Main steam isolation valve on-load test system and method

Abstract

The invention particularly relates to an on-load test system for a main steam isolating valve. The on-load test system comprises a first cartridge valve, a second cartridge valve, a first electromagnetic valve, a second electromagnetic valve, a regulating valve, a telescopic rod, a first isolating valve, a first oil pressure switch, a second isolating valve, a second oil pressure switch, a third isolating valve, a third oil pressure switch, a throttling element and a fourth isolating valve. The invention also relates to a main steam isolation valve on-load test method. According to the invention, the main steam isolation is not abnormally and quickly closed during the on-load test of the main steam isolation valve, the residual pressure between the cartridge valves does not cause a high-pressure alarm, and the residual pressure between the cartridge valves can be released after the on-load test of the main steam isolation valve is finished.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear power plant equipment, and in particular to a main steam isolation valve load test system and method. Background Art

[0002] The main steam isolation valve is one of the most critical safety-level valves in a nuclear power plant. It is designed to not only be able to remain open during daily operation, but also to be able to close quickly under accident conditions to ensure the main steam isolation function and avoid overcooling of the reactor core. The main steam isolation valve load test system of Fuqing Nuclear Power Units 5 and 6 is divided into two redundant columns, A and B. The main steam isolation valve load test is required every month to verify the availability of the main steam isolation valve fast closing circuit. If the test fails, the unit needs to be withdrawn within the specified time limit, which has a significant impact on the operation of the nuclear power plant.

[0003] See also Figure 1Taking the load test system of the main steam isolation valve of column A as an example, the load test system of the main steam isolation valve of the column includes the first cartridge valve DV1, the second cartridge valve DV2, the first solenoid valve SV1, the second solenoid valve SV2, the regulating valve FCA, the telescopic rod IA, the first isolation valve NNSV1, the first oil pressure switch PSSV1, the second isolation valve NNSV2, the second oil pressure switch PSSV2, the third isolation valve NVA, the third oil pressure switch PSA, the overpressure valve OVA and the fourth isolation valve NVY; the first cartridge valve DV1 is controlled by the first solenoid valve SV1 The switch state of the second cartridge valve DV2 is controlled by the second solenoid valve SV2; the inlet of the first cartridge valve DV1 is connected to the cylinder pipeline of the main steam isolation valve, and the outlet of the first cartridge valve DV1 is connected to the inlet pipeline of the second cartridge valve DV2; the piston side of the first cartridge valve DV1 is connected to the inlet pipelines of the first solenoid valve SV1 and the first isolation valve NNSV1 respectively; the outlet of the first isolation valve NNSV1 is connected to the pipeline of the first oil pressure switch PSSV1; the piston side of the second cartridge valve DV2 is connected to the second solenoid valve SV2 and the second isolation valve NNSV1 respectively The inlet pipeline of the second isolation valve NNSV2 is connected; the outlet of the second isolation valve NNSV2 is connected to the pipeline of the second oil pressure switch PSSV2; the outlet of the second cartridge valve DV2 is connected to the pipeline of the regulating valve FCA; the pipeline connecting the outlet of the first cartridge valve DV1 and the inlet of the second cartridge valve DV2 is respectively connected to the inlet of the telescopic rod IA and the third isolation valve NVA; the outlet of the third isolation valve NVA is respectively connected to the pipelines of the third oil pressure switch PSA and the overpressure valve OVA; the overpressure valve OVA is connected to the pipeline of the fourth isolation valve NVY; the inlet of the first isolation valve NNSV1 The inlet of the first isolation valve NNSV1 is connected to the pipeline of the first solenoid valve SV1, and the first pressure gauge interface TPSV1 is provided on the pipeline connected to the first solenoid valve SV1; the inlet of the second isolation valve NNSV2 is connected to the pipeline of the second solenoid valve SV2, and the second pressure gauge interface TPSV2 is provided on the pipeline connected to the inlet of the second isolation valve NNSV2; the inlet of the third isolation valve NVA is connected to the pipeline of the telescopic rod IA, and the third pressure gauge interface TPA is provided on the pipeline connected to the inlet of the third isolation valve NVA and the telescopic rod IA. The first cartridge valve DV1 and the second cartridge valve DV2 are connected in series and are normally closed, the first solenoid valve SV1 and the second solenoid valve SV2 are normally closed, the overpressure valve OVA opens at low pressure and closes at high pressure, and the fourth isolation valve NVY is normally open.

