CN112100772B - Evaluation method for influence of air supplement on draft tube pressure pulsation and unit dynamic characteristics - Google Patents
Evaluation method for influence of air supplement on draft tube pressure pulsation and unit dynamic characteristics Download PDFInfo
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- G06F30/00—Computer-aided design [CAD]
- G06F30/10—Geometric CAD
- G06F30/17—Mechanical parametric or variational design
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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Abstract
The method for evaluating the influence of the air supplement on the pressure pulsation of the draft tube and the dynamic characteristics of the unit comprises the following steps of; 1) Collecting data; 2) Calculating the ring quantity of the outlet of the rotating wheel at the full load section; 3) Calculating the pressure pulsation frequency of the draft tube of the full load section; 4) Two air supplementing working conditions are drawn according to the characteristic arrangement form of the power plant; 5) Counting the relative pulsation amplitude of the full-load section through a true machine test; 6) Performing two air supplementing working condition stability tests; 7) And evaluating the dynamic characteristics of the air supplement by combining simulation and measured data. The invention can calculate the pressure pulsation characteristic of the full load section, and the calculation method is simpler and more convenient under the condition of meeting the precision, and can be used as an important means for evaluating the stability of the unit.
Description
Technical Field
The invention relates to the technical field of hydraulic machinery fault diagnosis, in particular to an evaluation method for influence of air supplement on draft tube pressure pulsation and unit dynamic characteristics.
Background
The mixed flow turbine is easy to generate vibration phenomenon caused by the vortex belt of the draft tube in a partial load section, and the type of a unit and the special form of an overcurrent component determine the difference of influence effects. In the flow passage, the draft tube pressure pulsation amplitude is maximum, and the draft tube pressure pulsation propagates upwards in a gradual 'descending' manner. Unsteady acting force caused by unstable flow state can act on important parts such as a rotating wheel, a top cover, guide vanes and the like, so that the problems of serious operation conditions such as tremble, resonance, strong noise and the like of water passing parts and units, blade cracks, abrasion of a leakage-stopping ring and the like can be caused, and the safe operation of a power station is directly endangered.
For the put-into-operation unit, a certain measure is adopted to weaken the influence degree of pressure pulsation vortex strips in the draft tube, reduce the pressure pulsation of the water turbine, improve the hydraulic stability and enlarge the load operation interval of the unit which can be scheduled, so that the method has become one of important targets of hydraulic research of the water turbine. The domestic machine set mainly adopts forced air supply and natural air supply as improvement methods. The forced air supplementing method mainly utilizes compressed air to supplement air by a top cover or a bottom ring, has higher operation and maintenance cost, and is mainly applied to axial-flow rotating-propeller units, high-head units and the like; the natural qi-supplementing method comprises the following steps: the central hole of the large shaft supplements air, the cross supplements air, the short pipe supplements air and the like; the principle is that the atmospheric pressure principle and the vacuum degree generated by the runner outlet of the unit are utilized to form pressure difference for natural air supplement, the operation cost is lower, and the device has wide market application.
In recent years, the research means of vortex bands mainly comprise a numerical calculation method and a formula method, the numerical calculation method is mainly used for calculating the change condition of vortex viscosity values of a drainage cone line, a draft tube line, each section pressure, the vortex bands and fluid through finite element software, the calculation result is influenced by boundary conditions, and the calculation method is complex. The traditional formula method is summarized according to a large amount of statistical data, and the whole dynamic process is described by a single numerical value, so that the dynamic characteristic research on the pressure pulsation of the draft tube of the full-load section of the hydroelectric generating set is absent, and the experimental analysis on the air supplementing effect of a real machine is also absent.
