Originally Posted by

**xsman**
I have a 4ton A/C unit and I would like to improve the PF?.... Any help is appreciated

What final PF do you want to achieve? 1.0? or just 0.90?

Here it is (assuming a final PF of 0.9 lagging):

4 Tons A/C with EER of 10 (assumed) will be 4.8 kW electrical (4 X 12,000 BTU/Hr /10 BTU/W-Hr)

With an initial PF of 0.8:

The kVA = 4.8/0.8 = 6 kVA

The kVars = sqrt(6^2 - 4.8^2) = 3.6 kVars

If you correct the PF to 0.9:

The kVA = 4.8/0.9 = 5.333 kVA

The new kVar = sqrt(5.33^2-4.8^2) = 2.325 kVars

The difference in kVars will be the kVar of the capacitor:

Capacitor total kVars = 3.6 - 2.325 = 1.275 kVars

Per phase kVars = 1.275/3 = 425 Vars

If the supply voltage is 480V 3-phase and you will connect the capacitors in delta:

Xc = E^2/Qc = 480^2/425 = 542.12 ohms

C = 1/(2 X pi X f X Xc) = 1/(2 X 3.1416 X 60 X 542.12) = 4.89 uF

That's all.

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