Electric Transmission of Water Power

by Alton D. Adams

This Manchester sub-station is equipped with air-blast transformers from which the hot air is discharged into the same room that the transmission lines enter. Along one side of the sub-station there are twenty-seven of these five-inch circular openings in the slate slabs for entrance of the high-voltage lines, and on another side of the sub-station there are a greater number of smaller openings for the distribution circuits. Were it not for the air-blast transformers, all of these openings would probably admit more air than would be desirable in a climate as cold as that at Manchester.

Another example of openings in the walls of a station for the entrance of transmission circuits, where there is free movement of the air between the inside and outside of the building, is that of the 33,000-volt line between Santa Ana River and Los Angeles, Cal. In this case a sewer pipe twelve inches in diameter is built into the wall of the station for each wire of the line, so that there is a free opening of this size from inside to outside.

Each wire of the 33,000-volt circuit enters the station through the centre of one of these twelve-inch pipes, and is thus surrounded by six inches of air on every side. As the temperature near Los Angeles seldom or never goes down to zero, these large openings do not admit enough air to be objectionable. Besides this mild climate, air-blast transformers add to the favorable features in the stations having the twelve-inch openings.

In another case, however, where the openings for the entrance of wires of very high voltage allow free movement of air between the inside and outside of the station, the climate is cold and the winter temperatures go down to 30° or more below zero. This condition exists on the 25,000-volt line between Apple River Falls and St. Paul, where six No. 2 wires enter the generating station through plain circular openings in the brick side wall of a small extension where the lightning arresters are located. Air-blast transformers are located in the end of the station next to this lightning-arrester house, but it is not certain that the hot air from them escapes through the openings for the wires.

In another case where the climate is about as cold as that just named, a gallery is built along one side of the exterior of the station at some distance above the ground, and two openings are provided for each wire of the high-tension line. One of these two openings is in the horizontal floor of the gallery and allows the entrance of the wire from the outside, and the other opening is in the side wall of the station against which the gallery is built. The two openings for each wire being thus at right angles to each other, and the opening to the outside air being protected from the wind by its horizontal position, no more than a permissible amount of cold air, it is said, finds its way into the station.

In some cases with lines of moderate voltage, say 10,000 to 15,000, and in probably the majority of cases with lines of 25,000 volts or more, the entry for the high-tension wires is entirely closed. An example of this practice may be seen at the various sub-stations of the New Hampshire Traction Company, which are located along their 12,000-volt line between Portsmouth and Pelham, in that State.

For the entry of each wire on these lines a sixteen-inch square opening is made in the brick wall of the sub-station. On the outside of this wall a box is built about a group of three or more of these openings located side by side. The top or roof of this box is formed by a slab of bluestone three inches thick, which is set into the wall and extends twenty-six inches from the face of the wall, with a slight slope from the horizontal.

The ends, the bottom, and the outer side of this box are formed by slabs of slate one inch thick, so that the enclosed space has an area in vertical cross section at right angles to this building 15.5 inches high and twenty-two inches wide.