A magnetic-motion type fault current self-adaptive current limiting device and its parameter design method

Abstract

The present invention relates to a magnetically actuated fault current self-adaptive current limiting device. There is an air gap between the moving iron core and the static iron core. Under normal conditions, under the action of the spring reaction force, the magnetic circuit corresponding to the equivalent inductance of the current-carrying busbar includes an air gap, and the inductance value is very small, which will not affect the normal operation of the line. During a fault, when the current rises and the electromagnetic force between the moving and static iron cores is greater than the spring reaction force, the moving iron core moves towards the static iron core, the air gap decreases until the moving and static iron cores are completely attracted. As the moving iron core moves, the air gap in the magnetic circuit corresponding to the equivalent inductance of the current-carrying busbar gradually decreases, and the inductance gradually increases, thereby showing the effect of limiting the fault current. The present invention also relates to a parameter design method for a magnetically actuated fault current self-adaptive limiting device, which proposes the perimeter, longitudinal depth, iron core width, and number of turns of the current-carrying busbar coil according to the current limiting requirement. The present invention has the advantages of an equivalent inductance that can be self-adaptively adjusted according to the fault current and a remarkable current limiting effect.

Description

Technical Field

[0001] The invention belongs to the technical field of electrical equipment, and particularly relates to a magnetic-moving type fault current self-adaptive current-limiting device and a parameter design method thereof. Background Art

[0002] The problem of suppressing short-circuit fault current in a DC system is one of the core problems in current DC system protection. A DC current limiter can slow down the rising speed of the fault current to gain time for DC protection and DC circuit breakers, reduce the breaking capacity of DC circuit breakers, and is crucial for enhancing the fault defense ability of a multi-terminal DC system.

[0003] Currently, in multi-terminal DC demonstration projects, a passive current-limiting technology of installing reactors with inductance of dozens or hundreds of mH at the converter outlet is commonly used. Since the inductor also exhibits impedance during non-fault transient processes such as system power fluctuations, operation mode switching, and small disturbances, it has disadvantages such as deteriorating system stability, being prone to oscillation, and reducing system dynamic performance.

[0004] Currently, the main representatives of active current-limiting technologies are superconducting current limiters and power electronics current limiters. Superconducting current limiters require expensive superconducting tapes and a reliable liquid nitrogen cooling system, and are troublesome to maintain; power electronics current limiters require a large number of series and parallel connections of power electronics devices to actively achieve self-adaptive suppression of fault current.

[0005] Therefore, the invention proposes a magnetic-moving type fault current self-adaptive current-limiting device and a design method thereof. Summary of the Invention

[0006] The purpose of the invention is to overcome the deficiencies of the prior art, and provide a magnetic-moving type fault current self-adaptive current-limiting device and a parameter design method thereof. By reducing the air-gap distance between the moving iron core and the static iron core, the equivalent inductance of the current-carrying busbar is increased, demonstrating the effect of limiting fault current, and having advantages such as the equivalent inductance can be self-adaptively adjusted according to the fault current and the current-limiting effect is significant.

[0007] The invention solves its technical problems through the following technical solutions:

[0008] A magnetic-moving type fault current self-adaptive current-limiting device includes a static iron core, a current-carrying busbar, and a reaction spring device. The moving iron core, the current-carrying busbar, and the reaction spring device are sequentially arranged on the static iron core from top to bottom. An air gap is provided between the static iron core and the moving iron core.

[0009] Under normal conditions, under the action of the spring reaction force, there is an air gap between the moving iron core and the static iron core. The magnetic path corresponding to the equivalent inductance of the current-carrying busbar includes the air gap, the inductance value is very small, and the current change is very small. According to the loop voltage equation At this time, it will not affect the normal operation of the line.

