[Trade Journal] Publication: Electrical World and Engineer New York, NY, United States |
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Transmission of Niagara Power to Toronto. — I.
TWO lines of steel towers on a private right of way 75 miles long are to carry four circuits for the transmission of 40,000 horse-power at 60,000 volts from Niagara Falls to Toronto. On this right of way the minimum standard width is 80 feet, the grade toward Toronto is not expected to exceed 15 feet per mile, and toward Niagara Falls 53 feet per mile, and the rate of curvature will not be more than 3-1/2 degrees, or a radius of 1,637 feet. These figures for grade and curvature are especially important because a high-speed electric railway is to be operated with double tracks between the two rows of steel towers along the entire length of the line. Between the two lines of towers the clear width of the right of way is 34 feet, the centers of the double tracks are 13 feet apart, and the distance from the center of each track to the sides of the nearer towers is also 13 feet. From the center of each tower to that of the right of way is 24 feet, and the two lines of towers thus have their centers 48 feet apart. At the ground line the width from outside to outside of the tower lines is 62 feet, but at the level of the crossarms the width is 67 feet 6 inches. At present one line of these towers with its two transmission circuits is nearly completed, and the other line of towers will be erected as soon as the demand for power makes it desirable. On the straight portions of the line the steel towers are regularly erected 400 feet apart, but on curves the distances are less between towers, so that their total number is about 1,400 for each line. Standard curving along the line requires towers placed 50 feet apart, and a change in direction of not more than 10 degrees at each tower, except at the beginning and end of the curve where the change in direction is 3 degrees. When the change in direction of the line is not more than 6 degrees the corresponding spans allowed with each change are as follows:
If the line follows a rising grade with a span of zoo feet the elevation of the first tower beyond the level may be 7 feet above the one preceding, the elevation of the second tower 14 feet, with 21 feet rise between the second and third tower, 28 feet between the third and fourth, and a line that follows an up grade with a span of 300 feet may rise 24 feet in the first span beyond the level, 48 feet in a distance of 400 feet between towers, the rise of the first span beyond the level may be as much as 56 feet, of the second 112 feet, of the third 168 feet, and so on.
At the same points along the line conditions require a span between towers of more than 400 feet, the regular distance for straight work. One example of this sort occurs at Twelve Mile Creek, where the stream has cut a wide, deep gorge in the Erie plateau. At this point the lines makes a span of 625 feet between towers. In the case of this long span, as in some others, it is not thought desirable to have the transmission circuits at either side of the electric railway, and the right of way is therefore widened so that the towers can be set at one side. For the crossing at Twelve Mile Creek the center line of the nearer line of towers is moved to a distance of 63 feet to one side of the center line of the electric railway, and the distance between the centers of the two lines of towers is reduced to 30 feet. To provide for this sharp offset a special form of tower is provided.
The regular steel tower used in this transmission measures 46 feet in vertical height from its foot to the top of the lower insulators, and 51 feet 3 inches to the tops of the higher insulators. The lower six feet of this tower are embedded in the ground, so that the tops of the insulators measure about 40 feet and 45 feet 3 inches |