PCT Patent Application of Henry K Obermeyer

FIELD OF THE INVENTION

The present invention relates to reversible pump-turbines used for storage of electrical energy. Conventional pumped storage facilities as shown in Figure 1 b generally use an underground powerhouse to provide sufficient absolute pressure at the runner to prevent destructive cavitation. The elevation of the runner may be 100 meters below tailwater, for example. Constructing and maintaining such an underground facility is expensive and the expense does not decrease in proportion to size in the case of smaller facilities. There are therefore very few pumped storage facilities of less than 100 MW in North America. A typical conventional pump-turbine sectional elevation is shown in Figure 1 b. The prior art pump-turbine flow path with a 90 degree turn in the meridional plane is illustrated in Figure 1 c, this being similar to the flow path in the meridional plane of a conventional Francis turbine. The present invention relates to single purpose turbines and pumps as well as to reversible pump-turbines. With respect to prior art multi-stage pumps, the relationship between the impeller and diffuser in the meridional plane is shown in Figure 2, where the acceleration imparted by the runner (impeller) to the fluid is outward and downward, this results in an unnecessarily small runner tip diameter compared to the maximum water passageway diameter that in this case occurs in the diffuser. This unnecessarily small diameter results in limited head differential across each stage and in turn results in more stages and lower overall efficiency. SUMMARY OF THE INVENTION

The present invention establishes the required plant cavitation coefficient by positioning reversible pump-turbines with motor-generators, generally well below tailwater level in a generally vertical bore hole. Reversible pump-turbines with motor-generators will be referred to herein simply as "pump-turbines" or as "machines" The term "bore hole", rather than "shaft", is used herein to avoid confusion with the rotating shaft of the pump- turbine located therein.

Conventional pumped storage facilities position the runner well below tailwater elevation to suppress cavitation while keeping unit power and specific speed high. The critical cavitation coefficient for reversible pump-turbines is higher than it is for either turbines or pumps because the hydraulic profiles are a compromise between pumping and generating and are optimized for neither. Positioning of the runner below tailwater has heretofore required a deep and expensive excavation regardless of machine size and rating. The expense of excavation and underground construction has been cost prohibitive for small installations, of less than 100 MW, for example. Sites suitable for large installations are limited by geology, geography, competing land uses, and adequate transmission lines. Many suitable smaller scale sites exist, but existing reversible pump-turbines, even if scaled down in size and rating, still require excavation and construction costs that are prohibitive. The proposed configuration utilizes a simple and inexpensive bore hole of perhaps 1 to 3 meters in diameter to position a high specific output reversible pump-turbine sufficiently below tailwater elevation to suppress cavitation. Such bore holes are routinely drilled as a commodity construction service for reasonable prices. A steel liner and conduits for hoisting water, electrical and control cables, for example, may be grouted in place within the bore hole. Pump-turbines adapted to this type of installation may be configured as single stage machines or may be configured as multi-stage machines utilizing specially configured "diffuser bowls" similar in function to those used on multi-stage submersible pumps. These pump-turbines would not normally use conventional scroll cases. As such, stages of these pump-turbines may be stackable to allow standard hydraulic designs to be used over a wide range of head conditions. The use of standard pump-turbine stages is further facilitated by the fact that the required plant cavitation coefficient can be achieved by simply establishing the required vertical bore hole depth. Compared to conventional underground powerhouse pump-turbine installations, there is a less frequent need to design and manufacture site specific machinery and there is no need carry the penstock nor tailrace conduit to extraordinary depths, which would be cost prohibitive in conjunction with small pumped hydro installations at most locations. The use of standard components results in increased quantities of like parts at reduced cost. Reduced costs in turn enable a greater number of projects to be built with increased part quantities. Water flow to and from the reversible pump-turbine may be through coaxial penstocks positioned in the shaft above the pump-turbine assembly. The associated motor- generator may be submersible and in certain preferred embodiments located below the pump-turbine(s). Locating the motor-generator below the pump turbines allows for a larger diameter, and therefore more economical, motor-generator for a given bore hole size. Allocating substantially all of the bore hole cross sectional area to water

conveyance (up and down), rather than to space for the motor-generator, allows for the maximum power rating for a given diameter of bore hole.

The generator may alternatively be located outside of the water passageways and connected to the runner with a shaft. Such an arrangement may be cheaper than providing an underground powerhouse large enough to incorporate a scroll case, while allowing the use of a readily available air-cooled generator.

