This article was first published in THE ENGINEERING JOURNAL, the journal of the Engineering Institute of Canada (Volume XIV, Montreal, June 1931, Number 6 ). Mr. Marshall was the Resident Inspecting Engineer. Our thanks to Drew Wilson of Nepean, Ontario for sending us this article.
Paper presented before the Calgary Branch of The Engineering Institute of Canada, January 29th, 1931.
SUMMARY.— The hydro-electric power plant at Island Falls on the Churchill river is the first development of this nature in Saskatchewan. The 44,000 h.p. developed will be used for mining purposes at the Flin Flon and Sherritt-Gordon mines.
The paper describes the Churchill river basin and storage conditions. The construction of the plant presented considerable difficulty as a transportation system had to be provided. Forty-three miles of road had to be built and scow transportation arranged for on the lakes. In winter the material was handled by trains of sleighs hauled by 100 h.p. tractors, and carrying about 77 tons per train. The total freight dealt with during construction was 35,000 tons. Power during construction was supplied by a temporary hydro-electric plant developed at a site 14 miles from the job.
Three main turbine units are installed, each giving 14,000 h.p. under a 56-foot head at 163.6 r.p.m. The three vertical generators are rated at 12,000 kv.a., 3-phase, 60-cycle, and generate at 6,600 volts, the voltage being stepped up to 110,000 kv. for transmission over the 58 miles to Flin Flon and the 45 mile branch line to Sherritt-Gordon.
The power dam spans the river channel and has three ice chutes, four under sluices, and a spillway section with thirteen openings. There is a separate concrete spillway dam and a number of earth dams along the margin of the headpond to prevent overflow.
The total construction period was some two years, but power was supplied twelve months after first breaking ground.
The completion of the Island Falls power plant on the Churchill river marks the entrance of the province of Saskatchewan into the field of hydro-electric development, as this is the first plant of that nature to be placed in operation in that province.
The plant has been constructed mainly for industrial purposes by the Churchill River Power Company Ltd., and will not be used for the distribution of electrical energy for municipal purposes, as there is no market at present available for sale of the power, other than the mines in the vicinity of the plant. The power being developed, which amounts to 44,000 h.p., is used by the Flin Flon mine of the Hudson Bay Mining and Smelting Company, Ltd., and by the Sherritt-Gordon Mine at Cold lake in Manitoba.
Before proceeding with a description of the construction of the plant, it may be of interest to give some particulars of the source from which this hydro-electric energy is produced.
The Churchill river basin lies in the central and northern parts of the provinces of Manitoba and Saskatchewan and extends into the province of Alberta. The greater part of the area is included in the Pre-Cambrian peneplain of northern Canada and has a gently rolling surface characterized by rounded outlines that have resulted from long continued and profound erosion. The river is peculiar in that it is composed of chains of lakes connected by falls, rapids and stretches of swift water which makes it difficult to navigate and numerous portages are necessary to pass these points. In earlier days the river was used to a considerable extent by the fur traders, but traffic has practically ceased since, the advent of railway transportation.
The river rises in Churchill lake in western Saskatchewan, but some of the tributary headwaters are in Alberta, and the total length from Churchill lake to Churchill, where it enters Hudson bay, is approximately 1,325 miles. In this distance there is a fall of over 1,300 feet which is well concentrated in the numerous falls and rapids along its course, making it a very valuable stream for power purposes, particularly so as the large lakes in the drainage basin and extensive areas of swamp and muskeg afford means of natural regulation. The total drainage area is about 114,500 square miles of which possibly 80,000 square miles is above the power site. There are excellent facilities for storage as the drainage basin contains several large lakes of which Reindeer lake, Lac la Ronge and Ile à la Crosse lake may be mentioned, and it would be a comparatively simple matter to dam the outlets of these lakes and impound large quantities of water.
In the drainage basin above the power site the rock formations consist mainly of granite or gneisses which are exposed along the river channel. In the areas away from the river the rocks are covered with glacial drift, sometimes to considerable depths, and these consist of till, clay and sandy formations; where suitable cover exists the country is covered with thick growths of poplar, spruce, birch and jack-pine. Some good stands of merchantable timber are to be found in the valley bottoms, but most of the timber is too small for commercial use. At present little information has been obtained as to the flow of the stream, but a minimum of 10,000 c.f.s. and a maximum of 35,000 c.f.s. was recorded during the years 1928-1930, and there is reason to believe that a much higher maximum flow has been attained at some time in the past, which may have amounted to as much as 100,000 c.f.s., judging from old high water marks.
