Experiments on porcelain suspension insulator units

The author gives a very complete description of the experiments on porcelain suspension insulator units carried on at Stanford University by him and his assistants under the direction of Prof. H. J. Ryan. He explains the preliminary organization necessary, the scope of the tests, and the unusual equipment required to measure the very high resistance of sound, dry insulators. Preliminary resistance measurements were made on all normal batches of porcelain units and the results tabulated, as also were results obtained when the units were subjected to mechanical stress, to voltages ranging from 1,000 to 30,000, to temperature variation. Another set of tests was made to determine the effect of moisture in insulators. Drying insulators for a few hours in an oven at 150 deg. cent. produced very conclusive results of the effect of moisture in lowering resistance. Attempts were made to water-log units by soaking, by soaking with a temperature cycle applied, by subjecting units under various conditions to a steam pressure of 60 lb., and by a vacuum treatment of insulators before soaking. A brief statement is given of the conclusions arrived at.