[0004] The load test of the main steam isolation valve is to control the cartridge valves to open and close one by one through the solenoid valve, and judge the availability of the main steam isolation valve switch circuit through the changes in the pressure switch alarm signal and the movement of the telescopic rod. Taking the load test system of the main steam isolation valve of column A as an example, the logic of the load test of the main steam isolation valve is: when there is no high-pressure alarm on the third oil pressure switch PSA, the first solenoid valve SV1 is energized and opened - the low-pressure alarm of the first oil pressure switch PSSV1 appears - the first cartridge valve DV1 is opened - the high-pressure alarm of the third oil pressure switch PSA appears, and the telescopic rod IA extends - the first solenoid valve SV1 loses power and closes - the low-pressure alarm of the first oil pressure switch PSSV1 disappears - the first cartridge valve DV1 is closed - wait for 30 seconds and the telescopic rod IA extends and the high-pressure alarm of the third oil pressure switch PSA is maintained - the second solenoid valve SV2 is energized and opened - the low-pressure alarm of the second oil pressure switch PSSV2 appears - the second cartridge valve DV2 is opened - the high-pressure alarm of the third oil pressure switch PSA disappears, and the telescopic rod IA retracts - the second solenoid valve SV2 loses power and closes - the low-pressure alarm of the second oil pressure switch PSSV2 disappears - the second cartridge valve DV2 is closed.

[0005] The existing main steam isolation valve on-load test system has low reliability, which has caused the main steam isolation valve on-load test to fail many times. Taking the main steam isolation valve on-load test system of row A as an example, the main problems are as follows:

[0006] 1. During the 30s interval between the closing of the first cartridge valve DV1 and the opening of the second cartridge valve DV2, the telescopic rod IA retracted in advance and the high-pressure alarm of the third oil pressure switch PSA disappeared. At this time, it was impossible to prove whether the subsequent second cartridge valve DV2 was opened and closed normally, that is, it was impossible to prove the availability of the main steam isolation valve quick closing circuit, and it was impossible to prove that the main steam isolation valve on-load test was qualified. The confidence level of the main steam isolation valve on-load test was low.

[0007] 2. When the second cartridge valve DV2 is opened, the main steam isolation valve occasionally closes quickly, and there is a risk of accidental closure of the valve, resulting in unplanned shutdown of the reactor.

[0008] 3. After the second cartridge valve DV2 is closed, the high-pressure alarm of the third oil pressure switch PSA reappears, restricting the implementation of the next main steam isolation valve on-load test; if the main steam isolation valve on-load test is performed again when there is internal leakage in the first cartridge valve DV1 to eliminate the high-pressure alarm of the third oil pressure switch PSA, there is a risk of accidental closure of the main steam isolation valve. Summary of the invention

[0009] The purpose of the present invention is to provide a main steam isolation valve on-load test system and method to solve the problem that the high-pressure alarm of the third oil pressure switch disappears prematurely during the main steam isolation valve on-load test, resulting in the inability to prove that the main steam isolation valve is actually closing quickly and the high-pressure alarm of the third oil pressure switch reappears after the second cartridge valve is closed. The main steam isolation valve will not be abnormally closed quickly during the on-load test, and the residual pressure between the cartridge valves will not cause a high-pressure alarm, and the residual pressure between the cartridge valves can be released after the main steam isolation valve on-load test is completed.

