Turboset valve point working condition output calculation method

Abstract

The invention discloses a turbine set valve point working condition output calculation method. Firstly, a turbine set steam distribution end is constructed; according to the number m of the full-open high-pressure regulating valves and the number n of the static blades of the corresponding regulating stages, valve point working conditions and operation intervals are divided, and then according to the steam inlet parameters, geometric structures and sizes of the regulating stages, a least square method is adopted. Fitting a regulating stage pressure ratio epsilon-flow coefficient mu characteristic function and a regulating stage pressure ratio epsilon-regulating stage efficiency eta characteristic function, and carrying out related variable working condition calculation; according to the final calculation result, inlet and outlet parameters of each regulating stage nozzle arc section and the share of the respective inlet flow in the main steam flow are obtained; and when the technical output of the m-x valve point working condition is calculated, the full-open design working condition of m regulating valves is taken as a reference working condition, and iterative solution is carried out according to the consistency of two regulating-stage general characteristic functions and a single regulating-stage stationary blade characteristic area F and the reference working condition. The method is helpful for comprehensively observing and evaluating the safety and economy of steam turbine unit valve point operation.

Description

Technical Field

[0001] This invention relates to a method for calculating the output of a steam turbine unit under valve point operating conditions, belonging to the field of steam turbine operation technology. Background Technology

[0002] For nozzle-operated steam turbine units, valve-point sliding pressure operation is an advanced operating control strategy. It aims to minimize throttling losses and improve the unit's thermal economy under varying load conditions by optimizing the coordination between main steam pressure and regulating valve opening. Typically, different load ranges correspond to different optimal valve point combinations. For a typical nozzle-operated steam turbine unit with four high-pressure regulating valves, valve point modes include two-valve-point sliding pressure and three-valve-point sliding pressure. Two-valve-point sliding pressure refers to keeping both regulating valves fully open below the technical output of the two-valve-point operating condition, controlling the load by adjusting the main steam pressure. Three-valve-point sliding pressure refers to keeping all three valves fully open below the technical output of the three-valve-point operating condition and above the technical output of the two-valve-point operating condition, with the main steam pressure increasing as the load increases. Therefore, the technical output of the valve point operating condition is a key basis for dividing the turbine unit's operating range. Furthermore, the technical output of the valve point operating condition depends not only on the number of fully open high-pressure regulating valves but also on the number of stationary vanes in the regulating stage corresponding to the fully open high-pressure regulating valves.

[0003] A small number of domestically manufactured nozzle-type steam turbine units, based on imported technology, were initially designed with three valves operating under sliding pressure due to the high load rates in the regions where the foreign manufacturers were located. Therefore, since their commissioning, they have consistently operated under three-valve sliding pressure, lacking data on two-valve sliding pressure operation. Constant-power variable-pressure operation testing is an effective means of studying the valve-point sliding pressure operation characteristics of nozzle-type steam turbine units. Scientifically predicting the technical output under valve-point operating conditions helps refine the test plan, arrange reasonable and necessary test loads, and comprehensively observe and evaluate the safety and economy of the turbine unit's valve-point operation. Summary of the Invention

[0004] The purpose of this invention is to comprehensively observe and evaluate the safety and economy of turbine unit valve point operation. This invention proposes a method for calculating the output of turbine unit valve point operation.

[0005] The technical solution implemented by this invention is as follows:

[0006] The present invention provides a method for calculating the output of a steam turbine unit under valve point operating conditions, comprising the following steps:

[0007] S1. Consider a single high-pressure regulating valve and the single regulating stage nozzle arc segment it controls as a steam distribution unit; a single regulating stage nozzle arc segment is composed of n regulating stage stationary vanes; based on the number m of high-pressure regulating valves in the turbine unit and the steam distribution structure, connect m steam distribution units in parallel, and then connect them in series with the main steam valve to form the steam distribution end of the turbine unit;

[0008] S2. Based on the number m of fully open high-pressure regulating valves and the corresponding number n of stationary vanes in the regulating stage, divide the valve point conditions and operating ranges, including valve point condition m-1, valve point condition m-2, and valve point condition mx.

