Mechanical direct-current circuit breaker based on graded current injection and on-off method of mechanical direct-current circuit breaker

Abstract

According to the mechanical direct-current circuit breaker based on graded current injection and the breaking method thereof, in the circuit breaker, a switch branch comprises a mechanical switch K and a mutual inductor primary side Lp which are connected in series so as to bear path current in a bidirectional mode during normal operation and achieve breaking of fault current under the fault condition; the injection branch is connected to the two sides of a mechanical switch K of the switch branch in parallel so as to achieve current zero-crossing arc extinguishing of the mechanical switch K through graded injection of reverse current, and the injection branch comprises a multi-stage reverse current injection module, a mutual inductor secondary side Ls and an injection capacitor discharge loop. The multi-stage reverse current injection module comprises a multi-stage injection capacitor, a line stray inductor and a multi-stage fling-cut switch, the injection capacitor discharge loop comprises a discharge resistor R0 and a discharge switch K0, the energy consumption branch is connected to the two sides of the mechanical switch K in parallel, and energy in the loop after switching-off is dissipated through a piezoresistor; the control system detects the fault current rise rate and controls the number of input injection capacitors according to the fault current rise rate so as to realize on-off under different current levels.

Description

Technical Field

[0001] This invention relates to the field of circuit breaker technology, and in particular to a mechanical DC circuit breaker based on graded current injection. Background Art

[0002] High-voltage direct current (HVDC) transmission and medium- and low-voltage direct current (DC) distribution have developed rapidly due to their advantages. DC circuit breakers, as important protective power equipment in DC power systems, have received widespread attention in recent years. In traditional injection-type DC circuit breaker topologies, due to the fixed nature of the injection circuit capacitance and charging voltage, although they perform well when interrupting large currents, they often fail to interrupt under low-current interruption conditions because the injected current is too large, leading to circuit breakdown and interruption failure.

[0003] The information disclosed in the background section is only intended to enhance the understanding of the background of the present invention, and therefore may contain information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0004] To address the shortcomings or defects of the existing technology, a mechanical DC circuit breaker based on graded current injection and its interruption method are provided. Different numbers of injection capacitors are activated according to the rising rate of the detected fault current to achieve reliable interruption across the entire current range.

[0005] The objective of this invention is achieved through the following technical solutions.

[0006] A mechanical DC circuit breaker based on graded current injection includes, The switch branch includes a mechanical switch K connected in series and a current transformer primary side L. p It can carry bidirectional path current during normal operation and achieve fault current cutoff in case of a fault. An injection branch, connected in parallel across the mechanical switch K in the switch branch, enables the mechanical switch K to extinguish its arc by injecting reverse current in stages, achieving zero-crossing current injection. The injection branch includes a multi-stage reverse current injection module and a transformer secondary side L. s The multi-stage reverse current injection module includes multi-stage injection capacitors, stray inductors, and multi-stage switching devices. The injection capacitor discharge circuit includes a discharge resistor R0 and a discharge switch K0. The energy-consuming branch is connected in parallel across the mechanical switch K, and dissipates the energy in the circuit after the switch is broken through the varistor. The control system detects the rate of rise of the fault current and controls the number of injection capacitors to be put into operation according to its magnitude, so as to achieve the interruption at different current levels.

[0007] In the mechanical DC circuit breaker based on graded current injection, the mechanical switch K includes an arc-extinguishing chamber and a fast-acting mechanism. The arc-extinguishing chamber is selected from one of an air arc-extinguishing grid, a vacuum arc-extinguishing chamber, or an SF6 arc-extinguishing chamber.

[0008] In the mechanical DC circuit breaker based on graded current injection, the fast-acting mechanism is a repulsive mechanism or a permanent magnet mechanism, and the mechanical switch K is driven to open and close using a linear or linkage transmission method.

[0009] In the mechanical DC circuit breaker based on graded current injection, the energy-consuming branch includes a surge arrester (MOV) for absorbing residual energy of the system during the breaking process.

[0010] In the mechanical DC circuit breaker based on graded current injection, the current transformer is a coupled coil structure, wherein the primary side Lp is connected in series with the switching branch as the primary side of the coupled coil, and the secondary side Ls is used as the secondary side of the coupled coil for inductive charging of the injected capacitor.

