Abstract :
The paper first gives a summation of the items that are apparently the main causes of pin-type insulator failures in service. Each item is thereafter briefly discussed and the opinions of operating men are cited. A brief description is given of the method used to determine the form of the dielectric field about porcelain insulators under normal line voltage. Diagrams of the dielectric fleld and photographs of flash over tests of theoretical designs are shown. There-after, the necessary modifications of the theoretical designs, in order to meet operating and manufacturing conditions, are discussed. In the latter part of the paper, diagrams and illustrations are shown of a proposed type of commercial insulator design which has been evolved by linking together the theoretical and practical phases of the problem. A comparison is then made between the older types of design and the proposed type, as regards the resistance of each to the conditions that cause failure of the insulator in service. In conclusion, a summary is made of the advantages it is believed that the new type of design has over the present commercial insulator designs.
