Method for measuring roundness of draft tube of tubular turbine

Abstract

The invention discloses a method for measuring the roundness of a draft tube of a tubular turbine, which can effectively measure the roundness of the draft tube on the spot, so that the roundness and the installation accuracy of the draft tube meet the design requirements. The draft tube roundness measurement method comprises the following steps: establishing a draft tube model, and dividing the draft tube into a plurality of tube sections along the center line of the draft tube model; the draft tube model is imported into CAD, and the draft tube model is projected to a two-dimensional plane; establishing a polar coordinate system, and selecting a reference point; selecting an intermediate-diameter section from each pipe section, and determining a lofting point on the intermediate-diameter section of each pipe section; erecting a total station on the construction site, and measuring a lofting point on the pitch diameter section corresponding to each pipe section by using the total station; and carrying out roundness analysis according to the polar coordinates of the lofting points on each pipe section, and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of measurement, and in particular to a method for measuring the roundness of a draft tube of a tubular turbine. Background Art

[0002] A water turbine is a power machine that converts the energy of water flow into mechanical energy. In a hydropower station, the water upstream is led to the water turbine through a penstock, which drives the runner to rotate, drives the generator to generate electricity, and is discharged downstream through the draft tube. In a tubular turbine, the draft tube can not only smoothly lead the water flow at the runner outlet downstream, but also utilize the elevation difference between the downstream water level and the runner outlet to form a static vacuum at the runner outlet, thereby utilizing the suction height of the runner. It can also recover the kinetic energy of the water flow at the runner outlet, convert it into a dynamic vacuum at the runner outlet, reduce the kinetic energy loss at the runner outlet, and thus improve the efficiency of the water turbine. The installation of the draft tube requires its roundness to meet the requirements. If the roundness error of the draft tube is large, it will cause uneven flow of the water flow in the draft tube, resulting in eddy currents and local flow velocity changes, affecting the efficiency of the water turbine. It will also cause additional vibration and noise during the operation of the water turbine, leading to increased local wear on the inner wall of the draft tube and affecting the service life of the water turbine and the draft tube.

[0003] The measurement of roundness generally uses a micrometer for contact measurement. This measurement method is generally applicable to structures with small sizes. For large components such as the draft tube, which are installed at high altitudes, it is difficult to conduct on-site measurement using a micrometer. Therefore, how to measure the roundness of the draft tube on-site and make the roundness and installation accuracy design of the draft tube meet the requirements is an important technical problem faced in the process of measuring the roundness of the draft tube. Summary of the Invention

[0004] One of the purposes of the present invention is at least to provide a method for measuring the roundness of a draft tube of a tubular turbine, which can effectively measure the roundness of the on-site draft tube and make the roundness and installation accuracy of the draft tube meet the design requirements, aiming at how to overcome the problems existing in the above-mentioned prior art.

[0005] In order to achieve the above purpose, the technical solutions adopted by the present invention include the following aspects.

[0006] A method for measuring the roundness of a draft tube of a tubular turbine includes: Step S1: Establish a draft tube model and divide the draft tube into multiple pipe segments along the center line of the draft tube model; Step S2: Import the draft tube model into CAD and project the draft tube model onto a two-dimensional plane; Step S3: Establish a polar coordinate system and select a reference point; Step S4: Select a mid-diameter section from each pipe segment and determine the lofting points on the mid-diameter section of each pipe segment; Step S5: Set up a total station at the construction site and use the total station to measure the lofting points on the mid-diameter section corresponding to each pipe segment. Step S6: Conduct roundness analysis based on the polar coordinates of the lofting points on each pipe segment.

[0007] Preferably, the draft tube is a diffusive draft tube. When dividing the draft tube, divide the draft tube into three equal segments along the center line.

[0008] Preferably, in step S3, when establishing the polar coordinate system, determine the pole on the center line of the draft tube and use the direction perpendicular to the center line of the draft tube as the polar axis.

[0009] Preferably, in step S3, when selecting the reference point, follow the following principles: Select a location that can comprehensively observe the entire circular arc area of the draft tube as the reference point. If it is impossible to comprehensively observe the entire circular arc area of the draft tube through a single reference point, minimize the number of changes of the reference point. On the basis of meeting the aforementioned principles, determine the reference point on the center line of the draft tube.

