A switching operation method for a single valve / sequential valve of a steam turbine in a nuclear power plant

Abstract

The present invention discloses a method for the switching operation of a single valve / sequential valve of a steam turbine in a nuclear power plant, comprising the following steps: determining the adjustable steam pressure margin of the secondary loop of the unit; comparing the adjustable steam pressure margin of the secondary loop of the unit with the pressure drop during the running-in period of the steam generator, and judging whether to adopt a single valve control scheme or a sequential valve control scheme; when adopting the sequential valve control scheme, further determining to adopt a specific sequential valve mode according to the steam flow excitation state of the regulating valve. The method for the switching operation of a single valve / sequential valve of a steam turbine in the nuclear power plant according to the present invention first determines whether to perform the single-sequential valve mode switching according to the margin condition of the secondary loop of the unit, then determines to adopt a specific sequential valve mode according to the steam flow excitation state of the regulating valve, and finally realizes a non-disturbing switching method for the single-sequential valve switching. During the switching process, the unit state is stable, and the unit power fluctuation is less than 2 MW.

Description

Technical Field

[0001] The present invention specifically relates to a switching operation method for a single valve / sequential valve of a steam turbine in a nuclear power plant. Background Art

[0002] With the large-scale commercial operation of CRP1000 nuclear power units, problems such as frequent fluctuations in the valve position of the main steam regulating valve of the steam turbine in a certain type of unit have successively occurred, resulting in fatigue fractures of the high-pressure regulating oil supply hoses, seriously reducing the reliability and economy of the nuclear power plant equipment. After some nuclear power plants adopted various measures such as locally optimizing the flow characteristic curve of the regulating valve, reducing the curve slope, optimizing and adjusting the dead zone of the control module, and replacing the oil supply hoses with higher strength, the problems have been alleviated to a certain extent. During further reduction of the main steam pressure or during the extended operation of the unit, it will still bring great troubles to the safe and economic operation of the nuclear power plant.

[0003] The steam distribution mode of the steam turbines of China's CRP1000 nuclear power units is throttle steam distribution. The main reasons are as follows: The investment in nuclear power units is much larger than that of thermal power units with the same power, while the power generation cost is much lower. Therefore, nuclear power units generally do not participate in power grid peak shaving and maintain full power operation throughout the year. In addition, the inlet steam volume flow of nuclear power units is 4 to 6 times larger than that of thermal power units with the same power. If nozzle steam distribution is adopted, the circumferential power of the regulating stage is much larger than that of thermal power units with the same power, increasing the difficulty of moving blade design and even making it impossible to achieve. Existing operating experience also shows that most of the failures of nuclear power units using nozzle steam distribution are due to the damage of the moving blades in the regulating stage. In fact, there is no regulating stage in the steam turbine of the CPR1000 nuclear power unit, and the so-called regulating stage is actually the first pressure stage of the high-pressure cylinder.

[0004] Since the flow passages of nuclear power units are wet steam, it is very difficult to accurately calculate their flow areas, especially the area of the regulating stage. From the actual operating experience of some domestic nuclear power plants, the selected area of the regulating stage often tends to be too large or too small, which is similar to the situation in some models of CRP1000 units, that is, a too small regulating stage area leads to large fluctuations in the regulating valve during full power operation.

[0005] In the design of pressurized water reactor nuclear power units, the nuclear island model usually remains unchanged, following the principle of matching the conventional island to the nuclear island. However, the overall matching of the steam generator, main steam regulating valve, and the flow area of the high-pressure cylinder of the steam turbine during the entire service life should be considered. When the thermal parameters of the nuclear island are determined, during the optimization of the interface parameters of the conventional island, the characteristic of the regular change of the steam generator pressure during the service life cycle should be referred to, and various operating conditions during the service life should be taken into account as a whole. When selecting the regulating valve, a valve with good regulating characteristics within an opening range exceeding 70% should be designed and selected. For the operating units of CRP1000, when the commercial operation time is short, the benefit of retrofitting the diaphragms of the high-pressure cylinder of the steam turbine is not significant, and it may even cause a decrease in the output of the unit. Once the steam generator pressure passes the break-in period of steam pressure reduction and the main steam pressure gradually increases, it will inevitably cause the opening degree of the main steam regulating valve to be too low, resulting in a certain throttling loss. Summary of the Invention

[0006] In view of this, in order to overcome the defects of the prior art, the object of the present invention is to provide a method for switching operation of single valve / sequence valve of a steam turbine in a nuclear power plant.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for switching operation of single valve / sequence valve of a steam turbine in a nuclear power plant includes the following steps:

[0009] Determine the adjustable steam pressure margin of the secondary circuit of the unit;

[0010] Compare the adjustable steam pressure margin of the secondary circuit of the unit with the pressure drop during the break-in period of the steam generator, and determine whether to adopt a single valve control scheme or a sequence valve control scheme;

[0011] When adopting the sequence valve control scheme, further determine the specific sequence valve mode according to the steam flow excitation state of the regulating valve.