[0010] In order to achieve the above object, the present invention provides the following technical solutions:

[0011] A main steam isolation valve on-load test system is used for a main steam isolation valve on-load test to verify the availability of a main steam isolation valve quick-closing circuit, comprising: a first cartridge valve, a second cartridge valve, a first solenoid valve, a second solenoid valve, a regulating valve, a telescopic rod, a first isolation valve, a first oil pressure switch, a second isolation valve, a second oil pressure switch, a third isolation valve, a third oil pressure switch, a throttling element and a fourth isolation valve;

[0012] The first cartridge valve is controlled to switch state by the first solenoid valve, and the second cartridge valve is controlled to switch state by the second solenoid valve; the inlet of the first cartridge valve is connected to the oil cylinder pipeline of the main steam isolation valve, and the outlet of the first cartridge valve is connected to the inlet pipeline of the second cartridge valve;

[0013] The piston side of the first cartridge valve is connected to the inlet pipelines of the first solenoid valve and the first isolation valve respectively; the outlet of the first isolation valve is connected to the first oil pressure switch pipeline; the piston side of the second cartridge valve is connected to the inlet pipelines of the second solenoid valve and the second isolation valve respectively; the outlet of the second isolation valve is connected to the second oil pressure switch pipeline;

[0014] The outlet of the second cartridge valve is connected to the regulating valve pipeline; the pipeline connecting the outlet of the first cartridge valve and the inlet of the second cartridge valve is respectively connected to the telescopic rod and the inlet of the third isolation valve; the outlet of the third isolation valve is respectively connected to the third oil pressure switch and the throttling element pipeline; the throttling element is connected to the fourth isolation valve pipeline;

[0015] The inlet of the first isolation valve is connected to the inlet pipeline of the first solenoid valve, and a first pressure gauge interface is provided on the pipeline connecting the inlet of the first isolation valve and the first solenoid valve;

[0016] The inlet of the second isolation valve is connected to the inlet pipeline of the second solenoid valve, and a second pressure gauge interface is provided on the pipeline connecting the inlet of the second isolation valve and the second solenoid valve;

[0017] The inlet of the third isolation valve is connected to the telescopic rod pipeline, and a third pressure gauge interface is provided on the pipeline connecting the inlet of the third isolation valve and the telescopic rod.

[0018] As one possible implementation manner, the throttling element is a pipeline connector with a throttling function.

[0019] As one of the feasible ways, the fourth isolation valve is normally closed to achieve dual-channel isolation of the daily oil circuit.

[0020] The present invention also provides a main steam isolation valve load test method, using the main steam isolation valve load test system, comprising the following steps:

[0021] Step 1: When there is no high pressure alarm on the third oil pressure switch, the first solenoid valve is powered on and opened, and then the low pressure alarm on the first oil pressure switch appears, and then the first cartridge valve is opened;

[0022] Step 2: The high pressure alarm of the third oil pressure switch sounds and the telescopic rod extends;

[0023] Step 3, the first solenoid valve loses power and closes, then the low pressure alarm of the first oil pressure switch disappears, and the first cartridge valve closes;

[0024] Step 4: Wait for a while to ensure that the first cartridge valve is tightly closed;

[0025] Step 5, the second solenoid valve is energized and opened, then the second oil pressure switch low pressure alarm appears, and then the second cartridge valve is opened;

[0026] Step 6: The high pressure alarm of the third oil pressure switch disappears and the telescopic rod retracts;

[0027] Step 7, the second solenoid valve loses power and closes, then the low pressure alarm of the second oil pressure switch disappears, and then the second cartridge valve closes;

[0028] Step 8: Open the fourth isolation valve;

[0029] Step 9. Close the fourth isolation valve.

[0030] As one achievable method, in step 4, waiting for more than 30 seconds is performed to ensure that the first cartridge valve is tightly closed.

[0031] As one possible implementation method, in step 4, wait for 120 seconds.

[0032] As one achievable manner, the third oil pressure switch setting value is higher than the residual pressure between the first cartridge valve and the second cartridge valve during the load test of the main steam isolation valve.

[0033] As one achievable manner, the third oil pressure switch setting value is set to 1000 psi.

[0034] As one achievable manner, in step 8, the fourth isolation valve is opened for a period of time to release the residual pressure between the first cartridge valve and the second cartridge valve.

[0035] As one achievable manner, in step 8, the fourth isolation valve (5-10)s is opened.

