Inductive Interference as a Practical Problem

In this paper are given a review of the factors which affect inductive interference in telephone circuits from high-voltage power transmission circuits, a presentation of the practical considerations regarding the reduction of the interference, and a description of actual cases of the application of these means of reduction. Distinction is made between the effect of balanced and of residual voltages and currents on the power circuit and between the effect of voltages induced between the wires and those induced between wires and ground. The wave shapes of the voltages and currents in the power circuits have a very important effect in the amount of inductive interference in telephone circuits. The precision of the electrical balance of the power circuit is also important because of the relatively very large effects of unbalanced voltages and currents in producing inductive interference. A discussion is given of the principles to be used in the design of coordinated transposition schemes for power circuits and telephone circuits which parallel each other, and schemes are described which have been devised for application to the telephone circuits in order to simplify the design of transpositions in the power circuits which make it possible to balance the induced voltages. A detailed discussion is given of three particular cases of parallels showing the application to them of the different methods by which inductive interference can be reduced.