Variable stiffness inter-pole connection structure and method of designing the same

Abstract

This invention discloses a variable stiffness inter-pole connection structure and its design method. The inter-pole connection structure includes two connecting pieces distributed along the inner and outer sides. The two ends of each connecting piece are planar segments, and the middle portion is a curved segment. The planar segments of the two connecting pieces are in contact, and the curved segments are bent away from the other connecting piece. The outer connecting piece is the first connecting piece, and the inner connecting piece is the second connecting piece. The stiffness of the first connecting piece is higher than that of the second connecting piece. The design method finds the most suitable stiffness value for the inter-pole connection using a stiffness equivalence method. By controlling the stiffness of the inter-pole connection, the inter-pole connection and lead-in head achieve the most reasonable stiffness match with surrounding components.

Description

Technical Field

[0001] This invention relates to a variable stiffness inter-pole connection structure and its design method, belonging to the field of hydro-generator set structural design. Background Technology

[0002] Pumped storage power station turbine generator sets are characterized by high speed, large torque, and large size. This causes the generator rotor to withstand significant centrifugal force, requiring materials with sufficient strength and a rational structure. Furthermore, the generator frequently switches between power generation and pumping operations, necessitating high fatigue resistance in all components. The inter-pole connections and leads are crucial components of the generator rotor, and their structural stress and stiffness are critical to the overall operation of the generator set. Inter-pole connections are divided into internal and external connections; internal connections are shorter, while external connections are longer. The inter-pole connections, leads, and surrounding components are all connected. The inter-pole connections and lead ends are bolted together, the inter-pole connections and clamps are connected by clamping force, the clamps and yokes are welded together, and the lead ends and coils are connected. Under centrifugal force, the rotor expands outward. Due to inconsistent deformation between the magnetic poles and yoke, a deformation difference exists, often resulting in excessive stress at the root of the lead end. This leads to insufficient stress and fatigue requirements, and past units have frequently experienced lead end fractures at the root. There is an urgent need to find a way to improve this structure. Summary of the Invention

[0003] The purpose of this invention is to address the aforementioned problems by providing a variable stiffness inter-electrode connection structure and its design method. By controlling the stiffness of the inter-electrode connection, the inter-electrode connection and lead head can achieve the most reasonable stiffness matching with surrounding components.

[0004] The technical solution adopted in this invention is as follows: A variable stiffness interpole connection structure includes two connecting plates distributed along the inner and outer sides. The two ends of the connecting plates are planar segments and the middle part is a curved segment. The planar segments of the two connecting plates are in contact with each other, and the curved segments are bent away from the other connecting plate. The outer connecting plate is the first connecting plate, and the inner connecting plate is the second connecting plate. The stiffness of the first connecting plate is higher than that of the second connecting plate.

[0005] Alternatively, the planar segment is L1, and the curved surface segment includes L2, which connects to the planar segment, and L3, which connects to L2.

[0006] Alternatively, the planar segments can be joined by welding.

[0007] Alternatively, the contact surface of the first connecting piece and the second connecting piece is the center surface, and the two connecting pieces have an asymmetrical structure along the center surface.

[0008] Alternatively, the distance between the curved surface segment of the first connecting piece and the center surface is greater than the distance between the curved surface segment of the second connecting piece and the center surface.

[0009] Alternatively, the thickness of the first connecting piece may be greater than the thickness of the second connecting piece.

[0010] Alternatively, the first connecting piece may be composed of at least one layer, the second connecting piece may be composed of at least two layers, and the second connecting piece may have more layers than the first connecting piece.

[0011] Alternatively, each layer of the connecting piece may be connected by welding.

[0012] Alternatively, the first connecting piece and the second connecting piece can be made of different materials.

