Transmission Research and Design with the Field as a Laboratory

Overhead transmission lines are usually considered to be a class of equipment subject to certain types of troubles which cannot be avoided by means accepted as ordinary practise. It is the purpose of this paper: (1) to describe improvements in design of wood pole lines of the 33,000-volt class, which improvements have been developed and applied to the system with which the authors have been identified and which, it is believed, will greatly reduce the characteristic troubles, (2) to present an explanation of flashovers on wood structures, (3) to give the facts found in field investigations which form the basis for the improvements adopted, and (4) to describe the method used for field investigations and analysis of troubles. The studies and investigations referred to deal primarily with the matter of insulation. Considerable information relative to the insulation values of wood in a structure as developed by laboratory tests has been published. Experience is cited in this paper to show the value of wood insulation in the structure developed from field experience on 33,000-volt lines, and there is presented a practical economical design of wood pole structures using wood braces, in place of the usual metal braces, which, it is believed, will be practically immune to lightning troubles. Data from laboratory tests are given to substantiate the conclusions developed in the field investigations. The performance of insulators with respect to mechanical and electrical breakage is shown and the use of insulators of more sturdy designs is discussed.