[0009] S3. Based on the inlet parameters, geometry, and dimensions of the regulating stage, calculate the regulating stage pressure ratio ε-flow coefficient μ characteristic and the regulating stage pressure ratio ε-regulating stage efficiency η characteristic; using the least squares method, fit the regulating stage pressure ratio ε-flow coefficient μ characteristic function and the regulating stage pressure ratio ε-regulating stage efficiency η characteristic function when the stage critical pressure ratio < regulating stage pressure ratio < 0.95; and based on the above regulating stage pressure ratio ε-flow coefficient μ characteristic function and regulating stage pressure ratio ε-regulating stage efficiency η characteristic function, perform relevant variable operating condition calculations;

[0010] S4. Based on the mass conservation equation, energy balance equation, and regulating stage characteristics, the main steam pressure, main steam temperature, regulating stage pressure, monitoring section extraction steam pressure and temperature, reheat steam temperature, reheat steam pressure loss, back pressure, heater upper / lower end differential pressure, extraction pipeline pressure loss, feedwater pump efficiency, turbine efficiency, boiler desuperheating water flow rate, and low-pressure cylinder exhaust enthalpy are taken as known quantities, and the design values ​​under the condition of m fully open regulating valves are taken. The inlet pressure P1 of each regulating stage nozzle arc segment is taken as the unknown, and the characteristic area F of each regulating stage stator vane is taken as the target value. Iterative calculations of the turbine unit's thermal system are performed. During the calculation process, different characteristic areas F of individual regulating stage stator vanes are set, ensuring that the final main steam flow rate is equal to the main steam flow rate under the design condition of fully open regulating valves. Based on the final calculation results, the inlet and outlet parameters of each regulating stage nozzle arc segment and the proportion of their respective inlet flow rate to the main steam flow rate are obtained.

[0011] S5. When calculating the technical output of the mx valve point, the design condition with m control valves fully open is taken as the benchmark condition. Its thermodynamic parameters, the inlet and outlet parameters of each control stage nozzle arc segment, and the proportion of their respective inlet flow to the main steam flow are taken as benchmark parameters. x is the number of control valves that are closed. The inlet steam flow and efficiency of the control stage nozzle arc segments corresponding to the remaining mx fully open control valves are solved iteratively according to conventional methods, based on the two general characteristic functions of the control stages and the fact that the characteristic area F of a single control stage stator blade is consistent with the benchmark condition.

[0012] Furthermore, in step S2, mx ≥ 2.

[0013] Further, in step S3, when constructing the characteristic function of regulating stage pressure ratio ε - flow coefficient μ, the regulating stage pressure ratio is taken in the range of 0.00 to 1.05. Specifically, when the stage critical pressure ratio < regulating stage pressure ratio < 0.95, the flow coefficient ε is taken as the characteristic function value of regulating stage pressure ratio ε - flow coefficient μ; when 0.00 < regulating stage pressure ratio ≤ stage critical pressure ratio, the flow coefficient ε*μ = 1; when 1.00 ≤ regulating stage pressure ratio ≤ 1.05, the flow coefficient ε is taken as "zero"; when 0.95 ≤ regulating stage pressure ratio < 1, the flow coefficient ε is linearly interpolated according to the flow coefficient ε corresponding to regulating stage pressure ratio = 0.95 and the flow coefficient ε corresponding to regulating stage pressure ratio = 1.00.

