Water level control method and system for conventional island drain tank in nuclear power plant

Abstract

The present invention relates to the technical field of conventional islands in nuclear power plants, and in particular to a method and system for controlling the water level of a conventional island drain tank in a nuclear power plant. The method comprises: obtaining a first water level through a first water level transmitter and converting it into a first liquid level signal and then outputting it; obtaining a second water level through a second water level transmitter and converting it into a second liquid level signal and then outputting it; allowing a signal selector to determine and output a liquid level output value based on the received first liquid level signal and second liquid level signal; when confirming that at least one of the first water level transmitter and the second water level transmitter is operating normally, allowing a normal water level controller to control the opening of a normal drain valve based on the liquid level output value, and allowing an emergency water level controller to control the opening of an emergency drain valve based on the liquid level output value. The present invention ensures the reliability of drain valve control and the normal operation of the system when one of the first water level transmitter and the second water level transmitter fails.

Description

Technical Field

[0001] The invention relates to the technical field of conventional islands in nuclear power plants, and in particular to a method and system for controlling the water level of a drain tank in a conventional island in a nuclear power plant. Background Art

[0002] In the conventional island drain tank water level control system of a nuclear power plant, the current water level is determined by measuring with a single water level transmitter. In this way, when the water level transmitter fails and the water level measurement value is incorrect, it will directly affect the water level control result and cause the emergency drain to be opened. At this time, the drain is discharged to the condenser without doing work, affecting the thermal efficiency of the steam turbine. At present, with the gradual increase in the operating time of nuclear power plants, there have been many cases of emergency drains being opened due to single water level transmitter measurement failures, resulting in a decrease in the thermal efficiency of the steam turbine and a huge power loss. Summary of the invention

[0003] The embodiment of the present invention provides a method and system for controlling the water level of a conventional island drain tank in a nuclear power plant, and the present invention solves the problem of starting emergency draining due to a measurement failure of a single water level transmitter.

[0004] A method for controlling the water level of a conventional island drain tank in a nuclear power plant, comprising:

[0005] The first water level is obtained through the first water level transmitter, and the first water level transmitter is made to convert the first water level into a first liquid level signal and then output; the first upper sampling point of the first water level transmitter is connected to the upper sampling hole of the conventional island drain tank of the nuclear power plant, and the first lower sampling point of the first water level transmitter is connected to the lower sampling hole of the conventional island drain tank of the nuclear power plant;

[0006] The second water level is obtained through the second water level transmitter, and the second water level transmitter is made to convert the second water level into a second liquid level signal and then output; the second upper sampling point of the second water level transmitter is connected to the upper sampling hole of the conventional island drain tank of the nuclear power plant, and the second lower sampling point of the first water level transmitter is connected to the lower sampling hole of the conventional island drain tank of the nuclear power plant;

[0007] The signal selector is instructed to determine and output a liquid level output value according to the received first liquid level signal and the second liquid level signal; the signal selector is connected to the first water level transmitter and the second water level transmitter;

[0008] After confirming that at least one of the first water level transmitter and the second water level transmitter is operating normally, the normal water level controller is controlled to control the opening of the normal steam trap according to the liquid level output value, and the emergency water level controller is controlled to control the opening of the emergency steam trap according to the liquid level output value; the normal water level controller is connected between the signal selector and the normal steam trap; the emergency water level controller is connected between the signal selector and the emergency steam trap.

[0009] A water level control system for a conventional island drain tank of a nuclear power plant, used to execute the water level control method for a conventional island drain tank of a nuclear power plant; the water level control system for a conventional island drain tank of a nuclear power plant comprises a conventional island drain tank of a nuclear power plant, a first water level transmitter, a second water level transmitter, a signal selector, a normal water level controller, a normal drain valve, an emergency water level controller and an emergency drain valve;

[0010] The conventional island drain tank of the nuclear power plant is provided with an upper sampling hole and a lower sampling hole with a specified height difference; the first upper sampling point of the first water level transmitter is connected to the upper sampling hole, and the first lower sampling point of the first water level transmitter is connected to the lower sampling hole; the second upper sampling point of the second water level transmitter is connected to the upper sampling hole, and the second lower sampling point of the first water level transmitter is connected to the lower sampling hole;

[0011] The signal selector connects the first water level transmitter and the second water level transmitter;

[0012] The normal water level controller is connected between the signal selector and the normal steam trap; the emergency water level controller is connected between the signal selector and the emergency steam trap.

[0013] The water level control method and system of a conventional island drain tank of a nuclear power plant provided by the present invention obtain a first water level through a first water level transmitter, and make the first water level transmitter convert the first water level into a first liquid level signal and then output it; obtain a second water level through a second water level transmitter, and make the second water level transmitter convert the second water level into a second liquid level signal and then output it; make a signal selector determine and output a liquid level output value according to the received first liquid level signal and second liquid level signal; when confirming that at least one of the first water level transmitter and the second water level transmitter is operating normally, make a normal water level controller control the opening of a normal drain valve according to the liquid level output value, and make an emergency water level controller control the opening of an emergency drain valve according to the liquid level output value.

