A fast-recovery resistive superconducting fault current limiter and its working method

Abstract

The present invention provides a fast recovery resistive superconducting fault current limiter and its working method. The superconducting fault current limiter includes a cryogenic dewar, a fault current limiter coil, a first fast switch and a second fast switch. The fault current limiter coil is immersed in the cooling liquid in the cryogenic dewar. Each phase of the superconducting fault current limiter is composed of a main current-carrying branch and a main current-limiting branch connected in parallel. The main current-carrying branch is that the main current-carrying superconducting coil is led out through a tapping and then connected in series with the first fast switch. The main current-limiting branch is that the main current-limiting superconducting coil is led out through a tapping and then connected in series with the second fast switch. During a short-circuit fault, the first fast switch trips to cut off the main current-carrying superconducting coil, increasing the current-limiting impedance of the superconducting coil to achieve variable-impedance current limiting. After current limiting, the second fast switch trips to cut off the fault current. After the fault is cleared, when reconnecting, the main current-carrying superconducting coil cut off during current limiting is connected to achieve reclosing. The present invention is applicable to various AC and DC power transmission occasions and occasions with strict requirements on the switch volume, and can also be used in combination with other superconducting devices to reduce the refrigeration cost of the superconducting system.

Description

Technical Field

[0001] The present invention relates to the technical fields of superconducting fault current limiters and switching electrical appliances, and particularly relates to a resistive superconducting fault current limiter device that uses a fast switch to change the connection method and topological structure of superconducting coils in a superconducting fault current limiter to achieve multi-topology variable impedance current limiting and can quickly recover to meet the requirements of line reclosing. Background Art

[0002] Current limiting reactors have become very mature after a long period of development. Currently, commonly used current limiting reactors include concrete column type current limiting reactors, split reactors, dry-type air-core current limiting reactors, etc. However, with the continuous growth of urban loads and the continuous increase of system short-circuit capacity, using high-impedance transformers can reduce the short-circuit fault current level to a certain extent, but it will also increase power losses and affect power quality.

[0003] Due to the zero-resistance characteristic and large current density of superconducting materials in the superconducting state, the superconducting fault current limiter made has the characteristics of small volume, light weight, and low loss. When a resistive superconducting fault current limiter made of superconducting materials encounters a short circuit, the superconducting coil automatically quenches under the action of the short-circuit current to generate a large resistance for current limiting without control, and the superconducting quench speed is faster than that of other types of power current limiters. It can respond to current limiting within 5 ms in DC and the first half-wave in AC, with a large current limiting depth, and has been applied in both AC and DC power transmission fields. However, existing superconducting fault current limiters still have problems such as inflexible and uncontrollable quench resistance and long quench recovery time that need to be improved. Summary of the Invention

[0004] Aiming at the problems of unchangeable current limiting depth and slow recovery of existing superconducting fault current limiters, the present invention proposes a fast-recovery resistive superconducting fault current limiter and its working method. The present invention uses different connection methods and operating states of fast switches. During a short-circuit fault, through the opening action of the fast switch, part of the superconducting coil is cut off, changing the topological structure of the superconducting fault current limiter coil, increasing the current limiting impedance of the superconducting coil, and realizing the multi-topology current limiting function. After current limiting, the opening of the remaining short-circuit current is achieved through another fast switch to clear the system fault. During the automatic reclosing of the system, it is necessary to reconnect the superconducting coil after the fault. Since the tape disconnected first has a low quench degree and fast recovery, or does not quench, the coil disconnected first can be connected to meet the automatic reclosing of the system, and the remaining superconducting coils are reconnected after they are fully recovered. The two fast switches can simultaneously meet the variable impedance current limiting function and the current opening function during normal and fault conditions, and can be applied to AC and DC systems, forming an integrated superconducting current limiting AC / DC opening technology with a deeper coupling current limiting rate, and no additional circuit breaker is required to open the current.

