Direct-current circuit breaker with current smooth zero passage

Abstract

The invention discloses a current smooth zero-crossing DC circuit breaker, which comprises a main branch, a commutation branch and an energy absorption branch, and is characterized in that the main branch is provided with a first switch; the commutation branch comprises a first commutation capacitor, a commutation resistor, a second switch, a commutation inductor and a second commutation capacitor; a lightning arrester is arranged on the energy absorption branch; the first commutation capacitor is connected in parallel with the commutation resistor; the lightning arrester is connected in parallel with the second commutation capacitor; the main branch is connected in parallel with the commutation branch. By using the method, staged commutation can be realized, the first-stage main loop current is rapidly reduced, the second-stage main loop current is slowly reduced for zero crossing, rapid current commutation can be ensured, the reduction rate of zero crossing point current is reduced, and the on-off reliability of the DC circuit breaker is improved. The device can be widely applied to the technical field of power equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of power equipment, and in particular to a DC circuit breaker with smooth current zero crossing. Background Art

[0002] DC transmission is an emerging method of power transmission. Compared with AC transmission, it has many advantages such as large transmission capacity, low power loss, long transmission distance, and no synchronization problems. It is more suitable for new energy consumption and long-distance power transmission.

[0003] However, fault handling in DC grids is a key challenge, especially for DC circuit breakers, whose design and performance directly impact the stability and safety of the grid. As crucial control and protection devices in DC grids, DC circuit breakers perform the crucial role of conducting normal current and interrupting fault current, ensuring the stable operation of DC grids.

[0004] Due to the rapid rise rate of fault current in DC grids, DC circuit breakers must operate quickly to clear the fault. Traditional mechanical DC circuit breakers use a commutation branch consisting of pre-charged capacitors and inductors to inject a high-frequency reverse current into the main circuit, creating an artificial zero-crossing point to transfer and interrupt the fault current. This high-frequency reverse current, superimposed on the fault current, results in a high rate of change at the zero-crossing point, which can easily lead to arc reignition, resulting in current transfer failure and, consequently, current interruption failure, adversely affecting the safe and stable operation of the grid and its equipment. Summary of the Invention

[0005] In view of this, in order to solve the technical problem that the existing DC circuit breaker is prone to arc reignition due to the high current change rate at the current zero crossing, and thus has the problem of current interruption failure, the present invention proposes a DC circuit breaker with smooth current zero crossing, including a main branch, a commutation branch and an energy absorption branch, wherein:

[0006] A switch is provided on the main branch as the first switch, which is used to carry current during normal operation and quickly disconnect when a fault occurs; the disconnection speed of the fast mechanical switch directly affects the response time and breaking performance of the circuit breaker.

[0007] The commutation branch includes a first commutation capacitor, a commutation resistor, a second switch, a commutation inductor, and a second commutation capacitor. The first commutation capacitor is connected in parallel with the commutation resistor to provide reverse current in the event of a fault and create an artificial zero crossing. The commutation inductor is used to limit the current change rate and smooth the current zero crossing process. The second commutation capacitor is connected in parallel with the energy absorption branch to store and release energy and assist in current transfer.

[0008] A lightning arrester is installed on the energy absorption branch to absorb the overvoltage energy generated during the fault current interruption process and protect the circuit breaker and other equipment.

[0009] Based on the above structure, the working principle of the DC circuit breaker is as follows:

[0010] When working normally:

[0011] The first switch is closed and the second switch is open, the main circuit carries normal current, and the commutation branch and the energy absorption branch do not work.

[0012] When a fault occurs:

[0013] Fault detection and rapid mechanical switch opening: The circuit breaker receives the command and the first switch begins to open; an arc is generated between the contacts of the first switch, which burns and begins to lengthen.

[0014] The commutation branch starts operating: After the first switch opens, after a delay (to ensure the contacts reach a sufficient opening distance), the second switch closes, and the commutation branch starts operating. The pre-charged second commutation capacitor begins to discharge. During the discharge process, the first commutation capacitor is charged, and the voltage across it gradually increases. The reverse current generated by the commutation branch is superimposed on the fault current in the main circuit, and the current flowing through the first switch gradually decreases.

[0015] Smooth current zero crossing: Due to the conduction of the commutation resistor, the current rise rate of the commutation branch is slowed down, so that the current superimposed on the commutation current and the fault current on the first switch maintains a small decrease rate before the zero crossing point, thereby achieving smooth current zero crossing.

[0016] Arc extinction and fault current transfer: When the current in the main circuit passes through zero, the arc between the first switch contacts is extinguished and the fault current is successfully transferred to the commutation branch;

[0017] The energy-absorbing branch absorbs the remaining energy: the arrester absorbs the remaining energy, the fault current gradually decreases to zero, and the fault interruption process is completed.

