A medium- and high-voltage fast switching switch device and method for power supply guarantee

Abstract

The present invention discloses a medium-high voltage fast switching switch device and method for power supply guarantee. The medium-high voltage fast switching switch device can realize the dual functions of fast switching of dual power supplies and short-circuit fault current limiting. When the voltage of the main power supply circuit temporarily drops or is interrupted for a short time, the device of the present invention can realize the fast switching of the backup power supply circuit. When a short-circuit fault occurs on the load side, the device of the present invention can quickly realize the fault current limiting function, thereby avoiding the expansion of the fault, which is of great significance to the safe and reliable operation of the power system.

Description

Technical Field

[0001] The present invention belongs to the technical field of power control, and in particular relates to a medium- and high-voltage fast switching switch device and method for power supply guarantee. Background Art

[0002] With the development of science and technology, all walks of life have higher and higher requirements for power supply reliability. The switching of large impact loads or nonlinear loads, lightning strikes, and other reasons cause the distribution network system to produce voltage sags or short-term interruptions that cannot be avoided by conventional power grid technology. Such voltage quality problems will cause many sensitive equipment in the distribution network to fail to work properly, and even cause serious consequences. In view of the above reasons, sensitive power users are usually equipped with two or more power feeders, one as the common power supply and the other as the B-line power supply. Under normal circumstances, the common power supply is used to supply power to the load, and the two power supplies are quickly switched through the solid-state transfer switch (SSTS), which is also one of the representative devices for controlling voltage sags.

[0003] With the continuous expansion of the scale of power grid and the increasing complexity of its structure, the short-circuit capacity of the power system has also increased, endangering the safe and stable operation of the power system. When a short-circuit fault occurs on the load side of the feeder, the sharply increased short-circuit current will cause serious damage to the protective switch or customized power devices such as SSTS in the power system. Installing a fault current limiter (FCL) on the line can effectively limit the short-circuit current value during a short-circuit fault. At present, solid-state current limiters based on power electronics technology have developed rapidly. Its basic principle is to use the fast switching control of power electronic devices as the core, combined with components such as resistors and inductors to achieve fast switching of current limiting impedance, thereby limiting the short-circuit current. However, due to the low frequency of short-circuit faults in the power grid, the high investment cost of the current limiter and its single function, it has caused the problem of low utilization of power grid assets to a certain extent. Summary of the invention

[0004] The object of the present invention is to provide a medium- and high-voltage fast switching switch device and method for power supply guarantee, so as to solve the problem of low grid asset utilization rate caused by current limiters installed in the grid in the prior art.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] In a first aspect of the present invention, a medium- and high-voltage fast switching switch device for power supply guarantee includes a vacuum circuit breaker, a bidirectional thyristor valve group, and a current limiting reactor; a line A power supply is connected to a load device through a first bidirectional thyristor valve group, and a line B power supply is connected to a load device through a second bidirectional thyristor valve group; a vacuum circuit breaker S1 is arranged in parallel with the first bidirectional thyristor valve group, and a vacuum circuit breaker S2 is arranged in parallel with the second bidirectional thyristor valve group; the first bidirectional thyristor valve group is evenly divided into two parts: SCR1a1~SCR1 an and SCR1b1~SCR1bn, the current limiting reactor L1lim is connected in parallel with both ends of the thyristor valve group SCR1b1~SCR1bn; the second bidirectional thyristor valve group is evenly divided into two parts: SCR2a1~SCR2an and SCR2b1~SCR2bn, the current limiting reactor L2lim is connected in parallel with both ends of the thyristor valve group SCR2b1 and SCR2bn; when the voltage of the A power supply circuit drops temporarily or is interrupted for a short time, the vacuum circuit breaker S1 is disconnected and the thyristor valve SCR1 is triggered at the same time a1 ~SCR1 an 、SCR1 b1 ~SCR1 bn ; Then turn on the thyristor valve group SCR2 on the power supply side of line B a1 ~SCR2 an 、SCR2 b1 ~SCR2 bn ; Stop triggering thyristor valve group SCR1 a1 ~SCR1 an 、SCR1 b1 ~SCR1 bn ; Then the vacuum circuit breaker S2 is closed; When a short circuit occurs, the vacuum circuit breaker S1 is turned off, and the thyristor valve group SCR1 a1 ~SCR1 an Conducting, thyristor valve group SCR1 a1 ~SCR1 an Still remain off.

