Abstract:
A turbine replacement unit for replacement of at least one double runner horizontal submersible installation for a hydroelectric plant including at least one submerged coupling and at least one submerged bearing supported by a submerged bearing pedestal in which each of the two runners discharge a flow into a common draft tube. The replacement unit includes a single runner positioned to replace each of the two runners, the single runner receiving a flow and discharging the flow into the existing common draft tube. A dry pit assembly is positioned to surround the submerged pedestal and define an air space around the submerged pedestal and an oil-flooded bearing is positioned on the pedestal to replace the submerged bearing. A shaft supports the runner for rotation and is at least partially supported for rotation by the oil-flooded bearing. A generator is coupled to the shaft and is operable to produce an electrical power in response to rotation of the shaft.

Description:
BACKGROUND 
       [0001]    The present invention relates to a hydro turbine retrofit, and more particularly to a system and method for retrofitting a multi-runner hydro unit. 
         [0002]    Hydro turbines are used to generate electricity and control the flow of water on rivers throughout the world. Older hydro stations and particularly stations that include multi-runner units are subject to control difficulties and inefficiencies due to the arrangement of the controls and the flow through the various runners. 
       SUMMARY 
       [0003]    In one construction, the invention provides a turbine replacement unit for replacement of at least one double runner horizontal submersible installation for a hydroelectric plant including at least one submerged coupling and at least one submerged bearing supported by a submerged bearing pedestal in which each of the two runners discharge a flow into a common draft tube. The replacement unit includes a single runner positioned to replace each of the two runners, the single runner receiving a flow and discharging the flow into the existing common draft tube. A dry pit assembly is positioned to surround the submerged pedestal and define an air space around the submerged pedestal and an oil-flooded bearing is positioned on the pedestal to replace the submerged bearing. A shaft supports the runner for rotation and is at least partially supported for rotation by the oil-flooded bearing. A generator is coupled to the shaft and is operable to produce an electrical power in response to rotation of the shaft. 
         [0004]    In another construction, the invention provides a turbine replacement unit for replacement of a horizontal submersible unit for a hydroelectric plant wherein the unit includes at least two double runners including synchronized wicket gates, the runners supported on a preexisting foundation and coupled to a common shaft supported by at least two submerged bearings supported by a first submerged bearing pedestal and a second submerged bearing pedestal in which a first existing runner and a second existing runner discharge into a first draft tube and a third existing runner and a fourth existing runner discharge into a second draft tube. The replacement unit includes a first dry pit assembly positioned around the first bearing pedestal and defining an air space around the first bearing pedestal and a first oil-flooded bearing positioned on the pedestal to replace one of the submerged bearings. A first replacement runner assembly is connected to the first dry pit and includes an inlet positioned to receive a first flow and an outlet positioned to discharge the first flow into the first draft tube. The first flow is the only flow into the first draft tube. The first replacement runner assembly includes a first replacement runner. A second dry pit assembly is positioned around the second bearing pedestal and defines an air space around the second bearing pedestal and a second oil-flooded bearing is positioned on the pedestal to replace the other of the submerged bearings. A second replacement runner assembly is connected to the second dry pit and includes an inlet positioned to receive a second flow and an outlet positioned to discharge the second flow into the second draft tube. The second flow is the only flow into the second draft tube. The second replacement runner assembly includes a second replacement runner. A shaft supports the first replacement runner and the second replacement runner for rotation and is at least partially supported for rotation by the first oil-flooded bearing and the second oil-flooded bearing. A generator is coupled to the shaft and is operable to produce an electrical power in response to rotation of the shaft. 