[0018] Based on the above solution, the present invention provides a DC circuit breaker with smooth current zero crossing. By providing a first commutation capacitor C1 and a varistor VDR connected in parallel therewith, as well as a pre-charged second commutation capacitor C2 in the commutation circuit, the commutation current can rise rapidly, and the rise slows down when approaching the fault current amplitude. Ultimately, a smooth current zero crossing is generated by superimposing it on the fault current, limiting the current drop rate to within the breaking capacity of the fast mechanical switch S1, and avoiding the problem of arc reignition caused by the rapid current zero crossing. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a circuit topology diagram of a DC circuit breaker with smooth current zero crossing according to the present invention;

[0020] Figure 2 This is a schematic diagram of the normal current flow operation of a DC circuit breaker provided by an embodiment of the present invention;

[0021] Figure 3 This is a schematic diagram of the first stage of commutation operation of a DC circuit breaker provided by an embodiment of the present invention;

[0022] Figure 4 This is a schematic diagram of the second stage operation of the DC circuit breaker commutation according to an embodiment of the present invention;

[0023] Figure 5 This is a schematic diagram of the capacitor charging operation of a DC circuit breaker provided by an embodiment of the present invention;

[0024] Figure 6 This is a schematic diagram of the conduction operation of a DC circuit breaker lightning arrester provided by an embodiment of the present invention;

[0025] Figure 7 This is a schematic diagram of a fault current waveform when a DC circuit breaker is interrupted, provided by an embodiment of the present invention;

[0026] Reference numerals: S1, first switch; C1, first commutation capacitor; VDR, commutation resistor; S2, second switch; L, commutation inductor; C2, second commutation capacitor; SA, lightning arrester. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0028] It should be noted that, for ease of description, only the parts related to the invention are shown in the drawings. In the absence of conflict, the embodiments and features in the embodiments of this application can be combined with each other.

[0029] As used in this application and the claims, unless the context clearly indicates an exception, the terms "a," "an," "an," and / or "the" are not intended to refer to the singular and may include the plural, unless the context clearly indicates otherwise. Generally speaking, the terms "comprises" and "include" only indicate the inclusion of the steps and elements specifically identified, and these steps and elements do not constitute an exclusive list. A method or apparatus may also include other steps or elements. The phrase "comprises a..." does not preclude the presence of additional identical elements in the process, method, product, or apparatus that includes the elements.

[0030] In the description of the embodiments of this application, "plurality" refers to two or more than two. The terms "first" and "second" below are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, features specified as "first" or "second" may explicitly or implicitly include one or more of the features.

[0031] In addition, flow charts are used in this application to illustrate the operations performed by the system according to the embodiments of the present application. It should be understood that the preceding or following operations are not necessarily performed in exact order. Instead, the steps may be processed in reverse order or simultaneously. Furthermore, other operations may be added to these processes, or one or more operations may be removed from these processes.

[0032] Reference Figure 1 , which is a schematic structural diagram of an optional example of a DC circuit breaker with current zero-crossing smoothing proposed by the present invention. This method can be applied to computer equipment. The DC circuit breaker proposed in this embodiment may include but is not limited to the following structure:

[0033] The overall structure consists of a main branch, a commutation branch and an energy absorption branch.

[0034] The main branch includes a first switch S1 connected in series; the commutation branch includes a first commutation capacitor C1, a commutation inductor L, a second commutation capacitor C2, a commutation resistor VDR and a second switch S2, wherein the first commutation capacitor C1 is connected in parallel with the commutation resistor VDR; the energy absorption branch includes a lightning arrester SA; the main branch is connected in parallel with the commutation branch, and the energy absorption branch is connected in parallel with the second commutation capacitor C2 of the commutation branch.

[0035] The capacitance of the first commutation capacitor C1 is smaller than that of the second commutation capacitor C2 and the first commutation capacitor C1 is not pre-charged, the second commutation capacitor C2 is a pre-charged capacitor, the first commutation capacitor C1 has a discharge circuit connected in parallel with it, and the second commutation capacitor C2 has a charge and discharge circuit connected in parallel with it.

[0036] The commutation resistor VDR is a varistor.

[0037] The first switch S1 on the main circuit is a fast mechanical switch, specifically a vacuum switch, and its driving mechanism can be a fast repulsive mechanism, a permanent magnet operating mechanism, a spring operating mechanism, and a motor operating mechanism.

[0038] The second switch S2 is a discharge switch, which may specifically be a series-parallel combination of the following power electronic devices, including IGBT, IGCT, GTO, thyristor and diode.

[0039] The commutation resistor VDR may specifically be a zinc oxide varistor, a silicon carbide varistor, a titanium oxide varistor, a silicon germanium varistor, or a barium titanate varistor.

[0040] Based on the above structure, the working process of the present invention is as follows:

[0041] like Figure 2 As shown, when the system is flowing normally, the first switch S1 of the main circuit is closed, the second switch S2 of the commutation branch is opened, and the system current flows through the main circuit.

