Publication: National Electric Light Association Twenty-Eighth Convention; Papers, Reports and Discussions
New York, NY, United States
LONG-DISTANCE HIGH-TENSION TRANSMISSION IN CALIFORNIA
The state of California is entitled to the credit for initial, original and pioneer work in long-distance electrical transmission, not only in the actual operative length of lines, but also in the high pressures used in such transmission. The progress made by the financiers and engineers in this state, during the past ten years, has been so phenomenal as to attract world-wide attention, with the result that there is a constant stream, of those interested, from all parts of the world, to the Coast, to observe the original work being done. Not only is California concerned in its trials and triumphs in long-distance transmission, but it has been the pioneer in high-head hydraulic work, as developed for large units. A recitation of the developments of electric transmission in the state would occupy more time than your patience would admit of, but a brief resume of what has been accomplished in the past ten years, all now under the control of the California Gas and Electric Corporation, may not prove an uninteresting one.
In the year 1888, attention in the engineering world was attracted by the Folsom Water Power Company determining to build a dam across the American River, near the town of Folsom, and to erect a power house some two and one-half miles south of the dam- on the river, conveying water by a canal having a capacity of 40,000 miners' inches, to low-head turbine wheels, under a head of 65 feet. Four 750-kilowatt units were installed, generating current at 800 volts, stepping up to 10,000 volts, and conveying the current thus generated to the city of Sacramento, 22 miles distant. The promoters of this enterprise were discouraged by the inability at that time of engineers to guarantee that 10,000 volts could be safely carried that distance for commercial purposes. In 1895, this dream became a reality, and Sacramento city was supplied with current generated at Folsom. While the insulation provided gave more or less trouble initially, this was gradually overcome. In 1892, the late A. W. Decker, electrical engineer, acting for the San Antonio Light and Power Company, at Pomona, Cal., recommended the installation of electric equipment at the power plant of that company, to convey by means of step-up transformers a pressure of 10,000 volts over approximately 16 miles of line, to the city of Pomona. The generators as finally installed delivered single-phase current at a pressure of 500 volts, and the transformers were wound in the ratio of one to two. There were ten transformers in service on the primary, giving 10,000 volts with a capacity of 6 kilowatts each installed. Glass insulators were used upon this line.
In 1895, there was begun the construction of a water-power plant near Nevada City, in Nevada County, in the state of California, to transmit about I 000 horse-power a distance of five miles, with generators wound direct for 5000 volts. The water was conveyed from a dam on the South Yuba River through three and one-half miles of flume, having a capacity of 8500 cubic feet per minute, and delivered to a 42-inch pipe, 286 feet long, with a head of 190 feet. There were installed at that time two 330-kw units.
From these small beginnings has grown a system throughout the state, aggregating in generator capacity at present installed, over 50,000 kilowatts, and units of 5000 kilowatts with varying heads up to 1530 feet. In the central part of the state, utilizing the waters of the western slope of the Sierra Nevada mountains, there are at the present time, in continuous operation, 577 miles of ditches, 25.5 miles of flumes, operating 14 water-power plants, having installed 41 generators, with a rated capacity of 50,790 kilowatts, and having a water storage in numerous lakes aggregating over 3000 million cubic feet, or 1,500,000 miners' inches for 24 hours. From these power-houses there are in continuous service 715 miles of pole line and 734 miles of circuit operated at 50,000 to 60,000 volts, and 479 miles of circuit at voltages varying from 10,000 to 50,000, and 90 miles at lesser voltages, not including any local distribution. Power is delivered to 94 substations, with 75,000 kilowatts in transformer capacity installed, scattered over 21 counties and 33 cities in the state, representing a population of over 6o per cent of the entire state of California, and covering an area of 15,000 square miles. This power is regularly transmitted 232 miles, and by reason of certain conditions at times existing at the different power plants necessitating the transmission over all lines from one power plant, has been successfully operated 325 miles at 55,000 volts.