         [0005]    In another construction, the invention provides a method of replacing a horizontal submersible installation for a hydroelectric unit including at least two double runners including synchronized wicket gates, the runners supported on a preexisting foundation and coupled to a common shaft supported by at least two submerged bearings supported by a first submerged bearing pedestal and a second submerged bearing pedestal in which a first existing runner assembly and a second existing runner assembly discharge into a first draft tube and a third existing runner assembly and a fourth existing runner assembly discharge into a second draft tube. The method includes removing the first existing runner assembly and the second existing runner assembly, positioning a first dry pit assembly around the first submerged bearing pedestal to produce an air space around the first submerged bearing pedestal, and connecting a first new runner assembly including a first new runner to the first dry pit assembly. The first new runner assembly is arranged to receive a first flow and discharge the first flow into the first draft tube, the first flow being the only flow into the first draft tube. The method also includes positioning a first oil-flooded bearing on the first bearing pedestal, removing the third existing runner assembly and the fourth existing runner assembly, and positioning a second dry pit assembly around the second submerged bearing pedestal to produce an air space around the second submerged bearing pedestal. The method further includes connecting a second new runner assembly including a second new runner to the second dry pit assembly, the second new runner assembly arranged to receive a second flow and discharge the second flow into the second draft tube, the second flow being the only flow into the second draft tube. The method also includes positioning a second oil-flooded bearing on the second bearing pedestal, supporting the first new runner and the second new runner on a shaft, and supporting the shaft on the first oil-flooded bearing and the second oil-flooded bearing. 
         [0006]    In another construction, the method includes a turbine replacement unit for replacement of a horizontal submersible installation for a hydroelectric plant including at least two opposed double runners including synchronized wicket gates, a first existing runner and a second existing runner discharge flow into a first draft tube, and a third existing runner and a fourth existing runner discharge flow into a second draft tube. The replacement unit includes a first dry pit assembly, a second dry pit assembly, and a first replacement runner assembly connected to the first dry pit assembly and including an inlet positioned to receive a first flow and an outlet positioned to discharge the first flow into the first draft tube, the first flow being the only flow into the first draft tube, the first replacement runner assembly including a first replacement runner. A second replacement runner assembly is connected to the second dry pit assembly and includes an inlet positioned to receive a second flow and an outlet positioned to discharge the second flow into the second draft tube, the second flow being the only flow into the second draft tube, the second replacement runner assembly including a second replacement runner. A first series of wicket gates are positioned adjacent the first replacement runner and are operable to control the first flow into the first replacement runner and a second series of wicket gates are positioned adjacent the second replacement runner and are operable to control the second flow into the second replacement runner. The first series of wicket gates and the second series of wicket gates are movable independent of one another. 
         [0007]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a top schematic view of a hydro power unit including four double opposed runner horizontal submerged turbines; 
           [0009]      FIG. 2  is a side view of one of the double opposed runner horizontal submerged turbines of  FIG. 1 ; 
           [0010]      FIG. 3  is a side view of a replacement unit suitable to replace the hydro power unit of  FIG. 1  and embodying the invention; 
           [0011]      FIG. 4  is a side view of a dry pit suitable for use in the replacement unit of  FIG. 3 ; 
           [0012]      FIG. 5  is a front view of the dry pit of  FIG. 4 ; and 
           [0013]      FIG. 6  is a partially broken away side view of a thrust bearing suitable for use in the replacement unit of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
         [0015]      FIG. 1  illustrates an existing arrangement for a portion of hydro electric plant  10 . The illustrated arrangement includes a power house  15  that is constructed as part of or adjacent to a dam on a river or stream. The power house  15  contains a generator  20 , controls, switch gear, and other equipment that must be kept dry or that must be frequently maintained. 
         [0016]    A shaft  25  is connected to the generator  20  at one end and extends through a wall  30  of the power house  15 . In the illustrated construction, the shaft  25  extends to and interconnects four double opposed runner horizontal submerged turbines  35 . Thus, the arrangement illustrated in  FIG. 1 , includes eight runners  23  (shown in  FIG. 2 ) connected to a common shaft  25  that is connected to the single generator  20 . In preferred arrangements, several shaft segments are connected to one another using bolted couplings  40  to allow for easier assembly, disassembly, and maintenance. As one of ordinary skill will realize, arrangements exist with many different runner configurations. However, the invention described herein is particularly suited to double opposed horizontal runner arrangements and more particularly to arrangements that include multiple double opposed horizontal runner turbines  35 . 
         [0017]    With continued reference to  FIG. 1 , each of the double opposed runner horizontal submerged turbines  35  discharges flow into a centrally-located draft tube  45 . Thus, each draft tube  45  receives flow from two different runners  23  or turbines. 
         [0018]    The submerged turbines  35  are supported on a submerged turbine deck  50  that includes apertures  55  formed to receive the draft tubes  45  and to direct the flow to a tailrace or other discharge. A number of bearing pedestals  60  are supported by the turbine deck  50  and provide a stable platform to support shaft radial bearings  65 . In the illustrated construction, the pedestals  60  and bearings  65  operate while submerged in water. Thus, the use of oil-flooded bearings is prohibited. Rather, sacrificial bearings such as wood bearings are often employed. This bearing arrangement generally requires significant maintenance and frequent realignment to function properly. If the frequent realignments are not performed or are not performed properly, premature shaft failure and other problems can occur. 
