Generally characteristic impedance of cable is taken as _______

Concept:

The surge impedance or characteristic impedance of a long transmission line is given by,

\({Z_C} = \sqrt {\frac{Z}{Y}} \)

Z is series impedance per unit length per phase

Y is shunt admittance per unit length per phase

The surge Impedance for the transmission line is about 400 ohms it is around 40 ohms for underground cables.

For overhead line surge impedance is given by 100 - 200  Ω

For underground cable surge impedance is given by 40 - 60 Ω
 

Additional Information

Surge impedance loading (SIL):

Surge impedance loading is defined as the power load in which the total reactive power of the lines becomes zero. The reactive power generated by the shunt capacitance is consumed by the series inductance of the line.

SIL \( = \frac{{{V^2}}}{{{Z_C}}}\;MW\)