Cooling system for an exciter system of large salient-pole machines
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-05-28
- Publication Date
- 2026-04-08
AI Technical Summary
Existing cooling systems for excitation systems of large salient pole machines often form thermally insulating stationary vortex systems, reducing heat transfer and creating uneven cooling due to the steady inflow of the cooling medium, particularly on the suction side as the rotor rotates.
Incorporating obstacles within the channels that cause a time-varying fluctuation of the cooling medium, such as cylinders, prisms, or fluidic oscillators, to create coherent structures that interact with and flush out stationary vortices, improving cooling efficiency on both sides of the poles without requiring displacement bodies or special flow paths.
This approach enhances heat transfer by disrupting stationary vortices and ensuring improved cooling on the suction side, even when the flow is hindered, thus providing better thermal management for the excitation winding.
Smart Images
Figure EP2024064603_05122024_PF_FP_ABST
Abstract
Description
[0001] Cooling system for an excitation system of large salient pole machines
[0002] The invention relates to a cooling system for an excitation system of a salient-pole machine, wherein a fluid cooling medium, typically air, forces the cooling of the excitation winding. Such salient-pole machines are generally used as generators or motor generators, particularly in hydropower plants. Furthermore, the present invention relates to a method for retrofitting an existing salient-pole machine.
[0003] A salient pole machine comprises a rotor ring on which the rotor poles of the excitation system are arranged radially outwards. The rotor ring is generally made of sheet metal, i.e. metal disks stacked on top of one another in the axial direction, with each metal disk covering a segment of the contour of the rotor ring. At least one cavity is arranged radially inside the rotor ring. The so-called pole gaps extend in the circumferential direction between the rotor poles. A plurality of channels extend between the cavity(ies) and the pole gaps. The rotor poles carry the winding of the excitation system, which must be cooled during operation of the salient pole machine. The cooling medium flows from the at least one cavity through the channels into the pole gaps, past the winding of the excitation system.
[0004] Cooling systems for excitation systems of large salient-pole machines are known from the prior art. For example, WO 99 / 46848 A1 discloses such a cooling system. The cavity is formed by a cavity in the rotor shaft. As a special feature, the disclosed winding layers of the excitation system have openings that form flow paths through which the cooling medium is guided radially outward. The cooling medium flows radially outward both through the flow paths and through the pole gaps. In one embodiment of the disclosed cooling system, the salient-pole machine comprises elongated displacement bodies arranged in the pole gaps. The displacement bodies are aligned in the axial direction and extend over the greater part of the axial length of the limbs. The displacement bodies make it possible to increase the coolant velocity in the pole gaps and in the flow paths.
[0005] CN 205791875 U discloses a further cooling system. The salient-pole machine comprises a rotor holder consisting of two disks. The cavity is arranged between the two disks. The winding layers are rear-ventilated, i.e., cooling channels are arranged between the pole shaft and the winding. The disclosed salient-pole machine further comprises air guide blades (6) arranged in the channels of the rotor ring. The air guide blades comprise 2 to 3 air outlets, wherein the two outer air outlets are arranged such that air is guided into the cooling channels of the windings. If a third air outlet is provided, it is arranged in the middle of the other two air outlets. Air can flow into the relevant pole gap through the third air outlet.
[0006] CN 216872984 U discloses another cooling system. The salient-pole machine comprises a star-shaped rotor carrier (16). The cavity is arranged in the rotor carrier. The disclosed salient-pole machine comprises air guiding elements, which are attached to the rotor ring at their roots. The air guiding elements perform a similar function to the displacement bodies of WO 99 / 46848 A1. However, the windings in CN 216872984 U do not have openings that form flow paths.
[0007] The object of the invention is to provide an alternatively designed cooling system for an excitation system of a salient-pole machine, which has good cooling properties and does not require displacement bodies in the pole gaps or special flow paths in or on the winding layers. Furthermore, the object of the invention is to provide a method by which existing salient-pole machines can be retrofitted according to the invention.
