Guide vanes in Francis turbines

El Cajon, HONDURAS

Revelstoke, CANADA

La Grande 3, Canada P = 169 MW H = 72 m Q = 265 m3/S D0 = 6,68 m D1e = 5,71m D1i = 2,35 m B0 = 1,4 m n = 112,5 rpm

La Grande 3, Canada

La Grande 3, Canada

Guide vane cascade, Francis

Guide Vane End Seals High efficiency Less erosion Less leakage in closed pos.

Guide vanes Main function: Adjust the turbine load The guide vanes consist of number of blades that can be adjusted in order to increase or reduce the flow rate through the turbine. The vanes are arranged between two parallel covers normal to the turbine shaft.

Pressure distribution and torque L D Torque Arm L D

Guide vanes in closed position

Guide vanes in open position Pressure distribution can be found using Bernoulli’s equation: Pressure distribution along the contour of the guide vane: Trailing edge Trailing edge Contour of the guide vane

Pressure distribution along the contour of the guide vane: Small flow rate Large flow rate Stagnation- Point at Leading Edge Guide vane contour

Variation of the torque when the guide vane opening changes: 2 3 1 4 Sin a0

cm1 Powerplant ns a0 Skjærka 66 12 Dynjafoss 208 27,5 Nedre Vinstra 69 Oltesvik 264 38,5 Hol I 72 13 Iverland 269 31,5 Mesna 78 Fiskumfoss 308 40,5 Røssåga 104 18 36,5 Grønsdal 113 23 Gravfoss 346 37 Nore II 198 34 Solbergfoss 365 38

The guide vane maximum angle a0 at full load Powerplant ns a0 1 Skjærka 66 12 2 Nedre Vinstra 69 3 Hol I 72 13 4 Mesna 78 5 Røssåga 104 18 6 Grønsdal 113 23 7 Nore II 198 34 8 Dynjafoss 208 27,5 9 Oltesvik 264 38,5 10 Iverland 269 31,5 11 Fiskumfoss 308 40,5 36,5 Gravfoss 346 37 14 Solbergfoss 365 38 NB: This is for Norwegian designed GE-turbines Guide vane angle Specific speed, ns

The servo’s work

Take care of the torque from all guide vanes for all guide vane angles The servo has to: Take care of the torque from all guide vanes for all guide vane angles The torque consist of: Hydraulic torque Friction torque

Hydraulic torque The hydraulic torque can be found from a CFD-analysis

Friction torque ff (W,a)= empirical value m = friction factor H = Head

Stroke Friction Closing Opening Hydraulic forces Fully open High head Francis turbine Measurements of the servo’s work Force in 1000 kg

Horse shoe vortex damage

Cavitation damage

Sand erosion in the guide vanes Jhimruk Hydro Power Plant

Head cover Head cover Head cover Guide vane shaft k Bottom cover

The deflection of the head cover H = 435, P = 25 MW 1 2

Reduction of clearance

Efficiency of repaired turbine [MW] H = 430 m

Design of the Guide Vane Inlet Angle The inlet angle can be calculated by assuming a free vortex from the flow coming from the spiral casing B Dinlet Guide Vane rinlet Stay Vane

Design of the Guide Vane Outlet Angle The outlet angle can be calculated by assuming a free vortex from the flow in the gap between the runner and the guide vanes B0 r1 D0

Design of the Guide Vanes How to choose the number of vanes The number of guide vanes has to be different from the number of runner vanes.

Design of the Guide Vanes How to choose the number of vanes The number of guide vanes has to be different from the number of runner vanes.

Design of the Guide Vanes How to choose the guide vane maximum angle a0 at full load

Design of the Guide Vanes Overlapping of the guide vanes

Design of the Guide Vanes Number of guide vanes

Design of the Guide Vanes Diameter of guide vane shaft

Design Considerations Statement of Problem Givens Net head…………..….201.5m Flow rate…………...2.35m3/s Turbine speed….1000rpm Work out Design of Runner, Guide vanes, Stay vanes, Spiral casing andDraft tube Compare Design output with Jhimruk turbines Design Considerations Calculations - based on hydraulic principles only, Thickness of runner blades - neglected, Designs of components - done for the best efficiency point, Other several assumptions - mentioned locally in calculations.

Design of Guide Vanes Chosen: Nos. of guide vanes z =20 Diameter of guide vane axis D0 = D1 (0.29 Ω+1.07) .

Design of Guide Vanes Tangential and meridional velocities Assuming gap between runner and guide vanes 5% of the runner inlet diameter. . tan α(gvo) = Cm(gvo)/Cu(gvo) α(gvo) = 12.210 Value of αgvo in full guide vane open position is selected 180

Design of Guide Vanes L = 204 Velocities at outlet, axis and inlet of guide vanes (depending on varing values of α and t) Outlet agvo=12.210 tgvo=5mm Cm(gvo) = 8.582 m/sec Cu(gvo) = 39.65 m/sec Cgvo = 40.56 m/sec . Axis agvc=28.040 tgvc=30mm Cm(gvc) = 9.521m/sec Cu(gvc) = 17.87 m/sec Cgvc = 20.25 m/sec Inlet agci=340 tgvi=15mm Cm(gvi) = 7.864 m/sec Cu(gvi) = 11.65 m/sec Cgvi = 14.06 m/sec

Design of Guide Vanes .

Max. Opening Position Closed Position Runner inlet (Φ 0.870m) Guide vane outlet for designα) (Φ 0.913m) Max. Opening Position Closed Position

Water particle Water from spiral casing