Improving the Accuracy of Impedance Calculation for Distribution Power System

This paper compares different approximation methods and develops a new method for simplification of Carson´s equations to model distribution lines for unbalanced power flow and short-circuit analysis. The comparisons are made for real and imaginary parts of self and mutual impedances. The impedances obtained by application of different approximation methods are utilized for lines and cables of a long feeder with a load and the IEEE 123-node system. The effect of varying ground resistivity and frequency on impedances is observed. The unbalanced power-flow results of both systems are compared for voltage, current, active, and reactive power flow. It is observed that different approximation methods for impedance calculation have considerable effects on the results of power flow, especially on node voltages which are critical for power quality and steady-state analysis of distribution systems.