A method for correcting the axial displacement protection threshold of nuclear power steam turbine

Abstract

The invention discloses a method for correcting the axial displacement protection threshold of a nuclear power steam turbine, comprising: S1, performing a unit operation condition switching test to generate test data; wherein the unit operation condition switching test includes a steam turbine trip test, a steam turbine no-load rejection test and a steam turbine load rejection power cutting test; S2, calculating a protection threshold calculation value according to the test data; S3, judging whether the current protection threshold of the steam turbine meets the requirements according to the protection threshold calculation value, and executing S4 if it does not meet the requirements; S4, performing protection threshold correction processing to generate threshold correction data; the implementation of the invention can correct the protection threshold of the axial displacement of a nuclear power steam turbine, thereby avoiding unexpected steam turbine tripping of a nuclear power unit due to a too small design initial value of the steam turbine axial displacement protection threshold.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear power plant steam turbine commissioning, and in particular to a nuclear power steam turbine axial displacement protection threshold correction method. Background Art

[0002] Steam turbines in nuclear power plants are generally designed with an axial displacement tripping protection function. Specifically, the axial displacement of the steam turbine rotor is monitored in real time through a dedicated axial displacement monitoring device. If the steam turbine loses balance due to axial thrust, it will cause abnormal axial movement of the rotor. When the axial displacement reaches the preset tripping protection threshold, the steam turbine tripping protection action is automatically triggered.

[0003] At present, the axial displacement protection threshold of the impulse condensing half-speed steam turbine in nuclear power plants is provided by the turbine design and manufacturing unit. The axial displacement protection threshold provided by the turbine design and manufacturing unit is generally used directly during the commissioning, startup and operation stages of the unit. There is no method or content to check the applicability of the turbine axial displacement protection threshold in the commissioning test plan, nor is there a method to correct the turbine axial displacement trip protection threshold. If there are defects in the initial design value of the turbine axial displacement protection threshold, it may cause the turbine to trip during the turbine load shedding and load shedding test under rated load conditions due to the turbine axial displacement monitoring value exceeding the protection threshold, thereby causing an unplanned reactor trip event in the reactor; and the maximum axial displacement of individual turbines when they are load shedding and load shedding under rated load conditions is close to the trip protection threshold, but there is a lack of methods to correct the turbine axial displacement trip protection threshold, which is not conducive to the safe operation of the unit. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for correcting the axial displacement protection threshold of a nuclear power steam turbine in view of at least one defect of the prior art.

[0005] The technical solution adopted by the present invention to solve the technical problem is: constructing a nuclear power steam turbine axial displacement protection threshold correction method, which is characterized by comprising the following steps:

[0006] S1. Performing a unit operating condition switching test to generate test data; wherein the unit operating condition switching test includes a steam turbine trip test, a steam turbine no-load test, and a steam turbine load rejection test for power plant use;

[0007] S2. Calculate a protection threshold value according to the test data;

[0008] S3, judging whether the current protection threshold of the steam turbine meets the requirement according to the protection threshold calculation value, and if not, executing S4;

[0009] S4. Perform protection threshold correction processing to generate threshold correction data.

[0010] Preferably, the S1 comprises:

[0011] S11, judging whether all tests in the unit operation condition switching test are completed, if so, executing S2, otherwise executing S12; wherein the unit operation condition switching test includes a turbine trip test, a turbine no-load test and a turbine load rejection test;

[0012] S12, operating the nuclear power unit under the set operating conditions and ensuring that the nuclear power unit has the ability to perform one of the unfinished tests, performing the unfinished test and recording the axial displacement data of the test during the test;

[0013] S13, after recording the unit load value of the unfinished test as the unit load value before the test, returning to S11;

[0014] The axial displacement data of each test and the unit load value before the test constitute the test data.

[0015] Preferably, in S11, the steam turbine trip test includes: generating an emergency shutdown signal to trip the steam turbine; and determining that the steam turbine trip test has been completed when the steam inlet isolation valve and the steam inlet regulating valve of the steam turbine are completely closed.

