Publication: Electrical World and Engineer
New York, NY, United States
Power Transmission in Utah.
RESULTS AND LESSONS FROM THE OPERATION OF THE LONG-DISTANCE
POWER TRANSMISSION AND DISTRIBUTION SYSTEMS OF
THE UTAH LIGHT & POWER COMPANY.
BY J. R. CRAVATH.
THE various transmission plants and the distribution systems of the Utah Light & Power Company in and near the cities of Salt Lake and Ogden, Utah, are among the oldest and most important of their kind, and much can be learned from the experience of this company which is of value to those about to undertake long-distance transmission and distribution from water powers as well as from more recently installed transmission plants. For the many practical points here given as to the working of this company's system, acknowledgment is due to the kindness of R. F. Hayward, chief engineer of this company and consulting engineer for numerous other plants in Utah. Mr. Hayward's extensive experience, covering six years in this work, and his opportunities for observation, constitute him an authority on this branch of electrical engineering, and the readers of this article will appreciate the professional courtesy which has prompted him to furnish such complete information on a class of subjects about which none too much is generally known.
The system of the Utah Light & Power Company comprises three water-power plants, several high-tension transmission lines, and also light and power distribution apparatus in and near Salt Lake City and Ogden, Utah, together with one sub-station for supplying the Salt Lake City Railroad, and some reserve steam plants. Probably in no other city of its size in the United States has electrically transmitted power reached such a relatively important place in the community as at Salt Lake City. The development not only started early, but has been very rapid. The snow-fed mountain streams of the Wasatch Range, to the east of the Salt Lake Valley, offered opportunities to the hydraulic and electrical engineer which were not neglected. To understand the situation a short historical review will be necessary. Although coal is not excessively high, being from $2 a ton for slack to $4.50 for best lump, the proximity of water-power with high head to such a market as Salt Lake City and its surrounding smelters and other power consuming industries led to the erection several years ago of three different water-power plants by three different companies. The Big Cottonwood Power Company completed a plant in the Big Cottonwood Canon, 14 miles southeast of Salt Lake City in June, 1896. The Pioneer Electric Power Company started its plant in the Ogden Canon near Ogden, 37 miles from Salt Lake City in July, 1897. The Utah Power Company in 1897 built a plant in the Big Cottonwood Canon for transmitting power for the Salt Lake City Railroad. These three plants finally became consolidated with the electric lighting interests of Salt Lake City, and are now operated as parts of one complete and comprehensive system, owned by the Utah Light & Power Company, covering a district extending north and south about 6o miles, including Ogden, Salt Lake City, and a district 13 miles south of the latter place, including some large smelters. The accompanying map (Fig. I) shows the district covered and the lines and power houses.
A brief review of the equipment and location of the three waterpower stations will be necessary to a full understanding of the situation.
POWER HOUSE EQUIPMENT.
The plant at Ogden gets its water from the Ogden Canon, a narrow gorge about 6 miles long (see map, Fig. 1), through which a stream flows, draining a rather large area of high ground. At the head of the canon is a level valley 4 by 5 miles, which would make a good storage reservoir. At present, however, there is a dam 300 ft. wide and 20 ft. high across the cation, making a 5-acre reservoir. From this reservoir the water is drawn through two 5-ft. gates into a massive concrete tower, from which it flows in a pipe 6 ft. in diameter, 6 miles to the power house. Five miles of this pipe is wooden stave, and the last mile is steel, taking the water from the wooden pipe at 100-ft. head and delivering it at 450-ft. head. At the power house the pipe line divides into two 6-ft. diameter receivers, one along each side of the building, with 2-ft. delivery pipes running into the power house for each water wheel. This power house (see Figs. 2 and 3), is designed for 10 generators of 750 kilowatts, each direct connected to a waterwheel. Five of these have been put in. The waterwheels are the Knight impulse pattern, running at 300 r. p. m., and have Knight automatic electric relay governors. The generators are General Electric 60-cycle, three-phase, revolving armature, 750-kw machines, generating at 2300 volts. The exciters are two 500-volt, 100-kw generators direct connected to waterwheels. A Venturi watermeter is placed in each receiver just outside the power house, so that the water consumption can be measured continuously. The distribution in Ogden is direct from this station at 2300 volts. For transmission to Salt Lake City there are nine 250-kw air-blast transformers arranged in delta connection, stepping up to 16,000 volts. The transmission line is 36-1/2 miles long, and consists of two circuits of three No. 1 bare hard-drawn copper wires on the same pole line. The insulators are porcelain. The poles are from 35 to 50 ft. long. For 16 miles the pole line is just outside a railroad right of way, and the rest of the distance passes over open country.
