A short-circuit current self-driven fast switch and a design and control method thereof

Abstract

The application discloses a short-circuit current self-driven fast switch and a design and control method thereof. The short-circuit current self-driven fast switch comprises a vacuum arc-extinguishing chamber, an electromagnetic retaining mechanism, an electromagnetic repulsion mechanism and a controller which are connected in parallel to a measured system. The vacuum arc-extinguishing chamber is connected in parallel to a current limiting reactor connected to the measured system. The electromagnetic retaining mechanism comprises a second current transformer coupled to the measured system on a primary side, a rectifier circuit connected in series to a secondary side of the second current transformer and a driving coil connected in series to the rectifier circuit. The driving coil is aligned with an armature of the vacuum arc-extinguishing chamber, and there is an air gap between the armature and the driving coil. The driving coil is arranged inside a shell made of ferromagnetic material. The short-circuit current self-driven fast switch can act immediately when a system short-circuit fault occurs under any condition, and can act multiple times in a short time.

Description

Technical Field

[0001] The present invention relates to the technical field of electrical switches, and in particular to a short-circuit current self-driven fast switch and a design and control method thereof. Background Art

[0002] With the continuous development of power generation, the increasing load, and the close interconnection of AC and DC power grids across various regions, short-circuit current levels in power systems are increasing, posing a serious threat to the interrupting capacity of circuit breakers. Excessive short-circuit currents have become a common problem in densely loaded and power-intensive areas, hindering power development and the safe and stable operation of power grids. To address this issue, short-circuit currents need to be suppressed. This is achieved by increasing the equivalent short-circuit impedance at the fault point. Conventional approaches include: First, modifying the system structure or operating mode, including busbar segmentation, line shutdown, and line disconnection. These measures can significantly alter the grid structure, compromise its integrity, and significantly negatively impact normal system operation. Second, installing current-limiting reactors, primarily series reactors and split reactors, can effectively reduce short-circuit current levels, but they can lead to uneven current distribution, impacting the efficient utilization of the power grid. Furthermore, high-voltage current-limiting reactors occupy a large area and are expensive to manufacture. Site constraints make retrofitting difficult and impractical for load-center substations.

[0003] The fast-switching fault current limiter, which consists of a fast switch connected in parallel with a current-limiting reactor, is a widely adopted current-limiting method. When the power grid is operating normally, it controls the fast switch to close and bypass the current-limiting reactor. After a short-circuit fault occurs, it controls the fast switch to open within about one cycle to input the current-limiting reactor to exert its current-limiting function. After the fault is cleared, it controls the fast switch to reclose and bypass the current-limiting reactor again. However, existing fast switches have the following drawbacks: 1. Since the drive current for fast switches is generally provided by energy storage capacitors, which often require several seconds to tens of seconds to charge before they can be ready for the next operation, the fast-switching current-limiting reactor (FCL) cannot achieve continuous operation. It generally remains in the closed state for 1-2 seconds after opening, waiting for the reclosing procedure to complete or the relay protection to clear the short-circuit fault before the fast switch resumes the closed state. 2. Charging the energy storage capacitor requires an external power supply or power extraction device from the primary side of the system. The external power supply method requires the design of an isolation transformer and an insulating rod-generator platform to connect the station's low-voltage power supply and the FCL's high-voltage platform, which is large and costly. If a power extraction device such as a CVT (capacitor voltage transformer) is used to draw power from the primary side of the system, if a short circuit occurs in the system during the first power supply after the FCL is powered off, the energy storage capacitor will not have enough time to charge, and the FCL will not be able to operate immediately, resulting in increased power losses. Summary of the Invention

[0004] Technical problem to be solved by the present invention: In view of the above-mentioned problems in the prior art, a short-circuit current self-driven fast switch and a design and control method thereof are provided. The present invention aims to provide a short-circuit current self-driven fast switch that uses the fault current collected by the current sensor as the driving current, so that the current limiting inductor of the short-circuit current self-driven fast switch can be immediately activated and can be activated multiple times in a short period of time when a system short-circuit fault occurs under any circumstances.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A short-circuit current self-driven fast switch comprises a vacuum interrupter connected in parallel to a system under test, an electromagnetic holding mechanism, an electromagnetic repulsion mechanism, and a controller. The vacuum interrupter is connected in parallel to a current-limiting reactor connected to the system under test. The electromagnetic holding mechanism comprises a second current transformer coupled to the system under test on its primary side, a rectifier circuit connected in series with the secondary side of the second current transformer, and a drive coil connected in series with the rectifier circuit. The drive coil is aligned with the armature of the vacuum interrupter, with an air gap between the armature and the drive coil. The drive coil is disposed within a housing made of ferromagnetic material. The electromagnetic repulsion mechanism is aligned with the armature of the vacuum interrupter and comprises a first current transformer coupled to the system under test on its primary side, a static repulsion coil, a dynamic repulsion coil, and a bidirectional thyristor. The static repulsion coil is coupled to the secondary side of the first current transformer, the dynamic repulsion coil is coupled to the static repulsion coil, the dynamic repulsion coil is connected in series with the bidirectional thyristor, the bidirectional thyristor is electrically connected to the output end of the controller, and the input end of the controller is electrically connected to the first current transformer.

[0007] Optionally, the vacuum interrupter includes a switch circuit and a resistor-capacitor circuit connected in parallel, the armature is fixed on a movable arm of a switch on the switch circuit, and the resistor-capacitor circuit includes a resistor and a capacitor connected in series.

