Hydro unit retrofit and method of performing same

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.

BACKGROUND

The present invention relates to a hydro turbine retrofit, and more particularly to a system and method for retrofitting a multi-runner hydro unit.

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

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.

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.

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.

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.

DETAILED DESCRIPTION

FIG. 1illustrates an existing arrangement for a portion of hydro electric plant10. The illustrated arrangement includes a power house15that is constructed as part of or adjacent to a dam on a river or stream. The power house15contains a generator20, controls, switch gear, and other equipment that must be kept dry or that must be frequently maintained.

A shaft25is connected to the generator20at one end and extends through a wall30of the power house15. In the illustrated construction, the shaft25extends to and interconnects four double opposed runner horizontal submerged turbines35. Thus, the arrangement illustrated inFIG. 1, includes eight runners23(shown inFIG. 2) connected to a common shaft25that is connected to the single generator20. In preferred arrangements, several shaft segments are connected to one another using bolted couplings40to 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 turbines35.

With continued reference toFIG. 1, each of the double opposed runner horizontal submerged turbines35discharges flow into a centrally-located draft tube45. Thus, each draft tube45receives flow from two different runners23or turbines.

The submerged turbines35are supported on a submerged turbine deck50that includes apertures55formed to receive the draft tubes45and to direct the flow to a tailrace or other discharge. A number of bearing pedestals60are supported by the turbine deck50and provide a stable platform to support shaft radial bearings65. In the illustrated construction, the pedestals60and bearings65operate 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.

In addition to the radial bearings65, a thrust bearing (not shown) is positioned at some point along the length of the shaft25to accommodate the thrust load produced by the operation of the runners23or turbines. While the illustrated system10is substantially balanced and would ideally produce little or no thrust, a thrust bearing is still required.

FIG. 2is a section view of one of the double opposed runner horizontal submerged turbines35ofFIG. 1and is representative of each of the double opposed runner horizontal submerged turbines35ofFIG. 1. Each of the turbines35includes a runner23(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 runner23is attached to the shaft25for rotation such that as the runner23rotates, rotational torque is applied to the shaft25to rotate the generator20. The illustrated runner23is a Z-type Leffel turbine or a Francis turbine. However, other types of turbines could be employed if desired (e.g., Kaplan, Propeller, etc.).

A gate casing70surrounds the outer circumference of the runner23and supports a plurality of movable wicket gates75. The wicket gates75can be moved from a closed position to a full open position to control the quantity of flow through the runner23.

A draft chest80attaches to the gate casing70and directs the water from the discharge of the runner23to the draft tube45below. As illustrated inFIG. 2, both runners23discharge flow toward one another and into the common draft chest80that then directs that flow to the draft tube45and out through the tail race of the dam.

A governor shaft85extends above the runners23and is supported by a series of bearings65. As with the shaft25, the governor shaft85is preferably assembled from a number of shaft segments to simplify assembly, disassembly, and maintenance. The governor shaft85extends the full length of the various runners23and controls each set of wicket gates75for each runner23. Thus, a single control system positions all of the wicket gates75in substantially the same position during operation. In preferred constructions, a sensor senses the speed and/or load of the generator20and adjusts the wicket gate position to adjust that speed or load to a desired set point.

FIG. 3is a view of the turbine deck50ofFIG. 1following the implementation of the present invention. As can be seen, there are no significant structural changes to the turbine deck50, the power house15or any foundations. Rather, the present invention is installed using these existing features. For example, the pre-existing draft tube apertures55remain unchanged following the implementation of the present invention.

Three dry pit assemblies90similar to the one illustrated inFIG. 4are positioned on the turbine deck50with each dry pit assembly90surrounding one of the bearing pedestals60. The dry pit assemblies90include an egress tunnel95that extends above a high water line100and provides access to the interior of the dry pit90during operation. Each of the dry pits90thus defines an air space105around the bearing65that is accessible during operation.