[0036] Beneficial technical effects of the present invention:

[0037] The main steam isolation valve on-load test system and method of the present invention replaces the overpressure valve with a throttling element, modifies the opening and closing timing of the isolation valve, delays the action time interval of the cartridge valve, and optimizes the alarm setting of the oil pressure switch, thereby realizing dual-channel isolation of the daily oil circuit. During the main steam isolation valve on-load test, the main steam isolation valve will not close abnormally quickly, the residual pressure between the cartridge valves will not cause a high pressure alarm, and the residual pressure between the cartridge valves can be released after the main steam isolation valve on-load test is completed; the main steam isolation valve on-load test has a 100% pass rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of the use of an embodiment of an existing main steam isolation valve load test system;

[0039] Figure 2 The present invention is a schematic structural view of an embodiment of a main steam isolation valve load test system of the present invention.

[0040] In the figure, DV1 is the first cartridge valve; DV2 is the second cartridge valve; SV1 is the first solenoid valve; SV2 is the second solenoid valve; FCA is the regulating valve; IA is the telescopic rod; NNSV1 is the first isolating valve; PSSV1 is the first oil pressure switch; NNSV2 is the second isolating valve; PSSV2 is the second oil pressure switch; NVA is the third isolating valve; PSA is the third oil pressure switch; OVA is the overpressure valve; NVY is the fourth isolating valve; TPSV1 is the first pressure gauge interface; TPSV2 is the second pressure gauge interface; TPA is the third pressure gauge interface. DETAILED DESCRIPTION

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by technicians in the technical field of this application; the terms used in the specification of the application are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned drawings are intended to cover non-exclusive inclusions. The terms "first", "second", etc. in the specification and claims of this application or the above-mentioned drawings are used to distinguish different objects, not to describe a specific order.

[0042] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0043] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0044] The technical solution of the present invention is clearly and completely described below in conjunction with the accompanying drawings and specific embodiments.

[0045] The inventor further analyzed the problems existing in the main steam isolation valve on-load test system and found that the main causes of the problems existing in the main steam isolation valve on-load test system are as follows:

[0046] 1. The reliability of the overpressure valve OVA is poor, and the setting of the overpressure valve OVA is unreasonable. The overpressure valve OVA is designed to open at low pressure and close at high pressure as a fast-closing double-channel cartridge valve, that is, considering the theoretical non-zero leakage of the first cartridge valve, to avoid daily high-pressure alarms and meet the pressure requirements of the main steam isolation valve load test. The O-ring of the overpressure valve OVA is installed in the inclined groove. During the closing process, the O-ring of the overpressure valve OVA is squeezed, expanded and rolled, and the O-ring is prone to fall off or crush, resulting in internal leakage. The intermediate pressure disappears prematurely during the load test of the main steam separation valve; due to the unstable opening and closing performance of the overpressure valve OVA, it is easy for the residual oil pressure between the plug-in valves at the end of the load test of the main steam isolation valve to push the overpressure valve OVA to close, and the pressure is higher than the third oil pressure switch PSA, resulting in the recurrence of the high-pressure alarm; due to the setting of the overpressure valve OVA, the overpressure valve OVA is often opened on a daily basis, and the main steam isolation valve quick-closing circuit branch actually has only a single-channel seal on a daily basis, making the first plug-in valve DV1 a key sensitive component. Once the first plug-in valve DV1 is not sealed tightly and the oil pump cannot compensate to maintain the pressure, there may be a risk of valve closing and stack shutdown.

[0047] 2. The cartridge valve action interval is set unreasonably. The viscosity of hydraulic oil is greatly affected by temperature. For example, the viscosity of hydraulic oil at 20°C is three times that at 40°C. The viscosity of hydraulic oil affects the action performance of the cartridge valve. When the viscosity is high, the time required for a complete and tight closure is longer than when the viscosity is low. The factory setting of the cartridge valve action interval of 30s is not enough to ensure that the first cartridge valve is completely closed and tight when the second cartridge valve is opened under various conditions.

[0048] 3. The setting value of the third oil pressure switch PSA pressure switch is unreasonable. Since the quick-closing plug-in valve is lower than the oil tank, the quick-closing oil is squeezed into the oil tank from bottom to top. When the second plug-in valve DV2 is closed, the oil entity between the first plug-in valve DV1 and the second plug-in valve DV2 is squeezed and there is residual oil pressure. According to the external pressure gauge, the transient value of the residual pressure generated each time is between (500 and 700) psi. Since the alarm setting value of the third oil pressure switch PSA is 500psi; when the main steam isolation valve load test is completed, when the residual pressure between the plug-in valves is higher than the third oil pressure switch PSA setting value and lower than the overpressure valve OVA opening and closing value, the high-pressure alarm reappears and remains, restricting the next main steam isolation valve load test.

