Data of a number of transmission lines presented in the appended table illustrate the practice in some of the more recent and important cases as to the materials, size, number, and arrangement of the wires. The plants of which particulars are given include the greatest power capacities, the longest distances, and the highest voltages now involved in electrical transmissions. Each of the lines named is worked with alternating current of two- or three-phase. Each three-phase line must have at least three wires, and each two-phase line usually has four wires.
On ten of the lines the number of wires is greater than three or four, thus reducing the necessary size of each wire for a given conductivity of the line. The Butte, Oakland, and Hamilton lines are run on two sets of poles for greater security, and a second pole line has been added to the Niagara and Buffalo system to carry additional wires.
The largest wire used in any of these lines is the aluminum cable of 500,000 circular mils between Niagara Falls and Buffalo. This cable has 1.66 times the area in cross section of a copper cable of equal conductivity.
Sizes and Materials of Wires on Some American Transmission Lines.
| Location of Transmission. | Line Voltage. | Num- ber Wires. | Size of Each Wire B. & S. Gauge. | Metal in Wire. | Length of Trans- mission. Miles. | |
|---|---|---|---|---|---|---|
| Cañon Ferry to Butte | 50,000 | 6 | 0 | Copper | 65 | |
| Colgate to Oakland | 40,000 | 3 | 00 | Copper | 142 | |
| 3 | 000 | Aluminum | 142 | |||
| Electra to San Francisco | 40,000 | 3 | 471,034 C. M. | „ | 147 | |
| Santa Ana R. to Los Angeles | 33,000 | 6 | 1 | Copper | 83 | |
| Apple River to St. Paul | 25,000 | 6 | 2 | „ | 25 | |
| Welland Canal to Hamilton | 22,500 | 3 | 1 | „ | 35 | |
| 3 | 00 | „ | 37 | |||
| Cañon City to Cripple Creek | 20,000 | 3 | 3 | „ | 23 | 1⁄2 |
| Madrid to Bland | 20,000 | 6 | 4 | „ | 32 | |
| White River to Dales | 22,000 | 3 | 6 | „ | 27 | |
| Ogden to Salt Lake City | 16,000 | 6 | 1 | „ | 36 | 1⁄2 |
| San Gabriel Cañon to Los Angeles | 16,000 | 6 | 5 | „ | 23 | |
| To Victor, Col | 12,600 | 3 | 4 | „ | 8 | |
| Niagara Falls to Buffalo | 22,000 | 6 | 350,000 C. M. | „ | 23 | |
| Nia„ara Fa„s to Bu„ | 22,000 | 3 | 500,000 C. M. | Aluminum | 20 | |
| Yadkin River to Salem | 12,000 | 3 | 1 | Copper | 14 | .5 |
| Farmington Riv’r to Hartford | 10,000 | 3 | 336,420 C. M. | Aluminum | 11 | |
| Wilbraham to Ludlow Mills | 11,500 | 6 | 135,247 C. M. | „ | 4 | .5 |
| Niagara Falls to Toronto | 60,000 | 6 | 190,000 C. M. | Copper | 75 | |
Aluminum lines are now employed for the three longest electrical transmissions in North America. In the longest single line, that from Electra power-house to San Francisco, a distance of 147 miles, aluminum is the conductor used. The 142-mile transmission between Colgate and Oakland is carried out with three aluminum and three copper line wires. For the third transmission in point of length, that from Shawinigan Falls to Montreal, a distance of 85 miles, three aluminum conductors are employed.
The three transmissions just named have unusually large capacities as well as superlative lengths, the generators in the Electra plant being rated at 10,000, in the Colgate plant at 11,250, and in the Shawinigan plant at 7,500 kilowatts. Weight and cost of such lines are very large. For the three No. 0000 aluminum conductors, 142 miles each in length, between Colgate and Oakland, the total weight must be about 440,067 pounds, costing $132,020 at 30 cents per pound. Between Electra and Mission San José, where the line branches, is 100 miles of the 147-mile transmission from Electra to San Francisco. On the Electra and Mission San José section the aluminum conductors comprise three stranded cables of 471,034 circular mils each in sectional area and with a total weight of about 721,200 pounds. This section alone of the line in question would have cost $216,360 at 30 cents per pound. The 85-mile aluminum line from Shawinigan Falls to Montreal is made up of three-stranded conductors each with a sectional area of 183,708 circular mils. All three conductors have a combined weight of about 225,300 pounds, and at 30 cents per pound would have cost $67,590.
Aluminum lines are not confined to new transmissions, but are also found in additions to those where copper conductors were at first used. Thus, the third transmission circuit between the power-house at Niagara Falls and the terminal house in Buffalo, a distance of 20 miles by the new pole line, was formed of three aluminum cables each with an area of 500,000 circular mils, though the six conductors of the two previous circuits were each 350,000 circular mils copper.
From these examples it may be seen that copper has lost its former place as the only conductor to be seriously considered for transmission circuits. Aluminum has not only disputed this claim for copper, but has actually gained the most conspicuous place in long transmission lines. This victory of aluminum has been won in hard competition. The decisive factor has been that of cost for a circuit of given length and resistance.