[0007] Specifically, an overvoltage protector Z1nO is connected in parallel at both ends of the thyristor valve groups SCR1b1 ​​to SCR1bn.

[0008] Specifically, an overvoltage protector Z2nO is connected in parallel across the two ends of the thyristor valve groups SCR2b1 and SCR2bn.

[0009] Specifically, the current limiting reactor meets the following conditions:

[0010]

[0011] In the formula, α is the actual current limit rate, α′ is the expected current limit rate, U lim is the voltage across the current limiting branch after the current limiting reactance is connected, U znOis the breakdown voltage of the overvoltage protector, and β is the safety factor.

[0012] A second aspect of the present invention is a fault current limiting method based on a medium and high voltage fast switching switch device, comprising the following steps:

[0013] Under normal conditions, vacuum circuit breaker S1 is connected to the A power supply to work, and the other parts are bypassed;

[0014] When the voltage of the A power supply circuit drops temporarily or is interrupted for a short time, the vacuum circuit breaker S1 is disconnected and the thyristor valve SCR1 is triggered a1 ~SCR1 an 、SCR1 b1 ~SCR1 bn , the circuit is transferred to the thyristor valve circuit; then the thyristor valve group SCR2 on the power supply side of line B is turned on a1 ~SCR2 an 、SCR2 b1 ~SCR2 bn , forced commutation occurs; stop triggering thyristor valve group SCR1 a1 ~SCR1 an 、SCR1 b1 ~SCR1 bn , commutation is completed; then the vacuum circuit breaker S2 is closed, the B power supply works, and the other parts are bypassed;

[0015] When a short circuit occurs, the vacuum circuit breaker S1 is turned off and the thyristor valve group SCR1 a1 ~SCR1 an Fast conduction, thyristor valve group SCR1 a1 ~SCR1 an Still keep off, at this time the current limiting reactor passes through the thyristor valve group SCR1 a1 ~SCR1 an Connect in series to the system.

[0016] Furthermore, after a short circuit fault occurs, if the fault current continues to increase, the voltage drop on the current limiting reactor continues to increase, and the overvoltage protector limits the voltage drop of the current limiting reactor to below the withstand voltage of the parallel thyristor valve group.

[0017] Furthermore, when the following formula is satisfied, the voltage is judged to be temporarily depressed or temporarily interrupted:

[0018] U<0.9U phN , where U phN is the phase voltage reference value.

[0019] Furthermore, the method for determining whether a short circuit occurs is: obtaining the current value on the line between the power supply and the bidirectional thyristor valve group through a current transformer, and transmitting the current value to the controller, the controller compares the current value with a preset threshold, and determines that a short circuit occurs when the threshold is exceeded.

[0020] Furthermore, the controller controls the on and off of the thyristor valve group through the driving circuit.

[0021] Furthermore, the A-line power supply is the main power supply, and the B-line power supply is the backup power supply.

[0022] The beneficial effects of the present invention are as follows:

[0023] The medium and high voltage fast switching switch device provided in the embodiment of the present invention can realize the dual functions of fast switching of dual power supplies and short-circuit fault current limiting. When the voltage of the main power supply circuit temporarily drops or is interrupted for a short time, the device of the present invention can realize the fast switching of the backup power supply circuit. When a short-circuit fault occurs on the load side, the device of the present invention can quickly realize the fault current limiting function, thereby avoiding the expansion of the fault, which is of great significance to the safe and reliable operation of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary 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 1 is a topological diagram of a high-voltage fast switching switch device in an embodiment of the present invention.

[0026] Figure 2 Schematic diagram of current limiting control strategy in an embodiment of the present invention.

[0027] Figure 3 Schematic diagram of the current limiting control process in an embodiment of the present invention, (a) grid steady state, (b) fault current limiting transient state.

[0028] Figure 4 Schematic diagram of the working process of the fault current limiting method in an embodiment of the present invention.

[0029] Figure 5 1 is a state diagram of the working process of the fault current limiting method in an embodiment of the present invention, (a) steady-state mode of the power grid system, (b) fast switching mode, (c) forced commutation occurs, (d) commutation is completed, and (e) the voltage drop of the current limiting reactor is limited to below the withstand voltage of the parallel thyristor valve group.