[0008] Optionally, the primary side coil of the second current transformer has 1 turn and a transformation ratio of 1500:1.

[0009] Optionally, the static repulsion coil is made of copper, and the dynamic repulsion coil is made of aluminum.

[0010] Optionally, the static repulsion coil and the dynamic repulsion coil are both double-layer coils.

[0011] Optionally, the double-layer coil has a coil height of 8 mm, an outer diameter of 250 mm, a single-turn thickness of the coil of 0.84 mm, and a total number of double-layer turns of 212 turns.

[0012] In addition, the present invention also provides a design method for the aforementioned short-circuit current self-driven fast switch, comprising determining the electrical parameters of the electromagnetic repulsion mechanism, including the number of layers of the static repulsion coil and the dynamic repulsion coil, coil height, outer diameter, single turn thickness, and total number of double-layer turns, and designing the electrical parameters of the electromagnetic repulsion mechanism based on the discharge mode of the vacuum arc:

[0013] S101, calculate the electromagnetic repulsion between the static repulsion coil and the dynamic repulsion coil according to the following formula :

[0014] ,

[0015] In the above formula, is the driving current, which is the fault current of the system under test; is the induced current of the repulsion coil; Represents the mutual inductance between the static repulsion coil and the dynamic repulsion coil; Indicates the distance between the static repulsion coil and the dynamic repulsion coil;

[0016] S102, combining the electromagnetic repulsion between the static repulsion coil and the dynamic repulsion coil , calculate the acceleration a of the repulsive coil according to the following formula:

[0017] ,

[0018] In the above formula, is the electromagnetic repulsion between the static repulsion coil and the dynamic repulsion coil, Indicates the resistance encountered by the movable part of the quick switch during operation; Indicates the mass of the movable part of the quick switch;

[0019] S103, establishing a two-dimensional axisymmetric finite element simulation model of the electromagnetic repulsion mechanism:

[0020] ,

[0021] In the above formula, represents the Hamiltonian operator; It represents the magnetic field strength at a certain point of the dynamic repulsion coil; It represents the current density at that point of the dynamic repulsion coil; It represents the magnetic flux density at a certain point of the dynamic repulsion coil; Represents the vector magnetic potential at a point on the kinetic repulsion coil; Indicates the conductivity of the dynamic repulsion coil; It represents the electric field strength at a certain point of the dynamic repulsion coil; Indicates the velocity of charge movement at a point in the kinetic repulsion coil; represents the conduction current density in the dynamic repulsion coil; Indicates the number of turns of the dynamic repulsion coil; Represents the single-turn current of the dynamic repulsion coil; Indicates the cross-sectional area of ​​the dynamic repulsion coil;

[0022] S104, using the steady-state magnetic field module of the simulation software, calculate the electromagnetic repulsion force exerted on the dynamic repulsion coil of the electromagnetic repulsion mechanism:

[0023] ,

[0024] In the above formula, Indicates the electromagnetic repulsion force exerted on the dynamic repulsion coil; according to the electromagnetic repulsion force between the static repulsion coil and the dynamic repulsion coil Verify the accuracy of the simulation software calculation. If the electromagnetic repulsion between the static repulsion coil and the dynamic repulsion coil , the electromagnetic repulsion force on the repulsion coil If they are equal, jump to the next step;

[0025] S105, calculate the number of turns of the dynamic repulsion coil and the static repulsion coil:

[0026]

[0027]

[0028] In the above formula, is the number of turns of the dynamic repulsion coil; is the outer diameter of the dynamic repulsion coil and the static repulsion coil; is the inner diameter of the dynamic repulsion coil and the static repulsion coil; is the thickness of the repulsion coil; is the number of turns of the static repulsion coil; is the thickness of the static repulsion coil;

[0029] S106, under the premise that the average opening speed at the initial 75% opening distance is 1.8±0.2m / s, for different vacuum arc discharge modes, the current sensors with different coil layers, outer diameters, single turn thicknesses, and single turn heights of the dynamic repulsion coil and the static repulsion coil are simulated, and the simulation results are designed with the minimum capacity as the goal, so as to determine the optimal electrical parameters of the electromagnetic repulsion mechanism, including the number of layers, coil height, outer diameter, single turn thickness, and total number of double-layer turns of the static repulsion coil and the dynamic repulsion coil.

[0030] Optionally, the method further includes designing electrical parameters of the electromagnetic holding mechanism based on the set electromagnetic attraction force, wherein the electrical parameters of the electromagnetic holding mechanism include the width of the air gap between the housing and the armature:

[0031] S201, assuming that the air gap magnetic field between the housing of the electromagnetic holding mechanism and the armature is uniform, determine the function expression for calculating the electromagnetic attraction force of the electromagnetic holding mechanism as shown in the following formula:

[0032] ,

[0033] In the above formula, It is the electromagnetic attraction between the shell of the electromagnetic holding mechanism and the magnetic pole of the armature. is the effective surface area of ​​the electromagnetic holding mechanism's housing and the armature's magnetic poles, is the magnetic induction intensity of the shell of the electromagnetic holding mechanism and the magnetic pole surface of the armature; is the vacuum permeability;

[0034] S202, setting the magnetic induction intensity of the magnetic pole surface The relationship between the electromagnetic attraction force and the air gap width between the housing and the armature is drawn using finite element simulation software in combination with the function expression for calculating the electromagnetic attraction force of the electromagnetic holding mechanism.

