A fault current limiter, a fault current limiting system and a fault current limiting method

Abstract

The application discloses a kind of fault current limiter, fault current limiting system and fault current limiting method, it is related to power system fault protection technical field, including: iron core, first AC coil, second AC coil, first DC coil, second DC coil, transient component energy release circuit, the first end of first AC coil is connected with the first end of AC input system, and the second end is connected with the first end of second AC coil;First DC coil, second DC coil are connected with DC power supply;The first end of transient component energy release circuit is connected with the second end of second AC coil, and the second end is connected with the second end of AC power supply;When short-circuit fault occurs in power system, if the voltage change rate of first AC coil or second AC coil two ends exceeds preset threshold value, transient component in short-circuit current is discharged using transient component energy release circuit.The application can effectively accelerate the attenuation of transient component in short-circuit current, avoid the structure of fault current limiter to appear damage.

Description

Technical Field

[0001] This invention relates to the field of power system fault protection technology, and in particular to a fault current limiter, a fault current limiting system, and a fault current limiting method. Background Technology

[0002] Currently, with the increase in power system voltage levels and the continuous expansion of load scale, the short-circuit current level in power systems has risen sharply, even exceeding the breaking capacity of circuit breakers in some areas. The problem of excessive short-circuit current is becoming increasingly serious, posing a threat to the safe and stable operation of the power system, making the implementation of current-limiting measures in the power system imperative. Fault current limiters are a promising type of current-limiting device. They have low steady-state impedance and high transient impedance, and can automatically switch impedances, effectively limiting short-circuit current. Among them, saturated iron-core type fault current limiters are gradually gaining widespread attention due to their advantages such as good current-limiting effect, high withstand voltage, automatic triggering, and high reliability.

[0003] The AC short-circuit current is mainly composed of the steady-state component (SCSC). In previous studies on magnetic saturation fault current limiters, the transient component (SCTC) of the short-circuit current was generally ignored for ease of analysis of current-limiting capability. However, when the transient component is considered, the short-circuit current after superimposing the transient component may exceed the maximum short-circuit current that the magnetic saturation fault current limiter can restrict, which will affect the normal operation of the magnetic saturation fault current limiter. The transient component is mainly characterized by the time constant of the power system, which determines its decay rate. In some severe cases, an excessively large time constant may cause zero-point drift, damaging the structure of the magnetic saturation fault current limiter. Summary of the Invention

[0004] This invention provides a fault current limiter, a fault current limiting system, and a fault current limiting method to solve the technical problem in the related art where existing fault current limiters ignore the transient component of the short-circuit current, and the short-circuit current after superimposing the transient component may exceed the maximum short-circuit current that the fault current limiter can limit, resulting in damage to the structure of the fault current limiter.

[0005] Firstly, a fault current limiter is provided, comprising:

[0006] Iron core, wherein a permanent magnet is embedded inside the iron core;

[0007] A first AC coil and a second AC coil are wound on the iron core, wherein a first end of the first AC coil is connected to a first end of the AC input system, and a second end of the first AC coil is connected to a first end of the second AC coil.

[0008] A first DC coil and a second DC coil are wound on the iron core. The first end of the first DC coil is connected to the positive terminal of the DC power supply, the second end of the first DC coil is connected to the first end of the second DC coil, and the second end of the second DC coil is connected to the positive terminal of the DC power supply.

[0009] A transient component energy dissipation circuit, wherein the first terminal of the transient component energy dissipation circuit is connected to the second terminal of the second AC coil, and the second terminal of the transient component energy dissipation circuit is connected to the second terminal of the AC power supply;

[0010] When a short-circuit fault occurs in the power system, if the rate of change of voltage across the first AC coil or the second AC coil exceeds a preset threshold, the transient component energy discharge circuit is used to discharge the transient component in the short-circuit current.

[0011] In some embodiments, the fault current limiter further includes:

[0012] A voltage acquisition circuit is connected to the first AC coil or the second AC coil, and the voltage acquisition circuit is also connected to the transient component energy dissipation circuit.

[0013] The transient component energy dissipation circuit includes a first switching transistor, a second switching transistor, a DC blocking capacitor, and an energy dissipation resistor;

[0014] The first end of the first switch and the second switch connected in reverse parallel is connected to the second end of the second AC coil, the second end of the first switch and the second switch connected in reverse parallel is connected to the first end of the energy leakage resistor, and the second end of the energy leakage resistor is connected to the second end of the AC power supply.