[0014] The first water level transmitter and the second water level transmitter of the present invention are both connected between the upper sampling hole and the lower sampling hole of the conventional island drain tank of the nuclear power plant, and the measurement ranges of the two cover the first liquid level range corresponding to the normal drain valve (the minimum value of the first liquid level range is the first liquid level, the maximum value of the first liquid level range is the second liquid level; the first liquid level is flush with the lower sampling point) and the second liquid level range corresponding to the emergency drain valve (the minimum value of the second liquid level range is the third liquid level, the maximum value of the second liquid level range is the fourth liquid level; the fourth liquid level is flush with the upper sampling point). When one of the first water level transmitter and the second water level transmitter fails, the final liquid level output value can still be guaranteed to be reliable, avoiding the phenomenon that the on-site valve disturbance opens the emergency drain due to the measurement failure of a single water level transmitter, which in turn causes the thermal efficiency of the turbine to decrease and cause power loss.

[0015] At the same time, the normal water level controller of the present invention controls the opening of the normal steam trap according to the liquid level output value, and the emergency water level controller controls the opening of the emergency steam trap according to the liquid level output value; since the first liquid level range and the second liquid level range are redundant with each other (the third liquid level is less than the second liquid level and greater than the first liquid level, and the fourth liquid level is greater than the second liquid level), their redundancy constitutes an appropriate water level interlock, which can ensure that the normal water level controller and the emergency water level controller only control different steam traps to work within their respective liquid level ranges, do not interfere with each other, and improve the reliability of steam trap control. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0017] Figure 1 It is a flow chart of a method for controlling water level in a conventional island drain tank of a nuclear power plant in one embodiment of the present invention.

[0018] Figure 2 It is a flow chart of step S30 of the water level control method of the conventional island drain tank of a nuclear power plant in one embodiment of the present invention.

[0019] Figure 3 It is a schematic structural diagram of a water level control system for a conventional island drain tank in a nuclear power plant in one embodiment of the present invention.

[0020] The reference numerals in the specification are as follows:

[0021] 1. Conventional island drain tank of nuclear power plant; 2. First water level transmitter; 3. Second water level transmitter; 4. Signal selector; 5. Normal water level controller; 6. Normal drain valve; 7. Emergency water level controller; 8. Emergency drain valve. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] The water level control method for conventional island drain tanks in nuclear power plants provided by the present invention is applied in the following applications: Figure 1The conventional island drain tank water level control system of the nuclear power plant shown in the figure comprises a conventional island drain tank 1 of the nuclear power plant, a first water level transmitter 2, a second water level transmitter 3, a signal selector 4, a normal water level controller 5, a normal drain valve 6, an emergency water level controller 7 and an emergency drain valve 8; Figure 2 As shown, the conventional island drain tank water level control method of the nuclear power plant comprises the following steps:

[0024] S10, obtaining the first water level through the first water level transmitter 2, and allowing the first water level transmitter 2 to convert the first water level into a first liquid level signal and then output it; the first upper sampling point of the first water level transmitter 2 is connected to the upper sampling hole of the conventional island drain tank 1 of the nuclear power plant, and the first lower sampling point of the first water level transmitter 2 is connected to the lower sampling hole of the conventional island drain tank 1 of the nuclear power plant; the first lower sampling point and the lower sampling hole, as well as the first upper sampling point and the upper sampling hole are respectively connected by two sampling tubes.

[0025] S20, obtain the second water level through the second water level transmitter 3, and let the second water level transmitter 3 convert the second water level into a second liquid level signal and then output it; the second upper sampling point of the second water level transmitter 3 is connected to the upper sampling hole of the conventional island drain tank 1 of the nuclear power plant, and the second lower sampling point of the first water level transmitter 2 is connected to the lower sampling hole of the conventional island drain tank 1 of the nuclear power plant; the second lower sampling point and the lower sampling hole, and the second upper sampling point and the upper sampling hole are respectively connected by two sampling tubes. Although the present invention is provided with two water level transmitters (the first water level transmitter 2 and the second water level transmitter 3), only two sampling holes, the upper sampling hole and the lower sampling hole, are provided on the conventional island drain tank 1 of the nuclear power plant (the first water level transmitter 2 and the second water level transmitter 3 share the upper sampling hole and the lower sampling hole through four sampling tubes), which avoids the setting of additional sampling holes outside the two sampling holes to affect the pressure of the drain tank. The measuring ranges of the first water level transmitter 2 and the second water level transmitter 3 are consistent, and both of the measuring ranges are the corresponding measuring ranges between the lower sampling hole and the upper sampling hole.

