Publication: Electrical World and Engineer
New York, NY, United States
Transmission System of the Bay Counties Power Company, California.
ONE of the largest transmission undertakings in California has been carried on very quietly, so that it has by no means attracted the attention its size and importance deserves. The company now has power houses of an aggregate capacity of 16,000 hp, with room for enlargement, and in addition to supplying power to towns and mining districts in Yuba and Nevada Counties, northeast of Oakland, is now completing a double 140-mile pole line to deliver power to Oakland and the eastern shores of San Francisco Bay. The transmission line and apparatus is designed for 60,000 volts line pressure.
The Bay Counties Power Company is the result of a consolidation of two companies, which previously owned power plants and supplied power in Yuba and Nevada Counties, viz., the Yuba Electric Power Company and the Nevada County Electric Power Company.
The Bay Counties Power Company now has three power houses. The largest of these is at Colgate on the North Yuba River, which was originally started in September, 1899. It has been enlarged until, when machinery now contracted for is installed, it will have a capacity of 15,000 hp. There will be allowance made for extending this plant still further. The water is supplied by a flume 7.6 miles long, 7 ft. wide and 6 ft. deep, with a drop of 13 ft. to the mile. This flume terminates at a point on the hillside 700 ft. above the power house. Five pipe lines will take the water to the power house. These are cast iron at the bottom and steel at the top, so in. inside diameter. In the power house there will be three units of 3000 hp and four units of 1500 hp. Risdon Iron Works impulse water wheels direct-connected to Stanley three-phase generators and governed by Lombard type F governors are adopted for all the units. The large units will run 285 r. p. m., and the small units run 400 r. p. m. The generator voltage is 2400, and this is raised at present writing by transformers connected delta fashion to 24,000 volts for transmission. This will presently be changed to star connection, and consequently 40,000 volts. The new transformers for the 140-mile line to Oakland will give 60,000 volts, and will be connected star-fashion with grounded neutral. They will have three different connections, so that 40,000, 50,000 or 60,000 volts may be obtained. The start will be made at 40,000 volts, and according to the plans this will be raised to 50,000 and 60,000 when the line loss due to increasing load exceeds 10 per cent. Oil switches are to be put in on all the 2400-volt generator circuits at the power house.
What is known as the Old Yuba power house is so miles from the Colgate power house. It operates under a 300-ft head of water supplied by a pipe line 42 in. in diameter. It has three Pelton waterwheels direct-connected to two-phase Stanley generators, giving 2400 volts pressure. This is stepped up to 16,000 volts, three-phase, and is run in parallel with one of the circuits of the Colgate plant not before mentioned.
The South Yuba power house, 5 miles from Nevada City, formerly owned by the Nevada County Electric Power Company, is unique in having two different sources of water and necessarily operating under two different heads. Most of the time it is run by water supplied by a flume, and the head is 290 ft. When this water is low the supply is pieced out with water from a storage reservoir under an 800-ft. head. To accommodate these two different heads each generator has two Pelton wheels direct-connected on its shaft, one for high and one for low head. This plant has four 500-kw Stanley two-phase generators generating at 5000 volts.
Grass Valley, Nevada City, ()ravine, Marysville and neighboring mining districts arc now being supplied, besides a part of the Sacramento Electric Gas & Railway Company load. A maximum of 800 to 900 hp is being supplied to placer mining dredges alone.
The 140-mile transmission line to Oakland consists of two pole lines side by side, 25 ft. apart. Each pole line carries one three-phase circuit transposed every mile, and a telephone circuit 5 ft. below the power circuit. One circuit is of No. 00 medium hard-drawn copper, and the other of stranded aluminum cable of equal conductivity. It was considered that while aluminum is considerably cheaper it is still an experiment for use on transmission lines, and that the company could not afford to experiment on more than one line for the sake of the saving in first cost. The poles are round Oregon cedar, 35 ft. long, are spaced 132 ft. apart, and were painted with hot carbolinium avenarius around the ground line. The insulators (made by Locke) are porcelain with a very wide lip fastened by a sulphur joint onto a glass insulator with a very long petticoat. This is placed on a high wooden pin. This insulator is the result of experiments by R. H. Sterling, superintendent of the Bay division, who has charge of the construction of the transmission line, and sub-stations at the Oakland end of the line.
The line passes through and will supply Woodland, population 8000; Dickson, 4000; Vallejo, 7000; and other smaller towns. A branch of 12 miles will be run to Napa, 12,000 population. The main business will be in supplying power around the eastern side of San Francisco Bay to smelters, reduction works, powder works, etc. The Oakland Transit Company is also to be supplied with power. The latter sub-station will have three 450-kw motor generator sets, with G. E. 60-cycle synchronous motors driving railway generators. There will be there three 500-kw G. E. transformers in use, and one of the same size in reserve. Each side of the crossing of the Straits of Carquinez, north of Oakland, a 1500-kw sub-station, is being put in where transformers will be placed for 5000-volt distribution Each sub-station is to have three transformers in use, connected star on primary and delta on secondary, and one in reserve, and all transformers have regulating heads on the secondaries for varying the voltage.
One of the most novel and interesting features of the transmission aside from the high voltage is the crossing of the Straits of Carquinez with the transmission line. This is to be done with a span 4700 ft. long. Four 7/8-in. Roeblings steel cables, three in use and one in reserve, will make the enormous span. Steel towers were built by the Pacific Bridge Company on high ground, each side of the Straits, over which the cables pass. There will be 12 tons strain on each cable, and the design of 60,000-volt insulators for taking the strain and also for sustaining the weight was a nice problem. The weight is taken by porcelain insulators ,and the strain insulators depend on micanite to withstand the heavy pressure.
The officers of the Bay Counties Power Company are E. J. De Sabla, president and general manager; W. H. Pierson, vice-president, and C. R. Grow, secretary. R. H. Sterling is superintendent of the Bay division; T. E. Theberath superintendent of the Yuba division, and L. M. Hancock superintendent of the Nevada division. The work of these engineers is of unusual interest and importance, as the above account will indicate. It is not a little remarkable that California should have become in this manner the center of power transmission work on such a large scale, transcending in distance anything else of the kind in the world up to date.