Protection of electrical equipment

The subject that I wish to discuss in this paper is the protection of electrical apparatus and transmission lines from the danger of breakdown to which such apparatus is subjected by electrical surges. The most frequent and severe source of electrical surges is lightning. There are other causes, arising from the operation of a transmission line and the electrical apparatus that goes with it to make up a complete plant. For instance, switching, particularly on the high-tension side, may give rise to surges. Also grounding of high-tension transmission lines, particularly if the ground be an arcing one; for instance, such as would occur were the limb of a green tree to come occasionally in contact with one of the conductors of the line. Also a short-circuit on the transmission line or on other electrical apparatus may give rise to an electrical surge.