Publication: Western Electrician
Chicago, IL, United States
High-tension Work in the Far West.†
BY GEORGE H. LUKES.
To the central-station man of the East or the Middle West, the tremendous development in high-tension transmission in the West, and particularly on the Pacific coast, seems marvelous and inexplicable. Each issue of the electrical journals seems to chronicle some new achievement more remarkable than all before. Distances and line voltages have been doubled and quadrupled, and the whole country from Old Mexico to British Columbia is dotted with transmission plants. It is not the purpose in this paper to take up the subject of long-distance transmission in any detail, for to do this would reqdire a volume, but it is rather to point out some of the conditions that brought about this rapid development and the trend of growth at the present time.
When a sudden expansion in any industry takes the world by surprise it is generally found upon investigation that this rapid growth has been preceded by a slow growth extending over a considerable period of time. During this period various problems are met with and solved. Work is carried along on different, lines converging on a single point, and when the conditions are ripe an era of astonishingly rapid development follows.
buch has been the case with high-voltage long-distance transmission work on the Pacific, coast, the great mountain ranges that lie about 150 miles from the coast and extend north and south are the sources of innumerable streams of water that reach the Pacific through the larger rivers. These streams are of small volume, except at time of flood, but, on the other hand, the fall is exceedingly rapid, so that it is not unusual to finds heads utilized of from 500 to 1,500 feet, and even more. The installations consequently are of one general type, with variations here and there, to suit local conditions. A dam is thrown up at some point on a mountain stream where a reservoir can be created, and from this dam the water is carried by means of a wooden flume, ditch, or, in some cases a wooden-stave pipe line, with a grade of from five to 25 feet per mile to a point where the maximum drop can be utilized. From the penstock, the pipe line, which is sometimes of steel, sometimes of cast iron, or, in cases of low head, a wooden-stave pipe, is run down to the power house below. The waterwheels are of the Pelton type and are direct-connected to alternating-current generators, which supply two or three-phase current at a frequency of 60 and a voltage of 1,000 or 2,000. The exciters are direct-connected to separate waterwheels. The raising transformers are of the water-cooled oil-insulated-type and are generally located in a room separated from the dynamo room by fireproof walls. The lightning arresters are usually in a separate building to cut down the danger from fire. The high-tension switchboard is mounted on insulators, and consists of wooden frames upon which are placed air-break switches of various, types. The high-tension bus-bars are simply extensions of the transmission lines and are bare wires mounted on insulators like those used on. the lines. The transmission lines will be described in some detail later.
On seeing a plant of this character one realizes the importance of the hydraulic end of the enterprise. On looking further, it is seen that the hydraulic engineering is of a type peculiar to this part of the country and has been of comparatively slow growth. The country was originally a mining country, and still remains so, although the character of the mining has changed since the early davs. The first miners were placer miners, and, needing water for their operations, constructed ditches and flumes to divert the water from its natural courses to their mines. In the course of time the placer mines were worked out, and hydraulic mining began. In this method of mining large streams of water under tremendous heads were used to wash down the dirt from the hilsides, and in this way dirt containing a small percentage of gold could be worked at a profit. In order to get water under a sufficient head for this work it was necessary to construct dams and flume the water long distances along the sides of the mountains. Hydraulic mining was afterward prohibited by law because the dirt which was carried down the rivers from the mines devastated the farming lands in the valleys below. Quartz mining, which was carried on at the same time as hydraulic mining, and which is the principal method in use to-day, stimulated the advance in hydraulic engineering, and particularly the development of the waterwheel.
The evolution of the waterwheel of the Pelton type is very interesting. Early in the '50's a demand for small power arose, which was met by the invention of what was called the hurdy-gurdy wheel. This was a very crude affair, made of wood, and looked very much like a circular saw with straight-cut teeth, the difference being that it was two or three inches thick. A jet was tangentially applied to the wheel, and, striking the teeth, caused it to revolve. With the introduction of quartz mining the hurdy-gurdy wheek was found inadequate, and it was developed through many intermediate forms into the present type of tangential wheel, which is simple in design, reliable in operation, and gives an efficiency of 80 per cent. Thus, it is seen that the growth in hydraulic engineering which necessarily preceded long-distance transmission, covered a period of perhaps 40 years and was relatively slow.
