Reactive compensation for a feeder-current limit calculator

Minimum reactive compensation is calculated as Q_old − sqrt([sqrt(3) × V_LL × I_limit/1000]² − P²). Use the stated system boundary and matching input units.

Q_{\text{C,min}} = Q_{\text{old}} - \sqrt{\left(\frac{\sqrt{3} \times V_{\text{LL}} \times I_{\text{limit}}}{1000}\right)^{2} - P^{2}}

Calculator

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Worked example

Given

$P$ = 50 kW
$Q_{\text{old}}$ = 150 kVAR
$V_{\text{LL}}$ = 480 V
$I_{\text{limit}}$ = 150 A

Q_{\text{C,min}} = 150 - \sqrt{\left(\frac{\sqrt{3} \times 480 \times 150}{1000}\right)^{2} - {50}^{2}} \approx 35.755

Symbols and units

Symbol	Meaning	Unit
$Q_{\text{C,min}}$	minimum reactive compensation	kVAR
$P$	unchanged feeder real load	kW
$Q_{\text{old}}$	initial inductive reactive requirement	kVAR
$V_{\text{LL}}$	line-to-line voltage	V
$I_{\text{limit}}$	maximum allowed line current	A

Related calculators

Results are estimates for study and screening. Check the inputs, units and assumptions before you use them for design, billing or contract decisions.