Electric Transmission of Water Power

by Alton D. Adams

Fig. 89.—Cable Entering Building.

In the bottom of this box there is a circular opening for each wire, and into this opening fits a heavy glass or porcelain bushing through which the wire passes. After reaching the inside of the box the wire turns at right angles and passes through the sixteen-inch square opening into the sub-station. Beneath the box a special insulator is secured by an iron bracket to the outside of the brick wall for each line wire, and this insulator takes the strain of the wire before it is carried up through the bushing in the bottom of the box. This form of entry is permissible where the desire is to exclude cold air from the station, and where the voltage is not high enough to cause serious leakage over the surface of the bushing and the slate forming the bottom of the box. In all of the cases above mentioned the wires used to enter the stations were the regular line conductors and were bare.

Another type of entry in sub-stations is that employed on the extensive transmission system between Spier Falls, Schenectady, and Albany, N. Y. The maximum voltage on this system is 30,000, and the lines usually enter each sub-station through the brick wall at one of its gable ends. Outside of and about the entry of each circuit or group of circuits a wooden shelter is built on the brick wall of the sub-station. Each shelter has a slanting roof that starts from the brick wall at some distance above the openings for the entrance of the line, and terminates in a gutter. The front of each shelter is carried down three feet below the centre of the openings in the brick wall, and the ends go still lower. The front of each shelter is four feet in height, is four feet from the face of the brick wall, and has a circular opening of 10-inch diameter for each wire of the transmission line.

In line with each circular opening in the wooden shield there is an opening of 15-inch diameter in the brick wall of the sub-station, and into this opening in the brickwork fits a ring of wood with 15-inch outside and 11-inch inside diameter. To this wooden ring a 15-inch disc of hard fibre ¹⁄₈-inch thick is secured, and a porcelain tube 24 inches long and of 2-inch inside diameter passes through a hole in the centre of this disc. Within the wooden shield and in line with each circular opening in it and with the corresponding porcelain tube through the fibre disc a line insulator is secured. Within the sub-station and in line with each tube there is also an insulator, and the two insulators near opposite ends of each tube hold the line wire that passes through it in position.

Each wire of the transmission lines, of which the largest is No. 000 solid of 0.410-inch diameter, terminates at one of the insulators within the wooden shield, and is there connected to a special insulated wire that passes through one of the porcelain tubes into the sub-station. A copper trolley sleeve 12 inches long is used to make the soldered connection between the bare line wire and the insulated conductor that passes through the porcelain tube. Each of these entry cables, whatever its size, is insulated first with a layer of rubber ⁹⁄₃₂-inch thick, then with varnished cambric wound on to a thickness of ⁹⁄₃₂-inch, and lastly with two layers of weather-proof braid outside of the cambric. This form of closed entry for the transmission lines obviously excludes snow, rain, cold air, and dust from the station. Whether the fibre discs and wooden rings, together with the insulation on the entry cables, are as desirable as a glass disc at the entry is another question.

Another instance where the entry for a high-tension line is closed with the aid of combustible material is that of the 25,000-volt transmission between the water-power plant at Chambly, on the Richelieu River, and the sub-station in Montreal. The four three-phase circuits of this line are made up of No. 00 wires of 0.365-inch diameter each, which enter the power-station at Chambly and the terminal-house in Montreal bare, as they are outside.

At each end of the line the wires are secured to insulators on a horizontal arm with their centres twenty-two inches outside of an end wall of the station or terminal building. The insulators are mounted with their centres thirty inches apart, and a few inches above the tops of these insulators a corresponding row of wooden bushings pass through the wall with an outward slant.

At the Chambly end of the line each of these bushings is of oak, boiled in stearin, four inches in diameter and twelve inches long. At the Montreal end the wall bushings are of boxwood, and each is four inches square and twelve inches long. Each of the wooden bushings carries a glass tube, and is itself held in position by the concrete of the wall in which it is located. Entrance to the station by each of the bare No. 00 wires is gained through one of these glass tubes, and cold air is excluded.

Quite a different type of closed entry for the wires of a transmission line is in use on that between Shawinigan Falls and Montreal, which operates at 50,000 volts. For the entry of each of the three aluminum cables that make up this line, each cable being composed of seven No. 6 B. & S. gauge wires, a tile pipe of twenty-four-inches diameter was set into the station wall. The end of each tile pipe is closed by a glass plate, with a small hole at its centre, through which the cable passes.