Electromagnetic unbalance of transmission lines

A SIMPLE but satisfactorily approximate method of computing electromagnetic unbalances¹ for double circuit lines, either with or without ground wires, results if the following simplifying assumptions are made: 1. The two circuits are symmetrically arranged on the transmission tower. 2. Line currents in each of the two circuits are balanced and equal. 3. External impedances Zext terminating the lines are balanced. 4. Mutual impedances are small compared to self-impedances, and voltages induced through mutual impedance by small (negative- or zero-sequence) currents are negligible.