WO2014168486A1

WO2014168486A1 - Underwater electromechanical power converter

Info

Publication number: WO2014168486A1
Application number: PCT/NO2014/050052
Authority: WO
Inventors: Alexey Matveev
Original assignee: Smartmotor As
Priority date: 2013-04-10
Filing date: 2014-04-10
Publication date: 2014-10-16
Also published as: NO335892B1; NO20130479A1

Abstract

Underwater electromechanical power converter (UEMPC) for submerged applications, consisting of at least two axially arranged parts (13, 15), wherein the first part (13) includes at least active parts in the form of stator (17) with end windings (30) and rotor (18) of an electrical machine and the second part (15) includes at least parts of a cooling circuit for the electrical machine. Core of the stator (17) of the electrical machine is arranged in direct contact with a housing (14) of the first part (13) of the UEMPC for transferring heat directly from the core of the stator (17) to the housing (14) by means conduction and there is arranged a circulation path for cooling medium (22) inside the UEMPC, so that the cooling medium (22) goes from a gap (31) between the rotor (18) and the stator (17) directly into the second part (15) of the UEMPC, where the cooling medium (22) is cooled down and is returned back to the first part (13) of the UEMPC.

Description

Underwater electromechanical power converter

The present invention relates to underwater electromechanical power converter for submerged applications, according to claim 1.

Especially the present invention is related to cooling of submersible electrical machines and builds on effective utilization of other parts of a submerged system, wherein the electrical machine is integrated.

Background

Cooling of electrical machines is an area with a wide variety of possible solutions. For stand-alone machines the solutions are mapped, grouped and described in IEC-60034-6 standard. Still many new cooling solutions have been proposed. One of the recent examples, WO12080566, describes that the heat exchange is taking place at the stator's radial periphery, where cooling elements are placed. Heat from both stator and rotor is transported to the stator periphery where the cooling elements are located.

It should be mentioned that many of the cooling solutions are characterized by radial transfer of heat from the rotor and stator to the housing and further to either coolant or the outer environment.

For the machines integrated with either driven equipment (in motoring applications) or prime movers (in generating applications) the solution space is extended compared to the scope described in IEC- 60034-6 and mechanical elements around the machine often give new opportunities and/or set new constraints. For example, many special cooling arrangements are known for rotating electrical machines integrated into wind- and tidal turbines. One of them, US2004179934, describes cooling arrangement of a generator in a nacelle of a wind turbine, where heat from the stator is transferred in radial direction to the nacelle's housing portion which has increased heat conductivity.

It should be noted again that in this example, as well as in the previous one, heat from the rotor and stator is transported first to the housing and further to the moving air, in wind applications, or water, in submerged applications, respectively.

Submerged power conversion units, such as nacelles of tidal turbines, often have a special shape serving the purpose of reducing hydrodynamic losses. Usually end portion of the nacelle has a shape of a cone (dome, semi-ellipsoid). In some cases the "cone" is used for placing instrumentation and/or cooling equipment; for example US20070007772 describes pumps placed in the end portion of the housing and in GB1031428 elements of system cooling, such as pumps, pipes, etc., are arranged in the end portion of the housing. In another example, JP6237554, the "cone" is used as a heat exchanger with two chambers: one chamber filled with water and another one filled with gas. The hot air comes radially from the rotor to the stator, then through the stator to the machine periphery, and finally it is pushed to the "cone", where heat exchange takes place between the water and the air (the two chamber of the heat exchanger). In another variant of the same invention JP6237554 the hot air pushed through the stator directly exchanges heat with the housing of the "cone".

It should be noted again, that, firstly, the heat generated by losses in the rotor and the stator goes first in radial direction and, secondly, that almost all the heat goes through stator. Further, that heat from the stator goes first to the air circulating inside the nacelle and then to the nacelle housing and finally to the outer environment. This heat transfer chain is quite inefficient and leads to local overheating, e.g. of the stator windings or the rotor magnets.

