Power Factor Correction

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  #1  
Old 03-09-14, 12:17 PM
Justin Smith's Avatar
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Power Factor Correction

I have a number of motor loads, electronic loads, CFL and HID lighting at my land running off portable generators. The power factor on some of these items is horrendous, especially with the HID and CFL lights, measured as low as .26%. For instance, one 50W light uses almost 1.5 amps, which is killing me having to run multiple generators all night. I've been reading on the internet that capacitors will correct power factor, is this as simple as installing a capacitor across line and neutral, and if so, would capacitors from HVAC equipment work? I have a ton of them and get them for free when I scrap. As always, thanks for your help.
 
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Old 03-09-14, 12:25 PM
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A PF of .26 is really bad. Capacitors will only help on inductive loads.
 
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Old 03-10-14, 07:57 AM
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So last night I put a 45 UF capacitor on the line with my test ballast (50W mercury) and the power factor went up to about .60. Now the only thing I have to wonder is if too many capacitors could damage the generator.
 
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Old 03-10-14, 01:42 PM
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Are the P-F values you refer to the P-F values indicated by a P-F meter ?
 
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Old 03-10-14, 04:30 PM
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Yes, power factor correction is as simple as putting a capacitor across each load, however, there is a right size of capacitor to use.

The thing with power factor correction is that it is normally done at distribution voltages, rather than residential voltages like 120/240/480 etc. because it is much more efficient.

Yes, power factor correction is as simple as putting a capacitor across each load, but you need to know how much correction is needed. It's not a case of "just use the biggest capacitor I can find" because you'll be dissipating more and more power with the equivalent series resistance of larger capacitors. Oversize capacitors won't hurt your generator, however.

Calculating the reactive power, Q, of a load
.._________
√(VA[SUP]2[/SUP] - W[SUP]2[/SUP]) = Q vars

There's more to this to go from vars to MFD, so let me know if you want me to take it the rest of the way.
 
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Old 03-10-14, 08:29 PM
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Are the P-F values you refer to the P-F values indicated by a P-F meter ?
They are indicated by my kill-a-watt.
 
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Old 03-11-14, 10:39 AM
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Given that Volt-Amperes = Line Voltage X Line Current, what is the appox maximum value of the Volt-Amperes load ?
 
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Old 03-11-14, 02:30 PM
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There was an electronic circuit that came out in the 70s that claimed to correct the PF of your motor appliances in your home. I think it used voltage reduction at points in the sine wave to get the current in phase. Have not seen that unit around much these days so it may have not worked as advertized.

Real power can not just be measured by the voltage X Current unless you have no inductive or capacitance in the circuit. I'm pretty sure your power meter on your house measures real power so correcting PF will not save you money. But the power company gets a lot of current losses over their power lines with large PF loads so they fix it with capacitors on the pole.

Correct me if I'm wrong but that is what I was taught.
 
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Old 03-11-14, 04:53 PM
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Just as a note to others, in this case Justin is the power company. He is running the equipment off a generator.
 
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Old 03-11-14, 07:04 PM
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Now here's from experimenting:

Generac LP3250 generator. This is the one I primarily use to run the lighting, fridge, PA and a/c in my tent.

100' 16/3 extension cord plugged into GFCI outlet

100W Incandescent plugged into other GFCI outlet.

122.8V, 60.3Hz on extension cord leg with no load.

No load, 45uf 370V capacitor connected - 120.5V 2.55A 0.5W 310VA 60.0Hz 1.0 PF

50W mercury vapor, magnetic ballast - 121.4V 1.53A 68.7W 184VA 60.2Hz 0.37PF

50W mercury vapor, magnetic ballast, 45uf 370V capacitor connected - 121.3V 1.48A 68.3W 181VA 60.5Hz 0.37PF Also, ballast stopped buzzing.

Torture test (sound rack, hid lights, computer, 24'' monitor, laptop, cfl's, electric blanket) - 116.8V 6.10A 452W 718VA 60.0Hz 0.61PF

Torture test with capacitor - 115.9V 5.04A 435W 585VA 60.0Hz 0.75PF

It seems the capacitor definitely helps, except when there is no load. Can anyone tell me if using amperage but no wattage uses fuel?
 
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Old 03-11-14, 11:41 PM
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Can anyone tell me if using amperage but no wattage uses fuel?
AC power systems are NOT my area of expertise but as I understand things the answer to your question is very little fuel.

Forty-plus years ago I worked for a utility that generated most of its power via hydro but also had a couple of old steam plants for peaking and emergency use. The supervisor of the steam plants told me that in the past they would occasionally run to provide "reactive power" to the system to overcome a very low (lagging) power factor. The one plant had fourteen boilers and three turbo-generators but he told me when "running reactive" they only need about four to six boilers firing fairly lightly.

The utility also had a couple of "synchronous condensers" that they would use to boost the power factor. These were nothing more than large synchronous motors with no connected mechanical load. Overexciting the field caused them to run with a leading power factor which would raise the system power factor.

When I worked in a manufacturing facility that had several air compressors with synchronous motors I would regularly run them slightly overexcited to raise the overall plant power factor. When these compressors were replaced the new machines had power factor correction capacitors installed on the load side of the motor starters. They also had some fairly sophisticated voltage, current, load meters connected that would also show power factor and these machines with standard squirrel cage 3 phase motors (500 horsepower) would run better than 90% power factor.
 
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Old 03-12-14, 03:23 AM
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I would think your PF meter should read zero with only a pure inductance connected. It should also read zero with only a pure capacitor connected. It should read 1.0 with an incandescent bulb connected (resistive load).
 
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