The Big Cottonwood plant, which is southeast of Salt Lake City in the Big Cottonwood Canon, leads its water from a small reservoir through a 4-ft. steel pipe line, which passes first through a tunnel 500 ft. long, and then down a steep slope to the power house. The pipe line is 1800 ft. long and the head is 380 ft. The receiver at the power house is the same diameter as the pipe line. There are four 600-hp Felton waterwheels running 300 r. p. m., each with two nozzles. One nozzle is opened and closed by a gate valve, the other has a hood operated from a lever in front of the switchboard for regulation. The regulation is all done by hand. The generators are General Electric, 60-cycle, 500-volt, three-phase, 450-kw. There are two exciters separately driven by waterwheels. On the upper floor of the power house are six 250-kw transformers, air cooled, stepping up from 500 to 10,000 volts. The transmission line to Salt Lake City consists of two three-phase circuits of No. 2 wire (see Fig. 1), 14 miles long, part over rough, mountainous country and part along a country road. Porcelain insulators are used. Part of the distance these circuits are now run on the same poles as the line from the Utah station.
The Utah station is also located in the Big Cottonwood Canon, and gets its water from a small wooden dam just below the tail race of the other station. For 1-3/4 miles the water is taken in a wooden flume 4 ft. wide by 3 ft. deep, and is then delivered to a steel pipe 4 ft. diameter, and giving a head of 450 ft. The power house has two 1000-hp Pelton waterwheels running 300 r. p. m., direct connected to 750-kw, two-phase, 60-cycle, 500-volt Westinghouse generators. Exciters are independently driven. The main waterwheels are regulated by a Replogle relay governor, acting on a throttle valve. Step-up phase-changing transformers raise the voltage from 500 volts, two-phase to 11,000 volts, three-phase. The transmission line has two three-phase circuits of No. 3 bare copper wires on porcelain insulators, and is about 12 miles long. This station is operated in parallel with one generator in the Big Cottonwood plant to supply the Salt Lake City Railroad through a sub-station near the middle of the city.
The railway sub-station just mentioned has two two-phase, 300-kw rotary converters supplied from step-down transformers. One of the rotaries is usually sufficient to carry the load. The paralleling is, of course, necessarily done on the three-phase high-tension lines.
The light and power distribution at Salt Lake City is accomplished through the medium of another sub-station near the middle of the city. Here the high tension lines are run in from both the Ogden and Big Cottonwood plants. Both are stepped down to 2300 volts, and the 2300-volt lines are thrown in parallel, thus putting the Ogden and Big Cottonwood plants in parallel through the medium of the 2300-volt secondaries.
It has been Mr. Hayward's aim, ever since the consolidation of interests made it possible, to bring everything under one uniform simple scheme of generators and distribution. Fortunately the frequency of all the plants was the same (60 cycles), but there the uniformity ended. As the- secondary system is now uniform, so that the plants can be operated in parallel, the difference in transmission voltage is no great inconvenience save as it necessitates greater reserve capacity in transformers at the sub-station, and prohibits paralleling high-tension lines. However, it is contemplated to raise the transmission line voltage on both the Ogden and Big Cottonwood lines to about 24,000. This can be done on the Ogden line without rewinding transformers by changing from the delta to the Y method of connection. The Big Cottonwood transformers will have to be rewound. From the light and power sub-station a network of 2300-volt mains is fed. This network is shown in Fig. 4. The primaries of the street transformers are connected delta-fashion, but the secondaries are on Y-connection. When motors under 10 horse-power are to be run they are connected between the outside legs of the Y, which give zoo volts. Motors over 50 horse-power are put on separate transformers. The lights are balanced between the outside legs and the neutral on 115 volts. This makes a very satisfactory scheme of distribution. Six transformers are placed to a block, at opposite corners, and they feed into secondary mains running around the block. Adjacent blocks are tied together through fuses, so that the secondary system in the down-town district is also a complete network. This secondary network is shown in Fig. 5. In the residence district two secondary wires (a leg and a neutral) are first run down a street, balancing one street against another, and as customers increase the third and fourth wires are put in and connection is made with adjacent secondary systems, everything working toward the network idea. Mr. Hayward believes in network and parallel running throughout, as the only ways to secure reliability of service and minimum voltage variations.
At the sub-station there is a small steam plant in reserve which it is expected to increase as the system grows, to reduce as far as possible the chances for interruption of service. There is also an old electric light station near the sub-station which can be run in case of emergency. At present there are in this latter station some synchronous motors driving series arc-light machines. These motors can be run as generators on short notice. It is expected in time to replace all series continuous-current arcs with constant-potential alternating arcs. The series-alternating arc is not liked, because of the complications in the way of high-tension circuits on pole lines which it involves. It is desired to keep the circuits as few and simple and safe as possible. On all pole lines carrying 2000-volt mains, the inner wires between which linemen must climb are at the same potential, and everything possible is done to make it safe for linemen in their dangerous duties. In case constant-potential alternating arcs are run for street lighting, a magnetic switch will probably be used by which all the lights on a section of street can be turned on at once by an inspector. About 500 constant potential alternating commercial arcs are in use in Salt Lake and Ogden.
