Lightning arrester is a protective device used in both […]
Lightning arrester is a protective device used in both power system and telecommunication system to protect appartus from high voltage lightning surges. The arrester provides a low-impedance path to ground for the current from a lightning strike or transient voltage and then restores to a normal operating conditions. The earthing screen and ground wires fail to provide protection against traveling waves and the lightning arrester provides protection against these surges.
Since its diverts the HV surges, device is also known as surge diverter.
The action of the lightning arrester is as follows:
(i) Under normal operation, the lightning arrester is off the line i.e. it conducts no current to earth or the gap is non-conducting.
(ii) On the occurrence of over voltage, the air insulation across the gap breaks down and an arc is formed providing a low resistance path for the surge to the ground. In this way, the excess charge on the line due to the surge is harmlessly conducted through the arrester to the ground instead of being sent back over the line.
(iii) It is worthwhile to mention the function of non-linear resistor in the operation of arrester. As the gap sparks over due to over voltage, the arc would be a short-circuit on the power system and may cause power-follow current in the arrester. Since the characteristic of the resistor is to offer low resistance to high voltage (or current), it gives the effect of short-circuit. After the surge is over, the resistor offers high resistance to make the gap non-conducting.