Parallel liquid nitrogen pump system for superconducting cable, switching method and storage medium

Abstract

This invention discloses a parallel liquid nitrogen pump system for superconducting cables, comprising: a first branch including a first valve, a first pump, and a second valve connected in sequence; a second branch connected in parallel with the first branch, including a third valve, a second pump, and a fourth valve connected in sequence; a connecting branch connecting the first branch and the second branch, including a fifth valve, one end of which is connected between the first valve and the first pump, and the other end of which is connected between the second pump and the fourth valve; and a control device for controlling the on / off state of the valves and pumps in each branch. This invention also discloses a corresponding switching method and storage medium. Implementing this invention enables a smooth transition during parallel branch switching, improving the reliability, availability, and compatibility of the liquid nitrogen pump system.

Description

Technical Field

[0001] This invention relates to a parallel liquid nitrogen pump system, specifically to a parallel liquid nitrogen pump system for a superconducting cable system, a switching method, and a storage medium. Background Technology

[0002] With the continuous growth in electricity demand and the limitation of transmission corridors in some areas, high-temperature superconducting cables can simultaneously achieve efficient, low-loss, and high-capacity power transmission, providing a feasible solution to the challenges faced by urban power transmission and distribution. In the past two decades, multiple countries and regions have successively carried out demonstration projects of superconducting cables with various configurations and application scenarios, demonstrating the advantages of superconducting cables in power transmission, including high capacity, low loss, and minimal land occupation. With the continuous maturation of the technology, superconducting power transmission has gradually entered commercialization.

[0003] Superconducting cables typically use second-generation YBCO tape or first-generation BSCCO tape as the conductor. To maintain the superconducting state of the cable, circulating liquid nitrogen cooling is commonly used to keep it at a stable temperature distribution. A typical superconducting cable circulating liquid nitrogen system includes a cryogenic source, a liquid nitrogen pump, piping, and valves. The liquid nitrogen pump provides the circulation power for the subcooled liquid nitrogen cooled by the cryogenic source, maintaining the liquid nitrogen pressure and flow rate inside the superconducting cable to meet cooling requirements.

[0004] Existing technologies consider the reliability of the cold source by selecting at least two independent cold sources, one as the primary and one as a backup. For example, in some cases, a cryogenic refrigerator is used as the primary cold source, and a vacuum decompression system is used as the backup cold source. However, the presence of rotating parts inherently introduces issues regarding the backup and reliability of the liquid nitrogen pump, which is prone to failure. Therefore, to ensure the availability of the liquid nitrogen pump, it is necessary to periodically switch the pump for maintenance. This obviously helps improve the availability of the cryogenic refrigeration system, thereby improving the reliability of the superconducting cable system.

[0005] However, after examining the implementation schemes of the parallel liquid nitrogen pump system in existing superconducting cable systems, the inventors found that the existing technology has some shortcomings. Specifically, the two liquid nitrogen pumps are simply connected in parallel, and unfavorable transient processes inevitably occur during the switching control process, mainly including: (1) the switching of liquid nitrogen pumps is not smooth, which leads to a sudden drop in pressure and flow rate during liquid nitrogen circulation, which can easily cause the control and protection system to misjudge and report low pressure and / or low flow alarms or faults; (2) since the standby liquid nitrogen pump is generally cold standby, its internal temperature is higher than the temperature of the circulating liquid nitrogen. For a period of time after it is activated, it acts as a heat source to heat the supercooled liquid nitrogen flowing through, causing a temperature rise misjudgment and leading to malfunction of the cold source control; in some specific cases, even a gas-liquid two-phase situation may occur, which may cause pressure fluctuations, reduction of cooling capacity and other possible erroneous signals, and may also endanger the strength of the liquid nitrogen-PPLP main insulation of the superconducting cable.