[0012] According to some preferred implementation aspects of the present invention, the adjustable steam pressure margin of the secondary circuit of the unit is comprehensively obtained based on the margin of the steam generator of the unit and the linearly adjustable pressure loss of the main steam regulating valve of the steam turbine.

[0013] According to some preferred implementation aspects of the present invention, when the rated load remains unchanged, when the main steam regulating valve is gradually opened to 64% or fully opened, the amplitude of the decrease in the main steam pressure is the adjustable steam pressure margin of the secondary circuit of the unit.

[0014] According to some preferred implementation aspects of the present invention, when the pressure drop during the running-in period of the steam generator is less than the adjustable steam margin of the secondary circuit of the unit, the unit adopts a single-valve or sequence-valve scheme; when the pressure drop during the running-in period of the steam generator is greater than or equal to the adjustable steam pressure margin of the secondary circuit of the unit, the unit adopts a sequence-valve control scheme.

[0015] According to some preferred implementation aspects of the present invention, the sequence-valve control scheme includes the following three types: The first type: Two valves are opened simultaneously first, and the remaining two valves are then opened sequentially; The second type: Two valves are opened simultaneously first, and then the two valves are opened simultaneously; The third type: The four valves are opened simultaneously. After two of the valves are opened to 60-70% of the opening, they are directly opened to 100%.

[0016] According to some preferred implementation aspects of the present invention, for the first sequence-valve control scheme: Two valves are opened simultaneously first. After the opening reaches 50-60%, the third valve is opened. When the two valves opened first are fully opened and the opening of the third valve reaches 60-70%, the fourth valve is opened.

[0017] According to some preferred implementation aspects of the present invention, for the second sequence-valve control scheme: Two valves are opened simultaneously first. When the opening reaches 50-60%, the remaining two valves are then opened simultaneously.

[0018] According to some preferred implementation aspects of the present invention, for the second sequence-valve control scheme: The four valves are opened simultaneously. After two of the valves are opened to 64% of the opening, they are directly opened to 100%.

[0019] According to some preferred implementation aspects of the present invention, the steam-excited vibration state of the regulating valve is obtained based on the amplitude of the valve stem measured by a vibration sensor. When the regulating valve is at a small opening, when the valve stem vibration shows an amplitude peak within the medium and low frequency range of 0-1500 Hz, it indicates that the steam-excited vibration frequency is close to the natural frequency of the valve stem and resonance occurs, with relatively large vibration energy, which is likely to cause damage to the regulating valve.

[0020] According to some preferred implementation aspects of the present invention, when resonance does not occur at the small opening of the regulating valve, the first or second scheme is selected; when resonance occurs at the small opening of the regulating valve, the third scheme is selected. When the opening is less than 2-5%, it is considered a small opening.

[0021] According to some preferred implementation aspects of the present invention, under the stable operating conditions of the steam turbine, at this time, the following functional relationship exists among the steam turbine load N, the steam flow rate G, and the main steam regulating valve opening x:

[0022] N = f(G) = f(x)

[0023] Since the geometric dimensions of the four main steam regulating valves are the same and the flow characteristics are consistent, the following proportional relationship exists among N, G, and x:

[0024] H0 = K1·fd(x) + K2·fs(x)

[0025] K1 + K2 = 1

[0026] Wherein, fd(x) is the sum of the opening degrees of the regulating valves in the single-valve mode; fs(x) is the sum of the opening degrees of the regulating valves in the sequence-valve mode; H0 is the sum of the opening degrees of the regulating valves during the switching process; K1 is the single-valve coefficient; K2 is the sequence-valve coefficient;

[0027] When in the single-valve mode, K1 = 1 and K2 = 0;

[0028] When in the sequence-valve mode, K1 = 0 and K2 = 1;

[0029] If the valve is in the intermediate switching state, 0 < K1 < 1 and 0 < K2 < 1, and when H0 remains unchanged, the steam turbine load N and the steam flow rate G remain unchanged, that is, the unit power is stable, and a seamless switching is achieved.