[0010] When the fault current rises, the electromagnetic force between the moving iron core and the static iron core is greater than the spring reaction force, the moving iron core moves toward the static iron core, and the air gap decreases until the moving iron core and the static iron core are completely attracted; as the moving iron core moves, the air gap in the magnetic circuit corresponding to the equivalent inductance of the current-carrying busbar gradually decreases, and the inductance and inductance change rate gradually increase. According to the magnetic flux equation The increase in inductance and the rate of change of inductance leads to a decrease in the rate of change of current, which in turn reflects the effect of limiting the fault current.

[0011] Moreover, the magnetic permeability of the moving iron core and the stationary iron core is a thousand times that of air, and the fault current limitation is achieved by utilizing the difference in equivalent inductance of the magnetic flux corresponding to the equivalent inductance of the current-carrying busbar when the flux contains an air gap and when the flux does not contain an air gap.

[0012] A parameter design method for a magnetic fault current adaptive current limiting device is applied to the magnetic fault current adaptive current limiting device. The steps of the parameter design method are as follows:

[0013] 1) According to actual needs, set the ideal fault current value I of the ideal current limit fai ;

[0014] 2) obtaining the critical magnetic field intensity H0 in the unsaturated stage in advance according to the BH curve of the ferromagnetic material;

[0015] 3) According to the ideal fault current value I fai and critical magnetic field strength H0, calculate the ideal perimeter l of the current limiting device when the number of turns of the current-carrying busbar coil is 1 pi , which is calculated based on:

[0016] l pi =I fai / H0

[0017] Where: I fai is the ideal fault current value for ideal current limiting;

[0018] H0 is the critical magnetic field intensity in the unsaturated stage on the BH curve of the ferromagnetic material;

[0019] 4) According to actual needs, set the ideal current limiting device thickness d i and the ideal current limiting inductor value L c ;

[0020] 5) According to the critical magnetic field strength H0, combined with the BH curve of the ferromagnetic material, calculate the magnetic permeability u at this time m ;

[0021] 6) According to the calculated ideal circumference of the current limiting device l pi and the current limiting inductor value L c , calculate the ideal core width l of the current limiting device wi, and its calculation basis is:

[0022]

[0023] Where: L c is the ideal current-limiting inductance value;

[0024] l pi is the ideal perimeter of the current-limiting device;

[0025] u m is the magnetic permeability corresponding to the critical magnetic field strength;

[0026] d i is the ideal thickness of the current-limiting device;

[0027] 7) According to the calculated ideal perimeter l pi of the current-limiting device, the maximum core width l wm is obtained;

[0028] 8) Compare the ideal core width l wi with the maximum core width l wm : If the ideal core width l wi is less than or equal to the maximum core width l wm , the parameter design is reasonable; if the ideal core width l wi is greater than the maximum core width l wm , the parameter design is unreasonable and needs to be improved.

[0029] Moreover, the improvement steps in 8) are:

[0030] 1) According to the ideal perimeter l pi of the current-limiting device, the maximum core width l wm of the current-limiting device, the ideal thickness d i of the current-limiting device, and the magnetic permeability u m corresponding to the critical magnetic field strength, calculate the current-limiting inductance value L c1i at the ideal perimeter when the number of turns of the current-carrying busbar coil is 1, and its calculation basis is:

[0031]

[0032] Where: l wm is the maximum core width of the current-limiting device;

[0033] d i is the ideal thickness of the current-limiting device;

[0034] u m is the magnetic permeability corresponding to the critical magnetic field strength;

[0035] l pi is the ideal perimeter of the current-limiting device;

[0036] 2) According to the ideal current-limiting inductance value L c and the current-limiting inductance value L under the ideal perimeter c1i , calculate the multiple n by which the current-limiting inductance needs to be increased under the ideal perimeter. The calculation basis is as follows:

[0037]

[0038] 3) According to the multiple n by which the inductance needs to be increased, improve the number of turns and the perimeter of the current-carrying busbar coil of the current-limiting device. Modify the number of turns of the current-carrying busbar coil of the current-limiting device to n, and increase the perimeter of the current-limiting device to l p = nl pi , to obtain the final current-limiting inductance value L c0 , the calculation basis is as follows:

[0039]

[0040] Where: n is the number of turns of the current-carrying busbar coil;

[0041] l wm is the maximum core width of the current-limiting device;

[0042] d i is the ideal thickness of the current-limiting device;

[0043] u m is the magnetic permeability corresponding to the critical magnetic field strength;

[0044] l p is the final perimeter of the current-limiting device;

[0045] l pi is the ideal perimeter of the current-limiting device;

[0046] L c1i is the ideal current-limiting inductance value.

