A current-smoothed zero-crossing dc circuit breaker

Abstract

The application discloses a direct-current circuit breaker with current smooth zero-crossing, which comprises a main branch, a commutation branch and an energy absorption branch, wherein 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; the energy absorption branch is provided with a lightning arrester; the first commutation capacitor is connected in parallel with the commutation resistor; the lightning arrester is connected in parallel with the second commutation capacitor; and the main branch is connected in parallel with the commutation branch. By using the application, staged commutation can be realized, the main circuit current is rapidly reduced in the first stage, and the main circuit current is slowly reduced to zero in the second stage, so that the breaking reliability of the direct-current circuit breaker can be ensured, the falling rate of the zero-crossing current is reduced, and the breaking reliability of the direct-current circuit breaker is improved. The application can be widely applied to the technical field of power equipment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power equipment, and particularly relates to a direct current circuit breaker with smooth current zero-crossing. BACKGROUND

[0002] Direct current transmission is an emerging power transmission mode, which has many advantages such as large transmission capacity, small power loss, long transmission distance, no synchronization problem, and is more suitable for new energy consumption and long-distance power transmission compared with alternating current transmission.

[0003] However, fault handling in a direct current power grid is a key challenge, and the design and performance of a direct current circuit breaker directly affect the stability and safety of the power grid. As an important control and protection device in the direct current power grid, the direct current circuit breaker plays an important role in conducting and carrying normal current and cutting off fault current, and plays a crucial role in the stable operation of the direct current power grid.

[0004] Because of the fast rise rate of fault current in the direct current power grid, the direct current circuit breaker needs to act quickly to cut off the fault. The traditional mechanical direct current circuit breaker uses a commutation branch composed of a pre-charging capacitor and an inductor to inject a high-frequency reverse current into the main circuit to create an artificial zero-crossing point to achieve fault current transfer and breaking. The high-frequency reverse current superimposed on the fault current results in a high current change rate at the current zero-crossing point, which easily leads to the reignition of the arc, resulting in failure of current transfer and current breaking, and adversely affecting the safe and stable operation of the power grid and power grid equipment. SUMMARY

[0005] Therefore, in order to solve the technical problem that the existing direct current circuit breaker has a high current change rate at the current zero-crossing point, which easily leads to the reignition of the arc and further causes the failure of current breaking, the present application proposes a direct current circuit breaker with smooth current zero-crossing, which comprises a main branch, a commutation branch and an energy absorption branch, wherein:

[0006] The main branch is provided with a switch as a first switch for carrying current during normal operation and quickly disconnecting during fault occurrence; the disconnection speed of the fast mechanical switch directly affects the response time and breaking performance of the circuit breaker.

[0007] The commutation branch comprises 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 for providing a reverse current to create an artificial zero-crossing point during a fault; 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 for storing and releasing energy to assist current transfer;

[0008] The energy absorption branch is provided with a lightning arrester for absorbing overvoltage energy generated during the breaking process of the fault current to protect the circuit breaker and other equipment.

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

[0010] When working normally:

[0011] The first switch is closed, the second switch is opened, 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 fast mechanical switch opening: the circuit breaker receives an instruction, and the first switch starts to open; an arc is generated between the contacts of the first switch, and the arc burns and starts to lengthen.

[0014] The commutation branch is put into work: after the first switch is opened, a certain delay (to ensure that the contacts reach a sufficient opening distance) is allowed, the second switch is closed, and the commutation branch is put into work; the pre-charged second commutation capacitor starts to discharge; during the discharging process, the first commutation capacitor is charged, and the voltage across the first commutation capacitor gradually rises; 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 gradually decreases;

[0015] Smooth current zero crossing: due to the conduction of the commutation resistance, the current rising speed of the commutation branch slows down, so that the current superimposed on the first switch by the commutation current and the fault current maintains a small decreasing rate before the zero crossing point, thereby achieving smooth current zero crossing.

[0016] Arc extinguishing and fault current transfer: after the current of the main circuit crosses zero, the arc between the contacts of the first switch is extinguished, and the fault current is successfully transferred to the commutation branch;

[0017] The energy absorption branch absorbs the remaining energy: the lightning arrester absorbs the remaining energy, the fault current gradually decreases to zero, and the fault breaking process is completed

[0018] Based on the above scheme, the application provides a direct current circuit breaker with smooth current zero crossing. By arranging a first commutation capacitor C1 and a voltage-dependent resistor VDR connected in parallel with the first commutation capacitor C1 in a commutation circuit, and a pre-charged second commutation capacitor C2, the commutation current can be quickly raised, and the rising speed can be slowed down when approaching the fault current amplitude, so that a smooth current zero crossing point is finally generated by superimposing the fault current, the current decreasing rate is limited within the breaking capacity range of the fast mechanical switch S1, and the problem of arc reignition caused by rapid current zero crossing is avoided. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a circuit topology diagram of the direct current circuit breaker with smooth current zero crossing according to the application;

[0020] Figure 2 is a working schematic diagram of the direct current circuit breaker with normal current flow according to the embodiment of the application.