How to evaluate the effect of tonifying qi is a comprehensive problem.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention aims to provide an evaluation method for the influence of air supply on the pressure pulsation of a draft tube and the dynamic characteristics of a unit, the pressure pulsation characteristics of a full-load section can be calculated, and the calculation method is simple and convenient under the condition of meeting the precision and can be used as an important means for evaluating the stability of the unit.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
The method for evaluating the influence of the air supplement on the pressure pulsation of the draft tube and the dynamic characteristics of the unit comprises the following steps of;
1) Collecting data;
2) Calculating the ring quantity of the outlet of the rotating wheel at the full load section;
3) Calculating the pressure pulsation frequency of the draft tube of the full load section;
4) Two air supplementing working conditions are drawn according to the characteristic arrangement form of the power plant;
5) Counting the relative pulsation amplitude of the full-load section through a true machine test;
6) Performing two air supplementing working condition stability tests;
7) And evaluating the dynamic characteristics of the air supplement by combining simulation and measured data.
The step 1) specifically comprises the following steps:
the wheel model, the nominal diameter of the wheel, the number of blades and the rated flow are collected.
The step 2) is specifically as follows:
2.1 calculating absolute velocity tangential component from a blade exit velocity triangle consisting of absolute velocity v 2, relative velocity w 2, and entrainment velocity u 2,
V u2 is the component of the absolute speed of the runner outlet along the circumferential direction, V m2 is the component of the absolute speed of the runner outlet along the normal phase direction, R 2 is the radius of the runner outlet, A is the water passing area, R 2 is the radius of the inlet of the draft tube, Q 0 is the rated flow, Q is the actual flow, beta 2 is the blade outlet setting angle, omega 0 is the rotational angular velocity of the generator, and omega is the rotational angular velocity of the vortex belt.
When the unit operates near the optimal working point, the absolute speed is in a component v ' u2 =0 of the circumference, and as the load is reduced, the absolute speed moves from a point v 2 to a point v ' 2, and the corresponding positive annular quantity of v ' u2 > 0 with the same rotation direction is generated; similarly, as the load increases, the absolute speed moves from the point v 2 to v '2, and the corresponding negative ring quantity of v' u2 < 0 with the same rotation direction is generated; due to
The size of the ring of the runner outlet has a direct relation with the flow of the unit, and under the non-design working condition:
2.2 calculating the annular quantity values of the outlet vortex bands on different radiuses, and then calculating the average value gamma' expression of the outlet annular quantity of the rotating wheel according to the integral of the outlet annular quantity within the r 2≤ri≤R2 interval:
The step 3) is specifically as follows:
The method for deriving the vortex band frequency through the circulation quantity is based on the cause of the pressure pulsation of the draft tube, and the expression of the pressure pulsation of the draft tube of each load section of the unit can be completely reflected through a full load section pressure pulsation calculation formula:
Δh is draft tube pressure pulsation swing amplitude; f p is the draft tube pressure pulsation wobble frequency; n is the rotational speed of the unit; r 2 is the blade exit radius; r 2 wheel exit radius; vortex band relative coordinates; q is flow; and estimating the frequency of pressure pulsation of each load section by combining the parameters of the impractical rotating wheel and the draft tube.
The step 4) is to set a wind speed sensor for monitoring the change of wind speed through a gas supplementing pipeline, select a section of straight pipe section, install the wind speed sensor in the middle of the pipeline, introduce the obtained data into a dynamic monitoring system through the mode of obtaining air flow through the conversion of wind speed, take measures of temporarily closing and opening in the pipe section according to the actual arrangement form, and draw out two working conditions of gas supplementing and non-gas supplementing.
The step 5) is specifically as follows:
carrying out a real-machine load test on the tested unit, and counting the peak value delta H of the pressure pulsation peaks of the draft tubes under two air supplementing working conditions;
calculating the true head H of the water turbine;
The ratio of the peak value of the pressure pulsation to the actual water head of the measured data can be used for judging the stress value of the pressure pulsation acting on the unit, and the value of S needs to be represented by the measured data because the circumferential velocity component of the water flow and the eccentricity of the vortex core change along with the change of the load.