[0005] To achieve the above object, the present invention is implemented by adopting the following design scheme:

[0006] A fast - recovery resistive superconducting fault current limiter includes a cryogenic dewar 1, a fault current limiter coil 2, a first fast switch 4, and a second fast switch 5. Each - phase fault current limiter coil 2 is divided into a main - current - conducting superconducting coil and a main - current - limiting superconducting coil, and is immersed in the cooling liquid in the cryogenic dewar 1. Each phase of the superconducting fault current limiter is composed of a parallel - connected main - current - conducting branch and a main - current - limiting branch. The main - current - conducting branch is that the main - current - conducting superconducting coil is led out through a tapping 3 and then connected in series with the first fast switch 4, and the main - current - limiting branch is that the main - current - limiting superconducting coil is led out through a tapping 3 and then connected in series with the second fast switch 5.

[0007] Preferably, the number of parallel superconducting tapes of the main - current - conducting superconducting coil is more than that of the main - current - limiting superconducting coil. The main - current - conducting superconducting coil has a strong current - conducting ability and a small current - limiting impedance, and is mainly used for current conduction; the main - current - limiting superconducting coil has a weak current - conducting ability and a large current - limiting impedance, and is mainly used for fault current limiting.

[0008] Preferably, the main - current - conducting superconducting coil and the main - current - limiting superconducting coil are wound in parallel with superconducting tapes of the same critical current or are wound with superconducting tapes of different critical currents respectively; the double - pancake type or solenoid - type non - inductive winding method or the inductive winding method is adopted; the materials of the main - current - conducting superconducting coil and the main - current - limiting superconducting coil are yttrium - barium - copper - oxide YBCO or bismuth - strontium - calcium - copper - oxide BSCCO.

[0009] Preferably, the first fast switch (4) and the second fast switch (5) are used as load switches or circuit breakers, and the arc - quenching medium is SF6 or vacuum. The first fast switch (4) and the second fast switch (5) are placed inside or outside the cryogenic dewar of the superconducting fault current limiter. When the two fast switches are used as circuit breakers, they are AC circuit breakers in the AC system and DC circuit breakers in the DC system, and DC circuit breakers or artificial - zero - crossing DC circuit breakers are adopted. When fault current limiting, the fast switch of the main - current - conducting branch is disconnected to increase the current - limiting impedance. After current limiting, the fast switch of the main - current - limiting branch is disconnected to cut off the fault. Connecting the superconducting coil cut off first can realize reclosing. The two fast switches acting simultaneously can also realize the opening and closing under normal conditions. When the two fast switches are used as load switches, the circuit breaker of the line where the fault current limiter is located is required to break the remaining short - circuit current.

[0010] The working method of the above - mentioned fast - recovery resistive superconducting fault current limiter includes the following steps:

[0011] Step 1: When operating normally, the first fast switch 4 and the second fast switch 5 are both closed, and both the main - current - conducting superconducting coil and the main - current - limiting superconducting coil conduct current. When performing opening and closing operations under normal conditions, the two fast switches are opened or closed simultaneously to complete the normal opening and closing operations.

[0012] Step 2: When a short - circuit fault occurs, the main current - conducting superconducting coil and the main current - limiting device quickly quench, initially limiting the short - circuit current accordingly. At the same time, the first fast switch 4 trips, cutting off the main current - conducting superconducting coil in series with it, causing the current to transfer to the main current - limiting superconducting coil;

[0013] Step 3: After cutting off the main current - conducting superconducting coil, all the current flows through the main current - limiting superconducting coil. The impedance of the overall superconducting coil increases relative to that before cutting off, which will reduce the amplitude of the short - circuit current. At the same time, since the non - inductive winding of the overall superconducting coil is damaged after cutting off the main current - conducting superconducting coil, the superconducting coil presents a certain inductance, which will also limit the rising rate of the short - circuit current;

[0014] Step 4: After limiting the short - circuit current to the preset range, the second fast switch 5 trips, cutting off the main current - limiting superconducting coil, cutting off the remaining short - circuit current, clearing the short - circuit fault, and preparing for the next closing;

[0015] Step 5: When the current limiter has a requirement for automatic reclosing, since the main current - conducting superconducting coil that is disconnected first has a low degree of quenching and a fast recovery, the main current - conducting superconducting coil that was cut off first is connected during reclosing to meet the requirement of automatic reclosing; after the remaining main current - limiting superconducting coil is fully restored to the superconducting state, it is then connected to the circuit by the second fast switch 5.

