THE HEMSIL POWER PLANT

Transcription

1 THE HEMSIL POWER PLANT s" ' r- A.S.KMERNER BRUG.OSLO Kvaernervn Postal Address: Box Cable Address: Kvaerner - Telephone: 68181O - Telex: 1650 NORWAY C.

2 HEMSEDAL Hallingdalselvcn I i i i i 1 i i ; i.'... The catchment area in Hemsedal with power stations and water tunnels. 0 Dams. O Distributing basins. * Power stations.. Water tunnels. THE HEMSIL HYDRO-ELECTRIC PLANT Oslo Lysverker started the preliminary work on its hydro-electric plant at Hemsedal in Hemsedal is a valley in the centre of southern Norway, north-west of Gol station on the Oslo Bergen railroad in Hallingdal. The river Hemsil has given its name to the two largest power stations now7 erected in Hemsedal. Hemsil II producing 82 MW is situated near Gol railroad station, Hemsil I producing 70 MW is located abt. 20 km. further up in the valley. Both stations are built underground and have unusually long water conveying tunnels. Two additional smaller power plants, Gjuva of 10 MW capacity and Brekkefoss of 1.5 MW capacity, are located in the upper part of the valley. These four power stations were all recently put into operation, and Oslo Lysverker has thus completed the development scheme in Hemsedal. Hemsil I underground power-station is lying close to the beautiful waterfall «Brudesloret» (to the right on the picture). 1. Main supply tunnel. 2. Surge tank. 3. Pressure shaft. 4. Power station. 5. Cableshaft. 6. Entrance tunnel. 7. Tailrace tunnel. **<& -J''.. :- ;' :;f;;..., ; J^ -; fl ) : jm. : : - ftk^:4^,v;,,, '!*. ''S:MM > /:

3 ny Vertical section of the Hemsil I power station, showing the pressure shaft, the valve chamber and the surge tank. 1. Centre-line valves 1059,4 m above sea level. 2. Valve chamber. 3. Shaft to the upper surge tank. 4. Bottom headrace tunnel 1058,8 m a. s. I. 5. Normal tailwater level 569,7 m a. s. I. 6. Max. tailwater level 570,2 m a. s. I. 7. Min. tailwater level 566,2 m a. s. I. 8. Turbine setting 564,0 m a. s. I. 9. Plate lined pressure shaft. 10. Penstock in open shaft. Over and Under-Ground Layout for the Water Supply to Hemsil I Hemsil I utilizes a catchment of 225 sq. km with two lakes, Gyrinosvann and Flsevann at m high-water level. A rolled-fill dam, 700 m long and with 28 m max. height, has been completed for the primary supply. The main supply tunnel is m long with a cross-section of 11 sq. m. Two concrete dams are required along the main tunnel course to bring the flow of the side-streams Fagerd01a and Dyrja into the tunnel via 100 m long side shafts. At the end of the main tunnel a large surge tank with an upper and a lower chamber is excavated. The water is led into a penstock through trashracks and a steel plate entrance cone embedded in a strong concrete block. On the downstream side of the entrance cone, a 2.2 m dia. butterfly valve is installed in a valve chamber. Sealing surfaces are of bronze. The valve is hydraulically operated and equipped with a separate oil pump. The butterfly valve must normally not be closed or opened unless the pressure is equalized on the downstream and upstream side of the disc by means of a by-pass gate valve. The butterfly valve is furnished with a weight-loaded arm, closing the valve if a pipe fracture occurs. The oil in the servomotor system retards the valve disc before closing, which occurs automatically either by penstock water velocities above normal, or by operator's signal from the control room in the power station, or mechanically by a handle in the valve chamber. Two large air inlet valves are mounted on the upper end of the penstock just after the butterfly valve. The valves are spring loaded, hydraulically retarded disc valves with a dia. of 730 mm. They will supply air!to the pressure shaft when a vacuum develops. The water is brought from the distributing

