Calculation method for shutdown value and alarm value of axial differential expansion of steam turbine

Abstract

The invention discloses a method for calculating a shutdown value and an alarm value of axial differential expansion of a steam turbine, relates to the technical field of thermal expansion evaluation and analysis of a steam turbine set, and aims to solve the problem that the existing empirical judgment method cannot accurately provide the shutdown value and the alarm value of the axial differential expansion of the steam turbine. According to the method, an accurate shutdown value and alarm value calculation method is researched and developed based on the position gaps of all the positions in the steam turbine, the gap allowance of all the positions and the safety allowance allowed during alarming or shutdown, and two shutdown values and two alarm values can be obtained through the method provided by the invention; the numerical value interval of the two shutdown values is a safe working interval of the axial differential expansion, and the numerical value interval of the two alarm values is smaller than the numerical value interval of the two shutdown values, so that enough reaction time can be effectively provided for workers, and an early warning effect can be fully achieved. The method is mainly used for accurately calculating the shutdown value and the alarm value of the axial differential expansion of the steam turbine.

Description

Technical Field

[0001] The invention relates to the technical field of thermal expansion evaluation and analysis of steam turbine units, and in particular to a method for calculating a shutdown value and an alarm value of an axial expansion difference of a steam turbine. Background Art

[0002] For steam turbine expansion, the rotor is heated first in the flow stage, and the rotor mass is relatively smaller than the cylinder mass. Therefore, the heat transfer from steam to the rotor is much faster than that from the cylinder. During cold start, the average temperature of the rotor rises faster than that of the cylinder, and the axial expansion of the rotor is greater than that of the cylinder, resulting in an expansion difference between the two, referred to as the expansion difference here; during shutdown, the rotor temperature drops faster than that of the cylinder, and the rotor expansion is less than that of the cylinder. The expansion difference is the rotor relative to the cylinder, so it is called relative expansion.

[0003] In order to control the expansion difference and prevent the dynamic and static parts from rubbing against each other, the alarm value and shutdown value of the dynamic and static clearance and the expansion difference monitor need to be set during cold installation. There are mature algorithms for calculating the positive and negative expansion differences during the start-up and shutdown process. However, the setting of the alarm value and shutdown value is still in the stage of empirical judgment. Therefore, it is in line with practical needs to develop a calculation method that can accurately calculate the shutdown value and alarm value of the axial expansion difference of the steam turbine. Summary of the invention

[0004] In order to solve the problem that the existing empirical judgment method cannot accurately provide the shutdown value and alarm value of the axial expansion difference of the steam turbine, the present invention further provides a method for calculating the shutdown value and alarm value of the axial expansion difference of the steam turbine;

[0005] A method for calculating a shutdown value and an alarm value of an axial expansion difference of a steam turbine is implemented by the following steps:

[0006] Step 1: List the drawing clearances of the axial moving parts (including rotors and moving blades) and stationary parts (including cylinders and bearing boxes) at various positions in the steam turbine, and classify the drawing clearances, where the clearance values ​​at the positive clearance positions are recorded as X1, X2...Xn, and the clearance values ​​at the negative clearance positions are recorded as x1, x2...xn;

[0007] Step 2: According to the positive gap position and the negative gap position distinguished in step 1, the expansion differential value corresponding to each position in the steam turbine is determined respectively, wherein the expansion differential value corresponding to the positive gap position is the shutdown long transient expansion differential value Y, and the shutdown long transient expansion differential values ​​of each positive gap position are recorded as Y1, Y2...Yn in sequence, wherein the expansion differential value corresponding to the negative gap position is the short transient expansion differential value y, and the short transient expansion differential values ​​of each negative gap position are recorded as y1, y2...yn in sequence;

[0008] Step 3: Calculate the clearance allowance of each position according to step 1 and step 2, wherein the clearance allowance of the positive clearance position is Z, and the clearance allowances of each positive clearance position are recorded as Z1=X1-Y1, Z2=X2-Y2...Zn=Xn-Yn, wherein the clearance allowance of the negative clearance position is z, and the clearance allowances of each negative clearance position are recorded as z1=x1-y1, z2=x2-y2...zn=xn-yn;

[0009] Step 4: According to the clearance allowances of each position calculated in step 3, find the minimum clearance allowance in the positive clearance position and record it as the positive clearance danger point Zmin, and find the minimum clearance allowance in the negative clearance position and record it as the negative clearance danger point zmin;

[0010] Step 5: Based on the positive gap danger point Zmin and the negative gap danger point zmin determined in step 4, the calculation formulas for the positive gap differential expansion stop value Q1, the calculation formula for the positive gap differential expansion alarm value Q2, the calculation formula for the negative gap differential expansion stop value q1 and the calculation formula for the negative gap differential expansion alarm value q2 are constructed as follows:

[0011] Q1=Zmin+M1-N (1)

[0012] Q2=Zmin+M1-P (2)

[0013] q1=zmin+M2-N (3)

[0014] q2=zmin+M2-P (4)

[0015] Where: M1 is the long transient expansion difference at the measuring point, M2 is the short transient expansion difference at the measuring point, N is the allowable running gap during shutdown, and P is the allowable running gap during alarm.

