Cooling system for an exciter system of a salient-pole machine

Abstract

The invention relates to a cooling system for an exciter system of a salient-pole machine, wherein the cooling system comprises a multiplicity of rim channels (5); the axial length of a rim channel is l_RK; the axial distance between two rim channels opening into the same pole gap (4) is a; each pole gap is divided, by an axially parallel plane extending between the radially innermost winding layers of the associated poles (1), into an inner region (4.1) and an outer region (4.2); in at least one pole gap, the associated at least one pole gap channel has a continuous constriction in the inner region; a radial distance between a radially outer end of the rim channels opening into the pole gap in question and a radially inner end of the continuous constriction is h_rim_PL; and at least some of the rim channels opening into the pole gap in question are designed such that the following relationships are satisfied: 2 ≤ a / l_RK ≤ 20; h_rim_PL / l_RK ≤ 20.

Description

[0001] Cooling system of an excitation system of a salient pole machine

[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.

[0003] A salient pole machine comprises a rotor ring on which the poles of the excitation system are arranged radially outwards. The rotor ring is usually 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 poles. A large number of channels extend between the cavity(ies) and the pole gaps. The 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. 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 guide elements, which are attached to the rotor ring at their roots. The air guide 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.

[0005] In addition, cooling systems are also known from the prior art in which the rotor poles and pole gaps do not have any special features to improve cooling. In these embodiments, the cooling medium exiting the channels flows radially outward through the pole gaps. These simple embodiments are usually used when the pole gaps are comparatively narrow and have a small opening angle, so that harmful flow separation cannot occur. For example, see CN 101123381 A.

[0006] The object of the invention is to provide an alternatively constructed cooling system of an excitation system of a salient pole machine, which has very good cooling properties and is of simple construction.

[0007] 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.

[0008] The invention is explained below with reference to the figures. The figures show in detail:

[0009] Fig. 1 : Cooling system according to the state of the art

[0010] Fig. 2: Cooling system according to the state of the art

[0011] Fig. 3: Cooling system in a section parallel to the rotor axis Fig. 4a: Flow pattern in a cooling system according to the invention

[0012] Fig. 4b: Flow pattern in a cooling system according to the invention

[0013] Fig. 5: Cooling system according to the invention in a first embodiment

[0014] Fig. 6: Cooling system according to the invention in a second embodiment

[0015] Fig. 7: Cooling system according to the invention in a further embodiment

[0016] Fig. 8: Cooling system according to the invention in a further embodiment

[0017] Fig. 9a: Flow pattern in a cooling system according to the invention

[0018] Fig. 9b: Flow pattern in a cooling system according to the invention

[0019] Fig. 10: Flow pattern in a cooling system according to the invention

[0020] Fig. 11 : Cooling system according to the invention in a further embodiment

[0021] Fig. 12: Cooling system according to the invention in a further embodiment

[0022] Figure 1 shows a section of a cooling system of a salient-pole machine according to the prior art in a first embodiment. The salient-pole machine comprises a rotor which can rotate about an axis and which has a plurality of poles. Pole gaps are arranged between the poles. The section shows the salient-pole machine in the region of a pole gap and in the region 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 arranged between two poles, one of which is designated 1. A stator, designated 3, is arranged radially outward. The poles 1 are connected to a rotor rim, designated 2. A cavity, designated 6, is arranged radially inside the rotor rim 2. A so-called rim 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 rim channel 5 from the cavity 6 into the pole gap 4 to cool the winding of the excitation system. The winding of the excitation system is arranged at the poles 1.

[0023] In Figure 1, a distance is marked off that is also relevant for a cooling system according to the invention and is designated b_RK. This distance is the so-called (tangential) rim channel width, which is marked off perpendicular to a radius running centrally within the rim channel. If the width of a rim channel varies in the radial direction, the distance b_RK must be marked off at the radially outer end of the rim channel.

[0024] Since the cooling medium also flows through the pole gap 4, it can be considered a channel, which will also be referred to as the pole gap channel below. Unlike the rim channels 5, the pole gap channels 4 are not limited in the axial direction, i.e., in the direction of the rotational axis of the salient-pole machine, or are only limited at the axial ends of the poles. Each rim channel 5, however, is limited in the axial direction by parts of the rotor ring 2. A plurality of rim channels 5 open into each pole gap channel 4 (see Figure 3).