4 ^j The gate valve shown in 5 Kvasrner Brug's erecting shop " after the pressure test. The gate valve is operated by hand or by remote control from the control room. The picture shows equipment for operating the gate valve at the site plant. ~ ^ basin to the power station through a 650 m long penstock mounted in an open shaft. The last 250 m length of conduit is a lined pressure shaft. The first 650 m had to be built in an open shaft because great deposits of alun slate made concrete backing impossible. The inside dia. of both parts is 2.0 m and they are sloping at 35 degrees. The distance between the anchoring blocks of the penstock is 186 m and the 650 m penstock is constructed without expansion joints. The penstock is mounted on rollers, 15 m between each bearing. At the end of the pressure shaft a branch pipe with concrete backing divides the pressure shaft into two mm dia. conduits. The Hemsil I underground station has a 900 m long entrance tunnel, the opening of which is close to a beautiful little waterfall called «Brudes!0ret» («The Bridal Veil»).

5 Francis Turbines for Hemsil I The power producing plant has two vertical Francis type turbines, each of H.P., designed and manufactured by KV^ERNER. The turbines are running at 750 rpm, with a net head of 510 m (gross head 543 m). To our knowledge this is the highest operating head for a Francis turbine to date. Francis turbines were chosen from the following considerations: First of all - - the units could be designed for a higher speed than would have been possible with Pelton turbines. Even with 4 jets, a Pelton turbine would have a natural speed of only 428 rpm. A higher speed results in smaller overall dimensions as well as reduced cost of generators and station hall. Furthermore, the tailwater level fluctuates because the tailrace tunnel is as much as m long. Pelton runners must be mounted above the maximum tailwater level, and the application of this type would have meant a loss of head corresponding to the tailwater fluctuation. On the other hand the Francis turbine w7ill always utilize fully the available head. The advantages of the Francis turbines are perhaps in this particular case not so significent because the turbines are of a relatively modest size, and the fluctuation of the tailwater level is also relatively small. The advantage would certainly be greater for larger units, as the efficiency of the Francis type turbine increases with increasing geometrical dimensions. The unusually high head employed here for Francis turbines made it desirable to conduct extensive tests. For this purpose and by great courtesy and co-operation from Oslo Lysverker, runners of different designs wrere mounted, the object being to obtain data for general improvement of high head Francis turbines. The turbines are equipped with 900 mm dia. gate valves which are hydraulically operated by filtered water from the pressure shaft. Before the gate valve opens, a by-pass valve is automatically opened to equalize the pressure on the downstream side with that on the upstream side. When closing the gate valve under normal conditions, the by-pass is automatically kept open until the gate is closed. The all-welded Francis runners have a discharge diameter of 860 mm, and 32 vanes. The vanes are made from steel plate, hot shaped in a hydraulic press. Due to the welded design, the channels of the runner have very smooth surfaces, with a consequent improvement in efficiency. The runners have a coating of stainless steel applied to the inlet and outlet of boss and ring. To reduce the axial hydraulic forces, the boss and ring of the runner are equipped with labyrinth rings of stainless steel. These rings correspond with similar rings of bronze on the covers. The leakage water from the upper labyrinth rings is brought to a large deaerating tank serving as suction tank for the power station's The alt-welded runner of Hemsil I H.P. turbine with labyrinth rings.

