The Most Economical Power Factor A Practical Design Formula for Distribution Circuits

The use of power factor corrective devices on distribution circuits is justified, under certain conditions, by rather substantial savings in investment charges and by a reduction in the power losses of the system. The object of the present paper is to develop a practical working formula for calculating the most economical corrected power factor for a distribution circuit. Most economical conditions are assumed when the total of such annual circuit costs as are directly affected by a change in power factor, is a minimum. The usual methods for computing separately, the saving in I² R losses and the decrease in investment charges due to power factor improvement, are inadequate. Particularly in the design of new circuits and extensions has the need for a more accurate method for calculating optimum power factor and conductor sizes been expressed.² Since these equations were originally worked out, two other solutions for the most economical corrected power-factor angle have been published, each having been obtained independently of the other. Menjelou³ obtained his formula in the form: ?? sin ?? = 1 - ?? tan ?? in which ?? is the power-factor angle and ?? and ?? are constants computed from the circuit costs. Stevenson⁴ obtained a similar expression: sin ?? = ?? - ?? tan ?? the difference lying in the constants to be evaluated. The equation developed in this paper reduces to the simple form.