In addition to the transmission of power, as heretofore and hereafter enumerated, it may be interesting to know that the high-pressure wires supply 1961 miles of distribution wires in service, from 2300 to 5000 volts, and serve approximately 20,000 consumers for lighting, and motors of 100 horse-power and less, totaling 40,000 horse-power.
As the writer has been requested to confine his statements particularly to the subject of high-tension work, and, in a general way, avoid all technical descriptions, avoidance will be made of unnecessary details of power-house operation, or of the operation of the hydraulic systems in connection therewith, and only so far as it may be necessary to illustrate a point made, this paper will be concerned solely with the transmission lines.
In no other portion of the globe where long-distance transmission under extreme high potential has been used, do climatic conditions exist similar to those in California, and this must be particularly borne in mind when considering the work that has been done, the problems solved, and the successful conclusions arrived at in the determination that there is no limit, except that of the earning capacity on capital, to the carrying of current over wires to any distance.
As above stated, power is obtained from the waters flowing from the west slope of the Sierra Nevada mountains. These mountains are snow-capped the year round, and some of the power-houses are within the snow belt which exists during the winter season. Following down the mountain sides, these pole lines emerge into the vast Sacramento and San Joaquin valleys, which extend from Sierra County on the north to Kern County on the south, a distance of approximately 350 miles, and will average about 6o miles in width. After leaving the valleys, the pole lines cross the Coast Range, lying between the valleys and the Pacific Ocean, and generally follow the contour of the bays of San Francisco, San Pablo and Suisun, until they reach the commercial centres of distribution. In this long distance traversed, they are subjected to extreme climatic conditions—from the colds and frosts of the mountains to the severe heat of the valleys, and to the cooling fog-laden winds from the ocean.
The first transmission line to reach the bay shore was that of the Bay Counties Power Company, carrying current generated at Colgate on the Yuba River, about 28 miles northeast of the city of Marysville. This line was started at 44,000 volts, which voltage has since been raised to 55,000. The construction of the line was of round cedar poles, from the state of Oregon, an average height of 5o feet, and the character of construction substantially that now in use, but with a less separation in some instances than was subsequently found necessary. The very many alterations of plans from time to time, as different conditions obtained, to insure service, need not be here recapitulated, the details being confined to present method of construction, as will be illustrated by photographs and cuts annexed. The greatest difficulty encountered in the carrying of the high potential was in and about the bays mentioned, due to the heavy salt fogs that for certain periods of the year hang densely over the land, sometimes lasting for days. In these particular districts, the insulation has broken down at most unexpected places, causing the burning off of poles, and shortening the line. The new four-part insulator herewith illustrated, with iron pins, has entirely overcome this defect, and for the past season, under the most trying circumstances, no trouble has occurred, the number of hours of shut-downs upon all of these lines being of a negligible quantity.
In addition to the conditions named of transmission over and through countries of varying temperatures, it must be remembered that for seven months of the year, extending usually from April until the first of November, no rain falls within the district named, and where the pole lines run along or adjacent to the public highways, where heavy teaming for all purposes is carried on, they are covered with a fine dust, which arises from traffic, and are subjected at times to extremely hot north winds. For the remaining five months of the year the lines are subjected from time to time to heavy rains and to the high winds accompanying the winter storms. Bearing all these facts in mind, it is nothing short of remarkable that within a period of not over four years such wonderful results have been obtained in transmitting current over the distances involved; for the establishment of the Colgate plant, and the carrying of current into the city of Oakland, its initial distributing point, occurred in the year of 1901.
One of the greatest engineering feats ever accomplished, and one that has never received from the engineering world the attention which it deserves, was the construction, in 1901, of the famous Carquinez span of four steel cables, suspended from steel towers (see Figure 2). This span crosses the Carquinez Straits, connecting San Pablo and Suisun bays, and is 4427 feet in length between towers, having at its maximum point of dip an elevation of 206 feet above high-water line. The maximum sag of the wire between the two steel towers on the north and south sides of the straits is 257 feet. The main tower, in Solano County, on the north side of the straits, is 224 feet in height, and the bluff at the point of construction is 162 feet above tide water; on the south side the tower is 64 feet in height, and the bluff 400 feet above tide water. The accompanying sketch will convey a very accurate description of this span. It is interesting to note that this crossing has given absolutely no trouble in operation. Both of the towers mentioned are used for distributing stations to the different manufacturing cities along the bay shore, besides serving as general switching stations.
