Magnetic confinement hybrid superconductive DC current limiter

Abstract

The invention discloses a magnetic confinement hybrid superconductive DC current limiter, which comprises a current limiting unit and a quench protection unit, and is characterized in that the current limiting unit comprises a resistor R and a superconductive coupling coil L2, and the resistor R and the superconductive coupling coil L2 are connected in parallel; the quench protection unit comprises a superconducting coupling coil L1 and a capacitor discharge module, and the superconducting coupling coil L1 and the capacitor discharge module are connected in series to form a series loop; the superconducting coupling coil L2 of the current limiting unit is coupled with the superconducting coupling coil L1 of the quench protection unit. The short-circuit current peak value can be effectively suppressed, the breaking current of the direct-current circuit breaker is reduced, and the reliability of system fault removal is improved.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of direct current systems, and in particular to a magnetically confined hybrid superconducting direct current current limiter. Background Art

[0002] Compared with AC system, when short circuit occurs in DC system, the fault current has no natural zero crossing point, and the current must be forced to cross zero by means such as injecting reverse current, resulting in the technical difficulty of DC circuit breaker being much greater than that of AC circuit breaker. DC circuit breakers can generally be divided into three categories according to the breaking principle: mechanical circuit breaker, solid-state circuit breaker and hybrid circuit breaker. Among them, mechanical circuit breaker technology is mature and has strong breaking capacity, but the breaking speed is slow and the speed is insufficient; solid-state circuit breaker has a fast breaking speed, but small breaking capacity, and has the disadvantages of high cost of power electronic devices and large conduction loss; hybrid circuit breaker combines mechanical circuit breaker and solid-state circuit breaker in topological structure, which can achieve better speed and higher short-circuit current breaking capacity in function, but the structure is more complex, there are more breaking links, and the protection control is complex. From the research status of DC circuit breakers at home and abroad, it can be seen that it is difficult for existing DC circuit breakers to simultaneously meet the protection requirements of DC system with high breaking current capacity and fast breaking speed.

[0003] Fault current limiting devices can effectively limit fault current, inhibit the speed of fault development, and assist in the disconnection of DC circuit breakers. They are an effective means to solve the limited disconnection capacity and disconnection speed of DC circuit breakers. The main current limiting devices currently used in DC transmission (distribution) systems - explosive current limiting protection devices, PTC current limiters and solid-state current limiters, can all play a certain current limiting effect, but these current limiting schemes still have some unavoidable technical problems and cannot meet the highly automated protection requirements of DC systems. Therefore, research on new current limiting devices suitable for DC transmission (distribution) systems is urgently needed.

[0004] The ideal current limiter announced by the International Conference on Large Electric Grids should have the following four characteristics: 1. Low impedance when the power grid is transmitting normally; 2. Rapidly turn to high impedance when a short circuit occurs in the power grid, and limit the short circuit current; 3. Automatically and promptly restore to a low impedance state after current limiting; 4. Able to match the protection system of the power grid. Superconducting materials have zero impedance and complete anti-magnetism. Superconducting current limiters developed through appropriate topological structures and parameter matching can meet the above four characteristics and are the most ideal DC current limiters. In recent years, they have been widely studied and continuously developed.

[0005] The structure and principle of the resistive superconducting current limiter (R-SFCL) are very simple, and it is one of the most common types of DC SFCL currently being studied. In 2013, Shanghai Jiao Tong University developed a 10kV resistive DC SFCL prototype and completed the grid-connected test. In 2015, the Russian State Institute of Technical Physics and Automation developed a 3.5kV / 2kA resistive superconducting current limiting circuit breaker prototype, which limited the fault current from 15kA to 7kA, and the prototype successfully removed the fault within 8ms. In 2017, the University of Grenoble in France developed an 800V / 500A R-SFCL prototype for shipboard power grids, which can achieve fault isolation of two generator sets. In 2020, the 160 kV R-SFCL with the highest voltage level and largest capacity in the world, which was led by the State Grid Corporation of China, has been put into operation in the Nan'ao Flexible DC System in Guangdong.