[0026] S30, instruct the signal selector 4 to determine and output the liquid level output value based on the received first liquid level signal and the second liquid level signal; the signal selector 4 is connected to the first water level transmitter 2 and the second water level transmitter 3; that is, based on the first liquid level signal and the second liquid level signal, it can be determined whether the first water level transmitter 2 and the second water level transmitter 3 are faulty (or operating normally), respectively, and the liquid level output value finally output by the signal selector 4 to the normal water level controller 5 and the emergency water level controller 7 can also be jointly confirmed based on the first liquid level signal and the second liquid level signal. Optionally, when the first water level measured by the first water level transmitter 2 is flush with the upper sampling hole on the conventional island drain tank 1 of the nuclear power plant, the first liquid level signal is 4mA; when the first water level measured by the first water level transmitter 2 is flush with the lower sampling hole on the conventional island drain tank 1 of the nuclear power plant, the first liquid level signal is 20mA; when the first water level measured by the first water level transmitter 2 is between the lower sampling hole and the upper sampling hole, the first liquid level signal is between 4mA and 20mA; similarly, when the second water level measured by the second water level transmitter 3 is flush with the upper sampling hole on the conventional island drain tank 1 of the nuclear power plant, the second liquid level signal is 4mA; when the second water level measured by the second water level transmitter 3 is flush with the lower sampling hole on the conventional island drain tank 1 of the nuclear power plant, the second liquid level signal is 20mA; when the second water level measured by the second water level transmitter 3 is between the lower sampling hole and the upper sampling hole, the second liquid level signal is between 4mA and 20mA. S40, after confirming that at least one of the first water level transmitter 2 and the second water level transmitter 3 is operating normally, the normal water level controller 5 is controlled to control the opening of the normal steam trap 6 according to the liquid level output value, and the emergency water level controller 7 is controlled to control the opening of the emergency steam trap 8 according to the liquid level output value; the normal water level controller 5 is connected between the signal selector 4 and the normal steam trap 6; the emergency water level controller 7 is connected between the signal selector 4 and the emergency steam trap 8. That is, when the signal selector 4 confirms that at least one of the first water level transmitter 2 and the second water level transmitter 3 is operating normally (that is, the first water level transmitter 2 and the second water level transmitter 3 are not all faulty) according to the received first liquid level signal and the second liquid level signal, the normal water level controller 5 controls the opening of the normal steam trap 6 according to the liquid level output value, and the emergency water level controller 7 controls the opening of the emergency steam trap 8 according to the liquid level output value.

[0027] The first water level transmitter 2 and the second water level transmitter 3 of the present invention are both connected between the upper sampling hole and the lower sampling hole of the conventional island drain tank 1 of the nuclear power plant, and the measurement range of the two covers the first liquid level range corresponding to the normal drain valve 6 (the minimum value of the first liquid level range is the first liquid level, and the maximum value of the first liquid level range is the second liquid level; the first liquid level is flush with the lower sampling point; when the liquid level value corresponding to the liquid level output value is the first liquid level, the opening of the normal drain valve 6 should be set to 0%; when the liquid level value corresponding to the liquid level output value is the second liquid level, the opening of the normal drain valve 6 should be set to 100%) and the second liquid level range corresponding to the emergency drain valve 8 (the minimum value of the second liquid level range is the first liquid level, and the maximum value of the first liquid level range is the second liquid level; the first liquid level is flush with the lower sampling point; when the liquid level value corresponding to the liquid level output value is the first liquid level, the opening of the normal drain valve 6 should be set to 0%; when the liquid level value corresponding to the liquid level output value is the second liquid level, the opening of the normal drain valve 6 should be set to 100%). The value is the third liquid level, and the maximum value of the second liquid level range is the fourth liquid level; the fourth liquid level is flush with the upper sampling point; when the liquid level value corresponding to the liquid level output value is the third liquid level, the opening of the emergency drain valve 8 should be set to 0%; when the liquid level value corresponding to the liquid level output value is the fourth liquid level, the opening of the emergency drain valve 8 should be set to 100%). In this way, when one of the first water level transmitter 2 and the second water level transmitter 3 fails, the final liquid level output value can still be guaranteed to be reliable, avoiding the phenomenon that the on-site valve disturbance opens the emergency drain due to the measurement failure of a single water level transmitter, which in turn causes the thermal efficiency of the steam turbine to decrease and cause power loss.

[0028] At the same time, the normal water level controller 5 of the present invention controls the opening of the normal steam trap 6 according to the liquid level output value, and the emergency water level controller 7 controls the opening of the emergency steam trap 8 according to the liquid level output value; since the first liquid level range and the second liquid level range are redundant with each other (the third liquid level is less than the second liquid level and greater than the first liquid level, and the fourth liquid level is greater than the second liquid level), the redundancy constitutes an appropriate water level interlock, which can ensure that the normal water level controller 5 and the emergency water level controller 7 only control different steam traps to work within their respective liquid level ranges, do not interfere with each other, and improve the reliability of steam trap control.

[0029] In one embodiment, if Figure 3 As shown, in the step S30, the signal selector 4 is instructed to determine and output the liquid level output value according to the received first liquid level signal and the second liquid level signal, including:

[0030] S301, confirming whether the first water level transmitter 2 and the second water level transmitter 3 are both faulty according to the first liquid level signal and the second liquid level signal through the signal selector 4; in one embodiment, the step S301 includes:

[0031] Determining whether the first liquid level signal and the second liquid level signal belong to a preset signal value range by the signal selector 4;

[0032] When the first liquid level signal and the second liquid level signal both fall within the preset signal value range, confirming that the first water level transmitter 2 and the second water level transmitter 3 are both operating normally;

[0033] When both the first liquid level signal and the second liquid level signal exceed the preset signal value range, it is confirmed that both the first water level transmitter 2 and the second water level transmitter 3 are faulty;

[0034] When one of the first liquid level signal and the second liquid level signal exceeds the preset signal value range, it is confirmed that the first water level transmitter 2 or the second water level transmitter 3 that exceeds the preset signal value range is faulty, and the first water level transmitter 2 or the second water level transmitter 3 that does not exceed the preset signal value range is operating normally.