[0035] S203, determining the air gap width between the housing and the armature based on the relationship curve between the electromagnetic attraction and the air gap width between the housing and the armature and the set electromagnetic attraction value , and the air gap width between the housing and the armature Not greater than the preset threshold.

[0036] Optionally, the method further includes designing electrical parameters of a first current transformer based on the set driving current and driving voltage, wherein the electrical parameters of the first current transformer include a core cross-sectional area:

[0037] S301, determining a function expression for calculating the secondary side voltage of the first current transformer as shown in the following formula:

[0038] ,

[0039] In the above formula, is the secondary side voltage of the first current transformer; The resistance encountered by the movable part during the rapid opening and closing process; is the number of turns on the secondary side of the first current transformer; is the maximum magnetic flux density allowed in the core of the first current transformer; is the core cross-sectional area of ​​the first current transformer;

[0040] S302: Determine a function expression for calculating the capacity of the first current transformer as shown in the following formula:

[0041] ,

[0042] In the above formula, is the capacity of the first current transformer; is the secondary side current of the first current transformer; is the primary side current of the first current transformer; is the number of turns on the primary side of the first current transformer;

[0043] S303, the primary side current of the first current transformer , the ratio of the primary coil to the secondary coil, the secondary current , the capacity of the first current transformer , the maximum magnetic flux density allowed in the core of the first current transformer , the number of turns on the primary side of the first current transformer , the secondary turns of the first current transformer Substitute the function expression for calculating the capacity of the first current transformer into the formula to obtain the core cross-sectional area of ​​the first current transformer. .

[0044] In addition, the present invention also provides a control method for the aforementioned short-circuit current self-driven fast switch, comprising the following steps:

[0045] When the system under test operates normally, the armature of the vacuum interrupter is closed, and the current flows through the vacuum interrupter to bypass the current-limiting reactor;

[0046] When a short-circuit fault occurs in the system under test and the primary-side fault current of the first current transformer or the second current transformer is less than a set threshold, the bidirectional thyristor of the electromagnetic repulsion mechanism remains in a closed state, the armature of the vacuum interrupter is closed, and the current-limiting reactor is bypassed; when a short-circuit fault occurs in the system under test and the primary-side fault current of the first current transformer or the second current transformer is greater than or equal to the set threshold, the controller controls the bidirectional thyristor of the electromagnetic repulsion mechanism to be disconnected, and current passes through the static repulsion coil and the dynamic repulsion coil of the electromagnetic repulsion mechanism. The electromagnetic repulsion mechanism generates an electromagnetic repulsion force, driving the armature of the vacuum interrupter to separate, thereby putting the current-limiting reactor into the system under test; at the same time, if the primary-side coil current of the electromagnetic holding mechanism reaches the set threshold, the current value is reduced through the secondary coil and then coupled to the rectifier circuit, the driving coil is energized, and electromagnetic attraction is generated according to the principle of electromagnetic induction, attracting the armature of the vacuum interrupter to remain in an open state, and the current-limiting reactor is continuously put into operation;

[0047] When the short circuit fault of the system under test is eliminated, the fault current disappears, the current of the primary side coil of the electromagnetic holding mechanism decreases, the electromagnetic attraction decreases, the armature of the vacuum interrupter loses attraction and returns to the closed state, waiting for the next fault to occur.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] 1. No need to charge, it can restore to the non-current limiting state within tens of milliseconds after the fault is cleared and be ready to act again. If the system has a short circuit fault again or the relay protection is reclosed, as long as the fault current exceeds the set threshold, it can act multiple times in a short time;

[0050] 2. Since the driving current comes directly from the system fault current, the current limiting reactor can act immediately in any case of system short circuit fault;

[0051] 3. The energy storage capacitor and energy supply equipment are eliminated, the structure is relatively simple, the installation cost is low, the space occupied is small, and modular design can be realized, thus having the advantages of short construction period and flexible configuration. When the short-circuit capacity of the system may be further improved, the number of current limiting units can be increased to meet future current limiting needs; at the same time, since it does not rely on external power supply, the ground insulation cost is very low, especially when installed in ultra-high voltage power grids such as 500kV, it has great cost advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 4 is an equivalent circuit diagram of a short-circuit current self-driven fast switch in an embodiment of the present invention.

[0053] Figure 2 Schematic diagram of the electromagnetic holding mechanism in an embodiment of the present invention.

[0054] Figure 3 1 is a graph showing the relationship between the electromagnetic attraction force and the air gap width of the electromagnetic holding mechanism in an embodiment of the present invention.

[0055] Figure 4 Schematic diagram of the electromagnetic repulsion structure in an embodiment of the present invention.

[0056] Figure 5 Schematic diagram of the simulation of a short-circuit current self-driven fast switch in an embodiment of the present invention.

[0057] Legend: 1. Vacuum interrupter; 11. Armature; 2. Magnetic holding mechanism; 21. Second current transformer; 22. Rectifier circuit; 23. Drive coil; 24. Housing; 3. Electromagnetic repulsion mechanism; 31. First current transformer; 32. Static repulsion coil; 33. Dynamic repulsion coil; 34. Bidirectional thyristor. DETAILED DESCRIPTION

[0058] In order to make the purpose, technical solutions and advantages disclosed in the embodiments of the present invention clearer, the embodiments of the present invention are further described in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention and are not intended to limit the embodiments of the present invention. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, where the same or similar numbers throughout represent the same or similar elements or elements with the same or similar functions.