[0013] A design method for an inter-pole connection structure includes the following steps: S1. Establish a finite element model of the inter-pole connection structure and the overall connection of the magnetic pole and the magnetic yoke. Based on the original structure, change the stiffness of the inter-pole connection by changing the elastic model. Through comparative calculation of multiple schemes, find a more suitable stiffness value to minimize the stress at the root of the lead wire. S2. Establish a separate finite element model of the inter-pole connection structure, and determine the geometric parameters of the connecting pieces in the inter-pole connection structure by means of stiffness equivalence.

[0014] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. The present invention provides a variable stiffness inter-pole connection structure. The design of the connecting plate-shaped line increases flexibility while minimizing stress at that point. Axial tensile force is transmitted from the two end planar sections to the middle, and the two connection points of the traction bending section move towards both ends. Under tension, stiffness is reduced, and stress is minimized when a unit displacement is applied.

[0015] 2. The variable stiffness inter-electrode connection structure provided by the present invention is designed as two connecting pieces, which are designed separately. The stiffness of the outer first connecting piece is higher than that of the inner second connecting piece. By adapting the low stiffness side to high stress and the high stiffness side to low stress, the stress distribution of the lead end can be made more uniform.

[0016] 3. The present invention provides a variable stiffness inter-electrode connection structure. This asymmetrical structure enables a more uniform stress distribution at the root of the lead head, thereby reducing stress concentration. It can be further subdivided into various forms. By controlling the stiffness of the inter-electrode connection, the inter-electrode connection and the lead head can achieve the most reasonable stiffness match with the surrounding components.

[0017] 3. The present invention provides a design method for a variable stiffness inter-electrode connection structure. By using the stiffness equivalence method, the most suitable stiffness value of the inter-electrode connection is found, so that the inter-electrode connection obtains the most suitable stiffness value to match the surrounding components, thereby minimizing the stress at the root of the lead head, and thus greatly improving the lead head's resistance to damage and fatigue performance. Attached Figure Description

[0018] Figure 1 This is a stress distribution diagram of the lead wire end.

[0019] Figure 2 This is a schematic diagram of inter-pole connection.

[0020] Figure 3 This is a specification of the inter-pole connection dimensions. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings.

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0023] For the original inter-electrode connection, the location of maximum stress occurs at the root of the lead end, such as... Figure 1 As shown, the left figure represents the stress of the external connection lead tip, and the right figure represents the stress of the internal connection lead tip. Analysis of the stress distribution reveals that the stress in the internal connection lead tip is significantly greater than the overall internal stress, with the maximum stress located on one side and lower stress on the other. This stress concentration is caused by a mismatch in stiffness between the inter-electrode connection and the lead tip relative to surrounding components; the inter-electrode connection has excessive stiffness. The external connection is longer than the internal connection, resulting in lower stiffness and consequently, lower stress in its lead tip compared to the internal connection. Therefore, reducing lead stress can be achieved by reducing the stiffness of the inter-electrode connection.

[0024] A variable stiffness inter-pole connection structure, such as Figure 2-3 As shown, it includes two connecting pieces distributed along the inside and outside. The two ends of the connecting pieces are planar segments, and the middle part is a curved segment. The planar segments of the two connecting pieces are in contact with each other, and the curved segments are bent to the side away from the other connecting piece.

[0025] Analysis of the original design revealed that the excessive stress at the lead tip was due to excessive stiffness in the inter-pole connection between the lead tip and the clamp. Therefore, reducing the stiffness of the inter-pole connection helps reduce stress at the root of the lead tip. However, the stiffness of the inter-pole connection is not necessarily better the smaller it is; it must be a suitable value that matches the stiffness of the surrounding components. Only then will the stress at the lead tip be minimized. If the stiffness is too small, the stress at the lead tip will increase in the opposite direction. In this design, the connecting piece increases flexibility; therefore, the design of the profile at this point must minimize the stress while increasing flexibility. Since the main stress state at this point is tension, i.e., the displacement difference generated by the rotor's centrifugal force between the magnetic poles and the yoke, the two flat sections at both ends serve as the transmission points of the tensile force and constrain the connecting piece. The flexibility of the curved section in the middle is much greater than that of the flat section of the same length, and the central bending creates a flattenable geometry. Axial tensile force is transmitted from the two flat sections at both ends to the middle, pulling the two connection points of the bending section towards both ends, thus reducing stiffness under tension. Meanwhile, the stress generation is only related to the elastic strain of the material and is independent of the flattening of the geometric shape, resulting in minimal stress under a unit displacement. Furthermore, since the highest stress point at the root of the lead is distributed on one side while the stress is lower on the other, the stress distribution is uneven. Therefore, the inter-electrode connection is designed as two connecting pieces, designed separately. The outer first connecting piece has higher stiffness than the inner second connecting piece. By adapting the lower stiffness side to high stress and the higher stiffness side to low stress, the stress distribution at the lead end can be made more uniform.

