Explain How to Represent Power Lines?

The equivalent circuit of a power line depends on the length of the line and on the accuracy of the model required. In general, any power line may be represented as a two-port network, as shown in Figure, for which:

V_S = AV_R + B I_R

I_S = C V_R + D I_R

The line parameters used to determine the 2-port network constants (A, B, C and D) may be represented by lumped-constant circuits. For long transmission lines, a distributed-constant circuit model is used when accuracy is of importance.