MØRKFOSS-SOLBERGFOSS POWER PLANT ASKIM HØGRE SKOLE
NORWAY MØRKFOSS- SOLBERGFOSS POWER PLANT
OWNED BY
THE NORWEGIAN STATE
AND
THE CITY OF OSLO
Compiled by
Johan IF. Sohlherg, Chief Engineer, a I the instance of the worksmanagement of Mørkfoss—Solbergfossanlegget
Oslo 1926.
THE MØRKFOSS—SOLBERGFOSS power plant is
situated on the lower part of the river Glommen, the longest and largest river in Norway. This river has its source in Østerdalen and Gudbrandsdalen, and discharges into the fjord at Fredriksstad. The total drainage area amounts to 42 000 sq. kilometers or about one eighth of the area of the whole country.
In Østerdalen the Glommen receives a number of tributaries, including the Rena with the Osa, which have their source in Lakes Storsjoen and Osen respectively. Farther down the Glommen joins the Vormen, which drains Lake Mjosen, the largest lake in Norway with an area of 360 sq. kilometers. The main affluent to Lake Mjøsen is the Laagen with its tributaries the Vinstra Sjoa and Otta, which drain the largest reservoirs in Jotunheimen. After junction with the Vormen, the Glommen passes the first of the large power plants, Raanaasfoss, and about 30 kilometers below it flows into Lake Øieren, which has an area of 90 sq. kilometers. The surface of Lake Øieren is approx. 101 meters above sea level.
Along a distance of 60 kilometers between Lake Øieren and the sea the river forms a series of falls and rapids. First comes Mørkfoss at the outfall of Lake Øieren, then the Wittenberg rapids, Halfredsfoss, Solbergfoss, Fossumfoss, Kykkelsrudfoss, Vammafoss and finaly Sarpsfoss at the outlet of the river into the fjord. The three last named falls have been developed.
The average annual flow amounts to 600 cub.meters per sec., while the max.flood in the years 1910 and 1916, for instance, approximated 3000 cub.meters per sec.
Mørkfoss—SoIbergfoss Power Plant
As the minimum discharge during the last part of the winter was at times as low as 80 cub.meters per sec., regulation of the flow by storage came to the fore about the year 1900, when the construction of the power plant at Kykkelsrud and also those of Borregaard and Hafslund at Sarpsfoss were in progress. The first lake to be regulated was Mjøsen. At a regulated height of 2.2 meters, by which a reservoir with a capacity of 800 million cub. meters is obtained, it has since the year 1912 been endeavoured to maintain a min. regulated flow of 220 cub.- meters per sec. in the lower part of the river. During recent years 3 more of the largest lakes within the watershed have been regulated, increasing the winter flow to 240 cub.meters per sec. By means of projected future regulations it is expected that the flow will be increased to 300 cub. meters per sec.
After negotiations had been carried on for years between the Norwegian State as owner of Morkfoss with a head of 8 — 9 meters, and the City of Oslo, as owner of Wittenberg—Solbergfoss with a head of 12—13 meters, a contract between the parties for the joint development of the falls was made in the autumn of 1916.
Of the total energy at any time available at the plant one third belongs to the State and two thirds to Oslo. All constructional costs as well as the cost of upkeep and running expenses are divided in the same proportion. But turbines, generators, transformers and switching equipment are purchased separately by each party.
According to the contract the power plant should have been ready in 1922, but owing to divers circumstances it was not put in operation until 1924.
Mørkfoss-Solbergfoss power plant 7
The power plant, generally called "Solbergfossanlegget" is situated at Solbergfoss, about 5 kilometers below the outfall of Lake Øieren and comprises: Main dam, spillway section, log chute, power house with forebay and tailracc channel.
The main dam, is of the gravity type and is built across the deep river channel. It is made of concrete in proportion 1: 3: 5 and is faced with granite on those parts of the upstream and downstream side, which are exposed to the action of ice. The dimensions of the dam are approximately as follows: Width at top 4 meters, at base 30 meters, length at top 53 meters and max. height 45 meters. It is made in three sections, divided by two vertical expansion joints.
In order to control the river flow during construction of the dam it was necessary to drive two tunnels deep into the rock on the right side of the river. (Fig. 11). Each of the tunnels has an area of 50 sq. meters and a length of more than 200 meters. By means of these tunnels and coffer dams on each side, built to withstand a water pressure of 10 meters, the site of the dam was laid dry. The tunnels were permanently sealed by means of concrete plugs before the river was dammed up.