[0006] like Figure 1 The diagram illustrates a typical configuration of an existing parallel liquid nitrogen pump system. Subcooled liquid nitrogen from the heat exchanger enters the system via piping, splitting into two identical parallel branches. After passing through the liquid nitrogen pumps, these branches converge into a single pipeline leading to the superconducting cable. Each branch is equipped with either pump A or pump B, with a control valve before and after each pump. Pressure sensors P are installed before and after the liquid nitrogen pumps. Before the liquid nitrogen enters the superconducting cable, pressure, flow rate, and temperature sensors T are installed—the so-called inlet non-electrical quantities.

[0007] During normal operation, the initial state uses one branch to power the circulating liquid nitrogen; let's take branch A, where pump A is located, as an example. At this time, valves VA1 and VA2 are open, and valves VB1 and VB2 are closed. Liquid nitrogen pump A operates at a set speed, providing appropriate pressure and flow. If pump A malfunctions, or is shut down for maintenance as planned, the control system detects a fault signal, receives a maintenance command, and issues an instruction to shut down pump A and start pump B. At this time, valves VB1 and VB2 are opened, pump B is started, and valves VA1 and VA2 are closed. Pump A is now isolated and can be maintained, repaired, or replaced as planned. To avoid sudden increases in flow at the common outlet causing pressure or flow rate alarms or malfunctions, the switching of liquid nitrogen pumps generally uses a "close first, then open" logic sequence. Understandably, the initial state for branch B is completely similar.

[0008] Figure 2 As shown Figure 1 A schematic diagram of the flow dynamics during the liquid nitrogen pump switching process in the described technical implementation scheme. Figure 2(a) illustrates several characteristic timing sequences during the liquid nitrogen pump switching process and presents the flow rate changes of the two liquid nitrogen pumps and the common outlet, which is the input pipe of the superconducting cable. Pump A receives a shutdown command at time t1 and begins the shutdown operation. Since the drive motor of the liquid nitrogen pump cannot instantly reduce its speed to zero, its output flow rate needs to decrease to 0 over a period of time. The start command for pump B is at time t2, slightly later than t1. After pump B starts, for the same reason, the flow rate cannot instantly increase to the rated value, but reaches the rated value after a period of time until t4. Under ideal conditions, the decrease in flow rate of pump A is exactly compensated by the increase in flow rate of pump B, which can keep the flow rate at the common outlet basically constant. However, the above ideal conditions are obviously almost impossible. Due to long-term cold standby, although pump B has thermal contact with the liquid nitrogen circulation channel through the pipeline, the temperature of pump B is higher than that of the circulating liquid nitrogen because of the stagnant liquid nitrogen heat transfer. Thus, when pump B starts, it acts as a heat source to heat the circulating liquid nitrogen, and may even briefly cause some of the liquid nitrogen to vaporize, leading to local density changes. Consequently, its output flow rate will fluctuate significantly. Figure 2 As shown in (b). Since the parallel liquid nitrogen pumps cannot increase the pressure, a similar situation exists in the system outlet pressure during the switching process.

[0009] Under these conditions, the flow fluctuations at the public outlet are random, often reaching the set flow alarm or even abnormal values. Flow rate is a crucial non-electrical quantity for maintaining the stability of superconducting cables. Since it cannot be definitively confirmed that such anomalies are caused by liquid nitrogen pump switching transients, tripping and shutdown emergency measures are typically performed to ensure the absolute safety of the system. Therefore, the existing switching method significantly reduces the reliability and availability of the superconducting cable system. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a parallel liquid nitrogen pump system, switching method and storage medium for superconducting cables, which can realize a smooth transition when switching parallel branches and improve the reliability, availability and compatibility of the liquid nitrogen pump system.

[0011] To address the aforementioned technical problems, as one aspect of the present invention, a parallel liquid nitrogen pump system for superconducting cables is provided, comprising at least:

[0012] The first branch includes a first valve, a first pump, and a second valve connected in sequence. The first valve is connected to the output pipe of the heat exchanger, and the second valve is connected to the input pipe of the superconducting cable.

[0013] The second branch, connected in parallel with the first branch, includes a third valve, a second pump, and a fourth valve connected in sequence. The third valve is connected to the output pipe of the heat exchanger, and the fourth valve is connected to the input pipe of the superconducting cable.

