<p style="text-align:justify"><span style="font-size:14px"><img alt="" src="https://edupmquestionhelp.s3.ap-south-1.amazonaws.com/hint/uploads/images/16163217831616321783.jpg" style="height:513px; width:800px" /></span></p>

<p style="text-align:justify"><span style="font-size:14px">In monsoon season, there is lightning. The high frequency overvoltages are developed due to lightning. A typical wave shape of this overvoltage is shown in figure 5.2. The peak of this overvoltage can be as high as 1000 kV in the worst case. This wave of lightning overvoltage travels over transmission Line (from wherever it is incident) as a travelling wave and will reach a substation or a power station. The insulation of the electrical equipment will be intrinsically damaged by this overvoltage which is rising to its peak value within a very short time (typically 1.2 microsecond).</span></p>

<p style="text-align:justify"><span style="font-size:14px">High frequency overvoltages are developed by switching actions also. Switching off or ON is inevitable in any power system either manually or automatically by operation of protective gear. These overvoltages also travel over a line, reach the substation and can damage the insulation of the equipment. </span></p>

<p style="text-align:justify"><span style="font-size:14px">Lightning arresters are provided to protect the electrical equipment of a substation against overvoltages mentioned above. Lightning arrester (or Surge arrester) diverts (hence the name Surge diverter also) the energy of the overvoltage to ground, thereby reducing the peak of overvoltage. The action is so fast (5 to 10 milliseconds) that, however grounding the energy is a ground fault, protective relay does not operate so fast. LA is the first equipment at the entry of the transmission line in a substation.</span></p>