Power Factor Correction for Transformer no-load compensation
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:
Power Factor Correction where Load and present
Power Factor is Known
Power Factor is Known
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.
For φ’ < φ, we’ll get: cosφ’ > cosφ and tanφ’ < tanφ
This is illustrated on the diagram in the left.
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.
The following table can be used for direct determination.
Example:
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
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. :
Released for:Schneider Electric Thailand