In the ordinary construction, spans up to 1800 feet in length are constructed in the mountains across deep ravines, using ordinary 40-foot round cedar poles for this purpose. A good sample of this work is shown in the photograph attached, in connection with the spans from the de Sabla plant to the Valley Counties Power Company, in Butte County.
Experience has demonstrated that the form of lightning arrester which gives good service at low voltage is absolutely useless on high-tension lines. While these were first installed, they have since in every case been abandoned. At the present time nothing is used but the Horn Gap arrester. As the voltage of the lines has been raised, and the insulation increased, the damage due to lightning is steadily decreasing. It is well to state that beyond the line of the foot-hills of the Sierra Nevada mountains, lightning rarely occurs; possibly once a year throughout the Sacramento and San Joaquin valleys and along the bay shore are there any discharges of lightning that would be detrimental to the lines.
The first construction of lines in this state was 40 to 50 poles to the mile, insulators being used at a maximum cost of 15 cents.
All new lines are now being constructed on the basis of 20 poles to the mile, and the four-part insulators illustrated in Figures 3 and 4 are being used, costing approximately $2.00 each, and weighing about 30 pounds. These are the outcome of months of patient work and experiment by the engineers on the Pacific coast. Figure 5 exhibits graphically the character of construction of pole lines about six years ago, and the ravine illustrated in that picture is now crossed with a single span. Figure 6 shows the general construction of the pole top for 60,000 volts. Figure 7 shows the transmission line from the Folsom plant, heretofore mentioned operating to-clay as when it started, with four circuits at 10,000 volts at over 18 per cent loss. These circuits are now being changed to operate at 60,000 volts, and the type of construction As shown in Figure 6, and the loss in the 22 miles of transmission at 60,000 volts, with only one circuit, will be about 2 per cent. Figure 8 illustrates the method of construction at corners, giving a view of the insulated guards attached to the outward insulators to prevent wires from falling to the ground if pulled over. This has proved effective in more than one instance. The construction shown is at the top of a 6o-foot round cedar pole. Attention is particularly called to the very strong methods adopted in both cross-arm work and braces.
Much work has been done in designing and carrying out the construction of outdoor switches, as shown in Figure 9; and Figures 10 and 11 will show the switches in place, arranged for three-pole remote-control operation. Figure 12 is a record of the past, and exhibits some of the earlier attempts at a line disconnecting switch. Experiments have been continuous along the lines of oil switches, and experience has demonstrated sufficiently that this switch as at present constructed is entirely satisfactory and will handle heavy currents under high pressures. Double-break and quadruple-break oil switches are now being made, the latter being used for very heavy service in the large power-houses. Figure 13 shows one form of oil switch, and also shows the method of constructing fireproof switch galleries, the construction of which, so far as the writer is advised, is entirely original with the Pacific coast. The switching is done by opening the three legs at the same time, the single-pole arrangement having been found to be extremely unsatisfactory for obvious reasons. Figure 14 will illustrate a switch for disconnecting a bank of transformers from the bus-bars. Figure 15 will illustrate the past methods of construction of switches and transformers for high-pressure wires, while Figure 16 illustrates the present method, not only of the fireproof switch galleries, but of modern construction of a powerhouse, showing location of water-wheel, generator, exciter and switchboard. Figures 17 and 18 illustrate the present method of switching arrangements at substations for connecting and disconnecting lines.
As evidencing the care exercised in protecting low-tension circuits from high-pressure wires where the low-tension parallels the high-tension, in the event that there should be any fall to the ground of the insulation of the high tension, Figure 19 is fully illustrative.
Referring to chart Figure 1