[0049] In order to solve the problems existing in the existing main steam isolation valve on-load test system during the main steam isolation valve on-load test process, the present embodiment provides a main steam isolation valve on-load test system, which is used for the main steam isolation valve on-load test to verify the availability of the main steam isolation valve fast closing circuit, including: a first cartridge valve DV1, a second cartridge valve DV2, a first solenoid valve SV1, a second solenoid valve SV2, a regulating valve FCA, a telescopic rod IA, a first isolation valve NNSV1, a first oil pressure switch PSSV1, a second isolation valve NNSV2, a second oil pressure switch PSSV2, a third isolation valve NVA, a third oil pressure switch PSA, a throttling element and a fourth isolation valve NVY;

[0050] The first cartridge valve DV1 is controlled to switch state by the first solenoid valve SV1, and the second cartridge valve DV2 is controlled to switch state by the second solenoid valve SV2; the inlet of the first cartridge valve DV1 is connected to the oil cylinder pipeline of the main steam isolation valve, and the outlet of the first cartridge valve DV1 is connected to the inlet pipeline of the second cartridge valve DV2;

[0051] The piston side of the first cartridge valve DV1 is connected to the inlet pipelines of the first solenoid valve SV1 and the first isolation valve NNSV1 respectively; the outlet of the first isolation valve NNSV1 is connected to the pipeline of the first oil pressure switch PSSV1;

[0052] The piston side of the second cartridge valve DV2 is connected to the inlet pipelines of the second solenoid valve SV2 and the second isolation valve NNSV2 respectively; the outlet of the second isolation valve NNSV2 is connected to the pipeline of the second oil pressure switch PSSV2;

[0053] The outlet of the second cartridge valve DV2 is connected to the regulating valve FCA pipeline; the pipeline connecting the outlet of the first cartridge valve DV1 and the inlet of the second cartridge valve DV2 is respectively connected to the inlet of the telescopic rod IA and the third isolation valve NVA; the outlet of the third isolation valve NVA is respectively connected to the third oil pressure switch PSA and the throttling element pipeline; the throttling element is connected to the fourth isolation valve NVY pipeline;

[0054] The inlet of the first isolation valve NNSV1 is connected to the inlet pipeline of the first solenoid valve SV1, and a first pressure gauge interface TPSV1 is provided on the pipeline connecting the inlet of the first isolation valve NNSV1 and the first solenoid valve SV1;

[0055] The inlet of the second isolation valve NNSV2 is connected to the inlet pipeline of the second solenoid valve SV2, and a second pressure gauge interface TPSV2 is provided on the pipeline connecting the inlet of the second isolation valve NNSV2 and the second solenoid valve SV2;

[0056] The inlet of the third isolation valve NVA is connected to the telescopic rod IA pipeline, and a third pressure gauge interface TPA is provided on the pipeline connecting the inlet of the third isolation valve NVA and the telescopic rod IA.

[0057] In this embodiment, as one of the feasible ways, the throttling element is a pipe connector with a throttling function.

[0058] In this embodiment, as one of the feasible ways, the fourth isolation valve NVY is normally closed to achieve dual-channel isolation of the daily oil circuit.

[0059] This embodiment also provides a main steam isolation valve load test method, using the main steam isolation valve load test system, including the following steps:

[0060] Step 1: When there is no high pressure alarm on the third oil pressure switch PSA, the first solenoid valve SV1 is powered on and opened, and then the low pressure alarm on the first oil pressure switch PSSV1 occurs, and then the first cartridge valve DV1 is opened;

[0061] Step 2: The high pressure alarm of the third oil pressure switch PSA appears, and the telescopic rod IA extends;

[0062] Step 3, the first solenoid valve SV1 loses power and closes, then the low pressure alarm of the first oil pressure switch PSSV1 disappears, and the first cartridge valve DV1 closes;