The Flin Flon mine was first discovered in 1915 and some efforts were made to develop the property, but little success attended these efforts owing to lack of transportation facilities and a successful method of treatment of the ore. Sufficient work was, however, done to reveal the presence of a large body of copper-sulphide ore and an option on the property was secured by the Whitney interests in 1925. Experimental work was carried on during the years 1926-1927 and the results were sufficiently encouraging to warrant the purchase of the property. Arrangements were immediately concluded for the construction of a railway from The Pas to Flin Flon and investigations of possible water power sites were started. A considerable amount of study was given to the power possibilities of both the Churchill and Nelson rivers and the site at Island falls was finally selected as the one most suitable to the needs of the company.
The location of the power site was in a region remote from the point where power was to be used and the only means of access was by canoes with frequent portages between lakes. No roads existed in this area and the distance from the mine to the power site was about 70 miles.
It was therefore obvious that a transportation system would have to be built to connect the job with railhead, which would be capable of handling the large amount of material and supplies needed by the construction crews, during both the summer and winter seasons, and this work was started during the summer of 1928 and completed the following winter. During this period a total of 43 miles of forest road had been cleared and graded. Camps were established along the route, docks built at the end of each lake, and several large scows of 20 to 30 tons capacity had been constructed. A bush telephone line connected the camps and terminal points.
Winter transportation was handled by trains of sleighs hauled by tractors of 100 h.p. Each train was made up of about six sleighs, tractor and heated caboose, and operations were carried out on a definite running schedule, the time for the round trip varying from thirty-six to forty hours. The average load per train was 77 tons, but loads up to 120 tons were hauled.
The total amount of freight handled during the construction period was 35,000 tons, 70 per cent of which was handled during the first winter.
The work of erecting the construction camp was started during the winter. Operations were also commenced in connection with the location and clearing of the transmission line.
The permanent camp buildings were erected during the winter of 1928-1929, and the two sawmills were busily engaged in preparing lumber for building and construction purposes.
Power for construction purposes was first supplied by portable engines, but a small power site had been located at Spruce falls, about 14 miles from the job, and a temporary power plant was constructed at this point, with a transmission line to Island falls. Power was transmitted at 26,000 volts and stepped down at a substation to motor and lighting voltages.
This small plant was in operation for over a year and supplied 4,700,000 kw.h. of electrical energy. The dams and powerhouse were of timber construction and the plant consisted of two 1,250 h.p. units coupled to 1,000 kv.a. vertical type generators, 600-volt, 3-phase, 60-cycle, speed 400 r.p.m. 40-foot head. The transformers were located apart from the building and consisted of a bank of three 667 kv.a. units 600 to 6,600/26,400 volts with lightning arresters for protection purposes.
CONSTRUCTION AND DESIGN
The design of the plant was based upon the use of local material as far as was possible, in order to save transportation of structural material, and the layout of the plant was so arranged that space was also economized so as to keep the cost of construction within reasonable limits.
The general layout may be briefly described as follows:
To unwater the sites of the main dam and tailrace it was necessary to construct six cofferdams; these were of crib construction filled with rock and sheet-piled on the water face. The south channel closure was first made, building out from the river bank and a small island in midstream, the dam being closed by a key section. A side dam was built on the island and the downstream end closed by another dam, when the water was pumped out by two 12-inch centrifugal pumps. The tailrace was enclosed by one dam following the line of the south bank, and the north channel by two dams from the island to the north shore.
The cribs were constructed of rough lumber, squared on the connecting face and were built on the shore or existing cofferdam, and then launched and floated into position, being held by cables until ready to sink. Soundings were taken from projecting timbers and the bottom crib was then shaped to fit the river bottom. The sheet-piling in face of the dams was set by divers, three crews being employed, and upon the completion of the dams a banquette of clay was deposited on the water face, which made them practically water-tight.
The power-house is of concrete block construction with overall dimensions of 203 feet by 112 feet and has a maximum height of 125 feet. The initial development provides for three main units and two auxiliary units which are contained within the present building. A temporary wall is placed at the south end with a view to further extension to provide for three additional units. The superstructure is supported by a mass concrete substructure, which contains the turbine intakes, wheel pits and draft tubes for the units at present installed.
There are two gate openings for each of the main units, with areas of 293 square feet, and these are separated by piers six feet in width, the piers between the intakes being one foot wider. The gates are of the fixed roller type operated by electric hoists placed below the floor of the gate-house, wire rope being used for hoisting. Trash racks and emergency gates are provided in front of each inlet and are handled by a 40-ton gantry crane. The gates are equipped with a water seal, and seat on steel sills let flush into the floor of the intake; steel guides are placed in all gate openings and checks for stop-logs, to facilitate operation.