[0030] Due to the adoption of the above technical solution, compared with the existing single-valve control technology, the beneficial effects of the present invention are as follows: The method for switching operation of the single-valve / sequence-valve of the steam turbine for nuclear power plants of the present invention first determines whether to perform the single-sequence-valve mode switching according to the margin condition of the secondary circuit of the unit, then determines the specific sequence-valve mode according to the steam flow excitation state of the regulating valve, and finally realizes the seamless switching method of the single-sequence-valve switching. During the switching process, the unit state is stable, and the unit power fluctuation is less than 2 MW, which can provide guidance for the safe and economic optimal operation of the steam turbine of the CPR1000 unit in China. Brief Description of the Drawings

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0032] Figure 1 It is a schematic diagram of the secondary circuit margin of a certain pressurized water reactor nuclear power CPR1000 unit in the preferred embodiment of the present invention;

[0033] Figure 2 It is the flow characteristic curve of the main steam regulating valve of a certain pressurized water reactor nuclear power unit in the preferred embodiment of the present invention;

[0034] Figure 3 It is a schematic diagram of the regulating valve layout in the preferred embodiment of the present invention;

[0035] Figure 4 It is the sequence-valve control scheme one in the preferred embodiment of the present invention;

[0036] Figure 5 This is the second sequential valve control scheme in the preferred embodiment of the present invention;

[0037] Figure 6 This is the third sequential valve control scheme in the preferred embodiment of the present invention;

[0038] Figure 7 This is a partial enlarged view of the third sequential valve control scheme in the preferred embodiment of the present invention;

[0039] Figure 8 This is a schematic diagram of the valve management mode in the preferred embodiment of the present invention;

[0040] Figure 9 This is a schematic diagram of the non-disturbing switching process of the regulating valve in the preferred embodiment of the present invention;

[0041] Figure 10 This is a schematic diagram for verifying the valve characteristic curve in the third sequential valve control scheme mode of the preferred embodiment of the present invention;

[0042] Figure 11 This is a partial enlarged schematic diagram for verifying the valve characteristic curve in the third sequential valve control scheme mode of the preferred embodiment of the present invention. Detailed implementation manners

[0043] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

[0044] The purpose of the present invention is to provide an optimized operation method for the single-valve to sequential-valve switching of the steam turbine in the CRP1000 nuclear power unit, which can effectively solve various problems caused by unstable valve position control of the steam turbine in the nuclear power unit.

[0045] To achieve the above object, the optimized operation method for the single-valve to sequential-valve switching of the steam turbine in the CRP1000 nuclear power unit of the present invention includes the following steps:

[0046] Step 1: Determine the adjustable steam pressure margin of the secondary circuit of the unit.

[0047] Due to the operating characteristics of pressurized water reactor nuclear power units, the higher the unit load, the lower the steam pressure at the outlet of the steam generator. However, the steam pressure at the inlet of the steam turbine increases with the increase of the unit load. At the rated load, the difference between the interface pressure between the nuclear island and the conventional island and the steam pressure at the inlet of the steam turbine is the design margin ΔP2 of the secondary circuit steam pressure of the unit, as Figure 1 shown. Under the thermal design conditions of a certain CPR1000 unit, the steam generator pressure is 6.71 Mpa.a, the interface pressure is 6.63 Mpa.a, the pressure before the main steam valve is 6.43 Mpa.a, and the steam pressure at the inlet of the steam turbine is 6.076 Mpa.a. It can be seen that the design margin of the secondary circuit unit steam pressure is 0.554 Mpa.

[0048] The adjustable steam pressure margin of the secondary circuit of a nuclear power unit not only considers the margin of the steam generator, but also needs to take into account the pressure loss linearly adjustable by the main steam control valve of the steam turbine. The margin of a certain CPR1000 unit steam generator is about 130 kPa. When the unit is operating at the rated load, by controlling the average temperature of the primary circuit and gradually opening the control valve to 64%, the main steam pressure gradually decreases by about 180 kPa. Then, the adjustable steam pressure margin of the secondary circuit of the nuclear power unit is 180 kPa. The value of 64% is determined by the slope of the control valve characteristic curve and is an inflection point where the curve slope becomes larger. After the opening reaches 64%, the curve slope is relatively large and the control characteristics are not good.