[0010] Preferably, in step S4, when selecting the lofting points, rotate the polar axis uniformly by a preset angle along the circumferential direction of the mid-diameter section, and use the intersection point of the polar axis and the mid-diameter section as the lofting point to determine the coordinates of multiple lofting points.

[0011] Preferably, when rotating the polar axis, rotate the polar axis by 22.5 degrees each time to obtain 16 lofting points.

[0012] Preferably, in step S5, when setting up the total station, use the position of the reference point as the setup position of the total station; when measuring the lofting points, use the total station to measure the lofting points on the mid-diameter sections of the first pipe segment, the second pipe segment, and the third pipe segment in sequence, and obtain the distance and zenith angle from each lofting point on the mid-diameter section of the pipe segment to the total station. After measuring the lofting points on the mid-diameter section of each pipe segment, obtain a polar coordinate system with the center of the total station as the origin and the zenith angle of the total station as 0 degrees to record the information of each lofting point of this pipe segment.

[0013] Preferably, in step S6, during the roundness analysis, the polar radius of each lofting point is the radius of the corresponding draft tube segment; when conducting roundness analysis on a certain pipe segment, subtract the minimum polar radius Rmin from the maximum polar radius Rmax of this pipe segment to obtain the roundness error D. Compare the roundness error D of this pipe segment with the designed roundness error to determine whether the roundness of the installed draft tube meets the design requirements.

[0014] Preferably, the designed roundness error of the draft tube is not greater than 2 mm, the total station uses a 1″ level total station, and the distance between the reference point and the lofting point is not greater than 200 m.

[0015] Preferably, steps S5 and S6 are performed alternately. After each pipe section of the draft tube is installed, the lofting points on the median diameter section of this pipe section are measured in the same manner as in step S5, and the roundness error analysis is performed in the same manner as in step S6. When the roundness error meets the design requirements, the installation, lofting point measurement, and roundness error analysis of the next pipe section are carried out.

[0016] In summary, due to the adoption of the above technical solutions, the present invention has at least the following beneficial effects: By dividing the draft tube into multiple sections, selecting the median diameter section as the lofting section in each pipe section, taking the intersection points of the polar axis and the median diameter section contour as the lofting points in each median diameter section, and using a total station to sequentially measure the lofting points on each median diameter section, after obtaining the polar coordinates of each lofting point, performing roundness analysis is beneficial to reducing the on-site measurement difficulty of the draft tube roundness, simplifying the operation process, and ensuring the installation accuracy of the draft tube. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a flowchart of the roundness measurement of the draft tube of a tubular turbine according to an exemplary embodiment of the present invention.

[0018] Figure 2 is a schematic diagram of the cross-section of the draft tube according to an exemplary embodiment of the present invention.

[0019] Figure 3 is a schematic diagram of the median diameter section of the first pipe section according to an exemplary embodiment of the present invention.

[0020] Figure 4 is a schematic diagram of the median diameter section of the second pipe section according to an exemplary embodiment of the present invention.

[0021] Figure 5 is a schematic diagram of the median diameter section of the third pipe section according to an exemplary embodiment of the present invention.

[0022] Figure 6 is a schematic diagram of the lofting points of the draft tube according to an exemplary embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, so as to make the purpose, technical solution, and advantages of the present invention clearer and more understandable. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] Refer to Figure 1 , the method for measuring the roundness of the draft tube of a tubular turbine according to an exemplary embodiment of the present invention includes: Step S1, establish a draft tube model, and divide the draft tube into multiple pipe sections along the center line of the draft tube model; Step S2: Import the draft tube model into CAD and project the draft tube model onto a two-dimensional plane; Step S3: Establish a polar coordinate system and select a reference point; Step S4: Select the median diameter section from each pipe segment and determine the lofting points on the median diameter section of each pipe segment; Step S5: Set up a total station on the construction site and use the total station to measure the lofting points on the median diameter section corresponding to each pipe segment; Step S6: Conduct roundness analysis based on the polar coordinates of the lofting points on each pipe segment.

[0025] By dividing the draft tube of the overall structure into multiple segments, selecting the median diameter section of each pipe segment, determining the lofting points on the median diameter section of each pipe segment, using the total station to measure the lofting points on each median diameter section in sequence, and conducting roundness analysis after obtaining the polar coordinates of each lofting point, the difficulty of on-site roundness measurement of the draft tube is reduced, the operation process is simplified, and the installation accuracy of the draft tube is guaranteed.

