and unavoidable. This is why the capacitor banks mentioned by tunk are near the motors and not simply rented from some company 40km away.

This is not a physically correct analogy, but imagine a tall pole on top of which some person swings back and forth. Your goal is to keep the pole stable. A hard task, right? You are the electric grid, the person on the pole is the load. I believe we will both agree that giving you a task of stabilizing a second pole with another person swinging is not making that task any easier. What you need is both persons to be on the same pole, swinging in opposite direction.

Peabody:
Do things like air conditioning compressors have capacitors built in to correct the power factor?

Kleinstein:
3 phase motors usually don't have a capacitor for PFC correction build in.  With variable speed motors the power may go though a rectifier and inverter. In this case they should have PFC included for more than just the capacitive / inductive part but also the harmonics ( a simple rectifier gives pulsed current and thus harminics a simple capacitor does not correct very well).
With a 1 phase induction motor there normally is a capacitor as part of the normal motor function and this capacitor may very well also do some PFC correction.
Quite often the phase angle is noted on the name plate - at least there is often a field for this, though not always filled in. So one can see how bad it is. For normal private home use there is no much to worry about as the reactive power is not charged extra and the utilities take care of the phase shift by adding more or less capacitors at the distribution transformers (at least in Europe - the small ones in the US may not have this).

The inductive reactive power is mainly an issue with industrial use from multiple large motors and also in a 230 V country with old style balasts for fluorecent lamps. With the lamps it was common to have some (e.g. every 3rd or 2nd) run with a series capacitor and do some compensation (with additional flicker reduction). Those old style lamps are a thing of the past anyway.
There is no need to get perfect local compensation - as long as the reactive power is small the losses are also small as the resistive loss goes with the square of the current. So not much to worry about 10% reactive power: that would increas the wire losses by some 1% (1% of the loss not 1% of the total power).

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