A method and system for calculating the differential pressure flow coefficient of a bulb turbine

Abstract

The application provides a bulb-turbine differential pressure flow coefficient calculation method and system, and belongs to the technical field of water turbine operation characteristic calculation and analysis.The application calculates the correlation coefficient of the water pressure measurement value-power curve under the same test condition of multiple units, optimally selects the measurement point data curve with high correlation coefficient to participate in the calculation of the flow coefficient, deduces the calculation expression of the water turbine head and the differential pressure flow based on the field measurement data, combines the comprehensive characteristic diagram of the water turbine provided by the water turbine manufacturer, and gives the calculation steps of fitting the differential pressure flow coefficient based on the field measurement data of the hydropower station.The application avoids the uncertainty influence of the power measurement data caused by the rotatable blade of the bulb-turbine, and solves the problems of large size of the water diversion pipeline of the large bulb-turbine unit, difficulty in flow measurement, and difficulty in field fitting of the flow coefficient.

Description

Technical Field

[0001] This invention relates to the field of turbine operating characteristic calculation and analysis technology, and in particular to a method and system for calculating the differential pressure flow coefficient of a bulb turbine. Background Technology

[0002] Turbine flow rate is primarily used to calculate turbine operating efficiency and is a key parameter for analyzing turbine operating characteristics. Differential pressure flow meters are installed in all hydropower stations to measure flow rate, and the configuration of measuring points varies depending on the type of turbine. However, differential pressure flow meters require calibration of their differential pressure flow coefficients. With the increasing size of large hydropower plant units, accurate flow measurement in ultra-large diameter water intake systems presents significant challenges. Furthermore, due to various factors, the accuracy of water pressure data measured by on-site water pressure measuring instruments at hydropower stations is difficult to determine, leading to uncertainty in fitting differential pressure flow coefficients based on actual on-site data. These factors have resulted in most differential pressure flow measurement systems currently installed in hydropower station units operating under limitations.

[0003] Theoretically, the differential pressure flow coefficient is mainly determined by the geometric parameters of the measuring point cross-section and is independent of the operating conditions. However, in practice, the derivation of the differential pressure flow coefficient formula uses the cross-sectional average velocity. Under different flow rates, the distribution of the cross-sectional velocity along the pipe diameter varies significantly, leading to errors in equivalent calculations using the cross-sectional average flow rate, especially with larger cross-sectional areas or pipe diameters. Field measurements show that the flow coefficient varies slightly with load conditions or flow rates. In ultrasonic flow measurement, this non-uniform distribution of cross-sectional velocity remains the main cause of measurement errors. Although differential pressure flow measurement has certain errors, its application cost is low, and differential pressure flow meters are generally used in hydropower unit flow measurement. At hydropower station sites, there has been no good method for calibrating the turbine differential pressure flow coefficient using a relatively simple approach for large-diameter intake channels. For bulb turbines with low head and large flow rates, and large intake channel dimensions, calibrating the differential pressure flow coefficient on-site using higher-precision instruments is difficult and expensive. Summary of the Invention

[0004] The present invention aims to at least partially solve one of the technical problems in the related art.

[0005] Therefore, the first objective of this invention is to propose a method for calculating the differential pressure flow coefficient of a bulb turbine. Based on the actual operating conditions of the hydropower station and the bulb turbine unit, two assumptions are made. Under these two assumptions, a method for determining the differential pressure flow coefficient of a bulb turbine based on field measured data is presented. The theory is clear, the technical solution is simple, and the calculation is straightforward, thus solving the problem of field calibration of the differential pressure flow coefficient of large bulb turbine units.

[0006] The second objective of this invention is to provide a differential pressure flow coefficient calculation system for a bulb-type axial-flow turbine.

[0007] To achieve the above objectives, a first aspect of the present invention provides a method for calculating the differential pressure flow coefficient of a bulb turbine, comprising:

[0008] S1. Based on the layout information of water pressure measuring points of the bulb turbine unit and the measured water pressure data related to the head calculation, the turbine head calculation expression based on the measured data is obtained.

[0009] S2, Based on the water pressure measurement point layout information of the bulb turbine unit and the measured water pressure data related to flow calculation, the turbine differential pressure flow calculation expression based on the measured data is obtained;

[0010] S3. Based on the turbine head calculation expression and the turbine differential pressure flow calculation expression, as well as the measured water pressure data of multiple units in the hydropower station, calculate the correlation coefficient of the turbine head and flow differential pressure measurement point curves of multiple units.

[0011] S4 calculates the differential pressure flow coefficient based on the turbine differential pressure flow calculation expression, the measured data of the hydropower station, and the correlation coefficient.