[0035] That is, in this embodiment, the signal selector 4 can confirm whether the first water level transmitter 2 or the second water level transmitter 3 is faulty through the first liquid level signal and the second liquid level signal. Specifically, when the first liquid level signal belongs to the above-mentioned preset signal value range, it can be considered that the first water level transmitter 2 is operating normally; when the second liquid level signal belongs to the above-mentioned preset signal value range, it can be considered that the second water level transmitter 3 is operating normally. When the first liquid level signal exceeds the above-mentioned preset signal value range, it can be considered that the first water level transmitter 2 is faulty; when the second liquid level signal exceeds the above-mentioned preset signal value range, it can be considered that the second water level transmitter 3 is faulty.

[0036] Among them, the preset signal value range can be set according to demand. Optionally, the preset signal value range X is: 3.2mA≤X≤20.8mA. It can be seen from the above content that when the first water level measured by the first water level transmitter 2 is between the lower sampling hole and the upper sampling hole, the first liquid level signal is between 4mA and 20mA; when the second water level measured by the second water level transmitter 3 is between the lower sampling hole and the upper sampling hole, the second liquid level signal is between 4mA and 20mA. According to the above content, the preset signal value range is set to be slightly larger than the signal range of the first liquid level signal and the second liquid level signal corresponding to the water level between the upper sampling hole and the lower sampling hole. At this time, it can be avoided that when the first liquid level signal and the second liquid level signal are near the critical point corresponding to the upper sampling point or the lower sampling point, due to the influence of measurement accuracy, the result of judging the failure of the first water level transmitter 2 or the second transmitter is incorrect.

[0037] S302, when confirming that the first water level transmitter 2 and the second water level transmitter 3 are operating normally, obtain the deviation value between the first liquid level signal and the second liquid level signal; the deviation value refers to the ratio between the absolute value of the difference between the first water level and the second water level and the specified height difference, and the specified height difference refers to the height difference between the lower sampling hole and the upper sampling hole. It can be understood that the specified height difference is also the liquid level difference between the fourth liquid level and the first liquid level.

[0038] S303, when the deviation value is less than the preset deviation threshold, the average value of the first liquid level signal and the second liquid level signal is determined as the liquid level output value and output. Optionally, the preset deviation threshold is 5%, which is obtained according to the actual experimental results. With the preset deviation threshold of 5% as the dividing line, the liquid level output value needs to be determined in different ways. That is, when it is confirmed that the first water level transmitter 2 and the second water level transmitter 3 are both operating normally, on the one hand, when the deviation value is less than the preset deviation threshold, the average value of the first liquid level signal and the second liquid level signal is determined as the liquid level output value and output. On the other hand, after the step S302, it also includes: when the deviation value is greater than or equal to the preset deviation threshold, the maximum value between the first liquid level signal and the second liquid level signal is determined as the liquid level output value and output, and an alarm signal is sent to the main control room to prompt the main control room to pay attention to the state that the current deviation value is greater than or equal to the preset deviation threshold, and it needs to be adjusted and maintained later. It is understandable that if the ratio of the absolute value of the difference between the first water level and the second water level to the specified height difference exceeds 5%, it means that there is a problem in the measurement status of the two. It may be that one or both of the water level transmitters are faulty. However, the fault cannot be confirmed by whether the first liquid level signal and the second liquid level signal exceed the preset signal value range. Therefore, an alarm is required to prompt the main control room to pay attention. At the same time, the maximum value between the first liquid level signal and the second liquid level signal is used as the liquid level output value, which can ensure the safety of the nuclear power plant to a greater extent.

[0039] In one embodiment, after step S301, the method further includes:

[0040] When it is confirmed that both the first water level transmitter 2 and the second water level transmitter 3 are faulty, the historical output value of the liquid level of the signal selector 4 at the previous moment is determined as the liquid level output value and output, and an alarm signal is sent to the main control room to prompt the main control room to pay attention to the current state that both the first water level transmitter 2 and the second water level transmitter 3 are faulty, and immediately arrange for adjustment and maintenance. In this embodiment, when both the first water level transmitter 2 and the second water level transmitter 3 are faulty, the historical output value that was previously being output continues to be output as the liquid level output value to avoid disturbance.

[0041] In one embodiment, after step S301, it also includes: when confirming that one of the first water level transmitter 2 or the second water level transmitter 3 is faulty, the first liquid level signal or the second liquid level signal corresponding to the first water level transmitter 2 or the second water level transmitter 3 operating normally is determined as the liquid level output value and output, and an alarm signal is sent to the main control room to prompt the main control room to pay attention to the current state of one of the first water level transmitter 2 or the second water level transmitter 3 being faulty, and immediately arrange for adjustment and maintenance thereof. In this embodiment, when one of the first water level transmitter 2 or the second water level transmitter 3 is faulty, the final liquid level output value can still be guaranteed to be reliable.

