CAPACITANCE OF THREE PHASE TRANSMISSION LINES

Capacitance of a transmission line is the result of the potential difference between the conductors; it causes them to be charged in the same manner as the plates of a capacitor when there is a potential difference between them. The capacitance between the conductor is the charge per unit of potential difference. capacitance between parallel conductors is a constant depending on the size and spacing of the conductors. For power lines less than about 80 km (50mi) long the effect of capacitance is slight and is usually neglected. For longer lines of higher voltage, capacitance becomes increasingly important.

An alternating voltage impressed on a transmission line causes the charge on the conductors at any point to increase and decrease with the increase and decrease of the instantaneous value of the voltage between conductors at the point. The flow of charge is current, and the current caused by the alternate charging and discharging of a line due to an alternating voltage is called the charging current of the line. Charging current flows in a transmission line even when it is a open-circuited. It affects the voltage drop along the line as well as the efficiency and power factor of the line and the stability of the system of which the line is a part.