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A Quick Guide on Lightning arrester

The lightening arrestors are electrical devices used for protection of electrical power systems including the transmission conductors and the terminal apparatus from the effects of lightning strike and traveling waves. The basic function of a lightning arrester is to attract the lightning with its high voltage end and conduct the lightning to the ground. When a lightning surge travels through a transmission line to a lightning arrester, the arrester diverts the surge currents to the ground thus preventing the condition of fault in the line.

Generally, the lightning arresters are located at the generating stations as well as the smaller substations.

The two types of lightning strokes are :

  1. Direct Stroke - In case of a direct lightning stroke, a direct discharge of charges occur between the clouds and the transmission lines. The surge currents travels up the line and can also result in flash over condition at the insulators.
  1. Indirect Stroke - In the case of indirect stroke, there is no direct lightning discharge taking place between the clouds and the powers system components, rather the stroke results from the presence of static charges present around the conductor due to induction effect of the clouds.
The basic type of Lightning arresters are :-

·         Rod type arresters - These types of arresters are have polymer insulators thus are also called Polymer lightning arresters. It contains two bending rods turned like an ‘L’ facing each other. In normal condition, the voltage between the two rods is less and the air gap behaves a an insulator but, in case of surges, the potential difference between the two conductors increases and the surge current is conducted to the ground.
·         Horn type arresters- In horn type arresters, there are two metal sheets bend like horns, which contain an air gap between them. Under normal working conditions, the potential difference across the horned conductors is less thus the air gap works as an insulator. In case of surge current, the potential difference increases many folds, and thus, the air gap becomes conducting and the surge current is by passed to the earth.
·         Multiple gap type arresters- In these type of arresters, multiple air gaps are constructed to provide higher series resistance to the arc. Thus, the air gap reduces the arc power and the surge is cleared quickly.
·         Expulsion type arresters - These types of arresters contain a standard rod gap lightning arrester in series with another air gap inside a fiber tube. In case of surge traveling in the line, the potential drop across the air gap in the fiber tube increases, thus an arc is ignited. Due to the heat produced by the arc, the layers of the fiber tube walls are vaporized producing gasses. These gasses are expelled from the lower end cavity of the arrester and with it carries the ionized particles present in the air gap. These ionized particles are necessary for the sustenance of the arc, thus the arc is extinguished and the faults are cleared.
·         Valve type arresters - Valve types arresters contains a series of spark gaps in form of valves. These  valves are assembled in series with non linear resistors whose resistance increases with increase in the flow of current through them.