Testing for Defective Insulators on High-Tension Transmission Lines

This paper discusses the importance and necessity of field tests on high-tension insulators and three methods of making such tests, viz.; with the oscillator, the megger, and the telephone receiver. The latter is described in detail, and some data given on its development and use on a 60,000-volt line in western Washington, covering a period of 2.5 years. Laboratory checks on 13 of the defective insulators located, are given, and an approximate relation established between the telephone receiver test and the break-down value at 60 cycles. Success of test is shown in note on its effect on operation. Figures from regular routine tests show percentage defect on various lines, and cost of locating and replacing defective units is given at $1.13 each (labor only), and cost of testing only was 2.3 cents per insulator on the line. A method of studying the rate of depreciation is outlined and some data given in illustration.