[0042] In one embodiment, after step S301, it includes: when it is confirmed that both the first water level transmitter 2 and the second water level transmitter 3 are faulty, the normal water level controller 5 and the emergency water level controller 7 are switched to manual control. That is, when both the first water level transmitter 2 and the second water level transmitter 3 are faulty, it is not only necessary to determine the liquid level historical output value of the signal selector 4 at the previous moment as the liquid level output value and output it, but also necessary to switch the normal water level controller 5 and the emergency water level controller 7 to manual control, so as to avoid the phenomenon that the on-site valve disturbance opens the emergency drain under the condition of automatic control, thereby causing the turbine thermal efficiency to decrease and cause power loss.

[0043] In one embodiment, in step S40, the step of causing the normal water level controller 5 to control the opening of the normal steam trap 6 according to the liquid level output value includes:

[0044] The liquid level output value is converted into a liquid level value by a PI (proportional integral; PI regulation method refers to a proportional regulation and integral regulation method, which is used to improve the steady-state performance of a control system) regulation method, and the liquid level value is compared with a first liquid level range corresponding to the normal steam trap 6; the minimum value of the first liquid level range is a first liquid level, and the maximum value of the first liquid level range is a second liquid level; in one embodiment, the value of the first liquid level flush with the lower sampling point of the conventional island steam trap 1 of the nuclear power plant is 50 mm. The second liquid level is 110 mm.

[0045] When it is confirmed that the liquid level output value belongs to the first liquid level range, the percentage between the liquid level value and the first liquid level difference is recorded as the first opening, and the opening of the normal steam trap 6 is controlled to be adjusted to the first opening; the first liquid level difference refers to the liquid level difference between the second liquid level and the first liquid level. The purpose of converting the liquid level output value into a liquid level value is to match and compare the liquid level output value with the first liquid level range corresponding to the normal steam trap 6, so as to determine the valve opening corresponding to the normal steam trap 6 and the current liquid level within the first liquid level range. The normal water level controller 5 of the present invention controls the opening of the normal steam trap 6 according to the liquid level output value, which can ensure that the normal water level controller 5 only controls the normal steam trap 6 to work within its corresponding first liquid level range, and will not interfere with the work of the emergency steam trap 8, thereby improving the reliability of the control of the normal steam trap 6.

[0046] Furthermore, after comparing the liquid level value with the first liquid level range, it also includes: after confirming that the liquid level output value is greater than the second liquid level, controlling the opening of the normal steam trap 6 to 100%. That is, after the measured liquid level output value is greater than the maximum value of the first liquid level range, that is, the second liquid level, it is necessary to control the normal steam trap 6 to be fully opened, and at this time, since the second liquid level range of the emergency steam trap 8 and the first liquid level range of the normal steam trap 6 are mutually redundant, the emergency steam trap 8 will actually open a certain opening, and its opening is determined according to the specific value of the liquid level output value. Further, the action of controlling the opening of the normal steam trap 6 to be adjusted to 100% needs to be delayed for a first time after confirming that the liquid level output value is greater than the second liquid level, so that the measurement peak malfunction can be prevented. It can be understood that the first time can be set according to demand, and preferably, the first time is 2 seconds.

[0047] In one embodiment, in step S40, the step of instructing the emergency water level controller 7 to control the opening of the emergency steam trap 8 according to the liquid level output value includes:

[0048] The liquid level output value is converted into a liquid level value through the PI adjustment method, and the liquid level value is compared with the second liquid level range corresponding to the emergency drain valve 8; the minimum value of the second liquid level range is the third liquid level, and the maximum value of the second liquid level range is the fourth liquid level; the third liquid level is less than the second liquid level and greater than the first liquid level, and the fourth liquid level is greater than the second liquid level; in one embodiment, the value of the fourth liquid level flush with the upper sampling point of the conventional island drain tank 1 of the nuclear power plant is 150mm; the value of the first liquid level flush with the lower sampling point of the conventional island drain tank 1 of the nuclear power plant is 50mm; the value of the second liquid level is 110mm; the value of the third liquid level is 90mm.

[0049] When it is confirmed that the liquid level output value belongs to the second liquid level range, the percentage between the liquid level value and the second liquid level difference is recorded as the second opening, and the opening of the emergency drain valve 8 is controlled to be adjusted to the second opening; the second liquid level difference refers to the liquid level difference between the fourth liquid level and the third liquid level.

[0050] The emergency water level controller 7 of the present invention controls the opening of the emergency steam trap 8 according to the liquid level output value, which can ensure that the emergency water level controller 7 controls the operation of the emergency steam trap 8 only within the corresponding second liquid level range, and will not interfere with the operation of the normal steam trap 6, thereby improving the reliability of the control of the emergency steam trap 8. At the same time, since the first liquid level range and the second liquid level range are redundant with each other (the third liquid level is less than the second liquid level and greater than the first liquid level, and the fourth liquid level is greater than the second liquid level), the redundancy constitutes an appropriate water level interlock, further improving the reliability of the steam trap control.

