Power Factor Correction Capacitors

[Suraj143]

Without a line voltage (230V/50Hz) parallel capacitor, my refrigerator shows Power factor = 0.62 & It takes current exactly 1A.
I loaded a 5uF/450V capacitor to the same power outlet & the power factor increases to 0.82 & the current takes drop down to 770mA.

I have two questions

1) Is there any way to increase the power factor closer to 1?

2) When the refrigerator off (no load) the capacitor takes 350mA current which is too high.How to reduce this standby current?

 

[kubeek]

Why do you need PF=1? Distribution companies charge you for the real power you use, not apparent power, therefore power factor is irrelevant.

 

[Suraj143]

I don't need PF=1 as I mentioned, I need closer to 1.In other words I need to reduce more reactive power that far as I can.

 

[JimB]

1) Is there any way to increase the power factor closer to 1?

Yes, adjust the value of the capacitor.

2) When the refrigerator off (no load) the capacitor takes 350mA current which is too high.How to reduce this standby current?

Connect the capacitor so that it is switched out of circuit when the motor is not running.
ie connect it directly across the motor, not the incoming supply.

JimB

 

[Suraj143]

Hi Jim thanks for the reply.

Actually I'm making an DIY energy saving box. So it must permanently connected to wall outlet as other energy saving boxes do

 

[Nigel Goodwin]

Hi Jim thanks for the reply.

Actually I'm making an DIY energy saving box. So it must permanently connected to wall outlet as other energy saving boxes do

Except it doesn't save any energy - as already pointed out domestic supplies aren't subject to PF considerations, so it saves nothing.

 

[kubeek]

Well the power company saves maybe a little bit, and that is very generous of you.
Or not, since you don´t know if your inductive PF isn´t actually helping offset the capactive PF from all the switchmode power supplies in the grid.

 

[JimB]

Except it doesn't save any energy - as already pointed out domestic supplies aren't subject to PF considerations, so it saves nothing.

On an individual basis, that is correct.
In the UK the domestic user is charged for Watts rather than VA (Volt.Amperes)

However, if all refrigerators had a better power factor (nearer to 1) there would be a saving in the distribution system due to lower losses because of the lower current.

JimB

 

[schmitt trigger]

Most if not all the world, domestic users are not penalized by low power factors.
The utility companies charge you by the Kilo-watt-hour.......Real, not reactive energy.

Having said that, I do like to correct the power factor of larger motor loads a little. Why? Because as you noticed, it lowers the overall current (which is a vector sum of real and reactive currents), and therefore voltage drop in the wiring is reduced.
Don't over do it, though. The difference in current between a PF = 0.95 and PF = 1.0 is very low. The law of diminishing returns applies.
In my opinion, once that you have reached PF = 0.9, it is the best return on the investment.

But as someone mentioned, if you are going to correct power factor, do it right at the load.

 

[tcmtech]

I typically don't do any PF correction on inductive loads under 3 KVA. There's just not enough line loss power concerns below that level. Now what I do have is a number of .22 uf low ESR capacitors (line to line and line to ground) in different places working as HF and spike snubbers. They don't do a thing for PF adjustment but they do a good job of keeping line noise commutation from one place to another on my property down.
Welders and plasma cutters tend to be electrically noisy in the HF range.

Now as far as the utility companies side of things they do their own PF monitoring and correction on the go as they need to adjust it so whatever the average homeowner does has no measurable effect on their side.

From their perspective our individual homes are little more than ants on a very large elephant.

 

[bountyhunter]

As long as the power company is not charging you for VAR's, you don't want to do the PF correction. Around here, the power company puts the correction caps on the poles throughout the system to keep the overall power factor closer to unity. The guys I went to school with who worked for the company said that in a few cases they installed VAR meters and charged for it when the user had a highly reactive load but that's rare. I think it was from a shop with a lot of power tools (induction motors) but I never heard of a home consumer getting hit for VAR charge.

 

[Suraj143]

Ok thanks for your information.

Is there anyway to reduce standby current in a capacitor when there is no load condition?

 

[Suraj143]

I checked using a power meter and with a clamp meter.Also the simulation shows capacitor current.

 

[Tony Stewart]

Without a line voltage (230V/50Hz) parallel capacitor, my refrigerator shows Power factor = 0.62 & It takes current exactly 1A.
I loaded a 5uF/450V capacitor to the same power outlet & the power factor increases to 0.82 & the current takes drop down to 770mA.

I have two questions

1) Is there any way to increase the power factor closer to 1?

2) When the refrigerator off (no load) the capacitor takes 350mA current which is too high.How to reduce this standby current?

You don't need to reduce your fridge current or the capacitor standby current to save anyone energy costs.
Are you trying to run it from a VA limited inverter? Then it might help to reduce Amps.
Otherwise not.

It seems you need to read more about power measurements, pf , VAR and Watts.

Which part do you not understand?

 

[Suraj143]

Hi Tony.Now I only want to reduce capacitor standby current.I used a 8uF capacitor, now when no load it takes 650mA current which is too much.Help me to reduce this.

 

[kubeek]

If you want to lower the current then disconnect the capacitor or use lower capacitance.

 

[Nigel Goodwin]

Hi Tony.Now I only want to reduce capacitor standby current.I used a 8uF capacitor, now when no load it takes 650mA current which is too much.Help me to reduce this.

Well apart from it been a complete waste of time and effort anyway, you could simply connect it to the motor AFTER the thermostat, so it's switched out of circuit when the fridge isn't running.

 

[tomizett]

you could simply connect it to the motor AFTER the thermostat, so it's switched out of circuit when the fridge isn't running.

As far as I can see, this is the only correct way of doing it. If you leave the capacitor connected when the motor is not, then although you get a good power factor when the motor is running, you will get a very poor one when it is off.

 

[JonSea]

Geez oh grief. Suraj asked a question about power factor correction, and many of "most noted members" here proceeded to attack him. Nobody asked why he wanted to correct the power factor, but instead told him it was a waste of time! This forum seems to be filled with a bunch of grouchy old men, shaking their canes and yelling at the kids to get off their lawns!

As to the question of why, I have a similar problem. I have an industrial UPS connected to a bank of golf cart batteries to provide some backup power during power failures. It keeps the network gear up (got to have priorities you know), the small bit of power required to run a tank less gas water heater and the gas furnace.

The furnace blower motor is surprising small...a quarter or third of a horsepower...but it uses almost all of the capacity of the 1000VA UPS because of the power factor (and a frightening 50 amp draw on the battery bank). When YOU are the utility, you are paying the price of a crappy power factor.

So maybe keep an open mind, answer the question asked, and STFU if you have nothing to add?

 

[JimB]

Suraj asked a question about power factor correction, and many of "most noted members" here proceeded to attack him.

I thought that this "Most helpful member" (also a Grouchy Old Man) did answer his initial questions in post#4

Suraj went on to say that he was using this capacitor as a stand alone item which was not directly connected to the fridge motor. And there the circular argument starts.

So maybe keep an open mind, answer the question asked, and STFU if you have nothing to add?

Good advice, I urge you to follow it.

JimB