[0026] In step S1, to meet the usage requirements, by way of example, a diffuser draft tube with an upper bottom inner diameter of 5609.6 mm, a lower bottom inner diameter of 7904 mm, and a length of 6500 mm is designed (refer to Figure 2 ). For the convenience of subsequent measurement, the draft tube is evenly divided into three segments along the center line, namely the first pipe segment, the second pipe segment, and the third pipe segment, and adjacent pipe segments are connected by welding. Dividing the draft tube into multiple segments can reduce the on-site actual installation difficulty and the on-site roundness measurement difficulty of the total station.

[0027] In step S2, after projecting the draft tube model, a series of circular sections with gradually increasing diameters are obtained, which is convenient for determining the lofting points.

[0028] In step S3, when establishing the polar coordinate system, the pole is determined on the center line of the draft tube (the center position of the circular section), and the direction perpendicular to the center line of the draft tube is used as the polar axis. When selecting the reference point, the following principles are followed: Select a location that can comprehensively observe the entire arc area of the draft tube as the reference point. If it is impossible to comprehensively observe the entire arc area of the draft tube through a single reference point, try to reduce the number of changes of the reference point to reduce the workload and the later calculation amount. Based on the above principles, the reference point is determined on the center line of the draft tube, and the coordinates of the reference point are determined in combination with the draft tube model.

[0029] In step S4, when selecting the lofting points, the polar axis is evenly rotated by a preset angle (such as 15 degrees, 22.5 degrees, 30 degrees, 45 degrees, etc.) along the circumferential direction of the median diameter section, and the intersection point of the polar axis and the median diameter section is used as the lofting point to determine the coordinates of each lofting point. For example, when the polar axis rotates 22.5 degrees each time, 16 lofting points are obtained. The lofting points of the first pipe segment are denoted as A1~P1 (refer to Figure 6), the layout points of the second pipe section are denoted as A2 to P2, and the layout points of the third pipe section are denoted as A3 to P3. When selecting layout points, the rotation angle of the polar axis can be reduced to increase the number of layout points and ensure the accuracy of the roundness measurement result.

[0030] In step S5, when setting up the total station, the position of the reference point is used as the setup position of the total station. When measuring the layout points, the layout points on the mid-diameter section of the first, second, and third pipe sections are sequentially measured through the total station to obtain the distance and zenith angle of each layout point on the mid-diameter section of the pipe section from the total station. After measuring the layout points on the mid-diameter section of each pipe section, a polar coordinate system with the center of the total station as the origin and the zenith angle of the total station as 0 degrees is obtained to record the information of each layout point of the pipe section.

[0031] In step S6, during the roundness analysis, the polar radius of each layout point is the radius of the corresponding draft tube section, denoted as R1, R2...R 15 , R 16 ; when performing roundness analysis on a certain pipe section, the difference between the maximum polar radius Rmax and the minimum polar radius Rmin of the pipe section is calculated to obtain the roundness error D, that is, D = Rmax - Rmin. After obtaining the roundness error D of each pipe section, the roundness error D of each pipe section is compared with the designed roundness error to determine whether the roundness of the installed draft tube meets the design requirements.

[0032] When designing the draft tube, the designed roundness error of the draft tube is not greater than 2 mm to maintain the efficient and stable operation of the water turbine; to reduce the influence of instrument error on the measurement result, the present invention preferably uses a total station of 1″ level, whose angle measurement accuracy is 1″. At a measurement distance of every 100 meters, the error caused by the total station itself is about 0.485 mm. Therefore, to reduce the influence of measurement error on the installation accuracy of the draft tube and ensure the accuracy and reliability of the measurement, during the measurement process, the distance between the reference point and the layout point is not greater than 200 m to control the cumulative error and make the measurement error meet the preset requirements, so as to ensure that the installation accuracy of the draft tube meets the design requirements.

[0033] During the aforementioned measurement process, after all pipe sections are installed, the layout points on the mid-diameter section of each pipe section can be sequentially measured. After the layout points on all pipe sections are measured, the roundness error analysis is sequentially performed; alternatively, in combination with step S5 and step S6, after each pipe section is installed, the layout points on the mid-diameter section of the pipe section are measured in the same manner as in step S5, and the roundness error analysis is performed in the same manner as in step S6. When the roundness error meets the design requirements, the installation, layout point measurement, and roundness error analysis of the next pipe section are carried out until the roundness errors of all pipe sections meet the design requirements.

