Discussion on “suggested specifications for testing high-voltage insulators” (Peek, Sandford and Thomas) Cooperstown, New York, June 25, 1913

F. W. Peek, Jr.: The line insulator is an important factor in determining the success or failure of a transmission scheme. The requirements in present insulator specifications in no way provide for uniform porcelain. Destructive puncture tests are generally made on a few selected units which may indicate a very good insulator. On account of the great lack of uniformity in most porcelain these tests do not determine the performance of the bulk of the insulators which are manufactured later and put on the line. It is thus seen that uniformity of the porcelain is one of the most desirable features of a line insulator. I should like to bring out a few points that should be covered. In almost all other engineering work the strength of a given material is known and can be depended upon within a small per cent of the value indicated by test pieces. The material is uniform, and uniformity is a necessity. If structural steel varied a tenth as much as most porcelain used in present line insulators, there could be no “sky scrapers.” Tests then, should be such as to secure uniform porcelain. This might be accomplished by requiring the destructive uniformity test, or the impulse test, made on insulators taken at random from different parts of the kiln at each firing. Again the specifications might require that a certain percentage of the insulators of each kiln at each firing pass the factory test otherwise all the insulators of the kiln at the given firing be condemned. For instance — if in one firing in a given kiln 50 per cent of the insulators fail to pass the factory test, and if in the next firing only 10 per cent fail to pass the factory test, the insulators in firing No. 2 would be much more reliable. A greater percentage would stand voltage rises on the line.