The step 6) is specifically as follows:
61 Respectively connecting the water guide bearing swing degree signal, the top cover vibration signal and the pressure pulsation signal of the hydroelectric generating set into an online monitoring system;
62 Temporarily plugging the set position in the air supplementing pipeline with a filler, testing the unit according to 10% load working condition points, and recording the vibration and swing degree values of each characteristic position;
63 And (3) withdrawing the filler and recovering the pipeline, testing the unit according to 10% load working points, and recording the vibration and swing values of each characteristic position.
In order to ascertain the effect of large-shaft air supply on the dynamic operation of the hydraulic generator, a temporary baffle is added to an air supply pipeline of the hydraulic generator, two working conditions of air supply and non-air supply are simulated, and the air supply effect is evaluated through pressure pulsation of a draft tube of each load section, vibration and swing conditions of a unit and efficiency.
The specific operation process of the step 7) is as follows:
71 Counting the main frequency of the draft tube calculated by the numerical value of the full load section, the main frequency calculated by the empirical formula, and the data of each empirical formula and the result of the true machine test;
72 Counting the relative pulsation amplitude of the two air supplementing working conditions;
73 The vibration and swing characteristic data of the two air supplementing working conditions are compared, and the air supplementing effect is comprehensively judged.
The invention has the beneficial effects that:
1. The method can be used as a monitoring means to evaluate the effect of the pressure pulsation of the draft tube, avoid the influence of a vibration source generated by the vortex belt of the draft tube on the characteristics of the unit, quantitatively calculate the evaluated air supplementing effect, and avoid the accident of the unit caused by the vibration of the draft tube caused by the pulsation of the draft tube.
2. The invention provides a method for evaluating pressure pulsation of a draft tube in a full-load section, which is used for deducing an annular quantity formula from a runner outlet speed triangle. And deducing a draft tube pressure pulsation dominant frequency formula from the annular quantity formula. And introducing a calibration of the relative pressure pulsation amplitude to the pulsation pressure. The method overcomes the singleness of the original calculation method, has comprehensive and scientific analysis results, and can provide basis for pulsation characteristic analysis, vibration fault diagnosis and prediction.
3. The evaluation system adopts a method of combining analog calculation and air supplementing working condition operation vibration data to evaluate the dynamic characteristics of the unit, mutually verifies and has high accuracy. The evaluation result can accurately reflect the air supplementing effect, and provides accurate basis for stable operation and state maintenance of the unit.
Drawings
FIG. 1 is a schematic view of a turbine draft tube flow path vortex strip.
FIG. 2 is a graph of wheel exit velocity triangle.
Fig. 3 is a graph of draft tube pressure pulsation frequency.
FIG. 4 is a graph of draft tube pressure pulsation versus amplitude.
FIG. 5 is a schematic diagram of a method for evaluating the effect of air make-up on draft tube pressure pulsation and unit dynamics.
Detailed Description
The present invention will be described in further detail with reference to examples.
The invention relates to an evaluation method of the influence of air supplementing on the pressure pulsation of a draft tube and the dynamic characteristics of a unit, which mainly comprises the steps of deducing the outlet flow velocity of a rotating wheel under non-optimal working conditions, calculating the main frequency of the pressure pulsation of the draft tube, calculating the relative amplitude of the pressure pulsation of the draft tube, comparing the two air supplementing working conditions and carrying out dynamic test.
In combination with the example, the vibration characteristic evaluation of the guide bearing bracket of the vertical hydraulic generator comprises the following steps:
1) Data is collected and the data is collected,
2) Calculating the ring quantity of the outlet of the rotating wheel at the full load section,
3) Calculating the pressure pulsation frequency of the draft tube of the full load section,
4) Two air supplementing working conditions are drawn according to the characteristic arrangement form of the power plant,
5) The relative pulsation amplitude of the full-load section is counted through a true machine test,
6) Two kinds of stability tests of the air supplementing working condition are carried out,
7) And evaluating the dynamic characteristics of the air supplement by combining simulation and measured data.