[0025] A pole gap 4 can be conceptually divided into two regions. A first region extends between the outer edge of the rotor ring 2 to a plane which runs parallel to the axis and extends between the radially innermost winding layers of the associated poles 1. This spatial section of a pole gap 4, also referred to below as the inner region, is designated 4.1 in Figure 1. The bounding plane is indicated in Figure 1 by the dashed line. Outside of this plane extends the second region of the pole gap 4, which is also referred to below as the outer region and is designated 4.2 in Figure 1. The heat transfer from the winding to the cooling medium mainly takes place in the outer region 4.2.

[0026] The embodiment shown in Figure 1 is suitable for salient-pole machines where the distance between the poles and the opening angle of the pole gaps, i.e., the ratio between the inlet and outlet cross-sections of the outer region 4.2, are not too large. If this is not the case, reduced cooling quality may occur due to low flow velocities or a separation of the cooling medium flow.

[0027] Figure 2 shows a prior art embodiment that is also suitable for salient-pole machines with large pole gaps and / or large opening angles. The illustration and designations are the same as in Figure 1. The embodiment in Figure 2 additionally includes a displacement body (airguide), designated 7, which is arranged in the pole gap in such a way that the pole gap channel is split into two branches. This prevents the flow from separating from the winding.

[0028] Figure 3 shows a section of a generic cooling system in a cross-section parallel to the rotational axis of the salient-pole machine. The hatched areas represent parts of the rotor ring 2. Rim channels are arranged between these, one of which is designated 5. The axial distance between two adjacent rim channels that open into the same pole gap is designated a. The axial length of the rim channels is designated l_RK. On the right, the two regions 4.1 and 4.2 adjoin a pole gap. The rim channels 5 open into the inner region 4.1, through which the cooling fluid finally reaches the outer region 4.2.

[0029] Conventional cooling systems feature tangentially wide rim channels and a high number of rim channels per pole gap, resulting in low flow velocities and thus low total pressure losses in the rim channels. The inner region 4.1 of the pole gap channel represents an axially continuous air volume in which the flow is axially evened out before the cooling fluid reaches the outer region. This design achieves the most directed, homogeneous radial flow possible even before entering the outer region 4.2.

[0030] To improve the cooling effect, the winding layers usually include cooling fins that extend laterally into the pole gap channel. In Figures 1 and 2, this is indicated by the tapered winding layers. As the cooling fluid flows past the cooling fins, small stationary vortices can form in the cavities between two cooling fins in a radial-tangential plane. This means that the axis of these vortices is aligned parallel to the rotational axis of the salient pole machine. Lateral momentum exchange with the main flow then occurs only due to turbulent fluctuations, resulting in low heat transfer. The inventors set themselves the task of modifying the known design so that different flow conditions arise in the pole gap channel, leading to improved heat transfer.According to the invention, this is achieved by flushing the cavities between adjacent cooling fins through specifically designed zones of axial velocity. This reduces the insulating stationary radial-tangential vortices in the cavities.

[0031] Figures 4a and 4b show the flow conditions desired according to the invention. Figures 9a, 9b, and 10 show further embodiments of the flow conditions desired according to the invention. The figures show the axial-tangential portion of the cooling fluid flow upon entry into the outer region.

[0032] 4.2, ie at the boundary between the inner area 4.1 and the outer area

[0033] 4.2. The viewing direction of the figures is therefore radially oriented. The dashed rectangles represent the projected contours of the outlet opening of the rim channels. The vertical solid lines represent the side walls of the pole gap channels. Figure 4a shows a cooling system according to the invention without a displacement body (cf. Figure 5), while Figure 4b shows a cooling system according to the invention with a displacement body (cf. Figure 6). The cooling system according to Figure 4b therefore has one branched pole gap channel per pole gap or two pole gap channels per pole gap. The axial-tangential flow components shown are in the form of vortices. Between two axially adjacent rim channels, two (Figure 4a) or four (Figure 4b) vortex zones are arranged. The radially oriented main flow is superimposed on the vortex zones shown.