[0030] Figure 6 The simulation waveforms when the system loses voltage or is interrupted temporarily in the embodiment of the present invention are as follows: (a) temporary voltage loss, (b) forced commutation, and (c) voltage and current return to normal.

[0031] Figure 7 These are the simulation waveforms when the system is short-circuited in the embodiment of the present invention, (a) a short-circuit fault occurs, (b) the voltage waveform when the overvoltage protector starts to work, and (c) the fault current is significantly reduced. DETAILED DESCRIPTION

[0032] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other without conflict.

[0033] The following detailed description is an exemplary description, which is intended to provide further detailed description of the present invention. Unless otherwise specified, all technical terms used in the present invention have the same meaning as those generally understood by those skilled in the art to which the present application belongs. The terms used in the present invention are only for describing specific embodiments, and are not intended to limit exemplary embodiments according to the present invention.

[0034] The embodiment of the present invention provides a medium-high voltage fast switching switch device and method for power supply guarantee, which is used to cooperate with the power supply guarantee smart platform of the power grid company. The power supply guarantee smart platform monitors the voltage and current conditions of the power supply circuit through multiple sensors, and controls the medium-high voltage fast switching switch device according to the voltage and current conditions. Specifically, when the voltage of the main power supply circuit drops temporarily or is interrupted for a short time, the device of the present invention can realize the fast switching of the backup power supply circuit. When a short circuit fault occurs on the load side, the device of the present invention can quickly realize the fault current limiting function.

[0035] like Figure 1 As shown, in the first aspect of an embodiment of the present invention, a medium- and high-voltage fast switching switch device for power supply guarantee includes a vacuum circuit breaker, a bidirectional thyristor valve group, a current limiting reactor and an overvoltage protector ZnO; the A power supply is connected to the load device through the first bidirectional thyristor valve group, and the B power supply is connected to the load device through the second bidirectional thyristor valve group. In this embodiment, the A power supply is the main power supply and the B power supply is the backup power supply.

[0036] The vacuum circuit breaker S1 is connected in parallel with the first bidirectional thyristor valve group, and the vacuum circuit breaker S2 is connected in parallel with the second bidirectional thyristor valve group. The first bidirectional thyristor valve group is evenly divided into two parts: SCR1a1~SCR1an and SCR1b1~SCR1bn. The withstand voltage values ​​of the thyristor valve groups in the two parts are both rated voltage values. The current limiting reactor L1lim is connected in parallel with both ends of the thyristor valve group SCR1b1~SCR1bn to achieve the current limiting function of the fault short-circuit current. The overvoltage protector Z1nO is connected in parallel with both ends of the thyristor valve group SCR1b1~SCR1bn for overvoltage protection of the power electronic switch. The second bidirectional thyristor valve group is evenly divided into two parts: SCR2a1~SCR2an and SCR2b1~SCR2bn. The withstand voltage values ​​of the thyristor valve groups in the two parts are both rated voltage values. The current limiting reactor L2lim is connected in parallel with both ends of the thyristor valve group SCR2b1 and SCR2bn to achieve the current limiting function of the fault short-circuit current. The overvoltage protector Z2nO is connected in parallel with both ends of the thyristor valve group SCR2b1 and SCR2bn for overvoltage protection of the power electronic switch.

[0037] In a specific embodiment of the present invention, the current limiting effect of the device of the present invention depends on the size of the connected reactance. For medium and high voltage systems, a larger short-circuit fault current usually generates a larger overvoltage on the current limiting reactance, and the voltage is also directly applied to both ends of the switching device. Although the current limiting module is protected by the overvoltage protector ZnO, it must be ensured that its overvoltage is within the voltage tolerance range of the overvoltage protector. Therefore, the value of the current limiting reactance cannot be too large. At the same time, in order to ensure a better current limiting effect, the current limiting reactance must have a certain current limiting rate, which in turn requires that the value of the current limiting reactance cannot be too small.

[0038] This embodiment provides the selection of current limiting reactors. Taking one phase as an example, assuming that the phase voltage is U and the system impedance is X sys , the on-resistance of the thyristor valve group is Ron, and the current limiting impedance is L lim .