[0014] Further, in step S3, when constructing the characteristic function of regulating stage pressure ratio ε - regulating stage efficiency η, the regulating stage pressure ratio ranges from 0.00 to 1.05. Specifically, when the stage critical pressure ratio < regulating stage pressure ratio < 0.95, the regulating stage efficiency η is taken as the value of the characteristic function of regulating stage pressure ratio ε - regulating stage efficiency η; when the regulating stage pressure ratio = 0.00 and the regulating stage pressure ratio = 1.00, the regulating stage efficiency η is set to 0; when 0.00 < regulating stage pressure ratio ≤ stage critical pressure ratio, the regulating stage efficiency η is linearly interpolated according to the regulating stage efficiency η corresponding to regulating stage pressure ratio = 0.00 and the regulating stage efficiency η corresponding to regulating stage pressure ratio = stage critical pressure ratio; when 1.00 ≤ regulating stage pressure ratio ≤ 1.05, the regulating stage efficiency η is set to "zero"; when 0.95 ≤ regulating stage pressure ratio < 1, the regulating stage efficiency η is linearly interpolated according to the regulating stage efficiency η corresponding to regulating stage pressure ratio = 0.95 and the regulating stage efficiency η corresponding to regulating stage pressure ratio = 1.00.

[0015] Furthermore, a single regulating stage nozzle arc segment is composed of n regulating stage stator blades. For a regulating stage, the characteristic area of ​​all its individual regulating stage stator blades is the same, that is, the characteristic area F of the regulating stage stator blades is the same. The characteristic area of ​​a single regulating stage stator blade is calculated according to the inlet and outlet thermal parameters of the single regulating stage nozzle arc segment, according to formula (1).

[0016] Equation (1)

[0017] In the formula: F is the characteristic area of ​​a single regulating stage stator vane; G is the inlet flow rate of a single regulating stage nozzle arc segment; P1 is the inlet pressure of a single regulating stage nozzle arc segment; V1 is the inlet specific volume of a single regulating stage nozzle arc segment; n is the number of regulating stage stator vanes contained in a single regulating stage nozzle arc segment, taken as the design value; μ is the regulating stage flow coefficient; P2 is the outlet pressure.

[0018] Furthermore, the fully open flow coefficients of the main steam valve and the regulating valve in step S4 are calculated based on the expansion coefficient method of the International Electrotechnical Commission standard IEC 534-22 and the design thermodynamic parameters and pressure loss of the fully open valves under the condition of m regulating valves being fully open; the steam inlet flow rates of the main steam valve and the regulating valve under the condition of variable operation are calculated based on the expansion coefficient method of the International Electrotechnical Commission standard IEC 534-22 and the characteristic function of the regulating valve.

[0019] Furthermore, the ratio of the calculated technical output of the m fully open control valves obtained by "setting different characteristic areas F of the individual regulating stage stator vanes, so that the final main steam flow is equal to the main steam flow under the design condition of the fully open control valves" in step S4 to the actual technical output of the m fully open control valves of the unit is used as a correction coefficient for the calculated technical output of other valve point conditions.

[0020] Furthermore, in step S5, to ensure the accuracy of the variable operating condition calculation for the technical output of the mx valve point, the flow rate of the flow passage stage group other than the low-pressure cylinder last stage group is calculated according to the Flueger formula, and the efficiency within the flow passage stage group is taken as the design value and remains constant. For the efficiency of the low-pressure cylinder last stage group, the pressure ratio and efficiency characteristic curves of the low-pressure cylinder last stage group under various typical operating conditions and the exhaust loss curve must be fitted according to the thermodynamic characteristic data provided by the manufacturer to perform variable operating condition calculations.

[0021] Furthermore, in step S2, the two control valves that are initially opened are combined into one "equivalent control valve"; the fully open flow coefficient of the "equivalent control valve" is equal to twice the fully open flow coefficient of a single control valve; the number of stationary vanes in the control stage nozzle arc segment corresponding to the "equivalent control valve" is the sum of the number of stationary vanes in the control stage nozzle arc segment corresponding to the two control valves; the steam inlet flow of the "equivalent control valve" under variable operating conditions is calculated based on the expansion coefficient method and control valve characteristic function of the International Electrotechnical Commission standard IEC 534-22.