[0012] In one embodiment of the present invention, a bulb turbine measuring point diagram is obtained, and the turbine head is defined as the energy difference between the turbine inlet and outlet sections, that is, the energy difference between the pressure measuring section 1 at the inlet of the flow channel and the pressure measuring section 9 at the outlet of the tailrace pipe; the flow differential pressure measuring points of the bulb turbine unit are sections 2 and 5.

[0013] In one embodiment of the present invention, S1 includes:

[0014] S1-1, the elevations of the measuring points at pre-set cross-sections 1 and 9 are the same, and the turbine head is:

[0015] (1)

[0016] In the formula, H t It's the turbine head. H 1. H 9 represents the water pressure at sections 1 and 9, respectively. V 1. V 9 represent the flow velocities at sections 1 and 9, respectively. α 1 is the correction factor for section 1. g It is gravitational acceleration;

[0017] S1-2, the turbine head formula of equation (1) is rewritten as:

[0018] (2)

[0019] In the formula, It is the cross-sectional coefficient. A 1. A 9 represent the areas of cross-sections 1 and 9, respectively, and Q is the turbine flow rate. α 9 is the correction factor for section 9;

[0020] S1-3, according to the orifice outflow principle, the turbine flow rate is expressed as:

[0021] (3)

[0022] In the formula, K u It is the flow coefficient. Y It is the guide vane opening. H t It is the turbine head;

[0023] S1-4, at rated head and rated flow rate, satisfies , Q r , Y r , H tr These are the flow rate, guide vane opening, and turbine head under rated operating conditions, respectively. Using the rated operating parameters as the base values, the relative values ​​are as follows:

[0024] (4)

[0025] in, q = Q / Q r It is a relative value of traffic. h t = H t / H tr It is the relative value of the turbine head. y = Y / Y r It is the relative value of the guide vane opening;

[0026] S1-5, Substitute equation (4) into equation (2):

[0027] (5)

[0028] S1-6, In actual operation of a hydropower station, the guide vane opening of the governor is expressed as a relative value; if the base value of the guide vane opening is... Y B Then we have:

[0029] (6)

[0030] in, y r It is the relative value of the guide vane opening under rated operating conditions;

[0031] S1-7, the water pressure difference between measuring points 1 and 9 is recorded as... H 1_9 = H 1- H 9; Substituting equation (6) into equation (5) and rearranging, we get:

[0032] (7)

[0033] in, , H tr It is the rated head under rated operating conditions.

[0034] In one embodiment of the present invention, calculation is performed based on the geometric dimensions of the unit's flow channel structure. K f According to the turbine design parameters, the rated head H r and rated flow Q r Calculate coefficients K .

[0035] In one embodiment of the present invention, S2 includes:

[0036] S2-1, establish Bernoulli's equation between flow differential pressure measuring points at sections 2 and 5, where the elevations of the measuring points at both sections are the same:

[0037] (8)

[0038] in, H 2. H 5 represents the water pressure at sections 2 and 5, respectively. V 2. V 5 represent the flow velocities at sections 2 and 5, respectively. α 2. α 5 are the correction factors for sections 2 and 5, respectively. V It is the average flow velocity between section 2 and section 5. λ It is the equivalent hydraulic loss coefficient between cross-sections 2 and 5;

[0039] S2-2, Equation (8) above can be rewritten as:

[0040] (9)

[0041] in, H = H 2- H 5 represents the pressure difference between section 2 and section 5. A 2. A 5. A s These are the equivalent cross-sectional areas of section 2, section 5, and the area between section 2 and section 5, respectively. Q It is the flow rate across the cross-section;

[0042] S3-3, the water pressure difference between measuring points 2 and 5 is recorded as... H 2_5 = H 2- H 5; Equation (9) is rewritten as:

[0043] (10)

[0044] in, It's a light bulb with a continuous current.

[0045] In one embodiment of the present invention, the correlation coefficients of the turbine head and flow differential pressure measurement curves of multiple generating units in a hydropower station are calculated, and data curves with high correlation coefficients are selected for preprocessing to obtain the turbine head used to calculate the differential pressure flow coefficient. H 1_9 and differential pressure H 2_5 .

[0046] In one embodiment of the present invention, S3 includes:

[0047] S3-1 refers to multiple generating units installed in a hydropower station that have the same flow channel structure and hydraulic characteristics, and the turbine head measuring points and differential pressure measuring points are located in the same positions.

[0048] S3-2, Data curves of load changes of each water pressure random group were obtained by testing multiple units of a hydropower station under the same test conditions;

[0049] S3-3, Calculate the correlation coefficient:

[0050] (11)

[0051] Where r is the correlation coefficient between variables X and Y. , These are the standard deviations of variables X and Y, respectively. , It is the mean of variables X and Y;

[0052] S3-4, using formula (11) to calculate the measured data H of multiple units under the same test conditions. 1_9The correlation coefficient was calculated; 2-3 sets of data with high correlation coefficients were selected, and the average was taken as the calculation data. The same method was used to calculate the H-value for multiple units. 2_5 The correlation coefficient is used to select the data curve for calculation.

