# An overhead line with surge impedance 400 ohm is terminated through a cable of impedance Zc. A surcharge travelling over the line does NOT suffer any

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An overhead line with surge impedance 400 ohm is terminated through a cable of impedance Zc. A surcharge travelling over the line does NOT suffer any reflection at the junction. The value of Zc is
1. 40 ohms
2. 500 ohms
3. 450 ohms
4. None of these

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Correct Answer - Option 4 : None of these

When a loss-free overhead transmission line is terminated through a resistance equal to surge Impedance of the line, there will be no reflection of travelling wave hence the value of R is 400 Ω.

Important Points:

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

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

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 $= \frac{{{V^2}}}{{{Z_C}}}\;MW$