[0008] The object is achieved according to the invention by an embodiment according to the independent claim. Further advantageous embodiments of the present invention can be found in the subclaims. The invention is explained below with reference to figures. The figures show in detail:
[0009] Fig.1 Section of a salient pole machine in a first embodiment Fig.2 Section of a salient pole machine in a further embodiment
[0010] Fig.3 Section of a salient pole machine in another embodiment
[0011] Fig.4 Section of a salient pole machine in another embodiment
[0012] Fig.5 Channel insert
[0013] Fig.6 Section of a salient pole machine with a channel insert Fig.7 Section of a salient pole machine with a channel insert
[0014] Figure 1 shows a section of a salient pole machine. The section shows the salient pole machine in the area of a pole gap and in the area of a channel which supplies the pole gap with cooling medium. The illustration in Figure 1 shows a section perpendicular to the axis of rotation of the salient pole machine. The pole gap is designated 4 and is located between two poles, one of which is designated 1. A stator, designated 3, is arranged radially outwards. The poles 1 are connected to a rotor ring, designated 2. A cavity, designated 6, is arranged radially inside the rotor ring 2. A channel, designated 5, extends between the cavity 6 and the pole gap 4. During operation of the salient pole machine, cooling medium flows through the channel 5 from the cavity 6 into the pole gap 4 in order to cool the winding of the excitation system.The winding of the excitation system is arranged at the poles 1 and is only indicated schematically in Figure 1. The arrangement shown in Figure 1 is known from the prior art (e.g., from WO 99 / 46848 A1 in Figure 1). It can also be used in salient-pole machines according to the invention, since it is sufficient for only some of the channels 5 to be designed differently from the illustration in Figure 1. The embodiments that deviate from the prior art are described in the following figures.
[0015] The number of channels 5 for cooling the excitation winding can be very high. It is not unusual for 40 or more such channels 5 to open into each pole gap. The different channels 5, which open into one and the same pole gap, are arranged next to each other in the axial direction.
[0016] The inventors have recognized that in a cooling system comprising only channels according to the embodiment of Figure 1, the steady flow of cooling medium through the channels 5 between the cooling fins of the excitation winding results in stationary vortex systems forming. These vortex systems have a thermally insulating effect and therefore reduce the heat transfer from the windings of the excitation winding to the cooling medium in the pole gap. Furthermore, due to the rotation of the rotor during operation, the flow of the cooling medium is directed to one side of the poles, resulting in reduced cooling on the opposite side (the "suction side").
[0017] The inventors therefore propose an embodiment of the channels 5 which results in the flow of the cooling medium at the outlet of the channel 5 exhibiting a time-varying fluctuation. The embodiments according to the invention are characterized in that at least one obstacle is arranged in the channel 5, which is designed such that a time-varying fluctuation of the cooling medium can develop at the outlet of the channel 5 during operation of the salient-pole machine. As a result of this fluctuation, coherent structures ("wake vortices") are created which interact downstream with the stationary vortices between the cooling fins and flush them out of the cavities. This also results in improved cooling on the suction side of the poles. These positive effects occur even though the flow of the cooling medium is initially impeded by the obstacle arranged in the channel.The shape of the obstacle is only crucial insofar as it is suitable for causing a time-varying fluctuation of the cooling medium. Figure 2 shows a first embodiment, which differs from the prior art arrangement according to Figure 1 in that an obstacle, designated 7, is arranged in channel 5. The obstacle 7 has the shape of a cylinder. An obstacle shaped in this way causes a Karman vortex street, as indicated by the winding arrow in Figure 2.
[0018] Figure 3 shows a further embodiment of the invention. In the embodiment shown in Figure 3, the obstacle 7 is shaped like a prism with a triangular base. This geometry creates a vortex wake, which is indicated by the small curved arrows.
[0019] Other suitable obstacle shapes not shown in the figures include columns with rectangular or trapezoidal bases. It should be noted that the obstacles do not necessarily have to be positioned centrally in the channel. They can also be placed off-center.
[0020] Figure 4 shows a particularly advantageous embodiment of the invention. In the embodiment according to Figure 4, the obstacle 7 is formed by the channel 5 being designed as a fluidic oscillator. For this purpose, the lateral walls of the channel are specially shaped. Furthermore, two obstacles are located in the channel, which are designed to form the feedback channels characteristic of the fluidic oscillator. Fluidic oscillators that have more than two obstacles are also known from the prior art. All known forms of fluidic oscillators are suitable for a salient-pole machine according to the invention.
