Editing Overhead power line (section)

===Short and medium line model===
A short length of a power line (less than 80&nbsp;km) can be approximated with a resistance in series with an inductance and ignoring the shunt admittances. This value is not the total impedance of the line, but rather the series impedance per unit length of line. For a longer length of line (80–250&nbsp;km), a shunt capacitance is added to the model. In this case it is common to distribute half of the total capacitance to each side of the line. As a result, the power line can be represented as a [[two-port network]], such as with ABCD parameters.<ref name=Glover21>J. Glover, M. Sarma, and T. Overbye, ''Power System Analysis and Design, Fifth Edition'', Cengage Learning, Connecticut, 2012, {{ISBN|978-1-111-42577-7}}, Chapter 5 ''Transmission Lines: Steady-State Operation''</ref>

The circuit can be characterized as
:<math>Z = z l = (R + j \omega L)l </math>
where
*''Z'' is the total series line [[Electrical impedance|impedance]]
*''z'' is the series impedance per unit length
*''l'' is the line length
*<math>\omega \ </math> is the [[sinusoidal]] [[angular frequency]]
The medium line has an additional shunt [[admittance]]
:<math>Y = y l = j \omega C l </math>
where
*''Y'' is the total shunt line admittance
*''y'' is the shunt admittance per unit length

<gallery widths="230px" heights="100px" perrow="2">
File:Short Line Approximation.png|Short length of power line
File:Med Line Approximation.png|Medium length of power line
</gallery>