[0016] Currently, there is a similar patent for a high - temperature superconducting current limiter and current - limiting method with double - split reactor parallel resonance, application number 202111064448.6. This patent changes the coupling state of the reactor in the superconducting current limiter by triggering the conduction of IGBT through superconducting quenching, and mainly limits the current through the impedance of the reactor. Since two IGBTs are used, the device control is relatively complex, and due to the discharge of the resonant capacitor, it is difficult to achieve reclosing after a fault.

[0017] A 35kV power supply and distribution system based on a bridge - type superconducting current limiter, application number 201921905476.4. In this patent, the AC circuit is connected to the superconducting coil after being rectified by a diode rectifier bridge, and current limiting is achieved through the superconducting coil. However, in this scheme, the superconducting coil is in a long - term over - current - limiting state, resulting in a slow recovery speed of the superconducting coil and making it difficult to achieve reclosing.

[0018] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0019] Due to the ingenious application of the fast switch, compared with the existing superconducting current limiters, without changing the amount of superconducting coil used, by the action of the fast switch, part of the coil can be cut off, and the current - limiting impedance can be increased to N times the impedance of the existing superconducting current - limiting transformer (N≥1, N is the number of parallel low - voltage - side superconducting coils), greatly improving the current - limiting depth. When using non - inductive winding, the inductive reactance of the coil can also be increased by destroying the non - inductive balance, reducing the rising rate of the short - circuit current.

[0020] In an AC system, the fast switch can be used as a circuit breaker. Its opening time is much shorter than that of a conventional circuit breaker, usually ≤20 ms. And due to the superconducting current-limiting effect, the opening requirement is also reduced to the current after current-limiting, effectively extending the switch life. There is no need to use an additional circuit breaker in the line where the current limiter is located.

[0021] In a DC system, due to the high current-limiting rate of the superconducting current limiter of the present invention, a load switch can be used as a fast switch in the present invention. At the same time, it can also achieve current interruption after current-limiting, eliminating the use of a DC circuit breaker and greatly reducing the equipment cost. The functions of superconducting current-limiting and the fast removal of faults by the vacuum switch significantly reduce the short-circuit current impact on the system, improve the system reliability, and effectively extend the service life of power equipment.

[0022] During a short-circuit fault, all superconducting coils of a conventional superconducting current limiter exceed the limit and conduct current. Its recovery time can reach several seconds due to the inherent characteristics of superconductivity, which cannot meet the requirements of the system's automatic fast reclosing. The present invention uses a fast switch to first cut off the superconducting coils with a low degree of quench or no quench, greatly reducing the superconducting recovery time of the cut-off superconducting coils, so as to be able to achieve the fast reclosing function.

[0023] The present invention combines a resistive superconducting current limiter with a fast switch. By different connection methods and operating states of the fast switch, the number of parallel conductors of the superconducting current limiter coil is changed, increasing the current-limiting impedance and inductive reactance after the superconducting coil quenches, realizing variable-impedance current-limiting; the superconducting coils cut off first recover quickly and can be reconnected during the fault reclosing to achieve line reclosing; when the fast switch is used as a circuit breaker, normal operating conditions and current interruption after short-circuit current-limiting can be achieved through the operation of two fast switches. The invention is applicable to various AC and DC transmission occasions and occasions with strict requirements for the switch volume. The invention can also be used in combination with other superconducting devices to further reduce the refrigeration cost of the superconducting system. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings constituting the specification of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0025] Figure 1 is the topological structure diagram of the present invention when used in an AC system;

[0026] Figure 2 is the single-phase topological structure diagram of the present invention when used in an AC system and the topological structure diagram applied to a DC system. DETAILED IMPLEMENTATION METHOD

[0027] The following further describes the present invention in detail in conjunction with the accompanying drawings and specific embodiments.

