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Surge impedance

Definition according to Cigré guide 531 chapter 4.2.5

The characteristic impedance or surge impedance of a uniform transmission line is the ratio of the amplitudes of voltage and current of a single wave propagating along the line. It is a function of primary constants of the line and operating frequency.

For well-functioning transmission lines, with either $R$ and $G$ both very small, or with $\omega$ very high, or all of the above, the characteristic impedance is typically very close to being a real number which means the line is considered lossless.

Symbol
$Z_{ch}$
Unit
$\Omega$
Formulae
$\sqrt{\frac{\mathscr{z}_{int}}{Y_{cs}}}$Definition according to Cigré guide 531 chapter 4.2.5
$\sqrt{\frac{L_m}{C_b}}$Lossless line
Related
$C_b$
Capacitance of insulation [F/m]
$\gamma_{prop}$
Cable propagation constant
$L_m$
Inductance (mean) [H/m]
$Y_{cs}$
Admittance conductor - shield [S/m]
$\mathscr{z}_{int}$
Impedance internal of cable [$\Omega$/m]
Used in
$SIL$
Surge impedance loading [MW]