[0026] In another specific implementation, the planar segment is L1, and the curved segment includes L2, which connects to the planar segment, and L3, which connects to L2. At the connection points with different cross-sectional dimensions, a reasonable transition structure is designed to avoid local stress concentration. Specifically, the ratio of the total length of L2 to the length of L3 is approximately 2:1, meaning the curved segment is sequentially L2, L1, and L2, with each segment having approximately equal length. This minimizes the stress at the inter-segment connection.

[0027] In another specific implementation, the planar segments are connected by welding. Fixing the two connecting pieces ensures a stable connection during operation and prevents loosening that could lead to poor contact. This also reduces or eliminates rotor vibration and noise during rotation, ensuring normal generator operation and extending its service life.

[0028] In another specific implementation, the contact surface of the first connecting piece and the second connecting piece is the center plane, and the two connecting pieces have an asymmetrical structure along the center plane. For different deformation modes, the calculation method of stiffness, i.e. elastic modulus, is different, but it is generally related to its shape. Therefore, through the design of the asymmetrical structure, the stiffness of each of the two connecting pieces and the stiffness difference between them can be directly determined by their different shapes, and the deformation difference of the main structure on both sides can be coordinated by using different shapes.

[0029] Specifically, as an extension of the above-described implementation methods, the following approaches can be used to achieve the design of asymmetric structures.

[0030] In one specific implementation, the distance between the curved surface segment of the first connecting piece and the center surface is greater than the distance between the curved surface segment of the second connecting piece and the center surface. The raised heights a and b of the curved surface segments are set to be different in size, but the thickness at both ends is the same. The outer raised height a is smaller than the inner raised height b, increasing flexibility and thus reducing stiffness, achieving a stiffness difference design.

[0031] In another specific implementation, the thickness of the first connecting piece is greater than the thickness of the second connecting piece. For two connecting pieces of the same length and subjected to the same force, the greater the thickness, the larger the cross-sectional area, and thus the stronger the rigidity of the first connecting piece and the smaller the deformation.

[0032] In another specific implementation, the first connecting piece consists of at least one layer, and the second connecting piece consists of at least two layers, with the second connecting piece having more layers than the first connecting piece. When a sheet of equal thickness is split into multiple sheets, the flexibility of each single layer increases, and the more layers there are, the easier it is to deform, thus reducing the overall stiffness.

[0033] The above three asymmetric design methods can be selected or used in the design of connecting pieces. That is, in actual design, the bending height and / or thickness and / or number of layers of the first connecting piece and the second connecting piece are different, so as to achieve precise control of stiffness.

[0034] In another specific implementation, each layer of the connecting plates is connected by welding. Fixing the connecting plates between the layers can reduce or eliminate vibration and noise of the rotor during rotation, ensuring the normal operation of the generator and extending its service life.

[0035] In another specific implementation, the first connecting piece and the second connecting piece are made of different materials. Besides the asymmetrical structure along the central plane of the two connecting pieces, different materials can also achieve differences in stiffness. However, suitable materials must meet excellent electrical conductivity, comprehensive performance, and stiffness requirements simultaneously, making it difficult to find suitable materials at present. However, the feasibility of this implementation in future research and development is not excluded.