[0022] Furthermore, when the number n of regulating stage stator vanes contained in a single regulating stage nozzle arc segment is consistent with each other, the change of the regulating valve sequence does not affect the technical output of the MX valve point operating condition; when the number n of regulating stage stator vanes contained in a single regulating stage nozzle arc segment is different from each other, the technical output of the MX valve point operating condition must be recalculated based on the number n of regulating stage stator vanes in the regulating stage nozzle arc segment corresponding to the MX fully open regulating valve after the change of the regulating valve sequence.

[0023] The beneficial effects of this invention are

[0024] 1. The method described in this invention defines the steam distribution unit structure, divides the valve operating range, calculates the critical pressure ratio, establishes a universal flow coefficient curve, and combines the steam flow calculation of fully open and partially open regulating valves to accurately solve the technical output under valve operating conditions. This invention solves the problems of traditional methods relying on empirical charts and having high computational complexity. Through iterative optimization and simplification of the physical model, it significantly improves computational efficiency and accuracy, providing a reliable basis for refining test plans and arranging reasonable and necessary test loads.

[0025] 2. This invention helps to refine test plans, arrange reasonable and necessary test loads, and comprehensively observe and evaluate the safety and economy of turbine unit valve point operation. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the principles and effects of the present invention.

[0027] This embodiment of a method for calculating the output of a steam turbine unit under valve point operating conditions includes the following steps:

[0028] S1. Consider a single high-pressure regulating valve and the single regulating stage nozzle arc segment it controls as a steam distribution unit; a single regulating stage nozzle arc segment is composed of n regulating stage stationary vanes; based on the number m of high-pressure regulating valves in the turbine unit and the steam distribution structure, connect m steam distribution units in parallel, and then connect them in series with the main steam valve to form the steam distribution end of the turbine unit;

[0029] S2. Based on the number of fully open high-pressure regulating valves m and the corresponding number of stationary vanes n in the regulating stage, the valve point conditions and operating ranges are divided, including valve point condition m-1, valve point condition m-2, valve point condition mx, etc.; based on shaft safety, mx≥2.

[0030] S3. Based on the inlet parameters, geometry, and dimensions of the regulating stage, and following the methods described in the turbine principle, calculate the regulating stage pressure ratio ε-flow coefficient μ characteristic and the regulating stage pressure ratio ε-regulating stage efficiency η characteristic. Using the least squares method, fit the regulating stage pressure ratio ε-flow coefficient μ characteristic function and the regulating stage pressure ratio ε-regulating stage efficiency η characteristic function when the stage critical pressure ratio < regulating stage pressure ratio < 0.95. Based on the above two general regulating stage characteristic functions, perform relevant variable operating condition calculations using conventional methods.

[0031] Furthermore, to broaden the applicability of the variable operating condition calculation for the regulating stage pressure ratio, the regulating stage pressure ratio is set to range from 0.00 to 1.05 when constructing the piecewise characteristic function of regulating stage pressure ratio ε-flow coefficient μ. Specifically, when the stage critical pressure ratio < regulating stage pressure ratio < 0.95, the flow coefficient ε is taken from the characteristic function value of regulating stage pressure ratio ε-flow coefficient μ; when 0.00 < regulating stage pressure ratio ≤ stage critical pressure ratio, the flow coefficient ε*μ = 1; when 1.00 ≤ regulating stage pressure ratio ≤ 1.05, the flow coefficient ε is set to "zero"; when 0.95 ≤ regulating stage pressure ratio < 1, the flow coefficient ε is linearly interpolated according to the flow coefficient ε corresponding to regulating stage pressure ratio = 0.95 and the flow coefficient ε corresponding to regulating stage pressure ratio = 1.00. When constructing the piecewise characteristic function of regulating stage pressure ratio ε-regulating stage efficiency η, the regulating stage pressure ratio is set to range from 0.00 to 1.05. Specifically, when the critical pressure ratio of the stage < the regulating stage pressure ratio < 0.95, the regulating stage efficiency η is taken as the characteristic function value of regulating stage pressure ratio ε - regulating stage efficiency η; when the regulating stage pressure ratio = 0.00 and the regulating stage pressure ratio = 1.00, the regulating stage efficiency η is set to 0; when 0.00 < regulating stage pressure ratio ≤ the critical pressure ratio of the stage, the regulating stage efficiency η is linearly interpolated according to the regulating stage efficiency η corresponding to regulating stage pressure ratio = 0.00 and the regulating stage efficiency η corresponding to regulating stage pressure ratio = critical pressure ratio of the stage; when 1.00 ≤ regulating stage pressure ratio ≤ 1.05, the regulating stage efficiency η is set to "zero"; when 0.95 ≤ regulating stage pressure ratio < 1, the regulating stage efficiency η is linearly interpolated according to the regulating stage efficiency η corresponding to regulating stage pressure ratio = 0.95 and the regulating stage efficiency η corresponding to regulating stage pressure ratio = 1.00.