[0047] Moreover, the number of turns n and the perimeter l of the current-carrying busbar coil of the current-limiting device p increase in the same proportion to keep the ferromagnetic material in an unsaturated state.

[0048] The positive effects that the present invention can produce are:

[0049] 1. When the fault current of the present invention rises, when the electromagnetic force between the moving and static iron cores is greater than the spring reaction force, the moving iron core moves towards the static iron core, the air gap decreases until the moving and static iron cores are completely attracted. As the moving iron core moves, the air gap in the magnetic circuit corresponding to the equivalent inductance of the current-carrying busbar gradually decreases, and the inductance gradually increases, thereby reflecting the effect of limiting the fault current.

[0050] 2. The parameter design method of the present invention proposes the perimeter, longitudinal depth, core width, and number of turns of the current-carrying busbar coil of the current-limiting device according to the current-limiting requirement. Compared with the passive current-limiting scheme based on a constant inductance value, it has the advantages that the equivalent inductance can be adaptively adjusted according to the fault current and the current-limiting effect is remarkable. Description of the Drawings

[0051] Figure 1 It is a schematic diagram of the magnetomotive fault current adaptive limiting device of the present invention;

[0052] Figure 2 It is a diagram showing the change of inductance with the air gap distance when the magnetomotive fault current adaptive limiting device of the present invention is connected to the line and a fault occurs;

[0053] Figure 3 It is an effect diagram of limiting the fault current when the magnetomotive fault current adaptive limiting device of the present invention is connected to the line and a fault occurs. Detailed Embodiment

[0054] The present invention will be further described in detail below through specific embodiments. The following embodiments are only descriptive and not restrictive, and the protection scope of the present invention cannot be limited thereby.

[0055] As Figure 1 shown, a magnetomotive fault current adaptive current-limiting device includes a static core, a current-carrying busbar, a reaction spring device, and a fork. The moving core, the current-carrying busbar, and the reaction spring device are sequentially arranged on the static core from top to bottom. The innovation lies in that: an air gap is provided between the static core and the moving core.

[0056] Under normal conditions, under the action of the spring reaction force, there is an air gap between the moving core and the static core. The magnetic circuit corresponding to the equivalent inductance of the current-carrying busbar contains an air gap, the inductance value is very small, and the current change is very small. According to the loop voltage equation it will not affect the normal operation of the line at this time;

[0057] When the fault current rises, the electromagnetic force between the moving core and the static core is greater than the spring reaction force, and the moving core moves towards the static core direction, and the air gap decreases until the moving core and the static core are completely attracted; as the moving core moves, the air gap in the magnetic circuit corresponding to the equivalent inductance of the current-carrying busbar gradually decreases, and the inductance and the inductance change rate gradually increase. According to the magnetic flux linkage equation the increase of the inductance and the inductance change rate causes the current change rate to decrease, thereby reflecting the effect of limiting the fault current.

[0058] The magnetic permeability of the moving core and the static core is a thousand times that of the air magnetic permeability, and the fault current limitation is realized by using the equivalent inductance difference when the magnetic flux linkage corresponding to the equivalent inductance of the current-carrying busbar contains and does not contain an air gap.

[0059] like Figure 2 As shown, the magnetically-dynamic fault current adaptive limiting device of the present invention is connected to the line, and the inductance changes with the air gap distance during a fault. As the air gap distance decreases, the equivalent inductance gradually increases; when the moving and static iron cores are attracted, the air gap distance is 0, and the equivalent inductance suddenly increases.