[0049] Step 2: Compare the adjustable steam pressure margin of the secondary circuit of the unit with the pressure drop during the running-in period of the steam generator, and determine whether to adopt a single-valve control scheme or a sequence-valve control scheme.

[0050] When the pressure drop during the running-in period of the steam generator is less than the adjustable steam margin of the secondary circuit of the unit, the unit adopts a single-valve or sequence-valve scheme; when the pressure drop during the running-in period of the steam generator is greater than or equal to the adjustable steam pressure margin of the secondary circuit of the unit, the unit adopts a sequence-valve control scheme to prevent the control valve from shaking significantly during full-power operation.

[0051] For a certain CPR1000 unit, the steam pressure margin during the running-in period of the steam generator is 210 kPa. The adjustable steam margin of the secondary circuit of the unit is 180 kPa. When the steam pressure margin during the running-in period of the steam generator is greater than or equal to the adjustable steam margin of the secondary circuit, the opening of the control valve will be greater than 64%. At this time, it is advisable to switch to the sequence-valve mode.

[0052] The sequence-valve control scheme includes the following three types: The first type: Two valves are opened simultaneously first, and then the remaining two valves are opened sequentially; The second type: Two valves are opened simultaneously first, and then the two valves are opened simultaneously; The third type: Four valves are opened simultaneously. After two of the valves are opened to 60 - 70% of the opening, they are directly opened to 100%.

[0053] Specifically, for the first sequence valve control scheme: The two valves are opened simultaneously first. After the opening degree reaches 50 - 60%, the third valve is opened. When the first two opened valves are fully opened and the opening degree of the third valve reaches 60 - 70%, the fourth valve is opened. That is, GRE001VV and GRE002VV are opened first. After reaching a certain degree, GRE003VV is opened, and GRE004VV is opened last. It is similar to the sequence valve control scheme of a conventional thermal power plant.

[0054] For the second sequence valve control scheme: The two valves are opened simultaneously first. When the opening degree reaches 50 - 60%, the remaining two valves are then opened simultaneously. That is, GRE001VV and GRE002VV are opened first, and GRE003VV and GRE004VV are opened subsequently.

[0055] For the third sequence valve control scheme: The four valves are opened simultaneously. After two of the valves reach an opening degree of 64%, they are directly opened to 100%. That is, when GRE001VV and GRE002VV reach an opening degree of 64%, they are quickly opened to 100%, and then GRE003VV and GRE004VV are opened wider.

[0056] Step 3: When adopting the sequence valve control scheme, further determine the specific sequence valve mode according to the steam flow excitation state of the regulating valve.

[0057] The steam flow excitation state of the regulating valve is obtained based on the amplitude peak. When there is no resonance phenomenon at a small opening degree of the regulating valve, the first or second scheme is selected; when there is a resonance phenomenon at a small opening degree of the regulating valve, the third scheme is selected to avoid damage to the valve stem of the regulating valve. The amplitude can be obtained by a vibration sensor installed on the valve stem. If there is no resonance of the valve stem under the action of steam impact, the amplitude is usually very small. If resonance occurs, there will be a peak interval where the amplitude first increases and then decreases, which is simply referred to as the amplitude peak.

[0058] For example, when the high-pressure regulating valve is at a low opening degree such as 2 - 5%, the vibration spectrum is mainly excited by medium and low frequencies in the range of 0 - 1500 Hz, and an amplitude peak appears, indicating that resonance occurs; as the opening degree of the valve increases, the amplitude decreases as a whole and remains basically stable. Then, it is advisable to choose Scheme 3, that is, the compound control scheme, where the four valves are opened simultaneously during unit startup and only switched during high load of the unit to limit resonance damage when the valve is at a very small opening degree; if there is no resonance phenomenon at the low opening degree of the high-pressure regulating valve, Scheme 1 or Scheme 2 can be selected.

[0059] Under the stable operating conditions of the steam turbine, at this time, the steam turbine load N, steam flow G, and regulating valve opening x have the following functional relationship:

[0060] N = f(G) = f(x)

[0061] Since the geometric dimensions of the valves are the same and the flow characteristics are consistent, the following proportional relationships exist among N, G, and x:

[0062] H 0=K1·fd(x)+K2·fs(x)

[0063] K1+K2=1

[0064] In the formula, fd(x) is the sum of the opening degrees of the regulating valves in the single-valve mode; fs(x) is the sum of the opening degrees of the regulating valves in the sequence-valve mode; H0 is the sum of the opening degrees of the regulating valves during the switching process; K1 is the single-valve coefficient; K2 is the sequence-valve coefficient;

[0065] When in the single-valve mode, K1 = 1 and K2 = 0;

[0066] When in the sequence-valve mode, K1 = 0 and K2 = 1;

[0067] If the valve is in the intermediate state of switching, 0﹤K1﹤1, 0﹤K2﹤1, and when H0 remains unchanged, the steam turbine load N and the steam flow G remain unchanged, that is, the unit power is stable, realizing a seamless switch.

