How to Calculation of Reactive Energy Based on the Application

The transformer works on the principle of Mutual Induction.

The transformer will consume reactive power for magnetizing purpose.

Following equivalent circuit of transformer provides the details of reactive power demand inside the transformer:

The objective is to determine the requested reactive power (kvar) to be installed, in order to improve the power factor cosφ and reduce the apparent power S.
For φ’ < φ, we’ll get: cosφ’ > cosφ and tanφ’ < tanφ
This is illustrated on the diagram in the left.
can be determined from the formula : = P. (tanφ - tanφ‘), which is deduced from the diagram.
: power of the capacitor bank, in kvar
P : active power, in kW
tanφ: tangent of the phase angle - before compensation,
tanφ‘: tangent of the phase angle - after compensation
The parameters φ and tanφ can be obtained from the billing data, or from direct measurement in the installation.

Consider one 1000kW motor with cosφ 0.8 (tanφ = 0.75).
In order to get cosφ’= 0.95, it is necessary to install a capacitor
bank with a reactive power equal to
k x P, i.e. : = 0.42 x 1000 = 420 kvar