The 50,000-Volt Transmission Plant of the Missouri River Power Company

The 50,000-volt Transmission Plant of the Missouri River Power Company.

BY W. G. MCCONNON.

MUCH interest is being manifested in engineering circles in regard to recent developments in electrical power transmission over long distances and in the attendant use of higher and higher voltages. Although several plants have been proposed for the use of voltages higher than 40,000, the distinction of being the first to place in actual commercial service a large plant employing 30,000-volts transmission belongs to the Missouri River Power Company. This installation was completed and the apparatus placed in operation about the first of March, and much credit is due to the general manager and engineer of the company, Mr. M. H. Gerry, Jr., who planned and executed the work, as well as to the Westinghouse Company, which furnished the electrical equipment. Some earlier details of the work have already appeared in these pages.

It is to be noted that since the starting of the plant there has been no mishap of any kind to the line or apparatus. This, the writer believes, is somewhat exceptional in undertakings of this magnitude and character, since it is reasonably expected that at the start minor difficulties are liable to be met with, which, though possibly not serious, will nevertheless affect the continuous service of the plant.

The present power-house of the Missouri Power Company is located on the Missouri River about twenty miles almost directly east of Helena, Mont. To those who are familiar with the early history, of the Northwest it wilt be recalled that in the famous Lewis & Clark, expedition of 1803-4 up the Missouri River and across the continent to the Pacific, one of the resting places and points of interest spoken of is Black Rock Canyon, met with soon after entering the Rockies at the "Mouth of the Mountains," which is sonic miles to the east.

Black Rock Canyon is not now known by this name, but at the mouth of the canyon lies the present little town of Canyon Ferry and the power house of the Missouri River Power Company. A general view of the power house and town is given in Figs. 1 and 2, which show them located in a country not as rough as some parts of the Rocky Mountain district, but by no means level. The district immediately about Canyon Ferry has been one of the famous gold-mining camps of the West, the discovery of gold having been made there in 1863. Placer mining is the more common way in which mining has been carried on, and it can be seen to-day to a limited extent within a mile or so of the power house.

At the mouth of the canyon a dam has been thrown across the river, about 480 ft. in length and designed to give a 30-ft. head of water. The location of the dam at Canyon Ferry had enabled the company to take advantage of a low-lying valley just above the trance to the canyon, in which to hold at all times a large volume of water in reserve. At the upper end of the canyon the water spread-out over this valley, forming a lake about seven miles long by two three miles wide. The canyon by which the water conies to the power house is from 400 ft. to 700 ft. wide and less than one-half mile long. The water in it does not freeze over in winter, and although the lake above freezes over, water flows to the power house as free front ice in winter as in summer. The amount of water in the river at this point is considered sufficient to develop 10,000 hp the year around.

The project for a power plant at Canyon Ferry was first started about ten years ago. The men who have taken a continuous and extended interest are Mr. Barton Sewell, of New York City, and ex-Governor Hauser, one of the pioneers of Montana, and more thoroughly identified, probably, than any other living man with her history and interests. About four years ago the decision to carry out the work at Canyon Ferry took definite shape, and work was started on a plant of 4,000 hp. This plant consisted of four 750-kw, 550-volt, two-phase Westinghouse generators, driven by Dayton Globe Iron Works water-wheels, with two 90-kw exciters driven by independent wheels. The current from these generators was raised by eight oil-cooled transformers from 550 volts to 10,000 volts, and sent to Helena and East Helena, 20 miles and 14 miles away, respectively. At Helena the current was used, after transformation to 2,200 volts, for driving induction motors direct connected to arc light machines supplying city lights, and for distribution for general incandescent lighting. Two rotary converters furnishing current to the street car system of the city were also supplied. At East Helena the current was used mostly for driving induction motors in the large smelter located these and for general lighting about the works. One line from Canyon Ferry also furnished power and lights to a large ore concentrator between Helena and East Helena, known as the Peck concentrator. The line between Canyon Ferry and Helena consists of but one pole line, carrying, however, four independent circuits—one to East Helena, one to the Peck concentrator, and two to Helena, one of the latter for lighting and the other for railway work.