[0028] AsFigure 1 As shown in the figure, a fast recovery resistive superconducting fault current limiter mainly consists of a cryogenic dewar 1, a fault current limiter coil 2, a first fast switch 4, and a second fast switch 5. The fault current limiter coil 2 is immersed in the cooling liquid in the cryogenic dewar 1. Each phase of the superconducting fault current limiter consists of a main current-carrying branch and a main current-limiting branch. The main current-carrying branch is that the main current-carrying superconducting coil is led out through a tapping 3 and then connected in series with the first fast switch 4. The main current-limiting branch is that the main current-limiting superconducting coil is led out through a tapping 3 and then connected in series with the second fast switch 5. Among them, the main current-carrying branch and the main current-limiting branch are connected in parallel.

[0029] As Figure 2 shown, under normal operating conditions, both the first fast switch 4 and the second fast switch 5 are closed. At this time, all superconducting coils are carrying current, and the opening and closing of the circuit under normal operating conditions can be achieved by the combined action of the first fast switch 4 and the second fast switch 5. In the case of a short circuit, when the first fast switch 4 is opened, the main current-carrying superconducting coil can be cut off, reducing the number of parallel superconducting coils, increasing the current-limiting impedance after the superconducting coil quenches. At the same time, since part of the conductor is cut off by non-inductive winding, the remaining superconducting coils are inductive and have a certain inductive reactance, which can limit the rising rate of the short-circuit current. Then, the second fast switch 5 is opened to cut off the main current-limiting superconducting coil, cut off the remaining current, and eliminate the power grid fault. Assume that the total number of parallel superconducting coils in the present invention is n, the first fast switch 4 is connected to n - 1 conductors, and the second fast switch 5 is connected to 1 conductor. Then, when the first fast switch 4 is opened, (n - 1) / n of the current is cut off, and the current-limiting impedance after quenching increases by n times. When the first fast switch 4 is connected to m conductors and the second fast switch 5 is connected to n - m conductors, then when the first fast switch 4 is opened, m / n of the current is cut off, and the current-limiting impedance after quenching increases by n / (n - m) times.

[0030] The short-circuit current amplitude passing through the main current-carrying superconducting coil that is opened first is small, the time of bearing the short-circuit current is short, the quenching degree is low, and the quenching recovery speed is fast. Therefore, reconnecting the first fast switch 4 that is opened first can achieve reclosing.

[0031] When the present invention is applied to a DC system, the AC single-phase structure in Figure 2 can be directly used as a DC-type fast recovery resistive superconducting fault current limiting transformer. The first fast switch 4 and the second fast switch 5 using solid-state DC circuit breakers and hybrid DC circuit breakers can meet the requirements of reclosing. At the same time, due to the high current-limiting rate of the superconducting fault current limiter of the present invention, the fast switch does not need to interrupt a large short-circuit current. Therefore, a load switch can also be used to achieve the opening and closing of the circuit. When using an artificial zero-crossing DC fast switch, the possibility of two capacitor discharges or setting two charge-discharge circuits and fast charge-discharge needs to be considered under the reclosing condition.