[0011] In the mechanical DC circuit breaker based on graded current injection, the switching device includes a mechanical switch, a contactor, or a bidirectional power electronic device.

[0012] In the mechanical DC circuit breaker based on graded current injection, when the DC system is working normally, the switching branch carries a forward or reverse working current.

[0013] Breaking methods for mechanical DC circuit breakers based on graded current injection include: When a short circuit fault occurs, the control system detects an increase in current and sends a trip signal to the mechanical switch K. Based on the rate of rise of the fault current, the control system determines the number of injection capacitors to be put into operation and closes the corresponding switching switch to form a reverse current injection loop. Reverse current injection causes the current in mechanical switch K to cross zero, extinguishing the arc and forming an insulation break. The fault current is transferred to the series-connected injection capacitor for charging; When the injected capacitor voltage reaches the surge arrester's conduction voltage, the fault current is transferred to the energy-consuming branch to complete the interruption. After the interruption is completed, the control system controls the discharge switch K0 to close, and the injected capacitor is discharged and reset through the discharge resistor R0.

[0014] In the method described, the control system dynamically adjusts the number of injected capacitors connected by detecting the rise rate of the fault current, thereby adapting to the full range of interruption requirements.

[0015] The method described includes graded control of the injected capacitor: only a portion of the capacitor is injected during low-current faults, while all capacitors are injected during high-current faults, in order to avoid break-through due to excessive injected current.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention does not require pre-charging of the injection capacitor, and the provided interruption method can adjust the injection current amplitude to complete reliable bidirectional interruption for different levels of fault current, thus solving the problem of breakdown of the interruption point of traditional injection circuit breakers under low current.

[0017] The description provided is merely an overview of the technical solution of this invention. In order to make the technical means of this invention clearer and more understandable, so that those skilled in the art can implement it according to the contents of the specification, and to make the described and other objects, features and advantages of this invention more obvious and understandable, specific embodiments of this invention are described below. Attached Figure Description

[0018] Various other advantages and benefits of the present invention will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. Furthermore, the same reference numerals denote the same parts throughout the drawings.

[0019] In the attached diagram: Figure 1 This is a schematic diagram of a mechanical DC circuit breaker based on graded current injection and its interruption method according to the present invention. Figure 2 This is a schematic diagram of the current flow path during normal operation. Figure 3 This is a schematic diagram showing the current flow path when a short-circuit fault occurs. Figure 4 This is a schematic diagram of the current flow path during the current injection process when a small current is interrupted. Figure 5 This is a schematic diagram of the current flow path during the current injection process when a large current is interrupted. Figure 6 A schematic diagram showing the path through which fault current is transferred to the injected branch current. Figure 7 A schematic diagram showing the path through which fault current flows to the energy-consuming branch; Figure 8 This is a schematic diagram of the current flow path during the discharge process of the injected capacitor after the circuit is switched off.

[0020] The present invention will be further explained below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0021] Specific embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While specific embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0022] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions are preferred embodiments for carrying out the invention; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of the invention. The scope of protection of this invention is determined by the appended claims.

[0023] To facilitate understanding of the embodiments of the present invention, the following will provide further explanation and description with reference to the accompanying drawings and several specific embodiments, and the accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0024] To better understand, such as Figures 1 to 8 As shown, a mechanical DC circuit breaker based on graded current injection includes, The switch branch includes a mechanical switch K connected in series and a current transformer primary side L. p It can carry bidirectional path current during normal operation and achieve fault current cutoff in case of a fault. An injection branch, connected in parallel across the mechanical switch K in the switch branch, enables the mechanical switch K to extinguish its arc by injecting reverse current in stages, achieving zero-crossing current injection. The injection branch includes a multi-stage reverse current injection module and a transformer secondary side L. s The multi-stage reverse current injection module includes multi-stage injection capacitors, stray inductors, and multi-stage switching devices. The injection capacitor discharge circuit includes a discharge resistor R0 and a discharge switch K0. The energy-consuming branch is connected in parallel across the mechanical switch K, and dissipates the energy in the circuit after the switch is broken through the varistor. The control system detects the rate of rise of the fault current and controls the number of injection capacitors to be put into operation according to its magnitude, so as to achieve the interruption at different current levels.