[0016] Further, in step 2, the shutdown long transient expansion difference value Y=100% expansion of the rotor temperature at the corresponding position-75% expansion of the stationary component temperature at the corresponding position;

[0017] Further, in step 2, the short transient expansion difference value y=75% expansion of the rotor temperature at the corresponding position-100% expansion of the stationary component temperature at the corresponding position-Poisson effect contraction of the rotor at the corresponding position;

[0018] Further, in step 5, the transient expansion difference M1 of the start-up engine at the measuring point = 100% expansion of the rotor temperature at the testing point - 75% expansion of the stationary component temperature at the testing point - Poisson effect contraction of the rotor at the testing point;

[0019] Further, in step 5, the short transient expansion difference M2 of the measuring point = 75% expansion of the rotor temperature at the testing point - 100% expansion of the stationary component temperature at the testing point - Poisson effect contraction of the rotor at the testing point;

[0020] Furthermore, the allowed running clearance N during shutdown in step 5 is set to a constant of 1.1 mm;

[0021] Furthermore, the allowable running clearance P during the alarm in step 5 is set to a constant of 1.9 mm.

[0022] The beneficial effects of this application compared to the prior art are as follows:

[0023] The present application provides a method for calculating the shutdown value and alarm value of the axial expansion difference of a steam turbine. Based on the position gap at each position in the steam turbine, the gap margin at each position, and the safety margin allowed during alarm or shutdown, an accurate method for calculating the shutdown value and the alarm value is developed. Two shutdown values ​​and two alarm values ​​can be obtained by the method provided by the present application. The numerical range of the two shutdown values ​​is the safe working range of the axial expansion difference, and the numerical range of the two alarm values ​​is smaller than the numerical range of the two shutdown values, which can effectively give workers enough reaction time and can fully play an early warning role. The calculation method provided by the present application improves the thermal expansion evaluation and analysis of the steam turbine unit, reduces the impact of friction on the steam turbine during operation, improves the efficiency and safety level of the unit, and reduces the cost of steam turbine operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the dynamic and static clearance of the steam turbine;

[0025] Figure 2 for Figure 1 Schematic diagram of the dynamic and static clearance of the steam seal teeth at position Ⅰ in the middle;

[0026] Figure 3 for Figure 1 Schematic diagram of the dynamic and static clearance of the steam seal teeth at position II in the middle.

[0027] In the figure: 1 thrust plate, A and B are the positive clearance between the moving blade and the stationary blade, E and F are the negative clearance between the stationary blade and the moving blade, G, G1 and M are the positive clearance at the steam seal tooth position, and C and N are the negative clearance at the steam seal tooth position. DETAILED DESCRIPTION

[0028] Specific implementation method 1: Combination Figures 1 to 3 This embodiment is described. This embodiment provides a method for calculating the shutdown value and alarm value of the axial expansion difference of a steam turbine. The method is implemented by the following steps:

[0029] Step 1: List the drawing clearances of the axial moving parts (including rotors and moving blades) and stationary parts (including cylinders and bearing boxes) at various positions in the steam turbine, and classify the drawing clearances, where the clearance values ​​at the positive clearance positions are recorded as X1, X2...Xn, and the clearance values ​​at the negative clearance positions are recorded as x1, x2...xn;

[0030] Step 2: According to the positive gap position and the negative gap position distinguished in step 1, the expansion differential value corresponding to each position in the steam turbine is determined respectively, wherein the expansion differential value corresponding to the positive gap position is the shutdown long transient expansion differential value Y, and the shutdown long transient expansion differential values ​​of each positive gap position are recorded as Y1, Y2...Yn in sequence, wherein the expansion differential value corresponding to the negative gap position is the short transient expansion differential value y, and the short transient expansion differential values ​​of each negative gap position are recorded as y1, y2...yn in sequence;