[0051] Furthermore, after comparing the liquid level value with the second liquid level range corresponding to the emergency steam trap 8, the method further includes:

[0052] After confirming that the liquid level output value is less than the third liquid level, the opening of the emergency drain valve 8 is controlled to be adjusted to 0%.

[0053] That is, after the measured liquid level output value is less than the minimum value of the second liquid level range, that is, the third liquid level, it is necessary to control the opening of the emergency steam trap 8 to 0%. At this time, since the second liquid level range of the emergency steam trap 8 and the first liquid level range of the normal steam trap 6 are mutually redundant, the opening of the normal steam trap 6 must be less than 100%, and its opening is determined according to the specific value of the liquid level output value (that is, less than the percentage corresponding to the liquid level output value in the first liquid level range). Further, the action of controlling the opening of the emergency steam trap 8 to 0% needs to be delayed for a second time after confirming that the liquid level output value is less than the third liquid level, so as to prevent the measurement spike from malfunctioning. It is understandable that the second time can be set according to demand. Preferably, the second time is 2 seconds.

[0054] Specifically, in the present invention, since the above-mentioned preset signal value range X is: 3.2mA≤X≤20.8mA. Only when the first liquid level signal exceeds the above-mentioned preset signal value range, the first water level transmitter 2 is considered to be faulty; and only when the second liquid level signal exceeds the above-mentioned preset signal value range, the second water level transmitter 3 is considered to be faulty. Therefore, in step S40, after confirming that at least one of the first water level transmitter 2 and the second water level transmitter 3 is operating normally, there may be a situation where the first liquid level signal and / or the second liquid level signal belongs to 3.2mA~4mA, or 20mA~20.8mA (the first water level transmitter 2 or the second water level transmitter 3 corresponding to the liquid level signal within the above range will be judged to be operating normally). Therefore, there are the following situations:

[0055] When it is confirmed that the first water level transmitter 2 and the second water level transmitter 3 are operating normally, after obtaining the deviation value between the first liquid level signal and the second liquid level signal, regardless of whether the deviation value is less than the preset deviation threshold (the average value of the first liquid level signal and the second liquid level signal is the liquid level output value) or the deviation value is greater than or equal to the preset deviation threshold (at this time, the maximum value of the first liquid level signal and the second liquid level signal is the liquid level output value), the liquid level output value may belong to 3.2mA~4mA, or 20mA~20.8mA. Similarly, when it is confirmed that one of the first water level transmitter 2 or the second water level transmitter 3 is faulty, the first liquid level signal or the second liquid level signal corresponding to the first water level transmitter 2 or the second water level transmitter 3 operating normally is determined as the liquid level output value. At this time, the liquid level output value may also belong to 3.2mA~4mA, or 20mA~20.8mA. At this time, in the step S40, the normal water level controller 5 is controlled to control the opening of the normal steam trap 6 according to the liquid level output value, and the emergency water level controller 7 is controlled to control the opening of the emergency steam trap 8 according to the liquid level output value, including:

[0056] The liquid level output value is converted into a liquid level value by a PI adjustment method, the liquid level value is compared with a first liquid level range corresponding to the normal steam trap 6, and the liquid level value is compared with a second liquid level range corresponding to the emergency steam trap 8;

[0057] When it is confirmed that the liquid level output value is less than the first liquid level (at this time, the liquid level output value must be 3.2mA~4mA), the normal water level controller 5 controls the opening of the normal steam trap 6 to 0%, and at the same time, the emergency water level controller 7 controls the opening of the emergency steam trap 8 to 0%.

[0058] When it is confirmed that the liquid level output value is greater than the fourth liquid level (at this time, the liquid level output value must be between 20mA and 20.8mA), the normal water level controller 5 controls the opening of the normal steam trap 6 to 100%, and at the same time, the emergency water level controller 7 controls the opening of the emergency steam trap 8 to 100%.

[0059] In one embodiment, if Figure 1 As shown, a conventional island drain tank water level control system for a nuclear power plant is provided, and the conventional island drain tank water level control system for a nuclear power plant is used to execute the conventional island drain tank water level control method for a nuclear power plant; the conventional island drain tank water level control system for a nuclear power plant comprises a conventional island drain tank 1 of a nuclear power plant, a first water level transmitter 2, a second water level transmitter 3, a signal selector 4, a normal water level controller 5, a normal drain valve 6, an emergency water level controller 7 and an emergency drain valve 8;

[0060] The conventional island drain tank 1 of the nuclear power plant is provided with an upper sampling hole and a lower sampling hole with a specified height difference; the first upper sampling point of the first water level transmitter 2 is connected to the upper sampling hole, and the first lower sampling point of the first water level transmitter 2 is connected to the lower sampling hole; the second upper sampling point of the second water level transmitter 3 is connected to the upper sampling hole, and the second lower sampling point of the first water level transmitter 2 is connected to the lower sampling hole;

[0061] The signal selector 4 is connected to the first water level transmitter 2 and the second water level transmitter 3;

[0062] The normal water level controller 5 is connected between the signal selector 4 and the normal steam trap 6 ; the emergency water level controller 7 is connected between the signal selector 4 and the emergency steam trap 8 .