[0025] In a preferred embodiment of the mechanical DC circuit breaker based on graded current injection, the mechanical switch K includes an arc-extinguishing chamber and a fast-acting mechanism, wherein the arc-extinguishing chamber is selected from one of an air arc-extinguishing grid, a vacuum arc-extinguishing chamber, or an SF6 arc-extinguishing chamber.

[0026] In a preferred embodiment of the mechanical DC circuit breaker based on graded current injection, the fast-acting mechanism is a repulsive mechanism or a permanent magnet mechanism, and the mechanical switch K is driven to open and close using a linear or linkage transmission method.

[0027] In a preferred embodiment of the mechanical DC circuit breaker based on graded current injection, the energy-dissipating branch includes a surge arrester (MOV) for absorbing residual energy of the system during the breaking process.

[0028] In a preferred embodiment of the mechanical DC circuit breaker based on graded current injection, the transformer is a coupled coil structure, wherein the primary side Lp is connected in series with the primary winding of the coupled coil, and the secondary side Ls is used to inductively charge the injected capacitor.

[0029] In a preferred embodiment of the mechanical DC circuit breaker based on graded current injection, the switching switch includes a mechanical switch, a contactor, or a bidirectional power electronic device.

[0030] In a preferred embodiment of the mechanical DC circuit breaker based on graded current injection, when the DC system is operating normally, a forward or reverse working current flows through the switch branch.

[0031] Breaking methods for mechanical DC circuit breakers based on graded current injection include: When a short circuit fault occurs, the control system detects an increase in current and sends a trip signal to the mechanical switch K. Based on the rate of rise of the fault current, the control system determines the number of injection capacitors to be put into operation and closes the corresponding switching switch to form a reverse current injection loop. Reverse current injection causes the current in mechanical switch K to cross zero, extinguishing the arc and forming an insulation break. The fault current is transferred to the series-connected injection capacitor for charging; When the injected capacitor voltage reaches the surge arrester's conduction voltage, the fault current is transferred to the energy-consuming branch to complete the interruption. After the interruption is completed, the control system controls the discharge switch K0 to close, and the injected capacitor is discharged and reset through the discharge resistor R0.

[0032] In a preferred embodiment of the method, the control system dynamically adjusts the number of injected capacitors connected by detecting the rise rate of the fault current, thereby adapting to the full range of interruption requirements.

[0033] In a preferred embodiment of the method, the graded control of the injected capacitor includes: only a portion of the capacitor is engaged under low-current faults, while all capacitors are engaged under high-current faults, in order to avoid break-through due to excessive injected current.

[0034] In one embodiment, a mechanical DC circuit breaker based on graded current injection and its interruption method specifically include the following steps. Step a1: When the DC system current flows from top to bottom and a short-circuit fault occurs in the DC system, the rapidly rising short-circuit current flows through the current transformer L. p -L s Injecting capacitor C1-C n In parallel charging, after the system detects the short-circuit current, it sends an action signal to the mechanical switch K, and the mechanical switch K opens. Step a2: The control system detects the rate of rise of the fault current, determines the number of injection capacitors to be activated, and sends a signal to switch K. 01 , K 12 , K 23 ...K (n-1)n and K n2 A closing signal is sent, forming mechanical switch K and stray inductance L1-L in the circuit. n Injection capacitors C1-C n The directional current injection circuit is formed to inject reverse current into the switch branch, causing the current of mechanical switch K to cross zero and the arc to be extinguished, thus forming an insulation break. Step a3: After the current in mechanical switch K crosses zero, the fault current flows into the series-connected injection capacitors C1-C1. n Charge; Step a4, when the series-connected injection capacitors C1-C n Once the voltage on the surge arrester reaches the conduction voltage of the surge arrester in the energy-consuming branch, the surge arrester resistance drops rapidly, the fault current is transferred to the energy-consuming branch, and the interruption is completed. Step a5: After the switching is completed, the control system sends a closing signal to the discharge switch K0 to discharge the injected capacitor through the resistor R0.