[0032] S4. Based on the mass conservation equation, energy balance equation, and regulating stage characteristics, the main steam pressure, main steam temperature, regulating stage pressure, monitoring section extraction steam pressure and temperature, reheat steam temperature, reheat steam pressure loss, back pressure, heater upper / lower end difference, extraction pipeline pressure loss, feedwater pump efficiency, turbine efficiency, boiler desuperheating water flow rate, and low-pressure cylinder exhaust enthalpy are taken as known quantities, and the design values ​​under the condition of m fully open regulating valves are taken. The inlet pressure P1 of each regulating stage nozzle arc segment is taken as the unknown, and the characteristic area F of each regulating stage stator vane is taken as the target value. Iterative calculations of the turbine unit's thermal system are performed. During the calculation process, different characteristic areas F of individual regulating stage stator vanes are set, ensuring that the final main steam flow rate is equal to the main steam flow rate under the design condition of fully open regulating valves. Based on the final calculation results, the inlet and outlet parameters of each regulating stage nozzle arc segment and the proportion of their respective inlet flow rate to the main steam flow rate are obtained.

[0033] Furthermore, a single regulating stage nozzle segment is composed of n regulating stage stator vanes. For a regulating stage, the characteristic area of ​​all individual regulating stage stator vanes is the same, that is, the characteristic area F of the regulating stage stator vanes is the same. The characteristic area of ​​a single regulating stage stator vane is calculated according to the inlet and outlet thermal parameters of the single regulating stage nozzle segment, according to equation (1);

[0034] Equation (1)

[0035] In the formula: F is the characteristic area of ​​a single regulating stage stator vane; G is the inlet flow rate of a single regulating stage nozzle arc segment; P1 is the inlet pressure of a single regulating stage nozzle arc segment; V1 is the inlet specific volume of a single regulating stage nozzle arc segment; n is the number of regulating stage stator vanes contained in a single regulating stage nozzle arc segment, taken as the design value; μ is the regulating stage flow coefficient; P2 is the outlet pressure.

[0036] Furthermore, the full-open flow coefficients of the main steam valve and the regulating valve are calculated based on the expansion coefficient method of the International Electrotechnical Commission standard IEC 534-22 and the design thermodynamic parameters and pressure loss of the fully open valves under the condition of m regulating valves being fully open; the steam inlet flow of the main steam valve and the regulating valve under the condition of variable operation is calculated based on the expansion coefficient method of the International Electrotechnical Commission standard IEC 534-22 and the characteristic function of the regulating valve.

[0037] Furthermore, the ratio of the calculated technical output of the m fully open control valves obtained based on the step S4's "setting different characteristic areas F of the individual control stage stator vanes, so that the final main steam flow is equal to the main steam flow under the design condition of the control valves being fully open" to the actual technical output of the m fully open control valves of the unit is used as the correction coefficient for the calculated technical output of other valve point conditions.