In the fall of 1900 work was begun at Canyon Ferry with a view of making a very considerable extension of the company's plant, the plan being to enlarge the plant to a capacity of 10,000 hp by putting in additional generators, with exciters, transformers, etc., and to extend the service to Butte, Mont., where it was expected that all the power the company might furnish could be sold. To this end the company has installed six additional 750-kw Westinghouse generators, with the necessary transformers, exciters, etc. These generators, are of the same size and voltage as the first four, but are three-phase instead of two-phase. The water-wheels are 45 ins. horizontal McCormick wheels, furnished by S. Morgan Smith, of York, Pa. All generators in the power house are direct connected to the wheels, flexible coupling being used throughout. With the new generators there was also installed a 225-kw, 150-volt exciter, driven by a separate wheel, and a 225-kw, 150-volt exciter driven by all induction motor. To sum up, the power plant now consists of ten 750-kw direct-connected generators, with four exciters, of which two are 90-kw machines direct connected to separate wheels, one a 225-kw machine with a separate wheel, and one a 115-kw, motor-driven generator. To make the plant uniform throughout, the four old generators have been overhauled and changed front two-phase to three-phase. The general plan of the station is shown by the outline sketch, Fig. 12, the switchboard gallery being on the right and directly over the waterwheels. Each water-wheel has its own governor; all the new and one of the old wheels having Lombard governors, and the remaining old wheels Replogle governors.

The switchboard gallery, shown on the right of Fig. 3, extends the whole length of the building, and, besides carrying the switchboards, carries also twelve 550 to 10,000-volt, oil-cooled transformers for the Helena and East Helena service, as well as a plugboard for connecting these circuits as needed under various conditions. The offices of the company will be located on the floor, extending across the building at the end from which the view is taken.

The main switchboard and exciter switchboard, shown in Fig. 4, are both relatively simple boards in design, but massive and substantial in construction. The main board is 47 ft. 5 ins. long, and consists of seventeen panels of blue Vermont marble, 2 ins, thick. The weight of the board complete is about 20 tons, the copper alone being one-half of this weight. The general arrangement is as follows: The first five panels at each end are generator panels. The next two panels are feeder panels, and are intended for use with the 550 to 10,000-volt transformers. The eighth panel from the end on each side supplies a bank of transformers, 550 to 50,000 volts, for the Butte lines. The middle panel is a junction panel, so that any set of bus-bars on the two ends of the boards can be thrown together, there being three sets of bus-bars an each end of a board. The instruments mounted on the board consist of eight 750-volt, alternating-current voltmeters, one for each set of buses and one at each end for the machines, independently of the buses; ten direct-current field ammeters; twenty-eight alternating-current ammeters, with sixteen indicating polyphase wattmeters, and six recording polyphase wattmeters. The recording wattmeters are behind the board. The exciter board consists of four panels of blue Vermont marble, similar to the main board, one for each exciter, with two sets of bus-bars. All field rheostats are mounted under the gallery floor and are controlled by hand-wheels, the shafts of which come up through pedestals in front of the boards.

The feature distinguishing the Missouri River Power Company's plant is the high voltage employed on its new lines to Butte. This is 50,000 volts. The distance by pole line from Canyon Ferry to the Butte sub-station is 65 miles, the route corresponding nearly with that taken by the Great Northern Railway between East Helena arid Butte. The line starts out at an altitude of about 4,000 ft. above sea-level at Canyon Ferry and gradually rises until it reaches an altitude of 7,300 ft., where it passes over the Great Divide, a few miles east of Butte.

Figs. 13 and 14. - Arrangement of Transmission Conductors and Insulator With Glass Sleeve Over Pin.

The line itself (Fig. 9) consists of two lines of poles about 50 ft. apart, the cables being arranged in an equilateral triangle, with a spacing of 78 ins. between centers (Fig. 13). Each line consists of three seven-strand copper cables, each cable having a cross-section of slightly over 106,000 circ. mils. These cables are transposed five times between Canyon Ferry and Butte. The average distance apart of the poles is no ft. Fig. 14 shows a view and cross-section of the insulator used on the line, together with the glass sleeve fitting over the pill below the insulator. It has been found, after making exhaustive tests, that a thoroughly dry oak pin of the length used in this installation boiled in paraffin will readily hold up alone under 50,000 volts. Hence the object of the glass sleeve below the insulator is to keep as great a length as possible of the pin dry under all conditions of weather.

The transformers at each end of the line consist of six 950-kw oil-insulated transformers, with water-cooling coils in the cases. Those at Canyon Ferry transform from 550 to 50,000 volts, and at Butte the step-down transformer is made from 50,000 to 2,200 volts. The secondary circuits at Butte consist of 600,000 c.m. bare copper cable. All electrical apparatus in this plant was furnished by the Westinghouse Company.

The customers of the Missouri River Power Company at present number nine, as follows: At Helena and East Helena—Helena Power & Light Co., Helena & Livingston Smelting & Reduction Co., American Smelting & Refining Co., Big Indian Mining Co. At Butte—Anaconda Copper Co., Butte & Boston Copper Co., Colorado Smelting & Mining Co., Boston & Montana Copper Mining Co., Washoe Copper Co.

The general offices of the company are at Helena, Mont., and the New York office is at 71 Broadway. The officers of the Missouri River Power Company are: President, Barton Sewell; vice-president, W. S. Gunter, Jr.: secretary and treasurer, H. Suhr; general manager and chief engineer, M. H. Gerry, Jr.