         [0019]    In addition to the radial bearings  65 , a thrust bearing (not shown) is positioned at some point along the length of the shaft  25  to accommodate the thrust load produced by the operation of the runners  23  or turbines. While the illustrated system  10  is substantially balanced and would ideally produce little or no thrust, a thrust bearing is still required. 
         [0020]      FIG. 2  is a section view of one of the double opposed runner horizontal submerged turbines  35  of  FIG. 1  and is representative of each of the double opposed runner horizontal submerged turbines  35  of  FIG. 1 . Each of the turbines  35  includes a runner  23  (sometimes referred to as a turbine) arranged to receive an inlet flow of water around the outer circumference and in a substantially radial flow direction and to discharge the flow of water from the center in a substantially axial direction. The runner  23  is attached to the shaft  25  for rotation such that as the runner  23  rotates, rotational torque is applied to the shaft  25  to rotate the generator  20 . The illustrated runner  23  is a Z-type Leffel turbine or a Francis turbine. However, other types of turbines could be employed if desired (e.g., Kaplan, Propeller, etc.). 
         [0021]    A gate casing  70  surrounds the outer circumference of the runner  23  and supports a plurality of movable wicket gates  75 . The wicket gates  75  can be moved from a closed position to a full open position to control the quantity of flow through the runner  23 . 
         [0022]    A draft chest  80  attaches to the gate casing  70  and directs the water from the discharge of the runner  23  to the draft tube  45  below. As illustrated in  FIG. 2 , both runners  23  discharge flow toward one another and into the common draft chest  80  that then directs that flow to the draft tube  45  and out through the tail race of the dam. 
         [0023]    A governor shaft  85  extends above the runners  23  and is supported by a series of bearings  65 . As with the shaft  25 , the governor shaft  85  is preferably assembled from a number of shaft segments to simplify assembly, disassembly, and maintenance. The governor shaft  85  extends the full length of the various runners  23  and controls each set of wicket gates  75  for each runner  23 . Thus, a single control system positions all of the wicket gates  75  in substantially the same position during operation. In preferred constructions, a sensor senses the speed and/or load of the generator  20  and adjusts the wicket gate position to adjust that speed or load to a desired set point. 
         [0024]      FIG. 3  is a view of the turbine deck  50  of  FIG. 1  following the implementation of the present invention. As can be seen, there are no significant structural changes to the turbine deck  50 , the power house  15  or any foundations. Rather, the present invention is installed using these existing features. For example, the pre-existing draft tube apertures  55  remain unchanged following the implementation of the present invention. 
         [0025]    Three dry pit assemblies  90  similar to the one illustrated in  FIG. 4  are positioned on the turbine deck  50  with each dry pit assembly  90  surrounding one of the bearing pedestals  60 . The dry pit assemblies  90  include an egress tunnel  95  that extends above a high water line  100  and provides access to the interior of the dry pit  90  during operation. Each of the dry pits  90  thus defines an air space  105  around the bearing  65  that is accessible during operation. 
         [0026]    With the pedestal  60  now positioned in an air environment, the existing sacrificial bearing  65  can be replaced with a fluid bearing  110  and preferably with an oil-flooded bearing  110  such as an oil-flooded babbitted bearing  110 . The use of oil-flooded bearings  110  greatly reduces the maintenance requirements and increases the life of the bearings  110  and the shafts  25 . In addition, if necessary, maintenance can be performed on one of the bearings  110  without dewatering the unit and without disassembly of the shaft  25 . In preferred arrangements, the shaft couplings  40  are also positioned within the dry pits  90  to provide access to the couplings  40  if necessary. 
         [0027]    A runner assembly  115  is attached to each of the dry pits  90  and includes a replacement runner  120  or turbine and a series of wicket gates  125  supported for movement between an open and a closed position. The replacement unit includes four single-flow runners  120  with each single-flow runner  120  replacing one set of the prior double opposed runners  23 . Thus, while a similar runner design could be employed (e.g., Francis, Kaplan, Propeller, etc.) the runner  120  is typically larger to accommodate the additional flow through the runner  120  as each runner  120  must accommodate twice the flow of each of the prior runners  23 . 