[0060] like Figure 3 As shown, the magnetically driven fault current adaptive limiting device of the present invention is connected to the line, and the effect of limiting the fault current during a fault is: Figure 3 (a) is the comparison of fault current with and without current limiting device. It can be seen that after adding the current limiting device, the fault current is significantly limited. Figure 3 (b) is the parameter change of the current limiting device during fault, and Figure 3 (a) It can be seen from the combination that as the air gap gradually decreases, the equivalent inductance gradually increases, and the fault current rise rate gradually decreases; when the equivalent inductance rise rate increases to satisfy u=idL eq / dt, the fault current change rate drops to 0, and then the fault current decreases; when the moving and static iron cores are attracted, the air gap spacing is 0, at this time the equivalent inductance is the largest and the fault current is the smallest.

[0061] A parameter design method for a magnetic fault current adaptive current limiting device, the innovation of which is that: applied to the magnetic fault current adaptive current limiting device, the parameter design method comprises the following steps:

[0062] 1) According to actual needs, set the ideal fault current value I of the ideal current limit fai ;

[0063] 2) obtaining the critical magnetic field intensity H0 in the unsaturated stage in advance according to the BH curve of the ferromagnetic material;

[0064] 3) According to the ideal fault current value I fai and critical magnetic field strength H0, calculate the ideal perimeter l of the current limiting device when the number of turns of the current-carrying busbar coil is 1 pi , which is calculated based on:

[0065] l pi =I fai / H0

[0066] Where: I fai is the ideal fault current value for ideal current limiting;

[0067] H0 is the critical magnetic field intensity in the unsaturated stage on the BH curve of the ferromagnetic material;

[0068] 4) According to actual needs, set the ideal current limiting device thickness d i and the ideal current limiting inductor value L c ;

[0069] 5) Calculate the permeability μ at this time according to the critical magnetic field strength H0 and the B-H curve of the ferromagnetic material. m ;

[0070] 6) According to the calculated ideal perimeter l of the current-limiting device pi and the current-limiting inductance value L c , deduce the ideal core width l of the current-limiting device wi , and its calculation basis is:

[0071]

[0072] Where: L c is the ideal current-limiting inductance value;

[0073] l pi is the ideal perimeter of the current-limiting device;

[0074] μ m is the permeability corresponding to the critical magnetic field strength;

[0075] d i is the ideal thickness of the current-limiting device;

[0076] 7) Obtain the maximum core width l according to the calculated ideal perimeter l of the current-limiting device pi ; wm ;

[0077] 8) Compare the ideal core width l wi with the maximum core width l wm : If the ideal core width l wi is less than or equal to the maximum core width l wm , then the parameter design is reasonable; if the ideal core width l wi is greater than the maximum core width l wm , then the parameter design is unreasonable and needs to be improved.

[0078] The above parameter improvement steps are:

[0079] 1) According to the ideal perimeter l of the current-limiting device pi , the maximum core width l of the current-limiting device wm , the ideal thickness d of the current-limiting device i and the permeability μ corresponding to the critical magnetic field strength m , calculate the current-limiting inductance value L at the ideal perimeter when the number of turns of the current-carrying busbar coil is 1 c1i , and its calculation basis is:

[0080]

[0081] Where: l wm is the maximum core width of the current-limiting device;

[0082] d i is the ideal thickness of the current-limiting device;

[0083] u m is the magnetic permeability corresponding to the critical magnetic field strength;

[0084] l pi is the ideal perimeter of the current-limiting device;

[0085] 2) According to the ideal current-limiting inductance value L c and the current-limiting inductance value L c1i under the ideal perimeter, calculate the multiple n by which the current-limiting inductance needs to be increased under the ideal perimeter. The calculation basis is:

[0086]