[0006] Inductive superconducting current limiter (I-SFCL) uses the inductance property presented in the circuit to limit the short-circuit current, that is, when a fault occurs, the current flowing through the inductor on the line cannot change suddenly. Inductors have a very fast current limiting response speed in the early stage of a DC system fault, and have a good limiting effect on the fault current peak, but have a poor limiting effect on the stable current in the later stage of the fault. The topological structure of I-SFCL is relatively diverse, mainly including saturated iron core type, flux confinement type, magnetic shielding type and other structures.

[0007] With its various topological structures, the superconducting current limiter can also form a hybrid superconducting current limiter (H-SFCL) structure with DC circuit breakers (mechanical DC circuit breakers, solid-state DC circuit breakers, hybrid DC circuit breakers). The DC switchgear can realize the connection and disconnection of the SFCL through the opening and closing control, so the H-SFCL has flexible control and can realize various functions. In 2018, Huazhong University of Science and Technology proposed an H-SFCL topological structure for the fault current limiting protection needs of multi-terminal flexible DC transmission systems. The topology includes superconducting inductors, conventional resistors, DC fast switches and other structures. The energy transfer inside the H-SFCL is realized by the fast shutdown of the DC fast switch, which not only reduces the time of the superconducting inductor to experience large current impact, but also improves the current limiting response speed and current limiting efficiency. In 2016, Xi'an Jiaotong University proposed an H-SFCL topological structure that combines SFCL with self-excited oscillation DC circuit breaker in series, and developed a prototype, successfully completing the 10kV / 10kA breaking test. China Huaneng Clean Energy Research Institute proposed a method to protect DC short-circuit faults using SFCL and solid-state DCCB, and completed experimental verification. Wuhan University established a theoretical model combining SFCL and hybrid DCCB, and verified through simulation that the current limiting interruption has faster speed and higher reliability under the joint action of the two.

[0008] For DC transmission (distribution) systems, it takes a certain amount of time for R-SFCL to recover from quenching after being subjected to a large current shock, and it is not suitable for system fault reconstruction. In addition, there is still a risk of resistance quenching. In order to meet high reliability requirements, a non-quenching structure should be used as a priority; I-SFCL will induce a very high magnetic field and overvoltage after being subjected to a large current shock, which increases the difficulty of electromagnetic shielding and insulation design of other power equipment; H-SFCL can make full use of the advantages of superconducting current limiters, and its diversity of topological structures can better match system protection requirements. Therefore, H-SFCL is an effective topological structure of superconducting current limiters to solve short-circuit faults in DC transmission (distribution) systems. Summary of the invention

[0009] In view of the technical problems existing in the prior art, the present invention provides a magnetically confined hybrid superconducting DC current limiter which can effectively suppress the short-circuit current peak, reduce the breaking current of the DC circuit breaker, and improve the reliability of system fault removal.

[0010] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0011] A magnetic confinement hybrid superconducting DC current limiter comprises a current limiting unit and a quench protection unit, wherein the current limiting unit comprises a resistor R and a superconducting coupling coil L2, and the resistor R and the superconducting coupling coil L2 are connected in parallel; the quench protection unit comprises a superconducting coupling coil L1 and a capacitor discharge module, and the superconducting coupling coil L1 and the capacitor discharge module are connected in series to form a series loop; the superconducting coupling coil L2 of the current limiting unit is coupled with the superconducting coupling coil L1 of the quench protection unit.

[0012] Preferably, the superconducting coupling coils L1 and L2 are both wound from superconducting tapes.

[0013] Preferably, the superconducting coupling coils L1 and L2 have the same number of turns, consistent structure, and generate reverse coupling in magnetic flux direction.

[0014] Preferably, the superconducting coupling coils L1, L2 are hollow structures or have iron core structures.

[0015] Preferably, the capacitor discharge module includes a pre-charge capacitor C and a switch unit; the superconducting coupling coil L1, the pre-charge capacitor C and the switch unit are connected in series in sequence.

[0016] Preferably, the switch unit is a thyristor SCR.

[0017] Preferably, there are multiple capacitor discharge modules connected in parallel.

[0018] Preferably, the resistor R is a fixed value resistor.

[0019] The current limiting unit is connected in series to the head end or the end of the DC line.

