Publication: Electrical World
New York, NY, United States
GRADED SUSPENSION INSULATORS.
To the Editors of Electrical World:
Sirs: - The Proceedings of the American Institute of Electrical Engineers for March 1912, contains an article by Dr. Charles P. Steinmetz, entitled "Some Problems of High-Voltage Transmission." Among other interesting facts, Dr. Steinmetz states: "With a number of equal insulating disks sharing the voltage between line and ground, the potential difference across the insulators nearest the line is higher, and the potential difference across the insulators nearest the ground is lower, than the average potential difference per insulator, the more so the greater the number of insulator disks." Also, "From this it appears that the use of a larger number of small insulator disks is uneconomical at very high voltages, and a few large disks of high disruptive strength are preferable." Also, "To extend the insulating possibilities of the suspension insulator type far beyond the voltages now contemplated, therefore, requires a grading of the insulator disks in their capacity, so that the disk nearest the line has the highest, that nearest the ground the lowest capacity, or the addition of capacity at the surface of the insulator disks, in proportion to their distance from the ground." It will no doubt be of general interest to learn that I worked out those theories some years ago, and embodied them in a patent issued Feb. 15, 1910, No. 949,604, the application for which was filed Dec. 4, 1909.
This patent covers a number of new and very desirable features. In this patent, in place of disk-type insulators, I employed my then newly invented "thimble type" insulators. The title "thimble type" was coined to denote the general thimble form of the insulator body, to distinguish them from disk or hood-type insulators.
My earlier patents, No. 879,068, of Feb. 11, 1908, and No. 905,014, of Nov. 24, 1908, show that some years prior to the time of filing application for Patent No. 949,604, of Feb. 15, 1910, I was working along lines the very opposite of my later inventions. The two earlier patents show that I then believed it advisable to protect the lower insulator unit by placing a larger unit above it or by providing a separate shed or umbrella-like member above the lower insulator unit.
I have been greatly pleased to learn that others have recently arrived at conclusions reached by me several years earlier.
Brooklyn, N. Y. Louis Steinberger.