Turning now to the commercial side of the proposition, it is evident that until there was sufficient market for power there could be no long-distance transmission plants. Moreover, to make transmission of power necessary, natural conditions must also exist to prevent the utilization of power at the point where it is generated. In the East, where railroad facilities are good, manufacturing industries locate at the source of cheap power. Even at Niagara, the development of that great power with the express intention of transmitting it to Buffalo, has stimulated manufacturing at Niagara to an unexpected extent. In the West the power plants are necessarily located in the bottom of deep canyons, in mountainous districts, miles from any railroad, so that the market cannot move to the power, and the power has to be transmitted or not used at all. For well-known engineering reasons electrical energy cannot be transmitted efficiently over long distances, except in large amounts, and this calls for a large market for power. In California this market grew slowly, as the industries of the country became diversified. In the early days mining was the principal industry, but as the country grew older it was discovered that with irrigation large crops could be raised in the fertile valleys. The country became more thickly populated and towns grew into cities. With the introduction of electric lighting and electric railways a great demand was created for electric power.
The cost of fuel is the factor which determines whether or not a market exists for power transmitted from a distance. California has no coal beds to speak of, and hence the coal has to be imported. About three-fourths of the supply comes from British Columbia and Washington, and is semi-bituminous and lignite. As the country is practically covered by only one railroad, there is no competition, and freight rates to interior points have been excessive. The price of fuel, and therefore the cost of power, has been very high. In 1890 oil was discovered in Southern California, and has since been largely used for fuel. The consumption rose in 1900 to 4,000,000 barrels. The cost of fuel has fallen somewhat in consequence. As oil has only partially displaced coal, its price naturally hovers about that of coal, and the expectations of an extremely cheap fuel have not been realized. Still, from the point of view of the power-transmission man, the discovery of oil was a most unfortunate event.
Thus, for 40 years prior to 1890 the conditions had been slowly getting more favorable for long-distance transmission. A large amount of experience had been gained in the construction of dams, flumes and pipe lines. A waterwheel suitable for the purpose had been evolved and a market for power in large quantities had grown up. A method of transmitting power over long distances was lacking until the Frankfort-Laufen. transmission experiments were made in 1891. In less than two years after these experiments, the historic Pomona transmission of 30 miles at 10,000 volts was in actual commercial operation in Southern California. Since that time the development has been very rapid, the capacity of transmission plants alone now aggregating upward of 100,000 horsepower.
As is usual with any new industry, the thing was at first somewhat overdone. The idea of "harnessing the forces of nature" is so fascinating to most people that the promoter found abundant opportunity for activity. Plants were projected and built that were foredoomed to failure. In some of these the cost of hydraulic development per horsepower was so excessive that the fixed charges were more than the earnings. In others great errors were made in estimating the flow of the streams from which the power was derived, and in dry seasons water ran short, necessitating the erection at large expense of auxiliary steam stations. The years 1897-1898, in which the average rainfall fell from 23 inches to nine inches, were great educators, and probably checked many a project that looked feasible up to that time.
At the present time these enterprises are much more carefully planned than in the early days. The pioneering days are over to a certain extent, and the second stage of development has begun. It has been demonstrated that it is possible to transmit energy in large quantities for distances up to 150 miles and over. With the extension of the lines into large cities for the supply of electric lighting and power for street railways the policy is followed of spending more money in first investment in order to secure reliability of service and low operating and maintenance costs. This tendency is shown in the hydraulic end by the substitution of tunnels and paved and cemented canals, for wooden flumes. Duplicate pipe lines are now provided and the power house itself is built in a more substantial manner and as nearly fireproof as possible.
The pole line has been found to be the weakest part of the transmission system, and I give some of the details of the construction of the latest pole lines, in order to show the care and foresight now displayed in this part of the work.