[0015] The first terminal of the DC blocking capacitor is connected to the second terminal of the AC power supply, and the second terminal of the DC blocking capacitor is connected to the second terminal of the AC power supply.

[0016] When a short circuit fault occurs in the power system, the voltage acquisition circuit acquires the voltage change rate across the first AC coil or the second AC coil. If the voltage change rate across the first AC coil or the second AC coil exceeds a preset threshold, the voltage acquisition circuit controls the first switch and the second switch to turn on.

[0017] In some embodiments, the first switch and the second switch are thyristors.

[0018] In some embodiments, the DC blocking capacitor is an adjustable capacitor, and the energy dissipation resistor is an adjustable resistor.

[0019] In some embodiments, the core includes a left outer core post, a left inner core post, a middle core post, a right inner core post, and a right outer core post arranged at intervals. The upper and lower sides of the left outer core post, the left inner core post, the middle core post, the right inner core post, and the right outer core post are respectively provided with an upper transverse yoke and a lower transverse yoke. The permanent magnet is embedded in the middle of the middle core post.

[0020] The upper section of the left inner core is wound with the first AC coil, and the upper section of the right inner core is wound with the second AC coil.

[0021] The lower section of the left inner core column is wound with the first DC coil, and the lower section of the right inner core column is wound with the second DC coil.

[0022] In some embodiments, a gap is provided between the middle of the left outer core and the right outer core, and the width of the gap is less than the thickness of the permanent magnet.

[0023] In some embodiments, the permanent magnet is made of neodymium iron boron, a rare-earth permanent magnet material.

[0024] In some embodiments, the DC excitation circuit further includes a current-limiting inductor disposed between the first DC coil and the DC power supply.

[0025] Secondly, a fault current limiting system is provided, including the aforementioned fault current limiter.

[0026] Thirdly, a fault current limiting method is provided, including the following steps:

[0027] When a short-circuit fault occurs in the power system, if the voltage change rate across the first AC coil or the second AC coil exceeds a preset threshold, a transient component discharge circuit is used to discharge the transient component in the short-circuit current.

[0028] The beneficial effects of the technical solution provided by this invention include:

[0029] This invention provides a fault current limiter, a fault current limiting system, and a fault current limiting method. The fault current limiter is equipped with a transient component energy discharge circuit. When a short-circuit fault occurs in the power system, if the voltage change rate across the first AC coil or the second AC coil exceeds a preset threshold, the transient component energy discharge circuit can be used to discharge the transient component in the short-circuit current, effectively accelerating the attenuation of the transient component in the short-circuit current and preventing damage to the structure of the fault current limiter. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of a fault current limiter provided in an embodiment of the present invention;

[0032] Figure 2 This is a schematic diagram of the current flow direction of the transient component energy leakage circuit under normal and fault conditions in a power system, provided by an embodiment of the present invention.

[0033] Figure 3 A schematic diagram of the short-circuit current of a fault current limiter under different conditions is provided for an embodiment of the present invention;

[0034] Figure 4 A schematic diagram of the branch current where the DC blocking capacitor C is located in the transient component energy dissipation circuit under different RC parameters provided in the embodiments of the present invention;

[0035] Figure 5 This is a schematic diagram of the branch current where the energy discharge resistor R is located under different RC parameters in the transient component energy discharge circuit provided in the embodiments of the present invention. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] This invention provides a fault current limiter that solves the technical problem that existing fault current limiters ignore the transient component of the short-circuit current, and the short-circuit current after superimposing the transient component may exceed the maximum short-circuit current that the fault current limiter can limit, leading to structural damage to the fault current limiter.

[0038] See Figure 1 As shown, an embodiment of the present invention provides a fault current limiter, including: an iron core, a first AC coil, a second AC coil, a first DC coil, a second DC coil, and a transient component energy discharge circuit.

[0039] A permanent magnet is embedded inside the iron core. A first AC coil and a second AC coil are wound around the iron core. A first end of the first AC coil is connected to a first end of the AC input system, and a second end of the first AC coil is connected to the first end of the second AC coil. (See also...) Figure 1 As shown, specifically, the iron core includes a left outer core post, a left inner core post, a middle core post, a right inner core post, and a right outer core post arranged at intervals. The upper and lower sides of the left outer core post, left inner core post, middle core post, right inner core post, and right outer core post are respectively provided with an upper transverse yoke and a lower transverse yoke. The permanent magnet is embedded in the middle of the middle core post. The upper section of the left inner core post is wound with the first AC coil, and the upper section of the right inner core post is wound with the second AC coil. Optionally, the permanent magnet is made of neodymium iron boron, a rare-earth permanent magnet material.