Claims

1. A fast - recovery resistive superconducting fault current limiter, characterized in that: The fast recovery resistive superconducting fault current limiter includes a cryogenic dewar (1), a fault current limiter coil (2), a first fast switch (4) and a second fast switch (5); each phase of the fault current limiter coil (2) is divided into a main current-carrying superconducting coil and a main current-limiting superconducting coil, and is immersed in the cooling liquid in the cryogenic dewar (1). Each phase of the superconducting fault current limiter is composed of a main current-carrying branch and a main current-limiting branch connected in parallel. The main current-carrying branch is that the main current-carrying superconducting coil is led out through a tapping (3) and then connected in series with the first fast switch (4), and the main current-limiting branch is that the main current-limiting superconducting coil is led out through a tapping (3) and then connected in series with the second fast switch (5); The working method of the fast recovery resistive superconducting fault current limiter includes the following steps: Step 1: When operating normally, both the first fast switch (4) and the second fast switch (5) are closed, and both the main current-carrying superconducting coil and the main current-limiting superconducting coil are carrying current; when performing opening and closing operations under normal conditions, the two fast switches are opened or closed simultaneously to complete the normal opening and closing operations; Step 2: When a short-circuit fault occurs, the main current-carrying superconducting coil and the main current-limiting superconducting coil quickly lose superconductivity, correspondingly and initially limit the short-circuit current, and at the same time, the first fast switch (4) is opened to cut off the main current-carrying superconducting coil connected in series with it, so that the current transfers to the main current-limiting superconducting coil; Step 3: After cutting off the main current-carrying superconducting coil, all the current flows through the main current-limiting superconducting coil, and the impedance of the overall superconducting coil increases relative to that before cutting off, which will reduce the amplitude of the short-circuit current. At the same time, since the non-inductive winding of the overall superconducting coil is damaged after cutting off the main current-carrying superconducting coil, the superconducting coil presents a certain inductance, which will also limit the rising rate of the short-circuit current; Step 4: After limiting the short-circuit current to a preset range, the second fast switch (5) is opened to cut off the main current-limiting superconducting coil, cut off the remaining short-circuit current, eliminate the short-circuit fault, and prepare for the next closing; Step 5: When the fault current limiter has a requirement for automatic reclosing, since the main current-carrying superconducting coil that is disconnected first has a low degree of losing superconductivity and fast recovery, the first cut-off main current-carrying superconducting coil is connected during reclosing to meet the requirement of automatic reclosing; after the remaining main current-limiting superconducting coil is completely restored to the superconducting state, it is then connected to the circuit by the second fast switch (5).

2. The fast - recovery resistive superconducting fault current limiter according to claim 1, characterized in that: The number of parallel superconducting tapes of the main current-carrying superconducting coil is more than that of the main current-limiting superconducting coil. The main current-carrying superconducting coil has strong current-carrying capacity and small current-limiting impedance, and is mainly used for carrying current; the main current-limiting superconducting coil has weak current-carrying capacity and large current-limiting impedance, and is mainly used for fault current limiting.

3. The fast - recovery resistive superconducting fault current limiter according to claim 1, characterized in that: The main current-carrying superconducting coil and the main current-limiting superconducting coil are wound in parallel with superconducting tapes of the same critical current or are wound with superconducting tapes of different critical currents respectively; the double-wound pancake type or solenoid type non-inductive winding method or the inductive winding method is adopted; the materials of the main current-carrying superconducting coil and the main current-limiting superconducting coil are yttrium barium copper oxide YBCO or bismuth strontium calcium copper oxide BSCCO.

4. The fast - recovery resistive superconducting fault current limiter according to claim 1, characterized in that: The first fast switch (4) and the second fast switch (5) are used as load switches or circuit breakers, and the arc extinguishing medium is SF6 or vacuum. The first fast switch (4) and the second fast switch (5) are placed inside or outside the cryogenic dewar of the superconducting fault current limiter; when the two fast switches are used as circuit breakers, they are AC circuit breakers in the AC system and DC circuit breakers in the DC system, and DC circuit breakers or artificial zero-crossing DC circuit breakers are adopted; during fault current limiting, the fast switch of the main current-carrying branch is disconnected to increase the current-limiting impedance, and after current limiting, the fast switch of the main current-limiting branch is disconnected to cut off the fault. Connecting the superconducting coil that is cut off first can achieve reclosing, and the simultaneous operation of the two fast switches can also achieve opening and closing under normal conditions; when the two fast switches are used as load switches, the circuit breaker of the line where the current limiter is located is required to interrupt the remaining short-circuit current.

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