[0068] The method for optimizing the operation of the single-valve / sequence-valve switching of the steam turbine of the CPR1000 unit of the present invention is determined based on the pressure drop characteristics during the running-in period of the steam generator and the adjustable steam pressure margin of the secondary circuit of the unit, and the single-valve or sequence-valve operation control mode is selected. Combining the operating characteristics of the steam turbine and the characteristic curve of the regulating valve, the flow capacity of the steam turbine regulating valve under the single-valve and sequence-valve is calculated, and various adjustment methods under the sequence-valve control mode of the nuclear power unit are obtained. According to the characteristics of the regulating valve, the corresponding optimal control scheme can be selected. A seamless switching method for the single-valve and sequence-valve of the CPR1000 unit is established. A valve control management module for the steam turbine regulating valve is designed for the operator to manually select. During the automatic switching of the valve, the unit state is stable, and the power fluctuation of the unit does not exceed 2MW.

[0069] Specific case

[0070] The method for optimizing the operation of the single-valve / sequence-valve switching of the steam turbine of the CRP1000 nuclear power unit in this embodiment includes the following steps:

[0071] Step 1. Determine the adjustable steam pressure margin of the secondary circuit of the unit.

[0072] The flow characteristic curve of the regulating valve in the single-valve mode of a certain CRP1000 unit is as Figure 2As shown. When the valve opening is less than 64%, the linearity is good. After exceeding 64%, the curve slope becomes larger, indicating that the flow regulation characteristic is weakened, and the flow fluctuation of the unit is likely to cause large fluctuations in the valve opening of the regulating valve. After the valve opening of a certain CPR1000 unit exceeds 64%, the valve opening fluctuates frequently and largely, resulting in the fracture of the oil supply hose. Therefore, the maximum limit of the high-pressure regulating valve opening is set at 64%. For example, when the steam pressure of the steam generator of a certain CPR1000 unit drops by 210 kPa, it exceeds the adjustable steam margin of 180 kPa in the secondary circuit of the unit, and the valve opening of the high-pressure regulating valve frequently triggers the 64% opening upper limit, resulting in frequent triggering of GRE358KA. The reactor power is limited to about 2869 - 2880 MW, and the electric power is about 1067 - 1070 MW. The valve opening limits the reactor power from reaching the full power of 2905 MW of the CPR1000 unit, causing greater economic losses and seriously reducing the equipment reliability.

[0073] Step 2: Compare the adjustable steam pressure margin in the secondary circuit of the unit with the pressure drop during the running-in period of the steam generator, and determine whether to adopt a single-valve control scheme or a sequence-valve control scheme.

[0074] A certain CRP1000 nuclear power plant adopts a single-valve control mode. According to the valve flow characteristics, a valve control selection function is added on the basis of the existing valve control mode of the unit to achieve seamless switching between the single-valve control and the sequence-valve control of the unit. Here, referring to the idea of sequence-valve control in conventional thermal power plants, taking a certain CPR1000 unit as an example, the steam actually passing through 4 regulating valves will still be mixed before entering the steam admission of the turbine governing stage and then enter the diaphragm and moving blades to do work. Compared with the single-valve control, the impact force on the diaphragm is basically unchanged, and the diaphragm and blades should be in a safe state. The schematic diagram of the regulating valve is as Figure 3 shown.

[0075] The first sequence-valve control scheme of the regulating valve is similar to the sequence-valve control scheme of a conventional power plant, that is, when GRE001VV and GRE002VV are first opened to 51.5%, GRE003VV is then opened. When it is opened to 79.3%, GRE004VV is opened last. The second is that GRE001VV and GRE002VV are first opened. When it is opened to 51.5%, GRE003VV and GRE004VV are then opened; the third is that the four valves are opened simultaneously. When GRE001VV and GRE002VV are opened to 64% opening, they are quickly opened to 100%, and then GRE003VV and GRE004VV are opened further. The valve flow characteristic curves are respectively as Figures 4 to 7 shown.