[0053] In one embodiment of the present invention, S4 includes:

[0054] S4-1, based on the selected measured water pressure H 1_9 Relative opening of guide vanes y Calculate the turbine head according to formula (7) H t ;

[0055] S4-2, Under the condition of preset head, the turbine flow rate is related to the guide vane opening. The blade opening changes the efficiency of the turbine in converting mechanical energy, but has no effect on the turbine flow rate.

[0056] Based on the turbine head H t The turbine flow rate is read from the turbine's comprehensive operating characteristic diagram, along with the guide vane opening. Q i ;

[0057] S4-3, based on the selected measured data H 2_5 And Q, calculate the differential pressure flow coefficient K according to formula (10). Q ;

[0058] S4-4, Repeat the above calculation process S4-1, S4-2, and S4-3 to calculate the differential pressure flow coefficient under full load conditions. K Q ;

[0059] relative opening of the guide vanes y Plot the x-axis. K Q - y The curve is fitted to reduce data reading errors and obtain an accurate flow coefficient. K Q .

[0060] To achieve the above objectives, a second aspect of the present invention provides a differential pressure flow coefficient calculation system for a bulb turbine, comprising: a turbine head calculation module, used to obtain a turbine head calculation expression based on measured data according to the arrangement information of water pressure measuring points of the bulb turbine and the measured water pressure data related to the head calculation;

[0061] The turbine differential pressure flow calculation module is used to obtain the turbine differential pressure flow calculation expression based on the measured data, according to the layout information of the water pressure measuring points of the bulb turbine and the measured water pressure data related to the flow calculation.

[0062] The curve correlation coefficient calculation module is used to calculate the correlation coefficient of the turbine head and flow differential pressure measurement point curves of multiple units based on the turbine head calculation expression, the turbine differential pressure flow calculation expression, and the measured water pressure data of multiple units in the hydropower station.

[0063] The differential pressure flow coefficient module is used to calculate the differential pressure flow coefficient based on the turbine differential pressure flow calculation expression, the hydropower station measured data, and the correlation coefficient.

[0064] The method and system of this invention avoid the uncertainty of measured power data caused by the rotatable blades of bulb turbines, and solve the problems of large water intake pipe size, difficulty in flow measurement, and difficulty in determining flow coefficient on site for large bulb turbine units.

[0065] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0066] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0067] Figure 1 A flowchart illustrating a method for calculating the differential pressure flow coefficient of a bulb turbine provided in this application embodiment;

[0068] Figure 2 A diagram showing the arrangement of measuring points for a bulb-type axial-flow turbine provided in an embodiment of this application;

[0069] Figure 3 Measurement points provided for embodiments of this application H 1_9 Correlation coefficient heatmap;

[0070] Figure 4 Measurement points provided for embodiments of this application H 2_5 Correlation coefficient heatmap;

[0071] Figure 5 The turbine head provided in the embodiments of this application H t With guide vane opening y Change curve graph;

[0072] Figure 6The turbine flow rate Q as a function of guide vane opening is provided in the embodiments of this application. y Change curve graph;

[0073] Figure 7 The flow coefficients provided in the embodiments of this application K Q With guide vane opening y Change curve graph;

[0074] Figure 8 This is a structural diagram of a bulb turbine differential pressure flow coefficient calculation system provided in an embodiment of this application. Detailed Implementation

[0075] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0076] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0077] The following describes, with reference to the accompanying drawings, a method and system for calculating the differential pressure flow coefficient of a bulb turbine according to an embodiment of the present invention.

[0078] This invention calculates the correlation of water pressure measurement curves, selects the data with the smallest measurement error from the data of the same measurement points of multiple machines for curve fitting calculation, combines the comprehensive operating characteristic diagram of the water turbine provided by the manufacturer, and obtains the corresponding flow rate by looking up the water head and guide vane opening of the water turbine, and then fits to obtain the differential pressure flow coefficient of the water turbine.

[0079] Figure 1 This is a flowchart illustrating a method for calculating the differential pressure flow coefficient of a bulb turbine according to an embodiment of the present invention, as shown below. Figure 1 As shown, it includes:

[0080] S1. Based on the layout information of the water pressure measuring points of the bulb turbine unit and the measured water pressure data related to the head calculation, the turbine head calculation expression based on the measured data is obtained.

[0081] Understandably, the measuring point diagram of the bulb turbine is as follows: Figure 2 As shown, the turbine head is defined as the energy difference between the turbine inlet and outlet sections, that is, the energy difference between section 1 and section 9.

[0082] In one embodiment of the present invention, based on the arrangement of water pressure measuring points of the bulb turbine unit, the turbine head calculation expression based on measured data is derived as follows:

[0083]

[0084] in, , ;

[0085] Calculate based on the geometric dimensions of the unit's flow channel structure. K f According to the turbine design parameters, the rated head H r and rated flow Q r Calculate coefficients K .

[0086] Understandable, Figure 2 In the labels: 1 is the pressure measurement section at the inlet of the flow channel, 2 is the pressure measurement section at the turbine inlet, 3 is not yet installed, 4 is the pressure measurement section in front of the movable guide vane, 5 is the pressure measurement section at the turbine outlet, 6 is the pressure measurement section behind the movable guide vane, 7 is the pressure measurement section at the inlet of the tailrace pipe, 8 is the pressure pulsation measurement section of the tailrace pipe, and 9 is the pressure measurement section at the outlet of the tailrace pipe.

[0087] It is understandable that the "section" mentioned in the context refers to... Figure 2 The relevant labels have the following meanings: for example, section 1 is the pressure measurement section at the inlet of the flow channel; section 2 is the pressure measurement section at the inlet of the turbine flow rate; and so on.

[0088] Understandably, the "measuring points" mentioned below also refer to... Figure 2 The meanings of the relevant labels are as follows: for example, measuring points 1 and 9 are the pressure measurement sections at the inlet of the flow channel and the outlet of the tailwater pipe, respectively, and so on.

[0089] The specific steps of this embodiment of the invention are as follows:

[0090] The elevations of the measuring points at sections 1 and 9 are pre-set to be the same, and the turbine head is:

[0091] (1)

[0092] in, H t It is the turbine head (m). H 1. H 9 represents the water pressure (m) at sections 1 and 9, respectively. V 1. V 9 represent the flow velocities (m / s) at sections 1 and 9, respectively. α1 is the correction factor for section 1. g It is the acceleration due to gravity (m) 2 / s).

[0093] Equation (1) can be rewritten as:

[0094] (2)

[0095] in, It is the cross-sectional coefficient. A 1. A 9 represent the areas (m²) of sections 1 and 9, respectively. 2 Q is the turbine flow rate. α 9 is the correction factor for section 9.

[0096] According to the orifice outflow principle, the turbine flow rate is expressed as:

[0097] (3)

[0098] In the formula, K u It is the flow coefficient. Y It is the guide vane opening. H t It is the water turbine head.

[0099] At rated head and rated flow, it meets the following requirements. , Q r , Y r , H tr These are the flow rate, guide vane opening, and turbine head under rated operating conditions, respectively. Using the rated operating parameters as the base values, the relative values ​​are as follows:

[0100] (4)

[0101] in, q = Q / Q r It is a relative value of traffic. h t = H t / H tr It is the relative value of the turbine head. y = Y / Y r It is the relative value of the guide vane opening.

[0102] Substituting equation (4) into equation (2):

[0103] (5)

[0104] In actual operation of hydropower stations, the guide vane opening of the governor is expressed as a relative value. The base value of the guide vane opening is not necessarily... Y r If the guide vane opening base value is Y B Then we have:

[0105] (6)

[0106] in, y r It is the relative value of the guide vane opening under rated operating conditions.

[0107] The water pressure difference between measuring points 1 and 9 is denoted as H 1_9 = H 1- H 9. Substituting equation (6) into equation (5) and rearranging, we get:

[0108] (7)

[0109] in, , H tr It is the rated head (m) under rated operating conditions.

[0110] Furthermore, in step S1, the section correction coefficient is taken. α 1= α 9=1, calculated based on the geometric dimensions of the power station's flow channel. K f Then the coefficients are calculated. K From the coefficients K From the perspective of form, K A constant that is independent of operating conditions.

[0111] Furthermore, the approximation in step S1 mainly lies in assuming the turbine flow coefficient. K u Approximately unchanged, this coefficient is eliminated when taking the relative value form of the flow rate; in fact, the coefficient... K u It also varies. Subsequent calculations with examples show that even under rated load, the velocity-head term is less than 1%Hr, and the value is even smaller below rated load. This approximation will not cause large calculation errors.

[0112] S2, based on the water pressure measurement point layout information of the bulb turbine unit and the measured water pressure data related to flow calculation, obtain the turbine differential pressure flow calculation expression based on the measured data.

[0113] Understandably, based on the arrangement of water pressure measuring points in the bulb turbine unit, the formula for calculating the turbine differential pressure flow rate based on measured data is derived. In step S2, the flow rate differential pressure measuring points for the bulb turbine unit are cross-sections 2 and 5, as follows: Figure 2 As shown.

[0114] Furthermore, the specific steps for deriving the turbine differential pressure flow calculation expression based on measured data in step S2 are as follows:

[0115] Establish Bernoulli's equation between flow differential pressure measuring points at sections 2 and 5, where the measuring points at both sections have the same elevation:

[0116] (8)

[0117] in, H 2. H 5 represents the water pressure (m) at sections 2 and 5, respectively. V 2. V 5 represents the flow velocities (m / s) at sections 2 and 5, respectively. α 2. α 5 are the correction factors for sections 2 and 5, respectively. V It is the average flow velocity (m / s) between section 2 and section 5. λ It is the equivalent hydraulic loss coefficient between cross section 2 and cross section 5.

[0118] Equation (8) above can be rewritten as:

[0119] (9)

[0120] in, H = H 2- H 5 represents the pressure difference (m) between section 2 and section 5. A 2. A 5. A s These are the equivalent cross-sectional areas (m²) of section 2, section 5, and the area between section 2 and section 5. 2 ), Q It is the flow rate (m³) across the cross section. 3 / s).

[0121] The water pressure difference between measuring points 2 and 5 is recorded as H 2_5 = H 2- H 5. Equation (9) can be rewritten as:

[0122] (10)

[0123] in, It is the differential pressure flow coefficient of the bulb-type cross-flow turbine unit.

[0124] S3. Based on the turbine head calculation expression and the turbine differential pressure flow calculation expression, as well as the measured water pressure data of multiple units in the hydropower station, calculate the correlation coefficient of the turbine head and flow differential pressure measurement point curves of multiple units.

[0125] Specifically, the correlation coefficients of the turbine head and flow differential pressure measurement curves of multiple generating units in a hydropower station are calculated using the following formula:

[0126] (11)

[0127] Where r is the correlation coefficient between variables X and Y. , These are the standard deviations of variables X and Y, respectively. , It is the mean of variables X and Y.

[0128] Furthermore, the reason for using the correlation coefficient to reflect the pressure difference in step S3 is as follows: Assumption 1: The multiple units installed in the hydropower station have the same flow channel structure and hydraulic characteristics. The turbine head measuring point and differential pressure measuring point are in the same location. The probability of the same fault occurring at the water pressure measuring points of multiple units at the same time is very small.

[0129] Multiple generating units at a hydropower station were tested under the same experimental conditions, and data curves of load changes at each water pressure measurement point were obtained. If the trends are consistent, the correlation coefficient is high; conversely, if the trends of water pressure measurement point data changes are different, the correlation coefficient is low, which may be due to faults (blockage, pulsation, etc.) in the water pressure measurement point data, inducing measurement errors.

[0130] Further, in step S3, data curves with high correlation coefficients are selected for preprocessing to obtain the turbine head used to calculate the differential pressure flow coefficient. H 1_9 and differential pressure H 2_5 The specific steps are as follows:

[0131] Equation (11) is used to calculate the measured data of multiple units under the same test conditions. H 1_9 The correlation coefficient is calculated. Two to three sets of data with high correlation coefficients are selected, and their average is used as the calculation data. Alternatively, one set of data can be directly selected as the calculation data. The same method is used to calculate the correlation coefficients for multiple units. H 2_5 The correlation coefficient is used to select the data curve for calculation.

[0132] Select the same unit whenever possible H 1_9 and H 2_5This reduces errors caused by subtle differences in experimental testing conditions.

[0133] S4 calculates the differential pressure flow coefficient based on the turbine differential pressure flow calculation expression, the measured data of the hydropower station, and the correlation coefficient.

[0134] Specifically, the differential pressure flow coefficient is calculated based on measured data from the hydropower station and the comprehensive operating characteristic curve of the bulb turbine unit. The specific steps are as follows:

[0135] (1) Based on the selected measured water pressure H 1_9 Relative opening of guide vanes y Calculate the turbine head according to formula (7) H t .

[0136] (2) Assumption 2: Under the condition of constant head, the turbine flow rate is related to the guide vane opening. The blade opening only changes the efficiency of the turbine in converting mechanical energy, and has no effect on the turbine flow rate.

[0137] Based on this assumption, according to the turbine head H t The turbine flow rate is read from the turbine's comprehensive operating characteristic diagram, along with the guide vane opening. Q i .

[0138] (3) Based on the selected measured data H 2_5 and Q Calculate the differential pressure flow coefficient according to formula (10). K Q .

[0139] (4) Repeat the above calculation process (1), (2), and (3) to calculate the differential pressure flow coefficient under full load conditions. K Q .

[0140] Further, step S4 uses the relative opening of the guide vanes. y Plot the x-axis. K Q - y The curve is fitted to reduce data reading errors and obtain an accurate flow coefficient. K Q .

[0141] In one embodiment of the present invention, the method for calculating the differential pressure flow coefficient of the bulb-type turbine is described in detail.

[0142] Suppose a power station has 8 bulb turbine generator units installed. The measured data of the hydropower station under full load conditions includes the head measurement points. H 1.H 2. H 5. H 9 and the relative value of guide vane opening y .

[0143] Step 1: Based on the layout of the water pressure measuring points of the bulb turbine unit, derive the turbine head calculation expression based on measured data as follows:

[0144] Calculated based on the hydropower station channel structure data:

[0145] Area of ​​section 1: A 1 = 140.5488 (m) 2 );

[0146] Section 9 area: A 9 = 94.5 (m) 2 );

[0147] The local gravitational acceleration is: g =9.783 (m) 2 / s);

[0148] Take the section correction factor α 1= α 9 = 1;

[0149]

[0150] Design flow Q r =252.45 (m) 3 / s), H r =21.7 (m) y r =0.75 (pu). The coefficient K is calculated as follows:

[0151] ;

[0152] According to equation (7), the turbine head is:

[0153]

[0154] Under rated load conditions, the relative opening of the guide vanes y r =0.75 (75%), head correction term is 0.0164 y 2 =0.0092, or 0.92%Hr, which is less than 1% of the rated head. The correction factor is even smaller for operating conditions below rated load. Therefore, the derivation process assumes a turbine flow coefficient... K u The approximation remains unchanged, and this approximation will not cause large calculation errors.

[0155] Step 2: Based on the layout of water pressure measuring points in the bulb turbine unit, derive the formula for calculating the turbine differential pressure flow rate based on measured data:

[0156]

[0157] Step 3: Calculate the correlation coefficients of the turbine head and flow differential pressure measurement curves of multiple generating units in the hydropower station. Select the data curves with high correlation coefficients for preprocessing to obtain the turbine head used to calculate the differential pressure flow coefficient. H 1_9 and differential pressure H 2_5 .

[0158] For the power measurement points provided at the hydropower station site, ranging from 0-100% power, the actual power values ​​of the eight generating units varied slightly. Power was used as the x-axis, and water pressure as the y-axis. To ensure consistency at the measurement points, the power and water pressure curves for each generating unit were... PH 1_9 , PH 2_5 Curve fitting was performed, and then water pressure was interpolated according to power P to unify the abscissa of the measuring points of the 8 units to the same measuring point scale.

[0159] Calculate the water pressure of 8 generating units H 1_9 The correlation coefficients are represented using a correlation coefficient heatmap, such as... Figure 3 As shown.

[0160] Calculate the water pressure of 8 generating units H 2_5 The correlation coefficients are represented using a correlation coefficient heatmap, such as... Figure 4 As shown.

[0161] Figure 3 Among them, units 5, 7, and 8 H 1_9 The correlation coefficient is above 0.95. Figure 4 Among them, units 4, 5, 7, and 8 H 2_5 The correlation coefficient is above 0.999. Unit 5 was selected. H 1_9 and H 2_5 Used for subsequent calculations.

[0162] Step 4: Calculate the differential pressure flow coefficient based on the measured data of the hydropower station and the comprehensive characteristic curve of the bulb turbine unit.

[0163] (1) Based on the selected measured water pressure H 1_9 Relative opening of guide vanesy Calculate the turbine head according to formula (7) H t .

[0164] The turbine head varies with the guide vane opening as shown in the attached figure. Figure 5 As shown.

[0165] Appendix Figure 5 Whether to consider the correction factor is given. K Actual water head H 1_9 and H t A comparison of the differences. As can be seen from the figure, the hydropower station governor adopts... H 1_9 As the turbine head, there is a certain margin of error. The head error before and after correction when the rated output is reached is 0.87%Hr.

[0166] (2) Based on the turbine head H t The turbine flow rate is read from the turbine's comprehensive operating characteristic diagram, along with the guide vane opening. Q The turbine flow rate varies with the guide vane opening as shown in the attached figure. Figure 6 As shown.

[0167] (3) Based on the measured data of the selected Unit 5 H 2_5 and Q Calculate the differential pressure flow coefficient according to formula (10). K Q .

[0168] (4) Repeat the above calculation process (1), (2), and (3) to calculate the differential pressure flow coefficient under full load conditions. K Q Based on the relative opening of the guide vanes y Plot the x-axis. K Q - y The curve is fitted to reduce data reading errors.

[0169] K Q - y The curve and the fitted curve are attached. Figure 7 As shown.

[0170] from Figure 7 Looking at the vertical axis, the flow coefficient K Q The opening variation at full load is approximately 11.5%. A linear fit was used, and the deviation between the fitted data and the calculated data is within the range of -1.55% to +1.73%.

[0171] In summary, bulb turbines have adjustable blades. With the same guide vane opening, different blade angles result in varying turbine conversion efficiency, meaning there's no single-valued correlation between guide vane opening and turbine output power. This invention avoids this problem by using precisely measurable water pressure data combined with the manufacturer's comprehensive operating characteristic curves for calculation, making it convenient to apply. By fitting the flow coefficient under full opening conditions, a calculation method for a single-valued functional relationship between the flow coefficient and guide vane opening is established, solving the problem of large calculation errors under different flow rates caused by non-uniform velocity distribution in large-size flow channel cross-sections.

[0172] To achieve the above embodiments, such as Figure 8 As shown, this embodiment also provides a differential pressure flow coefficient calculation system 10 for bulb turbines, including:

[0173] The turbine head calculation module 100 is used to obtain the turbine head calculation expression based on the measured data according to the water pressure measurement point layout information of the bulb turbine and the measured water pressure data related to the head calculation.

[0174] The turbine differential pressure flow calculation module 200 is used to obtain the turbine differential pressure flow calculation expression based on the measured data, according to the water pressure measuring point layout information of the bulb turbine and the measured water pressure data related to flow calculation.

[0175] The curve correlation coefficient calculation module 300 is used to calculate the correlation coefficient of the turbine head and flow differential pressure measurement point curves of multiple units based on the turbine head calculation expression, the turbine differential pressure flow calculation expression, and the measured water pressure data of multiple units in the hydropower station.

[0176] The differential pressure flow coefficient module 400 is used to calculate the differential pressure flow coefficient based on the turbine differential pressure flow calculation expression, the measured data of the hydropower station, and the correlation coefficient.

[0177] The differential pressure flow coefficient calculation system for bulb turbines in this invention calculates the correlation coefficient between water pressure measurements and power curves under the same test conditions for multiple units. It prioritizes data curves from measurement points with high correlation coefficients for flow coefficient calculation, solving the problem of difficulty in interpreting on-site water pressure measurement data for potential errors. The system derives calculation expressions for turbine head and differential pressure flow based on on-site measured data. Combining this with the turbine manufacturer's comprehensive operating characteristic diagram, it provides calculation steps for fitting the differential pressure flow coefficient based on on-site measured data from hydropower stations. This invention avoids the uncertainty in measured power data caused by the rotatable blades of bulb turbines and solves the problems of large-scale bulb turbine units, large water intake pipe dimensions, difficulty in flow measurement, and difficulty in determining flow coefficients on-site.

[0178] In the description of this specification, the references to "one embodiment," "some embodiments," "example," "specific example," or "some examples" refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0179] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two or three, unless otherwise explicitly specified.

Claims

1. A method for calculating the differential pressure flow coefficient of a bulb turbine, characterized by, include: S1. Based on the layout information of water pressure measuring points of the bulb turbine unit and the measured water pressure data related to the head calculation, the turbine head calculation expression based on the measured data is obtained. S2, Based on the water pressure measurement point layout information of the bulb turbine unit and the measured water pressure data related to flow calculation, the turbine differential pressure flow calculation expression based on the measured data is obtained; S3. Based on the turbine head calculation expression and the turbine differential pressure flow calculation expression, as well as the measured water pressure data of multiple units in the hydropower station, calculate the correlation coefficient of the turbine head and flow differential pressure measurement point curves of multiple units. S4, the differential pressure flow coefficient is calculated based on the turbine differential pressure flow calculation expression, the measured data of the hydropower station and the correlation coefficient; Obtain the measuring point diagram of the bulb-type turbine and define the turbine head as the energy difference between the turbine inlet and outlet sections, that is, the energy difference between the pressure measuring section 1 at the inlet of the flow channel and the pressure measuring section 9 at the outlet of the tailrace pipe. The flow differential pressure measurement points for the bulb turbine unit are section 2 and section 5; S1 includes: S1-1, the elevations of the measuring points at pre-set cross-sections 1 and 9 are the same, and the turbine head is: (1) wherein H t is the water head of the turbine, H 1、 H 9 is the water pressure of the section 1, respectively section 9, V 1、 V 9 is the flow velocity of the section 1, respectively section 9, α 1 is the correction factor of the section 1, g is the acceleration of gravity; S1-2, the turbine head formula of equation (1) is rewritten as: (2) wherein is the cross-sectional coefficient, A 1、 A 9 is the area of the cross-section 1, 9, Q is the flow rate of the water turbine, α 9 is the correction coefficient of the cross-section 9; S1-3, according to the orifice outflow principle, the turbine flow rate is expressed as: (3) wherein K u is the flow coefficient, Y is the guide vane opening, H t is the water head of the turbine; S1-4, at rated head and rated flow, meet , Q r , Y r , H tr are respectively the flow, guide vane opening and water turbine head at rated conditions, with rated condition parameters as base values, in relative value form: (4) wherein q = Q / Q r is a flow relative value, h t = H t / H tr is a water turbine head relative value, y = Y / Y r is a guide vane opening relative value; S1-5, Substitute equation (4) into equation (2): (5) S1-6, In the actual operation of a hydropower station, the guide vane opening output by the governor is based on a certain base value. The relative value is given as a reference, and the measured guide vane opening relative value is assumed to be... The relative value of the rated opening degree to the base value is The relative value of the guide vane opening, based on the rated opening, used in the turbine characteristic analysis is... It is obtained by transforming the following formula: (6) wherein, y r is a known constant determined from the design parameters of the hydraulic turbine or from the measured opening at the rated operating conditions. S1-7, the water pressure difference between measuring points 1 and 9 = H 1- H 9 is substituted into equation (5), and is replaced by using equation (6), the final water turbine head calculation equation is obtained: (7) Wherein , , = Hm The measured water pressure difference between section 1 and section 9; according to the geometric size of the flow passage structure of the unit, the calculation K f , according to the design parameters of the water turbine rated water head H r And rated flow Q r The calculation coefficient K ; The S2 includes: S2-1, establish Bernoulli's equation between flow differential pressure measuring points at sections 2 and 5, where the elevations of the measuring points at both sections are the same: (8) wherein, H 2、 H 5 are the water pressures at the sections 2, 5 respectively, V 2、 V 5 are the flow rates at the sections 2, 5 respectively, α 2、 α 5 are the correction factors at the sections 2, 5 respectively, V is the average flow rate between the sections 2 and 5, λ is the equivalent hydraulic loss coefficient between the sections 2 and 5. S2-2, Equation (8) above can be rewritten as: (9) wherein, = H 2- H 5 is the measured differential pressure between section 2 and section 5, A 2、 A 5、 A s are the equivalent cross-sectional areas of section 2, section 5, and section 2 to section 5, respectively, Q is the flow rate through the section; S3-3, the measured differential pressure of points 2 and 5 is denoted as Δ = H 2- H 5; formula (9) is rewritten as: (10) wherein is the differential pressure flow coefficient of the bulb flow-through unit.

2. The method of claim 1, wherein, The correlation coefficient of the water head and flow differential pressure measuring point curve of the multiple units of the hydropower station is calculated, the data curve with high correlation coefficient is selected for preprocessing, and the water head of the water turbine for calculating the differential pressure flow coefficient is obtained H 1_9 and differential pressure H 2_5 .

3. The method of claim 1, wherein, S3 includes: S3-1 refers to multiple generating units installed in a hydropower station that have the same flow channel structure and hydraulic characteristics, and the turbine head measuring points and differential pressure measuring points are located in the same positions. S3-2, Data curves of load changes of each water pressure random group were obtained by testing multiple units of a hydropower station under the same test conditions; S3-3, Calculate the correlation coefficient: (11) where r is the correlation coefficient of the variables X, Y, , are the standard deviations of the variables X, Y, respectively, , are the means of the variables X, Y. S3-4, the same test conditions under the measured water pressure difference of multiple units is calculated by formula (11) correlation coefficient; select 2-3 groups of data with high correlation coefficient to take the average as the calculation data, and calculate the correlation coefficient of the measured differential pressure ΔH of multiple units in the same way 2_5 correlation coefficient, select the data curve for calculation.

4. The method of claim 3, wherein, S4 includes: S4-1, the measured water pressure difference according to the selection and the guide vane relative opening , the water head of the water turbine is calculated according to formula (7) H t ; S4-2, under the condition of preset head, the turbine flow rate is related to the guide vane opening. The blade opening changes the efficiency of the turbine in converting mechanical energy, but has no effect on the turbine flow rate. According to the water head of the water turbine H t And the guide vane opening degree is read from the water turbine operation comprehensive characteristic diagram Q i ; S4-3, the differential pressure ΔH is calculated according to the selected measured differential pressure ΔH 2_5 and the flow rate Q, the differential pressure flow rate coefficient K is calculated according to formula (10) Q ; S4-4, repeat the above calculation process S4-1, S4-2, S4-3, calculate the differential pressure flow coefficient under full load condition K Q ; relative opening of the guide vanes y Plot the x-axis. K Q - y The curve is fitted to reduce data reading errors and obtain an accurate flow coefficient. K Q .

5. A system for calculating the differential pressure flow coefficient of a bulb turbine using the method of claim 1, wherein include: The turbine head calculation module is used to obtain the turbine head calculation expression based on the measured data, according to the water pressure measurement point layout information of the bulb turbine and the measured water pressure data related to the head calculation. The turbine differential pressure flow calculation module is used to obtain the turbine differential pressure flow calculation expression based on the measured data, according to the layout information of the water pressure measuring points of the bulb turbine and the measured water pressure data related to the flow calculation. The curve correlation coefficient calculation module is used to calculate the correlation coefficient of the turbine head and flow differential pressure measurement point curves of multiple units based on the turbine head calculation expression, the turbine differential pressure flow calculation expression, and the measured water pressure data of multiple units in the hydropower station. The differential pressure flow coefficient module is used to calculate the differential pressure flow coefficient based on the turbine differential pressure flow calculation expression, the measured data of the hydropower station, and the correlation coefficient.

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