Abstract :
Review of the Subject. — A general survey is presented of the nature and distribution of failures and interruptions due to lightning upon the circuits of a large city supply system. Recommendations are given for improving conditions without specifying particular makes of arresters, in recognition of the fact that a considerable number of different types is proving adequate to meet the conditions imposed upon them on the moderate voltage systems under consideration. The subject is treated under three principal divisions: 1st. Troubles on 115–230 volt distribution circuits. 2nd. The 2300. volt circuits, and 3rd. The 13,200 volt circuits. It is shown that line failures on the low-voltage circuits are so infrequent as to be practically negligible, and that the blowing of fuses and injuries to other parts of the equipment on customer´s premises are infrequent except in the case of house meters. A considerable number of meter burn outs are recorded, and it is shown that trouble from this source increases with the length of the secondary circuit. To guard against future trouble, especially as secondary networks are developed, it is recommended that a simple spark gap or other equivalent type of arrester be installed at the customer´s premises as a part of the equipment in his service box. For the 2300 volt circuits, it is found that lines which run over high ground and open country are more exposed to transformer burn outs and the blowing of transformer fuses than lines in the built-up sections where buildings screen the circuit. Also, that the amount of damage to the exposed lines decreases as the number of arresters increases and that a transformer directly protected by an arrester is in a very large measure guaranteed against complete breakdown and to a less extent against the blowing of its fuses from lightning. Also, that the effectiveness of this protection is decreased with high resistance in the ground connection. Finally, for the 13,200-volt aer- al circuits, it is shown that on lines at a considerable distance from generating points most of the damage from lightning is in insulator breakages and without interruption to service, but where line reactance is not sufficient to prevent flow of heavy dynamic current at the time of discharge, the conductor is often fused allowing the line to fall. To guard against these troubles, arresters should be distributed along the line at not more than two mile intervals and near generating stations the three arresters of a group should be mounted on successive poles and provided with independent ground connections.