[0034] According to the invention, the flow conditions shown in Figures 4a and 4b are created in that in the relevant pole gap in the inner region 4.1, at least one pole gap channel has a continuous constriction. It should be noted that a positive effect according to the invention is already achieved if at least one pole gap is designed according to the invention. However, it is advantageous if all pole gaps are designed according to the invention. Figure 5 shows a cooling system according to the invention without displacement bodies in the pole gaps. In the inner region 4.1, the pole gap channel has a continuous constriction. For this purpose, corresponding walls or bodies can be provided, which are arranged to the right and left of the poles in such a way that they represent a corresponding boundary of the inner region 4.1.Alternatively, appropriately modified components can be used, which are also used in conventional cooling systems to construct the poles in order to create a continuous constriction in the inner area 4.1 (see Figure 12).

[0035] When cooling fluid enters the pole gap channel 4 from the rim channel 5, this flow is restricted in the tangential direction by the constriction in the inner region 4.1. This causes the cooling fluid to deflect in the axial direction. If this deflection is more pronounced on one side of the pole gap channel, it represents the beginning of a vortex flow, which intensifies as the flow continues through the constriction. Strictly speaking, the constriction must therefore exhibit an asymmetry, so that the constriction begins earlier or is more pronounced on one side than on the other. The constriction can be designed this way (see Figures 7 and 8), but the rotation of the rotor of the salient pole machine creates such an asymmetry simply due to the Coriolis force acting on the cooling fluid. Essentially, the vortex formation described is similar to water flowing out of a sink.In Figure 5, the direction of rotation of the rotor is indicated by the circular arrow. Due to the Coriolis force, cooling fluid flowing out of the rim channel 5 is deflected to the right, so that the right side of the geometrically symmetrical constriction acts more strongly than the left side. The side of the pole gap against which the cooling fluid flowing out of the rim channel is pressed is commonly referred to as the "pressure side." The opposite side of the pole gap is referred to as the "suction side."

[0036] In order for the vortices shown in Figure 4a to form undisturbed, there must be sufficient space in the axial direction between the rim channels. The inventors have recognized that the positive effect sought according to the invention occurs to a significant extent when the axial rim channel spacing normalized to the axial rim channel length is in a range from 2 to 20, i.e. when 2 < a / l_RK < 20. From a normalized rim channel spacing of 2, the desired vortices can form. In the value range below 2, the flow conditions arise that were described above for known generic cooling systems. If the normalized rim channel spacing exceeds the value 20, the cooling gradually deteriorates compared to conventional cooling systems because the positive effect according to the invention is used up or overcompensated by the smaller number of rim channels.

[0037] It is advantageous if all rim channels have the same axial length l_RK and the axial distance a between adjacent rim channels is also the same, as this makes it easier to manufacture the rotor ring. In principle, however, it is possible for a cooling system according to the invention to have rim channels with different axial lengths. The axial distances a between two adjacent rim channels do not have to be the same. In this case, for the relationship 2 < a / l_RK < 20, the dimensions to be taken are those belonging to the rim channel in question, i.e. the axial length l_RK of the rim channel and the corresponding distance a to the adjacent rim channels. If the distance a to the adjacent rim channels is also not the same, then the smaller of the two distances is to be taken. A positive effect according to the invention already results if at least some of the rim channels belonging to the pole gap in question satisfy the aforementioned relationship.However, it is advantageous if all rim channels belonging to the respective pole gap satisfy the above relationship.

[0038] Figure 5 shows two further distances that are relevant for the advantageous design of a cooling system according to the invention. The distance designated h_rim_PL is the radial distance between the radially outer end of the rim channel and the radially inner end of the continuous constriction. The distance designated b_fPL is the free width of the pole gap at the radially inner end of the continuous constriction. In embodiments with a displacement body, b_fPL is plotted across both continuous constrictions (see Figure 7). It is advantageous if the continuous constriction begins as close as possible to the outer end of the rim channel. If, on the other hand, the distance h_rim_PL becomes too large, the vortex flows according to the invention can no longer form. Therefore, three value ranges for the distance h_rim_PL are considered, whereby it is normalized to the axial rim channel length l_RK. It is particularly advantageous if h_rim_PL / l_RK < 10.If 10 < h_rim_PL / l_RK < 20, then an increasingly small but significant positive effect still results. If h_rim_PL / l_RK > 20, then the vortex flows according to the invention can no longer form.