[0016] Preferably, in S11, the turbine no-load test includes: generating a load disconnection signal to put the turbine into a no-load condition; when the load of the turbine drops to a first set value and the turbine speed is restored to a first allowable speed range after adjustment, it is determined that the turbine no-load test has been completed.

[0017] Preferably, in S11, the steam turbine load shedding and plant power cutting test includes: generating a signal to disconnect the generator main transformer from the power grid to cause the steam turbine to shed load and switch to the plant power operating condition; when the load of the steam turbine drops to the plant power setting value and the turbine speed is restored to the second allowable speed range after adjustment, it is determined that the steam turbine load shedding and plant power cutting test has been completed.

[0018] Preferably, in said S12, making the nuclear power unit operate under the set operating conditions includes: making the actual load of the nuclear power unit basically stable at 50% of the rated load.

[0019] Preferably, S2 includes:

[0020] Calculate the axial displacement calculation value corresponding to each test according to the maximum axial displacement value in the axial displacement data of each test and the corresponding pre-test unit load value;

[0021] The maximum value among the axial displacement calculation values ​​is taken as the protection threshold calculation value.

[0022] Preferably, in S2, the expression of the calculated value of the axial displacement is:

[0023] d m，c =kd m (P t / P o );

[0024] Among them, d m，c is the calculated value of the axial displacement, k is the calculation coefficient, d m is the maximum axial displacement, P t is the target load value, P o is the unit load value before the test.

[0025] Preferably, the S3 includes: if a first difference between the current protection threshold of the steam turbine and the calculated value of the protection threshold is not greater than a second set value, it is determined that the current protection threshold does not meet the requirements, and the S4 is executed.

[0026] Preferably, S4 includes:

[0027] Setting a second difference between the thickness of the babbitt alloy on the thrust bearing in the steam turbine and the upper limit correction value as the upper limit value of the threshold correction data;

[0028] The sum of the protection threshold calculation value and the lower limit correction value is set as the lower limit value of the threshold correction data.

[0029] Preferably, in S4, the upper limit correction value is 0.2 mm, and the lower limit correction value is 0.1 mm.

[0030] Preferably, the S4 further includes:

[0031] Determine whether the second difference is smaller than the product of the minimum value of the axial flow clearance of the turbine and the set percentage. If so, set the second difference as the upper limit value of the threshold correction data; otherwise, set the upper limit value of the threshold correction data according to the minimum value of the axial flow clearance.

[0032] Preferably, in S4, setting the upper limit value of the threshold correction data according to the minimum value of the axial flow clearance includes:

[0033] The upper limit value of the threshold correction data is set to the product of the minimum value of the axial flow clearance and one third.

[0034] The present invention has at least the following beneficial effects: a method for correcting the axial displacement protection threshold of a nuclear power steam turbine, comprising: S1, performing a unit operating condition switching test to generate test data; wherein the unit operating condition switching test includes a turbine trip test, a turbine no-load test and a turbine load rejection test for power plant power cutting; S2, calculating a protection threshold calculation value according to the test data; S3, judging whether the current protection threshold of the steam turbine meets the requirements according to the protection threshold calculation value, and executing S4 if it does not meet the requirements; S4, performing protection threshold correction processing to generate threshold correction data; the present invention can correct the protection threshold of the axial displacement of the nuclear power steam turbine, thereby avoiding unexpected turbine tripping caused by the nuclear power unit due to the small design initial value of the turbine axial displacement protection threshold. The present invention can not only meet the conventional requirements of the turbine axial displacement protection threshold (the allowable loss limit of the thrust bearing babbitt alloy), but also limit the threshold correction data in combination with the axial flow clearance of the high and medium pressure cylinder, further improving the effectiveness of the protection threshold correction, and playing a positive role in maintaining the safe operation of the nuclear power unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0036] Figure 1 It is a flow chart of a method for correcting a nuclear power steam turbine axial displacement protection threshold value provided by the present invention;