The specific operation process of the step 1) is as follows:
Important parameters such as the model number of the rotating wheel, the nominal diameter of the rotating wheel, the number of blades, rated flow and the like are collected, and the main parameters are shown in table 1.
TABLE 1 Main parameter Table of apparatus
The specific operation process of the step 2) is as follows:
21 Calculating absolute speed tangential component by a blade outlet speed triangle, wherein the size of the ring quantity of the runner outlet has a direct relation with the flow of the unit, and under the non-design working condition:
22 Calculating the annular quantity value of the outlet vortex belt on different radiuses, and calculating the average value gamma 'of the outlet annular quantity of the rotating wheel according to the integral of the outlet annular quantity within the interval r 2≤ri≤R2, wherein the average value gamma' is as follows:
The specific operation process of the step 3) is as follows:
the method for deriving the vortex band frequency through the circulation quantity is based on the cause of the pressure pulsation of the draft tube, and the expression of the pressure pulsation of the draft tube of each load section of the unit can be completely reflected through a full load section pressure pulsation calculation formula: Δh is draft tube pressure pulsation swing amplitude; f p is the draft tube pressure pulsation wobble frequency; n is the rotational speed of the unit; r 2 is the blade exit radius; r 2 wheel exit radius; vortex band relative coordinates; q is flow; the frequency of pressure pulsations in each load segment can be estimated by combining the parameters of the non-real runner and draft tube.
The specific operation process of the step 4) is as follows:
41 Adding a measuring wind speed sensor according to the straight pipe section of the air supplementing pipeline;
42 A temporary baffle is added to the air supplementing pipeline of the generator to simulate two working conditions of air supplementing and non-air supplementing.
The specific operation process of the step 5) is as follows:
51 Carrying out a real-machine load test on the tested unit, and counting the peak value delta H of the pressure pulsation peaks of the draft tubes under two air supplementing working conditions;
52 Calculating the true head H of the water turbine.
The specific operation process of the step 6) is as follows:
61 Respectively connecting the water guide bearing swing degree signal, the top cover vibration signal and the pressure pulsation signal of the hydroelectric generating set into an online monitoring system;
62 Temporarily plugging the set position in the air supplementing pipeline with a filler, testing the unit according to 10% load working condition points, and recording the vibration and swing degree values of each characteristic position;
63 And (3) withdrawing the filler and recovering the pipeline, testing the unit according to 10% load working points, and recording the vibration and swing values of each characteristic position.
The specific operation process of the step 7) is as follows:
71 Counting the main frequency of the draft tube calculated by the numerical value of the full load section, the main frequency calculated by the empirical formula, and the data of each empirical formula and the result of the true machine test;
72 Counting the relative pulsation amplitude of the two air supplementing working conditions;
73 The vibration and swing characteristic data of the two air supplementing working conditions are compared, and the air supplementing effect is comprehensively judged.
The method starts from the principle of generating the tail water vortex belt by the rotating wheel outlet speed triangle, and by comparing the main frequency value and the relative pressure pulsation value of tail water pressure pulsation under two air supplementing conditions and combining a water guide bearing swing time domain curve, the influence effect of air supplementing on hydraulic factors is emphasized and analyzed, and the influence degree of air supplementing on the stability of the unit is further evaluated.
The invention starts from the generation mechanism of the draft tube vortex belt, constructs a full-load section draft tube pressure pulsation calculation method, compares the full-load section draft tube pressure pulsation calculation method with an empirical formula, and summarizes the characteristics of several calculation results. And the two air supplementing working conditions are respectively analyzed by the assessment method, and the following conclusion is obtained by comparing the two air supplementing working conditions with the stability test result:
1. The frequency calculation result shows that the calculation difference of the full load section pressure pulsation calculation method and the traditional formula method in different load sections is obvious. The fluctuation trend of the main pulsation frequency of the draft tube under the two air supplementing states is basically consistent. Because the dynamic parameters are changed along with the working conditions, the application of the formula has certain limitation, but in the interval below 40% load section and above 60% load section, the full load section pressure pulsation calculation method has higher fitting degree with the test result, and the calculation result can accurately reflect the influence effect.
