Capacitance in Overhead Transmission Lines:

Transmission lines have inductance and capacitance due to the distributed nature of the line. The inductance of the line is responsible for the magnetic field that surrounds the conductor, while the capacitance is due to the electric field between the conductor and the ground. The capacitance of a transmission line is proportional to the length of the line, the spacing between the conductors and the distance from the conductors to the ground.

Effect of Capacitance:

Capacitance causes a voltage drop in the line, which is proportional to the current flowing through it. This voltage drop is called the charging current and is due to the charging and discharging of the capacitance. The charging current is in phase with the voltage, which means that it does not cause any power loss. However, it can cause voltage regulation problems and can lead to overvoltage conditions.

When the length of the line is very long, the effect of capacitance becomes significant and needs to be taken into account. The capacitance of the line causes the voltage to be reduced, which can lead to power losses and voltage regulation problems. Therefore, it is essential to consider capacitance when designing long transmission lines.

When the length of the line is short, the effect of capacitance can be neglected. This is because the voltage drop due to capacitance is small compared to the voltage drop due to resistance and inductance. Therefore, for short transmission lines, the effect of capacitance can be ignored, and only the resistance and inductance need to be taken into account.

Conclusion:

In overhead transmission lines, the effect of capacitance can be neglected when the length of the line is less than 80 km. Beyond this distance, the effect of capacitance becomes significant and needs to be taken into account when designing the transmission line.