To summarize, the common problems of many existing solutions are, first of all, poor cooling of the rotor due to that the resistance for the heat flow going from the rotor to the outer environment is high, and, secondly, stator overheating as a consequence of all heat flowing through the stator. Minor drawback of some prior art systems is presence of numerous cooling elements, e.g. small independently driven pumps or fans, reducing total system reliability.

Object

The main object of present invention is to solve the problems of prior art for the class of submerged systems by means of redirecting heat flows so that the path from each heat source to the cooling environment is the shortest.

It is further an object of the present invention to effectively utilize other parts of a submerged system, wherein an electrical machine is integrated, such as for example extending end portion of system housing for improved cooling.

Another object is to provide an underwater electromechanical power converter for submerged systems provided with natural cooling for avoiding extra cooling elements, such as independently run fans or pumps.

It is an object of the present invention to provide an underwater electromechanical power converter for submerged applications increasing the cooling capability of submerged electrical machines and thus improving the efficiency, reliability and achieve higher power densities and higher power ratings of the electrical machines. The invention

An underwater electromechanical power converter for submerged applications according to the present invention is described in claim 1.

Preferable features of the underwater electromechanical power converter are described in the remaining claims.

In the present invention machine is regarded together with other parts of a submerged system, where the electrical machine is integrated, forming a so-called "underwater electromechanical power converter" (UEMPC). An UEMPC includes at least two axially arranged parts, wherein the first part contains active parts of the electrical machine and the second part contains parts of a cooling circuit for the electrical machine.

According to the present invention, heat flows in the electrical machine are rearranged in such a manner that heat transfer paths from heat sources to the environment (which is water) are as short as possible. Main part of the heat produced in stator of the electrical machine is arranged to go in radial direction to a housing of the first part of the UEMPC and further to the environment, i.e. water outside, while minor part of the heat produced in the stator together with heat produced in rotor of the electrical machine is arranged to go in axial direction to the second part of the UEMPC, where it is cooled down and is returned back to active parts, i.e. rotor and stator (with windings) of the electrical machine.

According to an embodiment of the present invention there are arranged radial gaps and/or axial passages in the rotor through which some part of the cooling medium can flow.

According to the present invention, stator core (usually laminated iron) of the electrical machine is arranged to be in direct contact with the housing of the said first part of the UEMPC so that heat is transferred directly from the stator core to the housing by means of conduction.

To transport the mentioned minor part of the heat there is arranged a path for a cooling medium circulating inside the UEMPC so that hot gas or liquid goes from a gap between the rotor and the stator directly into the second part of the UEMPC, where the cooling medium is being cooled down, after which it is returned back to the said first part of the UEMPC and finally is returned again to the gap between rotor and stator.

According to the present invention there can be different patterns (paths) of circulation of the cooling medium. According to one embodiment of the present invention the cooling medium, after it is cooled down in the second part of the UEMPC, is returned to center of the first part of the UEMPC and finally returned again to the gap between rotor and stator.

According to another embodiment of the present invention the cooling medium, after it is cooled down in the second part of the UEMPC, is returned back to the gap between rotor and stator on a side on the electrical machine being opposite to the side where the cooling medium left the gap before entering the second part of the UEMPC.

According to the present invention circulation of the cooling medium can be provided by blades, fans, pumps or similar. The blades can be fastened to a shaft of the electrical machine. Further, the blades can have flexible adjustable parts directing the flow of the cooling medium.

According to the present invention the cooling medium may be a gas, such as air or hydrogen, or a liquid. The gas can be compressed and/or dried to avoid condensation.

The mentioned second part of the UEMPC according to the invention can have the shape of a cone or a semi-ellipsoid serving the double purpose: firstly, absorbing heat from the cooling medium and, secondly, preventing turbulence at the end of the UEMPC.

Furthermore, the second part of the UEMPC can have curvatures according to speed range and profile of external water flow so that turbulence of the external flow at the end of the UEMPC is reduced.

The said second part of the UEMPC includes a housing which consists of at least one layer with channels between the layers where the cooling medium can flow.