[0020] Compared with the prior art, the advantages of the present invention are:

[0021] The impedance presented by the current limiter of the present invention is close to zero under normal circumstances; at the same time, in a DC environment, the superconducting coupling coil L2 not only has a low loss characteristic, but also can eliminate current ripple, play the role of a smoothing reactor, and is beneficial to improving the safety and stability of the system; when a short-circuit fault occurs in the DC system, the current limiter can also respond quickly to current limiting, effectively suppress the short-circuit current peak, reduce the breaking current of the DC circuit breaker, and improve the reliability of system fault removal.

[0022] According to the characteristics of resistor and inductor parallel current limiting and the principle of magnetic confinement, the present invention proposes a current limiting mode with both inductor and resistor parallel current limiting mode and a quench protection unit for preventing the inductor coil from quenching, thereby effectively limiting the short-circuit fault of the DC system and protecting the current limiting device itself. The magnetic confinement hybrid superconducting DC current limiter of the present invention has a simple principle, is easy to be engineered, can take into account a variety of current limiting requirements, and meets a variety of current limiting performance indicators.

[0023] Compared with conventional current limiters, which are difficult to balance performance indicators such as cost, volume, system complexity, and triggering speed, the present invention is based on the design of resistor and inductor parallel current limiting mode and quench protection unit, and proposes a magnetic confinement hybrid superconducting DC current limiter topology structure including a quench protection unit to limit the short-circuit fault of the DC system. When the system is normal, the DC superconducting current limiter can be used as a smoothing reactor without energy loss. In the event of a short-circuit fault, the current limiter has a significant current limiting effect and compensates for the voltage drop of the DC system. Since a superconducting coupling coil parallel resistance structure is adopted in the current limiter structure, when a fault occurs, the current limiter quickly transfers the fault impulse current to the current limiting resistance branch, and quickly limits the short-circuit current peak. When the quench protection unit is started, the thyristor is turned on, and the current of the inductor branch is further limited under the action of magnetic flux coupling, ensuring that the superconducting inductor coil does not quench during the current limiting process, thereby ensuring the safety and stability of the superconducting structure.

[0024] The magnetically confined hybrid superconducting DC current limiter of the present invention is designed to be applied to DC transmission (distribution) systems, and is applicable to low-voltage lines to high-voltage DC transmission lines. The current limiter can not only effectively deal with single-pole grounding short-circuit faults, but also effectively handle double-pole short-circuit faults, thereby meeting the urgent demand for efficient fault current limiters under the increasing short-circuit capacity of the power grid, and greatly improving the breaking reliability of DC circuit breakers. Through its unique design, the current limiter can maintain the relay protection configuration and stability of the system, while significantly improving the transient stability and steady-state safety of the power grid, providing strong technical support for the reliable operation of the power grid.

[0025] The magnetic confinement hybrid superconducting DC current limiter device of the present invention achieves structural simplicity and high efficiency by virtue of its unique topological structure design. This design not only makes it more convenient in engineering implementation, but also can excellently balance the performance indicators of cost, volume, system complexity and triggering speed. Through this innovative design, the device not only ensures the stable operation of the power grid, but also significantly improves the economic benefits and engineering practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a topological structure diagram of the magnetic confinement hybrid superconducting DC current limiter in an embodiment of the present invention.

[0027] Figure 2 The figure is a schematic diagram of the operation principle of the magnetic confinement hybrid superconducting DC current limiter of the present invention in a specific application.

[0028] Figure 3 This is a connection diagram of the magnetic confinement hybrid superconducting DC current limiter of the present invention applied to a DC power transmission system.

[0029] Figure 4 This is a comparison diagram of system DC current changes when a two-pole grounding short circuit fault occurs in the high-voltage direct current transmission system of the present invention, when a current limiter is not installed and when a current limiter is installed.

[0030] Figure 5 This is a comparison diagram of system DC voltage changes when a bipolar short circuit fault occurs in the high-voltage direct current transmission system of the present invention, when a current limiter is not installed and when a current limiter is installed.

[0031] Figure 6 This is a diagram showing changes in the equivalent current limiting resistance of the superconducting DC current limiter when a two-pole grounding short circuit fault occurs in the high voltage DC power transmission system of the present invention.

[0032] Figure 7 This is a diagram showing the current shunting situation of each unit branch of the superconducting DC current limiter when a two-pole grounding short circuit fault occurs in the high voltage DC transmission system of the present invention.