In a preferred embodiment, a removable manifold may be used to connect the inner pipe to tailwater and connect the outer pipe to the penstock leading to headwater. It is generally more efficient to connect the smaller diameter pump inlet/turbine outlet with the smaller of the coaxial pipes while connecting the larger pump outlet/turbine inlet with the larger of the two coaxial pipes. Alternative embodiments of this invention may utilize another arrangement as may be the case when multiple pump turbines might be installed, on a bulkhead, for example, in a common bore hole. The removable manifold may include an integral pneumatically controlled pressure relief valve. This integral pressure relief valve will itself reduce civil works costs by eliminating the need for a surge shaft and by reducing penstock surge pressure and penstock cost. Additionally, or alternatively, an air cushion may be left under the cover of the bore hole. Removal of the manifold allows removal of the machinery from the borehole. Dedicated hoisting equipment will facilitate installation, service, and maintenance without the need for confined space work. A water pressure actuated piston attached to the bottom of the reversible pump turbine may be used for raising and lowering. A spacer between the piston and the machine may be used to allow the machine to be raised entirely clear of the borehole.

Variable speed operation is facilitated by the ready availability of power control electronics developed for the wind industry. As in the case of wind turbine power converters, full power converters may be used in conjunction with permanent magnet motor generators and partial power converters may be used in conjunction with

(generally larger) doubly fed induction generators.

The bore hole in which the reversible pump-turbine is installed may include provision for delivery of pressurized water to the bottom of the shaft, through a conduit separate from the main bore hole to hydraulically hoist the equipment for maintenance and repair and to controllably lower the equipment into operating position. The electrical power connection is preferably configured to automatically engage when the machine is lowered and to automatically disengage when the machine is raised. Such a connector may use conventional "wet mate" marine electrical connector technology or may be use a combination of compressed gas, insulating oil and inflatable seals, for example, to establish robust electrical connections isolated from ground potential.

The bore hole in which the equipment is located may terminate at the upper portal, the lower portal or at any convenient intermediate location. In the case of installation in conjunction with an existing pipeline, the vertical shaft may be located according to desired pressure profiles resulting from operation, load rejection, and other

considerations.

The shaft cover may incorporate a pressure relief valve and may be used to cap off a surge shaft containing air. Multiple machines may be installed in a single shaft, on a common bulkhead, for example. The reversible pump turbines in accordance with the present invention may be used in conjunction with Pelton turbines, for example to facilitate generation at low power levels if required. The reversible pump turbines may be used in conjunction with off-stream seasonal storage reservoirs, where their primary purpose may be to raise water to the storage reservoir during high flow periods and to return water while recovering energy when stored water is required downstream.

In accordance with certain embodiments of this invention, gas pressure balanced pressure relief valves may be used to limit overpressure from water hammer.

An elbow with actuatable seals may be used in order to connect the draft tube to the tail race during operation. Inflatable seals may be used to seal the elbow in its operating position while allowing it to move freely during hoisting and lowering operations.

Inflatable seals or supports may also be used to fix the machine into position during operation and to release it to allow it to be raised for maintenance.

In accordance with a further aspect of the invention a reversible pump turbine runner or pump impeller is provided that imparts to the flow an upward velocity component. This upward velocity component allows the flow to proceed directly up through the diffuser or a guide vane - diffuser combination in the case of a reversible pump-turbine, or directly to a diffuser (stator) stage in the case of a multi-stage pump, while maximizing the ratio of impeller tip diameter to maximum water passageway diameter. In the case of the present invention this ratio may be 1 .00. This maximizes the head per stage and allows a greater head to be achieved with a single stage machine. Figures 19a, 19b, and 19c illustrate the flow in the meridional plane as well as the X -shaped appearance of the impeller blades when viewed toward the trailing edge.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic of a conventional (prior art) pumped storage facility.

Figure 1 b and 1 c are sectional elevation drawings of a conventional pump-turbine. Figure 2 is a schematic of a pumped storage facility in accordance with the present invention.

Figure 3 is a section through the meridional plane of a multistage pump of prior art. Figure 3a is an elevation view of the pumped storage facility of Figure 3a shown with the pump-turbine assembly partially removed.

Figures 4a and 4b are sectional elevations of a pressure relief valve configured for use with the present invention. Figure 5a and 5b are sectional elevation drawings of a reversible pump-turbine in accordance with the present invention.

Figure 6 is a cutaway rendering of a reversible pump-turbine and associated pumped storage facility in accordance with the present invention.

Figure 7 is a cutaway view of an elbow connection to the tailrace tunnel with an inflatable seal to secure and seal it in accordance with the present invention.

Figure 8 is a sectional elevation drawing of a pump-turbine installation with the vertical borehole collocated with the headworks in accordance with the present invention.

Figure 9 is a sectional elevation drawing of a pump-turbine installation with the vertical borehole collocated with the tailrace portal in accordance with the present invention. Figure 10 is a sectional elevation drawing of a pump-turbine installation with the vertical borehole located between the with the headworks and the tailrace portal in accordance with the present invention.

Figure 1 1 is a sectional elevation drawing of a pump-turbine installation with the vertical borehole located in association with an underground pressured water storage cavity that serves as the "upper" reservoir.