The UEMPC according to the present invention can be integrated with other drive train elements of a submerged system, e.g. a gearbox or a brake, forming an elongated body with low resistance to the water flow.

According to the present invention, for some applications, maximum outer diameters of the other drive train elements, e.g. a gearbox or a brake, with which the UEMPC is integrated, should differ from the UEMPC's own diameter by not more than 20 %. Also diameters of the own parts of the UEMPC should not differ by more than 20%. Such small step changes in the diameter of the elongated body, formed by the drive train elements, will create small turbulence vortexes in the flow improving heat transfer from the surface.

Further preferable features and advantageous details of the present invention will appear from the following example description. Example

The present invention will below be described in further detail with references to the attached drawings, where:

Figure la-b show a comparison of differences in arrangement of heat flows in a prior art solution an the present invention,

Figure 2 is perspective view of an underwater electromechanical power converter being the part of tidal turbine,

Figures 3a-b is sectional view of an underwater electromechanical power converter according to the present invention having a cone-shaped end portion,

Figure 4 is sectional view of an underwater electromechanical power converter according to the present invention having a different cooling pattern from the one shown in Figures 3a-b,

Figure 5 is sectional view of an underwater electromechanical power converter according to the present invention having fans attached to a shaft,

Figure 6 is sectional view of an underwater electromechanical power converter according to the present invention having a straight end portion, and

Figure 7a-d show sectional views of variant of elements of the cooling circuits.

References are now made to Figures la-b which show the main differences between prior art solution and the present invention, respectively.

In Figure la a prior art system equivalent to the proposed underwater electromechanical converter

(UEMPC), in the form of a submerged turbine, is shown where heat 21 generated in a rotor 18 of an electrical machine goes first to a stator 17 of the electrical machine and further to a space 40 between a housing 11 for the electrical machine and a nacelle housing 12, before it is removed from the electrical machine through the nacelle housing 12. The resistance for flow 22 of the heat 21 is therefore very high and could result in that the rotor 18 is overheated or the load of the electrical machine should be reduced.

Reference is now made to Figure lb which shows an UEMPC, according to the present invention. In the present invention the UEMPC is divided into the two parts 13 and 15, where the first part 13 includes a housing 14 which contains the electrical machine and the second part 15 includes a housing 16.

According to the present invention the housing of the electrical machine is integrated in the housing 14 of the first part 13 and the second part 15 is arranged for the cooling purposes. The difference between the present invention and the prior art solution is that the heat 21 from the rotor 18 does not go in radial direction but instead is transported in axial direction directly to the second part 15 of the UEMPC.

Further, in the prior art solution (Figure la) heat 20 generated in the stator 17 is merged with the heat 21 coming from the rotorl8 and goes in radial direction into the space 40 between the electrical machine housing 11 and the nacelle housing 12, before it is removed from the electrical machine through the nacelle housing 12. In the present invention (Figure lb) heat 20 generated in the stator 17 has two removal paths; a radial one directly to external water flow through the housing 14 of the first part 13 of the UEMPC and axial one to the housing 16 of the second part 15 of the UEMPC.

An effect of the present invention is that the resistance for the heat flows 22 is minimized and overheating of both rotor 18 and stator 17 is avoided, and load of the electrical machine can be increased compared to the prior art solution.

Reference is now made to Figure 2 which shows an application example of a submerged energy conversion system according to the present invention in the form of a tidal turbine, with nacelle 29 including an axially arranged gearbox 26, brake 27 and the two parts 13 and 15 of the UEMPC. This system will be used as the main example further in the description, though other applications, e.g.

podded propulsion units, subsea pumps or dredging pumps could be used as examples as well.

Reference is now made to Figure 3a which shows a sectional view of the U MEPC according to the present invention which consists of two parts, first 13 and second 15a, and a part of other drive train components 23 with which the UEMPC can be integrated. Note that the second part 15a of the UEMPC in this embodiment is cone-shaped.

The other drive train components 23 can be, for example, brake 27 or gearbox 26 from Figure 2.

