# Capacitor size Calculator for 3 phase motors

Capacitor size Calculator for 3 phase motors – You have to fill Rating of motor and current Power Factor (from meter). Result Capacitor Size will be in KVAR.

Capacitor size Calculator for 3 phase motors

## Why we do KVAR calculation

As we know that motor is an inductive load. Which consumes both active and reactive power. That is, in addition to real power, there is also reactive power. As we know that real power is the actual power that works to drive the motor, and reactive power is a kind of lost power due to that loss occurs. But the energy spent measured by the electric meter is according to the sum of both the active power and the reactive power. To reduce the reactive power which is a kind of loss, a capacitor is used across the R Y B phase of the motor so that this loss can be minimized. If we installed a capacitor then the real power that is used to drive the motor is measured by the meter, and the reactive power is nullified through the capacitor. In this article, we will tell you about the capacitor size calculator for 3 phase motors and how many rating (KVR) capacitor banks will be used. It requires two parameters first one the rating of the motor and the second one is the power factor of the electric motor read by the meter. Hence, the power factor is noted through an electric meter installed across the motor. We will be able to calculate the capacitance of the capacitor near the motor through the formula given below using the capacitance rating of the motor and the power factor obtained through the meter.

### Formula for Capacitor size calculation for 3 phase motors-

Required Capacitor size (in kVAR) = P (Tan θ1 – Tan θ2)
where P= power rating of the motor
Tan θ1= tangent of the angle between true power and apparent power(for current PF)
Tan θ2=tangent of the angle between true power and apparent power(for required PF)

#### Benefit For Use of Capacitor in 3 phase motor-

By installing capacitors with the motor, the electricity bill comes lesser compare to without capacitors this is due losses get decreased if we use capacitor.
And the life of the motor also increases. Because the motor has to do more work due to more losses.

in this calculator, we need only the power rating of the motor and the power factor coming in the meter. then we can easily calculate the rating of capacitor required to place in it.

#### How Capacitor size Calculator for 3 phase motors works-

Let us see some examples for capacitor size calculation-
For example- suppose there is a 3 Phase, 50 kW Induction Motor that has a P.F (Power factor) of 0.8 lagging. What size of Capacitor in kVAR is required to improve the P.F (Power Factor) to 0.99?

Motor input = P = 50 kW
Original P.F = Cosθ1 = 0.8
Final P.F = Cosθ2 = 0.99
θ1 = Cos-1 = (0.8) = 36°.86; Tan θ1 = Tan (36°.86) = 0.74
θ2 = Cos-1 = (0.90) = 8°.10; Tan θ2 = Tan (8°.10) = 0.14
Required Capacitor kVAR to improve P.F from 0.8 to 0.99
Required Capacitor kVAR = P (Tan θ1 – Tan θ2)
= 5kW (0.74 – 0.14)
= 30 kVAR
And Rating of Capacitors connected in each Phase
30/3 = 10 kVAR
so ideally capacitor of 30 kvar is required but many a time it is suggested to use a little 5% lesser than 30 kvar due to over-voltage issue. so in this case, 28.5 kvar is perfect to use.

### 2 thoughts on “Capacitor size Calculator for 3 phase motors”

1. Nice and understandable article