[0014] A connecting branch is provided between the first branch and the second branch, and includes a fifth valve, one end of which is connected between the first valve and the first pump, and the other end of which is connected between the second pump and the fourth valve;

[0015] Control device, used to control the on / off state of valves and pumps in each branch.

[0016] Preferably, a pressure sensor is connected to both the input and output ends of the first pump; and a pressure sensor is connected to both the input and output ends of the second pump.

[0017] Preferably, a pressure sensor, a flow sensor, and a temperature sensor are installed on the input pipe of the superconducting cable.

[0018] Accordingly, another aspect of the present invention also provides a switching method for a parallel liquid nitrogen pump system for superconducting cables, which is applied to the system described above, the method comprising the following steps:

[0019] Step S1: During normal operation, the first branch is operational, the second branch is closed, and the fifth valve is closed.

[0020] Step S2: When it is necessary to switch to the second branch, first open the third valve and the fifth valve, and keep the second pump and the fourth valve in the closed state; the subcooled liquid nitrogen from the heat exchanger will enter the first pump through the first branch, and at the same time enter the first pump through the third branch formed by the third valve, the second pump and the fifth valve; at this time, because the pipeline of the third branch is long and the second pump does not rotate, the flow resistance of the third branch is much greater than that of the first branch, and only a small amount of subcooled liquid nitrogen passes through the third branch. After a certain period of time, the subcooled liquid nitrogen cools the second pump to the same temperature as the system.

[0021] Step S3: After the second pump cools down, the first pump is shut down and the second pump is started, while the first valve is closed; at this time, the third valve, the second pump, the fifth valve, the first pump, and the second valve form a third branch;

[0022] Step S4: After the first pump has completely stopped and the second pump has reached its operating point, open the fourth valve; since the second branch has low flow resistance, it becomes the path through which most of the flow passes.

[0023] In step S5, the fifth valve and the second valve can be closed, and the system will be completely switched to the second branch. The first pump is isolated by the first valve, the second valve and the fifth valve.

[0024] Preferably, step S3 further includes:

[0025] During the transient switching process, the flow rate and pressure provided by the first pump decrease, while the flow rate and pressure provided by the second pump increase. By adjusting the timing, the pressure and flow rate of the input pipe of the superconducting cable are kept stable.

[0026] Accordingly, as another aspect of the present invention, a computer-readable storage medium is also provided, on which a computer program is stored, which, when executed by a processor, implements the steps of the method as described above.

[0027] Implementing the embodiments of the present invention has the following beneficial effects:

[0028] This invention provides a parallel liquid nitrogen pump system for superconducting cables, a switching method, and a storage medium. By adding a connecting branch to an existing parallel liquid nitrogen pump system with two parallel branches, and controlling this connecting branch, functions such as standby pump precooling and transient series topology during switching can be added. This achieves a smooth transition during parallel branch switching, thereby significantly improving the reliability of the liquid nitrogen pump system. Abnormal changes in temperature, pressure, and flow rate during liquid nitrogen pump switching are essentially eliminated, improving the availability and compatibility of the liquid nitrogen pump system. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0030] Figure 1 This is a schematic diagram of a typical parallel liquid nitrogen pump system in the prior art;

[0031] Figure 2 yes Figure 1 A schematic diagram of the flow dynamics during the liquid nitrogen pump switching process in the implementation scheme;

[0032] Figure 3 This is a schematic diagram of an embodiment of a parallel liquid nitrogen pump system for superconducting cables proposed in this invention;

[0033] Figure 4 This is a schematic diagram of the main flow of an implementation of a switching method for a parallel liquid nitrogen pump system for superconducting cables proposed in this invention.