[0076] Step 3: When adopting the sequence-valve control scheme, further determine the specific sequence-valve mode according to the steam flow excitation state of the regulating valve.

[0077] The selection of the control scheme for the regulating valve sequence valve needs to be combined with the operating status of the unit, especially in the case where the regulating valve is induced by high-frequency turbulence at the valve stem. Usually, a piezoelectric acceleration sensor can be used to measure the axial and longitudinal vibration conditions at the valve stem. For example, when the high-pressure regulating valve is at a low opening degree, such as 2-5%, the vibration spectrum is mainly dominated by medium and low-frequency excitation in the range of 0-1500 Hz, and amplitude peaks appear, indicating resonance. As the valve opening increases, the overall amplitude decreases and remains basically stable. Then, it is advisable to select Scheme 3, that is, the composite control scheme, where the four valves are opened simultaneously during unit startup and only switched during high unit load to limit damage caused by resonance when the valve is at a very small opening. If the high-pressure regulating valve does not resonate at a low opening degree, Scheme 1 or Scheme 2 can be selected.

[0078] Similar to the main steam valve test module of a nuclear power plant, a valve characteristic management module is added to the DCS in this application; as Figure 8 shown; the switching of the valve management mode needs to be manually selected by the nuclear power plant operator, and the switching process is automatic. After the switching is completed, the power change is automatically carried out according to the actual power control requirements of the unit. There is no disturbance when the unit switches between single-valve control and sequence-valve control.

[0079] The management strategy for the high-pressure regulating valve is as Figure 9 shown. According to the flow characteristic curve and input into the corresponding function, the valve switching process is opened in accordance with the curve design sequence. In the figure, F1 d(x), F2d(x), F3d(x), F4d(x) are the single-valve flow characteristic curves, as shown by the curves in Figure 2 ; F1 s(x), F2s(x), F3s(x), F3s(x) are the sequence-valve flow characteristic curves, and the characteristic curve of Scheme 3 for composite control is as shown by the curve in Figure 6 . The steps of the following three switching methods are briefly described:

[0080] (a) Switching from single valve to sequence valve

[0081] (1) Confirm that the secondary circuit steam turbine is in a selected load stable state, such as above 90% Pn (nuclear power), the secondary circuit drain system of the unit has basically taken the normal path, and the moisture separator reheater has been fully put into operation, and then open the automatic control screen.

[0082] (2) Click on the valve mode operation management screen and click the sequence valve button.

[0083] (3) The button for switching to the sequence valve turns yellow, and the button for the ongoing switching turns red and flashes. The switching from single valve to sequence valve starts, and the valve opening in the screen status bar opens or closes according to the characteristic curve.

[0084] (4) Switch the "In Progress" button. It stops flashing and turns green, indicating that the switch is complete. The valve status in the picture status bar will show the sequence valve. The valve has been switched from the single valve to the sequence valve.

[0085] (5) The switching time is 10 minutes. When the valve position parameter value is greater than 99.9% (valve fully open) or less than 0.1% (valve fully closed), the switching process ends.

[0086] (b) Sequence valve to single valve

[0087] (1) Ensure that the steam turbine is in a certain selected stable load state, such as above 90% Pn, and then open the automatic control screen.

[0088] (2) Click on the valve mode, open the operation terminal, and click to switch to the single valve.

[0089] (3) The "Switch to Single Valve" button turns yellow. During the switching process, the button turns red and flashes, indicating that the sequence valve to single valve switching has started. The valve status display in the picture status bar disappears, indicating that the switching is in progress.

[0090] (4) The regulating valve opens or closes according to the single valve curve.

[0091] (5) During the switching process, the button stops flashing and turns green, indicating that the switching is complete. The valve status display in the picture status bar shows the single valve, and at this time, it has been switched from the sequence valve to the single valve.

[0092] (6) The switching time is 10 minutes (adjustable). When the valve position reference value is greater than 99.9% (valve fully open) or less than 0.1% (valve fully closed), the switching ends.