The auxiliary units have only one opening, and are equipped with gates similar to the main units.
The fixed roller type of gate has given no trouble in operation and seems to give better results than the type with the loose roller-train when working under fairly high heads. The gates were loaded with concrete to overcome the pressure head. All the gate operating mechanism of the power-house is enclosed within the gate-house.
The initial installation consists of three main units and two auxiliary units as previously stated. The hydraulic equipment includes the turbines, governors and pressure tanks, and a pumping plant for water supply and fire protection purposes is provided. The electrical installation includes generators, transformer banks and the necessary switching equipment for delivering power at 110 kv.a. to the transmission line.
The turbines which are of the single runner, vertical shaft, propeller type are capable of developing 14,000 h.p. when operating under a head of 56 feet and running at a speed of 163.6 r.p.m. The maximum expected efficiency of the turbines is 92 per cent.
These machines are direct-connected to conventional vertical shaft two-bearing generators with thrust bearing of the Kingsbury type located above the stator. The casing is formed in the concrete and is of the spiral type. Separate casing stay-vanes are set around the outside of the movable guide-vanes, and these carry the supporting ring to which the turbine head cover and pit lining are secured. These stay-vanes are designed to withstand the bursting pressure of the water in the casing and transmit the superimposed loads of concrete and machinery to the sub-structure.
The draft tube is of the Moody spreading type, formed in the concrete, with symmetrical collection chamber and a hydracone extending up to the runner, which is set to clear it. The upper parts of the draft tube and cone are protected with cast steel plates and semi-steel supporting vanes set around the draft tube carry the superimposed weights of concrete and machinery.
The runners are of cast steel of the diagonal flow propeller type, with six vanes, the shaft being fitted with cast steel sleeves where it passes through the guide-bearing and stuffing box. The guide-bearing is lined with strips of lignum vitae and is water lubricated.
The operating mechanism consists of two cast iron servo-motors which are connected to the operating ring and supported by the pit liner. A governor actuator of the Woodward type is set alongside the generator and is arranged to use oil as the pressure medium and equipped with electrical motor-driven mechanism. Each unit is equipped with a pressure system which includes oil pumps, accumulator tank, sump tank and compressor plant, and the systems for each unit are interconnected.
The generators are of the revolving field vertical shaft type rated at 12,000 kv.a., 3-phase, 60-cycle, speed 163.6 r.p.m., power factor 90 per cent. Current is generated at 6,600 volts. Excitation is provided by a 100 kw. 250-volt main exciter and a 2½ kw. pilot exciter both direct connected, and a 100 kw.-250-volt station exciter is also installed. Each generator is connected directly to the low tension side of the transformer bank.
The two small auxiliary units are of the vertical water wheel type rated at 1,250 h.p. each and are direct connected to 1,000 kv.a., 600-volt, 3-phase, 60-cycle generators which supply current for station services.
Three banks of main transformers and one spare are provided, also one bank of transformers for the auxiliary units. The main transformers are of the oil-filled, water-cooled type rated 4,000 kv.a., single-phase, 60-cycle, 6,600/110,000 v., D/Y with grounded neutral. Taps for 112,750/107,250/104,500/101,750 volts, full capacity. The auxiliary transformer bank consists of three 667 kv.a., single-phase, 60-cycle, 600/6,600 volt D/D oil insulated self-cooled transformers, with grounded neutral. All transformers are mounted on steel trucks and can be readily moved as required.
Current and potential transformers are installed in fire-proof compartments opposite the main transformers.
The high tension oil circuit-breakers connecting the transformers to the high tension bus bars and outgoing lines are of the solenoid operated type, 125 volts, 3-pole, single-throw, 400 amperes, 110,000 volts, with automatic overload trip. The three individual poles of the breaker are entirely insulated from one another. The disconnecting switches are of the three-pole, single-throw, gang operated type, 600 amperes, .110,000 volts, and operation is effected by means of hand levers.
The transfer bus is located on the floor adjoining the breaker rooms, immediately above the main transformer bay, and the main disconnects and high tension busses are on the top floor of the building. The 110 kv. busses are of l½ inch copper tubing and low tension busses of copper bars.
The main and auxiliary switchboards, relay panels, rheostats and voltage regulators are placed in the control room from which the operation of the station is directed by a complete signal system.