[0034] The above is only a detailed description of the specific implementation manner of the present invention, rather than a limitation to the present invention. Various substitutions, modifications and improvements made by those skilled in the relevant technical fields without departing from the principle and scope of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for measuring the roundness of the draft tube of a tubular turbine, characterized in that Including: Step S1: Establish a draft tube model and divide the draft tube into multiple pipe segments along the center line of the draft tube model. Step S2: Import the draft tube model into CAD and project the draft tube model onto a two-dimensional plane. Step S3: Establish a polar coordinate system and select a reference point. Step S4: Select a mid-diameter section from each pipe segment and determine the lofting points on the mid-diameter section of each pipe segment. Step S5: Set up a total station at the construction site and use the total station to measure the lofting points on the mid-diameter section corresponding to each pipe segment. Step S6: Perform roundness analysis based on the polar coordinates of the lofting points on each pipe segment.

2. The method for measuring the roundness of the draft tube according to claim 1, wherein The draft tube is a diffusive draft tube. When dividing the draft tube, the draft tube is evenly divided into three sections along the center line.

3. The method for measuring the roundness of a draft tube according to claim 1, characterized in that, In step S3, when establishing the polar coordinate system, the pole is determined on the center line of the draft tube, and the direction perpendicular to the center line of the draft tube is used as the polar axis.

4. The method for measuring the roundness of the draft tube according to claim 1, wherein, In step S3, when selecting the reference point, the following principle is followed: Select a location that can comprehensively observe the entire arc area of the draft tube as the reference point. If it is impossible to comprehensively observe the entire arc area of the draft tube through a single reference point, try to reduce the number of changes of the reference point. On the basis of meeting the foregoing principle, the reference point is determined on the center line of the draft tube.

5. The method for measuring the roundness of a draft tube according to claim 1, wherein In step S4, when selecting the lofting points, the polar axis is evenly rotated by a preset angle along the circumferential direction of the mid-diameter section, and the intersection point of the polar axis and the mid-diameter section is used as the lofting point to determine the coordinates of multiple lofting points.

6. The method for measuring the roundness of the draft tube according to claim 5, wherein When rotating the polar axis, the polar axis is rotated 22.5 degrees each time to obtain 16 lofting points.

7. The method for measuring the roundness of the draft tube according to claim 2, characterized in that, In step S5, when setting up the total station, the location of the reference point is used as the setup location of the total station. When measuring the lofting points, the total station is used to measure the lofting points on the mid-diameter sections of the first pipe segment, the second pipe segment, and the third pipe segment in sequence, and the distance and zenith angle of the lofting points on the mid-diameter section of each pipe segment from the total station are obtained. After measuring the lofting points on the mid-diameter section of each pipe segment, a polar coordinate system with the center of the total station as the origin and the zenith angle of the total station as 0 degrees is obtained to record the information of the lofting points of this pipe segment.

8. The method for measuring the roundness of a draft tube according to claim 1, wherein In step S6, in the roundness analysis, the polar radius of each lofting point is the radius of the corresponding draft tube segment of the lofting point. When performing roundness analysis on a certain pipe segment, the difference between the maximum polar radius Rmax and the minimum polar radius Rmin of this pipe segment is obtained to get the roundness error D. The roundness error D of this pipe segment is compared with the designed roundness error to judge whether the roundness of the installed draft tube meets the design requirements.

9. The method for measuring the roundness of a draft tube according to any one of claims 1 to 8, characterized in that, The designed roundness error of the draft tube is not greater than 2 mm. The total station uses a 1″ level total station, and the distance between the reference point and the lofting point is not greater than 200 m.

10. The method for measuring the roundness of the draft tube according to claim 9, wherein, Steps S5 and S6 are alternately performed. After each pipe segment of the draft tube is installed, the lofting points on the mid-diameter section of this pipe segment are measured in the same way as in step S5, and the roundness error analysis is performed in the same way as in step S6. When the roundness error meets the design requirements, the installation, lofting point measurement, and roundness error analysis of the next pipe segment are carried out.

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