[0033] Figure 8 This is a diagram showing the improved topological structure of the magnetically confined hybrid superconducting DC current limiter of the present invention.

[0034] Fig. 9 This is a comparison diagram of the inductor currents of the first-stage capacitor discharge and the multi-stage capacitor discharge of the magnetic confinement hybrid superconducting DC current limiter of the present invention.

[0035] Fig.10 This is a comparison diagram of the current limiting effects of the primary capacitor discharge and multi-stage capacitor discharge of the magnetically confined hybrid superconducting DC current limiter of the present invention. DETAILED DESCRIPTION

[0036] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0037] like Figure 1 As shown, the magnetic confinement hybrid superconducting DC current limiter of the embodiment of the present invention includes a current limiting unit and a quench protection unit, the current limiting unit includes a conventional resistor R and a superconducting coupling coil L2, the resistor R and the superconducting coupling coil L2 are connected in parallel; the quench protection unit includes a superconducting coupling coil L1 and a capacitor discharge module, the superconducting coupling coil L1 and the capacitor discharge module are connected in series to form a series loop; the superconducting coupling coil L2 of the current limiting unit is coupled with the superconducting coupling coil L1 of the quench protection unit.

[0038] Specifically, the capacitor discharge module includes a pre-charge capacitor C and a thyristor SCR; the superconducting coupling coil L1, the pre-charge capacitor C and the thyristor SCR are connected in series in sequence. The number of capacitor discharge modules is multiple and they are connected in parallel with each other, which can further suppress the short-circuit current of the superconducting coil, prevent the superconducting coil from quenching, and ensure its safety and stability (see the following description for the specific principle).

[0039] Specifically, the superconducting coupling coils L1 and L2 are both wound by superconducting tapes, and the turns of L1 and L2 are the same, the structures are consistent, and the directions of the generated magnetic flux are reversely coupled; the superconducting coupling coils L1 and L2 are in a superconducting state under various working conditions, and belong to a non-quenching superconducting current limiter; L1 and L2 can be hollow structures or have iron core structures. The bypass resistor R (fixed value resistor) and the superconducting inductor L2 are connected in parallel to form a current limiting unit, and the two sides of the current limiting unit are connected in series at the beginning or end of the DC line; the pre-charge capacitor C, the thyristor SCR and the superconducting inductor L1 form a quench protection unit, which can be regarded as a capacitor and inductor charging and discharging circuit.

[0040] In specific applications, due to the current limiting method of the superconducting coupling coil and the bypass resistor in parallel, the superconducting coupling coil L2 can quickly respond to a very high impedance value in the event of a fault, hindering the current from rising, and most of the fault current is transferred to the bypass resistor R branch. In order to prevent the current in the L2 branch from continuing to rise and causing the coil to quench, the quench protection unit starts protection; at this time, the thyristor SCR closes (when it is detected that the current amplitude of the L2 coil is close to the critical current of the coil, the thyristor SCR is immediately turned on), the pre-charged capacitor C begins to discharge, and the inductor L1 and the capacitor C oscillate in series. Figure 1 The coupling mode of the same-name ends of the superconducting coupling coils L1 and L2 is that the resonant current flows in from the same-name ends, and the current induced in L2 flows out from the same-name ends. The direction of this current is opposite to the direction of the fault current, thereby suppressing the rise of the L2 current. The L1 coil current has a half-sine wave oscillation characteristic. When the L1 coil current reaches the peak, the thyristor SCR is turned off.

[0041] The impedance presented by the current limiter of the present invention is close to 0 under normal circumstances; at the same time, in a DC environment, the superconducting coupling coil L2 not only has a low loss characteristic, but also can eliminate current ripple, play the role of a smoothing reactor, and is beneficial to improving the safety and stability of the system; when a short-circuit fault occurs in the DC system, the current limiter can also respond quickly to current limiting, effectively suppress the short-circuit current peak, reduce the breaking current of the DC circuit breaker, and improve the reliability of system fault removal.