[0037] Figure 2 It is a flow chart of step S1 in the method for correcting the axial displacement protection threshold value of a nuclear power steam turbine provided by the present invention. DETAILED DESCRIPTION

[0038] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0039] It should be noted that the flowcharts shown in the accompanying drawings are only exemplary and do not necessarily include all the contents and operations / steps, nor do they have to be executed in the order described. For example, some operations / steps can be decomposed, while some operations / steps can be combined or partially combined, so the actual execution order may change according to actual conditions.

[0040] The block diagrams shown in the accompanying drawings are merely functional entities and do not necessarily correspond to physically independent entities. That is, these functional entities may be implemented in software form, or in one or more hardware modules or integrated circuits, or in different networks and / or processor devices and / or microcontroller devices.

[0041] refer to Figure 1The present invention provides a method for correcting an axial displacement protection threshold of a nuclear power steam turbine, comprising: step S1, step S2, step S3 and step S4.

[0042] Step S1 includes: performing a unit operating condition switching test and generating test data; wherein the unit operating condition switching test includes a turbine trip test, a turbine no-load test, and a turbine load shedding test. Specifically, the purpose of performing the unit operating condition switching test is to collect the corresponding axial displacement data when the turbine switches from normal operating conditions to abnormal operating conditions or other working modes, in preparation for subsequent steps.

[0043] In some embodiments, Figure 2 As shown, step S1 includes: step S11, step S12 and step S13.

[0044] Step S11 includes: judging whether all tests in the unit operation condition switching test are completed, if so, executing step S2, otherwise executing step S12. Specifically, the more tests (including turbine trip test, turbine no-load test and turbine load shedding test) protected by the unit operation condition switching test, the longer the test time will be, but the generated test data will be more specific and comprehensive, so that the subsequent steps will correct the protection threshold more accurately.

[0045] In some embodiments, in step S11, the steam turbine trip test includes: generating an emergency stop signal to trip the steam turbine; and determining that the steam turbine trip test has been completed when the steam inlet isolation valve and the steam inlet regulating valve of the steam turbine are completely closed. The emergency stop signal can cause an emergency stop button arranged in the main control room of the nuclear power unit to trigger the steam turbine trip.

[0046] In some embodiments, in step S11, the turbine no-load test includes: generating a load disconnection signal to put the turbine into a no-load condition; when the load of the turbine drops to a first set value and the turbine speed is restored to a first allowable speed range after adjustment, it is determined that the turbine no-load test has been completed. The load disconnection signal can disconnect the switch at the turbine output port that controls the on-off of the load, thereby triggering the turbine no-load test. In addition, the first set value is generally set to be close to 0 or 0; the setting of the first allowable speed range needs to be determined based on the performance and operating conditions of the on-site nuclear power unit.

[0047] In some embodiments, in step S11, the steam turbine load shedding and power-cutting test includes: generating a signal to disconnect the main transformer of the generator from the power grid, so as to cause the steam turbine to shed load and switch to the power-cutting condition; when the load of the steam turbine drops to the power-cutting setting value, and the speed of the steam turbine is adjusted to return to the second allowable speed range, it is determined that the steam turbine load shedding and power-cutting test has been completed. The signal to disconnect the main transformer of the generator from the power grid can disconnect the ultra-high voltage circuit breaker between the main transformer of the generator and the power grid, so as to cause the steam turbine to shed load and switch from the set condition to the power-cutting condition.

[0048] Step S12 includes: making the nuclear power unit operate under set operating conditions, and ensuring that the nuclear power unit has the ability to perform one of the unfinished tests, performing the unfinished test, and recording the axial displacement data of the test during the test.