[0059] It should be noted that the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or server that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products or devices.

[0060] Like reference numerals and letters denote like items in the following drawings, and thus, once an item is defined in one drawing, it does not require further definition or explanation in subsequent drawings.

[0061] In the description of the present invention, it should be noted that the terms "upper", "lower", "inside", "outside", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the inventive product is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they should not be understood as limiting the present invention.

[0062] In the description of the present invention, it should also be noted that, unless otherwise expressly specified or limited, the terms "disposed," "installed," and "connected" should be understood broadly. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0063] like Figure 1 As shown, the short-circuit current self-driven fast switch of this embodiment includes a vacuum interrupter 1 connected in parallel to the system under test, an electromagnetic holding mechanism 2, an electromagnetic repulsion mechanism 3 and a controller. The vacuum interrupter 1 is connected to the system under test (in Figure 1 In the equivalent circuit shown in FIG, the system under test is equivalent to a current-limiting reactor connected in parallel on a circuit formed by an equivalent power supply, an impedance, and a current-limiting reactor; Figure 2 As shown, the electromagnetic holding mechanism 2 includes a second current transformer 21 coupled to the measured system on the primary side, a rectifier circuit 22 connected in series with the secondary side of the second current transformer 21, and a drive coil 23 connected in series with the rectifier circuit 22. The drive coil 23 is aligned with the armature 11 of the vacuum interrupter 1, and there is an air gap between the armature 11 and the drive coil 23. The drive coil 23 is placed inside a shell 24 made of ferromagnetic material; the electromagnetic repulsion mechanism 3 is aligned with the armature 11 of the vacuum interrupter 1, and the electromagnetic repulsion mechanism 3 includes a primary side coupled to the measured system. The first current transformer 31, the static repulsion coil 32, the dynamic repulsion coil 33 and the bidirectional thyristor 34, the static repulsion coil 32 is coupled to the secondary side of the first current transformer 31, the dynamic repulsion coil 33 is coupled to the static repulsion coil 32, the dynamic repulsion coil 33 is connected in series with the bidirectional thyristor 34, the bidirectional thyristor 34 is electrically connected to the output end of the controller, and the input end of the controller is electrically connected to the first current transformer 31, thereby realizing the use of the first current transformer 31 to provide repulsive force to drive the dynamic repulsion coil 33 in the electromagnetic repulsion mechanism 3.

[0064] like Figure 1 As shown, the vacuum interrupter 1 in this embodiment includes a switch circuit and a resistor-capacitor circuit connected in parallel, the armature 11 is fixed on the movable arm of the switch on the switch circuit, and the resistor-capacitor circuit includes a resistor and a capacitor connected in series.

[0065] As an optional implementation, the primary coil of the second current transformer 21 in this embodiment has one turn and a transformation ratio of 1500:1. The second current transformer 21 is used to provide electromagnetic attraction to maintain the armature 11 of the vacuum interrupter 1 in the open state, so its transformation ratio is 1500:1. The short-circuit current self-driven fast switch of this embodiment needs to consider the minimum short-circuit current. The first current transformer 31 provides the repulsive force that drives the dynamic repulsion coil 33 in the electromagnetic repulsion mechanism 3. The short-circuit current is set to 3.68 kA, and the secondary current is calculated based on the transformation ratio to be 184 A.

[0066] As an optional embodiment, the static repulsion coil 32 in this embodiment is made of copper, and the dynamic repulsion coil 33 is made of aluminum. As an optional embodiment, both the static repulsion coil 32 and the dynamic repulsion coil 33 in this embodiment are double-layer coils. As an optional embodiment, the double-layer coils in this embodiment have a coil height of 8 mm, an outer diameter of 250 mm, a single-turn thickness of 0.84 mm, and a total of 212 turns.

[0067] In addition, this embodiment also provides a design method for the aforementioned short-circuit current self-driven fast switch, including determining the electrical parameters of the electromagnetic repulsion mechanism 3, including the number of layers, coil height, outer diameter, single turn thickness, and total number of double-layer turns of the static repulsion coil 32 and the dynamic repulsion coil 33, and designing the electrical parameters of the electromagnetic repulsion mechanism 3 based on the discharge mode of the vacuum arc:

[0068] S101, calculate the electromagnetic repulsion between the static repulsion coil 32 and the dynamic repulsion coil 33 according to the following formula :

[0069] ,

[0070] In the above formula, is the driving current, which is the fault current of the system under test; is the induced current of the dynamic repulsion coil 33; represents the mutual inductance between the static repulsion coil 32 and the dynamic repulsion coil 33; represents the distance between the static repulsion coil 32 and the dynamic repulsion coil 33;

[0071] S102, combining the electromagnetic repulsion between the static repulsion coil 32 and the dynamic repulsion coil 33 , calculate the acceleration a of the repulsive coil 33 according to the following formula:

[0072] ,

[0073] In the above formula, is the electromagnetic repulsion between the static repulsion coil 32 and the dynamic repulsion coil 33, Indicates the resistance encountered by the movable part of the quick switch during operation; Indicates the mass of the movable part of the fast switch; in this embodiment, the mass of the movable part of the fast switch mainly includes the mass of the dynamic repulsion coil 33, the mass of the armature 11 and the mass of the moving part of the vacuum interrupter 1;