The poles commonly in use on the newest transmission lines are either of square sawed redwood, tapered from butt to top, or Oregon or Washington cedar. The Oregon cedar poles used by the Bay Counties company in its lines from Colgate to Oakland, a distance of 142 miles, are painted with hot tar from the top of the pole to a point six inches below the bottom cross-arm. The butts are saturated with hot carbolineum for 3 1/2 feet where the pole enters the ground. The following table gives the data on the poles:
The redwood poles are from the hearts of young trees, not more than four poles being taken from one tree, and, being free from sap when set, they will last from 25 to 35 years. The following table gives the dimensions and other data on the redwood poles used by the Standard Electric Company on the transmission line from its power house at Electra to San Francisco:
The cross-arms are made of selected kiln-dried Oregon pine six by six inches square and an overall length depending on the, distance between wires. After passing through the dry-kiln they are placed in an enclosed boiler containing asphaltum oil and subjected to a temperature of 220° F. for several hours. This preserves the wood and at the same time increases the insulation of the pole top. The arms are gained into the pole a distance of one inch and are held in position by two five-eighths-inch through bolts with cast-iron washers three inches in diameter under both head and nut. The cross-arms are surfaced all around and crowned on top to shed the water. The insulator pin's are of oak, locust, or eucalyptus wood. The latter wood is universally used on the coast on account of its immunity from attack by worms and bugs, even the deadly Tornado not touching it. The eucalyptus pins are treated in the following manner: The timber is sawed into sticks three inches square and placed in boiling water for 24 hours. After being air-dried for several months it is worked up into pins. The pins are then placed in a vat of boiled linseed oil and kept at a temperature of 210° F. for several hours. The pins are 16 7/8 inches long over all and the diameter at the lower shoulder is 2 3/4 inches. They are driven into the cross-arm with special care, a hardwood pin-set being used. The pin holes in the arm are 2 1/4 inches in diameter and five inches deep, leaving one inch of solid wood below the pin. On each side of the pin, at a distance of three inches from the pin and two inches from the top of the cross-arm, one-half-inch carriage bolts are placed, in order to prevent the arm from splitting when unusual strains are thrown on the pins. That this accomplished the purpose is shown by the result of a series of tests made by the Standard Electric Company, in which the cross-arm was split without the bolts from a pull on the thread of the pin of 1,200 pounds, whereas with the bolts in position the pin broke at the shoulder with a pull of 2,000 pounds, thus almost doubling the strength of the arm.
One very noticeable feature of the pole-line construction is the absence of guy wires. On account of the high voltage, the ordinary strain insulator is of no use, and the common practice is to use wooden struts. These are six by six inch timbers fastened to a dead man buried five feet in the ground and bolted through the pole at the cross-arm. Sometimes when a guy cannot be avoided, the strut is used as an anchor, or, if a guy is used, a six by six-inch timber 20 feet long is inserted in the guy as a strain insulator. The poles are usually set about 130 feet apart, and whenever a small angle is made in the line two poles are placed close together in order to divide the strain. On all angles double arms are used and double cap pieces bound with wrought-iron bands support the top wire. In single construction the pole pin is usually driven into the top of the pole and a wrought-iron band driven down on to the pole to keep it from splitting. In some cases a bracket pin three feet long and four by four inches in section is bolted through the pole.
As an illustration of scientific methods applied to pole-line construction, I will state that the line is staked out by a surveyor, the poles are set with a plumb bob, and the foreman of construction carries a thermometer and a set of curves, from which he fixes the proper sag to give to the wires. The wires are placed at the points of an equilateral triangle. The wires are from 36 to 42 inches apart and are spiraled, one-third of a twist being made every mile. The Telluride line in Utah is unique in that no iron was used in the construction. The cross-arms are mortised through the poles and wooden pins are used instead of bolts. Wooden cross-arm braces are fastened to the poles and cross-arms with wooden pins. The object of all this is to increase the insulation of the pole head, but it is open to the criticism that it is mechanically weak.
The insulator is without doubt the most important part of the line. As long as the voltage did not exceed 20,000 and the wires to be supported were of small size the problem of providing a satisfactory insulator was comparatively easy. When 150-mile lines, transmitting 10,000 horsepower at 40,000 volts over aluminum cables seven-eighths inch in diameter were designed, great difficulty was experienced in finding an insulator that was both electrically and mechanically strong. The insulator in common use for this purpose is of the two-part type, the upper petticoat being of porcelain and the lower part of glass cemented into the porcelain. The upper petticoat is nearly flat and is provided with a rim and spout to drain the water clear of the cross-arm. The lower petticoat is shaped like a truncated cone and protects the pin. This insulator measures 11 inches in diameter across the top petticoat and is 11 inches in height. When in position on the arm the wire is 15 inches above the cross-arm. There is much difference in opinion among power-transmission engineers on the insulator question. Some condemn glass and others porcelain. Some insulators are strong mechanically and weak electrically, and others are just the opposite. The difference in opinion is probably due to the different nature of the troubles encountered. For instance, the engineers of one company were very much surprised to find that their insulators gave less trouble in wet weather than in dry. As soon as the fall rains began the insulator trouble ceased. An investigation showed that where the lines ran near railroad tracks the insulators got very dirty and insects of various kinds lodged under the petticoats. This decreased the striking distance and the insulators broke down. The remedy applied in this case was to shut down the line periodically and wash off the insulators. The general feeling among power-transmission men is that no insulator in use at the present time would be safe to use on 60,000 volts. The large transmission companies intend to go up to 60,000 volts as soon as additional line capacity is needed, but as this means changing every insulator on their lines at an expense of several hundred dollars per mile, they will delay action until they are reasonably sure that they have secured the proper insulator.
Aluminum wire has been used largely for transmission purposes on the coast with good results. The Standard Electric Company's line from Electra to Mission San Jose is aluminum cable of 37 strands, with a total cross-section of 471,034 circular mils. The weight per mile is 2,404 pounds, and its tensile strength is 28,000 pounds per square inch. Owing to the high coefficient of expansion of aluminum, care must be taken in stringing the wires to allow sag enough so that the wire will not be too taut in cold weather. A peculiarity of aluminum wire which makes its use in small sizes objectionable is its low melting point. Aluminum melts at 1,157° F., copper at 1,929° F., and wrought iron at about 2,800° F. When an iron wire falls across an aluminum circuit and makes a short-circuit the aluminum wire is melted through and the iron wire remains intact. Thus the trouble is cleared from the circuit at the expense of opening the line. This peculiarity was taken advantage of a year or two ago in a sub-station supplied from a long-distance line at 30,000 volts. A short-circuit occurring on one of the distributing circuits, the switchboard attendant pulled an air-break switch in the circuit. A tremendous arc resulted, which set fire to the sub-station. Not being able to reach the power house by telephone to have the line shut down, the sub-station was in imminent danger of being burned up. A quick-witted lineman seeing the danger drew a coil of iron wire over the aluminum transmission line outside of the station, and thus opened the circuit.
Transmission lines at these extremely high voltages are run as far as possible on private rights-of-way from 50 to 300 feet in width. In timbered country the trees are cleared out far enough on each side of the line so that no trees in falling can cross the line. The lines are patroled very carefully, each patrolman having a section 10 or 15 miles long. He reports frequently to the station over a private telephone circuit run on a cross-arm about five feet below the power circuit. At intervals of two or three miles taps are brought down from the telephone line to booths at the foot of the poles and insulated stools are provided in the booths for the patrolman to use while connecting his portable telephone set. The telephone wires are transposed frequently to cut down the induction, and, as a rule, work fairly well as long as the load is in a balanced condition on the transmission line. When something, such as a short-circuit occurs, which unbalances the power line, the telephone line goes out of commission. As the telephone is most urgently needed at times of trouble on the power line, the value of a telephone line on the same set of poles with the power line is questionable. For the reason also that crosses occur between the power line and the telephone line, thus endangering life, the plan of removing the telephone wires from the transmission pole line and installing on a separate pole line has been suggested more than once.
That pole lines are not absolutely reliable, and, moreover, are expensive to maintain, is shown by the fact that one company is seriously considering the plan of substituting a series of steel towers about 90 feet in height and 1,000 feet apart, the wires to be suspended from tower to tower and separated about nine feet. Although this construction will be more expensive than that of the ordinary pole line, it is thought that, the decreased number of breakdowns and lower maintenance and depreciation charges would warrant the extra investment.