[0042] According to the characteristics of resistor and inductor parallel current limiting and the magnetic confinement principle, the present invention proposes a current limiting mode with both an inductor and resistor parallel current limiting mode and a quench protection unit for preventing the inductor coil from quenching, thereby effectively limiting the short-circuit fault of the DC system and protecting the current limiting device itself. The magnetic confinement hybrid superconducting DC current limiter including the quench protection unit of the present invention has a simple principle, is easy to be engineered, can take into account a variety of current limiting requirements, and meets a variety of current limiting performance indicators.

[0043] Compared with conventional current limiters, which are difficult to balance performance indicators such as cost, volume, system complexity, and triggering speed, the present invention is based on the design of resistor and inductor parallel current limiting mode and quench protection unit, and proposes a magnetic confinement hybrid superconducting DC current limiter topology structure including a quench protection unit to limit the short-circuit fault of the DC system. When the system is normal, the DC superconducting current limiter can be used as a smoothing reactor without energy loss. In the event of a short-circuit fault, the current limiter has a significant current limiting effect and compensates for the voltage drop of the DC system. Since a superconducting coupling coil parallel resistance structure is adopted in the current limiter structure, when a fault occurs, the current limiter quickly transfers the fault impulse current to the current limiting resistance branch, and quickly limits the short-circuit current peak. When the quench protection unit is started, the thyristor is turned on, and the current of the inductor branch is further limited under the action of magnetic flux coupling, ensuring that the superconducting inductor coil does not quench during the current limiting process, thereby ensuring the safety and stability of the superconducting structure.

[0044] The magnetically confined hybrid superconducting DC current limiter of the present invention is designed to be applied to DC transmission (distribution) systems, and is applicable to low-voltage lines to high-voltage DC transmission lines. The current limiter can not only effectively deal with single-pole grounding short-circuit faults, but also effectively handle double-pole short-circuit faults, thereby meeting the urgent demand for efficient fault current limiters under the increasing short-circuit capacity of the power grid, and greatly improving the breaking reliability of DC circuit breakers. Through its unique design, the current limiter can maintain the relay protection configuration and stability of the system, while significantly improving the transient stability and steady-state safety of the power grid, providing strong technical support for the reliable operation of the power grid.

[0045] The magnetic confinement hybrid superconducting DC current limiter device of the present invention achieves structural simplicity and high efficiency by virtue of its unique topological structure design. This design not only makes it more convenient in engineering implementation, but also can excellently balance the performance indicators of cost, volume, system complexity and triggering speed. Through this innovative design, the device not only ensures the stable operation of the power grid, but also significantly improves the economic benefits and engineering practicality.

[0046] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0047] like Figure 1 As shown, the magnetic confinement hybrid superconducting DC current limiter including a quench protection unit in the present invention mainly includes a current limiting unit and a quench protection unit. The current limiting unit is composed of a conventional resistor R and a coupled coil superconducting inductor L2 in parallel, and the quench protection unit includes a coupled coil inductor L1, a pre-charge capacitor C and a thyristor SCR.

[0048] The current limiter of the present invention can provide a superconducting smoothing reactance for the transmission line under the normal state of the DC system, reduce the AC pulsation component of the system transmission line and filter out some harmonics, while ensuring that the smoothing reactance has no resistive loss. When a single-pole grounding fault or a two-stage short-circuit fault occurs in the DC system, the current limiter of the present invention responds quickly, and utilizes the principle that the inductor current cannot suddenly change and the inductor parallel resistor structure. At the moment of the fault, the inductor quickly responds to a larger impedance value, and the fault current quickly transfers to the bypass resistor, forming a larger equivalent current limiting impedance to effectively suppress the short-circuit current. In order to further reduce the short-circuit current impact borne by the overall structure of the superconducting inductor coil, the thyristor in the quench protection unit starts to conduct, the pre-charged capacitor is discharged, L1 and C oscillate, the reverse-coupled L2 induces a reverse voltage, and generates a current opposite to the fault current in the L2 branch, thereby suppressing the current rise of the L2 branch and preventing the superconducting coil from quenching.

[0049] Figure 2 The figure is an operating principle diagram of the magnetically confined hybrid superconducting DC current limiter including a quench protection unit in the present invention. The working principle of the current limiter can be divided into three stages.

[0050] In normal operation, the impedance of superconducting inductor L2 in a DC environment is close to 0, so the rated current on the DC side only flows through the L2 branch. Superconducting inductor L2 not only has low loss characteristics, but also can eliminate current ripple, play the role of smoothing reactor, and is conducive to improving system safety and stability.

