Insulators on Transmission Lines.
| Location of Line. | Inches from Top of Insulator to Cross-arm. | Inches from Outside Petticoat to Cross-arm. | Inches from Lowest Petticoat to Cross-arm. | Inches from Edge of Outside to Edge of Lowest Petticoat. | ||||
|---|---|---|---|---|---|---|---|---|
| Electra to San Francisco | 14 | 1⁄2 | 11 | 3 | 1⁄2 | 7 | 1⁄2 | |
| Colgate to Oakland | 15 | 11 | 1⁄2 | 4 | 7 | 1⁄2 | ||
| Cañon Ferry to Butte | 13 | 1⁄2 | 7 | 3⁄4 | 1 | 1⁄2 | 6 | 1⁄4 |
| Shawinigan Falls to Montreal | 16 | 1⁄4 | 11 | 3⁄4 | 3 | 1⁄4 | 8 | 1⁄2 |
| Santa Ana River to Los Angeles | 8 | 5⁄8 | 3 | 3⁄4 | 3 | 3⁄4 | 0 | |
| Spier Falls to Schenectady | 10 | 3⁄4 | 7 | 3⁄8 | 4 | 1⁄4 | 3 | 3⁄8 |
| Niagara Falls to Buffalo | 10 | 5 | 1⁄2 | 3 | 2 | 1⁄2 | ||
| Chambly to Montreal | 8 | 1⁄2 | 4 | 1⁄2 | 2 | 2 | 1⁄2 | |
| On each of the lines named in this table the wires are strung on the tops of their insulators. | ||||||||
The Cañon Ferry line is carried on insulators each of which has three short petticoats and a long separate sleeve that runs down over the pin to within 11⁄2 inches of the cross-arm. This sleeve makes contact with its insulator near the pin hole. The outside petticoat of each insulator on this line is 73⁄4 inches above the cross-arm and 61⁄4 inches above the lower end of the sleeve. Both the main insulator and the sleeve, in this case, are of glass.
White porcelain insulators are used to support the 50,000-volt Shawinigan line, and are of a recent design. Each of these insulators has three petticoats ranged about a central stem so that their lower edges are 41⁄2 inches, 9 inches, and 13 inches respectively, below the top. The highest petticoat is 10 inches, the intermediate 93⁄4 inches, and the lowest 41⁄4 inches in diameter. The height of this insulator is 13 inches, compared with 111⁄4 inches for those used on the Electra and Colgate lines and 12 inches for the combined insulator and sleeve used on the Cañon Ferry line. When mounted on its pin, this insulator on the Shawinigan line holds its wire 161⁄4 inches above the cross-arm, compared with a corresponding distance of 141⁄2 inches on the Electra, 15 inches on the Colgate, and 131⁄2 inches on the Cañon Ferry line. The two upper petticoats on each of these insulators are much less concave than the lowest one, and the edges of all three stand respectively 113⁄4, 71⁄4, and 31⁄4 inches above the cross-arm. From the edge of the top to the edge of the bottom petticoat the direct distance is 81⁄2 inches.
Of the three transmission lines above named that operate at 50,000 to 60,000 volts, that between Shawinigan Falls and Montreal leads as to distances between the line wire and insulator petticoats and the cross-arm. On the Santa Ana line, where the voltage is 33,000, the insulator is of a more ordinary type, being of porcelain, 63⁄4 inches in diameter, 47⁄8 inches high, and having the lower edges of its three petticoats in the same plane. Each of these insulators holds its wire 85⁄8 inches above the cross-arm, and has all of its petticoats 31⁄2 inches above the cross-arm. Unlike the three insulators just described, which are mounted on wooden pins, this Santa Ana insulator has a pin with an iron core, wooden threads, and porcelain base. This base extends up from the cross-arm a distance of 31⁄8 inches, and the wooden sleeve, in which the threads for the insulator are cut, runs down over the central bolt of the pin to the top of the porcelain base, which is 5⁄8-inch below the petticoats.
The 30,000-volt lines from Spier Falls are carried 103⁄4 inches above their cross-arms by triple petticoat porcelain insulators. Each of these insulators is 81⁄2 inches in diameter, 63⁄4 inches high, and is built up of three parts cemented together. A malleable-iron pin cemented into each insulator with pure Portland cement carries the outside petticoat 71⁄2 inches and its lowest petticoat 41⁄4 inches above the cross-arm. When the voltage on the Spier Falls lines was raised from about 13,000 to 30,000, the circuits being carried in part by one-piece porcelain insulators, a number of these insulators were punctured at the higher pressures, and some cross-arms and poles were burned as a result. No failures resulted on those parts of these lines where the three-part insulators were in use. The second pole line between Niagara Falls and Buffalo was designed to carry circuits at 22,000 volts, or twice that for which the first line was built. Porcelain insulators were employed on both of these lines, but while the 11,000-volt line was carried on three-petticoat insulators, each with a diameter of 7 inches and a height of 51⁄2 inches, the 22,000-volt line was mounted on insulators each 71⁄2 inches in diameter and 7 inches high, with only two petticoats. The older insulator has its petticoats 2 inches above the cross-arm, and the lower petticoat of the new insulator is 3 inches above the arm. These two insulators illustrate the tendency to lengthen out along the insulator axis as the voltage of the circuits to be carried increases.
Fig. 93A.—The Old and New Insulators on the Niagara Falls-Buffalo Line.
For future work at still higher voltages, the advantage as to both first cost and insulating qualities seems to lie with insulators that are very long in an axial direction, and which have their petticoats arranged one below the other and all of about the same diameter, rather than with insulators of the umbrella type, like those on the Electra and Colgate lines.