The spillway is made up of three sections, each 20 meters wide, and consists of a concrete rimway surmounted by roller gates, by which the pond level is kept 8.75 meters over the concrete crest. The gate on the west side is supplied with an electric heating device, in order to facilitate operation in winter, and is controlled from the switchboard in the power house. The gates are opened and closed in the course of 30 minutes by means of electrically operated hoists.
If the pond level were to rise as high as the crest of the main dam (elev. 107 a. s. 1.) the spillway would have a capacity of about 4000 cub.meters per sec., while the max. flood on record (in 1860) is estimated at 3300 cub. meters per sec. In order to make an easier way for the flood it was found necessary to widen the channel below Lake Øieren for a distance of about 2 kilometers, which involved the blasting and removal of large quantities of rock.
Mørkfoss-Solbergfosss power plant 8
As extensive logging operations take place in the river, amounting to about 7—8 millions annually, a log chute 700 meters long lias been constructed as a bypass to the plant. (Figs. 10,18). The chute is carried through tunnels over a distance of 400 meters and has a slope of 1:7] and the capacity is 12000 logs an hour at a flow of 10 cub.meters of water per sec. The transition from the variable head water-level to the chute is accomplished by a funnel shaped steel structure, which is adjusted to a required water level by means of a hoist.
The power house, which is made of concrete, in part heavily reinforced, has the following dimensions: Width 32 meters, extreme height 62 meters, length 150 meters when completed. The distance from c. to c. of units is 9.75 and 11 meters resp. The substructure is built for 13 units and the superstructure temporarily for 10. The dam along the forebay, which is 150 meters long, forms part of the substructure.
The power plant is directly connected with the stale railroads by means of a private, normal gage railroad to Askim railroad station. The construction of this road, which is 8 kilometers long, was started at the same time as the power plant.
A railroad bridge is built across the forebay for transport of the machinery into the unloading room of the power house. By means of a 40 tons electric travelling crane the machinery is lifted off the railroad cars and lowered to the floor of the power house. The generator room is equipped with a 100 tons travelling crane.
The bridge piers are furnished with guides for three gates, 14 by 12 meters, which will be installed if later on it should be necessary to empty the forebay basin. At the end of the forebay there is an ice gate and a bottom gate for draining.
From the forebay the water is conducted through the screens into the pressure tubes, which are moulded in the croncrete without steel lining. The entrances to the pressure tubes are closed by sluice gates of structural steel, mounted on rollers. The gates can be lowered.
Mørkfoss-Solbergfoss power plant 9
under full water pressure in the course of four minutes, while raising the gates necessitates the elimination of pressure and takes about 14 minutes. The gates are controlled from the gate house but can also be closed from the main switchboard and automatically closed by being connected with the centrifugal pendulum on the turbines. This pendulum is released in the event of the governor being out of function, and the revolutions of the turbine exceeding 185.
The turbines are of the Francis type with vertical shaft and single runner. The scroll case is moulded in the concrete without steel plate lining, but the upper part of the draft tube has such a lining. Each turbine is designed to develop 11 500 H. P. under a head of 21 meters by 150 rev. per min. Weight 120 tons. Owing to the great variation of flow in the river, the head decreases during the summer flood to 16—17 meters. By eventually regulating Lake Øieren it will be possible to raise the head in winter to 23—24 meters. Testing of the turbines is in progress and it is expected to obtain a max. efficiency of about 94%.
To each turbine is directly connected one 3 phase, 50 cycle, 10 500 V. generator. The output of the generator is 11 000 k.V.A., power factor = 0,75 at winter temperature and 10000 k.V.A., power factor = 0,75 at summer temperature. The connection is star with neutral brought out. The exciter is mounted on the top of the generator with the thrust bearing between, which carries the weight of runner, rotor, exciter and also the water pressure, aggregating about 150 tons. The weight of the generator is 160 tons.
Each generator is directly connected with a transformer without intermediary oil switch. These oil transformers are water cooled, the connection is delta-star. They step the voltage up from 10 500 to 65 000 V. and work through an oil switch on one of the two sets of 65 000 V. bus bars.
On the 10 500 V. side the generators can be connected with the two sets of bus bars.
