For certain geometry and operating voltage of the uncompensated transmission line, the ratio of power transfer capability to the surge impedance loading with an increase in length

For certain geometry and operating voltage of the uncompensated transmission line, the ratio of power transfer capability to the surge impedance loading with an increase in length

Right Answer is:

Remains unchanged

SOLUTION

The SIL (or the natural loading) of a transmission line is defined as the power delivered by the line to a purely resistive load equal to its surge impedance.

In power systems, if the line is lossless, the characteristic impedance Zc, of a line is sometimes called surge impedance.

${Z_c} = \sqrt {\frac{L}{C}}$

Where

L = inductance

C = Capacitance

Therefore, for a loss-free line, its series resistance and shunt conductance are zero. It is a function of the line inductance and capacitance as shown and is independent of the line length.

Note:-

The approximate value of surge impedance for overhead lines is 400 ohm and for cables, it is 40 ohm. Since distances between cable conductors are small, the value of inductance is smaller and capacitance is relatively higher compared to overhead lines, thus low surge impedance.

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