Convert KVAR to Farads (For Power factor improvement)

Here is a simple calculation for converting KVAR to Farads and vice versa. It is help you to find actual capacitor size. 

Example for calculating KVAR values.

Example:

A Single phase 380V, 50Hz, motor with rated current of 30A at a P.F (Power factor) of 0.6. The motor power factor has to be improved to 0.9 by connecting a capacitor in parallel with it. Calculate the required capacity of Capacitor in both KVAR and Farads.

Solution: Two Methods for Finding KVAR

Method 1: (By PF Multiplier Table)

Motor Input Power, P = V x I x Cosθ

                        = 380V x 30A x 0.6

                        = 6840 W

                        = 6840 / 1000 KW

                        = 6.84 KW

From PF Multiplier Table, improve PF from 0.60 to 0.90 is 0.849

Required Capacitor KVAR to improve P.F from 0.60 to 0.90

Required Capacitor, KVAR = KW x Table Multiplier of 0.60 and 0.90

= 6.84 KW x 0.849

= 5.807 KVAR

Method 2: (Classical Calculation Method)

Motor Input Power, P = V x I x Cosθ

                        = 380V x 30A x 0.6

                        = 6840 W

                        = 6840 / 1000 KW

                        = 6.84 KW

Actual P.F, Cosθ₁ = 0.60

Required P.F, Cosθ₂ = 0.90

θ₁ = Cos^-1 (0.60) = 53°.13; Tan θ₁ = Tan (53°.13) = 1.3333

θ₂ = Cos^-1 (0.90) = 25°.84; Tan θ₂ = Tan (25°.50) = 0.4843

Required Capacitor KVAR to improve P.F from 0.60 to 0.90,

Required Capacitor KVAR = P * (Tan θ₁ – Tan θ₂)

= 6.84 kW * (1.3333– 0.4843)

= 5.807 KVAR

Solution: Two Methods for Converting Farads to KVAR and vice versa

Method 1: (Applying a Simple Formula)

We just get the KVAR value for improving power factor for the motor. Now we just convert KVAR value to Farads.

Required Capacity of Capacitor in Farads/Microfarads

C = KVAR / (2 π f V²) [here unit is μF]

Putting the Values in the above formula

 = (5.807 kVAR) / (2 x π x 50 x 380²)

= 1.28 x 10^-4

= 128 μF

Method 2: (Simple Calculation Method)

KVAR = 5.807 ………………………………………….… (i)

We know that;

I_C = V/ X_C

Here, X_C = 1 / 2 π F C

So, I_C = V / (1 / 2 π F C)

I_C = V 2 π F C

= (380) x 2π x (50) x C

I_C = 119380.8 x C

And,

KVAR = (V x I_C) / 1000                    [KVAR = (V x I) / 1000]

= 380 x 119380.8 x C

KVAR = 45364.704 x C ……………………………..…. (ii)

Equating Equation (i) & (ii), we get,

45364.704 x C = 5.807

C = 5.807 / 45364.704

C = 1.28 x 10^-4

C = 128 μF

Note:

Just remember for converting KVAR into Farads and Vice Versa

Convert Capacitor Farads into KVAR:

C = KVAR / (2 π f V²) in microfarad

Convert Capacitor KVAR into Farads:

KVAR = C x (2 π f V²)