2. From the analysis of the relative amplitude data, the main action area of the draft tube pressure pulsation is found in a 40% load section, and the dynamic characteristics of the pressure pulsation can be accurately reflected by applying the full load section pressure pulsation calculation method in the area. The relative amplitude change trend of the draft tube pressure pulsation is basically consistent in the two air supplementing working conditions, and the air supplementing is taken as a necessary means to positively reduce the draft tube pressure pulsation effect.
3. The dynamic operation quality of the two air supplementing working condition units is compared through a unit stability test. The method has the advantages that the swing degree parameter of the water guide bearing is directly influenced by the relative amplitude of the draft tube pressure pulsation, the reliability of a numerical simulation calculation result is proved, the action characteristic of air supplementing on the draft tube pressure pulsation is disclosed, and theory and data support are provided for the research work of the dynamic characteristic of the unit.
As shown in fig. 1: draft tube pressure pulsations occur at the wheel exit and create maximum effect at the elbow section.
As shown in fig. 2: the turbine blade outlet speed triangle consists of an absolute speed V 2, a relative speed w 2 and a traction speed u 2, V u2 is the component of the absolute speed of the runner outlet along the circumferential direction, and V m2 is the component of the absolute speed of the runner outlet along the normal phase direction. At low flow rates, the absolute speed of the runner outlet is moved from v 2 to v ' 2, the corresponding dragging speed is moved from w 2 to w ' 2, and at high flow rates, the absolute speed of the runner outlet is moved from v2 to the corresponding dragging speed is moved from w2 to w ' 2.
As shown in fig. 3: and comparing a theoretical calculation formula, an empirical formula and curves of the pressure pulsation frequency of the draft tube with load change under the working conditions of actual measurement and non-air supplement.
As shown in fig. 4: and comparing the change curve of the relative amplitude of the draft tube pressure pulsation with the load under the air supplementing and non-air supplementing working conditions.
As shown in fig. 5: the specific steps of the evaluation method.
The foregoing description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and any simple modification, variation and equivalent structural changes made to the above embodiment according to the technical substance of the present invention still fall within the scope of the technical solution of the present invention.
Claims (1)
1. The method for evaluating the influence of the air supplement on the pressure pulsation of the draft tube and the dynamic characteristics of the unit is characterized by comprising the following steps of;
1) Collecting data;
2) Calculating the ring quantity of the outlet of the rotating wheel at the full load section;
3) Calculating the pressure pulsation frequency of the draft tube of the full load section;
4) Two air supplementing working conditions are drawn according to the characteristic arrangement form of the power plant;
5) Counting the relative pulsation amplitude of the full-load section through a true machine test;
6) Performing two air supplementing working condition stability tests;
7) The simulation and measured data are combined to evaluate the pneumatic characteristic of the air supplement;
The step 1) specifically comprises the following steps:
collecting the type of a rotating wheel, the nominal diameter of the rotating wheel, the number of blades and the rated flow;
the step 2) is specifically as follows:
2.1 calculating an absolute speed tangential component by a blade outlet speed triangle, wherein the water turbine blade outlet speed triangle consists of an absolute speed v 2, a relative speed w 2 and a traction speed u 2; v u2 is a component of the absolute speed of a runner outlet along the circumferential direction, V m2 is a component of the absolute speed of the runner outlet along the normal phase direction, R 2 is a runner outlet radius, A is a water passing area, R 2 is a draft tube inlet radius, Q 0 is a rated flow, Q is an actual flow, beta 2 is a blade outlet mounting angle, omega 0 is a generator rotation angular velocity, and omega is a vortex belt rotation angular velocity;
When the unit operates near the optimal working point, the absolute speed is in a component v ' u2 =0 of the circumference, and as the load is reduced, the absolute speed moves from a point v 2 to a point v ' 2, and the corresponding positive annular quantity of v ' u2 > 0 with the same rotation direction is generated; similarly, as the load increases, the absolute speed moves from the point v 2 to v '2, and the corresponding negative ring quantity of v' u2 < 0 with the same rotation direction is generated; due to