[0074] S103, establishing a two-dimensional axisymmetric finite element simulation model of the electromagnetic repulsion mechanism 3:

[0075] ,

[0076] In the above formula, represents the Hamiltonian operator; represents the magnetic field strength at a point on the dynamic repulsion coil 33; represents the current density at this point of the dynamic repulsion coil 33; represents the magnetic flux density at a point on the dynamic repulsion coil 33; represents the vector magnetic potential at a point on the dynamic repulsion coil 33; represents the conductivity of the dynamic repulsion coil 33; represents the electric field strength at a point on the dynamic repulsion coil 33; It represents the charge movement speed at a certain point of the dynamic repulsion coil 33; represents the conduction current density in the dynamic repulsion coil 33; Indicates the number of turns of the dynamic repulsion coil 33; represents the single-turn current of the dynamic repulsion coil 33; represents the cross-sectional area of ​​the dynamic repulsion coil 33;

[0077] S104, using the steady-state magnetic field module of simulation software (such as COMSOL simulation software, etc.) to calculate the electromagnetic repulsive force exerted on the dynamic repulsive coil 33 of the electromagnetic repulsive mechanism 3:

[0078] ,

[0079] In the above formula, Represents the electromagnetic repulsion force of the dynamic repulsion coil 33; according to the electromagnetic repulsion force between the static repulsion coil 32 and the dynamic repulsion coil 33 Verify the accuracy of the simulation software calculation. If the electromagnetic repulsion between the static repulsion coil 32 and the dynamic repulsion coil 33 , the electromagnetic repulsion force on the repulsion coil 33 If they are equal, jump to the next step;

[0080] S105, calculate the number of turns of the dynamic repulsion coil 33 and the static repulsion coil 32:

[0081]

[0082]

[0083] In the above formula, is the number of turns of the dynamic repulsion coil 33; is the outer diameter of the dynamic repulsion coil 33 and the static repulsion coil 32; is the inner diameter of the dynamic repulsion coil 33 and the static repulsion coil 32; is the thickness of the repulsive force coil 33; is the number of turns of the static repulsion coil 32; is the thickness of the static repulsion coil 32, as Figure 4 As shown, wherein a is epoxy resin;

[0084] S106: Under the assumption that the average opening speed at the initial 75% opening distance is 1.8±0.2 m / s, current sensors are simulated for different coil layers, outer diameters, single-turn thicknesses, and single-turn heights of the dynamic repulsion coil 33 and the static repulsion coil 32, targeting different vacuum arc discharge modes. The simulation results are designed with minimum capacity as the design goal, thereby determining the optimal electrical parameters of the electromagnetic repulsion mechanism 3, including the number of layers, coil height, outer diameter, single-turn thickness, and total number of turns of the static repulsion coil 32 and the dynamic repulsion coil 33. Vacuum arc discharge modes include the following four main types: diffuse arc mode, dot-spot mode, anode spot mode, and strong arc mode. The anode spot mode and dot-spot mode occur at high currents and long opening distances, causing severe armature erosion and significantly reducing the probability of interrupting short-circuit currents. Furthermore, when the rapid switch opening speed is too fast, the opening distance may already be very large when the fault current limiting reaches its peak, simultaneously meeting the high current and long opening distance requirements, which is not conducive to the opening of the vacuum switch. Strong arcing occurs when the armature gap is small, causing some ablation of the armature and the generation of metal droplets or vapor. In this embodiment, simulations were performed for single-layer and double-layer coil structures. The tripping speed and current transformer capacity obtained for the single-layer coil structure are shown in Table 1, and the tripping speed and current transformer capacity for the double-layer coil structure are shown in Table 2.

[0085] Table 1 Tripping speed and current transformer capacity under single-layer coil structure

[0086]

[0087] As shown in Table 1, based on the simulation results of a single-layer coil, at similar opening speeds, the current transformer capacity is smallest when the coil height is 14 mm and the outer diameter is 250 mm-300 mm.

[0088] Table 2 Tripping speed and current transformer capacity of self-driven fast switch with double-layer coil structure

[0089]

[0090] Refer to Table 2. According to the simulation results of the double-layer coil, at a similar opening speed, the current transformer capacity is the smallest when the coil height is 8mm and the outer diameter is about 250mm. The double-layer coil structure is better than the single-layer coil. This structure is the optimal structure of the electromagnetic repulsion mechanism. Finally, the number of layers of the static repulsion coil 32 and the dynamic repulsion coil 33 obtained in this embodiment is double-layered, the double-layer coil height is 8mm, the outer diameter is 250mm, the thickness of a single turn of the coil is 0.84mm, and the total number of double-layer turns is 212. The simulation result thermal diagram of the double-layer coil under this parameter is as follows: Figure 5 shown.