[0049] Specifically, the purpose of making the nuclear power unit work under the set operating conditions is to make the state of the nuclear power unit as consistent as possible before each unit operating condition switching test, so that the generated test data is more objective and comparable. If the nuclear power unit is not capable of completing the test, the test will not only fail to collect test data normally, but may also cause unexpected failures in the nuclear power unit. Therefore, before each test, it is necessary to ensure that the nuclear power unit is capable of implementing the test before conducting the test; among them, the high-speed recorder can be used to continuously collect the axial displacement during the test based on the set period, and these axial displacements constitute the axial displacement data.

[0050] In some embodiments, in S12, making the nuclear power unit operate under the set operating conditions includes: making the actual load of the nuclear power unit substantially stable at 50% of the rated load.

[0051] If the axial displacement protection threshold is small, the turbine trip may be triggered before the turbine no-load test and the turbine load shedding test are completed. Therefore, in some embodiments, step S12 also includes: in the embodiment where the unit operating condition switching test includes a turbine trip test, the turbine trip test is performed first; and it is determined whether the difference between the current protection threshold of the turbine and the maximum axial displacement collected by the turbine trip test is greater than a third set value during the turbine trip test. If so, other tests are allowed; otherwise, the current protection threshold is adjusted before other tests are allowed.

[0052] Specifically, if the difference between the current protection threshold and the maximum axial displacement collected in the turbine trip test is greater than the third set value, it means that the current protection threshold has a sufficient safety margin for other tests.

[0053] In some embodiments, adjusting the current protection threshold may include: setting the protection threshold to the sum of the maximum axial displacement collected from the turbine trip test and a third set value. Optionally, the third set value is 0.1 mm. It should be noted that the setting of the protection threshold in this step is temporary and not the final correction value.

[0054] Step S13 includes: recording the unit load value of the unfinished test as the unit load value before the test, and then returning to step S11.

[0055] In this embodiment, the axial displacement data of each test and the load value of the unit before the test constitute the test data.

[0056] Step S2 includes: calculating a protection threshold value according to the test data.

[0057] In some embodiments, step S2 includes: calculating the corresponding axial displacement calculated value of each test based on the maximum axial displacement value in the axial displacement data of each test and the corresponding pre-test unit load value; taking the maximum value of each axial displacement calculated value as the protection threshold calculated value.

[0058] Further, in some embodiments, in step S2, the expression of the axial displacement calculation value is:

[0059] d m，c =kd m (P t / P o ) (1);

[0060] Among them, d m，c is the calculated value of axial displacement, k is the calculation coefficient, d m is the maximum axial displacement, P t is the target load value, P o is the load value of the unit before the test. Optionally, the value range of k is 0.9~1.2. In addition, the target load value P t Generally, the rated load value of the unit is taken, which is close to 100%.

[0061] Specifically, take the turbine no-load test as an example: k is 1, assuming that during the turbine no-load test, the maximum axial displacement in the recorded axial displacement data is d m1 , the unit load value measured before the turbine no-load test is P o1 , k, d m1 , P t , P o1Substituting into formula (1), the axial displacement calculation value corresponding to the turbine no-load test can be calculated; similarly, the axial displacement calculation values ​​corresponding to the turbine no-load test and the turbine load shedding test can be calculated respectively, that is, three axial displacement calculation values ​​are obtained; the maximum value of these three axial displacement calculation values ​​is the protection threshold calculation value.

[0062] Step S3 includes: judging whether the current protection threshold of the steam turbine meets the requirements according to the calculated value of the protection threshold, and executing step S4 if it does not meet the requirements.

[0063] In some embodiments, step S3 includes: if the first difference between the current protection threshold of the steam turbine and the calculated value of the protection threshold is not greater than the second set value, it is determined that the current protection threshold does not meet the requirements, and step S4 is executed; conversely, if the first difference between the current protection threshold of the steam turbine and the calculated value of the protection threshold is greater than the second set value, it is determined that the current protection threshold meets the requirements, and the process can be terminated at this time. Optionally, the second set value is 0.1 mm.