Wherein r 2 is the radius of the outlet of the rotating wheel, A is the water passing area, and the direct relation between the annular quantity of the outlet of the rotating wheel and the flow of the unit can be seen, and under the non-design working condition:
2.2 calculating the annular quantity values of the outlet vortex bands on different radiuses, and then calculating the average value gamma' expression of the outlet annular quantity of the rotating wheel according to the integral of the outlet annular quantity within the r 2≤ri≤R2 interval:
The step 3) is specifically as follows:
The method for deriving the vortex band frequency through the circulation quantity is based on the cause of the pressure pulsation of the draft tube, and the expression of the pressure pulsation of the draft tube of each load section of the unit can be completely reflected through a full load section pressure pulsation calculation formula:
Δh is draft tube pressure pulsation swing amplitude; f p is the draft tube pressure pulsation wobble frequency; n is the rotational speed of the unit; r 2 is the blade exit radius; r 2 wheel exit radius; Vortex band relative coordinates; q is flow; estimating the frequency of pressure pulsation of each load section by combining parameters of an impractical rotating wheel and a draft tube;
The step 4) is to set a wind speed sensor for monitoring the change of wind speed through a gas supplementing pipeline, select a section of straight pipe section, install the wind speed sensor in the middle of the pipeline, introduce the obtained data into a dynamic monitoring system through the mode of obtaining air flow through the conversion of wind speed, take the measure of temporarily closing and opening in the pipe section according to the actual arrangement form, and draw two gas supplementing working conditions of gas supplementing and non-gas supplementing;
The step 5) is specifically as follows:
carrying out a real-machine load test on the tested unit, and counting the peak value delta H of the pressure pulsation peaks of the draft tubes under two air supplementing working conditions;
calculating the true head H of the water turbine;
The stress value of the pressure pulsation acting on the unit can be judged through the ratio of the pressure pulsation peak value to the actual water head of the measured data, and the value of S is required to be represented through the measured data because the circumferential velocity component of the water flow and the eccentricity of the vortex core are changed along with the change of the load, wherein S=delta H/H;
The step 6) is specifically as follows:
61 Respectively connecting the water guide bearing swing degree signal, the top cover vibration signal and the pressure pulsation signal of the hydroelectric generating set into an online monitoring system;
62 Temporarily plugging the set position in the air supplementing pipeline with a filler, testing the unit according to 10% load working condition points, and recording the vibration and swing degree values of each characteristic position;
63 The filler is withdrawn and the pipeline is restored, the unit is tested according to 10% load working condition points, and the values of vibration and swing degree of each characteristic position are recorded;
The specific operation process of the step 7) is as follows:
71 Counting the main frequency of the draft tube calculated by the numerical value of the full load section, the main frequency calculated by the empirical formula, and the data of each empirical formula and the result of the true machine test;
72 Counting the relative pulsation amplitude of the two air supplementing working conditions;
73 The vibration and swing characteristic data of the two air supplementing working conditions are compared, and the air supplementing effect is comprehensively judged.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202010953683.8A CN112100772B (en) | 2020-09-11 | 2020-09-11 | Evaluation method for influence of air supplement on draft tube pressure pulsation and unit dynamic characteristics |
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| CN202010953683.8A CN112100772B (en) | 2020-09-11 | 2020-09-11 | Evaluation method for influence of air supplement on draft tube pressure pulsation and unit dynamic characteristics |
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| CN112100772A CN112100772A (en) | 2020-12-18 |
| CN112100772B true CN112100772B (en) | 2024-05-17 |
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