A small motor generator set in duplicate is installed for charging batteries used in connection with the emergency lighting system and other purposes and the building is heated throughout by electrical heaters. A complete machine shop is provided at the north end of the building for repair work and an electrically operated 75-ton gantry crane is placed in the generator room to handle the heavy equipment.
The pumping-plant is located in the basement below the machine shop, and water for fire protection and operating and domestic purposes is taken direct from the river, the domestic supply being chlorinated.
The main dam, which occupies the river channel, adjoins the power-house ort the north side and contains three ice-chutes with stop-log control, four large undersluices with submerged gates and a spillway section with thirteen openings fitted for stop-log regulation. The guides for the stop-logs are electrically heated to facilitate winter operation and a stop-log machine is placed on the deck for placing the logs in position or withdrawing them. The undersluice, gates are of the fixed roller type, loaded with concrete and raised or lowered by a 30-ton gantry crane with link connections to the gates.
The rollways are of mass concrete and are separated by piers, extending to the river level. The. crest is of a compound curve section and is connected by tangents of varying lengths to a reversed curve at the bucket. The north shore connection is made by means of a mass concrete bulwark dam and the overall length of the combined structures from the power-house to the north bank is 468 feet.
The headworks extension south of the power-house is similar in design to the existing works at the power-house and has a length of 139 feet. The south shore connection is an extension of the headworks and is a mass concrete bulwark dam 497 feet long. The proportions for plain concrete were 1:2-1/2:5 used in dams and mass work and 1:2:4 for reinforced concrete with a minimum mixing time of 1½ minutes. The total length of the power dam from shore to shore is approximately one quarter of a mile.
The main spillway dam is located about one mile to the south of the power dam and is a concrete structure of about 1,000 feet in length with a maximum height of approximately 40 feet. The rollways are of mass concrete separated by piers which support the operating deck. Forty-six openings 15 feet 6 inches in width are provided to pass the main flow of the river, which is diverted into a spillway channel discharging 1½ miles below the powerhouse. The deck is 18 feet wide, of tee beam construction, and carries two stop-log machines, and a compressed air system is installed to agitate the water in front of the dam during the winter months. Power is brought from the main plant by a 6,600-volt pole line and is stepped down at the dam to operating voltage.
Nine cut-off dams were constructed at various points along the river bank to prevent the escape of stored water. The dams were made of clay obtained from borrow-pits located away from the dams, and excavated by machine shovels or other means.
The dams varied in height from 5 to 20 feet, had 10-foot crests and side-slopes 2:1, 3:1 with benches on the slopes of the larger dams. The slopes were riprapped on the water side, and a rock-filled toe placed on the dry side with suitable drainage.
In constructing the dams the surface soil was stripped to a solid bottom, longitudinal drains were excavated, and the filling material brought up in layers of about eight inches, with a slope rising from the water side, when the whole surface was rolled and sprinkled. The larger dams were constructed from trestles and the material dumped from side cars, after which it was spread by teams and scrapers. Cut-off trenches were excavated wherever a porous substratum was encountered, and refilled with impervious material.
The main transmission line to Flin Flon is 58 miles in length with 125 feet cleared right-of-way. The branch to Sherritt-Gordon mine is about 45 miles in length and is of pole construction. The main line is carried on suspension type double circuit towers set in concrete foundation or grouted into rock, and is strung for two 3-phase circuits. A lightning arrester is provided at the power-house end of the line, located on the tailrace operating platform.
The majority of the plant used on the job was electrically operated. Several miles of standard gauge track were laid and equipped for use of electric locomotives of which five 8-ton and four 20-ton were in use. Material was hauled in side-tip wagons of five cubic yards capacity and flat cars. Two gasoline motors were also used at outlying points.
The mixing and crushing plant was very complete and operated on the gravity system. Two one-yard concrete mixers, a jaw crusher and a cone crusher were installed in this plant and also a plant for making concrete block for the power-house. Concrete was placed by the tower and chute system. An air compressor station containing two 600-cubic foot air compressors and some smaller machines supplied air for the drills and other purposes. Electrical shop, machine shop and carpenters' shop were located adjacent to the power-house, also a plant for welding and general repair work.
The quantities of work comprised in the development exclusive of the transmission line, are indicated by the following figures:—
|Excavation and earthworks||194,000||cubic yards|
From start to finish the whole of the work was completed in a little over two years, but actual construction of the permanent works was completed in sixteen months, and power was being supplied to the mine twelve months after the first ground was broken. Construction of the works was carried out by the Fraser-Brace Engineering Company Ltd., of Montreal, who were also responsible for the general design, and the cost of the undertaking was approximately $7,100,000.