[0091] In addition, the design method of this embodiment also includes designing electrical parameters of the electromagnetic holding mechanism 2 based on the set electromagnetic attraction force. The electrical parameters of the electromagnetic holding mechanism 2 include the width of the air gap between the housing 24 and the armature 11:

[0092] S201. According to Maxwell's force equation, when the air gap between the drive coil and the armature is small, the air gap magnetic field is approximately considered uniform. Therefore, assuming that the air gap magnetic field between the housing 24 of the electromagnetic holding mechanism 2 and the armature 11 is uniform, the following function expression for calculating the electromagnetic force of the electromagnetic holding mechanism 2 is determined:

[0093] ,

[0094] In the above formula, is the electromagnetic attraction between the housing 24 of the electromagnetic holding mechanism 2 and the magnetic poles of the armature 11, is the effective surface area of ​​the magnetic poles of the housing 24 of the electromagnetic holding mechanism 2 and the armature 11, is the magnetic induction intensity between the housing 24 of the electromagnetic holding mechanism 2 and the magnetic pole surface of the armature 11; is the vacuum magnetic permeability; the electromagnetic attraction is proportional to the square of the magnetic induction intensity on the surface of the magnetic pole, that is, the magnetic potential generated in the coil F m Under the condition of no change, the magnetic resistance of the magnetic circuit R m The higher the magnetic flux φ The smaller the magnetic induction intensity on the surface of the magnetic pole B In the magnetic circuit, the air gap reluctance is much greater than the ferromagnetic material reluctance, so the magnetic induction intensity on the pole surface is B Mainly affected by air gap d Air gap d When the magnetic resistance decreases, R m Decrease, magnetic induction intensity on the pole surface B Increase, electromagnetic attraction F Increase;

[0095] S202, setting the magnetic induction intensity of the magnetic pole surface The relationship between the electromagnetic attraction force and the air gap width between the housing 24 and the armature 11 is plotted using finite element simulation software, as shown in FIG. Figure 3 As shown;

[0096] S203, determining the air gap width between the housing 24 and the armature 11 based on the relationship curve between the electromagnetic attraction and the air gap width between the housing 24 and the armature 11 and the set electromagnetic attraction value , and the air gap width between the housing 24 and the armature 11 Not greater than the preset threshold. Figure 3 As can be seen, as the air gap width d increases from its minimum value, the electromagnetic attraction drops sharply. Therefore, the electromagnetic holding mechanism only functions when the distance between the electromagnet and the armature is very close, that is, when the armature of the fast switch is wide open. When the air gap width d is large, the electromagnetic attraction generated by the electromagnetic holding mechanism is very small. When the air gap width d is greater than 10mm, it has almost no effect. This characteristic of the electromagnetic holding mechanism enables the self-actuated fast switch to achieve both open-holding and automatic recovery functions. Therefore, the air gap width d in step S24 is not greater than 10mm.

[0097] In addition, the design method of this embodiment further includes designing electrical parameters of the first current transformer 31 based on the set drive current and drive voltage. The electrical parameters of the first current transformer 31 include the core cross-sectional area:

[0098] S301, determine the function expression for calculating the secondary side voltage of the first current transformer 31 shown in the following formula:

[0099] ,

[0100] In the above formula, is the secondary side voltage of the first current transformer 31; The resistance encountered by the movable part during the rapid opening and closing process; is the number of turns on the secondary side of the first current transformer 31; is the maximum magnetic flux density allowed in the core of the first current transformer 31; is the core cross-sectional area of ​​the first current transformer 31;

[0101] S302, determining a function expression for calculating the capacity of the first current transformer 31 as shown in the following formula:

[0102] ,

[0103] In the above formula, is the capacity of the first current transformer 31; is the secondary side current of the first current transformer 31; is the primary side current of the first current transformer 31; is the number of turns on the primary side of the first current transformer 31;

[0104] S303: The primary side current of the first current transformer 31 , the ratio of the primary coil to the secondary coil, the secondary current , the capacity of the first current transformer 31 , the maximum magnetic flux density allowed in the core of the first current transformer 31 , the number of turns on the primary side of the first current transformer 31 , the secondary side turns of the first current transformer 31 Substitute the function expression for calculating the capacity of the first current transformer 31 into the equation to obtain the core cross-sectional area of ​​the first current transformer 31. Specifically, in this embodiment, the primary side current of the first current transformer is =3.68kA, the ratio of the primary coil to the secondary coil is 1:20, the secondary current =184A, capacity =47kVA, =0.2T, =6, =120, substitute into the function expression for calculating the capacity of the first current transformer 31, and we get =0.05mm 2 .

[0105] This embodiment further provides a method for controlling the aforementioned short-circuit current self-driven fast switch, comprising the following steps:

[0106] When the system under test operates normally, the armature 11 of the vacuum interrupter 1 is closed, and the current flows through the vacuum interrupter 1 to bypass the current-limiting reactor;

[0107] When a short circuit fault occurs in the system under test and the primary side fault current of the first current transformer 31 or the second current transformer 21 is less than the set threshold, the bidirectional thyristor 34 of the electromagnetic repulsion mechanism 3 remains in a closed state, the armature 11 of the vacuum interrupter 1 is closed, and the current limiting reactor is bypassed; when a short circuit fault occurs in the system under test and the primary side fault current of the first current transformer 31 or the second current transformer 21 is greater than or equal to the set threshold, the controller controls the bidirectional thyristor 34 of the electromagnetic repulsion mechanism 3 to be disconnected, and the electromagnetic repulsion mechanism 3 is disconnected. When current flows through the static repulsion coil 32 and dynamic repulsion coil 33 of mechanism 3, the electromagnetic repulsion mechanism 3 generates an electromagnetic repulsive force, driving the armature 11 of the vacuum interrupter 1 to separate, thereby engaging the current-limiting reactor in the system under test. At the same time, if the primary-side coil current of the electromagnetic holding mechanism 2 reaches a set threshold, the current value is reduced by the secondary coil and then coupled to the rectifier circuit 22, energizing the drive coil 23. Based on the principle of electromagnetic induction, an electromagnetic attraction is generated, which attracts the armature 11 of the vacuum interrupter 1 to remain in the disconnected state, and the current-limiting reactor is continuously engaged.

