BY J. C. BOGLE. | October 11, 1913
Nine years ago irrigation began the exploitation of Central Oregon. So rapidly did settlers flock into the new country, and consequent development obtain, that in 1910 two railroads were racing their construction through the canyon of the Deschutes to Bend, predetermined as the distributing city.
Any traveler along these roads, be he technically inclined or otherwise, is startled with a succession of available water powers. From Benham Falls to the mouth of the Deschutes the river splashes down a 4000 foot drop of elevation, an average of over 25 ft. per mile. The flowage is unbelievable. At Benham Falls the government gauge, maintained for four years, shows a minimum of 1800 sec. ft., and such is the steady supply to this river that during that period there has been no maximum flow in excess of three times the minimum. Grass grown banks corroborate the government report, which asserts that there has been no variation in stage more than 26 in.
Three years ago there was initiated at Bend a project contemplating an ultimate development of 1400 electrical h.p. The head works, including the dam, the spillway and the head gates, were completed. At this point the policy of the holding company decided it to discontinue for the present the course as originally outlined, and to supply meanwhile the needs of a growing town with electric service from a temporary plant. This was done, and 150 kw. were realized.
Towns in the Northwest have surprising growth. In a short time the temporary plant was overloaded, and rapid enlargement was forcibly indicated. This work was undertaken by McMeen and Miller for the Central Oregon Power Company, which had recently come into possession of the property.
The dam is of the rock fill type, and extends from the west bank to the south end of the spillway. A levee containing the headgates connects the north end of the spillway with the east bank. These headgates were originally intended to communicate with a canal leading to the proposed power house.
To continue the work as originally laid out met with the difficulty of building a forebay which would be of sufficient size, and yet in its construction not necessitate shutting down the plant already in service. Work was greatly cramped by the existence of the old flume, which necessarily had to be maintained during later construction. Obviously water had to be carried around the old flume to the new power house until the latter was carrying the load.
To accomplish this end there was constructed a battered concrete wall backed with counterforts, extending from the headgates to the new power house. Eventually this will retain the forebay, which will be simply an arm of the river, cut off at its lower end with an earth fill. But at present it is being used as one side of a flume, the other side being a timber bulkhead, spaced 13 ft. 6 in. from the wall and secured to it with rods and caps. This flume leads to the new power house and will be used until the forebay is put in service, after which time the timber bulkhead will be removed.
Only half the ultimate power house has been completed, and in that only one unit installed. Provision has, however, been made for the rapid addition of another unit as soon as the load will warrant, and excavation has been completed for the half of the sub structure unbuilt. Construction will be carried on behind a gravity bulkhead already in place, which shuts off the river from the excavation.
The power house substructure is of reinforced slab construction. No attempt was made to place the wall plate, water bearing or draft tube rings coincident with the pouring of concrete, but by a system of tongued and grooved openings the parts were later grouted in place with no difficulty and with no subsequent leaks. The main shaft, being horizontal, pierces the cross wall and enters the generator room through a stuffing box. No waterproofing was used in this wall other than separately mixed grout, which was carefully spaded next the forms to a thickness of one inch. The resulting wall is quite impervious.
Either wheel pit may be drained after shutting off the flow from the forebay. For this purpose stop logs are provided, and these slide vertically in slots having reinforced corners. Such an arrangement provides for closure at long intervals in an entirely satisfactory manner, and avoids the expense attendant upon the installation of gates and the necessary rigging to operate them.
In this country anchor ice is a problem, frequently developing suddenly and with great speed. On several occasions racks have been obstructed between regular times of inspection, and at light loads the loss in head due to the obstruction will not evince itself immediately. With this in mind the racks were designed to carry considerable head. The anchor ice is spongy, and it is almost impossible to rake it from the racks. The most efficient method of dealing with it thus far found is to have the rack screens made sectional, and by opening the screen a section at a time to allow the spongy mass to pass through the wheel. The greatest difficulty is encountered at about midnight, at which time the temperature is lowest and the velocity in the wheel pit the least. Next winter it may prove interesting to experiment with a water rheostat suspended in front of the racks. A good load and consequent velocity of water will be obtained and quite a large amount of heat available for fusion will thus be liberated at a critical point.
At present the plant is operating under 14 ft. head, which may be raised at any time to 17 ft.
The turbine, furnished by the S. Morgan Smith Company, is supported on two concrete beams which form a part of the wheel pit floor. It is quadruplex, with 30 in. wheels, and operates at 200 r.p.m.
Speed regulation is obtained with a Woodward oil pressure governor of 7000 ft. lb. capacity. As there is at present but one alternator on the line, the governor is adjusted to flat regulation. Oil pump and governor are belted from opposite sides of the main shaft, and both are located close in to the cross wall and well out of the way.
A 250 k.v.a. alternator, operating at 2300 volts is directly connected to the main shaft, to which the exciter is also belted. The exciter is designed to carry a slight overload when the alternator is fairly loaded. Alternator, switchboard and exciter are all General Electric Company make.
In addition to the plant machinery, the generator room contains remote control of a motor driven pump for city water service, and a series arc rectifier set for magnetite street lamps with which the city is provided.
The plant was in operation 30 days after the substructure was finished, although it was necessary to transport the machinery completely around the temporary plant and to raise it into the building from the tail race level. All the turbine parts were elevated through the openings left for draft tubes. The generator had to be “snaked” up with a stump puller. Such an apparatus is easily obtainable in most localities, and will be found remarkably effective on small jobs. All erection was accomplished with chain blocks from an overhead timber, and at no time was the need for a crane in any part of the building at all apparent.
The installation of this first unit was made very satisfactorily and while ample for present requirements, a rapid growth of the plant is anticipated.