[0038] S5. When calculating the technical output of the mx valve point, the design condition with m control valves fully open is taken as the benchmark condition. Its thermodynamic parameters, the inlet and outlet parameters of each control stage nozzle arc segment, and the proportion of their respective inlet flow to the main steam flow are taken as benchmark parameters. x is the number of control valves that are closed. The inlet steam flow and efficiency of the control stage nozzle arc segments corresponding to the remaining mx fully open control valves are solved iteratively according to conventional methods, based on the two general characteristic functions of the control stages and the fact that the characteristic area F of a single control stage stator blade is consistent with the benchmark condition.

[0039] Furthermore, to ensure the accuracy of the variable operating condition calculation for the technical output of the MX valve point, the flow rate of the flow passage stage group other than the low-pressure cylinder final stage group is calculated according to the Flueger formula, and the efficiency within the flow passage stage group is taken as the design value and remains constant. For the efficiency of the low-pressure cylinder final stage group, it is necessary to perform variable operating condition calculations by fitting the pressure ratio and efficiency characteristic curves of the low-pressure cylinder final stage group under various typical operating conditions and the exhaust loss curve based on the thermodynamic characteristic data provided by the manufacturer.

[0040] Furthermore, to reduce the complexity of the solution, and considering shaft safety (mx≥2), the two control valves that open first are combined into one "equivalent control valve" in the calculation; the fully open flow coefficient of the "equivalent control valve" is equal to twice the fully open flow coefficient of a single control valve. The number of stationary vanes in the control stage nozzle arc corresponding to the "equivalent control valve" is the sum of the number of stationary vanes in the control stage nozzle arc corresponding to the two control valves; the steam inlet flow of the "equivalent control valve" under variable operating conditions is calculated based on the expansion coefficient method and control valve characteristic function according to the International Electrotechnical Commission standard IEC 534-22.

[0041] When the number of stage vanes n contained in a single stage nozzle arc segment is consistent, the change of control valve sequence does not affect the technical output of the MX valve point. When the number of stage vanes n contained in a single stage nozzle arc segment is different, the technical output of the MX valve point must be recalculated based on the number of stage vanes n in the corresponding stage nozzle arc segment of the MX fully open control valve after the control valve sequence change.

[0042] The above provides a detailed description of the method for suppressing load fluctuations in the steam distribution system of a full-cycle steam turbine unit provided by this invention. Specific examples in this embodiment illustrate the principle and implementation of the invention. The descriptions of the above embodiments are merely for the purpose of helping to understand the method and core ideas of this invention. It should be noted that those skilled in the art can make various improvements and modifications to this invention without departing from its principles, and these improvements and modifications also fall within the protection scope of the claims of this invention.

