On Deviations From Standard Practise in Lightning Arresters

This paper is an endeavor to answer questions of practise and criticism of arresters brought out by an investigation conducted by the Protective Devices Committee. For the most part practise in lightning arresters is standardized. In fundamental principles there have been no changes for many years. Improvements in details, especially of construction, are still being made. A new arrester, the oxide film arrester, gets rid of the oil and electrolyte and avoids the necessity of daily charging, but fundamentally it is designed along the same principles as the aluminum arrester. The important principle is the electric valve action??there are but a few milliamperes of discharge rate at normal line voltage, but at abnormal line voltages the discharge current rise to hundreds of amperes. In answer to criticisms made by a few prominent engineers, it is maintained as fundamental that a large discharge rate for an arrester is an absolute essential. The burden of proof falls on those engineers who use arresters of low discharge rate. These arresters cannot discharge the dangerous lightning. surges on overhead lines. Since there are lightning arresters of low discharge rate in apparently satisfactory use, an explanation for this anomaly is found in the use of insulators of low arc-over voltage. Either the lightning potential is relieved locally at the insulator or the resultant traveling wave is of too low voltage when it reaches the transformer greatly to endanger the insulation. Poor line insulation is not a solution of the problem of continuity of service.