[0063] The operation modes of the various components in the conventional island drain tank water level control system of the nuclear power plant of the present invention refer to the above-mentioned conventional island drain tank water level control method of the nuclear power plant. In the present invention, when only two sampling holes are provided in the conventional island drain tank 1 of the nuclear power plant, a pair of redundant water level transmitters (the first water level transmitter 2 and the second water level transmitter 3) sharing the two sampling ports are provided. When one of the water level transmitters of the first water level transmitter 2 and the second water level transmitter 3 fails, the final liquid level output value can still be guaranteed to be reliable, thereby avoiding the phenomenon that the on-site valve disturbance opens the emergency drain due to the measurement failure of a single water level transmitter, thereby causing the thermal efficiency of the steam turbine to decrease and cause power loss, and will not affect the control of the on-site valves (the emergency drain valve 8 and the normal drain valve 6); at the same time, before the drain valve is controlled by the water level controller (the normal water level controller 5 controls the opening of the normal drain valve 6, and the emergency water level controller 7 controls the opening of the emergency drain valve 8), the liquid level output value is converted into a liquid level value by the PI adjustment method, that is, the range conversion is performed to adapt to the liquid level range (the first liquid level range and the second liquid level range) designed for the valve. In addition, the present invention also sets up appropriate water level interlocking to ensure that the normal water level controller 5 and the emergency water level controller 7 only work within their respective water level adjustment ranges and do not interfere with each other. The present invention has been applied to the conventional island drain system of a nuclear power plant, which can prevent the abnormality of the conventional island drain tank water level control system of the nuclear power plant caused by the abnormality of the water level transmitter, thereby ensuring the normal operation of the system.

[0064] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A method for controlling the water level of a conventional island drain tank in a nuclear power plant, characterized in that: include: The first water level is obtained through the first water level transmitter, and the first water level transmitter is made to convert the first water level into a first liquid level signal and then output; the first upper sampling point of the first water level transmitter is connected to the upper sampling hole of the conventional island drain tank of the nuclear power plant, and the first lower sampling point of the first water level transmitter is connected to the lower sampling hole of the conventional island drain tank of the nuclear power plant; The second water level is obtained through the second water level transmitter, and the second water level transmitter is made to convert the second water level into a second liquid level signal and then output; the second upper sampling point of the second water level transmitter is connected to the upper sampling hole of the conventional island drain tank of the nuclear power plant, and the second lower sampling point of the first water level transmitter is connected to the lower sampling hole of the conventional island drain tank of the nuclear power plant; The signal selector is instructed to determine and output a liquid level output value according to the received first liquid level signal and the second liquid level signal; the signal selector is connected to the first water level transmitter and the second water level transmitter; After confirming that at least one of the first water level transmitter and the second water level transmitter operates normally, a normal water level controller is controlled to control the opening of a normal steam trap according to the liquid level output value, and an emergency water level controller is controlled to control the opening of an emergency steam trap according to the liquid level output value; the normal water level controller is connected between the signal selector and the normal steam trap; the emergency water level controller is connected between the signal selector and the emergency steam trap; The signal selector determines and outputs a liquid level output value according to the received first liquid level signal and the second liquid level signal, comprising: Confirming, by the signal selector, whether both the first water level transmitter and the second water level transmitter are faulty according to the first liquid level signal and the second liquid level signal; When confirming that the first water level transmitter and the second water level transmitter are operating normally, obtaining a deviation value between the first liquid level signal and the second liquid level signal; the deviation value refers to a ratio between an absolute value of a difference between the first water level and the second water level and a specified height difference, and the specified height difference refers to a height difference between the lower sampling hole and the upper sampling hole; When the deviation value is less than a preset deviation threshold, determining an average value of the first liquid level signal and the second liquid level signal as the liquid level output value and outputting the value; The normal water level controller is made to control the opening of the normal steam trap according to the liquid level output value, comprising: The liquid level output value is converted into a liquid level value by a PI adjustment method, and the liquid level value is compared with a first liquid level range corresponding to the normal steam trap; the minimum value of the first liquid level range is a first liquid level, and the maximum value of the first liquid level range is a second liquid level; When it is confirmed that the liquid level output value belongs to the first liquid level range, the percentage between the liquid level value and the first liquid level difference is recorded as the first opening, and the opening of the normal steam trap is controlled to be adjusted to the first opening; the first liquid level difference refers to the liquid level difference between the second liquid level and the first liquid level.

2. The method for controlling the water level of a conventional island drain tank in a nuclear power plant according to claim 1, characterized in that: After obtaining the deviation value between the first liquid level signal and the second liquid level signal, the method further includes: When the deviation value is greater than or equal to a preset deviation threshold, the maximum value between the first liquid level signal and the second liquid level signal is determined as the liquid level output value and output, and an alarm signal is sent to the main control room.

