Friday, October 30, 2009

What are Lightning Arresters?


Lightning arresters or surge diverters are used to protect the earth screen and ground wires in an electrical system against direct lightning strokes. They conduct the high voltage surges to the ground without getting affected to the system. The lightning arrestor provides a cone of protection which has a ground radius approximately equal to its height above the ground.

The surge diverters consist of a spark gap in series with a nonlinear resistor. The function of non linear resistor is very important. As the gap sparks over, due to the over voltage, the arc would get short circuited and may cause power flow current in the arrester. Since the characteristic of the resistor is to offer high resistance to high voltage, it prevents the effect of a short circuit. After the surge is over, the resistor offers high resistance to make the gap non-conducting.

One end of the arrestor would be connected to the terminal of the equipment to be protected and other end would be grounded. The length of the spark gap is set in such a way that normal line voltage is enough to cause an arc across the gap but high voltage would break down the air insulation and form an arc.

Different types of surge diverters are available depending on the purpose. Some of them are Rod gap arrester, Horn gap arresters, Multigap arresters, Expulsion type lightning arrester and valve gap arrester. Each of them has variety of range of operating conditions.

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