How to Calculate Capacitor Required to Compensate Given KVAR?

I'm sure a formula exists but if you have some large capcitors of sufficient voltage rating it may be easier to do a trial by error approach adding and then checking the PF as you go.

Your current load is 509w with 0.685pf. Assuming that freq is 50HZ

Target pf is 0.95

QC = K x P

K =Necessary compensation power from pf 0.685 to 0.95

P = Actual power

QC = 0.88 x 508

QC = 447VAR

C = QC/2 x pie x f x vseq

C = =(447/(2*3.14*50*215*215)) * 1000000

C = 30.8uf

http://www.nokiancapacitors.com/documents/04%20-%20theory/EN-TH01-11_2004-Power_Factor_Correction.pdf

Dear Signode, I have gone through the link given by you and found a table where value of K to be selected for required p.f..But in that file there is not any formula for K. But I think K= (tanǾ1-tanǾ2), where Ǿ1= new pf angle and Ǿ2=old pf angle it is correct ????????

I am sorry for one mistaking. For target K value (0.88) is for target cosǾ 0.98 not for 0.95.

The base is,

K = tan1 – tan2

where

tan1 = tan of existing cosǾ
tan2 = tan of target cosǾ

tan1 of cosǾ 0.68 = 1.08

tan2 of target cosǾ = 0.2

K = 0.88

Since you have calculated the VAr = 685 at pf = 0.685

This is the amount you need to compensate to obtain pf = 1

(any other target can be deducted...use the vector diagram showing the active power on the X axis and the reactive powers vertically with Capacitive going down while inductive going up)

VAr is a power same as VA or as VAactive = watt

Therefore VAr = Impedence x Amps^2 here Impedence is the Inductance to compensate with the capacitance, which is 1/(C x 2xpixf) and taking f = 50 Hz will give approx 1/(c x 314.15)

From here on use your maths....

Dear Mr. dhanesh.koshti,

I need not explain how to calculate to get the required KVAR for improving Power Factor from 0,685 to say 0.9 and that is the Impedence by way Capacitive Reactance.

For calculating Farads. Capacitive Impedence in OHMS = 1/(2x3.142xFxC) Hence C an be calculated.

DHAYANANDHAN.S

कोष्ठी जी नमस्कार ,

मुझे ख़ुशी हुई की आप इस फोरम में है , मैं आपको बताना चाहूँगा की इसी फोरम के

डिस्कशन से मुझे capacitor के calculation का पता चला है । मैंने इसके लिए एक excel sheet

भी तैयार की है जिसमे मोटर के नेमप्लेट की डाटा डालते ही , जनरेटर के लिए दोनों मोड (star & delta) के

capacitor का साइज़ बता देता है । अगर आप चाहे तो आपको वो मेल कर सकता हूँ ।

thanks ,
अतुल देशमुख