Claims

1. A method for calculating the output of a steam turbine unit under valve point operating conditions, characterized in that, The method includes the following steps: S1. Consider a single high-pressure regulating valve and the single regulating stage nozzle arc segment it controls as a steam distribution unit; a single regulating stage nozzle arc segment is composed of n regulating stage stationary vanes; based on the number m of high-pressure regulating valves in the turbine unit and the steam distribution structure, connect m steam distribution units in parallel, and then connect them in series with the main steam valve to form the steam distribution end of the turbine unit; S2. Based on the number m of fully open high-pressure regulating valves and the corresponding number n of regulating stage stationary vanes, divide the valve point working conditions and operating ranges, including the m-1 valve point working condition, the m-2 valve point working condition, and the mx valve point working condition. S3. Based on the inlet parameters, geometry, and dimensions of the regulating stage, calculate the regulating stage pressure ratio ε-flow coefficient μ characteristic and the regulating stage pressure ratio ε-regulating stage efficiency η characteristic; using the least squares method, fit the regulating stage pressure ratio ε-flow coefficient μ characteristic function and the regulating stage pressure ratio ε-regulating stage efficiency η characteristic function when the stage critical pressure ratio < regulating stage pressure ratio < 0.95; and based on the above regulating stage pressure ratio ε-flow coefficient μ characteristic function and regulating stage pressure ratio ε-regulating stage efficiency η characteristic function, perform relevant variable operating condition calculations; S4. Based on the mass conservation equation, energy balance equation, and regulating stage characteristics, the main steam pressure, main steam temperature, regulating stage pressure, monitoring section extraction steam pressure and temperature, reheat steam temperature, reheat steam pressure loss, back pressure, heater upper / lower end difference, extraction steam pipeline pressure loss, feedwater pump efficiency, small turbine efficiency, boiler desuperheating water flow rate, and low-pressure cylinder exhaust enthalpy are taken as known quantities and the design values ​​under the condition of m regulating valves being fully open are taken. The inlet pressure P1 of the nozzle arc segment of each regulating stage is taken as the unknown, and the characteristic area F of the stationary blade of each regulating stage is taken as the target value. Iterative calculation of the turbine unit's thermal system is carried out. During the calculation process, different characteristic areas F of the stationary vanes of a single regulating stage are set so that the final main steam flow rate is equal to the main steam flow rate under the design condition of the regulating valve being fully open. Based on the final calculation results, the inlet and outlet parameters of the nozzle arc segment of each regulating stage and the proportion of their respective inlet flow rate to the main steam flow rate are obtained. S5. When calculating the technical output of the mx valve point, the design condition with m control valves fully open is used as the benchmark condition. Its thermodynamic parameters, the inlet and outlet parameters of each control stage nozzle arc segment, and the proportion of their respective inlet flow to the main steam flow are used as benchmark parameters. x is the number of control valves that are closed. The inlet steam flow and efficiency of the control stage nozzle arc segments corresponding to the remaining mx fully open control valves are calculated separately. Finally, based on the two general characteristic functions of the control stage and the fact that the characteristic area F of the single control stage stator blade is consistent with the benchmark condition, iterative solution is performed.

2. The method for calculating the output of a steam turbine unit under valve point operating conditions according to claim 1, characterized in that, In step S2, mx ≥ 2.

3. The method for calculating the output of a steam turbine unit under valve point operating conditions according to claim 1, characterized in that, In step S3, when constructing the characteristic function of regulating stage pressure ratio ε - flow coefficient μ, the regulating stage pressure ratio is taken in the range of 0.00 to 1.

05. Specifically, when the stage critical pressure ratio < regulating stage pressure ratio < 0.95, the flow coefficient ε is taken as the characteristic function value of regulating stage pressure ratio ε - flow coefficient μ; when 0.00 < regulating stage pressure ratio ≤ stage critical pressure ratio, the flow coefficient ε*μ = 1; when 1.00 ≤ regulating stage pressure ratio ≤ 1.05, the flow coefficient ε is "zero"; when 0.95 ≤ regulating stage pressure ratio < 1, the flow coefficient ε is linearly interpolated according to the flow coefficient ε corresponding to regulating stage pressure ratio = 0.95 and the flow coefficient ε corresponding to regulating stage pressure ratio = 1.

00.

4. A method for calculating the output of a steam turbine unit under valve point operating conditions according to claim 1, 2, or 3, characterized in that, In step S3, when constructing the characteristic function of regulating stage pressure ratio ε - regulating stage efficiency η, the regulating stage pressure ratio is set to a range of 0.00 to 1.

05. Specifically, when the stage critical pressure ratio < regulating stage pressure ratio < 0.95, the regulating stage efficiency η is taken as the value of the characteristic function of regulating stage pressure ratio ε - regulating stage efficiency η; when the regulating stage pressure ratio = 0.00 and the regulating stage pressure ratio = 1.00, the regulating stage efficiency η is set to 0; when 0.00 < regulating stage pressure ratio ≤ stage critical pressure ratio, the regulating stage efficiency η is linearly interpolated according to the regulating stage efficiency η corresponding to regulating stage pressure ratio = 0.00 and the regulating stage efficiency η corresponding to regulating stage pressure ratio = stage critical pressure ratio; when 1.00 ≤ regulating stage pressure ratio ≤ 1.05, the regulating stage efficiency η is set to "zero"; when 0.95 ≤ regulating stage pressure ratio < 1, the regulating stage efficiency η is linearly interpolated according to the regulating stage efficiency η corresponding to regulating stage pressure ratio = 0.95 and the regulating stage efficiency η corresponding to regulating stage pressure ratio = 1.