[0039] The short-circuit fault current is:

[0040] I f =U / X sys (1)

[0041] When the fault current flows through the thyristor valve group branch:

[0042] I′ f =U / (X sys +n·R on ) (2)

[0043] After the current limiting reactor is connected, the short-circuit fault current is:

[0044] Ilim =U / (X sys +2πf·L lim ) (3)

[0045] The current limit rate is:

[0046] α=(I f -I lim ) / I f (4)

[0047] After the current limiting reactance is connected, the voltage across the current limiting branch is:

[0048]

[0049] Considering a certain overvoltage margin, the limiting condition of the current limiting reactance should be:

[0050]

[0051] Where α′ is the desired current limit rate, U ZnO is the breakdown voltage of the ZnO overvoltage protector, and β is the safety factor, which is generally between 1.2 and 1.5.

[0052] A second aspect of an embodiment of the present invention provides a fault current limiting method, based on the above-mentioned medium and high voltage fast switching switch device, such as Figure 3 As shown in (a), when the grid is in steady state, the current limiting reactor is bypassed and the current limiting module has no effect on the system. Once a short circuit fault occurs, the current limiter will enter the fault current limiting transient state, as shown in Figure 3 As shown in (b), after the controller determines that a short-circuit fault occurs, it controls the thyristor valve group connected in parallel with the current-limiting reactor to be disconnected, and the current-limiting reactor is put into the fault line to limit the current. Specifically, the control strategy is divided into three types: system steady state, system temporary pressure loss or interruption, and system short-circuit fault. In the three states, the device of the present invention can realize the switching of the corresponding working mode. The specific switching process is as follows: Figure 4 As shown, Figure 5 It is the working state corresponding to the mode switching of the device of the present invention.

[0053] (1) Under normal conditions, the vacuum circuit breaker S1 is connected to the A power supply to work, and the other parts are bypassed. The switch conduction loss is minimal. At this time, the device works in the system steady-state mode, such as Figure 5 As shown in a.

[0054] (2) When the voltage of the A power supply circuit drops or is interrupted for a short time, the device needs to start the fast switching function, and the device enters the fast switching mode. The vacuum circuit breaker S1 is disconnected and the thyristor valve SCR1 is triggered. a1 ~SCR1 an 、SCR1 b1 ~SCR1bn , the circuit is transferred to the thyristor valve circuit, which plays the role of extinguishing the arc of vacuum circuit breaker S1, such as Figure 5 As shown in b.

[0055] Then turn on the thyristor valve group SCR2 on the power supply side of line B a1 ~SCR2 an 、SCR2 b1 ~SCR2 bn , forced commutation occurs, such as Figure 5 c. Stop triggering the thyristor valve group SCR1 a1 ~SCR1 an 、SCR1 b1 ~SCR1 bn , complete the commutation, such as Figure 5 d. After that, the vacuum circuit breaker S2 is closed, the B power supply starts to work, and the other parts are bypassed.

[0056] In this embodiment, the method for identifying a transient voltage loss or interruption fault is as follows:

[0057] In order to judge the transient voltage loss or line break fault, it is necessary to obtain the phase voltage amplitude. Assume that the phase voltage is a sine function, denoted as u α :

[0058]

[0059] Where U is the effective value of the phase voltage, ω is the voltage angular frequency, is the initial phase.

[0060] Delay the phase voltage by π / 2ω, denoted as u β :

[0061]

[0062] will u α 、u β Perform dq transformation, and we get

[0063]

[0064] u q The opposite of is the phase voltage amplitude.

[0065] Let U phN is the phase voltage reference value. For 10kV transmission system, U phN ≈5.77kV. The voltage is judged to be temporarily depressed or interrupted for a short time when the following formula is satisfied:

[0066] U<0.9U phN

[0067] (3) When a short circuit occurs, the device of the present invention quickly switches on the current limiting reactor. At this time, the device operates in the fault current limiting mode, and the short circuit fault current is quickly limited to a lower level. The specific solution is to shut down the fast vacuum circuit breaker S1, and at the same time, the thyristor valve group SCR1 a1 ~SCR1 an Fast conduction, but thyristor valve group SCR1 connected in parallel with current limiting reactor a1 ~SCR1 an Still keep off, at this time the current limiting reactor passes through the thyristor valve group SCR1 a1 ~SCR1 an The thyristor valves are connected in series to the system, thereby realizing rapid suppression of fault current in the power grid. If the fault current continues to increase, the voltage drop on the current limiting reactor continues to increase. The overvoltage protector limits the voltage drop of the current limiting reactor to below the withstand voltage of the parallel thyristor valve group, thereby ensuring the safety of the parallel thyristors. Figure 5 As shown in e.