[0040] The first DC coil and the second DC coil are wound on the iron core. A first end of the first DC coil is connected to the positive terminal of a DC power supply, and a second end of the first DC coil is connected to the first end of the second DC coil. The second end of the second DC coil is also connected to the positive terminal of the DC power supply. (See also...) Figure 1 As shown, specifically, the lower section of the left inner core column is wound with the first DC coil, and the lower section of the right inner core column is wound with the second DC coil. Optionally, the DC excitation circuit further includes a current-limiting inductor Lf, which is disposed between the first DC coil and the DC power supply.

[0041] The first terminal of the transient component energy dissipation circuit is connected to the second terminal of the second AC coil, and the second terminal of the transient component energy dissipation circuit is connected to the second terminal of the AC power supply. When a short-circuit fault occurs in the power system, if the voltage change rate across the first AC coil or the second AC coil exceeds a preset threshold, the transient component energy dissipation circuit is used to dissipate the transient component in the short-circuit current.

[0042] See Figure 1 As shown, the fault current limiter further includes: a voltage acquisition circuit, which is connected to the first AC coil or the second AC coil, and the voltage acquisition circuit is connected to the transient component energy discharge circuit.

[0043] The transient component energy dissipation circuit includes a voltage acquisition circuit, a first switching transistor D1, a second switching transistor D2, a DC blocking capacitor C, and an energy dissipation resistor R.

[0044] The first end of the first switch D1 and the second switch D2 connected in reverse parallel is connected to the second end of the second AC coil. The second end of the first switch D1 and the second switch D2 connected in reverse parallel is connected to the first end of the energy leakage resistor R. The second end of the energy leakage resistor R is connected to the second end of the AC power supply.

[0045] The first end of the DC blocking capacitor C is connected to the second end of the AC power supply, and the second end of the DC blocking capacitor C is connected to the second end of the AC power supply.

[0046] When a short circuit fault occurs in the power system, the voltage acquisition circuit acquires the voltage change rate across the first AC coil or the second AC coil. If the voltage change rate across the first AC coil or the second AC coil exceeds a preset threshold, the voltage acquisition circuit controls the first switch D1 and the second switch D2 to conduct.

[0047] See Figure 1 and Figure 2 As shown below, the working principle of the fault current limiter in the embodiments of the present invention will be further explained:

[0048] (1) When the power system is operating normally, the DC flux generated by the permanent magnet, the first DC coil, and the second DC coil causes the left inner core and the right inner core to be deeply saturated. At this time, the permeability of the left inner core and the right inner core is very small, the reluctance of the left inner core and the right inner core is very large, and the inductance of the first AC coil and the second AC coil is very small. Therefore, it has no impact on the normal operation of the power system. At this time, the first switch D1 and the second switch D2 are in the off state, the energy leakage resistor R is disconnected, and the current flows through the DC blocking capacitor C. At this time, the DC blocking capacitor C plays the role of series compensation, which can improve the static stability and the ultimate transmission power of the power system and increase the static stability reserve coefficient.

[0049] (2) After a short-circuit fault occurs in the power system, the short-circuit current level surges instantaneously, causing the peak value of the total short-circuit current to be much higher than the rated current of the power system. At this time, the AC magnetic flux generated by the surge in AC current is much greater than the AC magnetic flux during normal operation of the power system. In the left inner core and the right inner core, the AC and DC magnetic fluxes are in the same direction on one side and opposite directions on the other side. During a complete AC cycle of the short-circuit current, the AC and DC magnetic fluxes on one side of the left inner core and the right inner core alternately cancel each other out, while the saturation on the other side deepens. After the left inner core and the right inner core alternately desaturate, they operate in the linear region of the magnetization characteristic curve. The AC inductance increases instantaneously, causing electromagnetic coupling between the AC and DC windings on the desaturated core. The AC and DC coils are equivalent to a single-phase transformer. The current-limiting inductor Lf in the DC excitation circuit will be connected in series with the AC side, increasing the external inductance of the entire fault current limiter, which can limit the short-circuit current throughout the entire cycle. The current-limiting inductor Lf, the inductance of the first AC coil, and the inductance of the second AC coil together limit the short-circuit current. At this time, the fault short-circuit current level surges, causing a surge in the voltage across either the first or second AC coil, exhibiting a large rate of change. The voltage acquisition circuit collects the rate of change of voltage across either the first or second AC coil. If the rate of change exceeds a preset threshold, the voltage acquisition circuit controls the first switch D1 and the second switch D2 to conduct, allowing the transient component of the fault short-circuit current to flow through the energy-draining resistor R and attenuate. The transient component of the short-circuit current can be understood as a temporary direct current (DC). Since the frequency of DC current is 0, the DC blocking capacitor C is effectively disconnected for DC. The transient component of the short-circuit current flowing through the energy-draining resistor R promotes energy consumption, accelerates attenuation, and reduces the time constant of the transient component. After the fault is cleared, the left inner core and the right inner core return to magnetic saturation, the fault current limiter returns to low inductance, and the power system operates normally.

