When any two conductors are separated by an insulating material it will form a capacitor. In case of overhead transmission line air acts as an insulating medium between two conductors. So there will be capacitance between two conductors which is defined as charge per unit potential difference
Capacitance, C = q/v farad
Unlike resistance and inductance, the capacitance of transmission line is also uniformly distributed along the whole length of the line. It may be treated as a uniform series of capacitors connected between the conductors as shown in the Fig. 1 and Fig. 2.
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The charge on the conductors at any point increases with increase and decrease of the instantaneous value of the voltage between conductors at that point. Due to this a current known as charging current flows through the conductors even though the line is open circuited. The voltage drop, efficiency and power factor of line depends on the value of capacitance.
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Capacitance of Transmission Line
Capacitance of Transmission Line