[0063] Step 4: Wait for a while to ensure that the first cartridge valve DV1 is tightly closed;

[0064] Step 5, the second solenoid valve SV2 is powered on and opened, then the second oil pressure switch PSSV2 low pressure alarm appears, and then the second cartridge valve DV2 is opened;

[0065] Step 6: The high pressure alarm of the third oil pressure switch PSA disappears, and the telescopic rod IA retracts;

[0066] Step 7, the second solenoid valve SV2 loses power and closes, then the low pressure alarm of the second oil pressure switch PSSV2 disappears, and then the second cartridge valve DV2 is closed;

[0067] Step 8, open the fourth isolation valve NVY;

[0068] Step 9: Close the fourth isolation valve NVY and the test ends.

[0069] In this embodiment, as one of the feasible methods, in step 4, waiting for more than 30 seconds is performed to ensure that the first cartridge valve DV1 is tightly closed when the second cartridge valve DV2 is opened, so as to avoid the risk of the main steam isolation valve being quickly closed due to the first cartridge valve DV1 not being tightly closed when the second cartridge valve DV2 is opened.

[0070] In this embodiment, as one of the feasible methods, in step 4, waiting for 120 seconds is performed to ensure that the first cartridge valve DV1 is tightly closed when the second cartridge valve DV2 is opened, so as to avoid the risk of the main steam isolation valve being quickly closed due to the first cartridge valve DV1 not being tightly closed when the second cartridge valve DV2 is opened.

[0071] In this embodiment, as one of the feasible ways, the set value of the third oil pressure switch PSA is higher than the residual pressure between the first cartridge valve DV1 and the second cartridge valve DV2 during the load test of the main steam isolation valve, thereby eliminating the recurrence of the high pressure alarm caused by the residual pressure between the first cartridge valve DV1 and the second cartridge valve DV2 during the load test of the main steam isolation valve.

[0072] In this embodiment, as one of the feasible ways, the third oil pressure switch PSA is set to 1000psi to eliminate the high pressure alarm recurrence caused by the residual pressure between the first cartridge valve DV1 and the second cartridge valve DV2 during the load test of the main steam isolation valve.

[0073] In this embodiment, as one of the achievable ways, the fourth isolation valve NVY is opened for a period of time to release the residual pressure between the first cartridge valve DV1 and the second cartridge valve DV2.

[0074] The pressure relief between the first cartridge valve DV1 and the second cartridge valve DV2 is achieved through the fourth isolation valve NVY; after the main steam isolation valve load test is completed, the fourth isolation valve NVY is opened to release the residual pressure between the first cartridge valve DV1 and the second cartridge valve DV2 to ensure that the residual pressure between the first cartridge valve DV1 and the second cartridge valve DV2 before the next main steam isolation valve load test will not cause a high pressure alarm.

[0075] In this embodiment, as one of the feasible ways, in step 8, the fourth isolation valve NVY (5-10)s is opened.