[0039] It is advantageous if the free width of the pole gap b_fPL approximately corresponds to the rim channel width b_RK. The inventors have recognized that it is advantageous if the ratio b_fPL / b_RK lies in a value range of 0.5 to 1.75. Furthermore, it is advantageous if the width of the rim channels is greater than their axial length. The inventors have recognized that it is advantageous if the ratio b_RK / l_RK lies in a value range of 1.2 to 100.

[0040] Figure 6 shows a cooling system according to the invention with a displacement body 7 in the pole gaps. A constriction is provided in the inner region 4.1 for each of the two branches of the pole gap channel. The constrictions on the pole sides are designed analogously to Figure 5. In the center, the constrictions are defined by a tapered extension of the displacement body 7 in the direction of the rotor ring 2. Compared to Figure 2, it is even more accurate to speak of two pole gap channels in the illustrated pole gap, since there is only a very small portion in the inner region 4.1 in which the two pole gap channels communicate with each other.

[0041] Figure 7 shows a further embodiment of a cooling system according to the invention. As in the embodiment according to Figure 5, the pole gap does not include a displacement body. The constriction in the inner region 4.1 is geometrically asymmetrical. In the illustrated embodiment, the constriction is formed exclusively by the phase on the pressure side, since the boundary of the pole gap on the suction side follows the direction of the cooling fluid flow. It should be noted that this also shifts the rim channel 5 to the right with respect to the centerline of the pole gap in the outer region 4.2, so that the outlet of the rim channel corresponds to the mouth opening of the constriction.

[0042] Figure 8 shows a further embodiment with geometrically asymmetric constrictions for the case of a pole gap with displacement body.

[0043] Figures 9a and 9b show the flow conditions corresponding to Figures 7 and 8 at the boundary between the inner region 4.1 and the outer region 4.2, analogous to Figures 4a and 4b.

[0044] Figure 10 shows the flow conditions at the boundary between the inner region 4.1 and the outer region 4.2 for a pole gap with a symmetrically acting constriction. This means that the cooling fluid flowing out of the rim channel is restricted to the same extent on both sides of the constriction and is deflected equally in the axial direction on both sides. This creates four vortex zones per rim channel, i.e. twice as many as with an asymmetrically acting constriction. Due to the Coriolis force, a symmetrically acting constriction must be geometrically asymmetric. Figure 11 shows a pole gap with a geometrically slightly asymmetric constriction so that, in interaction with the Coriolis force, the constriction acts symmetrically with regard to the deflection of the cooling fluid in the axial direction, allowing the flow conditions shown in Figure 10 to develop.

[0045] Embodiments according to the invention also exist for pole gaps with a displacement body, in which flow conditions analogous to those shown in Figure 10 are established for each pole gap channel.

[0046] Figure 12 shows a further embodiment of a cooling system according to the invention. The boundaries of the constriction are formed by components such as those used in conventional cooling systems. Part of the constriction is formed by the so-called insulation frames, the left of which is designated 9. For this purpose, the insulation frame is chamfered towards the pole gap and can be made thicker in the radial direction than would be required for the insulating effect. This offers the advantage that the inner end of the constriction can be brought closer to the outlet of the rim channel. Alternatively, or in combination, this can also be achieved by structural adjustments to the rotor ring. In addition, the innermost winding layer or several inner winding layers can form part of the boundary of the constriction. One winding layer is designated 8 and does not have a cooling fin and is chamfered accordingly.As a result, in the embodiment shown in Figure 12, the constriction extends somewhat into the outer region 4.2. Another component that can be used to limit the constriction is the so-called pressure frame. In Figure 12, a pressure frame is designated 10, which, however, is not used to limit the constriction in the embodiment shown. In addition to the components shown in Figure 12, additional walls or bodies can also be used to limit the constriction, as described above. It is particularly advantageous if such additional walls or bodies fill the entire space between the rotor ring and the underside of the pressure frame. In this way, the continuous constriction can begin directly at the radially outer edge of the rim channel (h_rim_PL = 0).