The first part 13 of the UEMPC consists of a housing 14, active parts of the electrical machine, i.e. stator 17 with end windings 30 and rotor 18, and mechanical components like shaft 19 and bearings 24.

In the present invention the heat from stator 17 and rotor 18 goes first to a gap 31 between the stator 17 and the rotor 18 and then together with a cooling medium 50, e.g. air, goes directly to the second part 15 of the UEMPC, where the cooling medium 50 is cooled down by means of transferring the heat to the housing 16 of the second part 15 and further to the environment, i.e. water. The cooling medium 50 is returned back to the gap 31 through inner side of rotor's 18 active parts. Additionally this path collects the heat from inner side of the rotor 18, thus providing efficient cooling.

As the second part 15 of the UEMPC has the shape of a cone, turbulence in the external flow is reduced. The solution also provides a space 28 for auxiliary equipment, e.g. electrical instrumentation. The housing 16 of the second part 15 of the UEMPC can be double-layer, providing a system of guiding channels, thus allowing larger contact area for more efficient heat exchange.

Reference is now made to Figure 3b which shows a sectional view of the U MEPC according to the present invention where part of the cooling medium 50 goes through passages in the rotor 18 are shown.

Reference is now made to Figure 4 which shows an embodiment according to the present invention with another pattern of cooling medium circulation. The cooling medium 50, after it is cooled down in the second part 15 of the UEMPC, is returned back to the gap 31 between the rotor 18 and stator 17 on the side of the electrical machine being opposite to the one where the cooling medium 50 left the gap 31 before entering the second part 15 of the UEMPC.

A space 28 inside the second part 15 of the UEMPC can be used for auxiliary equipment. Alternatively, it can be filled with water having direct contact with the external water to provide better cooling.

Reference is now made to Figure 5 which shows an alternative embodiment of the one shown in Figures 3a-b. In this embodiment fans 25 are arranged for providing circulation of the cooling medium 50. The natural benefit of the present invention is that diameter of the elongated body formed by the neighboring parts, i.e. drive train components 23 and parts 13, 15 of the UEMPC changes in small steps to arrange small turbulence vortexes in the external water flow on surface of the unit, thus improving heat transfer from the surface.

Reference is now made to Figure 6 showing an embodiment of the present invention where the housing 16 of the second part 15 of the UEMPC has a more traditional cylindrical shape. There can be other equipment integrated with the second part 15 in axial direction.

According to the present invention heated cooling medium can be used for pre-heating other components, e.g. electronics placed in the free space 28 of the second part 15 of the UEMPC. For example, when the submerged system, which the UEMPC is a part of, is to be started from cold state, it is beneficial to warm the cooling medium 50 (e.g. air) inside the UEMPC and then use it to heat up parts which need pre-heating before switching on.

Reference is now made to Figures 7a-d showing several variants of elements of the cooling circuit.

The cooling of the cooling medium 50 takes place in the second part 15 of the UEMPC. There can be arranged channels 32 for the cooling medium by having the housing 16 consisting of layers 35. There can be two layers, as shown in Figures 7a, c and d or more as shown in Figure 7b. There can be arranged fins on outer surface 33 of the UEMPC and inside 34 the layers 35 of the housing 16 of second part 15 of the UEMPC. The channels 32 can go around the whole periphery of the UEMPC, as shown in Figures 7a-c, or its parts, as shown in Figure 7d.

List of numerals:

11. Housing of electrical machine in prior art

12. Housing of a nacelle of a tidal turbine in prior art

13. First part of underwater electromechanical power converter

14. Housing of the first part of underwater electromechanical power converter

15. Second part of underwater electromechanical power converter

16. Housing of the second part of underwater electromechanical power converter

17. Stator of electrical machine

18. Rotor of electrical machine

19. Main shaft of underwater electromechanical power converter

20. Source of losses in stator

21. Source of losses in rotor

22. Heat flows

23. Drive train components with which the underwater converter can be integrated

24. Bearings

25. Fans

26. Gearbox

27. Brake

28. Free available space in the second part of underwater electromechanical power converter 29. Nacelle of a tidal turbine