With the pedestal60now positioned in an air environment, the existing sacrificial bearing65can be replaced with a fluid bearing110and preferably with an oil-flooded bearing110such as an oil-flooded babbitted bearing110. The use of oil-flooded bearings110greatly reduces the maintenance requirements and increases the life of the bearings110and the shafts25. In addition, if necessary, maintenance can be performed on one of the bearings110without dewatering the unit and without disassembly of the shaft25. In preferred arrangements, the shaft couplings40are also positioned within the dry pits90to provide access to the couplings40if necessary.

A runner assembly115is attached to each of the dry pits90and includes a replacement runner120or turbine and a series of wicket gates125supported for movement between an open and a closed position. The replacement unit includes four single-flow runners120with each single-flow runner120replacing one set of the prior double opposed runners23. Thus, while a similar runner design could be employed (e.g., Francis, Kaplan, Propeller, etc.) the runner120is typically larger to accommodate the additional flow through the runner120as each runner120must accommodate twice the flow of each of the prior runners23.

As illustrated inFIGS. 4 and 5, the wicket gates125are positioned around the outer circumference of the runner120and include a portion that extends into the adjacent dry pit90to provide for inspection during maintenance cycles or during operation. In addition, the linkage and hydraulic or electrical actuator130used to move the wicket gates125can be positioned within the dry pit90. For example, in one arrangement each wicket gate125is supported on a shaft that extends through the wall of the dry pit90. A common ring interconnects each shaft such that rotation of the ring produces a common rotation of each of the wicket gates125about their shaft axis. The ring, a portion of the wicket gate125, and the linkages therebetween are disposed within the dry pit90to facilitate periodic lubrication and maintenance.

As illustrated inFIG. 4, the wicket gates125are movable between a closed position and an open position. After the flow of water passes through the wicket gates125and the runner120, the flow is discharged into a draft chest assembly135(shown inFIG. 3) that receives only the flow from that particular runner120. The draft chest135then discharges the water to the draft tube45and out through the tailrace.

Each of the draft chests135includes a pipe140that operates as a vacuum breaker as will be discussed. One end of the pipe140is positioned within the draft chest135and the opposite end is positioned above the water line100. A valve145is positioned between the two ends to selectively provide fluid communication between the draft chest80and the atmosphere above the water line100.

A powerhouse dry pit150is positioned adjacent the outer wall of the powerhouse15to enlarge the space available for an improved thrust bearing155. The powerhouse dry pit150defines an air space160sized to receive a coupling165and the improved thrust bearing155. In preferred constructions, the thrust bearing155shown inFIG. 6, includes a dual action thrust bearing155that includes babbitted surfaces and oil lubrication. The thrust bearing155is larger than the prior thrust bearing due to an increase in operational flexibility as will be discussed below.

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 unit10. The replacement is accomplished with virtually no changes being made to the existing foundation, thereby reducing the cost of implementing the replacement.

The replacement of eight runners23that discharged through four draft tubes45with four runners120that discharge through four draft tubes45improves the overall efficiency of the runners120and reduces turbulence downstream of the runners120.

In addition, the operation of the wicket gates125for the individual runners120is separated with the upgraded design. Thus, all of the wicket gates125do 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 gates125is transmitted to the individual wicket gate actuators130via 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 runner120(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.

In addition to a wider load range, the unit can operate using only one runner120, two runners120, three runners120, or all four as may be desired. The separate vacuum breakers140allow a runner120to operate in air. With the wicket gates125closed, the valve145in the vacuum breaker pipe140is opened to allow the water within the runner120and draft chest135to drain. In some arrangements, compressed air is directed to the runner120to assure that all of the water is removed and the runner120is operating in air. Depending on which runners120are operating, the thrust load can change significantly thereby requiring the larger dual acting thrust bearing155. For example, if the two end runners120are receiving flow with the remaining runners120operating in air, the thrust would be somewhat balanced. However, if only the first end runner120or the first and second runners120from the left are operating, the trust would be significantly larger.

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.