Grounding wire running over the tower or substation provides good protection to the electrical system against direct lightning stroke but they fail to provide protection against traveling high voltage or current waves that reach terminal equipment.
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The lightning arrester or surge arresters provide protection against such waves.
The above diagram shows the basic construction of lightning arresters (Surge arresters). This arrester consists of a spark gap in series with a nonlinear resistor which provides high resistance to normal voltage and low resistance to surge voltage.
The connection of lightning arresters on the transmission line is shown in the diagram. one end of the diverter is connected to the terminal of the apparatus to be protected and the other end of the arrester is connected to the ground through a Nonlinear resister series with a spark gap.
The length of the gap is set so that the normal line voltage is not sufficient to cause the breakdown of air between the gap and to form an arc. But high surge voltage will break down the air insulation and form an arc between the gap and series-connected nonlinear resistor offering low resistance to high surge voltage.
Working Of Lightning Arrester
The lightning arrester working principle is, Under normal operating conditions, a lightning arrester does not conduct any current to earth.
But on the occurrence of overvoltage due to lightning or other means, the air between the spark gap breaks down and arc forms. providing a low resistance path for the surge to ground hence excess charge on the line due to surge is conducted through the arrester to earth.
The purpose of a nonlinear resister is in the operation of a lightning arrester as a gap spark over due to surge voltage, the arc would be a short circuit on the power system and may cause power to follow the current in the arrester.
Since the characteristics of nonlinear resister provide high resistance to high voltage/current. it prevents the effect of the short circuit after a surge over. the resister offers high resistance to make the gap not conducting.
If arc one does not go away after the surge over it will carry current to ground through the spark gap.
Advantages
The advantages of lightning arrester are
- Equipment damage can be reduced from lighting stroke
- Outdoor equipment of the substation can be protected
- Provide protection to transmission lines against lightning strike
- Simple to use
Disadvantages
The disadvantages of lightning arrester are
- Required more space
- The installation cost is high.
Continue Reading Types of Lightning Arresters