[0042] like Figure 3 As shown in the figure, when a short circuit fault occurs in the system, after the circuit breaker receives the action command, the first switch S1 opens and an arc burns between the contacts; after a specified delay, the contacts reach a sufficient opening distance, the second switch S2 of the commutation branch closes, and the pre-charged second commutation capacitor C2 discharges through the circuit in the direction of second commutation capacitor C2-commutation inductor L-second switch S2-first commutation capacitor C1-first switch S1. The first commutation capacitor C1 is charged, and the voltage at both ends gradually increases. The reverse current generated by the commutation branch is superimposed on the fault current of the main circuit, and the current flowing through the first switch S1 gradually decreases.

[0043] like Figure 4 As shown, the voltage on the first commutation capacitor C1 continues to rise to the operating voltage of the varistor VDR. The current in the commutation branch stops charging the first commutation capacitor C1, and the discharge loop of the commutation branch shifts to C2-L-S2-VDR-S1. The rise of the commutation current generated by the commutation branch slows down. This ensures that the current flowing through the first switch S1, which is the superposition of the commutation current and the fault current, maintains a low rate of decrease before the zero crossing, resulting in a smooth current zero crossing.

[0044] like Figure 5 As shown in the figure, after the current in the main circuit passes through zero, the arc is extinguished, the fault current is transferred to the commutation branch, and the voltage on the second commutation capacitor C2 gradually increases.

[0045] like Figure 6 As shown, the second commutation capacitor C2 reaches the operating voltage of the lightning arrester SA connected in parallel therewith, and the fault current is transferred to the energy absorption branch and gradually decreases to zero.

[0046] Figure 7 This is a schematic diagram of the fault current waveform when the DC circuit breaker arrester interrupts the fault according to an embodiment of the present invention. The figure shows the currents in the DC circuit breaker main circuit, the commutation branch, and the energy absorption branch. The main circuit current includes two stages during the decreasing process: the rapid decrease stage corresponds to the first commutation stage, and the slow decrease stage before zero crossing corresponds to the second commutation stage.

[0047] The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the embodiments. Those skilled in the art can make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A DC circuit breaker with smooth current zero crossing, comprising a main branch, a commutation branch, and an energy absorption branch, characterized in that: The main branch is provided with a first switch; The commutation branch includes a first commutation capacitor, a commutation resistor, a second switch, a commutation inductor and a second commutation capacitor; A lightning arrester is provided on the energy absorbing branch; The first end of the first switch, the first end of the first commutation capacitor and the first end of the commutation resistor are connected, the second end of the first commutation capacitor, the second end of the commutation resistor and the first end of the second switch are connected, the first commutation capacitor, the second switch, the commutation inductor and the second commutation capacitor are connected in sequence, the first end of the second commutation capacitor, the second end of the commutation inductor and the first end of the lightning arrester are connected, and the second end of the first switch, the second end of the second commutation capacitor and the second end of the lightning arrester are connected.

2. A DC circuit breaker with current smoothing zero crossing according to claim 1, characterized in that: The capacitance of the first commutation capacitor is smaller than that of the second commutation capacitor. The first commutation capacitor is not precharged, and the second commutation capacitor is precharged.

3. A DC circuit breaker with current smoothing zero crossing according to any one of claims 1-2, characterized in that: The first switch is a vacuum switch.

4. A DC circuit breaker with current smoothing zero crossing according to claim 3, characterized in that: The driving mechanism of the first switch includes but is not limited to a fast repulsive mechanism, a permanent magnet operating mechanism, a spring operating mechanism and a motor operating mechanism.

5. A DC circuit breaker with current smoothing zero crossing according to any one of claims 1-2, characterized in that: The second switch includes an IGBT, an IGCT, a GTO, a thyristor and a diode.

6. A DC circuit breaker with current smoothing zero crossing according to any one of claims 1-2, characterized in that: The varistors include, but are not limited to, zinc oxide varistors, silicon carbide varistors, titanium oxide varistors, silicon germanium varistors, and barium titanate varistors.

7. A DC circuit breaker with current smoothing zero crossing according to any one of claims 1-2, characterized in that: Here's how it works: When the system is flowing normally, the first switch is closed, the second switch is opened, and the system current flows through the main circuit; When a short circuit fault occurs in the system, the first switch opens and an arc burns between the contacts. After a preset time delay, the contacts reach the determined opening distance, the second switch closes, the second commutation capacitor discharges, and the first commutation capacitor charges. The voltage across the first commutation capacitor gradually increases, the reverse current generated by the commutation branch is superimposed on the fault current in the main circuit, and the current flowing through the first switch gradually decreases. The voltage on the first commutation capacitor continues to increase to the operating voltage of the commutation resistor, the current in the commutation branch stops charging the first commutation capacitor, and the commutation current generated by the commutation branch rises slowly, so that the current on the first switch, which is the superposition of the commutation current and the fault current, maintains a small decrease rate before crossing zero, allowing the current to cross zero smoothly. After the current in the main circuit crosses zero, the arc is extinguished, the fault current is transferred to the commutation branch, and the voltage on the second commutation capacitor gradually increases until it reaches the operating voltage of the lightning arrester. The fault current is transferred to the energy absorption branch and gradually decreases to zero.

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