[0034] Figure 5 This invention relates to a schematic diagram of the flow dynamics during the liquid nitrogen pump switching process. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0036] like Figure 3 The diagram illustrates a schematic representation of an embodiment of a parallel liquid nitrogen pump system for superconducting cables proposed in this invention. In this embodiment, the parallel liquid nitrogen pump system includes at least:

[0037] The first branch includes a first valve VA1, a first pump A, and a second valve VA2 connected in sequence. The first valve is connected to the output pipe of the heat exchanger, and the second valve is connected to the input pipe of the superconducting cable.

[0038] The second branch, connected in parallel with the first branch, includes a third valve VB1, a second pump B, and a fourth valve VB2 connected in sequence. The third valve is connected to the output pipe of the heat exchanger, and the fourth valve is connected to the input pipe of the superconducting cable.

[0039] A connecting branch is connected between the first branch and the second branch, and includes a fifth valve VAB, one end of which is connected between the first valve and the first pump, and the other end of which is connected between the second pump and the fourth valve;

[0040] Control device, used to control the on / off state of valves and pumps in each branch.

[0041] More specifically, a pressure sensor P is connected to both the input and output ends of the first pump A; and a pressure sensor is connected to both the input and output ends of the second pump B.

[0042] A pressure sensor P, a flow sensor F, and a temperature sensor T are respectively installed on the input pipe of the superconducting cable.

[0043] like Figure 4 The diagram illustrates the main flow of an implementation of a switching method for a parallel liquid nitrogen pump system for superconducting cables proposed in this invention; combined with... Figure 5 As shown, in this embodiment, the method is applied as described above. Figure 3 In the described system, the method includes the following steps:

[0044] Step S1: During normal operation, the first branch VA1, pump A and VA2 are open, the second branch VB1, pump B and VB2 are closed, and the fifth valve VAB is closed.

[0045] In step S2, when switching to the second branch is required, at time t1, the third valve VB1 and the fifth valve VAB are opened, while the second pump B and the fourth valve VB2 remain closed. Subcooled liquid nitrogen from the heat exchanger enters the first pump A through the first branch VA1, and simultaneously enters the first pump A through the third branch formed by the third valve VB1, the second pump B, and the fifth valve VAB. At this time, due to the longer pipeline and the fact that the second pump does not rotate, the flow resistance in the third branch is much greater than in the first branch, and only a small amount of subcooled liquid nitrogen passes through it. Furthermore, the flow rate of liquid nitrogen through this branch can be controlled by adjusting the opening of VB1. After a certain period of time, this subcooled liquid nitrogen is sufficient to cool the second pump B to the same temperature as the system, thus avoiding the aforementioned density fluctuation problem.

[0046] Step S3: After the second pump cools down, at time t2, the first pump A is shut down and the second pump B is started, while the first valve VA1 is closed; at this time, the third branch is formed by the third valve VB1, the second pump B, the fifth valve VAB, the first pump A, and the second valve VA2;

[0047] More specifically, step S3 further includes:

[0048] During the transient switching process, the flow rate and pressure provided by the first pump decrease, while the flow rate and pressure provided by the second pump increase. By adjusting the timing, the pressure and flow rate in the input pipe of the superconducting cable can be kept stable. It is understood that with proper timing, the pressure and flow rate at the common output port (the input pipe of the superconducting cable) will not change significantly. Because a pre-cooling strategy using a backup pump has been implemented, local density changes will not occur during the switching process.

[0049] Step S4: After the first pump A has completely stopped and the second pump B has reached its operating point, at time t3, the fourth valve VB2 is opened to make the second branch open; since the second branch has low flow resistance, it becomes the path through which most of the flow passes.

[0050] In step S5, the fifth valve VAB and the second valve VA2 are closed, and the system will be completely switched to the second branch. The first pump A is isolated by the first valve VA1, the second valve VA2, and the fifth valve VAB. This enables on-site maintenance or removal maintenance of pump A.

[0051] Accordingly, as another aspect of the present invention, a computer-readable storage medium is also provided, on which a computer program is stored, which, when executed by a processor, implements the aforementioned... Figure 4 and Figure 5 The steps of the described method. For more details, please refer to and combine with the foregoing descriptions. Figure 4 and Figure 5 The description of that will not be repeated here.