         [0028]    As illustrated in  FIGS. 4 and 5 , the wicket gates  125  are positioned around the outer circumference of the runner  120  and include a portion that extends into the adjacent dry pit  90  to provide for inspection during maintenance cycles or during operation. In addition, the linkage and hydraulic or electrical actuator  130  used to move the wicket gates  125  can be positioned within the dry pit  90 . For example, in one arrangement each wicket gate  125  is supported on a shaft that extends through the wall of the dry pit  90 . A common ring interconnects each shaft such that rotation of the ring produces a common rotation of each of the wicket gates  125  about their shaft axis. The ring, a portion of the wicket gate  125 , and the linkages therebetween are disposed within the dry pit  90  to facilitate periodic lubrication and maintenance. 
         [0029]    As illustrated in  FIG. 4 , the wicket gates  125  are movable between a closed position and an open position. After the flow of water passes through the wicket gates  125  and the runner  120 , the flow is discharged into a draft chest assembly  135  (shown in  FIG. 3 ) that receives only the flow from that particular runner  120 . The draft chest  135  then discharges the water to the draft tube  45  and out through the tailrace. 
         [0030]    Each of the draft chests  135  includes a pipe  140  that operates as a vacuum breaker as will be discussed. One end of the pipe  140  is positioned within the draft chest  135  and the opposite end is positioned above the water line  100 . A valve  145  is positioned between the two ends to selectively provide fluid communication between the draft chest  80  and the atmosphere above the water line  100 . 
         [0031]    A powerhouse dry pit  150  is positioned adjacent the outer wall of the powerhouse  15  to enlarge the space available for an improved thrust bearing  155 . The powerhouse dry pit  150  defines an air space  160  sized to receive a coupling  165  and the improved thrust bearing  155 . In preferred constructions, the thrust bearing  155  shown in  FIG. 6 , includes a dual action thrust bearing  155  that includes babbitted surfaces and oil lubrication. The thrust bearing  155  is larger than the prior thrust bearing due to an increase in operational flexibility as will be discussed below. 
         [0032]    Once the replacement is complete, the new unit arrangement is able to operate more efficiently across a larger load range and requires less maintenance than the prior unit  10 . The replacement is accomplished with virtually no changes being made to the existing foundation, thereby reducing the cost of implementing the replacement. 
         [0033]    The replacement of eight runners  23  that discharged through four draft tubes  45  with four runners  120  that discharge through four draft tubes  45  improves the overall efficiency of the runners  120  and reduces turbulence downstream of the runners  120 . 
         [0034]    In addition, the operation of the wicket gates  125  for the individual runners  120  is separated with the upgraded design. Thus, all of the wicket gates  125  do not have to move in unison, thereby greatly enhancing the efficient operating range of the unit. In one construction, the control signal for the individual wicket gates  125  is transmitted to the individual wicket gate actuators  130  via an electrical signal or wireless signal, while others include a hydraulic connection or a combination thereof. For example, the prior arrangement was operable between 20 percent and 100 percent of full load. Following the replacement, the unit is operable between 20 percent of the load of one runner  120  (i.e., 5 percent of the total unit output) and 100 percent of full load. Thus, the unit can operate efficiently at much lower loads, such as may be desirable when water levels are low. 
         [0035]    In addition to a wider load range, the unit can operate using only one runner  120 , two runners  120 , three runners  120 , or all four as may be desired. The separate vacuum breakers  140  allow a runner  120  to operate in air. With the wicket gates  125  closed, the valve  145  in the vacuum breaker pipe  140  is opened to allow the water within the runner  120  and draft chest  135  to drain. In some arrangements, compressed air is directed to the runner  120  to assure that all of the water is removed and the runner  120  is operating in air. Depending on which runners  120  are operating, the thrust load can change significantly thereby requiring the larger dual acting thrust bearing  155 . For example, if the two end runners  120  are receiving flow with the remaining runners  120  operating in air, the thrust would be somewhat balanced. However, if only the first end runner  120  or the first and second runners  120  from the left are operating, the trust would be significantly larger. 
         [0036]    Thus, the invention provides, among other things, a replacement hydro turbine arrangement suited for replacing a multi-runner hydro turbine. Various features and advantages of the invention are set forth in the following claims.