[0031] Step 3: Calculate the clearance allowance of each position according to step 1 and step 2, wherein the clearance allowance of the positive clearance position is Z, and the clearance allowances of each positive clearance position are recorded as Z1=X1-Y1, Z2=X2-Y2...Zn=Xn-Yn, wherein the clearance allowance of the negative clearance position is z, and the clearance allowances of each negative clearance position are recorded as z1=x1-y1, z2=x2-y2...zn=xn-yn;

[0032] Step 4: According to the clearance allowances of each position calculated in step 3, find the minimum clearance allowance in the positive clearance position and record it as the positive clearance danger point Zmin, and find the minimum clearance allowance in the negative clearance position and record it as the negative clearance danger point zmin;

[0033] Step 5: Based on the positive gap danger point Zmin and the negative gap danger point zmin determined in step 4, the calculation formulas for the positive gap differential expansion stop value Q1, the calculation formula for the positive gap differential expansion alarm value Q2, the calculation formula for the negative gap differential expansion stop value q1 and the calculation formula for the negative gap differential expansion alarm value q2 are constructed as follows:

[0034] Q1=Zmin+M1-N (1)

[0035] Q2=Zmin+M1-P (2)

[0036] q1=zmin+M2-N (3)

[0037] q2=zmin+M2-P (4)

[0038] Where: M1 is the long transient expansion difference when the measuring point is started, M2 is the short transient expansion difference when the measuring point is started, N is the allowable running gap when shutting down, and P is the allowable running gap when alarming.

[0039] The calculation method provided in this embodiment is based on the expansion differential theory. Generally speaking, the expansion differential expands from the thrust plate to both sides. The rotor expansion is greater than the cylinder expansion, which is called positive expansion differential. The rotor expansion is less than the cylinder expansion, which is called negative expansion differential. When the steam turbine is started, a long transient expansion differential will be generated in the corresponding cylinder of the steam turbine. When the steam turbine is shut down, a short transient expansion differential will be generated in the corresponding cylinder of the steam turbine. When the steam turbine is in steady-state operation, a steady-state expansion differential will be generated in the corresponding cylinder of the steam turbine. When the steam turbine is shut down due to a fault at startup, the speed drops rapidly, and the rotor stretches rapidly, and a long shutdown transient will be generated in the corresponding cylinder of the steam turbine. The transient process of starting and shutting down the steam turbine is the working condition with the largest positive and negative expansion differentials. The positive and negative clearances at each position must meet the maximum expansion differential requirements of the corresponding position, that is, the long and short transient expansion differential requirements. This method is provided to meet such expansion differential requirements.

[0040] Specific implementation method 2: Combination Figures 1 to 3 This embodiment is described. The difference between this embodiment and the first embodiment is that the shutdown long transient expansion difference value Y in step 2 = 100% expansion of the rotor temperature at the corresponding position - 75% expansion of the stationary component temperature at the corresponding position. Other components and connection methods are the same as those in the first embodiment.

[0041] Specific implementation method three: Combination Figures 1 to 3 This embodiment is described. The difference between this embodiment and the third embodiment is that the short transient expansion difference value y in step 2 = 75% expansion of the rotor temperature at the corresponding position - 100% expansion of the stationary component temperature at the corresponding position - Poisson effect contraction of the rotor at the corresponding position. Other components and connection methods are the same as those in the third embodiment.

[0042] Specific implementation method four: Combination Figures 1 to 3 This embodiment is described. The difference between this embodiment and the third embodiment is that in step 5, the transient expansion difference M1 of the start-up engine length at the measuring point = 100% expansion of the rotor temperature at the testing point - 75% expansion of the stationary component temperature at the testing point - Poisson effect contraction of the rotor at the testing point. Other components and connection methods are the same as those of the fourth embodiment.

[0043] Specific implementation method five: Combination Figures 1 to 3 This embodiment is described. The difference between this embodiment and the fifth embodiment is that in step 5, the short transient expansion difference M2 of the measuring point = 75% expansion of the rotor temperature at the testing point - 100% expansion of the stationary component temperature at the testing point - Poisson effect contraction of the rotor at the testing point. Other components and connection methods are the same as those of the fifth embodiment.

[0044] In combination with the description of specific implementation mode four and specific implementation mode five, the test point mentioned in this implementation mode is determined based on the specific structure of the turbine, and is usually selected near the rotor end face of the cylinder away from the thrust plate side, and the measuring probe is generally mounted on the bearing box. The measuring probe is the test point of this section of the cylinder.

[0045] Specific implementation method six: Combination Figures 1 to 3 This embodiment is described. The difference between this embodiment and the sixth embodiment is that the running clearance N allowed during shutdown in step 5 is set to a constant of 1.1 mm. The other components and connection methods are the same as those in the sixth embodiment.