[0021] Figures 2 to 4 show, by way of example, particularly advantageous shapes of obstacles 7. However, according to the invention, all shapes of obstacles 7 known from the prior art are suitable, which are suitable for causing a time-varying fluctuation of the cooling medium at the outlet of channel 5 during operation of the salient-pole machine. As already mentioned above, not all channels 5 need to have obstacles 7. It is sufficient to achieve the inventive effect if some of the channels 5 have such obstacles. For example, every second channel could have an obstacle 7 according to the invention.
[0022] The obstacles 7 according to the invention can be inserted into the channels 5 when the rotor ring 2 is built up layer by layer. The obstacles can be glued or otherwise fastened to the parts of the rotor ring 2 that are axially adjacent to the channels 5. Further advantages arise when the one or more obstacles 7 of a channel form part of an assembly, which is referred to below as a "channel insert." Such channel inserts can either be inserted into corresponding recesses in the rotor ring 2 during construction of the same, or can be subsequently inserted into the channels of an existing rotor ring, which enables easy retrofitting of an existing salient-pole machine with obstacles according to the invention.
[0023] Figure 5 shows the structure of such a channel insert using the example of a fluidic oscillator. The upper part of Figure 5 shows a lateral section through a channel insert. The viewing direction when the channel insert is in the installed position is the radial direction. The different parts of the channel insert are marked by the section lines AA and BB. The corresponding sections are shown in the lower part of Figure 5. The viewing direction when the channel insert is in the installed position is the axial direction. Section BB runs in an area that can be referred to as the cover. In the axial direction, one cover each forms the end of the channel insert. Between the two covers there is an area that could be referred to as the intermediate layer. Section AA runs in the intermediate layer. At least one obstacle is part of the intermediate layer.
[0024] In the lateral direction, the channel insert shown in Figure 5 is terminated by solid walls, which is advantageous in a fluidic oscillator because the lateral walls also form the lateral outer contour of the oscillator. In the case of differently shaped obstacles (e.g. like the shapes shown in Figures 2 or 3), lateral walls can be omitted. The outer contours of the two covers then adjoin the corresponding parts of the recesses in the rotor ring. In this case, various webs can be provided to additionally connect the two covers to stabilize the channel insert. Channel inserts can advantageously be made of plastic. A channel insert can be constructed from several connected cast parts or, particularly advantageously, can be manufactured from a single piece using an additive manufacturing process.
[0025] The channel insert shown in Figure 5 is designed such that it can completely fill the recess in the rotor ring 2 shown in Figure 1. In this case, i.e. if the channel insert from Figure 5 were inserted into the arrangement of Figure 1, the channel which connects the cavity 6 to the pole gap 4 would be formed entirely by the fluidic oscillator of the channel insert. Other embodiments are also conceivable in which the channel insert only fills part of the recess in the rotor ring. In this case, the channel between the cavity 6 and the pole gap 4 is partially formed by part of the recess and by the channel insert. Without a channel insert, i.e. as shown for example in Figures 1 to 3, the channel 5 is formed completely by the respective recess in the rotor ring 2.
[0026] Figure 6 shows a channel insert in its installed position. The obstacle 7 is shaped analogously to Figure 2. The use of a channel insert offers the advantage that the channel 5 can be extended radially beyond the outer contour of the rotor ring 2. The outer contour of the rotor ring 2 is indicated by the dot-dash line. This also allows the obstacle 7 to be positioned further outward in the radial direction. It is therefore closer to the excitation windings. In the embodiment shown, the obstacle 7 is even located completely outside the contour of the rotor ring 2. Since the fluctuation generated by an obstacle 7 decreases with the distance from the obstacle 7, the desired effect can be improved with the arrangement shown in Figure 6, since the obstacle 7 is positioned closer to the excitation winding than in the comparable embodiment according to Figure 2.In the radially outward direction, the channel insert rests against parts of the poles 1, so that the channel insert cannot slip out of the recess in the rotor ring 2 due to the centrifugal force acting during operation of the salient-pole machine. It could also be secured against slipping out in other ways, e.g., by gluing or another suitable connection to the rotor ring 2. Or by designing the channel insert as shown in Figure 7. Here, the channel insert is supported by means of projections on the inside of the rotor ring 2.