Figure 12 is a schematic of a pump in accordance with the present invention in association with an air/water accumulator, most likely underground, and a gas turbine.

Figure 13 is a schematic of a pump in accordance with the present invention in association with an air/water accumulator, most likely underground, and a gas turbine, wherein the air may be nearly isothermally compressed with the aid of water spray cooling. Figure 14 illustrates a tailrace connection elbow in accordance with the present invention that incorporates an inflatable seal that also serves as an adjustable pressure relief element. The inflatable seal (63) features a flow separation control fin 51 to reduce vibration during operation. Figure 15 illustrates a pumped storage installation in accordance with the present invention including a a tailrace connection elbow.

Figure 16 illustrates a pumped storage installation in accordance with the present invention including a tailrace connection elbow and a penstock entering the borehole at an elevation higher than the tailrace tunnel. Figure 17 illustrates a pumped storage installation in accordance with the present invention including a tailrace connection elbow.

Figure 18 illustrates a pumped storage installation in accordance with the present invention including a tailrace connection elbow.

Figures 19a and 19b are meridional plane sections of a multistage pump impeller in accordance with the present invention.

Figure 19c is and end on view looking into the discharge edge of the impeller of Figure 19b.

Figure 20 is a plan view schematic of 3 pump turbines installed in association with a single penstock and a single tailrace tunnel. Figure 22a is a pump turbine installation including a pressure relief valve.

Figure 22b is a schematic of a torque key positioned at the bottom of a bore hole for the purpose of preventing unintended rotation of the pump-turbine.

Figure 23 is a pressure relief valve in accordance with the present invention.

Figure 224a and 24b is a pressure relief valve in accordance with the present invention shown closed and open respectively.

Figure 25a and 25b is a pressure relief valve in accordance with the present invention shown closed and open, repectively. Figures 26a and 26b show a pressure relief valve in accordance with the present invention shown closed and open respectively.

Figures 27a and 27b show an installation of multiple pump-turbine/motor generators in a sigle bore hole. Figure 28 shows schematically one version of the pump turbine of the present invention.

Figure 29 shows another version of the pump turbine of the present invention.

Figure 30 shows another version of the pump turbine of the present invention

incorporating a cylinder gate rather than wicket gates.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to Figure 1 a, 1 b, and 1 c, a conventional pumped storage plant with a reversible pump-turbine is shown. There are several notably expensive features in such a conventional installation. These include;

1 ) A surge shaft that is typically needed to relieve waterhammer that can result from a load rejection.

2) An underground powerhouse below tailwater level. Such a powerhouse is

expensive to construct and is at risk of flooding due to human error or component failure. Flooding of an underground powerhouse is a hazard to the facility itself as well as to its operators.

3) The penstock and tailrace conduit must be routed, at great expense to the same low elevation as the powerhouse itself. Referring to Figures3a and Figure 3b, a reversible pump-turbine installation in accordance with the present invention is shown. No underground powerhouse is required. Instead, a vertical borehole or shaft 4 allows the pump-turbine and motor- generator assembly 1 to be installed, removed for maintenance as needed, and reinstalled, while providing the desired low height-of-setting of thee unit below tailwater. The height of setting must be sufficiently low that the plant cavitation coefficient (plant sigma) is greater than the critical cavitation coefficient (critical sigma), the cavitation coefficient being defined as the ratio of absolute pressure at the low-pressure side of the runner divided by the vapor pressure of water at the temperature of the water. Shaft 16 connects submersible motor-generator 8 to pump-turbine stages 9, 10, 1 1 , and 12. Vertical tailwater conduit 5 connects to diffuser 14 above the point of entry of penstock 2. Pressure relief valve 7 is preferably mounted to removable manifold 6. Removable manifold 6 bolts down to foundation 13 and connects to tailrace conduit 3 at flange 15a. Tailrace conduit 3 leads to the lower reservoir not shown. It should be noted that the number of stages may be adjusted according to head, height of setting, speed, installation rating and other factors. Penstock 2 connects to upper reservoir 70.

Tailrace conduit 3 connects to the lower reservoir 71 . Water flows through outer annulus 17 of borehole 4 toward the upper reservoir 70 as a pump and towards the pump turbine 43.

It should be noted that the removable portion may be further divided into conveniently separable subassemblies 6, 7, 14 and 5. For example, the manifold 6 might be lifted off first, the vertical portion of the tailrace conduit 5 might be lifted next, and the pump- turbine stages 9, 10, 1 1 , and 12 might be lifted last along with the motor-generator 8. In the case of a motor generator on top, the stator might be left in place while the rotor, shaft, and balance of the assembly might be lifted out last. Referring to Figures 4a and 4b, a cross section of a pressure relief valve suitable of use in conjunction with the present invention is shown in its opened and closed positions respectively. Diffuser 14 is connected to ribs 25. Ribs 25, ring 23, and ring 24 together radially support bladder 18 on its inner diameter surface when its inflation pressure is greater than the pressure in shaft 17. Inflatable bladder 18 is supported from below by flange 26 and on its OD by enclosure 7. The air pressure in bladder 18 may be precisely adjusted to just stop leakage from shaft 17 into manifold 6 (at tailwater pressure).