As long as the business of the transmission companies was confined to the supply of power for mining purposes and lighting small towns the question of reliability of service was not of vital importance. Interruptions of small duration of time, although annoying, could be tolerated, but with the construction of long-distance lines, using high voltages, for the purpose of supplying current to large lighting and railway companies, the requirements became much more severe. No large central-station manager could afford .to buy current, even at a very low rate, if the source of supply was not reliable. This situation led to the construction of duplicate transmission lines. At first two lines were installed on the same set of poles, but it was found that when trouble occurred on one line it was usually communicated to the other line, and so this practice has been abandoned and duplicate lines on separate pole lines .are now considered necessary. Even with the introduction of duplicate pole lines, the situation is not entirely satisfactory, on account of the short shutdowns caused by the difficulties in switching high-tension lines. The switches in ordinary use are of the air-break tvpe, and while it has been claimed time and again that they can be opened safely under load, yet the fact remains that it is dangerous to do so, both on account of the surges set up in the transmission line, and the arc at the switch, which is often disastrous. When one transmission line is held in reserve and trouble occurs on the line in use it takes some little time to switch in the good line. When the two lines are run in multiple and a short-circuit occurs the usual practice has been to either burn off the trouble or shut down the station and start up on the good line. If the short-circuit is serious and is burned off, the disturbance in frequency and voltage is usually sufficient to cause all synchronous apparatus at the end of the line to drop out of step. The same operating problem, to a certain extent, confronts the eastern central-station manager who contemplates the erection of a large station generating alternating current at high voltage to be transmitted to sub-stations and there converted into direct current. The eastern man may avoid possible shut-downs by the use of time-limit oil switches and reverse-current relays, or he may as a last resource subdivide his station into several distinct parts, supplying separate lines, and use storage batteries as a reserve. In the West oil switches for voltages of 40,000 and over have not yet been developed, or if they have the price is prohibitive. Storage batteries can be used to a limited extent on direct-current and railway loads, but the high price has retarded their use.
The problem of securing good regulation on long lines has been a very troublesome one. Some of the difficulties due to inductive loads and charging currents have been overcome by the proper use of induction and synchronous motors, combined with reactance coils connected across the circuit, but the facts remain that a railway load on the end of a long-transmission line is a bad thing as far as regulation is concerned, and the time will come when the transmission companies will be forced to refuse railway business, unless storage batteries are installed to keep down the rapid fluctuations in load.
The transmission companies are wholesalers of electric current. They generate current, transmit it to the market, and sell it in large quantities to the local companies, reserving the right, as a rule, to sell current directly to larce power consumers. The usual method of charging is by the horsepower per year. The rate varies from $18 to $90 per horse-power per year. The best price is obtained at points remote from railroads where fuel must be hauled by wagon, such as at mines. The lowest price is obtained at cities on the water where fuel is cheaper. Other lines of charging are in use in special cases, current is sold to a street railway, for instance; on a car-mile basis; to a flour mill at so much per barrel of flour turned out. In one case it is sold to a local company for a certain percentage of its gross receipts. It is needless to say that this local company is selling light in large quantities at flat rates and is making money. Charging by the horse-power-year method is supposed to be logical for waterpower plants, because the operating expense does not vary with the load. Nevertheles; the method has all the objections that apply to any flat- rate system. It encourages waste and demoralizes rates. As long as the local companies can buy current on the horsepower-year basis they will sell light at flat rates. It is not impossible that the method of charging will have to be changed at some future time, for the following reasons: The water supply in this country is not unlimited. Already some of the companies find it necessary to provide storage to carry them through the dry season. As each company approaches the limit of hydraulic development it begins to cast about for some means of increasing its capacity. Some companies have found it practical to construct storage reservoirs at the heads of their pipe lines. During the hours of small load the water runs from the flume into this reservoir and when the peak comes on the reservoir is discharged into the pipe line, and thus helps to take care of the peak. When this point is reached by any company it is evident that any method of charging which reduces the waste, even at the hours of small load, becomes highly desirable, and so it seems quite likely that in the course of time it will be necessary to get on some sort of maximum-demand basis.
The future of long-distance high-voltage transmission in the West depends largely upon the development of oil as a fuel. If the production of the oil fields continues to increase so that oil entirely displaces coal as a fuel in certain sections of the country, it is evident that the price of fuel will be so lowered that the transmission plant will be unable to compete with local plants using oil as fuel. On the other hand, in certain sections, fuel will always be high on account of high cost of transportation. It is in these localities that the power-transmission companies will find their best field for growth.
†Paper read before the Association of Edison Illuminating Companies at Mount Washington Hotel, White Mountains, N. H., September 9 to 11, 1902. Mr. Lukes is night operating superintendent of the Chicago Edison Company, Chicago
|Date completed:||August 30, 2009 by: Bob Stahr;|