[0087] 3) According to the multiple n by which the inductance needs to be increased, improve the number of turns and the perimeter of the current-carrying busbar coil of the current-limiting device. Modify the number of turns of the current-carrying busbar coil of the current-limiting device to n, and increase the perimeter of the current-limiting device to l p = nl pi to obtain the final current-limiting inductance value L c0 The calculation basis is:

[0088]

[0089] where: n is the number of turns of the current-carrying busbar coil;

[0090] l wm is the maximum core width of the current-limiting device;

[0091] d i is the ideal thickness of the current-limiting device;

[0092] u m is the magnetic permeability corresponding to the critical magnetic field strength;

[0093] l p is the final perimeter of the current-limiting device;

[0094] l pi is the ideal perimeter of the current-limiting device;

[0095] L c1i is the ideal current-limiting inductance value.

[0096] The number of turns n and the perimeter l p of the current-carrying busbar coil of the current-limiting device increase in the same proportion to keep the ferromagnetic material in an unsaturated state.

[0097] Perform simulation on a current self-adaptive current-limiting device and its parameter design method of the present invention. The simulation parameters are: the fault current value I for which current limiting is ideally performedfai = 30 A, the critical magnetic field strength H0 = 30 A / m, from which the ideal perimeter l of the current-limiting device can be obtained p = 1 m, the ideal thickness d of the current-limiting device i = 1 m, the ideal current-limiting inductance value L c = 4 mH, the magnetic permeability corresponding to the critical magnetic field strength is u = 0.0273 H / m, from the above, the ideal core width l can be obtained wi = 0.18 m, and according to the constraints such as the core perimeter, the maximum core width l is obtained wm = 0.04 m.

[0098] Since the ideal core width is greater than the maximum core width, the parameters need to be improved. When the number of turns of the current-carrying busbar coil is 1, the current-limiting inductance value L under the maximum core width and the ideal perimeter is calculated c1i = 1.1 mH, and then the multiple n = 4 by which the current-limiting inductance needs to be increased under the condition of satisfying the core width constraint and the ideal perimeter is calculated. To ensure that the core is always in an unsaturated state, the number of turns and the perimeter of the current-carrying busbar coil of the current-limiting device are both expanded to n = 4 times, and the final current-limiting inductance value L is obtained c0 = 4.4 mH;

[0099] It can be seen that this magnetomotive fault current adaptive limiting device can reflect the effect of limiting the fault current.

[0100] A magnetomotive fault current adaptive current-limiting device and its parameter design method of the present invention show the effect of limiting the fault current by reducing the air gap distance between the moving core and the static core, resulting in an increase in the equivalent inductance of the current-carrying busbar, and have the advantages of an equivalent inductance that can be adaptively adjusted according to the fault current and a significant current-limiting effect.

[0101] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art can understand that: various substitutions, changes, and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the content disclosed in the embodiments and drawings.