[0036] A design method for an inter-pole connection structure includes the following steps: S1. Establish a finite element model of the inter-pole connection structure and the overall connection of the magnetic pole and the magnetic yoke. Based on the original structure, change the stiffness of the inter-pole connection by changing the elastic model. Through comparative calculation of multiple schemes, find a more suitable stiffness value to minimize the stress at the root of the lead wire. S2. Establish a separate finite element model of the inter-pole connection structure, and determine the geometric parameters of the connecting pieces in the inter-pole connection structure by means of stiffness equivalence.

[0037] By finding the most suitable stiffness value for the inter-electrode connection through the stiffness equivalence method, the inter-electrode connection can achieve the most suitable stiffness value to match the surrounding components, thereby minimizing the stress at the root of the lead head, and thus greatly improving the lead head's resistance to damage and fatigue performance.

[0038] Furthermore, in this embodiment, based on the lead head shape, finite element calculations show that the stiffness of the second connecting piece is 0.7 to 0.9 times that of the first connecting piece. In subsequent designs, the actual stiffness of the two connecting pieces is designed according to this ratio.

[0039] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. The invention extends to any new features or combinations disclosed in this specification, and any modifications, equivalent substitutions, and improvements made within the spirit and principles of the invention should be included within the scope of protection of the invention. It is obvious to those skilled in the art that the invention is not limited to the details of the above exemplary embodiments, and that any detailed technical features not disclosed in these embodiments are prior art, which can be obtained by those skilled in the art from the prior art. Those skilled in the art can understand the specific manner in which the above terms are used in the embodiments of the present invention according to the specific circumstances, and this disclosure does not specifically limit the embodiments in this regard.

Claims

1. A variable stiffness inter-pole connection structure, characterized in that: It includes two connecting pieces distributed along the inner and outer sides, with planar segments at both ends and a curved segment in the middle; the planar segments of the two connecting pieces are in contact with each other, and the curved segments are bent away from the other connecting piece respectively; the outer connecting piece is the first connecting piece, and the inner connecting piece is the second connecting piece, with the first connecting piece having higher stiffness than the second connecting piece.

2. The inter-electrode connection structure as described in claim 1, characterized in that: The planar segment is L1, and the curved segment includes L2, which connects to the planar segment, and L3, which connects to L2.

3. The inter-electrode connection structure as described in claim 1, characterized in that: The planar segments are connected by welding.

4. The inter-electrode connection structure as described in claim 1, characterized in that: The contact surface of the first connecting piece and the second connecting piece is the center surface, and the two connecting pieces have an asymmetrical structure along the center surface.

5. The inter-electrode connection structure as described in claim 4, characterized in that: The distance between the curved surface segment of the first connecting piece and the center surface is greater than the distance between the curved surface segment of the second connecting piece and the center surface.

6. The inter-electrode connection structure as described in claim 4, characterized in that: The thickness of the first connecting piece is greater than the thickness of the second connecting piece.

7. The inter-electrode connection structure as described in claim 4, characterized in that: The first connecting piece is composed of at least one layer, the second connecting piece is composed of at least two layers, and the second connecting piece has more layers than the first connecting piece.

8. The inter-electrode connection structure as described in claim 7, characterized in that: The layers of the connecting piece are connected by welding.

9. The inter-electrode connection structure as described in claim 1, characterized in that: The first connecting piece and the second connecting piece are made of different materials.

10. A design method for an inter-pole connection structure, comprising the following steps: S1. Establish a finite element model of the inter-pole connection structure and the overall connection of the magnetic pole and the magnetic yoke. Based on the original structure, change the stiffness of the inter-pole connection by changing the elastic model. Through comparative calculation of multiple schemes, find a more suitable stiffness value to minimize the stress at the root of the lead wire. S2. Establish a separate finite element model of the inter-pole connection structure, and determine the geometric parameters of the connecting pieces in the inter-pole connection structure by means of stiffness equivalence.

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