[0108] When the short circuit fault of the system under test is eliminated, the fault current disappears, the primary side coil current of the electromagnetic holding mechanism 2 decreases, the electromagnetic attraction decreases, the armature 11 of the vacuum interrupter 1 loses attraction and returns to the closed state, and continues to wait for the next fault to occur.

[0109] In summary, the short-circuit current self-driven fast switch, design method and control method based on the current transformer in this embodiment can effectively utilize the fault current collected by the current sensor as the driving current. In any case, when a system short-circuit fault occurs, the current limiting inductor can be operated immediately and can be operated multiple times in a short period of time.

[0110] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application may take the form of a computer program product implemented on one or more computer-readable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of processes and / or boxes in the flowchart and / or block diagram, may be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the functions described in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 These computer program instructions can also be stored in a computer-readable memory that can guide a computer or other programmable data processing device to work in a specific way, so that the instructions stored in the computer-readable memory produce a product including the instruction device, which implements the function specified in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0111] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiment. All technical solutions based on the concept of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A design method for a short-circuit current self-driven fast switch, characterized in that: The short-circuit current self-driven fast switch comprises a vacuum interrupter (1) connected in parallel to the measured system, an electromagnetic holding mechanism (2), an electromagnetic repulsion mechanism (3) and a controller, wherein the vacuum interrupter (1) is connected in parallel to the current limiting reactor connected to the measured system; the electromagnetic holding mechanism (2) comprises a second current transformer (21) coupled to the measured system on the primary side, a rectifier circuit (22) connected in series with the secondary side of the second current transformer (21), and a drive coil (23) connected in series with the rectifier circuit (22), the drive coil (23) is aligned with the armature (11) of the vacuum interrupter (1), and there is an air gap between the armature (11) and the drive coil (23), and the drive coil (23) is placed inside a shell (24) made of ferromagnetic material; the electromagnetic repulsion mechanism (3) is aligned with the armature (11) of the vacuum interrupter (1), and the electromagnetic repulsion mechanism (3) includes a first current transformer (31) coupled to the measured system on the primary side, a static repulsion coil (32), a dynamic repulsion coil (33) and a bidirectional thyristor (34), wherein the static repulsion coil (32) is coupled to the secondary side of the first current transformer (31), the dynamic repulsion coil (33) is coupled to the static repulsion coil (32), the dynamic repulsion coil (33) is connected in series with the bidirectional thyristor (34), the bidirectional thyristor (34) is electrically connected to the output end of the controller, and the input end of the controller is electrically connected to the first current transformer (31); the design method includes determining the electrical parameters of the electromagnetic repulsion mechanism (3) including the number of layers, coil height, outer diameter, single turn thickness and total number of double turns of the static repulsion coil (32) and the dynamic repulsion coil (33), and designing the electrical parameters of the electromagnetic repulsion mechanism (3) based on the discharge mode of the vacuum arc: S101, calculate the electromagnetic repulsion between the static repulsion coil (32) and the dynamic repulsion coil (33) according to the following formula: : ， In the above formula, is the driving current, which is the fault current of the system under test; is the induced current of the repulsive force coil (33); represents the mutual inductance between the static repulsion coil (32) and the dynamic repulsion coil (33); Indicates the distance between the static repulsion coil (32) and the dynamic repulsion coil (33); S102, combining the electromagnetic repulsion between the static repulsion coil (32) and the dynamic repulsion coil (33) , calculate the acceleration a of the repulsive coil (33) according to the following formula: ， In the above formula, is the electromagnetic repulsion between the static repulsion coil (32) and the dynamic repulsion coil (33), Indicates the resistance encountered by the movable part of the quick switch during operation; Indicates the mass of the movable part of the quick switch; S103, establish a two-dimensional axisymmetric finite element simulation model of the electromagnetic repulsion mechanism (3): ， In the above formula, represents the Hamiltonian operator; represents the magnetic field strength at a certain point of the dynamic repulsion coil (33); represents the current density at this point of the dynamic repulsion coil (33); represents the magnetic flux density at a certain point of the dynamic repulsion coil (33); represents the vector magnetic potential at a point on the dynamic repulsion coil (33); represents the conductivity of the dynamic repulsion coil (33); represents the electric field intensity at a certain point of the dynamic repulsion coil (33); represents the velocity of the charge at a point in the repulsive coil (33); represents the conduction current density in the dynamic repulsion coil (33); represents the number of turns of the dynamic repulsion coil (33); represents the single-turn current of the dynamic repulsion coil (33); represents the cross-sectional area of ​​the dynamic repulsion coil (33); S104, using the steady-state magnetic field module of the simulation software to calculate the electromagnetic repulsion force exerted on the dynamic repulsion coil (33) of the electromagnetic repulsion mechanism (3): ， In the above formula, Indicates the electromagnetic repulsion force exerted on the dynamic repulsion coil (33); according to the electromagnetic repulsion force between the static repulsion coil (32) and the dynamic repulsion coil (33) Verify the accuracy of the simulation software calculation. If the electromagnetic repulsion between the static repulsion coil (32) and the dynamic repulsion coil (33) , the electromagnetic repulsion force on the repulsion coil (33) If they are equal, jump to the next step; S105, calculate the number of turns of the dynamic repulsion coil (33) and the static repulsion coil (32): In the above formula, is the number of turns of the dynamic repulsion coil (33); is the outer diameter of the dynamic repulsion coil (33) and the static repulsion coil (32); is the inner diameter of the dynamic repulsion coil (33) and the static repulsion coil (32); is the thickness of the repulsive force coil (33); is the number of turns of the static repulsion coil (32); is the thickness of the static repulsion coil (32); S106, under the premise that the average opening speed at the initial 75% opening distance is 1.8±0.2m / s, for different vacuum arc discharge modes, the current sensors of different coil layers, outer diameters, single turn thicknesses, and single turn heights of the dynamic repulsion coil (33) and the static repulsion coil (32) are simulated, and the simulation results are designed with the minimum capacity as the goal, so as to determine the optimal electrical parameters of the electromagnetic repulsion mechanism (3), including the number of layers, coil height, outer diameter, single turn thickness, and total number of double-layer turns of the static repulsion coil (32) and the dynamic repulsion coil (33).