In order to bring the voltage right on the 2300-volt mains in both Salt Lake City and Ogden and allow for line loss between Ogden and Salt Lake, the step-up transformers on the Ogden line are wound 7 to 1 and 6 to 1 on the step-down. A certain degree of regulation at Salt Lake can be obtained by varying the exciter motors driving arc-light machinery. With heavy load on the line, a variation of 10 per cent can be obtained in this way. Regulation of voltage at Salt Lake City is also obtained by varying the exciting current at the Big Cottonwood generators. As explained elswehere, the waterwheels at the Big Cottonwood plant have no automatic regulators. Those at the Ogden power house have. The hand regulators at the Big Cottonwood power house are, therefore, left untouched, so that they supply constant power, and the variations in demand are taken up by the governors at Ogden. But the exciting current on the Ogden generators is maintained nearly constant, except that such adjustment as necessary is made to regulate the voltage on the Ogden distributing circuits. If the Salt Lake City voltage is to be raised, the Big Cottonwood generators have their fields strengthened. The regulation is controlled by telephone from the Salt Lake sub-station.
It is of value to note the ease with which the different stations having types of alternators are run in parallel. At light loads there is a slight interchange of current between the two stations sometimes, but at heavy loads all these induction and resonance effects are drowned out.
All of the power houses were originally built with the transformers and transformer switching arrangements on a different floor from the generators and generator switchboard. Under the circumstances, this is an undesirable arrangement. In the Big Cottonwood and Ogden plants, the transformer switches will be moved down onto the main floor where they can be got at quickly by the men attending the waterwheels and generators. Both economy of labor and reliability of service demand this. The high-tension 16,000-volt switchboard at the Ogden plant, as it is at present, is shown in Fig. 6. The low-tension 2300-volt board is shown in Fig. 7.
The securing of a reliable supply of water is the cause of much thought and anxiety in connection with an enterprise of this kind. Of course, with several different plants, the liability to interruption decreases, but the experience in Utah as well as elsewhere shows that the constancy of water supply is something about which little was known when the first plants were built. In Utah, where the power houses are located in canons from 4000 to 5000 ft. above the sea, where the temperature reaches 40 degs. Fahr. at times, and where the snow falls heavily in places there is a constant menace to water power plants from snowslides and ice dams, this being the more serious because of the small actual volume of water in the streams. In the Big Cottonwood Canon, for example, two or three snowslides may be expected each year, which will dam the stream partially for 20 hours. On the other hand, in the dry season, the irrigation, which has the right of way over everything demands the entire flow of the stream. For these reasons it is important both for power and irrigation to construct large reservoirs for storage of water. This more easily said than done in some of these Wasatch canons, owing to the difficulty of finding bed rock. A large storage dam contemplated for the Ogden plant was never built because of the great depth of bed rock upon which to found it. To provide for irrigation and allow water to be used with economy at Ogden a storage reservoir has been built below the plant so that water need not be wasted by the plant to provide irrigation, as had at first to be done. It is, of course, desirable to have storage reservoirs away from the current of the main stream to prevent them filling up with boulders in flood seasons, but so far the construction of such reservoirs has not been possible for these plants.
The load has had a remarkable growth. That at Ogden, for example, has doubled in two years. Plans are under way for the enlargement of the water storage capacity in both the Ogden and Big Cottonwood Canons. The great depth of bed rock has made worthless many of the original plans for storing water. Unless a dam is sunk to bed rock there is an immense amount of leakage. In the Ogden Canon the plan is to build four low inexpensive dams, as shown by the accompanying map, farther up the river than the originally proposed dam. These will give within 25 per cent of as much water as the one big dam originally contemplated, and cost far less. The locations of these proposed dams are shown in Fig. 5.
At Ogden, where the velocity of the water around the intake is slow, owing to the volume of standing water at that point, there is little trouble with ice around the screens, but in the Cottonwood Canon, where there is a temporary intake and high velocity of water, there is trouble with ice forming on the screens. The reservoir originally constructed for the Big Cottonwood plant could not be used, because of its porosity, but a concrete dam is contemplated, which will give a good intake.
In regard to methods of conveying water the open flume has proven rather unsatisfactory for use around these steep canons, where falling rocks or snowslides are liable to carry away the whole structure that happens to lie in their path, and cut off the supply of water completely. The "Utah" plant of this company is supplied through a flume, which several times has been broken by falling rocks so that the plant had to shut down until repairs were made. Mr. Hayward believes in general that if the development of a water power is so expensive in proportion to the power produced that the cheapest construction must be chosen on account of its cheapness, the water power is not worth developing. Reliability is essential to the success of every power-transmission scheme, and any pipe line or flume for conveying water to the plant should be thoroughly ' protected from snow and landslides, and a tunnel or buried pipe line will often be found more economical than a flume or ditch. Mr. Hayward finds that the examination of smooth, gentle slopes at the foot of cliffs shows that these smooth places are frequently caused by snowslides, and are places to be avoided, and in such cases nothing but a buried pipe line or flume heavily timbered over the top should be used.
One of the largest wooden pipe lines ever built is that at the Ogden plant. It is 6 ft. diameter outside and 5 miles long. It is laid in an earth-and-rock cut on the south side of the Ogden Canon. Unlike many pipe lines