THE HEMSILPOWER PLANT

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A.S.KMERNER BRUG.OSLOKvaernervn. 10 - Postal Address: Box 3610 - Cable Address: Kvaerner - Telephone: 68181O - Telex: 1650

NORWAY

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HEMSEDAL

I i i i i 1 i i ; i .'....The catchment area in Hemsedal with power stations and water tunnels.

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0 Dams.O Distributing basins.* Power stations.. Water tunnels.

THE HEMSIL HYDRO-ELECTRIC PLANT

Oslo Lysverker started the preliminary workon its hydro-electric plant at Hemsedal in 1956.Hemsedal is a valley in the centre of southernNorway, north-west of Gol station on the Oslo—Bergen railroad in Hallingdal. The river Hemsilhas given its name to the two largest power sta-tions now7 erected in Hemsedal. Hemsil II pro-ducing 82 MW is situated near Gol railroad sta-tion, Hemsil I producing 70 MW is located abt. 20

km. further up in the valley. Both stations arebuilt underground and have unusually longwater conveying tunnels. Two additional smallerpower plants, Gjuva of 10 MW capacity andBrekkefoss of 1.5 MW capacity, are located in theupper part of the valley. These four power sta-tions were all recently put into operation, andOslo Lysverker has thus completed the develop-ment scheme in Hemsedal.

Hemsil I underground power-station is lying close to the beautifulwaterfall «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.

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Vertical section of the Hemsil I power station, showing the pressureshaft, 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 theWater Supply to Hemsil I

Hemsil I utilizes a catchment of 225 sq. kmwith two lakes, Gyrinosvann and Flsevann at1.108 m high-water level. A rolled-fill dam, 700m long and with 28 m max. height, has been com-pleted for the primary supply. The main supplytunnel is 13.850 m long with a cross-section of11 sq. m. Two concrete dams are required alongthe main tunnel course to bring the flow of theside-streams Fagerd01a and Dyrja into the tunnelvia 100 m long side shafts. At the end of themain tunnel a large surge tank with an upper anda lower chamber is excavated.

The water is led into a penstock through trash-racks and a steel plate entrance cone embeddedin a strong concrete block. On the downstreamside of the entrance cone, a 2.2 m dia. butterflyvalve is installed in a valve chamber. Sealingsurfaces are of bronze. The valve is hydraulicallyoperated and equipped with a separate oil pump.

The butterfly valve must normally not be closedor opened unless the pressure is equalized on thedownstream and upstream side of the disc bymeans of a by-pass gate valve. The butterfly valveis furnished with a weight-loaded arm, closingthe valve if a pipe fracture occurs. The oil in theservomotor system retards the valve disc beforeclosing, which occurs automatically either bypenstock water velocities above normal, or byoperator's signal from the control room in thepower station, or mechanically — by a handle inthe valve chamber.

Two large air inlet valves are mounted on theupper end of the penstock just after the butterflyvalve. The valves are spring loaded, hydraulicallyretarded disc valves with a dia. of 730 mm. Theywill supply air !to the pressure shaft when avacuum develops.

The water is brought from the distributing

^j The gate valve shown in5 Kvasrner Brug's erecting shop" after the pressure test.

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The gate valve is operated byhand or by remote controlfrom the control room. Thepicture shows equipment foroperating the gate valve atthe site plant.

basin to the power station through a 650 m longpenstock mounted in an open shaft. The last 250

^ m length of conduit is a lined pressure shaft. Thefirst 650 m had to be built in an open shaftbecause great deposits of alun slate made con-crete backing impossible. The inside dia. of bothparts is 2.0 m and they are sloping at 35 degrees.The distance between the anchoring blocks of thepenstock is 186 m and the 650 m penstock isconstructed without expansion joints. Thepenstock is mounted on rollers, 15 m betweeneach bearing. At the end of the pressure shaft abranch pipe with concrete backing divides thepressure shaft into two 1.100 mm dia. conduits.

The Hemsil I underground station has a 900 mlong entrance tunnel, the opening of which isclose to a beautiful little waterfall called «Brude-s!0ret» («The Bridal Veil»).

Francis Turbines for Hemsil I

The power producing plant has two verticalFrancis type turbines, each of 48.500 H.P., desig-ned and manufactured by KV^ERNER. The tur-bines are running at 750 rpm, with a net head of510 m (gross head 543 m). To our knowledge thisis the highest operating head for a Francis tur-bine to date.

Francis turbines were chosen from the fol-lowing considerations: First of all - - the unitscould be designed for a higher speed than wouldhave been possible with Pelton turbines. Evenwith 4 jets, a Pelton turbine would have a naturalspeed of only 428 rpm. A higher speed results insmaller overall dimensions as well as reducedcost of generators and station hall. Furthermore,the tailwater level fluctuates because the tailracetunnel is as much as 3.162 m long. Pelton runnersmust be mounted above the maximum tailwaterlevel, and the application of this type would havemeant a loss of head corresponding to the tail-water fluctuation. On the other hand the Francisturbine w7ill always utilize fully the availablehead.

The advantages of the Francis turbines areperhaps in this particular case not so significentbecause the turbines are of a relatively modestsize, and the fluctuation of the tailwater level isalso relatively small. The advantage would cer-tainly be greater for larger units, as the efficiencyof the Francis type turbine increases with in-creasing geometrical dimensions.

The unusually high head employed here forFrancis turbines made it desirable to conductextensive tests. For this purpose and by greatcourtesy and co-operation from Oslo Lysverker,runners of different designs wrere mounted, theobject being to obtain data for general improve-ment of high head Francis turbines.