[0064] Step S4 includes: performing protection threshold correction processing to generate threshold correction data, so that the staff can correct the axial displacement protection threshold of the steam turbine based on the threshold correction data.

[0065] In some embodiments, step S4 includes: setting the second difference between the thickness of the babbitt alloy on the thrust bearing in the steam turbine and the upper limit correction value as the upper limit value of the threshold correction data; setting the sum of the protection threshold calculation value and the lower limit correction value as the lower limit value of the threshold correction data. It can be understood that the lower limit correction value should not be less than the second set value.

[0066] Optionally, in step S4, the upper limit correction value is 0.2 mm and the lower limit correction value is 0.1 mm.

[0067] Due to the existence of the axial flow clearance of the high- and medium-pressure combined cylinders, the medium-pressure steam inlet regulating valve may become stuck during the turbine load shedding and power-cutting test, causing the axial thrust of the medium-pressure cylinder to instantly far exceed the axial thrust of the high-pressure cylinder, resulting in an increase in the measured value of the axial displacement of the turbine. Therefore, the upper limit value of the final threshold correction data should be limited in combination with the minimum value of the axial flow clearance of the high- and medium-pressure combined cylinders. Therefore, in some embodiments, step S4 also includes: determining whether the second difference is less than the product of the minimum value of the axial flow clearance of the turbine and the set percentage. If so, the second difference is set to the upper limit value of the threshold correction data; otherwise, the upper limit value of the threshold correction data is set according to the minimum value of the axial flow clearance. Optionally, the set percentage can be one-third.

[0068] Further, in some embodiments, in step S4, setting the upper limit value of the threshold correction data according to the minimum value of the axial flow clearance includes: setting the upper limit value of the threshold correction data to the product of the minimum value of the axial flow clearance and one third.

[0069] It can be understood that the implementation of the present invention can correct the protection threshold of the axial displacement of the nuclear power steam turbine, thereby avoiding unexpected turbine tripping of the nuclear power unit due to the small design initial value of the turbine axial displacement protection threshold. The present invention can not only meet the conventional requirements of the turbine axial displacement protection threshold (the allowable loss limit of the thrust bearing Babbitt alloy), but also limit the threshold correction data in combination with the axial flow clearance of the high and medium pressure cylinders, thereby further improving the effectiveness of the protection threshold correction and playing a positive role in maintaining the safe operation of the nuclear power unit.

[0070] The steps of the method or algorithm described in conjunction with the embodiments disclosed herein may be implemented directly using hardware, a software module executed by a processor, or a combination of the two. The software module may be placed in a random access memory (RAM), a memory, a read-only memory (ROM), an electrically programmable ROM, an electrically erasable programmable ROM, a register, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.

[0071] It can be understood that the above embodiments only express the preferred implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the patent scope of the present invention. It should be pointed out that, for ordinary technicians in this field, the above technical features can be freely combined without departing from the concept of the present invention, and several deformations and improvements can be made, which all belong to the protection scope of the present invention. Therefore, all equivalent changes and modifications made to the scope of the claims of the present invention should belong to the coverage of the claims of the present invention.

