The Gerry 50,000-Volt Insulator

[Trade Journal]

Publication: The Journal of Electricity, Power and Gas

San Francisco, CA, United States
vol. 13, no. 2, p. 154, col. 1-2



Information is frequently sought concerning the type of insulator used on the high voltage transmission between Canyon Ferry and Butte, and especially is it desired to know the dimensions of the insulator and the success which has attended its use. As is generally known, the insulator is made of glass, produced by the Hemingray Glass Company of Covington, Ky., and its outlines and dimensions are as given in the accompanying sectional sketch, which is from the original drawings of Mr. M. H. Gerry Jr., chief engineer and manager of the Missouri River Power Company, and who designed the insulator.




In view of the completeness of the drawing and the appearance thereon of all dimensional data, a detailed description of this remarkable insulator is unnecessary, beyond stating that it, together with its tapered glass sleeve, is all glass, non-cemented. It is stated that these insulators have proven to be absolutely reliable when in operation under 50,000 volts, and that the only defect which has occurred in their design rested in the belief that it would have been better to have given more body to the walls supporting the cap of the insulator at the section of the horizontal plane of the top of the pin, where a thickness of seven-eighths of an inch is shown. This belief is held for the reason that several—probably half a dozen—caps have broken off at the point stated, which would indicate slight structural weakness at that point. Were a new lot of insulators to be ordered the only change which would be made in the specification for them would be in the direction of increased strength in the body of the insulator supporting the cap.

One further notation: The ratio in which the transformers are wound is 552 1/2 to 50,000. The generator voltage was stated to be 630 volts, which would give a line potential of approximately 57,000 volts. The weather was clear, cold, dry and crisp.


Keywords:Power Transmission : Butte : Gerry : Hemingray Glass Company : CD 303-310
Researcher notes:The insulator is the Hemingray "Muncie Type" CD 303/310.
Supplemental information: 
Researcher:Elton Gish
Date completed:December 26, 2009 by: Elton Gish;