power factor correction capacitors?

[lovingHDTV]

I know these are used/required at facilities that have a large inductive load. I've also seen some marketed to the home owner, and specifically the pool owner. Claims range from a savings of 10%-30%, obviously it depends on your power load.

Do the pool pump motors already have the capacitors built into them? Is there a way to find out what your power factor for the pump motor is? Is it related to the SF of the motor?

Hoping someone more knowledgable about motors can chime in.

thanks,

 

[JohnT]

Power factor is unrelated to service factor. Without doing any calculations, I'd guess that correction would be a waste of money for a home user. The reason industrial plants worry about PF correction is that utilities charge industrial companies higher rates if their PF isn't close to 1, so they have a real financial incentive to improve it. There's also some risk since an improperly chosen capacitor can create a resonant tank and cause the motor winding to generate a high voltage surge on power down.

 

[lovingHDTV]

The biggest problem I see is figuring out what the pf of the motor is. What I see given as examples online are for a PF of .85. If this were true then you could realize a power savings by pushing it to .95, but as you stated it is not good to put too big a cap on there.

I would think that some of the more expensive pool pump motors would already have this added in.

 

[mas985]

Here is a great article which explains power factor in detail:

http://www.electricianeducation.com/the ... factor.htm

And another which explains capacitor adjustments for residential customers:

http://powerelectronics.com/power_manag ... 5PET23.pdf

The article explains that since reactive power moves back and forth over the wires to the device, there is some resistive losses that reactive power can cause. The larger the wire, the less this matters. Also, the power company doesn't like reactive power since there are losses along the long lines to the home.

In addition, residential mechanical meters measure real power and reative power is net neutral. So you are not being charged for reactive power anyway, other than what was explained above. Some newer digital meters do measure reactive power and thus the power company could charge for it but I don't think they do for residential customers. However, the above article does explain that there are some small savings.

So adding a capacitor to your home will improve the power factor but I am not sure it will actually reduce your power bill by much. In fact, since these devices are not purely capacitive and have some resistance, they draw power themselves so the net result could be little savings at all. I think the only thing these devices do is to help the power company out so they do not need to do it at the point of generation.

 

[mas985]

One more reference:

http://www.energyideas.org/default.cfm? ... c=z,z,4158

It is a myth that motors run cooler after power factor correction. Motors see no difference in current, regardless what the corrected power factor is. They draw no more or less power, have no more or less current, and run at the same temperature, regardless of power factor. Power factor correction only affects the power upstream of the motor.

 

[lovingHDTV]

i had read those articles. I want not concerned about reactive power loss in the wiring, but instead in the ineffeciency that it creates in the motors.

I looked my motor up on A.O. Smith webpage, but they do not give a power factor. It is a two speed 2/.33 SF 1.1 motor. not sure if this is a "good" motor or not.

I then looked at my AC to see how it would fair, but is is only a 1/5 hp motor in the compressor. It is a 15 seer 4 ton unit.

The 12 seer 4 ton unit next to it has a 1/4 hp motor.

I had no idea how big the pump motors are compared to others in the home.

 

[mas985]

The blower motor in my furnace is a 1 HP and I think the compressor motor in the air conditioner is more than that so they are similar in power draw. However, they do not run as long during the day as a pump motor.

The point in the articles is that the resistive load in a motor does not change with power factor so correcting for it does not change how much power a motor draws.

The only savings is in the wiring.

 

[lovingHDTV]

One more reference:

http://www.energyideas.org/default.cfm? ... c=z,z,4158

It is a myth that motors run cooler after power factor correction. Motors see no difference in current, regardless what the corrected power factor is. They draw no more or less power, have no more or less current, and run at the same temperature, regardless of power factor. Power factor correction only affects the power upstream of the motor.

Good link, thanks.

 

[kirbinster]

Power factor is a non-issue for most (if not all) residential users. You are billed for kwh not kvar. If you have a second meter that registers kvars and are billed on it then you might care about PF, if not forget about it. The low power factor is costing the utility not you.

 

[Titanium]

lovingHDTV,

Re: "i had read those articles. I want not concerned about reactive power loss in the wiring, but instead in the ineffeciency that it creates in the motors."

I think you have cause and effect misplaced. Reactive power loss isn't causing inefficiency in the motor, rather it is the motor itself which is causing the reactive power loss. Some electrical loads, such as incandescent lights or electrical space heaters, are purely resistive loads. Other loads, such as motors, have a resistive component and a reactive component.

Single-phase motors, such as are commonly used for residential swimming pools, normally do use a capacitor. However, this capacitor is not for power factor correction, but is used to create a rotating torque (redundant phrase, I know) at starting. Without this "starting capacitor" functioning properly, a single phase motor on startup will merely sit still and hum (until it burns up, of course).

In my experience, capacitors or other devices marketed to the residential market in order to increase "efficiency" or increase "power factor" are almost always marketing scams.

Titaniium

 

[DaveNJ]

The attached link is a good read. The lab. I work in uses power line filters (DC to 400Hz). They are inductive in nature and require a Power Factor Correction unit applied when using 400Hz power. The filters are (inductive - capactive) balanced for 60Hz power and need the added correction to balance the inductance at 400Hz. I believe industrial motors, high hp do benefit from correction. Much different inductive load, most are three phase.

http://www.wagesterlease.com/aboutus/ar ... actor.html