Claims

1. A method for correcting the axial displacement protection threshold of a nuclear power steam turbine, characterized in that: The following steps are involved: S1. Performing a unit operating condition switching test to generate test data; wherein the unit operating condition switching test includes a steam turbine trip test, a steam turbine no-load test, and a steam turbine load rejection test for power plant use; S2. Calculate a protection threshold value according to the test data; S3, judging whether the current protection threshold of the steam turbine meets the requirement according to the protection threshold calculation value, and if not, executing S4; S4, performing protection threshold correction processing to generate threshold correction data; The S1 includes: S11, judging whether all tests in the unit operation condition switching test are completed, if so, executing S2, otherwise executing S12; wherein the unit operation condition switching test includes a turbine trip test, a turbine no-load test and a turbine load rejection test; S12, operating the nuclear power unit under the set operating conditions and ensuring that the nuclear power unit has the ability to perform one of the unfinished tests, performing the unfinished test and recording the axial displacement data of the test during the test; S13, after recording the unit load value before the unfinished test as the unit load value before the test, return to S11; the axial displacement data of each test and the unit load value before the test constitute the test data; The step S2 includes: calculating the axial displacement calculation value corresponding to each test according to the maximum axial displacement value in the axial displacement data of each test and the corresponding pre-test unit load value; taking the maximum value of each axial displacement calculation value as the protection threshold calculation value; In S2, the expression of the axial displacement calculation value is: d m，c =kd m (P t / P o ); Among them, d m，c is the calculated value of the axial displacement, k is the calculation coefficient, d m is the maximum axial displacement, P t is the target load value, P o is the unit load value before the test.

2. The method for correcting the axial displacement protection threshold of a nuclear power steam turbine according to claim 1, characterized in that: In the S11, the steam turbine trip test includes: generating an emergency shutdown signal to trip the steam turbine; and determining that the steam turbine trip test has been completed when the steam inlet isolation valve and the steam inlet regulating valve of the steam turbine are completely closed.

3. The method for correcting the axial displacement protection threshold of a nuclear power steam turbine according to claim 1, characterized in that: In S11, the turbine no-load test includes: generating a load disconnection signal to put the turbine into a no-load condition; when the load of the turbine drops to a first set value and the turbine speed is restored to a first allowable speed range after adjustment, it is determined that the turbine no-load test has been completed.

4. The method for correcting the axial displacement protection threshold of a nuclear power steam turbine according to claim 1, characterized in that: In S11, the steam turbine load shedding and plant power cutting test includes: generating a signal to disconnect the generator main transformer from the power grid to cause the steam turbine to shed load and switch to the plant power condition; when the load of the steam turbine drops to the plant power setting value and the turbine speed is restored to the second allowable speed range after adjustment, it is determined that the steam turbine load shedding and plant power cutting test has been completed.

5. The method for correcting the axial displacement protection threshold of a nuclear power steam turbine according to claim 1, characterized in that: In said S12, making the nuclear power unit operate under the set working condition includes: making the actual load of the nuclear power unit basically stable at 50% of the rated load.

6. The method for correcting the axial displacement protection threshold of a nuclear power steam turbine according to any one of claims 1 to 5, characterized in that: The step S3 includes: if a first difference between the current protection threshold of the steam turbine and the calculated value of the protection threshold is not greater than a second set value, determining that the current protection threshold does not meet the requirement, and executing the step S4.

7. The method for correcting the axial displacement protection threshold of a nuclear power steam turbine according to claim 1, characterized in that: The S4 includes: Setting a second difference between the thickness of the babbitt alloy on the thrust bearing in the steam turbine and the upper limit correction value as the upper limit value of the threshold correction data; The sum of the protection threshold calculation value and the lower limit correction value is set as the lower limit value of the threshold correction data.

8. The method for correcting the axial displacement protection threshold of a nuclear power steam turbine according to claim 7, characterized in that: In S4, the upper limit correction value is 0.2 mm, and the lower limit correction value is 0.1 mm.

9. The method for correcting the axial displacement protection threshold of a nuclear power steam turbine according to claim 7 or 8, characterized in that: The S4 further comprises: Determine whether the second difference is smaller than the product of the minimum value of the axial flow clearance of the turbine and the set percentage. If so, set the second difference as the upper limit value of the threshold correction data; otherwise, set the upper limit value of the threshold correction data according to the minimum value of the axial flow clearance.

10. The method for correcting the axial displacement protection threshold of a nuclear power steam turbine according to claim 9, characterized in that: In S4, setting the upper limit value of the threshold correction data according to the minimum value of the axial flow clearance includes: The upper limit value of the threshold correction data is set to the product of the minimum value of the axial flow clearance and one third.

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