2. The design method of the short-circuit current self-driven fast switch according to claim 1, characterized in that: The vacuum interrupter (1) comprises a switch circuit and a resistor-capacitor circuit connected in parallel, the armature (11) is fixed on a movable arm of a switch on the switch circuit, and the resistor-capacitor circuit comprises a resistor and a capacitor connected in series.

3. The design method of the short-circuit current self-driven fast switch according to claim 2, characterized in that: The number of turns of the primary side coil of the second current transformer (21) is 1 turn, and the transformation ratio is 1500:

1.

4. The design method of the short-circuit current self-driven fast switch according to claim 3, characterized in that: The material of the static repulsion coil (32) is copper, and the material of the dynamic repulsion coil (33) is aluminum.

5. The design method of the short-circuit current self-driven fast switch according to claim 4, characterized in that: The static repulsion coil (32) and the dynamic repulsion coil (33) are both double-layer coils.

6. The design method of the short-circuit current self-driven fast switch according to claim 5, characterized in that: The double-layer coil has a coil height of 8 mm, an outer diameter of 250 mm, a single-turn thickness of 0.84 mm, and a total number of double-layer turns of 212.

7. The design method of a short-circuit current self-driven fast switch according to claim 1, characterized in that: The method also includes designing electrical parameters of the electromagnetic holding mechanism (2) based on the set electromagnetic attraction force, wherein the electrical parameters of the electromagnetic holding mechanism (2) include the width of the air gap between the housing (24) and the armature (11): S201, assuming that the air gap magnetic field between the housing (24) and the armature (11) of the electromagnetic holding mechanism (2) is uniform, determine the functional expression for calculating the electromagnetic attraction force of the electromagnetic holding mechanism (2) as shown in the following formula: ， In the above formula, is the electromagnetic attraction between the housing (24) of the electromagnetic holding mechanism (2) and the magnetic poles of the armature (11), is the effective area of ​​the magnetic pole surface of the housing (24) of the electromagnetic holding mechanism (2) and the armature (11), The magnetic induction intensity of the housing (24) of the electromagnetic holding mechanism (2) and the magnetic pole surface of the armature (11); is the vacuum permeability; S202, setting the magnetic induction intensity of the magnetic pole surface The relationship between the electromagnetic attraction force and the width of the air gap between the housing (24) and the armature (11) is drawn using finite element simulation software in combination with a function expression for calculating the electromagnetic attraction force of the electromagnetic holding mechanism (2); S203, determining the air gap width between the housing (24) and the armature (11) based on the relationship curve diagram of the drawn electromagnetic attraction and the air gap width between the housing (24) and the armature (11) and the set electromagnetic attraction value , and the air gap width between the housing (24) and the armature (11) Not greater than the preset threshold.

8. The design method of the short-circuit current self-driven fast switch according to claim 7, characterized in that: The method further includes designing electrical parameters of a first current transformer (31) based on the set driving current and driving voltage, wherein the electrical parameters of the first current transformer (31) include a core cross-sectional area: S301, determining a function expression for calculating the secondary side voltage of the first current transformer (31) as shown in the following formula: ， In the above formula, is the secondary side voltage of the first current transformer (31); The resistance encountered by the movable part during the rapid opening and closing process; is the number of turns on the secondary side of the first current transformer (31); is the maximum magnetic flux density allowed in the core of the first current transformer (31); is the core cross-sectional area of ​​the first current transformer (31); S302, determining a function expression for calculating the capacity of the first current transformer (31) as shown in the following formula: ， In the above formula, is the capacity of the first current transformer (31); is the secondary side current of the first current transformer (31); is the primary side current of the first current transformer (31); is the number of turns on the primary side of the first current transformer (31); S303, the primary side current of the first current transformer (31) , the ratio of the primary coil to the secondary coil, the secondary current , the capacity of the first current transformer (31) , the maximum magnetic flux density allowed in the core of the first current transformer (31) , the number of turns on the primary side of the first current transformer (31) , the number of turns on the secondary side of the first current transformer (31) Substitute into the function expression for calculating the capacity of the first current transformer (31), thereby obtaining the core cross-sectional area of ​​the first current transformer (31) .

Images