[0051] When a fault occurs, the fault current has a high rate of increase. L2 can quickly respond with a high impedance value, and most of the fault current is transferred to the bypass resistor R branch. To prevent the current in the L2 branch from continuing to rise and causing the coil to quench, the quench protection unit starts to start protection. At this time, the thyristor SCR is closed, the pre-charged capacitor C begins to discharge, and the inductor L1 and the capacitor C oscillate in series. Figure 1 The coupling mode of the same-name ends of the superconducting coupling coils L1 and L2 is that the resonant current flows into the same-name ends, and the current induced in L2 flows out from the same-name ends. The direction of this current is opposite to the direction of the fault current, thereby playing a role in suppressing the rise of the fault current.

[0052] Figure 3 The diagram of the DC power transmission system access of the magnetically confined hybrid superconducting DC current limiter including the quench protection unit in the present invention is an application scenario of the superconducting DC current limiter in the present invention, which is a simple VSC high-voltage DC power transmission system. The current limiter is designed to be installed at the end of the transmission line. The system assumes that a ground short circuit fault occurs at the end of the transmission line, the fault occurrence time is set at t1=2s, and the thyristor start-up time is t2=4s.

[0053] Figure 4 and Figure 5 This is a comparison chart of the changes in the system DC current and voltage when the two-pole grounding short circuit fault occurs in the high-voltage direct current transmission system without and with the current limiter. Without the current limiter, the fault current continues to rise after the fault occurs, reaching a maximum value of 51.3kA at t=12ms, and the DC side voltage decays rapidly after the fault, and the system voltage compensation effect is not good; with the current limiter, the fault current reaches a peak value of 13.1kA when the thyristor is closed, that is, at t=4ms, and the peak current limiting rate of the short-circuit current reaches 74.46%. At the same time, the DC side voltage decays immediately after the fault, and then the DC side voltage is continuously compensated and increased, and finally remains in a relatively stable state. In the later stage of the fault, the current limiter can also play a stable current limiting effect, and the voltage compensation basically returns to the rated state. This shows that the current limiter can respond to the current limiting quickly, can continue to play a good role in suppressing the DC side fault current, and at the same time improve the stability of the DC side system.

[0054] Figure 6 This is the change of equivalent current limiting resistance of DC superconducting current limiter when two poles of HVDC transmission system are grounded and short-circuited. The DC circuit breaker is activated 5ms after the fault occurs. Figure 6 The figure shows that the current limiter has a fast response speed. When a short circuit fault occurs, the current limiting equivalent resistance can quickly change from 0Ω to 0.52Ω, and the maximum value can reach 0.6Ω. When the current limiter equivalent resistance presents high impedance, the current limiter can effectively limit the short circuit current.

[0055] Figure 7 This is the current sharing situation of each unit branch of the superconducting DC fault current limiter during a pole-to-ground short-circuit fault in a high-voltage DC transmission system. In the stage of 2 ms < t < 4 ms, the current on the inductor L2 branch rises slowly due to inductor current limiting, and most of the fault current transfers to the resistor R branch. At t = 4 ms, the thyristor SCR conducts, and the quench protection unit starts. Due to the rapid discharge of the capacitor C, i1 gradually increases, generating a half-wave impulse current, with a maximum value approaching 3 kA. In this process, according to the principle of electromagnetic induction, the coupling coil L2 will generate a current waveform opposite to the current waveform of the L2 branch. During the rising stage of i1, it can suppress the current of the superconducting inductor L2 branch, playing a role in protecting the coil from quenching. From the perspective of the total fault current, the input of the quench unit L1 increases the inductive reactance of the inductor branch and improves the impedance value of the line. Therefore, the quench protection unit can not only protect L2 from quenching but also enhance the overall current limiting effect of the current limiter.