[0068] Specifically, Figure 2 As shown, in this embodiment, the method for determining whether a short circuit occurs is: the current value on the line between the power supply and the bidirectional thyristor valve group is obtained through a current transformer, and the current value is transmitted to the controller, the controller compares the current value with a preset threshold value, and determines that a short circuit occurs when the threshold value is exceeded, and the controller controls the on and off of the thyristor valve group through a driving circuit. While completing the short circuit fault detection, the controller also monitors the driving state of the switching device in real time.

[0069] In the third aspect of the embodiment of the present invention, in order to verify the effectiveness and feasibility of the topological structure of the device of the present invention, a simulation model was built on the PSIM simulation platform to verify the effect. There are two types of mode switching of the device of the present invention, one is the mode switching when the system loses pressure or interrupts temporarily, and the other is the mode switching when the system is short-circuited. The simulation results are as follows.

[0070] (1) Analysis of the effects of temporary system pressure loss or interruption

[0071] When the system loses voltage or is interrupted temporarily, the device of the present invention will enter the fast switching mode, quickly disconnect the main power supply that has failed, and switch to the backup power supply. The system loses voltage temporarily at 0.3s. The voltage and current on both sides of the device of the present invention are as follows: Figure 6 When a short-term voltage loss occurs, the voltage of the main power supply drops, and the voltage of the B power supply remains stable, as shown in Figure 6 At this time, by using the fast switching principle of the device of the present invention, after determining that the voltage is temporarily reduced, the controller triggers the thyristor valve groups on the A power supply side and the B power supply side at the same time, and quickly switches after completing the forced commutation. The voltage and current can return to normal after only a drop of less than half a cycle. Figure 6 (b) with Figure 6 As shown in (c), it means that the mode switching is successful and the B power supply starts to supply power.

[0072] (2) Simulation waveform of the effect analysis when the system is short-circuited

[0073] When a short circuit fault occurs in the system, the device of the present invention will enter the fault current limiting mode and transfer the short circuit fault current to the current limiting module for current limiting. Assuming that a short circuit fault occurs in the system at 0.5s, the voltage and current on both sides of the device of the present invention are as follows: Figure 7 When a short circuit occurs in the system, the controller first determines the occurrence of the short circuit, and the circuit breaker transfers the fault current to the current limiting circuit within half a cycle, as shown in Figure 1. Figure 7 After being transferred to the current limiting circuit, the thyristor valve group is divided into two types. The valve group not connected in parallel with the current limiting reactance is triggered to conduct, and the thyristor valve group in the current limiting module remains off. The current limiting module is put into use to play a current limiting role, limiting the fault current from more than 15kA to about 10kA, and the current limiting depth is 40%, as shown in Figure 7 As shown in (a). When the voltage across the current limiting module continues to rise, the overvoltage protector connected in parallel across the current limiting reactor begins to function, and its voltage waveform is as follows Figure 7 As shown in (b), the voltage is always less than 10kV, and the overvoltage protector plays a role in protecting power electronic devices. The load side current has a short-term current surge due to the short-circuit fault. After the current limiting module is connected, the fault current is significantly reduced, and the waveform is as follows: Figure 7 (c) as shown.

[0074] It is known from common technical knowledge that the present invention can be implemented by other embodiments that do not deviate from its spirit or essential features. Therefore, the above disclosed embodiments are only illustrative in all respects and are not exclusive. All changes within the scope of the present invention or within the scope equivalent to the present invention are included in the present invention.