[0052] It is understood that, compared with the direct switching of two simple parallel branches, this invention adds functions such as standby pump precooling and transient series topology during the switching process, realizing a smooth transition when switching parallel branches, significantly improving the reliability of the liquid nitrogen pump system, and basically eliminating abnormal changes in temperature, pressure, and flow rate during liquid nitrogen pump switching, thereby improving the availability and compatibility of the liquid nitrogen pump system.

[0053] Implementing the embodiments of the present invention has the following beneficial effects:

[0054] This invention provides a parallel liquid nitrogen pump system for superconducting cables, a switching method, and a storage medium. By adding a connecting branch to an existing parallel liquid nitrogen pump system with two parallel branches, and controlling this connecting branch, functions such as standby pump precooling and transient series topology during switching can be added. This achieves a smooth transition during parallel branch switching, thereby significantly improving the reliability of the liquid nitrogen pump system. Abnormal changes in temperature, pressure, and flow rate during liquid nitrogen pump switching are essentially eliminated, improving the availability and compatibility of the liquid nitrogen pump system.

[0055] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, apparatus, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media containing computer-usable program code, including but not limited to disk storage, CD-ROM, optical storage, etc.

[0056] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0057] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A switching method for a parallel liquid nitrogen pump system for superconducting cables, characterized in that, The parallel liquid nitrogen pump system for superconducting cables includes at least: The first branch includes a first valve, a first pump, and a second valve connected in sequence. The first valve is connected to the output pipe of the heat exchanger, and the second valve is connected to the input pipe of the superconducting cable. The second branch, connected in parallel with the first branch, includes a third valve, a second pump, and a fourth valve connected in sequence. The third valve is connected to the output pipe of the heat exchanger, and the fourth valve is connected to the input pipe of the superconducting cable. A connecting branch is provided between the first branch and the second branch, and includes a fifth valve, one end of which is connected between the first valve and the first pump, and the other end of which is connected between the second pump and the fourth valve; Control device, used to control the on / off state of valves and pumps in each branch; The switching method for the parallel liquid nitrogen pump system used for superconducting cables includes the following steps: Step S1: During normal operation, the first branch is operational, the second branch is closed, and the fifth valve is closed. Step S2: When it is necessary to switch to the second branch, first open the third valve and the fifth valve, and keep the second pump and the fourth valve in the closed state; the subcooled liquid nitrogen from the heat exchanger will enter the first pump through the first branch, and at the same time enter the first pump through the third branch formed by the third valve, the second pump and the fifth valve; at this time, because the pipeline of the third branch is long and the second pump does not rotate, the flow resistance of the third branch is much greater than that of the first branch, and only a small amount of subcooled liquid nitrogen passes through the third branch. After a certain period of time, the subcooled liquid nitrogen cools the second pump to the same temperature as the system. Step S3: After the second pump cools down, the first pump is shut down and the second pump is started, while the first valve is closed; at this time, the third valve, the second pump, the fifth valve, the first pump, and the second valve form a third branch; Step S4: After the first pump has completely stopped and the second pump has reached its operating point, open the fourth valve to open the second branch; since the second branch has low flow resistance, it becomes the path through which most of the flow passes. Step S5: Close the fifth valve and the second valve. The system will be completely switched to the second branch. The first pump is isolated by the first valve, the second valve and the fifth valve.

2. The method as described in claim 1, characterized in that, A pressure sensor is connected to both the input and output ends of the first pump; a pressure sensor is also connected to both the input and output ends of the second pump.

3. The method as described in claim 2, characterized in that, A pressure sensor, a flow sensor, and a temperature sensor are installed on the input pipe of the superconducting cable.

4. The method as described in claim 3, characterized in that, Step S3 further includes: During the transient switching process, the flow rate and pressure provided by the first pump decrease, while the flow rate and pressure provided by the second pump increase. By adjusting the timing, the pressure and flow rate of the input pipe of the superconducting cable are kept stable.

5. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method as described in any one of claims 1 to 4.

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