[0093] (c) Smooth switching

[0094] The single valve / sequence valve switching should be carried out under stable operating conditions of the steam turbine. At this time, the steam turbine load N, steam flow G, and throttle valve opening x are in a functional relationship:

[0095] N = f(G) = f(x)

[0096] Since the four throttle valves of this machine have the same geometric dimensions and basically the same flow characteristics (if different, the valve curve can be corrected), then there is a proportional relationship among N, G, and x:

[0097] H0 = K1fd(x) + K2fs(x)

[0098] K1 + K2 = 1

[0099] Where, fd(x) is the sum of the throttle valve openings of the regulating valve in the single valve mode; fs(x) is the sum of the throttle valve openings of the regulating valve in the sequence valve mode; H0 is the sum of the throttle valve openings during the switching process; K1 is the single valve coefficient; K2 is the sequence valve coefficient;

[0100] In the single-valve mode, K1 = 1 and K2 = 0;

[0101] In the sequence-valve mode, K1 = 0 and K2 = 1;

[0102] If the valve is in the intermediate state of switching, 0 < K1 < 1 and 0 < K2 < 1. When H0 remains unchanged, the steam turbine load N and the steam flow G remain unchanged, that is, the unit power is stable, realizing disturbance-free switching.

[0103] The actual opening command of each valve is obtained by adding the product of the single-valve coefficient and the single-valve opening value to the product of the sequence-valve coefficient and the sequence-valve opening value. The commands of both modes are obtained by converting through the single-valve curve and the sequence-valve curve according to the current load command.

[0104] The single-valve coefficient K1 decreases from 1 at a rate of 0.00167 / s, that is, the switching time is 10 minutes. When K1 becomes 0, the coefficient K1 remains K1 = 0; the single-valve to sequence-valve switching is completed, and the unit switches to the sequence-valve control mode; when switching from the sequence-valve to the single-valve, when K1 changes from 0 to 1 at a rate of 0.00167 / s, the sequence-valve to single-valve switching is completed, and the unit switches to the single-valve control mode.

[0105] At the same time, since the relationship between the valve opening X and N is not a completely linear relationship, it will affect the change of the unit operation condition. When performing single-valve / sequence-valve switching operation when the regulating system is in open-loop operation, load disturbances of different degrees will occur. When power closed-loop control or regulating stage pressure closed-loop control is put into operation, the load disturbance will be greatly improved. When power closed-loop is put into operation, when the actual power differs from the load set value by 4%, the switching will automatically abort; when this difference reaches within 3%, the switching automatically resumes. When regulating stage pressure closed-loop is put into operation, the control accuracy of the regulating stage pressure is within 1.5%.

[0106] Step 4: Verification of the sequence-valve control scheme.

[0107] Verify the control mode and characteristic curve of Scheme 3 on the full-scope simulator of the nuclear power plant. The comparison between the actual control characteristics and the theoretical characteristics is as Figure 10 and Figure 11 shown.

[0108] Figure 10 and Figure 11 In, the theoretical valve position is the solid line and the actual valve position is the dashed line. By comparison, it can be seen that the actual valve control characteristics are basically consistent with the theoretical curve. During the process of increasing and decreasing the load, the unit load control is stable, and the power fluctuation is less than 2 MW, which can meet the actual control requirements of the nuclear power plant.

[0109] To achieve the purpose of minimizing the changes in the steam turbine operating conditions before and after the switching, it is generally advisable to select the design condition or slightly below the design condition. At this time, whether in the single-valve mode or the sequential-valve mode, the opening of the control valve is in a relatively small throttling state. This unit selects a load of 1000 MW, approximately 90% of Pn. During the switching, the main steam pressure, the temperature of the primary loop, the vacuum, and the reactor power should be stable to reduce the excessive change in the regulating stage pressure caused thereby. Pay attention to the operation of the regulating system to prevent the speed control system from oscillating. Pay attention to the normal operation of auxiliary machines and auxiliary equipment.

[0110] When the following conditions are met, the unit will automatically switch back to the original single-valve steam distribution mode: the generator power is less than 90% of Pn; the unit is disconnected or tripped; the unit experiences excessive vibration or large vibration in the oil supply circuit. When the unit is disconnected or tripped, or when the high-pressure control valves are fully open or fully closed, the switching of the steam distribution mode of the unit to the single valve is immediately completed.

