Magnetomotive fault current adaptive current limiting device and parameter design method thereof

Abstract

An air gap exists between a movable iron core and a static iron core, in a normal state, under the counter-force effect of a spring, a magnetic circuit corresponding to equivalent inductance of a current-carrying bus contains the air gap, the inductance value is very small, and normal operation of a circuit cannot be affected; when a fault occurs, the current rises, and the electromagnetic force between the movable iron core and the static iron core is larger than the reaction force of the spring, the movable iron core moves towards the static iron core, the air gap is reduced until the movable iron core and the static iron core are completely attracted, along with the movement of the movable iron core, the air gap in a magnetic circuit corresponding to the equivalent inductance of the current-carrying bus is gradually reduced, the inductance is gradually increased, and then the effect of limiting the fault current is reflected. The invention further relates to a parameter design method of the magnetomotive fault current self-adaptive limiting device, and the perimeter, the longitudinal depth, the iron core width and the number of turns of a current-carrying bus coil of the current limiting device are provided according to current limiting requirements. The method has the advantages that the equivalent inductance can be adaptively adjusted according to fault current, and the current limiting effect is remarkable.

Description

Technical Field

[0001] The invention belongs to the technical field of electrical equipment, and in particular relates to a magnetically driven fault current adaptive current limiting device and a parameter design method thereof. Background Art

[0002] The problem of short-circuit fault current suppression in DC systems is one of the core issues in current DC system protection. DC current limiters can slow down the rise of fault current to buy time for DC protection and DC circuit breakers, reduce the breaking capacity of DC circuit breakers, and are critical to improving the fault defense capabilities of multi-terminal DC systems.

[0003] At present, the passive current limiting technology of installing dozens or hundreds of mH reactors at the converter outlet is commonly used in multi-terminal DC demonstration projects. Since the inductor also exhibits impedance in non-fault transient processes such as system power fluctuations, operating mode switching, and small disturbances, it has the disadvantages of degrading system stability, easily inducing oscillations, and reducing system dynamic performance.

[0004] The main representatives of active current limiting technology are superconducting current limiters and power electronic current limiters. Superconducting current limiters require expensive superconducting tapes and reliable liquid nitrogen cooling systems, which are difficult to maintain; power electronic current limiters require a large number of power electronic devices to be connected in series and parallel to actively achieve adaptive suppression of fault current.

[0005] Therefore, the present invention proposes a magnetic fault current adaptive current limiting device and a design method thereof. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a magnetically driven fault current adaptive current limiting device and a parameter design method thereof, which increases the equivalent inductance of the current-carrying busbar by reducing the air gap spacing between the moving iron core and the stationary iron core, thereby reflecting the effect of limiting the fault current. The device has the advantages that the equivalent inductance can be adaptively adjusted according to the fault current and the current limiting effect is significant.

[0007] The present invention solves the technical problem by the following technical solutions:

[0008] A magnetically driven fault current adaptive current limiting device comprises a stationary 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 sequence from top to bottom, and an air gap is arranged between the stationary iron core and the moving iron core.

[0009] 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;

[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) The critical magnetic field strength H in the unsaturated stage is obtained in advance based on the BH curve of the ferromagnetic material. 0 ;

[0015] 3) According to the ideal fault current value I fai and the critical magnetic field strength H 0 , calculate the ideal circumference 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 / H 0

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

[0018] H 0 is the critical magnetic field intensity in the unsaturated stage on the BH curve of ferromagnetic materials;

[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 H 0 , combined with the BH curve of the ferromagnetic material to calculate the magnetic permeability u at this time m ;

[0021] 6) According to the calculated ideal circumference of the current limiting device lpi 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:

[0022]

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

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

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

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

[0027] 7) According to the calculated ideal circumference of the current limiting device l pi Get the maximum core width l wm ;

[0028] 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.