[0056] Figure 8 This is the improved topology diagram of the magnetic confinement hybrid superconducting DC fault current limiter containing a quench protection unit in the present invention. It can be seen from the circuit of the quench protection unit that the current generated on the inductor L1 side has the oscillation characteristics of a sine half-wave. The first 1 / 2 half-wave acts on the inductor L2 to play an inhibitory role, and the inhibitory effect decreases in the latter 1 / 2 half-wave. Therefore, Figure 8 the capacitor multi-stage discharge measures shown in the figure can be adopted. When the quench protection unit starts, first close SCR1. When the discharge current of the capacitor C1 reaches the peak, trigger and close SCR2. Control the voltage of C2 to be greater than C1. At this time, the discharge currents of C2 are superimposed, and the current i L1 continues to increase, continuously playing a role in suppressing i L2 . By analogy, new capacitors can be continuously added to enhance the current of the quench protection unit, thereby suppressing the current flowing through the inductor L2, further improving the current limiting efficiency, and fully protecting the safety and stability of the superconducting coil.

[0057] Fig. 9 This is the comparison diagram of the inductor coil current of the magnetic confinement hybrid superconducting DC fault current limiter containing a quench protection unit in the present invention for single-stage capacitor discharge and multi-stage capacitor discharge. Let the value of each capacitor be 0.837 mF, and the charging voltages of the first, second, third, and fourth-stage capacitors are 10, 12, 14, and 16 kV respectively. System simulations are carried out using single-stage capacitor discharge and four-stage capacitor discharge respectively. From Fig. 9 it can be seen that the four-stage capacitor discharge has a better current limiting effect on the inductor L2. Under reasonable parameter selection, it can maintain a relatively low over-current situation of the superconducting inductor L2, which is beneficial to further improving the safety and stability of the equipment.

[0058] Fig.10 This is the comparison diagram of the current limiting effects of the magnetic confinement hybrid superconducting DC fault current limiter containing a quench protection unit in the present invention for single-stage capacitor discharge and multi-stage capacitor discharge. From Fig.10 It can be seen that the four-stage capacitor discharge has a better current limiting effect on the total line current than the one-stage capacitor discharge, and is more conducive to the DC circuit breaker to cut off the fault line. Therefore, the use of capacitor graded discharge measures in the quench protection unit can not only reduce the current overcurrent of the superconducting coil, improve the quench protection function, but also further improve the current limiting effect of the equipment.

[0059] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A magnetically confined hybrid superconducting DC current limiter, characterized in that: It comprises a current limiting unit and a quench protection unit, wherein the current limiting unit comprises a resistor R and a superconducting coupling coil L2, and the resistor R and the superconducting coupling coil L2 are connected in parallel; the quench protection unit comprises a superconducting coupling coil L1 and a capacitor discharge module, and the superconducting coupling coil L1 and the capacitor discharge module are connected in series to form a series loop; the superconducting coupling coil L2 of the current limiting unit is coupled with the superconducting coupling coil L1 of the quench protection unit.

2. The magnetic confinement hybrid superconducting DC current limiter according to claim 1, characterized in that: The superconducting coupling coils L1 and L2 are both wound from superconducting tapes.

3. The magnetic confinement hybrid superconducting DC current limiter according to claim 1, characterized in that: The superconducting coupling coils L1 and L2 have the same number of turns and consistent structure, and generate reverse coupling in the direction of magnetic flux.

4. The magnetic confinement hybrid superconducting DC current limiter according to claim 1, characterized in that: The superconducting coupling coils L1 and L2 are hollow structures or have iron core structures.

5. The magnetically confined hybrid superconducting DC current limiter according to any one of claims 1 to 4, characterized in that: The capacitor discharge module includes a pre-charge capacitor C and a switch unit; the superconducting coupling coil L1, the pre-charge capacitor C and the switch unit are connected in series in sequence.

6. The magnetically confined hybrid superconducting DC current limiter according to claim 5, characterized in that: The switch unit is a thyristor SCR.

7. The magnetic confinement hybrid superconducting DC current limiter according to claim 5, characterized in that: The capacitor discharge modules are multiple and connected in parallel.

8. The magnetically confined hybrid superconducting DC current limiter according to any one of claims 1 to 4, characterized in that: The resistor R is a fixed value resistor.

9. The magnetically confined hybrid superconducting DC current limiter according to any one of claims 1 to 4, characterized in that: The current limiting unit is connected in series to the head end of the DC line.

10. The magnetic confinement hybrid superconducting DC current limiter according to any one of claims 1 to 4, characterized in that: The current limiting unit is connected in series at the end of the DC line.

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