The improvement of power factor

Abstract

The economical limit of power factor improvement in relation to capital outlay. It is shown that if C is the capital cost of generating and transmission plant per kilowatt, and c is the cost of phase-improving plant per wattless kilovolt-ampere; then, writing α = c/C, it is economical (from the capital outlay point of view) to go on improving the power factor until sin φ = α, where φ is the angle of lag. The saving thereby effected is equal to 100[l – cos (φo – φ)] per cent, where cos φ0 is the original power factor before improvement. A practical example is worked out to show the operation of this rule. The synchronous motor and static condenser serving exclusively for injecting leading kVA are considered. The rotary converter and the synchronous induction motor serving the double purpose of supplying power and injecting leading kVA are dealt with and their province is described. Various methods of starting the synchronous induction motor are illustrated. The paper then goes on to treat of phase advancers of the rotating type connected to the slip-rings of induction motors. The effect of such advancers upon the performance of the induction motor is illustrated by several examples, and the change in the shape of the circle diagram is worked out. The author then proceeds to give an expression for the apparent capacity of his “vibrator” in terms of the constants of the machine, and shows how to arrive at the size of vibrator required to suit any given conditions. The last section of the paper deals with meters and tariffs. Various methods of indicating kW maximum demand and wattless kVA are described and particulars are given of the tariffs employed by various power companies. Observations are made as to the fairness of these to consumers who improve their power factor.