Claims

1. A method for designing parameters of a magnetically driven fault current adaptive current limiting device, characterized in that: The current limiting device comprises a stationary iron core, a moving iron core, a current-carrying busbar and a reaction spring device, wherein the moving iron core, the current-carrying busbar and the reaction spring device are arranged on the stationary iron core in order from top to bottom, and is characterized in that an air gap is arranged between the stationary iron core and the moving iron core. Under normal conditions, there is an air gap between the moving iron core and the stationary iron core due to the reaction force of the spring. The magnetic circuit corresponding to the equivalent inductance of the current-carrying busbar contains the air gap, the inductance value is very small, and the current changes very little. According to the loop voltage equation At this time, it will not affect the normal operation of the line; When the fault current rises, the electromagnetic force between the moving iron core and the static iron core is greater than the spring reaction force, the moving iron core moves toward the static iron core, and the air gap decreases until the moving iron core and the static iron core are completely attracted; as the moving iron core moves, the air gap in the magnetic circuit corresponding to the equivalent inductance of the current-carrying busbar gradually decreases, and the inductance and inductance change rate gradually increase. According to the magnetic flux equation The increase in inductance and the rate of change of inductance leads to a decrease in the rate of change of current, which in turn reflects the effect of limiting the fault current; The steps of the parameter design method are: 1) According to actual needs, set the ideal fault current value I of the ideal current limit fai ; 2) obtaining the critical magnetic field intensity H0 in the unsaturated stage in advance according to the BH curve of the ferromagnetic material; 3) According to the ideal fault current value I fai and critical magnetic field strength H0, calculate the ideal perimeter l of the current limiting device when the number of turns of the current-carrying busbar coil is 1 pi , which is calculated based on: the pi =I fai / H0 Where: I fai is the ideal fault current value for ideal current limiting; H0 is the critical magnetic field intensity in the unsaturated stage on the BH curve of the ferromagnetic material; 4) According to actual needs, set the ideal current limiting device thickness d i and the ideal current limiting inductor value L c ; 5) According to the critical magnetic field strength H0, combined with the BH curve of the ferromagnetic material, calculate the magnetic permeability u at this time m ; 6) According to the calculated ideal circumference of the current limiting device l pi and the current limiting inductor value L c , calculate the ideal core width l of the current limiting device wi , which is calculated based on: Where: L c is the ideal current limiting inductor value; l pi is the ideal circumference of the current limiting device; u m is the magnetic permeability corresponding to the critical magnetic field intensity; d i is the ideal thickness of the current limiting device; 7) According to the calculated ideal circumference l of the current limiting device pi Get the maximum core width l wm ; 8) The ideal core width l wi With the maximum core width l wm For comparison: If the ideal core width l wi Less than or equal to the maximum core width l wm , then the parameter design is reasonable; if the ideal core width l wi Greater than the maximum core width l wm , then the parameter design is unreasonable and needs to be improved.

2. The method for designing parameters of a magnetically driven fault current adaptive current limiting device according to claim 1, characterized in that: The magnetic permeability of the moving iron core and the stationary iron core is one thousand times that of air, and the fault current limitation is achieved by utilizing the difference in equivalent inductance of the magnetic flux corresponding to the equivalent inductance of the current-carrying busbar when the flux contains an air gap and when the flux does not contain an air gap.

3. The method for designing parameters of a magnetic fault current adaptive current limiting device according to claim 1, characterized in that: The improvement steps in 8) are: 1) According to the ideal circumference l of the current limiting device pi , the maximum core width of the current limiting device l wm , ideal current limiting device thickness d i and the corresponding magnetic permeability u under critical magnetic field strength m , calculate the current-limiting inductance value L under the ideal circumference when the number of turns of the current-carrying busbar coil is 1 c1i , which is calculated based on: Among them: wm is the maximum core width of the current limiting device; d i is the ideal thickness of the current limiting device; u m is the magnetic permeability corresponding to the critical magnetic field intensity; l pi is the ideal circumference of the current limiting device; 2) According to the ideal current limiting inductor value L c And the current limiting inductance value L under the ideal circumference c1i , calculate the multiple n to which the ideal circumference lower current limit inductance needs to be increased, and the calculation basis is: 3) According to the multiple n to which the inductance needs to be increased, the number of turns and circumference of the current-carrying busbar coil of the current-limiting device are improved. The number of turns of the current-carrying busbar coil of the current-limiting device is changed to n, and the circumference of the current-limiting device is increased to l p =nl pi , get the final current limiting inductor value L c0 , which is calculated based on: Where: n is the number of turns of the current-carrying busbar coil; l wm is the maximum core width of the current limiting device; d i is the ideal thickness of the current limiting device; u m is the magnetic permeability corresponding to the critical magnetic field intensity; l p is the final circumference of the current limiting device; l pi is the ideal circumference of the current limiting device; L c1i is the ideal current limiting inductor value.

4. The method for designing parameters of a magnetically driven fault current adaptive current limiting device according to claim 3 is characterized in that: The number of turns n and the circumference l of the current-carrying busbar coil of the current limiting device p grow in the same proportion to keep the ferromagnetic material in an unsaturated state.

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