        # Document Library

Basic Formulas

The following pages of formulas, some derivations and discussions are intended to assist in designing and applying capacitor banks properly. Also, refer to Capacitor Bank Inrush Calculations for additional information. 1. Ohm’s Law

 RI = V or V = IZ (1) (2) Then Z = (3) and I = (4) P=I * V (5) From (4) This becomes V = (6) Let P = VAR Then Z = (7) or Z = (8) Or Z = (9) Letting Z = XC Or XL (10) We have XC (Or XL) = (11)

This will allow you to determine the reactance of a capacitor or reactor when voltage and KVAR is given.

Example:

A three-phase 600KVAR capacitor bank at 12,470 will yield

Xc = = = 259.168 Ohms

A three-phase shunt reactor of 150KVAR, at 13.8KV will yield

Xc = = = 1269.6 Ohms

 XC = (12) But, as stated VAR = (6) VAR = (13) Or = (14) Then VAR = (15) KVAR = (16)

Example:

From above 600KVAR at 12.47KV equals 259.168 Ohms and from (12)

XC = . Then C = Let f = 60 Hertz From (16) KVAR = KVAR = 600 (17) VAR = from (6) = (18) KVAR = (19)

From above 150KVAR at 13.8KV equals 1269.6 Ohms and from (17) . Let f = 60 Hertz Then L = = = 3.36773 Henries

Or 3367.73 millihenries.

From (19) KVAR = = KVAR = 150

 LEGEND R Resistance I Amps V Volts Z Impedance P Power (in Watts and/or Vars) VAR Reactive Power K Kilo (103) XC Capacitive Reactance XL Inductive Reactance M Mega (10>6)