30. End windings of the stator

31. Gap between stator and rotor

32. Channels for cooling medium in the second part

33. Fins on the outer converter surface

34. Fins inside the layers of the housing of second part of converter

35. Layers of the housing

40. Space between a housing for the electrical machine and a nacelle housing

50. Cooling medium

Claims

ims

Underwater electromechanical power converter (UEMPC) for submerged applications, consisting of at least two axially arranged parts (13, 15), wherein the first part (13) includes at least active parts in the form of stator (17) with windings (30) and rotor (18) of an electrical machine and the second part (15) includes at least parts of a cooling circuit for the electrical machine, characterized in that

- core of the stator (17) of the electrical machine is arranged in direct contact with a housing (14) of the first part (13) of the UEMPC for transferring heat directly from the core of the stator (17) to the housing (14) of the first part (13) by means of conduction, and

- there is arranged a circulation path for cooling medium (22) inside the UEMPC, so that the cooling medium (22) goes from a gap (31) between the rotor (18) and the stator (17) directly into the second part (15) of the UEMPC, where the cooling medium (22) is cooled down and is returned back to the first part (13) of the UEMPC.

Underwater electromechanical power converter according to claim 1, characterized in that the second part (15) has the shape of a cone or a semi-ellipsoid and is arranged for absorbing heat from the cooling medium (22) and preventing turbulence at end of the UEMPC.

Underwater electromechanical power converter according to claim 2, characterized in that the second part (15) is provided with curvatures according to speed range and profile of external water flow reducing turbulence of the water flow at the end of the UEMPC.

Underwater electromechanical power converter according to claim 1, characterized in that the cooling medium (22), after it is cooled down in the second part (15) of the UEMPC, is returned back to center of the first part (13) of the UEMPC and finally is returned again to the gap (31) between rotor (18) and stator (17).

Underwater electromechanical power converter according to claim 1, characterized in that the cooling medium (22), after it is cooled down in the second part (15), of the UEMPC is returned back to the gap (31) between the rotor (18) and stator (17) on a side of the electrical machine being opposite to the side where the cooling medium (22) left the gap (31) before entering the second part (15) of the UEMPC.

6. Underwater electromechanical power converter according to claim 1, characterized in that the second part (15) of the UEMPC includes a housing (16) of consisting of at least one layer (35) with channels (32) between the layers (35) where the cooling medium (22) can flow. 7. Underwater electromechanical power converter according to any one of the claims 1-6,

characterized in that fins are arranged inside or outside the second part (15) of the UEMPC, e.g. in the channels (32) or on outer surface (33) of the UEMPC.

8. Underwater electromechanical power converter according to claim 1, characterized in that it is filled, at least partly with pressurized gas, such as air or helium.

9. Underwater electromechanical power converter according to claim 1, characterized in that the

second part (15) is filled, at least partly with water having contact with the external water. 10. Underwater electromechanical power converter according to claim 1, characterized in that

circulation of the cooling medium (22) is provided by means of blades, fans or pumps.

11. Underwater electromechanical power converter according to claim 10, characterized in that the blades are fixed to a shaft (19) of electrical machine.

12. Underwater electromechanical power converter according to claim 11, characterized in that the blades have flexible adjustable parts directing the cooling medium flow.

13. Underwater electromechanical power converter according to claim 1, characterized in that it is integrated with other drive train components (23) of a submerged application, such as a gearbox (26) or a brake (27), forming an elongated body with low resistance to the water flow.

14. Underwater electromechanical power converter according to claim 13, characterized in that

maximum outer diameters of the other drive train components (23), such as a gearbox (26) or a brake (27), with which the UEMPC is integrated, differ from the UEMPC's own diameter by not more than 20 %.

15. Underwater electromechanical power converter according to claim 1, characterized in that there are radial gaps and/or axial passages in the rotor (18) through which a part of the cooling medium can flow. 16. Underwater electromechanical power converter according to claim 1, characterized in that the heated cooling medium (22) can be used for pre-heating other components, such as electronics placed in free space 28 of the second part (15) of the converter.