[0027] The method according to the invention for retrofitting an existing salient pole machine comprises the following step:
[0028] - Inserting one channel insert into at least some of the existing recesses in the rotor ring 2 of the salient pole machine
[0029] In this case, a channel insert inserted into a recess forms a channel with an obstacle arranged in the channel, which obstacle is designed in such a way that a time-varying fluctuation of the cooling medium can develop at an outlet of the respective channel during operation of the salient pole machine.
[0030] There are two ways of inserting them. The channel inserts can be inserted from the outside, i.e. from the pole gap 4, or from the inside, i.e. from the cavity 6. In the first case, at least the rotor must be removed from the stator 3. In the second case, the cavity 6 must offer sufficient space. Channel inserts without projections for support, such as the channel insert shown in Figure 5, can be inserted from both sides. A channel insert as shown in Figure 6 can only be inserted from the outside. In the case of Figure 6, this would also require the poles 1 to be removed from the rotor ring 2. A channel insert as shown in Figure 7 can only be inserted from the inside. Inserting from the inside is preferable to inserting from the outside, if applicable, as it requires considerably less effort.
[0031] Finally, it should be mentioned that in a salient pole machine according to the invention, different shapes of obstacles and / or differently designed channel inserts can be used, ie not all obstacles or channel inserts of the salient pole machine in question have one and the same shape or position.
[0032] List of reference symbols
[0033] 1 pole
[0034] 2 Rotor ring 3 Stator
[0035] 4 pole gap
[0036] 5 channel
[0037] 6 cavity
[0038] 7 Obstacle
Claims
Patent claims 1. A cooling system for an excitation system of a large salient-pole machine, wherein the salient-pole machine comprises a plurality of poles (1), pole gaps (4) arranged between the poles (1), a rotor ring (2), and at least one cavity (6) arranged radially within the rotor ring (2), and wherein the salient-pole machine comprises a plurality of channels (5), each channel (5) extending between the at least one cavity (6) and a pole gap (4), and wherein, during operation of the salient-pole machine, cooling medium can flow through the channels (5) from the at least one cavity (6) into the pole gaps (4), characterized in that at least one obstacle (7) is arranged in at least some of the channels (5), which obstacle is designed such that, during operation of the salient-pole machine, a time-varying fluctuation of the cooling medium can develop at an outlet of the associated channel (5).
2. Cooling system according to claim 1, wherein the at least one obstacle (7) has the shape of a cylinder.
3. Cooling system according to claim 1, wherein the at least one obstacle (7) has the shape of a prism with a triangular base.
4. Cooling system according to claim 1, wherein the at least one obstacle (7) and the associated channel (5) are designed to form a fluidic oscillator.
5. Cooling system according to one of the preceding claims, wherein the at least one obstacle (7) is part of a channel insert, and wherein the channel insert comprises two covers lying outward in an axial direction and an intermediate layer arranged between the covers, and wherein the obstacle (7) is part of the intermediate layer.
6. Cooling system according to claim 5, wherein the channel insert projects in the radial direction beyond an outer contour of the rotor ring (2).
7. Cooling system according to one of claims 5 or 6, wherein the channel insert has been manufactured using an additive manufacturing process.
8. A method for retrofitting an existing salient pole machine, wherein the salient pole machine comprises a plurality of poles (1), pole gaps (4) arranged between the poles (1), a rotor ring (2) and at least one cavity (6) arranged radially inside the rotor ring (2), and wherein the salient pole machine comprises a plurality of recesses, and wherein each recess extends between at least one cavity (6) and a pole gap (4), and wherein the method comprises the following step: - Inserting one channel insert each into at least some of the existing recesses in the rotor ring (2) of the salient pole machine; and wherein each channel insert comprises two covers lying on the outside in an axial direction and an intermediate layer arranged between the covers, and wherein a channel insert inserted into a recess forms a channel (5) with an obstacle (7) arranged in the channel (5), which is designed such that a time-varying fluctuation of a cooling medium can form at an outlet of the relevant channel (5) during operation of the salient pole machine, and wherein the obstacle (7) is part of the intermediate layer of the channel insert.