6 ,4 - i ft,vt * two cooling water pumps. As the clearances of the labyrinth rings are kept to a minimum, no other filtration of the cooling water is necessary. A relatively small leakage through the sealing surfaces of the guide vanes in high head Francis turbines represents a marked reduction of the turbine effeciency. The clearances between guide vanes and covers should therefore be as small as possible. The covers are of a special inflexible and rigid design, which minimizes deflections under load and thus keep the clearances practically constant at all conditions. For the same reason the spiral casings have strong stay vanes close to the guide vanes. A layer of stainless steel is applied to the guiding surfaces of the covers to reduce hydraulic wear. The guide vanes are die forged from stainless steel, machined by copy milling and ground. They are mounted with bronze bushings in the upper and lower covers. The bearing surfaces are grease lubricated through holes in the vane spindles. The guide vane levers are keyed to the upper end The cast steel coverplate is made very rigid in order to obtain minimum deflection. Field erection view of the self-lubricating j^ turbine bearing. ff '"-' *»,&<? '

7 Turbine no. 1 seen from below with draft tube cone and bottom cover removed. The cast steel spiral casing ready for railway transport from the workshop to the plant. '! * \» # '^* &»- "- Siv*,?' '

8 of the vane spindles. All connecting links between the guide vanes and the governor are made with very small clearances to reduce lost motion. The turbine bearing is mounted close to the runner and is self-lubricated. The bearing has abt mm clearance on its diameter, which ensures exact centering of the shaft. The oil circulation in the bearing is maintained by centrifugal force, and no special oil pump is necessary. For safety reasons there is a spiral for cooling water in the bearing cover, but cooling water is normally not necessary. A float switch gives signal in the control room when the oil level in the bearing is too high or too low. The temperature of the oil is controlled by a contact thermometer which first gives a warning signal and finally stops the unit if the temperature should reach the danger point. To prevent cavitation on the runners, the turbine centers are fixed at 3.3 m below minimum tailwater level. The turbines are therefore equipped with labyrinth sealing boxes for the shaft to prevent leakage. The boxes have brass sealing rings inserted, and are drained by ejectors to the draft tubes of the turbines. The hydraulic ejectors are operated automatically. From the runner the water discharges into a draft tube cone equipped with man holes. The cone may easily be removed for dismantling runner and guide vanes. The draft tubes are plate lined for a length of 10 m from the turbine center. The top cover and the regulating ring as well as the hydraulic sealing box are dismantled upwards. The turbine guide bearing consists of two parts, which may be easily removed without disconnecting the generator- and turbine shafts. 92 K 9/ 9(5 \ 31 x u Z «7 Met Head 5IOm150rPm SI db. J zo 30 TURBINE OUTPUT, MW 8b Efficiency Tests by Thermodynamic Method. 1. Turbine no 1 with runner no 1 measured Turbine no 1 with runner no 2 measured

9 >» Schematic drawing of the governing system.

10 11 r i & ^ The oil hydraulic governor and actuator cabinet are build together in one unit. Governing Equipment of Hemsil I The governing system is based on a combination of hydraulically and electrically operated elements, developed in co-operation with Brown Boveri & Cie, Baden, delivered through NEBB, Oslo. As stations are being joined together in greater interconnected networks, the units will have more complicated governing tasks which are solved simpler by electric devices than by the corresponding mechanical designs usually employed up to now. The Hemsil governors are equipped with main oil pumps driven by A.C. motors, and reserve pumps driven by D.C. motors, the latter being supplied from the power station accumulator battery. The governor is built as a compact selfcontained unit and thoroughly tested before delivery. This type of governor has in service proved reliable and efficient. To prevent extreme pressure rises after a sudden shut-down, the turbines are equipped with 400 mm dia. relief valves. The pressure rise is reduced to 10 per cent at a full shut-down of two units. The discharge from the relief valve flows through an energy absorber into the draft tube. Power for internal use in the Hemsil I station is provided by an impulse type turbine with one jet. The water is supplied from the pressure shaft branch of a main turbine. The output is 400 H.P. and the speed is 1000 rpm. The runner has a cast steel boss-plate with stainless steel buckets. The turbine is equipped with an oil pressure operated governor and a water presure operated 150 mm gate valve. The governor has belt driven pendulum and oil pumps, being independent of current supply to the power station. The magnetizing current for the generator is taken from an accumulator battery. All facilities of the station Hemsil I are designed for remote control from the Hemsil II power station.