00.

5. The method for calculating the output of a steam turbine unit under valve point operating conditions according to claim 1, characterized in that, A single regulating stage nozzle arc segment is composed of n regulating stage stator blades. For a regulating stage, the characteristic area of ​​all its individual regulating stage stator blades is the same, that is, the characteristic area F of the regulating stage stator blades is the same. The characteristic area of ​​a single regulating stage stator blade is calculated according to the inlet and outlet thermal parameters of the single regulating stage nozzle arc segment, according to formula (1). Equation (1) In the formula: F is the characteristic area of ​​a single regulating stage stator blade; G is the inlet flow rate of a single regulating stage nozzle arc segment; P1 is the inlet pressure of a single regulating stage nozzle arc segment; V1 is the inlet specific volume of a single regulating stage nozzle arc segment; n is the number of regulating stage stator vanes contained in a single regulating stage nozzle arc segment, taken as the design value; μ is the regulating stage flow coefficient; P2 is the outlet pressure.

6. The method for calculating the output of a steam turbine unit under valve point operating conditions according to claim 1, characterized in that, The fully open flow coefficients of the main steam valve and regulating valve mentioned in step S4 are calculated based on the expansion coefficient method of the International Electrotechnical Commission standard IEC 534-22 and the design thermodynamic parameters and pressure loss of the fully open valves under the condition of m regulating valves being fully open; the steam inlet flow rates of the main steam valve and regulating valve under variable operating conditions are calculated based on the expansion coefficient method of the International Electrotechnical Commission standard IEC 534-22 and the characteristic function of the regulating valve.

7. The method for calculating the output of a steam turbine unit under valve point operating conditions according to claim 1, characterized in that, The ratio of the calculated technical output of the m fully open control valves obtained by "setting different characteristic areas F of the individual regulating stage stator vanes, so that the final main steam flow rate is equal to the main steam flow rate under the design condition of the fully open control valves" in step S4 to the actual technical output of the m fully open control valves of the unit is used as the correction coefficient for the calculated technical output of other valve point conditions.

8. The method for calculating the output of a steam turbine unit under valve point operating conditions according to claim 7, characterized in that, In step S5, to ensure the accuracy of the variable operating condition calculation for the technical output of the mx valve point, the flow rate of the flow passage stage group other than the low-pressure cylinder last stage group is calculated according to the Flueger formula, and the efficiency within the flow passage stage group is taken as the design value and remains constant. For the efficiency of the low-pressure cylinder last stage group, the pressure ratio and efficiency characteristic curves of the low-pressure cylinder last stage group under various typical operating conditions and the exhaust loss curve must be fitted according to the thermodynamic characteristic data provided by the manufacturer to perform variable operating condition calculations.

9. The method for calculating the output of a steam turbine unit under valve point operating conditions according to claim 1, characterized in that, In step S2, the two control valves that are initially opened are combined into one "equivalent control valve"; the fully open flow coefficient of the "equivalent control valve" is equal to twice the fully open flow coefficient of a single control valve; the number of stationary vanes in the control stage nozzle arc segment corresponding to the "equivalent control valve" is the sum of the number of stationary vanes in the control stage nozzle arc segment corresponding to the two control valves; the steam inlet flow of the "equivalent control valve" under variable operating conditions is calculated based on the expansion coefficient method and control valve characteristic function of the International Electrotechnical Commission standard IEC 534-22.

10. The method for calculating the output of a steam turbine unit under valve point operating conditions according to claim 9, characterized in that, When the number of stage vanes n contained in a single stage nozzle arc segment is consistent, the change of control valve sequence does not affect the technical output of the MX valve point. When the number of stage vanes n contained in a single stage nozzle arc segment is different, the technical output of the MX valve point must be recalculated based on the number of stage vanes n in the corresponding stage nozzle arc segment of the MX fully open control valve after the control valve sequence change.

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