Capacitor Bank Calculation For APFC Panel

Welcome to this introductory part on capacitor bank calculation for an APFC  panel. When I first started working on the calculation of capacitor bank  I have struggled for many hours to figure out what was going on in this Capacitor bank calculation. Therefore, I have decided to write this tutorial for the ones who are new to these topic.
In this tutorial, we will discuss the calculation for capacitor bank in a simple way.

There are two methods for calculation of capacitor bank –

1. Simple Table Method for Capacitor bank calculation

2. Classical Capacitor bank Calculation Method

Let us take a example of 3Phase induction motor

1.Simple Table Method for capacitor bank calculation – 

Motor Input = 5kW
From Table, Multiplier to improve Power factor from 0.7 to 0.96 is 0.692
Required Capacitor kVAR to improve P.F from 0.7 to 0.96
Required Capacitor kVAR = kW x Table  Multiplier of 0.7 and 0.96

= 5kW x 0.692
= 3.46 kVAR

And Rating of Capacitors connected in each Phase

3.46/3 = 1.15 kVAR

2. Classical capacitor bank Calculation Method

Motor input = P = 5 kW, Voltage- 400V

Original Power factor= Cosθ₁ = 0.7

Final Power factor = Cosθ₂ = 0.96

θ₁ = Cos^-1  (0.7) = 0.7953; Tan θ₁ = Tan (0.7953) = 1.0200

θ₂ = Cos^-1 (0.96) = 0.2837; Tan θ₂ = Tan (0.2837) = 0.2915

Required Capacitor kVAR to improve Power factor from 0.7 to 0.96

Required Capacitor kVAR = P (Tan θ₁ – Tan θ₂)

= 5kW (1.0200 – 0.2915)

= 3.46 kVAR

And Rating of Capacitors connected in each Phase

3.46/3 = 1.15 kVAR

These are the main Formulas to Convert Capacitor kVAR into Farads and Vice Versa

C = kVAR / (2 π f V²) in microfarad

C = 3.46/ (2 π* 50*400²) in microfarad

C= 6.88* 10^-8 microfarad