[0111] The method for optimizing the operation of converting the single valve to the sequential valve of the steam turbine in a nuclear power plant according to the present invention is determined based on the pressure drop characteristics during the running-in period of the steam generator and the adjustable steam pressure margin of the secondary loop of the unit, and a single-valve or sequential-valve operation control scheme can be selected. Combining the operating characteristics of the steam turbine and the characteristic curve of the control valve, the flow capacity of the steam turbine control valve under the single-valve and sequential-valve conditions is calculated to obtain various adjustment methods under the sequential-valve control mode of the steam generator. According to the characteristics of the control valve, the corresponding optimal control scheme can be selected. A method for seamless switching between the single valve and the sequential valve of the CPR1000 unit is established, and precautions during the valve switching process are provided to ensure the stable state of the unit during the single-sequential valve switching process. By using the seamless switching between the single valve and the sequential valve, it is realized that the control valve of the nuclear power unit does not resonate due to steam flow excitation during low-load operation, and the valve position of the control valve is stable during high-load operation without large fluctuations causing fatigue fracture of the oil supply hose, providing a new scheme for the control of the control valve of the CPR1000 unit steam turbine and filling the blank in the management field of control valves of the same type of CPR1000 steam turbine.

[0112] The above embodiments are only for explaining the technical concept and characteristics of the present invention, and their purpose is to enable those familiar with this technology to understand the content of the present invention and implement it accordingly, and should not be used to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for switching operation of a single valve / sequence valve of a steam turbine in a nuclear power plant, characterized in that, It includes the following steps: Determine the adjustable steam pressure margin of the secondary circuit of a pressurized water reactor nuclear power unit; Compare the adjustable steam pressure margin of the secondary circuit of the nuclear power unit with the pressure drop during the running-in period of the steam generator, and determine whether to adopt a single-valve control scheme or a sequence-valve control scheme; when the pressure drop during the running-in period of the steam generator is greater than the adjustable steam pressure margin of the secondary circuit of the unit, the unit adopts a sequence-valve control scheme; When adopting a sequence-valve control scheme, further determine the specific sequence-valve mode according to the steam flow excitation state of the regulating valve; The adjustable steam pressure margin of the secondary circuit of the unit is comprehensively obtained based on the margin of the steam generator of the unit and the linearly adjustable pressure loss of the main steam regulating valve of the steam turbine; When the rated load remains unchanged, when the main steam regulating valve is gradually opened to 64% or fully opened, the amplitude of the reduction in the main steam pressure is the adjustable steam pressure margin of the secondary circuit of the unit.

2. The switching operation method according to claim 1, wherein When the pressure drop during the running-in period of the steam generator is less than the adjustable steam margin of the secondary circuit of the unit, the unit adopts a single-valve or sequence-valve scheme.

3. The switching operation method according to claim 1 or 2, characterized in that The sequence-valve control scheme includes the following three types: The first type: Two valves are opened simultaneously first, and the remaining two valves are then opened sequentially; The second type: Two valves are opened simultaneously first, and then the two valves are opened simultaneously; The third type: Four valves are opened simultaneously, and after two of the valves are opened to 60-70% opening, they are directly opened to 100%.

4. The switching operation method according to claim 3, wherein The first sequence-valve control scheme: Two valves are opened simultaneously first. After the opening reaches 50-60%, the third valve is opened. When the two valves opened first are fully opened and the opening of the third valve reaches 60-70%, the fourth valve is opened.

5. The switching operation method according to claim 3, wherein The second sequence-valve control scheme: Two valves are opened simultaneously first. When the opening reaches 50-60%, the remaining two valves are then opened simultaneously.

6. The switching operation method according to claim 3, wherein The third sequence-valve control scheme: Four valves are opened simultaneously, and after two of the valves are opened to 64% opening, they are directly opened to 100%.

7. The switching operation method according to claim 3, wherein When there is no resonance amplitude peak under the steam flow excitation of the regulating valve, select the first or second scheme; when there is a resonance amplitude peak under the steam flow excitation of the regulating valve, select the third scheme.

8. The switching operation method according to claim 1, wherein Under the stable operating conditions of the steam turbine, at this time, the turbine load N, the main steam flow G, and the opening x of the main steam regulating valve have the following functional relationship: N = f (G) = f (x) Since the geometric dimensions of the four main steam regulating valves are the same and the flow characteristics are consistent, there is the following proportional relationship: H0 = K1·fd (x) + K2·fs (x) K1 + K2 = 1 In the formula, fd (x) is the sum of the opening degrees of the regulating valves in the single-valve mode; fs (x) is the sum of the opening degrees of the regulating valves in the sequence-valve mode; H0 is the sum of the opening degrees of the regulating valves during the switching process; K1 is the single-valve coefficient; K2 is the sequence-valve coefficient; When in the single-valve mode, K1 = 1 and K2 = 0; When in the sequence-valve mode, K1 = 0 and K2 = 1; If the main steam regulating valve is in the intermediate state of switching, 0﹤K1﹤1 and 0﹤K2﹤1.

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