[0076] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A main steam isolation valve load test system, used for the main steam isolation valve load test to verify the availability of the main steam isolation valve fast closing circuit, characterized in that: include: The first cartridge valve (DV1), the second cartridge valve (DV2), the first solenoid valve (SV1), the second solenoid valve (SV2), the regulating valve (FCA), the telescopic rod (IA), the first isolation valve (NNSV1), the first oil pressure switch (PSSV1), the second isolation valve (NNSV2), the second oil pressure switch (PSSV2), the third isolation valve (NVA), the third oil pressure switch (PSA), the throttling element and the fourth isolation valve (NVY); The first cartridge valve (DV1) controls the switch state through the first solenoid valve (SV1), and the second cartridge valve (DV2) controls the switch state through the second solenoid valve (SV2); the inlet of the first cartridge valve (DV1) is connected to the oil cylinder pipeline of the main steam isolation valve, and the outlet of the first cartridge valve (DV1) is connected to the inlet pipeline of the second cartridge valve (DV2); The piston side of the first cartridge valve (DV1) is connected to the inlet pipelines of the first solenoid valve (SV1) and the first isolation valve (NNSV1) respectively; the outlet of the first isolation valve (NNSV1) is connected to the pipeline of the first oil pressure switch (PSSV1); the piston side of the second cartridge valve (DV2) is connected to the inlet pipelines of the second solenoid valve (SV2) and the second isolation valve (NNSV2) respectively; The outlet of the second isolation valve (NNSV2) is connected to the pipeline of the second oil pressure switch (PSSV2); The outlet of the second cartridge valve (DV2) is connected to the regulating valve (FCA) pipeline; the outlet of the first cartridge valve (DV1) is connected to the inlet of the second cartridge valve (DV2) through pipelines connected to the telescopic rod (IA) and the inlet of the third isolation valve (NVA); the outlet of the third isolation valve (NVA) is connected to the third oil pressure switch (PSA) and the throttling element pipeline respectively; the throttling element is connected to the fourth isolation valve (NVY) pipeline; The inlet of the first isolation valve (NNSV1) is connected to the inlet pipeline of the first solenoid valve (SV1), and a first pressure gauge interface (TPSV1) is provided on the pipeline connecting the inlet of the first isolation valve (NNSV1) and the first solenoid valve (SV1); The inlet of the second isolation valve (NNSV2) is connected to the inlet pipeline of the second solenoid valve (SV2), and a second pressure gauge interface (TPSV2) is provided on the pipeline connecting the inlet of the second isolation valve (NNSV2) and the second solenoid valve (SV2); The inlet of the third isolation valve (NVA) is connected to the telescopic rod (IA) pipeline, and a third pressure gauge interface (TPA) is provided on the pipeline connecting the inlet of the third isolation valve (NVA) and the telescopic rod (IA).

2. The main steam isolation valve load test system according to claim 1 is characterized in that: The throttling element is a pipe connecting piece with throttling function.

3. The main steam isolation valve load test system according to claim 1 is characterized in that: The fourth isolation valve (NVY) is normally closed.

4. A main steam isolation valve load test method, characterized in that: The main steam isolation valve load test system according to any one of claims 1 to 3 comprises the following steps: Step 1: When the third oil pressure switch (PSA) has no high pressure alarm, the first solenoid valve (SV1) is powered on and opened, and then the first oil pressure switch (PSSV1) has a low pressure alarm, and then the first cartridge valve (DV1) is opened; Step 2: The high pressure alarm of the third oil pressure switch (PSA) sounds, and the telescopic rod (IA) extends; Step 3, the first solenoid valve (SV1) loses power and closes, then the low pressure alarm of the first oil pressure switch (PSSV1) disappears, and the first cartridge valve (DV1) closes; Step 4: Wait for a while to ensure that the first cartridge valve (DV1) is tightly closed; Step 5, the second solenoid valve (SV2) is energized to open, then the second oil pressure switch (PSSV2) low pressure alarm appears, and then the second cartridge valve (DV2) opens; Step 6: The high pressure alarm of the third oil pressure switch (PSA) disappears, and the telescopic rod (IA) retracts; Step 7, the second solenoid valve (SV2) loses power and closes, then the low pressure alarm of the second oil pressure switch (PSSV2) disappears, and then the second cartridge valve (DV2) closes; Step 8, open the fourth isolation valve (NVY); Step 9. Close the fourth isolation valve (NVY).

5. The main steam isolation valve load test method according to claim 4 is characterized in that: In step 4, wait for more than 30 seconds to ensure that the first cartridge valve (DV1) is tightly closed.

6. The main steam isolation valve load test method according to claim 5 is characterized in that: In step 4, wait for 120 seconds.

7. The main steam isolation valve load test method according to claim 4 is characterized in that: The third oil pressure switch (PSA) is set at a value higher than the residual pressure between the first cartridge valve (DV1) and the second cartridge valve (DV2) during the main steam isolation valve load test.

8. The main steam isolation valve load test method according to claim 4 is characterized in that: The third oil pressure switch (PSA) is set to 1000psi.

9. The main steam isolation valve load test method according to claim 4 is characterized in that: In step 8, the fourth isolation valve (NVY) is opened for a period of time to release the residual pressure between the first cartridge valve (DV1) and the second cartridge valve (DV2).

10. The main steam isolation valve load test method according to claim 9 is characterized in that: Open the fourth isolation valve (NVY) for (5-10) seconds.

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