[0046] Specific implementation method seven: Combination Figure 1 to Figure 2 This embodiment is described. The difference between this embodiment and the sixth embodiment is that the allowed running clearance P during the alarm in step 5 is set to a constant of 1.9 mm. The other components and connection methods are the same as those in the sixth embodiment.

[0047] The present invention has been disclosed as above with preferred implementation cases, but it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent implementation cases with equivalent changes by using the above-disclosed structures and technical contents without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above implementation cases based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for calculating the shutdown value and alarm value of a steam turbine axial expansion difference, characterized in that: The method is achieved by the following steps: Step 1: List the drawing clearances of the axial moving parts (including rotors and moving blades) and stationary parts (including cylinders and bearing boxes) at various positions in the steam turbine, and classify the drawing clearances, where the clearance values ​​at the positive clearance positions are recorded as X1, X2...Xn, and the clearance values ​​at the negative clearance positions are recorded as x1, x2...xn; Step 2: According to the positive gap position and the negative gap position distinguished in step 1, the expansion differential value corresponding to each position in the steam turbine is determined respectively, wherein the expansion differential value corresponding to the positive gap position is the shutdown long transient expansion differential value Y, and the shutdown long transient expansion differential values ​​of each positive gap position are recorded as Y1, Y2...Yn in sequence, wherein the expansion differential value corresponding to the negative gap position is the short transient expansion differential value y, and the short transient expansion differential values ​​of each negative gap position are recorded as y1, y2...yn in sequence; Step 3: Calculate the clearance allowance of each position according to step 1 and step 2, wherein the clearance allowance of the positive clearance position is Z, and the clearance allowances of each positive clearance position are recorded as Z1=X1-Y1, Z2=X2-Y2...Zn=Xn-Yn, wherein the clearance allowance of the negative clearance position is z, and the clearance allowances of each negative clearance position are recorded as z1=x1-y1, z2=x2-y2...zn=xn-yn; Step 4: According to the clearance allowances of each position calculated in step 3, find the minimum clearance allowance in the positive clearance position and record it as the positive clearance danger point Zmin, and find the minimum clearance allowance in the negative clearance position and record it as the negative clearance danger point zmin; Step 5: Based on the positive gap danger point Zmin and the negative gap danger point zmin determined in step 4, the calculation formulas for the positive gap differential expansion stop value Q1, the calculation formula for the positive gap differential expansion alarm value Q2, the calculation formula for the negative gap differential expansion stop value q1 and the calculation formula for the negative gap differential expansion alarm value q2 are constructed as follows: Q1=Zmin+M1-N (1) Q2=Zmin+M1-P (2) q1=zmin+M2-N (3) q2=zmin+M2-P (4) Where: M1 is the long transient expansion difference when the measuring point is started, M2 is the short transient expansion difference when the measuring point is started, N is the allowable running gap when shutting down, and P is the allowable running gap when alarming.

2. A method for calculating the shutdown value and alarm value of a steam turbine axial expansion difference according to claim 1, characterized in that: In step 2, the shutdown long transient expansion difference value Y=100% expansion of the rotor temperature at the corresponding position-75% expansion of the stationary component temperature at the corresponding position.

3. A method for calculating the shutdown value and alarm value of a steam turbine axial expansion difference according to claim 2, characterized in that: In step 2, the short transient expansion difference value y=75% expansion of the rotor temperature at the corresponding position-100% expansion of the stationary component temperature at the corresponding position-Poisson effect contraction of the rotor at the corresponding position.

4. A method for calculating the shutdown value and alarm value of a steam turbine axial expansion difference according to claim 3, characterized in that: In step 5, the transient expansion difference M1 at the start of the measuring point = 100% expansion of the rotor temperature at the test point - 75% expansion of the stationary component temperature at the test point - Poisson effect contraction of the rotor at the test point.

5. A method for calculating the shutdown value and alarm value of a steam turbine axial expansion difference according to claim 4, characterized in that: In step 5, the short transient expansion difference M2 of the measuring point = 75% expansion of the rotor temperature at the testing point - 100% expansion of the stationary component temperature at the testing point - Poisson effect contraction of the rotor at the testing point.

6. A method for calculating the shutdown value and alarm value of a steam turbine axial expansion difference according to claim 5, characterized in that: In step 5, the allowable running clearance N during shutdown is taken as a constant of 1.1 mm.

7. A method for calculating the shutdown value and alarm value of a steam turbine axial expansion difference according to claim 6, characterized in that: The allowable running clearance P when the alarm is sounded in step 5 is taken as a constant of 1.9 mm.

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