[0050] In summary, the fault current limiter in this embodiment of the invention is equipped with a transient component energy discharge circuit. When a short-circuit fault occurs in the power system, if the voltage change rate across the first AC coil or the second AC coil exceeds a preset threshold, the transient component energy discharge circuit can be used to discharge the transient component in the short-circuit current, effectively accelerating the attenuation of the transient component in the short-circuit current and preventing damage to the structure of the fault current limiter.

[0051] As an optional implementation, in one embodiment of the invention, the first and second switching transistors are thyristors. Thyristors have advantages such as small size, high efficiency, and long lifespan. In automatic control systems, they can be used as high-power driving devices to control high-power equipment with low-power controls. They are widely used in AC / DC motor speed control systems, power regulation systems, and servo systems.

[0052] As an optional implementation, in one embodiment of the invention, the DC blocking capacitor is an adjustable capacitor, and the energy dissipation resistor is an adjustable resistor.

[0053] See Figure 3 As shown, when the fault current limiter does not have a transient component discharge circuit, the short-circuit current reaches its maximum peak value at 125ms, reaching 7.65kA, with a time constant of 144.43ms. This can easily cause zero-point drift, threatening the structure of the fault current limiter. When the fault current limiter has a transient component discharge circuit, in Case 1, the short-circuit current reaches its maximum peak value at 125ms, with a time constant of 38.68ms when the short-circuit current reaches 6.91kA. In Case 2, the short-circuit current reaches its maximum peak value at 125ms, with a time constant of 52.11ms when the short-circuit current reaches 7.16kA. In Case 3, the short-circuit current reaches its maximum peak value at 125ms, with a time constant of 63.62ms when the short-circuit current reaches 7.30kA. Cases 1, 2, and 3 represent the test results for the discharge resistor R and the DC blocking capacitor C under different parameters.

[0054] See Figure 4 As shown, the branch current containing the DC blocking capacitor C in the transient component energy dissipation circuit is mainly the short-circuit current SCSC, with almost no transient component. It can be observed that in Case 1, the total current first experiences a brief surge, decreasing from a peak of 8.50 kA. After several cycles, the short-circuit current SCSC remains stable. The SCSC of the short-circuit current amplitude is approximately 4.77 kA. Cases 2 and 3 are similar to Case 1, with the peak currents decaying from 9.42 kA and 9.62 kA to 4.73 kA and 5.12 kA respectively, before stabilizing.

[0055] See Figure 5As shown, the branch current in the transient component discharge circuit containing the discharge resistor R is mainly the SCTC of the short-circuit current. In Case 1, the fault current amplitude experienced a brief increase, at which point a small portion of the SCTC remained, before it began to oscillate and decay. After several cycles of oscillation and decay, the SCTC of the fault current weakened, with the amplitude decreasing from 2.06kA to 0.60kA. The decay changes in Case 2 and Case 3 were similar to those in Case 1, with the peak current decreasing from 7.63kA and 3.72kA to 4.72kA and 3.19kA, respectively. The only difference was that the branch current amplitude in Case 2 containing the discharge resistor R was the largest, which is related to the RC parameter value, causing the SCTC to decay faster.

[0056] In summary, transient component discharge circuits can reduce the time constant of power systems. Furthermore, by adjusting the parameters of the discharge resistor R and the DC blocking capacitor C, the time constant can be further reduced, the attenuation of transient components can be accelerated, and the current limiting effect of the fault current limiter can be improved.