[0035] A mechanical DC circuit breaker based on graded current injection and its interruption method specifically include the following steps: Step b1: When the DC system current direction is from bottom to top and a short-circuit fault occurs in the DC system, the rapidly rising short-circuit current flows through the current transformer L. p -L s Injecting capacitor C1-C n In parallel charging, after the system detects the short-circuit current, it sends an action signal to the mechanical switch K, and the mechanical switch K opens. Step b2: The control system detects the rate of rise of the fault current, determines the number of injection capacitors to be activated, and sends a signal to switch K. 02 , K 12 , K 23 ...K (n-1)n and K n2 A closing signal is sent, forming mechanical switch K and stray inductance L1-L in the circuit. n Injection capacitors C1-C n The directional current injection circuit is formed to inject reverse current into the switch branch, causing the current of mechanical switch K to cross zero and the arc to be extinguished, thus forming an insulation break. Step b3: After the current in mechanical switch K crosses zero, the fault current flows into the series-connected injection capacitors C1-C. n Charge; Step b4, when the series-connected injection capacitors C1-C n Once the voltage on the surge arrester reaches the conduction voltage of the surge arrester in the energy-consuming branch, the surge arrester resistance drops rapidly, the fault current is transferred to the energy-consuming branch, and the interruption is completed. Step b5: After the switching is completed, the control system sends a closing signal to the discharge switch K0 to discharge the injected capacitor through the resistor R0.

[0036] In one embodiment, a mechanical DC circuit breaker based on graded current injection includes; The switching branch, which carries bidirectional current during normal operation and cuts off fault current in case of a fault, includes a mechanical switch K connected in series and a current transformer primary side L. p ; An injection branch, connected in parallel across the mechanical switch K in the switch branch, extinguishes the arc at zero current crossing of the mechanical switch K by injecting reverse current in stages. It includes a multi-stage reverse current injection module and a transformer secondary side L... s The injection capacitor discharge circuit, the multi-stage reverse current injection module includes multi-stage injection capacitors (C1-C1). n Stray inductance of the line (L1-L) n ), multi-stage switching (K) 11 -K nn The injected capacitor discharge circuit includes a discharge resistor R0 and a discharge switch K0; The energy-dissipating branch is connected in parallel across the mechanical switch K of the switching branch, and dissipates the energy in the circuit after the circuit is turned off through the varistor. The control system controls each switch by monitoring the circuit current.

[0037] This invention achieves adaptive control of fault currents of different levels through multi-stage selectively energized injection capacitors and corresponding switching switches. It dynamically adjusts the injection current based on the detected fault current rise rate; avoids breakdown due to excessive injection current during low-current interruption; provides sufficient reverse current for reliable zero-crossing during high-current interruption; and achieves stable interruption across the entire current range, improving system reliability.

[0038] The coupling structure between the primary side Lp and secondary side Ls of the instrument transformer utilizes the magnetic field generated by the main circuit current on the primary side of the transformer to induce a voltage on the secondary side, charging the injection capacitor. Pre-charging of the injection capacitor can be completed without an external power supply; adaptive charging is achieved, independent of the direction of the main circuit current; improving system response speed and energy efficiency. The control system selectively engages the injection capacitor based on the fault current rise rate. By monitoring the rise rate of the short-circuit current (di / dt) in real time, the severity of the fault is determined, and the number of injection capacitors to be engaged is decided accordingly. This avoids a "one-size-fits-all" approach to large current injection, improving the success rate of small current interruption. Dynamic optimization of the injection strategy adapts to various operating conditions; improving the overall intelligence and adaptive capability of the circuit breaker. The mechanical switch K is equipped with a fast-acting mechanism and an arc-extinguishing chamber. It employs a fast-opening mechanism such as repulsion or permanent magnet combined with a high-efficiency arc-extinguishing device (such as a vacuum arc-extinguishing chamber or SF6 arc-extinguishing chamber) to ensure rapid interruption of the main circuit. This shortens fault response time, improves circuit breaker operating speed, enhances arc-extinguishing capability, reduces the probability of arc reignition, and improves the circuit breaker's breaking capacity and service life. The energy-dissipating branch (MOV surge arrester) is used to absorb residual energy. After the fault current is transferred, the MOV absorbs the residual energy in the system to prevent damage to the equipment due to excessive voltage. It effectively suppresses the recovery voltage at the break point; prevents re-breakdown caused by energy accumulation; and improves the safety and stability of the entire circuit breaker system. The discharge circuit (R0 + K0) is used for capacitor reset after interruption. After each interruption, the residual charge injected into the capacitor is released through the discharge resistor R0 for reuse. This avoids residual capacitor voltage affecting the next operation, improves the reusability of the circuit breaker, extends capacitor life, and enhances system reliability. The bidirectional current-carrying design and bidirectional injection paths support both forward and reverse operating currents; when faults occur in different current directions, an effective reverse injection circuit can be formed, suitable for bidirectional current scenarios that may occur in DC systems; improves the adaptability of the circuit breaker in complex operating environments; and expands its application range, especially suitable for multi-terminal DC systems.