3. The method for controlling the water level of a conventional island drain tank in a nuclear power plant according to claim 1, characterized in that: The preset deviation threshold is 5%.

4. The method for controlling the water level of a conventional island drain tank in a nuclear power plant according to claim 1, characterized in that: After confirming whether both the first water level transmitter and the second water level transmitter are faulty, the method further includes: When it is confirmed that both the first water level transmitter and the second water level transmitter are faulty, the historical output value of the liquid level of the signal selector at the previous moment is determined as the liquid level output value and output, and an alarm signal is sent to the main control room.

5. The method for controlling the water level of a conventional island drain tank in a nuclear power plant according to claim 1, characterized in that: After confirming whether both the first water level transmitter and the second water level transmitter are faulty, the method further includes: When it is confirmed that one of the first water level transmitter or the second water level transmitter is faulty, the first liquid level signal or the second liquid level signal corresponding to the normally operating first water level transmitter or the second water level transmitter is determined as the liquid level output value and output, and an alarm signal is sent to the main control room.

6. The method for controlling the water level of a conventional island drain tank in a nuclear power plant according to claim 1, characterized in that: The step of confirming whether both the first water level transmitter and the second water level transmitter are faulty according to the first liquid level signal and the second liquid level signal by the signal selector includes: Determining, by the signal selector, whether the first liquid level signal and the second liquid level signal belong to a preset signal value range; When both the first liquid level signal and the second liquid level signal are within a preset signal value range, confirming that both the first water level transmitter and the second water level transmitter are operating normally; When both the first liquid level signal and the second liquid level signal exceed a preset signal value range, confirming that both the first water level transmitter and the second water level transmitter are faulty; When one of the first liquid level signal and the second liquid level signal exceeds the preset signal value range, it is confirmed that the first water level transmitter or the second water level transmitter that exceeds the preset signal value range is faulty, and the first water level transmitter or the second water level transmitter that does not exceed the preset signal value range is operating normally.

7. The method for controlling the water level of a conventional island drain tank in a nuclear power plant according to claim 6, characterized in that: The preset signal value range X is: 3.2mA≤X≤20.8mA.

8. The method for controlling the water level of a conventional island drain tank in a nuclear power plant according to claim 1, characterized in that: After confirming whether the first water level transmitter and the second water level transmitter are both faulty, the method further comprises: When it is confirmed that both the first water level transmitter and the second water level transmitter are faulty, both the normal water level controller and the emergency water level controller are switched to manual control.

9. The method for controlling the water level of a conventional island drain tank in a nuclear power plant according to claim 1, characterized in that: After comparing the liquid level value with the first liquid level range, the method further includes: After confirming that the liquid level output value is greater than the second liquid level, the opening of the normal steam trap is controlled to be adjusted to 100%.

10. The method for controlling the water level of a conventional island drain tank in a nuclear power plant according to claim 1, characterized in that: The emergency water level controller is instructed to control the opening of the emergency steam trap according to the liquid level output value, comprising: The liquid level output value is converted into a liquid level value by a PI adjustment method, and the liquid level value is compared with a second liquid level range corresponding to the emergency steam trap; the minimum value of the second liquid level range is a third liquid level, and the maximum value of the second liquid level range is a fourth liquid level; the third liquid level is less than the second liquid level and greater than the first liquid level, and the fourth liquid level is greater than the second liquid level; When it is confirmed that the liquid level output value belongs to the second liquid level range, the percentage between the liquid level value and the second liquid level difference is recorded as the second opening, and the opening of the emergency drain valve is controlled to be adjusted to the second opening; the second liquid level difference refers to the liquid level difference between the fourth liquid level and the third liquid level.

11. The method for controlling the water level of a conventional island drain tank in a nuclear power plant according to claim 10, characterized in that: After comparing the liquid level value with the second liquid level range corresponding to the emergency steam trap, the method further includes: After confirming that the liquid level output value is less than the third liquid level, the opening of the emergency drain valve is controlled to be adjusted to 0%.

12. A water level control system for a conventional island drain tank in a nuclear power plant, characterized in that: The conventional island drain tank water level control system of the nuclear power plant is used to execute the conventional island drain tank water level control method of the nuclear power plant described in any one of claims 1 to 11; the conventional island drain tank water level control system of the nuclear power plant comprises a conventional island drain tank of the nuclear power plant, a first water level transmitter, a second water level transmitter, a signal selector, a normal water level controller, a normal drain valve, an emergency water level controller and an emergency drain valve; The conventional island drain tank of the nuclear power plant is provided with an upper sampling hole and a lower sampling hole with a specified height difference; the first upper sampling point of the first water level transmitter is connected to the upper sampling hole, and the first lower sampling point of the first water level transmitter is connected to the lower sampling hole; the second upper sampling point of the second water level transmitter is connected to the upper sampling hole, and the second lower sampling point of the first water level transmitter is connected to the lower sampling hole; The signal selector connects the first water level transmitter and the second water level transmitter; The normal water level controller is connected between the signal selector and the normal steam trap; the emergency water level controller is connected between the signal selector and the emergency steam trap.

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