Claims

1. A medium and high voltage fast switching switch device for power supply guarantee, characterized in that: It includes a vacuum circuit breaker, a bidirectional thyristor valve group, and a current limiting reactor; the A-line power supply is connected to the load device through the first bidirectional thyristor valve group, and the B-line power supply is connected to the load device through the second bidirectional thyristor valve group; the vacuum circuit breaker S1 is arranged in parallel with the first bidirectional thyristor valve group, and the vacuum circuit breaker S2 is arranged in parallel with the second bidirectional thyristor valve group; the first bidirectional thyristor valve group is evenly divided into two parts: SCR1a1~SCR1an and SCR1b1~SCR1bn, and the current limiting reactor L1lim is connected in parallel with both ends of the thyristor valve group SCR1b1~SCR1bn; the second bidirectional thyristor valve group is evenly divided into two parts: SCR2a1~SCR2an and SCR2b1~SCR2bn, and the current limiting reactor L2lim is connected in parallel with both ends of the thyristor valve group SCR2b1 and SCR2bn; When the voltage of the A power supply circuit drops temporarily or is interrupted for a short time, the vacuum circuit breaker S1 is disconnected and the thyristor valve SCR1 is triggered a1 ~SCR1 an 、SCR1 b1 ~SCR1 bn ; Then turn on the thyristor valve group SCR2 on the power supply side of line B a1 ~SCR2 an 、SCR2 b1 ~SCR2 bn ; Stop triggering thyristor valve group SCR1 a1 ~SCR1 an 、SCR1 b1 ~SCR1 bn ; Then the vacuum circuit breaker S2 is closed; When a short circuit occurs, the vacuum circuit breaker S1 is turned off, and the thyristor valve group SCR1 a1 ~SCR1 an Conducting, thyristor valve group SCR1 a1 ~SCR1 an Still remain off.

2. The medium and high voltage fast switching switch device for power supply guarantee according to claim 1 is characterized in that: Overvoltage protector Z1nO is connected in parallel across the two ends of thyristor valve group SCR1b1~SCR1bn.

3. The medium and high voltage fast switching switch device for power supply guarantee according to claim 2 is characterized in that: An overvoltage protector Z2nO is connected in parallel across the thyristor valve groups SCR2b1 and SCR2bn.

4. The medium and high voltage fast switching switch device for power supply guarantee according to claim 1 is characterized in that: The current limiting reactor meets the following conditions: In the formula, α is the actual current limit rate, α′ is the expected current limit rate, U lim is the voltage across the current limiting branch after the current limiting reactance is connected, U Zno is the breakdown voltage of the overvoltage protector, and β is the safety factor.

5. A fault current limiting method, based on the medium and high voltage fast switching switch device according to claim 3, characterized in that: The steps include: Under normal conditions, vacuum circuit breaker S1 is connected to the A power supply to work, and the other parts are bypassed; When the voltage of the A power supply circuit drops temporarily or is interrupted for a short time, the vacuum circuit breaker S1 is disconnected and the thyristor valve SCR1 is triggered a1 ~SCR1 an 、SCR1 b1 ~SCR1 bn , the circuit is transferred to the thyristor valve circuit; then the thyristor valve group SCR2 on the power supply side of line B is turned on a1 ~SCR2 an 、SCR2 b1 ~SCR2 bn , forced commutation occurs; stop triggering thyristor valve group SCR1 a1 ~SCR1 an 、SCR1 b1 ~SCR1 bn , commutation is completed; then the vacuum circuit breaker S2 is closed, the B power supply works, and the other parts are bypassed; When a short circuit occurs, the vacuum circuit breaker S1 is turned off and the thyristor valve group SCR1 a1 ~SCR1 an Fast conduction, thyristor valve group SCR1 a1 ~SCR1 an Still keep off, at this time the current limiting reactor passes through the thyristor valve group SCR1 a1 ~SCR1 an Connect in series to the system.

6. The fault current limiting method according to claim 5, characterized in that: When a short circuit fault occurs, if the fault current continues to increase, the voltage drop on the current limiting reactor continues to increase, and the overvoltage protector limits the voltage drop of the current limiting reactor to below the withstand voltage of the parallel thyristor valve group.

7. The fault current limiting method according to claim 5, characterized in that: When the following formula is met, the voltage is judged to be temporarily dropped or interrupted for a short time: U<0.9U phN , where U phN is the phase voltage reference value.

8. The fault current limiting method according to claim 5, characterized in that: The method for determining whether a short circuit occurs is: obtaining the current value on the line between the power supply and the bidirectional thyristor valve group through a current transformer, and transmitting the current value to the controller. The controller compares the current value with a preset threshold value, and determines that a short circuit occurs when the threshold value is exceeded.

9. The fault current limiting method according to claim 8, characterized in that: The controller controls the on and off of the thyristor valve group through the driving circuit.

10. The fault current limiting method according to claim 5, characterized in that: Power supply A is the main power supply, and power supply B is the backup power supply.

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