[0039] The basic principles of this application have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in this application are merely examples and not limitations, and should not be considered as essential features of each embodiment of this application. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the application to the necessity of employing the aforementioned specific details for implementation.

[0040] The above description has been given for purposes of illustration and description. Furthermore, this description is not intended to limit the embodiments of this application to the forms disclosed herein. Although numerous exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations thereof.

Claims

1. A mechanical DC circuit breaker based on graded current injection, characterized in that, It includes, The switch branch includes a mechanical switch K connected in series and a current transformer primary side L. p It can carry bidirectional path current during normal operation and achieve fault current cutoff in case of a fault. The injection branch, connected in parallel across the mechanical switch K in the switch branch, enables the mechanical switch K to extinguish its arc by injecting reverse current in stages to achieve zero-crossing of the current in the mechanical switch K. The injection branch includes a multi-stage reverse current injection module and a transformer secondary side L. s The multi-stage reverse current injection module includes multi-stage injection capacitors, stray inductors, and multi-stage switching devices. The injection capacitor discharge circuit includes a discharge resistor R0 and a discharge switch K0. The energy-consuming branch is connected in parallel across the mechanical switch K, and dissipates the energy in the circuit after the switch is broken through the varistor. The control system detects the rate of rise of the fault current and controls the number of injection capacitors to be put into operation according to its magnitude, so as to achieve the interruption at different current levels.

2. The mechanical DC circuit breaker based on graded current injection as described in claim 1, characterized in that, Preferably, the mechanical switch K includes an arc-extinguishing chamber and a rapid-action mechanism, wherein the arc-extinguishing chamber is selected from one of an air arc-extinguishing grid, a vacuum arc-extinguishing chamber, or an SF6 arc-extinguishing chamber.

3. The mechanical DC circuit breaker based on graded current injection as described in claim 2, characterized in that, The rapid action mechanism is a repulsive force mechanism or a permanent magnet mechanism, and it uses a linear or linkage transmission method to drive the mechanical switch K to open and close.

4. The mechanical DC circuit breaker based on graded current injection as described in claim 1, characterized in that, The energy-dissipating branch includes a surge arrester (MOV) for absorbing residual energy of the system during the interruption process.

5. The mechanical DC circuit breaker based on graded current injection as described in claim 1, characterized in that, The current transformer has a coupled coil structure, in which the primary side Lp is connected in series with the switching branch as the primary winding of the coupled coil, and the secondary side Ls is used as the secondary winding of the coupled coil for inductive charging of the injected capacitor.

6. The mechanical DC circuit breaker based on graded current injection as described in claim 1, characterized in that, The switching device includes a mechanical switch, a contactor, or a bidirectional power electronic device.

7. The mechanical DC circuit breaker based on graded current injection as described in claim 1, characterized in that, When the DC system is operating normally, the switch branch carries either a forward or reverse working current.

8. The breaking method of a mechanical DC circuit breaker based on graded current injection as described in any one of claims 1-7, characterized in that, It includes: When a short circuit fault occurs, the control system detects an increase in current and sends a trip signal to the mechanical switch K. Based on the rate of rise of the fault current, the control system determines the number of injection capacitors to be put into operation and closes the corresponding switching switch to form a reverse current injection loop. Reverse current injection causes the current in mechanical switch K to cross zero, extinguishing the arc and forming an insulation break. The fault current is transferred to the series-connected injection capacitor for charging; When the injected capacitor voltage reaches the surge arrester's conduction voltage, the fault current is transferred to the energy-consuming branch to complete the interruption. After the interruption is completed, the control system controls the discharge switch K0 to close, and the injected capacitor is discharged and reset through the discharge resistor R0.

9. The method as described in claim 8, characterized in that, The control system dynamically adjusts the number of injected capacitors connected by detecting the rise rate of the fault current, thereby adapting to the full range of interruption requirements.

10. The method according to claim 8, characterized in that, The graded control of the injected capacitor includes: only a portion of the capacitor is connected under low current faults, while all capacitors are connected under high current faults, in order to avoid the break-through caused by excessive injected current.

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