[Trade Journal]
Publication: Elektrotechnisches Echo
Magdeburg, Germany
vol. 12, no. 9, p. 91, col. 1-2
The "Provo" High Voltage Insulator
(With 1 figure.)
The "Provo" type high-voltage insulator made by the Hemingray Glass & Co. of Covington, Ky., — which reportedly performed exceptionally well in a long-distance power transmission system in Utah operating at 40,000 volts — is made of the cheapest insulating material available: glass.
The model shown in Figure 1 is 14.5 cm high with a diameter of 17.5 cm and features five skirts — or, more precisely, three ribs and two skirts. Two ribs are located close to the line wire; they serve to interrupt the surface area between the wire and the pin, thereby preventing the current from arcing across. Another advantage of these ribs situated beneath the line wire is that they create narrow, high-resistance annular zones that prevent surface leakage losses at the source. In actual practice, these areas have been found to remain free of moisture and snow. The skirts on the underside increase the surface distance from the line wire to the pin to 40 cm. Serrations are provided along the lower edge of the outer skirt to facilitate water runoff.
The line wire is tied into the uppermost groove of the insulator. This method has proven most advantageous when the insulator must withstand tension directed upwards, downwards, or to the side.
The thickness of the glass is well-proportioned, and the insulator is exceptionally resistant to mechanical breakage or electrical breakdown.
Tests involving voltage differences of 125,000 volts between the wire and the pin reportedly caused no damage to the insulator. The glass is nearly colorless, making the insulators almost invisible on the poles.
