Protective apparatus engineering

The main object of this paper is to describe the methods which have been in use in the development of lightning apparatus, so that some or all of these methods may be adopted or recommended as standard in the investigation of the value of any particular apparatus. As an introduction, it is pertinent to point out the differences and identities in the operation of the arrester in test as compared with its operation in actual service. Generators, motors, arc lights, practically all electrical apparatus except lightning-arresters — are tested under the conditions, under which they are to operate. The lightning-arrester in service comes into action only intermittently, with long intervals between operations, and each operation is under conditions more or less different from the previous ones. It protects, fails, or is destroyed according to its adaptation to meet the imposed conditions. The arrester may operate for years before it encounters conditions which it is incapable of meeting. The conditions which caused the failure are usually unknown, therefore little or no progress can be made in the design without studying the actual conditions which caused the failure of the arrester. Since this cannot be done at present with cloud lightning, we must experiment with artificial lightning in the laboratory until this condition causing failure is found. Simply noting whether an arrester-fails and then making an adjustment, elimination, or addition of parts of the arrester is a cut-and-try method and has already been carried to the limit of its efficacy in the development of protective apparatus.