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

[0030] 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:

[0031]

[0032] Among them: 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 mis the magnetic permeability corresponding to the critical magnetic field intensity;

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

[0036] 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:

[0037]

[0038] 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:

[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 intensity;

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

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

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

[0047] Moreover, the number of turns n and the circumference l of the current-carrying busbar coil of the current limiting device are p grow 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 toward the static iron core, and 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 circumference, longitudinal depth, core width and number of turns of the current-carrying busbar coil of the current limiting device according to the current limiting requirements. 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 significant. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0052] Figure 2 This is a diagram showing the variation of inductance with air gap spacing when a fault occurs in a line connected to the magnetically driven fault current adaptive limiting device of the present invention;

[0053] Figure 3 This is a diagram showing the effect of limiting the fault current when the magnetically driven fault current adaptive limiting device of the present invention is connected to a fault in the line. DETAILED DESCRIPTION

[0054] The present invention is further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0055] like Figure 1 As shown, a magnetically driven fault current adaptive current limiting device comprises a stationary iron core, a current-carrying busbar, a reaction spring device and a shift fork, wherein the moving iron core, the current-carrying busbar and the reaction spring device are sequentially arranged on the stationary iron core from top to bottom, and the innovation thereof lies in that an air gap is arranged between the stationary iron core and the moving iron core,

[0056] 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;

[0057] 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.

[0058] 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.

[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) The critical magnetic field strength H in the unsaturated stage is obtained in advance based on the BH curve of the ferromagnetic material. 0 ;

[0064] 3) According to the ideal fault current value I fai and the critical magnetic field strength H 0 , calculate the ideal circumference 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 / H 0

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

[0067] H 0 is the critical magnetic field intensity in the unsaturated stage on the BH curve of ferromagnetic materials;

[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) According to the critical magnetic field strength H 0 , combined with the BH curve of the ferromagnetic material to calculate the magnetic permeability u at this time m ;

[0070] 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:

[0071]

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

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

[0074] u m is the magnetic permeability corresponding to the critical magnetic field intensity;

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

[0076] 7) According to the calculated ideal circumference of the current limiting device l pi Get the maximum core width l wm ;

[0077] 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.

[0078] The steps to improve the above parameters are:

[0079] 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:

[0080]

[0081] Among them: 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 intensity;

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

[0085] 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:

[0086]

[0087] 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:

[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 intensity;

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

[0094] lpi is the ideal circumference of the current limiting device;

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

[0096] 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.

[0097] A current adaptive current limiting device and parameter design method of the present invention are simulated, and the simulation parameters are: the ideal fault current value I fai =30A, critical magnetic field strength H 0 =30A / m, from which we can get the ideal circumference of the current limiting device l p =1m, ideal current limiting device thickness d i =1m, ideal current limiting inductance value L c =4mH, the corresponding magnetic permeability under critical magnetic field strength is u=0.0273H / m, from which we can get the ideal core width l wi =0.18m, and according to the constraints such as the core circumference, the maximum core width l is obtained wm =0.04m.

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

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

[0100] The present invention discloses a magnetically-dynamic fault current adaptive current limiting device and a parameter design method thereof, which increases the equivalent inductance of the current-carrying busbar by reducing the air gap distance between the moving iron core and the stationary iron core, thereby achieving the effect of limiting the fault current. The device has the advantages that the equivalent inductance can be adaptively adjusted according to the fault current and the current limiting effect is remarkable.

[0101] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate 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 contents disclosed in the embodiments and drawings.

Claims

1. A magnetically driven fault current adaptive current limiting device, comprising a stationary 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 sequence from top to bottom, characterized in that: An air gap is provided between the static 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.

2. The magnetically driven fault current adaptive current limiting device according to claim 1 is 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. A method for designing parameters of a magnetically driven fault current adaptive current limiting device, characterized in that: Applied to the magnetic fault current adaptive current limiting device according to any one of claims 1 to 2, 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.

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 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: Where: 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 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.

5. The method for designing parameters of a magnetic fault current adaptive current limiting device according to claim 4, 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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