Extent to which water Runner and blades are not completely Water completely fills all the fills the wheel/turbine filled or covered by water passages between the blades throughout the operation of the turbine Installation unit Always installed above the tail race. Unit may be installed above or below No draft tube is used. the tail race – use of draft tube is made. Relative velocity of When water glides over the moving Since there is continuous drop in water blades, its relative velocity either pressure during flow through the remains constant or reduces slightly blade passages, the relative velocity due to friction. increases. Flow regulation Flow regulated by needle valve fitted Flow regulated by guide vanes. into the nozzle Comparison of turbines Pelton Francis Kaplan Operating head (m) 100-1700 80-500 Upton 400 Maximum power 55 40 30 output (MW) Best efficiency 93 94 94 Regulation mechanism Spear nozzle and Guide vanes, surge tank Guide vanes, surge tank deflector plate Criteria for selection of turbine S. N Type of Head H(m) Specific Speed ratio Max. Remarks Turbine Speed(Ns) (Ku) Hydraulic efficiency (%) 1 Pelton: 0.43 – 0.48 89 Employed for 1 Jet Up to 2000 12 to 30 high head 2 Jets Up to 1500 17 to 50 4 jets Up to 500 24 to 70
Extent to which water fills the wheel/turbine Runner and blades are not completely filled or covered by water Water completely fills all the passages between the blades throughout the operation of the turbine Installation unit Always installed above the tail race. No draft tube is used. Unit may be installed above or below the tail race – use of draft tube is made. Relative velocity of water When water glides over the moving blades, its relative velocity either remains constant or reduces slightly due to friction. Since there is continuous drop in pressure during flow through the blade passages, the relative velocity increases. Flow regulation Flow regulated by needle valve fitted into the nozzle Flow regulated by guide vanes. Comparison of turbines Pelton Francis Kaplan Operating head (m) 100-1700 80-500 Upton 400 Maximum power output (MW) 55 40 30 Best efficiency 93 94 94 Regulation mechanism Spear nozzle and deflector plate Guide vanes, surge tank Guide vanes, surge tank Criteria for selection of turbine S. N Type of Turbine Head H(m) Specific Speed(Ns) Speed ratio (Ku) Max. Hydraulic efficiency (%) Remarks 1 Pelton: 1 Jet 2 Jets 4 jets Up to 2000 Up to 1500 Up to 500 12 to 30 17 to 50 24 to 70 0.43 – 0.48 89 Employed for high head
34568800-Hydraulic-Turbine-I.docx