[0021] Figure 3 is a first-stage working schematic diagram of a DC circuit breaker provided by an embodiment of the application;

[0022] Figure 4 is a second-stage working schematic diagram of a DC circuit breaker provided by an embodiment of the application;

[0023] Figure 5 is a capacitor charging working schematic diagram of a DC circuit breaker provided by an embodiment of the application;

[0024] Figure 6 is a working schematic diagram of a DC circuit breaker arrester conduction provided by an embodiment of the application;

[0025] Figure 7 is a fault current waveform breaking schematic diagram of a DC circuit breaker provided by an embodiment of the application;

[0026] The reference signs: S1, first switch; C1, first commutation capacitor; VDR, commutation resistance; S2, second switch; L, commutation inductance; C2, second commutation capacitor; SA, arrester. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0028] It should be noted that, for the convenience of description, only the parts related to the application are shown in the drawings. The embodiments in the application and the features in the embodiments can be combined with each other without conflict.

[0029] As shown in the application and the claims, unless the context clearly indicates otherwise, “one”, “a”, “an” and / or “the” do not specifically refer to the singular, but also include the plural. Generally, the terms “include” and “contain” only indicate the inclusion of the steps and elements explicitly identified, and these steps and elements do not constitute an exclusive list, and the method or device can also include other steps or elements. The element defined by the statement “including a” does not exclude the presence of another same element in the process, method, product or device including the element.

[0030] In the description of the embodiments of the present application, "multiple" refers to two or more than two. The following terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features.

[0031] In addition, flowcharts are used in the present 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 subsequent operations are not necessarily performed in sequence. On the contrary, each step can be processed in reverse order or simultaneously. Meanwhile, other operations can be added to these processes, or one or more steps of operations can be removed from these processes.

[0032] Reference Figure 1 The structure schematic diagram of an optional example of the current smooth zero-crossing DC circuit breaker proposed in the present application, the method can be applied to computer equipment, and the DC circuit breaker proposed in the embodiment can include but is not limited to the following structure:

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

[0034] The main branch contains a first switch S1 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 contains a surge 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 thereto, and the second commutation capacitor C2 has a charge-discharge circuit connected in parallel thereto.

[0036] The commutation resistor VDR is a pressure-sensitive resistor.

[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 repulsion 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 can be a series-parallel combination of the following power electronic devices, including IGBT, IGCT, GTO, thyristor and diode.

[0039] The commutation resistor VDR can be a zinc oxide pressure-sensitive resistor, a silicon carbide pressure-sensitive resistor, a titanium oxide pressure-sensitive resistor, a germanium silicon pressure-sensitive resistor, and a barium titanate pressure-sensitive resistor.

[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 direct current circuit breaker with smooth current zero-crossing, comprising a main branch, a commutation branch and an energy absorption branch, characterized in that: a first switch is arranged on the main branch; the commutation branch comprises a first commutation capacitor, a commutation resistor, a second switch, a commutation inductor and a second commutation capacitor; the commutation resistor is a pressure sensitive resistor; an arrester is arranged on the energy absorption branch; a first end of the first switch, a first end of the first commutation capacitor and a first end of the commutation resistor are connected, a second end of the first commutation capacitor, a second end of the commutation resistor and a 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, a second end of the second switch and a first end of the commutation inductor are connected, a first end of the second commutation capacitor, a second end of the commutation inductor and a first end of the arrester are connected, a second end of the first switch, a second end of the second commutation capacitor and a second end of the arrester are connected; a capacitance of the first commutation capacitor is smaller than that of the second commutation capacitor, the first commutation capacitor is not pre-charged, and the second commutation capacitor is pre-charged; when the system is normally on, the first switch is closed and 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 is opened, and an arc burns between the contacts; after a preset time delay, the contacts reach a determined opening distance, the second switch is closed, the second commutation capacitor discharges, the first commutation capacitor charges, a voltage across the first commutation capacitor gradually rises, a reverse current generated by the commutation branch is superimposed on a fault current of the main circuit, a current flowing through the first switch gradually decreases; the voltage across the first commutation capacitor continuously rises to an operating voltage of the commutation resistor, the current of the commutation branch stops charging the first commutation capacitor, the commutation current generated by the commutation branch rises at a slower rate, so that the commutation current and the fault current superimposed on the current at the first switch maintain a small decreasing rate before the zero-crossing point, so that the current smoothly crosses zero; after the current of the main circuit crosses zero, the arc is extinguished, the fault current is transferred to the commutation branch, the voltage across the second commutation capacitor gradually rises until the operating voltage of the arrester is reached, and the fault current is transferred to the energy absorption branch and gradually decreases to zero. The first switch is a vacuum switch. A driving mechanism of the first switch comprises a quick repulsion mechanism, a permanent magnet operating mechanism, a spring operating mechanism and a motor operating mechanism. The second switch comprises an IGBT, an IGCT, a GTO, a thyristor and a diode. The pressure sensitive resistor comprises a zinc oxide pressure sensitive resistor, a silicon carbide pressure sensitive resistor, a titanium oxide pressure sensitive resistor, a germanium silicon pressure sensitive resistor and a barium titanate pressure sensitive resistor. ​ ​ ​ ​ 2. The DC circuit breaker with smooth current zero crossing according to claim 1, characterized in that, ​ 3. The DC circuit breaker with smooth current zero crossing according to claim 2, characterized in that, ​ 4. The DC circuit breaker with smooth current zero crossing of claim 1, wherein, ​ 5. The DC circuit breaker with smooth current zero crossing of claim 1, wherein, ​

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