Lightning arresters, designed for the protection of transmission lines, must perform this function with a minimum impairment of the insulation of the lines.
In general the construction of lightning arresters comprise
- 1. Air gaps;
- 2. Resistances;
- 3. Inductances;
- 4. Arc suppressing devices.
Ques. What are the causes of static charges?
Ans. They may be caused by sandstorms in dry climates, or may be due to grounds on the high pressure side of a system.
Ques. What causes high frequency oscillations?
Ans. They are usually due to lightning discharges in the vicinity of the line.
Ques. What are the requirements of lightning protection devices?
Ans. They must prevent excessive pressure differences between line and ground, line and line, and between conductor turns in the electrical apparatus.
Air Gap Arresters.—method of relieving any abnormal pressure condition is to connect a discharge air gap between some point on an electric conductor and the ground. The resistance thus interposed between the ground and the conductor is such that any voltage very much in excess of the maximum normal will cause a discharge to ground, whereas at other times the conductor is ungrounded because of the air gap. This forms the principle of air gap arresters.