Having difficulty increasing my load power factor above 0.95

[electricalguy]

I have an inductive load (120 volts AC at 0.5 amps AC at 60 Hz, 0.9 power factor before correction) that is a connected to the grid. I have been trying to increase the power factor above 0.95, but no matter how much I tune the power factor correction capacitors I cannot increase the power factor above 0.95. I can decrease it by a dramatic amount, as low as 0.24. Is the reason for this because I can't increase the power factor of my load above the power factor of the grid which is supplying my load?

 

[anorlunda]

What do you mean by tune? Capacitors are usually switched on and off.

How do you know that you have enough capacitors to fully compensate?

Is there a step down transformer?

Are the capacitors in parallel with the load?

Is the PF measurement done at the utility interface?

 

[berkeman]

And how are you measuring the power factor? Harmonic distortion (and other distortions) reduce the effective power factor as well.

 

[electricalguy]

By tuning, I mean I am manually placing capacitors in parallel with the load. I am using a Kill a Watt power meter and measuring the power factor on the utility end. Before I place a capacitor in parallel with the load I take the measurements of the voltage, current and watts at the applied frequency, then use an online power factor correction calculator to determine the appropriate capacitor needed to compensate the inductive reactance to give a power factor of 1.0. Between the utility and the load I am using a step down transformer, I have even tried to compensate the power factor on the primary side of the transformer with a parallel capacitor.

 

[berkeman]

Can you do this test with an incadescent light bulb as the load? That's about as close to PF = 1.00 as you can get without using power resistors...

 

[anorlunda]

then use an online power factor correction calculator to determine the appropriate capacitor needed to compensate the inductive reactance to give a power factor of 1.0.

Can you link the calculator and tell us what numbers you entered into the calculator?

 

[electricalguy]

https://www.rapidtables.com/calc/electric/power-factor-calculator.html

That is the site for the power factor correction calculator I used. The voltage I used was 119.6 volts, Current was 0.49 amps, 0.054 Kw, 60 Hz, and a preferred power factor of 1.0. This brought the power factor to 0.921 with a capacitor value of 4.229368 uFarad.

I just did a test using a 60 watt incadescent light bulb and the power factor shifted from a power factor between 0.98 and 1.0.

So I can see from the test that a power factor of 1.0 across a load is possible, is there anyway to achieve this with an inductuve load?

Thank you for the assistance so far it has been very useful!

 

[anorlunda]

Yes it is possible to completely compensate. It is also possible to overcompensate such that the net load becomes capacitive. If you over compensate, the PF begins going down again.If you are switching in capacitors one at a time, it is possible that N-1 capacitors gives you .95 PF lagging, and N capacitors gives you .95 PF leading.

 

[Windadct]

I am thinking the same as Anorlunda, Is your device showing leading and lagging PF?
Or make a table of Cap added ( uF) and the PF reported... I think you will see what is going on.

 

[electricalguy]

Okay that makes total sense. I can't see whether it's a leading or lagging power factor. If it was a leading power factor it should have a negative sign infront of the power factor number. My meter doesn't show that. So I will need to try to set up the appropriate cap to compensate it fully. I do have two more questions related to theis topic. Does it matter if I compensate the power factor on the primary side of the transformer or the secondary side? The second question is, will I need to change the value of the capacitor once I tune it to a power factor of 1.0 if my load stays the same? I'm wondering if the grid has any effect on the power factor of the load.

 

[anorlunda]

If it was a leading power factor it should have a negative sign infront of the power factor number.

You might think so, but PF is always positive. The real way is to measure reactive power Q. You want Q=0, so sign doesn't matter.

Does it matter if I compensate the power factor on the primary side of the transformer or the secondary side?

Yes. The purpose of compensation is to lower your utility bill, right? So you want unity PF at the meter.

The second question is, will I need to change the value of the capacitor once I tune it to a power factor of 1.0 if my load stays the same? I'm wondering if the grid has any effect on the power factor of the load.

Probably not. Some loads may be sensitive to small changes in voltage, but I would say that is secondary.

p.s. It is correct that your bill is the reason for wanting PF=1, right?

 

[DaveE]

Is the reason for this because I can't increase the power factor of my load above the power factor of the grid which is supplying my load?

I don't think there is such a thing as the "power factor of the grid". You need to take into account the load impedance when calculating power factor. You saw this when you connected a resistive load vs. an inductive load; same grid, different power factors.

I'm wondering if the grid has any effect on the power factor of the load.

Yes, it could theoretically. If the grid voltage is distorted so that in addition to the 60Hz sine wave you want it also has components at 120Hz, 360Hz, etc. Then you will not be able to correct an inductive load with capacitors at all of those frequencies. If you balance it at 60Hz, it will be unbalanced at 120Hz...

But 5% seems like a lot of distortion for the "grid"; that is more likely to happen with more localized distortion from harmonic generating loads near you (like all of the computers and TVs around you). Even so, it seems like a lot to me, but I've never worried about this sort of thing for such small loads. If you live in a very rural area with long distribution lines then this would be more reasonable, I think.

Maybe some one with more "grid" experience can comment on what they see typically.

This article looks like a good source for learning more about these issues.
EVALUATING THE LEVEL OF HARMONIC DISTORTION IN A TYPICAL DISTRIBUTION FEEDER
In Table 3.1 it shows an IEEE standard at <5% THD for low voltage distribution.

 

[Averagesupernova]

@electricalguy , where are you at in the world and is this a residential load or commercial/industrial? If you are trying to save money on the electric bill by tuning your power factor, residential customers generally don't pay for having a poor power factor, at least in the USA. If you are in a situation that you DO pay for poor power factor, I can't believe a .5 amp load will cause enough change to make it worth going to a tremendous amount of trouble to tune it perfect.
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If you're just experimenting/learning about power factor, that's different. Hands on experimentation is a great way to learn. Be safe!