Referring to Figures 5a and 5b a sectional elevation of a pump-turbine in accordance with the present invention is shown. Runner 27 is designed around a toroidal flow path wherein water reverses direction by approximately 180 degrees in the meridional plane. Wicket gates 28 make up an axial flow distributor. Turbine diffuser 29 recovers turbine runner exit energy. Stay vanes 30 provide mechanical support to the distributor hub 31 , turbine diffuser 29 as well as wicket gate servo system 32. Generator 33 is preferably located below the turbine. Hoisting piston 34 may be used to raise and lower, using water pressure, the entire pump-turbine assembly with connected draft tube segments, pressure relief valve and elbow. Hoisting piston 34 may incorporate upper seal ring 35 and lower seal ring 36 to maintain a seal while passing across the tailrace connection.

Hollow shaft 72 may be used as a heat pipe evaporator in conjunction with the runner 27 serving as a condenser. Electrical connector 73 engages electrical receptacle assembly 74 when the machine is lowered. Shifting rings 75 and 76 provide torque to actuate wicket gates 28.

Borehole 4 is associated with rock face 77, grout 78 and steel liner 79.

Shaft seal assembly 80 keeps the generator enclosure dry.

Referring to Figure 6, Piston assembly 34 supports generator 33 and pump-turbine 37 during raising and lowering. Valve 38 may be used to shut off water from penstock 39. Tailrace conduit 40 connects to tailwater. Cover assembly 41 is removable. Referring to Figure 6, valve 42 may be used to fill vertical shaft 4 during hydraulic raising and lowering of pump-turbine-motor-generator assembly 43 with attached pipe, elbow, and pressure relief assemblies 44.. Lower portal 45 serves to launch TBM during construction phase and serves as pumping inlet works. Headworks 47 serves as upper portal during construction and as service platform during maintenance. Crane 48 may be used to disassemble draft tube segments, elbow assembly and pressure relief valve from pump-turbine for maintenance.

Referring to Figure 7 an elbow assembly 49 is shown. Inflatable seal 50 seals the upper end. Inflatable seal 51 closes the lower end. Elbow 52 directs flow to the tailrace conduit. Spool 53 travels with the pump-turbine during maintenance moves.

Referring to Figure 8 an installation is shown wherein the machine shaft 54 is located under the headworks 55.

Referring to Figure 9, the machine shaft 54 is located below the tailrace portal 56.

Referring to Figure 10, machine shaft 54 is located at a location between the headworks 55 and tailrace portal 56.

Referring to Figure 1 1 , Machine shaft 54 provides a connection to pressurized reservoir 58 as well as to tailrace tunnel 59.

Referring to Figure 12 a pressurized water reservoir 58 is shown in conjunction with a pressurized air column 59. Pump or pump/turbine 60 may be in accordance with this invention or may be conventional. Air 59 may be fed to a gas turbine generator set 61 .

Referring to Figure 13, spray cooling of the air being compressed may be used to provide isothermal air compression.

Referring to Figures 52a and 52b, multiple submersible pump-turbines 62a through 62f, installed together in the same machine shaft 54 are shown. Figures 54 and 55 show pump-turbines configured for installation on a bulkhead in a common machine shaft. Figures 56, 57, 16, and 17 depict one of many possible construction sequences.

Referring to Figure 18, a combined seal and PRV 63 positioned in machine shaft 54 is shown in conjunction with elbow 52 and tailrace conduit 40. Machine shaft liner 64 is shown. Referring to Figure 17, another embodiment is shown wherein inflatable seal 63 may also serve as a pressure relief valve.

Referring to Figure 18 another embodiment is shown with vanes 65 in elbow 52.

Referring to Figures 19a and 19b a runner for a pump or reversible pump turbine is shown wherein flow is directed along a smooth sinusoidal path within the meridional plane. Blades (vanes) impart circumferential acceleration vector and acceleration vectors within meridional plan to guide water through water passageway. Blade sequences may be normal to vector sum. The larger impellar is more efficient and provides higher head per stage. Impellars may be best made by 3D printing.

Referring to Figure 24 splitter vanes are used. Referring to Figure 27, multiple pump turbines are shown sharing a common penstock 2 and tailrace conduit 3.

Referring to Figures 30 to 41 , various pressure relief valve configurations are shown. Referring to Figures 46, 47, and 48, various installation alternatives are shown.

Claims: