Method and system for calculating efficiency of low-pressure cylinder of steam turbine on line

Abstract

According to the method and system for calculating the efficiency of the low-pressure cylinder of the steam turbine on line, under the reference working condition and multiple working conditions, parameters such as steam pressure, temperature and back pressure of an inlet and an outlet of a first stage, a second stage and a third stage of the low-pressure cylinder are collected, the efficiency of each stage and the efficiency of the low-pressure cylinder are calculated, dimensionless processing is carried out, and the efficiency of the low-pressure cylinder is calculated; and establishing a multiple regression model which takes the superheated steam stage efficiency as an independent variable and takes the low-pressure cylinder efficiency as a dependent variable. And considering the influence of the back pressure on the efficiency of the low-pressure cylinder, establishing a compensation model, and correcting the predicted efficiency of the low-pressure cylinder. In actual operation, the parameters are collected in real time, the efficiency of the current stage is calculated and substituted into the regression model and the compensation model, and the real-time efficiency of the low-pressure cylinder is obtained. According to the method, direct measurement of wet steam parameters is avoided by utilizing superheated steam stage data which are easy to obtain, real-time and accurate calculation of the efficiency of the low-pressure cylinder under different working conditions is realized, and the method can be widely applied to performance monitoring, operation optimization and fault diagnosis of a turboset.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of steam turbine performance monitoring and optimization, and in particular to a method and system for online calculation of low-pressure cylinder efficiency of a steam turbine. BACKGROUND

[0002] As the core equipment of thermal power plants, the operating efficiency of steam turbines is directly related to the economic benefits and energy utilization level of power plants. Among all the components of a steam turbine, the low-pressure cylinder is the last stage of energy conversion, and its efficiency has a significant impact on the thermal economy of the entire machine. However, since the exhaust steam of the low-pressure cylinder is usually in a wet steam state, traditional measurement methods cannot accurately obtain the thermodynamic parameters of the exhaust steam, especially the enthalpy and dryness. This makes it difficult to directly calculate and evaluate the efficiency of the low-pressure cylinder through online monitoring methods.

[0003] Currently, the accurate value of the low-pressure cylinder efficiency is mainly obtained through performance tests. Performance tests require specific operating conditions, involve complex testing equipment and strict test conditions, are time-consuming and labor-intensive, and can only reflect the state of the equipment at the time of the test, which cannot meet the real-time monitoring needs of the low-pressure cylinder efficiency. In addition, the enthalpy of the low-pressure cylinder exhaust steam needs to be calculated indirectly during the test process, which is complex and has limited accuracy, and cannot meet the demand for high-precision and real-time data in modern power plants.

[0004] On the other hand, a running steam turbine unit provides a large amount of real-time data, but due to the lack of accurate measurement methods for the dryness of the low-pressure cylinder exhaust steam, these data cannot be directly used to calculate the efficiency of the low-pressure cylinder. In particular, the difficulty in measuring wet steam parameters is the main obstacle to the online calculation of low-pressure cylinder efficiency.

[0005] To address the above problems, some research attempts to estimate the efficiency of the low-pressure cylinder through thermodynamic models and numerical simulation methods, but these methods usually require a large amount of computing resources and have high requirements for the accuracy of the model and the quality of the operating data, making it difficult to be widely applied in actual production. At the same time, these methods often ignore environmental factors such as the influence of back pressure on the efficiency of the low-pressure cylinder, resulting in deviations in the calculation results. SUMMARY

[0006] The present application provides a method and system for online calculation of low-pressure cylinder efficiency of a steam turbine, which addresses the problem of real-time calculation of low-pressure cylinder efficiency due to the wet steam state of the low-pressure cylinder exhaust steam and the inability to directly measure its thermodynamic parameters.

[0007] To achieve the above-mentioned purposes, the present application adopts the following technical solutions: A method for online calculation of low-pressure cylinder efficiency of a steam turbine, comprising the following steps: Performing a reference operating condition steam turbine performance test to obtain the efficiency of the low-pressure cylinder superheated steam stage and the efficiency of the low-pressure cylinder under the reference operating condition; Multi-condition tests are performed to obtain the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under different conditions; The data is dimensionless, the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under the reference condition are taken as reference values, and the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under each condition are dimensionless; Based on the dimensionless data, a low-pressure cylinder efficiency prediction model is established; Considering the influence of back pressure, a compensation model is established by analyzing the relationship between the back pressure and the low-pressure cylinder efficiency; The unit operation data is obtained, and the low-pressure cylinder efficiency prediction is calculated online in real time through the low-pressure cylinder efficiency prediction model and the compensation model; Based on the results of online real-time calculation and low-pressure cylinder efficiency prediction, a low-pressure cylinder efficiency change curve is drawn.

[0008] The further improvement of the present application is that the reference condition turbine performance test is performed to obtain the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under the reference condition, which comprises the following steps: The test is performed in spring or autumn of a year, and the environmental conditions are relatively stable during the test period; The unit load is adjusted to be within ±1.5% of the rated load, so that the unit is operated close to the rated condition; The low-pressure cylinder steam flow is adjusted to meet the test requirements; The inlet steam pressure, temperature and outlet steam pressure, temperature of the low-pressure cylinder superheated steam stage, and the unit load and back pressure measurement point data are recorded, wherein the low-pressure cylinder superheated steam stage corresponds to the first stage of the low-pressure cylinder, i.e., LP1, the second stage, i.e., LP2, and the third stage, i.e., LP3; The IAPWS-IF97 international water and steam thermal property formula is used to calculate the inlet and outlet steam enthalpy values of each stage; The isentropic enthalpy drop and the actual enthalpy drop of each stage are calculated to obtain the efficiency of each stage under the reference condition , wherein ; The low-pressure cylinder exhaust steam enthalpy is indirectly calculated through mass balance and energy balance, and then the low-pressure cylinder efficiency under the reference condition is calculated .

[0009] The further improvement of the present application is that the test conditions are as follows: The unit load fluctuates within ±1.5% of the rated load; The low-pressure cylinder steam pressure and temperature are within the allowable deviation range of the rated parameters, the pressure deviation is ±0.25 MPa, and the temperature deviation is ±4℃; the unit operation mode is the sequence valve operation mode; The data acquisition sampling period is less than or equal to 10 seconds.

[0010] The further improvement of the present application is that multi-condition tests are carried out to obtain the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under different conditions, including: The steam turbine performance test is repeated under different load levels to obtain multiple sets of test data; At each load level, the corresponding measurement point data is recorded, and the low-pressure cylinder extraction steam superheated steam stage efficiency and the low-pressure cylinder efficiency are calculated.

[0011] The further improvement of the present application is that the data is dimensionless, and the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under the reference condition are taken as reference values for the dimensionless processing of the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under each condition, including: The data under the reference condition is taken as the reference value for the dimensionless processing of the low-pressure cylinder extraction steam superheated steam stage efficiency and the low-pressure cylinder efficiency under each condition: ,

[0012] Among them: is the efficiency of the i-th stage of the low-pressure cylinder, is the efficiency of the i-th stage of the low-pressure cylinder under the reference condition, is the dimensionless value of the efficiency of the i-th stage of the low-pressure cylinder, is the efficiency of the low-pressure cylinder, is the efficiency of the low-pressure cylinder under the reference condition, is the dimensionless value of the efficiency of the low-pressure cylinder.

[0013] The further improvement of the present application is that based on the dimensionless processed data, a low-pressure cylinder efficiency prediction model is established, including: The dimensionless stage efficiency is taken as the independent variable, and the low-pressure cylinder efficiency is taken as the dependent variable to construct a data set; A multiple linear regression model is established by using the least square method:

[0014] Among them, is the regression coefficient.

[0015] The further improvement of the present application is that the influence of back pressure is considered, a compensation model is established by analyzing the relationship between the back pressure and the low-pressure cylinder efficiency, including: The real-time back pressure is collected A compensation model is established by analyzing the relationship between the back pressure and the low-pressure cylinder efficiency:

[0016] Among them, is the back pressure influence coefficient, is the back pressure under the reference condition, The back pressure compensation amount for the low pressure cylinder efficiency.

[0017] The further improvement of the present application is that the unit operation data is acquired, and the low pressure cylinder efficiency prediction is calculated in real time online through the low pressure cylinder efficiency prediction model and the compensation model, including: The real-time operation data of the inlet and outlet steam pressure, temperature, back pressure, and unit load of the low pressure cylinder LP1, LP2, and LP3 stages are derived from the DCS system, and the sampling period is less than or equal to 30 seconds; The data with the load fluctuating within the range of the rated load ± 1.5% is reserved, and the rest of the data is deleted; The actual efficiency of the current stage is calculated ; The dimensionless current stage efficiency is substituted into the regression model to calculate the predicted dimensionless low pressure cylinder efficiency :

[0018] The actual low pressure cylinder efficiency without compensation is calculated according to the predicted dimensionless efficiency :

[0019] The predicted low pressure cylinder efficiency is corrected by using the compensation model: .

[0020] The further improvement of the present application is that the low pressure cylinder efficiency change curve is drawn based on the result of the online real-time calculation and the low pressure cylinder efficiency prediction, including: The low pressure cylinder efficiency data in the statistical period is arranged in time sequence, and the curve of the low pressure cylinder efficiency changing with time is drawn with time as the horizontal axis and the low pressure cylinder efficiency as the vertical axis.

[0021] A system for online calculation of the low pressure cylinder efficiency of a steam turbine, including: A reference working condition steam turbine performance test module obtains the low pressure cylinder superheated steam stage efficiency and the low pressure cylinder efficiency under the reference working condition; A multi-working condition test module obtains the low pressure cylinder superheated steam stage efficiency and the low pressure cylinder efficiency under different working conditions; A data dimensionless processing module takes the low pressure cylinder superheated steam stage efficiency and the low pressure cylinder efficiency under the reference working condition as the reference value, and performs dimensionless processing on the low pressure cylinder superheated steam stage efficiency and the low pressure cylinder efficiency under each working condition; A prediction model establishment module establishes a low pressure cylinder efficiency prediction model based on the dimensionless processed data; A compensation model establishment module considers the back pressure influence, establishes a compensation model by analyzing the relationship between the back pressure and the low pressure cylinder efficiency; The calculation and prediction module obtains the unit operation data, and calculates and predicts the low-pressure cylinder efficiency in real time through the low-pressure cylinder efficiency prediction model and the compensation model; The curve drawing module draws the low-pressure cylinder efficiency change curve based on the result of the online real-time calculation and the low-pressure cylinder efficiency prediction.

[0022] Compared with the prior art, the present application has at least the following beneficial technical effects: The method and system for online calculation of the low-pressure cylinder efficiency of a steam turbine provided by the present application use easily obtained superheated steam stage operation data, avoid direct measurement of wet steam parameters, and solve the technical problem that the low-pressure cylinder efficiency cannot be calculated in real time online; by establishing a multiple regression model with the superheated steam stage efficiency as the independent variable and the low-pressure cylinder efficiency as the dependent variable, and considering the influence of the back pressure on the low-pressure cylinder efficiency, a compensation model is established, and the accuracy and reliability of the calculation result are improved; the method is simple to operate and has strong applicability, and can be used to monitor the low-pressure cylinder efficiency in real time under different working conditions, provide effective decision support for the operating personnel, facilitate timely discovery of changes in the performance of the equipment, operation optimization and fault diagnosis, and thus improve the economy and safety of the unit. The present application has the advantages of simple operation, high precision and strong applicability, has significant economic benefits and promotional value, and can be widely applied to performance monitoring, operation optimization and fault diagnosis of steam turbine units. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description are briefly introduced as follows; obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0024] Figure 1 is a flowchart of a method for online calculation of the low-pressure cylinder efficiency of a steam turbine.

[0025] Figure 2 is a schematic diagram of the principle thermal system of a steam turbine and the overall benchmark test point arrangement; Figure 3 is a low-pressure cylinder efficiency and monitoring month curve graph in a statistical period.

[0026] Figure 4 is a structural block diagram of a system for online calculation of the low-pressure cylinder efficiency of a steam turbine. DETAILED DESCRIPTION

[0027] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0028] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0029] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0030] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0031] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0032] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0033] Example 1 like Figure 1 As shown, the present invention provides a method for online calculation of the efficiency of a steam turbine low-pressure cylinder, comprising the following steps: (1) Test the turbine performance under the reference operating conditions to obtain the efficiency of the superheated steam stage of the low-pressure cylinder and the efficiency of the low-pressure cylinder under the reference operating conditions; (2) Conduct multi-condition tests to obtain the efficiency of the superheated steam stage of the low-pressure cylinder and the efficiency of the low-pressure cylinder under different conditions; (3) Dimensionless data processing: The efficiency of the superheated steam stage of the low-pressure cylinder and the efficiency of the low-pressure cylinder under the reference working condition are used as reference values ​​to perform dimensionless processing on the efficiency of the superheated steam stage of the low-pressure cylinder and the efficiency of the low-pressure cylinder under each working condition. (4) Based on the dimensionless data, a low-pressure cylinder efficiency prediction model is established; (5) Considering the influence of back pressure, a compensation model is established by analyzing the relationship between back pressure and low-pressure cylinder efficiency; (6) Obtain the unit operation data, and calculate the low-pressure cylinder efficiency prediction through the low-pressure cylinder efficiency prediction model and the compensation model in real time; (7) Based on the results of online real-time calculation and low-pressure cylinder efficiency prediction, draw the low-pressure cylinder efficiency change curve.

[0034] In this embodiment, the reference condition turbine performance test is carried out to obtain the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under the reference condition, including: Select the spring or autumn of the year to carry out the test, and the environmental conditions are relatively stable during the test period; Adjust the unit load to be within ±1.5% of the rated load, and ensure that the unit is running near the rated condition; Adjust the low-pressure cylinder steam flow to meet the test requirements; Record the inlet steam pressure, temperature and outlet steam pressure, temperature of the low-pressure cylinder superheated steam stage (corresponding to the first stage (LP1), the second stage (LP2) and the third stage (LP3) of the low-pressure cylinder), as well as the unit load, back pressure and other measured point data; Use the IAPWS-IF97 international water and steam thermodynamic property formula to calculate the inlet and outlet steam enthalpy of each stage; Calculate the isentropic enthalpy drop and actual enthalpy drop of each stage to obtain the efficiency of each stage under the reference condition , wherein ; Calculate the low-pressure cylinder exhaust steam enthalpy indirectly through mass balance and energy balance, and then calculate the low-pressure cylinder efficiency under the reference condition .

[0035] The test conditions are as follows: The unit load fluctuates within ±1.5% of the rated load; The low-pressure cylinder steam pressure and temperature are within the allowable deviation range of the rated parameters, with a pressure deviation of ±0.25 MPa and a temperature deviation of ±4℃; the unit operation mode is the sequential valve operation mode.

[0036] The data acquisition sampling period is less than or equal to 10 seconds to improve the data accuracy.

[0037] In this embodiment, multi-condition tests are carried out to obtain the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under different conditions, including: Repeat the turbine performance test under different load levels (such as 90%, 80%, and 70% rated load) to obtain multiple sets of test data; At each load level, the corresponding measuring point data is recorded, and the low-pressure cylinder extraction steam efficiency and the low-pressure cylinder efficiency are calculated.

[0038] In the embodiment, the data is dimensionless, the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under the reference condition are taken as reference values, and the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under each condition are dimensionless, including: The data under the reference condition is taken as the reference value, and the low-pressure cylinder extraction steam efficiency and the low-pressure cylinder efficiency under each condition are dimensionless, including: ,

[0039] Wherein: η i is the efficiency of the i th stage of the low-pressure cylinder, η i0 is the efficiency of the i th stage of the low-pressure cylinder under the reference condition, η i is the dimensionless value of the efficiency of the i th stage of the low-pressure cylinder, η is the efficiency of the low-pressure cylinder, η 0 is the efficiency of the low-pressure cylinder under the reference condition, η is the dimensionless value of the efficiency of the low-pressure cylinder.

[0040] In the embodiment, based on the dimensionless data, a low-pressure cylinder efficiency prediction model is established, including: The dimensionless stage efficiency is taken as the independent variable, and the low-pressure cylinder efficiency is taken as the dependent variable to construct a data set; A multiple linear regression model is established by using the least square method:

[0041] Wherein, is the regression coefficient.

[0042] The regression model can be extended to a nonlinear regression model as needed, introducing a quadratic term, a cross term, or using a nonlinear function to improve the fitting accuracy of the model.

[0043] In the embodiment, considering the influence of back pressure, a compensation model is established by analyzing the relationship between the back pressure and the low-pressure cylinder efficiency, including: The real-time back pressure is collected A compensation model is established by analyzing the relationship between the back pressure and the low-pressure cylinder efficiency:

[0044] Wherein, is the back pressure influence coefficient, is the back pressure under the reference condition, is the back pressure compensation amount of the low-pressure cylinder efficiency.

[0045] The back pressure influence coefficient b in the compensation model is obtained by fitting experimental data.

[0046] In the embodiment, the unit operation data is acquired, and the low-pressure cylinder efficiency is predicted in real time by the low-pressure cylinder efficiency prediction model and the compensation model, including: The real-time operation data of the low-pressure cylinder LP1, LP2, and LP3, including the inlet and outlet steam pressure, temperature, back pressure, and unit load, are derived from the DCS system, and the sampling period is less than or equal to 30 seconds; The data with the load fluctuating within ±1.5% of the rated load is retained, and the rest is deleted; The actual efficiency of the current stage is calculated

[0047] The dimensionless current stage efficiency is substituted into the regression model to calculate the predicted dimensionless low-pressure cylinder efficiency :

[0048] The actual low-pressure cylinder efficiency without compensation is calculated according to the predicted dimensionless efficiency :

[0049] The predicted low-pressure cylinder efficiency is corrected by the compensation model: .

[0050] The data screening criteria are: The unit load fluctuates within ±1.5% of the rated load; The low-pressure cylinder inlet steam parameters are within the allowable deviation range of the rated value; The data groups meeting the above conditions are retained, and the rest are deleted.

[0051] In the embodiment, based on the results of the online real-time calculation and low-pressure cylinder efficiency prediction, a low-pressure cylinder efficiency change curve is drawn, including: The low-pressure cylinder efficiency data in the statistical period is arranged in time sequence, with time as the horizontal axis and low-pressure cylinder efficiency as the vertical axis, to draw a curve of low-pressure cylinder efficiency change over time for reference by the operating personnel.

[0052] In addition, in the low-pressure cylinder efficiency calculation process, the mass balance and energy balance method is used to indirectly calculate the low-pressure cylinder exhaust steam enthalpy.

[0053] The method is suitable for different types of steam turbines, and by adjusting the data and model parameters of the reference working condition, the online calculation of the low-pressure cylinder efficiency of various steam turbines is realized.

[0054] The online calculation result can be used for steam turbine operation optimization and fault diagnosis, and provides decision support for operation personnel, and improves the economy and safety of the unit.

[0055] The method can be integrated in a steam turbine monitoring system, and provides a visual efficiency monitoring interface, and facilitates real-time monitoring of the performance state of the low-pressure cylinder.

[0056] Embodiment 2 This embodiment takes a certain 600 MW steam turbine unit as an example, and describes how to apply the method of the application to realize real-time calculation and monitoring of the efficiency of the low-pressure cylinder.

[0057] (1) Reference working condition steam turbine performance test: 1. Test condition selection The test is performed in spring or autumn to ensure that the environmental conditions are relatively stable, and to reduce the influence of external factors on the test results. The unit load is adjusted to 600 MW, that is, 100% of the rated load, and the allowable fluctuation range is ±1.5% (that is, 591 MW to 609 MW). The low-pressure cylinder inlet steam pressure and temperature are adjusted to the rated values, and the pressure deviation is not more than ±0.25 MPa, and the temperature deviation is not more than ±4℃. The unit adopts sequential valve operation mode to ensure stable steam flow and valve state.

[0058] 2. Data acquisition The performance reference test points in the performance monitoring project of the steam turbine low-pressure cylinder are recommended to be arranged and installed according to the requirements of the comprehensive test in the American Society of Mechanical Engineers ASME PTC 6-2004 “Steam Turbine Performance Test Code”. Figure 2 is a typical schematic diagram of the principle thermal system of the steam turbine and the arrangement of the comprehensive reference test points.

[0059] The 0.075 level high-precision absolute pressure transmitter and relative pressure transmitter are used to measure pressure, and the measured value is corrected by instrument calibration value, atmospheric pressure, instrument zero and instrument installation difference. Four exhaust pressure test points are installed for each condenser, and the 0.075 level high-precision absolute pressure transmitter is used for measurement, and the measured value is corrected by instrument zero and instrument calibration value. The following pressure measurement point parameters need to be collected: main steam pressure left, main steam pressure right, regulated stage steam pressure, high-pressure cylinder exhaust pressure, reheat steam pressure left, reheat steam pressure right, medium-pressure cylinder exhaust pressure, low-pressure cylinder inlet steam pressure, low-pressure cylinder exhaust pressure 1, low-pressure cylinder exhaust pressure 2, low-pressure cylinder exhaust pressure 3, low-pressure cylinder exhaust pressure 4, first-stage extraction steam pressure, No. 1 high-pressure heater inlet steam pressure, No. 2 high-pressure heater inlet steam pressure, third-stage extraction steam pressure, No. 3 high-pressure heater inlet steam pressure, fourth-stage extraction steam pressure, deaerator inlet steam pressure, four-extraction to small machine inlet steam pressure, fifth-stage extraction steam pressure, No. 5 low-pressure heater inlet steam pressure, sixth-stage extraction steam pressure, No. 6 low-pressure heater inlet steam pressure, seventh-stage extraction steam pressure, eighth-stage extraction steam pressure, deaerator inlet water pressure, final feedwater pressure, feedwater pump outlet main pipe pressure, reheat heater desuperheating water main pipe pressure, high-pressure balance disc steam leakage pressure left upper, high-pressure balance disc steam leakage pressure right upper, high-medium-pressure rear shaft seal steam leakage to SSR pressure, atmospheric pressure.

[0060] The precision E-type thermocouple and platinum resistance are installed as the primary measuring element for the test, and the secondary instrument adopts temperature transmitter for measurement. The temperature signal is sent to the data acquisition system to realize automatic storage and recording, and the measured value is corrected by the thermocouple calibration value. The following temperature parameters need to be collected: main steam temperature left 1, main steam temperature left 2, main steam temperature right 1, main steam temperature right 2, regulated stage steam temperature, high pressure cylinder exhaust steam temperature 1, high pressure cylinder exhaust steam temperature 2, hot reheat steam temperature left 1, hot reheat steam temperature left 2, hot reheat steam temperature right 1, hot reheat steam temperature right 2, medium pressure cylinder exhaust steam temperature 1, medium pressure cylinder exhaust steam temperature 2, low pressure cylinder inlet steam temperature 1, low pressure cylinder inlet steam temperature 2, first stage extraction steam temperature, No. 1 high pressure heater inlet steam temperature, No. 2 high pressure heater inlet steam temperature, third stage extraction steam temperature, No. 3 high pressure heater inlet steam temperature, fourth stage extraction steam temperature, deaerator inlet steam temperature, fourth extraction to A small machine inlet steam temperature, fourth extraction to B small machine inlet steam temperature, fifth stage extraction steam temperature, No. 5 low pressure heater inlet steam temperature, sixth stage extraction steam temperature, No. 6 low pressure heater inlet steam temperature, hot well outlet water temperature, shaft heater inlet water temperature, No. 8 low pressure heater inlet water temperature, No. 8 low pressure heater drain water temperature, No. 7 low pressure heater drain water temperature, No. 7 low pressure heater outlet water temperature, No. 6 low pressure heater drain water temperature, No. 6 low pressure heater outlet water temperature, No. 5 low pressure heater drain water temperature, No. 5 low pressure heater outlet water temperature, deaerator inlet water temperature, deaerator outlet water temperature 1, deaerator outlet water temperature 2, No. 3 high pressure heater inlet water temperature, No. 3 high pressure heater drain water temperature, No. 3 high pressure heater outlet water temperature, No. 2 high pressure heater drain water temperature, No. 2 high pressure heater outlet water temperature, No. 1 high pressure heater drain water temperature, No. 1 high pressure heater outlet water temperature, final feed water temperature 1, final feed water temperature 2, reheater desuperheating water main temperature, superheater desuperheating water main temperature, high pressure balance disc leakage steam temperature left upper, high pressure balance disc leakage steam temperature right upper, high and medium pressure rear shaft seal leakage steam to SSR temperature.

[0061] The main condensate flow at the deaerator inlet is used as the test reference flow, and the flow differential pressure is measured by a 0.05 differential pressure transmitter. The measured value is corrected by the instrument zero and instrument calibration value. The reheater desuperheating water main flow, superheater desuperheating water main flow, left upper / right upper high pressure balance disc leakage steam flow, high and medium pressure rear shaft seal leakage steam to SSR flow, and fourth stage extraction steam flow are recommended to be measured by standard orifice or standard nozzle. The following flow differential pressure signals need to be collected: condensate flow nozzle differential pressure (No. 1 orifice), condensate flow nozzle differential pressure (No. 2 orifice), fourth stage extraction steam flow differential pressure, high pressure balance disc leakage steam flow differential pressure left upper, high pressure balance disc leakage steam flow differential pressure right upper, superheater desuperheating water main flow differential pressure, reheater desuperheating water main flow differential pressure, high pressure door rod to shaft heater inlet steam flow differential pressure, high and medium pressure rear shaft seal leakage steam to SSR flow differential pressure.

[0062] A 0.1 WT3000 test power meter is used, the CT and PT secondary terminals at the generator outlet are connected by wires, and the three-phase three-wire connection method is used to measure the generator output power. The generator output active power and power factor are automatically recorded by the computer every 30 seconds.

[0063] 3. Calculation of enthalpy and low-pressure cylinder efficiency: Using IAPWS-IF97 international water and steam thermodynamic property formula, the inlet and outlet steam enthalpy of each stage is calculated and , wherein .

[0064] The isentropic enthalpy drop is calculated:

[0065] , wherein is the outlet enthalpy under the assumption of isentropic process at the outlet pressure.

[0066] The actual enthalpy drop is calculated:

[0067] The efficiency of each stage of the low-pressure cylinder extraction steam as superheated steam is calculated:

[0068] According to the extraction steam flow rate and the inlet and outlet steam flow rate, a mass balance equation is established. Using the mass balance results and the measured thermodynamic parameters, an energy balance equation is established to indirectly calculate the low-pressure cylinder exhaust steam enthalpy . The isentropic enthalpy drop and the actual enthalpy drop of the low-pressure cylinder are calculated, and then the low-pressure cylinder efficiency is calculated.

[0069] 4. Determining the reference value The low-pressure cylinder efficiency of each superheated steam stage and the low-pressure cylinder efficiency calculated above are taken as reference values for subsequent calculations.

[0070] (2) Variable condition turbine performance test: The test is carried out in spring or autumn of the year. During the test period, the unit load is adjusted to 100% rated load (±1.5%), the unit main steam temperature is adjusted to the rated temperature (±4℃), the unit valve sequence operating state is the sequence valve, the manual operating mode, the valve opening degree is selected as the reference condition valve point, the sampling period is set to be less than or equal to 10 seconds, and the unit meets the above conditions. After being stable, the data is continuously collected for half an hour to complete one test condition. The comprehensive valve position of the unit is changed by 0.2% (increased or decreased), the steam turbine low-pressure cylinder inlet steam quantity is adjusted, and the next condition is carried out. According to the method of the reference condition test, the operating data under each condition is collected, and the corresponding stage efficiency and the low-pressure cylinder efficiency are calculated.

[0071] (3) Data dimensionless processing The data under the reference condition are taken as reference values, and the stage efficiency and low-pressure cylinder efficiency under each condition are dimensionless processed: ,

[0072] Among them: is the efficiency of the i-th stage of the low-pressure cylinder, is the efficiency of the i-th stage of the low-pressure cylinder under the reference condition, is the dimensionless value of the efficiency of the i-th stage of the low-pressure cylinder, is the efficiency of the low-pressure cylinder, is the efficiency of the low-pressure cylinder under the reference condition, is the dimensionless value of the efficiency of the low-pressure cylinder.

[0073] The dimensionless data are arranged into a table to construct a data set for use in regression model training.

[0074] (4) Establishing a low-pressure cylinder efficiency prediction model The dimensionless stage efficiency is taken as the independent variable, and the low-pressure cylinder efficiency is taken as the dependent variable to construct a data set and establish a multiple linear regression model:

[0075] The dimensionless data set is used to solve the regression coefficients by the least squares method . The determination coefficient and the mean square error (MSE) of the regression model are calculated to evaluate the fitting effect of the model. If necessary, consider introducing a quadratic term or a cross term to establish a nonlinear regression model to improve the accuracy.

[0076] (5) Considering the influence of back pressure and establishing a compensation model Under each condition, the relationship between back pressure and low-pressure cylinder efficiency is analyzed. Assuming that the influence of back pressure on low-pressure cylinder efficiency is linear, a compensation model is established:

[0077] Among them, b is the back pressure influence coefficient, is the back pressure under the reference condition, is the back pressure compensation amount of the low-pressure cylinder efficiency. The test data are used to solve the back pressure influence coefficient b by linear regression method. The accuracy of the compensation model is tested to ensure that it can effectively reflect the influence of back pressure on the low-pressure cylinder efficiency.

[0078] (6) Online real-time calculation and low-pressure cylinder efficiency prediction Export the real-time operating data of the inlet and outlet steam pressure, temperature, back pressure, and unit load of the low-pressure cylinder LP1, LP2, and LP3 from the DCS system, with a sampling period less than or equal to 30 seconds. Keep the data with load fluctuations within ±1.5% and delete the rest.

[0079] Calculate the actual efficiency of the current stage , and perform dimensionless processing:

[0080] Substitute the dimensionless current stage efficiency into the regression model to calculate the predicted dimensionless low-pressure cylinder efficiency :

[0081] According to the predicted dimensionless efficiency, calculate the uncompensated actual low-pressure cylinder efficiency :

[0082] Calculate the back pressure compensation amount by calculating the back pressure difference :

[0083] Use the compensation model to correct the predicted low-pressure cylinder efficiency:

[0084] (7) Draw the low-pressure cylinder efficiency change curve Arrange the real-time calculated low-pressure cylinder efficiency in chronological order to form time series data. Use data analysis and visualization tools such as MATLAB, Python's Matplotlib, or commercial software to draw the curve of low-pressure cylinder efficiency change over time, as shown in Figure 3 . Observe the trend of low-pressure cylinder efficiency change through the curve to determine whether there is a decrease or abnormal fluctuation in efficiency. If a significant decrease in efficiency is found, notify the operating personnel to check the equipment status in time to prevent faults.

[0085] (8) Application effect Through the method of the application, the real-time online calculation of the low-pressure cylinder efficiency is successfully realized, and the demand of power plants for real-time monitoring of the performance of key equipment is met. The calculated low-pressure cylinder efficiency is compared with the results of periodic performance tests to verify the accuracy of the method, and the error is within the allowable range. According to the real-time changes of the low-pressure cylinder efficiency, the operating personnel can timely adjust the operating parameters, such as adjusting the back pressure and optimizing the cooling water temperature, to improve the overall economy of the unit. Through monitoring the changes in efficiency, signs of performance degradation of the equipment can be detected early, preventive maintenance can be performed, and the failure rate can be reduced.

[0086] (9) Matters needing attention Ensure that the real-time data collected is accurate and reliable, and calibrate the measuring instruments regularly. As the operating condition of the equipment changes, update the regression model and compensation model regularly to improve the prediction accuracy. In addition to back pressure, other environmental factors such as ambient temperature and humidity can also be considered to extend the model.

[0087] (10) Applicable scope The method is applicable to steam turbine units of different capacities and models, and can be applied to different units by adjusting the reference operating condition and model parameters. The method is simple to operate and low in cost, and has a wide application prospect, which can be popularized in the power industry.

[0088] Example 3 As shown in Figure 4 The system for online calculation of low-pressure cylinder efficiency of a steam turbine provided by the application comprises: A reference operating condition steam turbine performance test module obtains the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under the reference operating condition; A multi-condition test module obtains the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under different operating conditions; A data dimensionless processing module takes the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under the reference operating condition as reference values, and performs dimensionless processing on the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under each operating condition; A prediction model establishment module establishes a low-pressure cylinder efficiency prediction model based on the dimensionless processed data; A compensation model establishment module considers the influence of back pressure, analyzes the relationship between back pressure and low-pressure cylinder efficiency, and establishes a compensation model; A calculation and prediction module obtains unit operating data, and performs online real-time calculation and low-pressure cylinder efficiency prediction through the low-pressure cylinder efficiency prediction model and the compensation model; A curve drawing module draws a low-pressure cylinder efficiency change curve based on the results of online real-time calculation and low-pressure cylinder efficiency prediction.

[0089] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the scope of the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0090] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for online calculation of a steam turbine low pressure cylinder efficiency, characterized in that, The method comprises the following steps: a reference working condition turbine performance test is performed to obtain low-pressure cylinder superheated steam stage efficiency and low-pressure cylinder efficiency under the reference working condition; a multi-working condition test is performed to obtain low-pressure cylinder superheated steam stage efficiency and low-pressure cylinder efficiency under different working conditions; data is dimensionless processed, the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under the reference working condition are taken as reference values, and the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under each working condition are dimensionless processed; a low-pressure cylinder efficiency prediction model is established based on the dimensionless processed data; a compensation model is established by analyzing the relationship between back pressure and low-pressure cylinder efficiency in consideration of the influence of back pressure; unit operation data is obtained, and online real-time calculation and low-pressure cylinder efficiency prediction are performed through the low-pressure cylinder efficiency prediction model and the compensation model; a low-pressure cylinder efficiency change curve is drawn based on the results of the online real-time calculation and the low-pressure cylinder efficiency prediction.

2. A method for on-line calculation of the efficiency of the low pressure cylinder of a steam turbine according to claim 1, characterized in that, The reference working condition turbine performance test is performed to obtain low-pressure cylinder superheated steam stage efficiency and low-pressure cylinder efficiency under the reference working condition, comprising: the test is performed in spring or autumn in a year, and the environmental conditions are relatively stable during the test; the unit load is adjusted to be within ±1.5% of the rated load, so that the unit is operated close to the rated working condition; the low-pressure cylinder steam flow is adjusted to meet the test requirements; the inlet steam pressure, temperature and outlet steam pressure, temperature of the low-pressure cylinder superheated steam stage, and the unit load and back pressure measurement point data are recorded, wherein the low-pressure cylinder superheated steam stage corresponds to the first stage LP1, the second stage LP2 and the third stage LP3 of the low-pressure cylinder; the IAPWS-IF97 international water and steam thermal property formula is used to calculate the inlet and outlet steam enthalpy values of each stage; The isentropic enthalpy drop and actual enthalpy drop of each stage are calculated to obtain the efficiency of each stage under the reference working condition wherein ; The low-pressure cylinder exhaust steam enthalpy is indirectly calculated through mass balance and energy balance, and then the low-pressure cylinder efficiency under the reference working condition is calculated .

3. A method for on-line calculation of the efficiency of the low pressure cylinder of a steam turbine according to claim 2, characterized in that, the test conditions are as follows: the unit load fluctuates within ±1.5% of the rated load; the low-pressure cylinder steam pressure and temperature are within the allowable deviation range of the rated parameters, the pressure deviation is ±0.25 MPa, and the temperature deviation is ±4℃; and the unit is operated in a sequence valve operation mode; the data acquisition sampling period is less than or equal to 10 seconds.

4. A method for on-line calculation of the efficiency of the low pressure cylinder of a steam turbine according to claim 2, characterized in that, The multi-working condition test is performed to obtain low-pressure cylinder superheated steam stage efficiency and low-pressure cylinder efficiency under different working conditions, comprising: turbine performance tests are repeatedly performed under different load levels to obtain multiple sets of test data; under each load level, corresponding measurement point data are recorded, and the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency are calculated.

5. A method for on-line calculation of efficiency of low pressure cylinder of steam turbine as claimed in claim 1 wherein, The data is dimensionless processed, the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under the reference working condition are taken as reference values, and the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under each working condition are dimensionless processed, comprising: the data under the reference working condition is taken as the reference value, and the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under each working condition are dimensionless processed; ， wherein: is the efficiency of the i-th stage of the low pressure cylinder, is the efficiency of the i-th stage of the low pressure cylinder at the reference operating condition, is the non-dimensionalized value of the efficiency of the i-th stage of the low pressure cylinder, is the efficiency of the low pressure cylinder, is the efficiency of the low pressure cylinder at the reference operating condition, is the non-dimensionalized value of the efficiency of the low pressure cylinder.

6. A method for on-line calculation of efficiency of low pressure cylinder of steam turbine as claimed in claim 1 wherein, The low-pressure cylinder efficiency prediction model is established based on the dimensionless processed data, comprising: the dimensionless processed stage efficiency is taken as the independent variable, and the low-pressure cylinder efficiency is taken as the dependent variable to construct a data set; a multiple linear regression model is established by using the least square method: wherein is the regression coefficient.

7. A method for on-line calculation of efficiency of low pressure cylinder of steam turbine as claimed in claim 1 wherein, The compensation model is established by analyzing the relationship between back pressure and low-pressure cylinder efficiency in consideration of the influence of back pressure, comprising: Collecting real-time back pressure By analyzing the relationship between back pressure and low-pressure cylinder efficiency, a compensation model is established: wherein, is a back pressure influence coefficient, is a back pressure at a reference operating condition, is a back pressure compensation amount for the low-pressure cylinder efficiency.

8. A method for on-line calculation of the efficiency of the low pressure cylinder of a steam turbine according to claim 7, characterized in that, The unit operation data is acquired, and the low-pressure cylinder efficiency prediction model and the compensation model are used to calculate and predict the low-pressure cylinder efficiency in real time, including: The real-time operation data of the low-pressure cylinder LP1, LP2, and LP3, including the inlet and outlet steam pressure, temperature, back pressure, and unit load, are exported from the DCS system, and the sampling period is less than or equal to 30 seconds; The data with the load fluctuating within ±1.5% of the rated load is retained, and the rest of the data is deleted; calculating the actual efficiency of the current stage ; Substituting the non-dimensionalized current stage efficiency into the regression model, the predicted non-dimensionalized low pressure cylinder efficiency is calculated : According to the predicted dimensionless efficiency, the uncompensated actual low-pressure cylinder efficiency is calculated : The predicted low-pressure cylinder efficiency is corrected by using the compensation model: 。 9. A method for on-line calculation of the efficiency of the low pressure cylinder of a steam turbine according to claim 8, characterized in that, Based on the results of the online real-time calculation and the low-pressure cylinder efficiency prediction, the low-pressure cylinder efficiency change curve is drawn, including: The low-pressure cylinder efficiency data in the statistical period is arranged in time sequence, and the curve of the low-pressure cylinder efficiency change with time is drawn with time as the horizontal axis and the low-pressure cylinder efficiency as the vertical axis.

10. A system for online calculation of a steam turbine low pressure cylinder efficiency, characterized by, Including: The reference condition steam turbine performance test module obtains the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under the reference condition; The multi-condition test module obtains the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under different conditions; The data dimensionless processing module takes the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under the reference condition as the reference value, and performs dimensionless processing on the low-pressure cylinder superheated steam stage efficiency and the low-pressure cylinder efficiency under each condition; The prediction model establishment module establishes the low-pressure cylinder efficiency prediction model based on the dimensionless processed data; The compensation model establishment module considers the influence of back pressure, analyzes the relationship between back pressure and low-pressure cylinder efficiency, and establishes the compensation model; The calculation and prediction module acquires the unit operation data, and calculates and predicts the low-pressure cylinder efficiency in real time through the low-pressure cylinder efficiency prediction model and the compensation model; The curve drawing module draws the low-pressure cylinder efficiency change curve based on the results of the online real-time calculation and the low-pressure cylinder efficiency prediction.

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