[0047] It should also be noted that the boundary walls of the constrictions do not necessarily have to be flat, as shown in the figures of this document. They can also have a curved shape or moderate kinks. Sharp steps are disadvantageous in any case. As an example of an unsuitable design of the pole gap channels, reference is made to the figures of the CN 216872984 U cited at the beginning. Although one can speak of a section-wise continuous narrowing of the pole gap channels in the inner region 4.1, the shape of the boundary of the pole gap channels on the pole side prevents vortex formation according to the invention, particularly due to the abruptly projecting winding.

[0048] 1 pole

[0049] 2 rotor rim

[0050] 3 Stator

[0051] 4 Pole gap or pole gap canal

[0052] 4.1 Inner region of the pole gap

[0053] 4.2 Outer region of the pole gap

[0054] 5 Rim Canal

[0055] 6 cavity

[0056] 7 Displacement body (airguide)

[0057] 8 winding layers

[0058] 9 insulation frames

[0059] 10 printing frames

Claims

Patent claims 1 . Cooling system of an excitation system of a salient-pole machine, wherein the salient-pole machine comprises a rotor rotatable about an axis, which rotor comprises a plurality of poles (1) with winding layers (8), 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 cooling system comprises a plurality of rim channels (5), and wherein each rim channel (5) extends between the at least one cavity (6) and a pole gap (4), and wherein the axial length of a rim channel (5) is l_RK, and wherein the axial distance between two adjacent rim channels (5) which open into the same pole gap (4) is a, and wherein each pole gap (4) comprises at least one pole gap channel, and wherein each pole gap (4) is separated by an axis-parallel plane which extends between the radially innermost winding layers of the associated poles (1) into an inner region (4).1 ) and an outer region (4.2), characterized in that in at least one pole gap (4) the associated at least one pole gap channel has a continuous constriction which is arranged in the inner region (4.1 ), and wherein a radial distance between a radially outer end of the rim channels (5) opening into the relevant pole gap (4) and a radially inner end of the continuous constriction is h_rim_PL, and wherein at least some of the rim channels (5) opening into the relevant pole gap (4) are designed such that the following relationships are satisfied:. 2 < a / l_RK < 20; h_rim_PL / l_RK < 20; so that during operation of the salient pole machine, axially tangentially extending vortex zones can form on the associated axis-parallel plane in a cooling fluid flowing through the rim channels (5) and the pole gap channels formed in this way.

2. Cooling system according to claim 1, wherein a tangential width of a rim channel (5) is b_RK, and wherein a free width of a pole gap (4) at a radially inner end of a continuous constriction is b_fPL, and wherein in the at least one pole gap (4) for at least some of the rim channels (5) which open into the at least one pole gap (4), the following relationship is satisfied: 0.5 < b_fPL / b_RK < 1.

75.

3. Cooling system according to claim 1 or 2, wherein a tangential width of a rim channel (5) is b_RK, and wherein in the at least one pole gap (4) for at least some of the rim channels (5) which open into the at least one pole gap (4), the following relationship is satisfied: 1.2 < b_RK / l_RK < 100.

4. Cooling system according to one of the preceding claims, wherein a displacement body (7) is arranged in each pole gap (4) such that each pole gap (4) comprises two pole gap channels.

5. Cooling system according to one of the preceding claims, wherein at least some of the rim channels (5) opening into the respective pole gap (4) are designed such that the following relationship is satisfied for them: h_rim_PL / l_RK < 10.

6. Cooling system according to one of the preceding claims, wherein all pole gap channels have a continuous constriction which is arranged in the inner region (4.1).

7. Cooling system according to claim 6, wherein all rim channels (5) are designed such that the relationships mentioned in claim 1 are satisfied for them.

8. Cooling system according to claim 7, wherein all rim channels (5) are designed such that the relationship mentioned in claim 2 is satisfied for them.

9. Cooling system according to claim 7 or 8, wherein all rim channels (5) are designed such that the relationship mentioned in claim 3 is satisfied for them.

10. Cooling system according to one of claims 7 to 9, wherein all rim channels (5) are designed such that the relationship mentioned in claim 5 is satisfied for them.

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