Hemingray Glass Company - Muncie, Indiana

The "Provo" Type Insulator.

The subject of insulators for high-potential transmission lines has received the very serious attention of electrical engineers, and as a result some very efficient types have been produced.

The "Provo" type high-potential insulator, manufactured by the Hemingray Glass Company, Covington, Ky., has won for itself a reputation by its successful use since February last on the 40,000-volt transmission line of the Telluride Power Transmission Company in Utah. The design of this insulator was arrived at by a careful study of the action on insulators of high-potential currents as employed in actual practice. The insulator is made of glass, and is said to be homogeneous and impervious to liquids. It has an extra long surface distance between the line and pin, namely, 16 inches. The point of support of the wire is high above the cross arm and the petticoats near the line wire protect surface of small area of high resistance and prevent the accumulation of moisture, thus checking leakage near its source. The insulator withstands an extra high test between the line and pin, 125,000 volts having, it is stated, been applied in a number of tests without puncturing. The edge of the outer petticoat is finished off in some points for the purpose of facilitating the shedding of water. The thread of the insulator is 2 1/2 inches long. It is stated that this insulator has a strong resistance to mechanical breakage and is not affected by changes of temperature. The strain of the wire is brought squarely on the pin. An illustration of this insulator, together with some facts of interest concerning the same, was published on page 596 of The Electrical World of December 3 last.

The line on which these insulators are used extends from Provo to Mercur, and reaches an altitude of 10,000 feet above sea level. Three miles of the line are of strictly mountain construction.