Liquid control jet during part load operation in a hydraulic turbine

Abstract

A hydraulic turbine including: a passageway permitting liquid to pass through the turbine; a draft tube defining a portion of the passageway through which liquid normally flows in a vortex flow path during optimal turbine operating conditions; a rotatable runner mounted upstream of the draft tube and rotating about a central axis passing through the runner and extending into the draft tube; at least one nozzle head device positioned relative to the central axis of the runner and adjacent to an upper portion of the draft tube, the at least one nozzle head device has at least one nozzle from which a corresponding control jet of high velocity liquid is injected axially downstream of the runner and into liquid flowing into the upper portion of the draft tube during part load turbine operation, so as to mitigate breakdown of the vortex flow path.

1 . A hydraulic turbine comprising:
 a passageway permitting liquid to pass through the turbine;   a draft tube defining a portion of the passageway through which liquid normally flows in a vortex flow path during optimal turbine operating conditions;   a rotatable runner mounted upstream of the draft tube and rotating about a central axis passing through the runner and extending into the draft tube;   at least one nozzle head device positioned relative to the central axis of the runner and adjacent to an upper portion of the draft tube, the at least one nozzle head device has at least one nozzle from which a corresponding control jet of high velocity liquid is injected axially downstream of the runner and into liquid flowing into the upper portion of the draft tube during part load turbine operation, so as to mitigate breakdown of the vortex flow path.   
     
     
         2 . The hydraulic turbine of  claim 1  wherein the at least one nozzle locates the corresponding control jet of high velocity liquid in one position of along a central axis of the turbine and offset from the turbine central axis. 
     
     
         3 . The hydraulic turbine of  claim 1  wherein the runner has a crown portion and the crown portion houses the at least one nozzle head device. 
     
     
         4 . The hydraulic turbine of  claim 3  wherein the runner comprises a jet generation and control system located in one of the crown portion and a shaft portion for the runner. 
     
     
         5 . The hydraulic turbine of  claim 3  wherein the at least one control jet of high velocity liquid is ejected from the nozzle axially into a central portion of the vortex flow path of the liquid flowing in the draft tube. 
     
     
         6 . The hydraulic turbine of  claim 1  wherein the at least one nozzle head device further comprises at least one valve located upstream of the at least one nozzle for controlling the pressure of the liquid of the corresponding control jet. 
     
     
         7 . The hydraulic turbine of  claim 1  wherein the at least one valve is able to switch the corresponding control jet between on and off states. 
     
     
         8 . The hydraulic turbine of  claim 1  the at least one nozzle head device is supported in liquid flow communication with conduit extending from the draft tube wall into an upper portion of the draft tube. 
     
     
         9 . The hydraulic turbine of  claim 1  wherein further comprising one or more pressure sensors in the draft for measuring the liquid pressure in the upper portion of the draft tube and relaying these measurements to an active control device which in turn controls movement of the nozzle head device in order to adjust the velocity of control jet of high velocity liquid. 
     
     
         10 . A method of controlling part load operation of a hydraulic turbine during part load conditions having a runner, a draft tube located downstream of the runner and a liquid passageway extending through the runner and the draft tube, the method comprising the step of injecting one or more control jets of high velocity liquid axially of the turbine, downstream of the turbine runner and into at least an upper portion of the draft tube. 
     
     
         11 . The method of  claim 10  comprising the step of locating the one or more control jets centrally of the runner prior to the step of injecting. 
     
     
         12 . The method of  claim 11  wherein during the step of injecting the one or more control jets of high velocity liquid, the one or more control jets are injected in one direction selected from the group consisting of along an axis of the turbine, parallel to the turbine axis, converging on a focal point adjacent the upper portion of the draft tube lying on the turbine axis, and converging on a focal point adjacent the upper portion of the draft tube lying on a parallel axis adjacent to the turbine axis. 
     
     
         13 . The method of  claim 11  wherein the step of locating comprises locating the control jet or jets of high velocity liquid offset from a turbine axis.