[0057] As an optional implementation, in one embodiment of the invention, a gap is provided in the middle of the left outer core and the right outer core, and the width of the gap is smaller than the thickness of the permanent magnet, which can reduce the eddy current loss and demagnetization risk of the permanent magnet.

[0058] This invention provides a fault current limiting system, including the aforementioned fault current limiter.

[0059] This invention provides a fault current limiting method using the fault current limiter according to any one of claims 1-8, comprising the following steps:

[0060] When a short-circuit fault occurs in the power system, if the voltage change rate across the first AC coil or the second AC coil exceeds a preset threshold, a transient component discharge circuit is used to discharge the transient component in the short-circuit current.

[0061] In the description of this invention, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0062] It should be noted that in this invention, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0063] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features of the invention herein.

Claims

1. A fault current limiter, characterized in that, include: Iron core, wherein a permanent magnet is embedded inside the iron core; A first AC coil and a second AC coil are wound on the iron core, wherein a first end of the first AC coil is connected to a first end of the AC input system, and a second end of the first AC coil is connected to a first end of the second AC coil. A first DC coil and a second DC coil are wound on the iron core. The first end of the first DC coil is connected to the positive terminal of the DC power supply, the second end of the first DC coil is connected to the first end of the second DC coil, and the second end of the second DC coil is connected to the positive terminal of the DC power supply. A transient component energy dissipation circuit, wherein the first terminal of the transient component energy dissipation circuit is connected to the second terminal of the second AC coil, and the second terminal of the transient component energy dissipation circuit is connected to the second terminal of the AC power supply; The transient component energy dissipation circuit includes a first switching transistor, a second switching transistor, a DC blocking capacitor, and an energy dissipation resistor; The first end of the first switch and the second switch connected in reverse parallel is connected to the second end of the second AC coil, the second end of the first switch and the second switch connected in reverse parallel is connected to the first end of the energy leakage resistor, and the second end of the energy leakage resistor is connected to the second end of the AC power supply. The first terminal of the DC blocking capacitor is connected to the second terminal of the AC power supply, and the second terminal of the DC blocking capacitor is connected to the second terminal of the AC power supply. When a short-circuit fault occurs in the power system, the voltage acquisition circuit collects the voltage change rate across the first AC coil or the second AC coil. If the voltage change rate across the first AC coil or the second AC coil exceeds a preset threshold, the voltage acquisition circuit controls the first and second switching transistors to conduct and discharge the transient component in the short-circuit current.

2. The fault current limiter according to claim 1, characterized in that, Also includes: A voltage acquisition circuit is provided, which is connected to the first AC coil or the second AC coil, and is also connected to the transient component energy dissipation circuit.

3. The fault current limiter according to claim 2, characterized in that: The first and second switching transistors are thyristors.

4. The fault current limiter according to claim 2, characterized in that: The DC blocking capacitor is an adjustable capacitor, and the energy dissipation resistor is an adjustable resistor.

5. The fault current limiter according to claim 1, characterized in that: The iron core includes a left outer core post, a left inner core post, a middle core post, a right inner core post, and a right outer core post arranged at intervals. The upper and lower sides of the left outer core post, the left inner core post, the middle core post, the right inner core post, and the right outer core post are respectively provided with an upper transverse yoke and a lower transverse yoke. The permanent magnet is embedded in the middle of the middle core post. The upper section of the left inner core is wound with the first AC coil, and the upper section of the right inner core is wound with the second AC coil. The lower section of the left inner core column is wound with the first DC coil, and the lower section of the right inner core column is wound with the second DC coil.

6. The fault current limiter according to claim 5, characterized in that: A gap is provided in the middle of the left outer core and the right outer core, and the width of the gap is less than the thickness of the permanent magnet.

7. The fault current limiter according to claim 1, characterized in that: The permanent magnet is made of neodymium iron boron, a rare-earth permanent magnet material.

8. The fault current limiter according to claim 1, characterized in that: The fault current limiter also includes a current limiting inductor, which is located between the first DC coil and the DC power supply.

9. A fault current limiting system, characterized in that, Includes the fault current limiter as described in any one of claims 1-8.

10. A fault current limiting method, using the fault current limiter according to any one of claims 1-8, characterized in that, Includes the following steps: When a short-circuit fault occurs in the power system, if the voltage change rate across the first AC coil or the second AC coil exceeds a preset threshold, a transient component discharge circuit is used to discharge the transient component in the short-circuit current.

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