Guide vanes in Francis turbines

transcript

El Cajon, HONDURAS

Revelstoke, CANADA

P = 169 MWH = 72 mQ = 265 m3/SD0 = 6,68 mD1e = 5,71mD1i = 2,35 mB0 = 1,4 mn = 112,5 rpm

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 adjustedin 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 torqueLL

Torque

Guide vanes in closed position

ZDl 0⋅π

= lBHgF 00 ⋅⋅⋅⋅ρ=

000 aFMTorque ⋅==

Guide vanes in open positionTr

Contour of the guide vane

Pressure distribution along the contour of the guide vane:

⋅⋅ξ

∑−⋅

lossesg2

Pressure distribution can be found using Bernoulli’s equation:

Pressure distribution along the contour of the guide vane:

Stagnation-Point at Leading Edge

Small flow rateLarge flow rate

Guide vane contour

gc⋅2

Variation of the torque when the guide vane opening changes:

( )020

DM2C α=⋅ρ⋅⋅

Sin α0

cm145s H

Horsepowernn ⋅=

α0nsPowerplantα0nsPowerplant

38365Solbergfoss34198Nore II37346Gravfoss23113Grønsdal

36,5308Fiskumfoss18104Røssåga40,5308Fiskumfoss1378Mesna31,5269Iverland1372Hol I38,5264Oltesvik1269Nedre Vinstra27,5208Dynjafoss1266Skjærka

38365Solbergfoss14

34198Nore II7

31,5269Iverland10

38,5264Oltesvik9

27,5208Dynjafoss8

36,5308Fiskumfoss12

40,5308Fiskumfoss11

37346Gravfoss13

α0nsPowerplant

23113Grønsdal6

18104Røssåga5

1378Mesna4

1372Hol I3

1269Nedre Vinstra

1266Skjærka1

The guide vane maximum angle α0 at full load

NB: This is for Norwegian designed GE-turbines

45s HHorsepowernn ⋅=

Specific speed, ns

Guide vane angle

The servo’s work

The servo has to:Take care of the torque from all guide vanesfor all guide vane angles

The torque consist of:Hydraulic torqueFriction torque

Hydraulic torque

⋅ρ⋅⋅

( )0m fC α=

The hydraulic torque can be found from a CFD-analysis

Friction torque

DBHd,fM ff

⋅⋅⋅⋅µ⋅αΩ±=

ff (Ω,α)= empirical valueµ = friction factor

H = Head

Stroke

Friction

Closing

Opening

Hydraulic forces

Opening

High head Francis turbineMeasurements of the servo’s work

Horse shoe vortex damage

Cavitation damage

Sand erosion in the guide vanes

Jhimruk Hydro Power Plant

Head coverHead cover

Bottom cover

Guide vane shaft

Head cover

The deflection of the head cover

H = 435, P = 25 MW

Reduction of clearance

Efficiency of repaired turbine

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

StayVaneinletStayVaneinletuGuideVaneinletGuideVaneinletu rCrC ⋅=⋅

BDQCGuideVaneinlet

GuideVaneinletm ⋅⋅=π 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

110 rCrC uou ⋅=⋅

00 BDQCmo ⋅⋅

Design of the Guide VanesHow to choose the number of vanes

• The number of guide vanes has to be different from the number of runner vanes.

Integerzz

VanesRunner

VanesGuide ≠

Design of the Guide VanesHow to choose the number of vanes

• The number of guide vanes has to be different from the number of runner vanes.

Integerzz

VanesRunner

VanesGuide ≠

Design of the Guide VanesHow to choose the guide vane maximum

angle α0 at full load

( )11344 2 +Ω⋅+Ω⋅−⋅=oα

Design of the Guide VanesOverlapping of the guide vanes

Design of the Guide VanesNumber of guide vanes

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6

Speed Number

Design of the Guide VanesDiameter of guide vane shaft

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6

Speed number

07,129,01

0 +Ω⋅=DD

Statement of ProblemGivens Net head…………..….201.5m

Flow rate…………...2.35m3/sTurbine speed….1000rpm

Work out Design of Runner, Guide vanes,Stay vanes, Spiral casing andDraft tube

Compare Design output with Jhimruk turbines

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 Considerations

Design of Guide Vanes

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6

Speed numberD

07,129,01

0 +Ω⋅=DD

Diameter of guide vane axisD0 = D1 (0.29 Ω+1.07)

−−−−⋅=Ω Qω

602 n⋅⋅

gH2/ωω =−−

66.1=−−ω

gHQQ 2/=−−

319.0=Ω

Chosen:Nos. of guide vanes z =20

mD 011.10 =

037.0=−−

−−−−⋅=Ω Qω

Tangential and meridional velocities

)(CuC gvou = smC gvou /64.39)( =

smC gvom /58.8)( =

Assuming gap between runner and guide vanes5% of the runner inlet diameter.

[ (( )

∗−∗

)( )Cosz

gvogvo

tan α(gvo) = Cm(gvo)/Cu(gvo)α(gvo) = 12.210

Value of αgvo in full guide vane open position is selected 180

Velocities at outlet, axis and inlet of guide vanes(depending on varing values of α and t)

Outlet agvo=12.210 tgvo=5mmCm(gvo) = 8.582 m/secCu(gvo) = 39.65 m/secCgvo = 40.56 m/sec

Axis agvc=28.040 tgvc=30mmCm(gvc) = 9.521m/secCu(gvc) = 17.87 m/secCgvc = 20.25 m/sec

Inlet agci=340 tgvi=15mmCm(gvi) = 7.864 m/secCu(gvi) = 11.65 m/secCgvi = 14.06 m/sec

Cm(gvi)=7.86 m/secCgvi=14.06 m/sec

Cu(gvi)=11.65 m/secCgvc=20.25 m/secCm(gvc)=9.521 m/secCu(gvc)=17.87 m/sec

Cgvo=40.56 m/sec

Cm(gvo)=8.58 m/secCu(gvo)=39.65 m/sec

L = 204

Guide vane at DesignPosition = 12.21°

Guide vane at closed position

Guide vane at Max. openPosition = 18°

Guide vanesGuide vanesGuide vanesGuide vanesGuide vanesGuide vanes

Runner inlet (Φ 0.870m)

Guide vane outlet for designα) (Φ 0.913m)

ClosedPosition

Max. Opening Position

R a d i a l v i e wrunner guide vanes and stay vanes

R a d i a l v i e wrunner guide vanes and stay vanesR a d i a l v i e wrunner guide vanes and stay vanes

Water from spiral casing

Water particle

Guide vanes in Francis turbines

Documents