The turbines are equipped with 900 mm dia.gate valves which are hydraulically operated byfiltered water from the pressure shaft. Before thegate valve opens, a by-pass valve is automaticallyopened to equalize the pressure on the down-stream side with that on the upstream side.When closing the gate valve under normal condi-tions, the by-pass is automatically kept openuntil the gate is closed.

The all-welded Francis runners have a dischar-ge diameter of 860 mm, and 32 vanes. The vanesare made from steel plate, hot shaped in ahydraulic press. Due to the welded design, thechannels of the runner have very smooth surfa-ces, with a consequent improvement in efficiency.The runners have a coating of stainless steelapplied to the inlet and outlet of boss and ring.

To reduce the axial hydraulic forces, the bossand ring of the runner are equipped with laby-rinth rings of stainless steel. These rings corres-pond with similar rings of bronze on the covers.

The leakage water from the upper labyrinthrings is brought to a large deaerating tankserving as suction tank for the power station's

The alt-welded runner of Hemsil I 48.500H.P. turbine with labyrinth rings.

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two cooling water pumps. As the clearances ofthe labyrinth rings are kept to a minimum, noother filtration of the cooling water is necessary.

A relatively small leakage through the sealingsurfaces of the guide vanes in high head Francisturbines represents a marked reduction of theturbine effeciency. The clearances between guidevanes and covers should therefore be as small aspossible. The covers are of a special inflexibleand rigid design, which minimizes deflectionsunder load and thus keep the clearances practi-

cally constant at all conditions. For the samereason the spiral casings have strong stay vanesclose to the guide vanes. A layer of stainless steelis applied to the guiding surfaces of the covers toreduce hydraulic wear.

The guide vanes are die forged from stainlesssteel, machined by copy milling and ground. Theyare mounted with bronze bushings in the upperand lower covers. The bearing surfaces are greaselubricated through holes in the vane spindles.The guide vane levers are keyed to the upper end

The cast steel coverplate is made very rigidin order to obtain minimum deflection.

Field erection view of the self-lubricating j^turbine bearing. ff

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Turbine no. 1 seen from below with drafttube cone and bottom cover removed.

The cast steel spiral casing ready for rail-way transport from the workshop to the plant.

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of the vane spindles. All connecting links betweenthe guide vanes and the governor are made withvery small clearances to reduce lost motion.

The turbine bearing is mounted close to therunner and is self-lubricated. The bearing hasabt. 0.25 mm clearance on its diameter, whichensures exact centering of the shaft. The oil circu-lation in the bearing is maintained by centrifugalforce, and no special oil pump is necessary. Forsafety reasons there is a spiral for cooling waterin the bearing cover, but cooling water is nor-mally not necessary. A float switch gives signal inthe control room when the oil level in the bearingis too high or too low. The temperature of the oilis controlled by a contact thermometer whichfirst gives a warning signal and finally stops theunit if the temperature should reach the dangerpoint.

To prevent cavitation on the runners, the tur-bine centers are fixed at 3.3 m below minimumtailwater level. The turbines are thereforeequipped with labyrinth sealing boxes for theshaft to prevent leakage. The boxes have brasssealing rings inserted, and are drained by ejectorsto the draft tubes of the turbines. The hydraulicejectors are operated automatically.

From the runner the water discharges into adraft tube cone equipped with man holes. Thecone may easily be removed for dismantling run-ner and guide vanes. The draft tubes are platelined for a length of 10 m from the turbine center.

The top cover and the regulating ring as wellas the hydraulic sealing box are dismantled up-wards. The turbine guide bearing consists of twoparts, which may be easily removed withoutdisconnecting the generator- and turbine shafts.

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TURBINE OUTPUT, MW

Efficiency Tests by Thermodynamic Method.1. Turbine no 1 with runner no 1 measured 25.-1-60.2. Turbine no 1 with runner no 2 measured 8.-1-61.

> »Schematic drawing of the governing system.

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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 combina-tion of hydraulically and electrically operatedelements, developed in co-operation with BrownBoveri & Cie, Baden, delivered through NEBB,Oslo.

As stations are being joined together in greaterinterconnected networks, the units will havemore complicated governing tasks which aresolved simpler by electric devices than by thecorresponding mechanical designs usually em-ployed up to now.

The Hemsil governors are equipped with mainoil pumps driven by A.C. motors, and reservepumps driven by D.C. motors, the latter beingsupplied from the power station accumulatorbattery. The governor is built as a compact self-contained unit and thoroughly tested before deli-very. This type of governor has in service provedreliable and efficient.

To prevent extreme pressure rises after asudden shut-down, the turbines are equipped

with 400 mm dia. relief valves. The pressure riseis reduced to 10 per cent at a full shut-down oftwo units. The discharge from the relief valveflows through an energy absorber into the drafttube.

Power for internal use in the Hemsil I stationis provided by an impulse type turbine with onejet. The water is supplied from the pressure shaftbranch of a main turbine. The output is 400 H.P.and the speed is 1000 rpm. The runner has a caststeel boss-plate with stainless steel buckets. Theturbine is equipped with an oil pressure operatedgovernor and a water presure operated 150mm gate valve. The governor has belt drivenpendulum and oil pumps, being independent ofcurrent supply to the power station. The mag-netizing current for the generator is taken froman accumulator battery.

All facilities of the station Hemsil I are designedfor remote control from the Hemsil II powerstation.