Snoqualmie transmission line

The Snoqualmie-Seattle-Tacoma Transmission With Aluminum Live Wire.

SECOND to none in importance among the water power transmission projects that are being carried out this year is the undertaking which will bring the water power of the Snoqualmie Falls to the cities of Seattle and Tacoma, Wash. It is expected that within a few months this company will be able to furnish 4,000 kilowatts at Seattle, and 2,000 kilowatts at Tacoma, the latter city being the most distant from the falls. The company is backed by Chicago capital and brains, William T. Baker, formerly president of the Chicago Board of Trade, being the financial backer, and Thomas T. Johnston, a prominent Chicago engineer, consulting engineer of the drainage canal, and president of the Western Society of Engineers, engineer of the new project, under whose direction the work has been planned and is being carried out. Chas. H. Baker, of Seattle, is president and manager of the company, while J. J. Reynolds, formerly chief engineer of the Chicago Terminal Railway, is superintendent of construction.

Map of Snoqualmie Falls Transmission.

The falls of the Snoqualmie River are about twenty-four miles (air line) east of Seattle, and thirty- four miles (air line) northeast of Tacoma. The Snoqualmie is fed by the western slopes of the Cascade range and drains about 400 square miles The falls have a drop of 268 feet. Readers of The Electrical Engineer will remember the picture published of the falls in these pages, four or five years ago.

Construction work began early the past spring. Three hundred feet up the river from the falls a dam will be built along a ledge of rock at that point. The dam will be 450 feet long, fifteen feet wide at the base, eight feet wide at the top, and of solid concrete. In the centre of the dam will be a bear trap dam for the escape of flood water. The water intake will be a 20-foot channel extending 60 feet up and down stream. From the intake the water will be piped through two 7-foot steel pipes down a vertical shaft cut down 250 feet in the solid rock. The shaft is being cut 25 by 8 feet. The water wheels and generators will be in a cave at the foot of the shaft, 200 feet long, 50 feet wide and 25 feet high. A tunnel is being driven in horizontally from below the falls to serve as a tail race. This tail race will extend from the wheels, 660 feet to an outlet in the face of the cliff below the falls. In order to clear the river for the building of the dam, the current will be turned through the shaft and tail race as soon as they are finished and allowed to run there until the dam is finished. In other words, Snoqualmie Falls will go dry for a time. The rock taken from the shaft is being crushed for use in the concrete dam, The dam being completed, the current will again be turned into the river, and Snoqualmie Falls will again exist. Then the two steel pipes and an elevator will be put in the shaft, and the water wheels and dynamos placed in the cave at the bottom. There will be four 1,500 kilowatt, 1,000 volt Westinghouse three-phase generators with a frequency of 7,200 alternations per minute. They will be direct connected to water wheels running 300 revolutions per minute. These generators are to be of the revolving armature type. The current will be conducted at 1,000 volts to the top of the shaft where the switchboard and static step-up transformer house will be located.

The full load voltage for the transmission line will be 29,000 at the Falls, and 25,000 at points of delivery. This will probably be the first large transmission plant to start with such a high regular working voltage. By altering the method of connecting the step-up and step-down transformers, the voltage can be reduced to 21,000 with a correspondingly greater loss in the line, but without interfering with the power consumers' voltage at Seattle and Tacoma.

For the first twenty miles the transmission lines to Seattle and Tacoma will run over the same right of way. At Renton, they separate, and one goes northwest about twelve miles to Seattle, while the other goes southwest about twenty-seven miles to Tacoma. At Renton there will be facilities provided for switching the Seattle circuit onto the Tacoma circuit and vice versa.

The company has decided on the use of aluminum wire for the transmission line, Engineer Johnston being authority for the statement that "We have succeeded in making contracts for a supply of aluminum wire at prices that make it cheaper than copper for our purpose. The metal we are to use will be of remarkably pure quality, being guaranteed to contain 99.30 per cent. of aluminum, and not more than 0.25 per cent. of iron and 0.30 per cent. of silicon . This will be alloyed with 1.50 per cent. of pure lake copper. We shall use about 150,000 pounds of it."

This is the first large transmission to use aluminum, and marks an important step in electrical engineering, for while aluminum has been talked of for some time for this purpose, price or some other factor seems to have stood in the way of its practical use to any extent over long distances.

The pole line is for the most part on the country roads, but in some cases a private right of way has been secured for a small sum. Large trees liable to fall on the line have all been cleared away. The poles were all purchased in the surrounding country. Wooden pins and cross arms will be used. Two circuits of three No. 2 aluminum wires each will run to Seattle, and two circuits of three No. 3 aluminum wires each will run to Tacoma. Thus each pole line will carry six wires. There will be two cross arms on a pole and the pins will be arranged so as to bring the three wires of each circuit at the corner of an equilateral triangle. Triple petticoated porcelain insulators known as the Redlands type because used on the Redlands, Cal., transmission, will support the aluminum conductors. Poles will be set about 120 feet apart. Like other companies developing large water powers for electric transmission purposes, this company will aim to do a wholesale rather than a retail power selling business, and will sell mainly to existing companies in the light, power and rail way business. Already a large output has been contracted for. Coal in Seattle and Tacoma is cheap, being about the same as in Pittsburg, but it is of such poor quality as to be of only about half the calorific value of Pittsburg coal. The flow of the Snoqualmie River is such that 30,000 horse power will be available at extreme low water, but a system of catching flood water might increase this many times, should it ever be demanded by the needs of the two cities. About 12,000 horse power is to be made immediately available at the falls, according to the present work being carried out.