PF capacitor INCREASES consumption

[kripacharya]

It has been generally noticed by many home consumers in my neighbourhood that addition of a Power Factor Correction capacitor actually INCREASES the billing.

Now ideally the addition of such a capacitor should have no effect on the actual consumption or billing of the consumer. All it should do is to improve the PF as seen by the electric discom.

So is there any situation where addition of this cap would actually increase the billing (i.e. real power as measured by the local meter) ?

 

[KlausST]

Hi,

i know how mature and modern energy meters work.
All i have seen don´t increase the energy with the addition of a PF capacitor.

It truly measures real power.

But keep in mind: if your capacitor gets warm - then this is real power, the same is with the wires to the capacitor.

Best is to try it: Maybe at night - switch off all unnecessary load (switch off fuses).
wait for an exactely one hour and see how much your energy meter conts up.
Then install your PF capacitor and wait another hour and see again how much your energy meter conts up.

Good luck

 

[dick_freebird]

That's why the power company likes to make big users have a
resistive power factor - it makes dumb meters read right.
That's high, for them.

 

[FvM]

It has been generally noticed by many home consumers in my neighbourhood that addition of a Power Factor Correction capacitor actually INCREASES the billing.

First question, why did they install PFC capacitors at their home, how did they calculate the VAr number, what did they expect?

Second question, how did they exactly observe increased energy consumption?

First comment, depending on the wiring and correct size, PFC capacitors can either increase or decrease cable voltage drops and so indirectly affect the power consumption of other loads. Usually the effect will be very small.

Second comment, at first sight, I won't believe the reports.

 

[kripacharya]

FvM :
at first sight, i didn't believe the reports either.

The capacitor value was prescribed by the discom based on the sanctioned max load for that home. What calculations the discom did is unknown. The lowest max load category is 10KVAr

There is no 'exact observation' in so far as a controlled test. However the 'general feeling' amongst the neighbourhood is that their bills were higher than the previous months/ year.

There could be an element of psychosis involved here, but so many folks reported this that I felt its worth looking into.

The only thing I could come up with is that the PFC cap itself is consuming energy continously - it does get warm - but would that be a noticeable amount ?

Also since these are single fixed caps (3-phase), would it not overcompensate the PF on light load, and hence possibly lead to a higher meter reading ?

- - - Updated - - -

Hi,

i know how mature and modern energy meters work.
All i have seen don´t increase the energy with the addition of a PF capacitor.

It truly measures real power.

But keep in mind: if your capacitor gets warm - then this is real power, the same is with the wires to the capacitor.

Best is to try it: Maybe at night - switch off all unnecessary load (switch off fuses).
wait for an exactely one hour and see how much your energy meter conts up.
Then install your PF capacitor and wait another hour and see again how much your energy meter conts up.

Good luck

I would like to do this, but in a multi-family home very hard to do !!

 

[FvM]

I wonder which inductive loads have been recognized needing compensation? I can only imagine AC has a relevant load in homes, doesn't modern AC use individual compensation? Has reactive power been measured before installing capacitors?

Fixed compensation is an outdated method in my view, I think it hasn't been used in Western Europe in the last decades. You either have individual compensation (e.g. with fluorescent lamp ballasts or induction motors) or central automatic compensators (in industry and large office buildings).

Knowing a bit about power supply quality in India, I can imagine that utility companies clutch any straw that promises to improve the situation.

 

[Orson Cart]

It has been generally noticed by many home consumers in my neighbourhood that addition of a Power Factor Correction capacitor actually INCREASES the billing.

Now ideally the addition of such a capacitor should have no effect on the actual consumption or billing of the consumer. All it should do is to improve the PF as seen by the electric discom.

So is there any situation where addition of this cap would actually increase the billing (i.e. real power as measured by the local meter) ?

If you add C to the AC line it will contribute to a slight resonant rise in the mains voltage at the site, thus all the resistive devices connected to the mains now run off a slightly higher AC voltage - thus the total power consumed goes up slightly.
Regards, Orson.
p.s. this effect is exploited by certain types of static var compensator to raise the volts at the end of a long AC line for large motor starting.

 

[kripacharya]

....
Knowing a bit about power supply quality in India, I can imagine that utility companies clutch any straw that promises to improve the situation...

Thats for sure. Your observations are spot-on !
A bit off topic, but I was curious to know how you 'know a bit ..' ?

- - - Updated - - -

If you add C to the AC line it will contribute to a slight resonant rise in the mains voltage at the site, thus all the resistive devices connected to the mains now run off a slightly higher AC voltage - thus the total power consumed goes up slightly.
Regards, Orson.
p.s. this effect is exploited by certain types of static var compensator to raise the volts at the end of a long AC line for large motor starting.

Would this rise be measurable with - say- a DVM ?

 

[Orson Cart]

Yes you can measure it with a DVM, however as the mains fluctuates quite a bit at any time, you will need to take a well averaged reading for one minute, then do same with cap applied, then repeat with cap removed to get close to accurate results.

 

[chuckey]

I do not think that PF correction is useful in a domestic situation. Make a list of all the inductive power consumers in a typical house, typically motors, A/C units, freezers, fridges, fans, turbo heaters, some washing machines, solenoids in HVAC kit, CH pumps and well pumps and some wall wart power supplies. Most TVs, radios, PCs, washing machine motors - most modern devices have SMPSs in and so are actually capacitive in their own right. Only the first three items on my list have motors that consume any power, typically 1 KW between them and that only when they run. So if their PF is .8, i.e. ~200 W of inductance, you need 200W of capacitance to offset it, so when they are all on, you have unity PF, as they go ofF (A/C at night?), you are consuming 200 W of capacitive current, i.e. an extra 200/230 A which is flowing through your wiring for 15 Hrs/day as opposed to the same current flowing due to the inductive losses for the 9 Hrs/day. Because fridges and freezers run for much less then 15 Hrs more like 4 Hrs, and A/C units only for 12 Hrs, the capacitive current/Hrs are much greater then the Inductive current hours. Oh, that also presumes that the capacitance has been "tuned" to the specific units.
Don't bother, unless you are clever enough to switch in the correct amount of C at the correct time.
Frank

 

[kripacharya]

...... you need 200W of capacitance to offset it, so when they are all on, you have unity PF, as they go ofF (A/C at night?), you are consuming 200 W of capacitive current....

what -exactly- does 200w of capacitance mean ?

 

[chuckey]

This is a ball park argument, 200 W of capacitive power is more truthfully a leading current of 200/230~ .7A.
Frank