A high voltage direct current circuit breaker

Abstract

This invention discloses a high-voltage DC circuit breaker, comprising a working branch, a voltage equalization unit, a transfer and energy dissipation unit, and a fast-breaking unit. The working branch consists of n circuit breakers DL1 connected in series and connected in series with the main circuit breaker DL. The voltage equalization unit comprises m resistors R1 connected in series, with each voltage equalization unit connected in parallel across each circuit breaker DL1. The transfer and energy dissipation unit comprises a bridge rectifier element D1, with the input terminal of each bridge rectifier element D1 connected in parallel across each resistor R1 in the voltage equalization unit. The fast-breaking unit comprises fast-breaking elements T1 and T2, a resistor R2, and a capacitor C. Fast-breaking element T1 is connected in parallel with the output terminal of the bridge rectifier element D1, capacitor C is connected in parallel with fast-breaking element T1, and fast-breaking element T2 is connected in series with resistor R2 and then in parallel with capacitor C. The control terminals of fast-breaking elements T1 and T2 are connected to a breaking signal controller. This invention achieves voltage equalization of the rated DC voltage.

Description

Technical Field

[0001] This invention relates to the field of DC system switching technology, and more particularly to a high-voltage DC circuit breaker. Background Technology

[0002] DC circuit breakers are one of the key devices for ensuring the stable, safe, and reliable operation of DC systems. In AC systems, the AC current has two natural zero-crossing points within one cycle, and AC circuit breakers utilize these natural zero-crossing points to interrupt the current. However, in DC systems, the DC current does not have natural zero-crossing points, making DC current interruption far more difficult than AC current interruption. Furthermore, the line impedance of DC transmission systems is very low, and the fault current rises rapidly after a short-circuit fault occurs on the DC side, reaching its peak value within milliseconds. This places stringent requirements on the operating time and breaking capacity of DC circuit breakers, making DC current interruption extremely difficult.

[0003] Currently, there are three main types of DC circuit breaker technologies: traditional mechanical DC circuit breakers based on conventional switches, solid-state DC circuit breakers based on pure power electronic devices, and hybrid DC circuit breakers combining both. Traditional mechanical DC circuit breakers have longer breaking times, while solid-state DC circuit breakers suffer from higher losses. Currently, hybrid DC circuit breaker technology, which combines the characteristics of conventional mechanical switches and power electronic devices, still struggles to address the problem of breaking large currents.

[0004] Currently, various design schemes for high-voltage DC circuit breakers exist, most of which focus on achieving a zero-current point through circuit oscillation for breaking. A common method is to obtain a zero-current point based on the superposition of self-excited oscillations to achieve current breaking. For example... Figure 1The circuit diagram of this scheme is shown. Here, I is the DC current to be interrupted, and K1 is the main switch, i.e., the AC circuit breaker. Under normal operating conditions, the main switch K1 remains closed, and all DC current flows through it. When a short circuit occurs and I needs to be interrupted, the main switch K1 is opened first. During the process of opening the main switch K1, the circuit breaker K1 may experience unstable arcing, and self-excited oscillations may occur between capacitor C1 and inductor L1. This oscillating current is superimposed on the DC current I, causing the current through the main switch K1 to oscillate up and down based on the DC current I, with the amplitude continuously increasing until a point is reached where the instantaneous current value is zero. When the instantaneous current through the main switch K1 drops to zero, the main switch K1 is completely interrupted. On the other hand, a large amount of energy is still stored in the line inductance at this time. This energy will cause the voltage of capacitor C1 to rise. When the voltage of capacitor C1 exceeds the threshold of energy dissipation element M0V1, energy dissipation element M0V1 starts to work, dissipating a certain amount of energy. Finally, the main current becomes 0, and the breaking process ends. The advantage of this design is its circuit simplicity. The disadvantage is that capacitors C1 and L1 may not oscillate. If the oscillation does not cross zero, the breaking process will fail. This has occurred many times in actual engineering projects, making DC breaking a challenging problem.

[0005] Therefore, researching low-cost DC circuit breakers with reclosing capabilities that can limit high-voltage and high-current DC circuit breakers is of great significance for ensuring the reliable operation of DC transmission systems. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the above-mentioned technology and provide a high-voltage DC circuit breaker to solve the problem of difficulty in extinguishing arcs during the DC circuit breaker disconnection process.

[0007] Therefore, the present invention achieves the above objectives through the following technical solution:

[0008] A high-voltage DC circuit breaker includes a working branch, a voltage equalization unit, a transfer and energy dissipation unit, and a fast-breaking unit. The working branch consists of n circuit breakers DL1 connected in series and connected in series with the main circuit breaker DL. The voltage equalization unit includes m resistors R1 connected in series, with each voltage equalization unit connected in parallel across each of the circuit breakers DL1. The transfer and energy dissipation unit includes a bridge rectifier element D1, with the input terminal of each bridge rectifier element D1 connected in parallel across each of the resistors R1 in the voltage equalization unit. The fast-breaking unit includes a fast-breaking element T1, a fast-breaking element T2, a resistor R2, and a capacitor C. The fast-breaking element T1 is connected in parallel with the output terminal of the bridge rectifier element D1, the capacitor C is connected in parallel with the fast-breaking element T1, and the fast-breaking element T2 is connected in series with the resistor R2 and then in parallel with the capacitor C. The control terminals of the fast-breaking elements T1 and T2 are connected to a breaking signal controller. The values ​​of n and m depend on the voltage level in the main circuit and are determined by matching the voltage level of the main circuit, the withstand voltage capability of the fast-breaking element, and the withstand voltage level of the capacitor.

[0009] When a short-circuit fault occurs in the high-voltage main circuit of the DC power grid, if the short-circuit current on the working branch exceeds the relay protection setting value, the circuit breaker DL1 on the working branch will trip, i.e., disconnect. During the disconnection process, the circuit breaker DL1 generally uses a mechanical circuit breaker. Because the impedance changes after the air gap of the mechanical circuit breaker contacts increases, the arc across the contacts burns into a plasma state. A DC arc is a high-temperature plasma, and plasma arcs exhibit negative temperature resistance characteristics. Its volt-ampere characteristics are as follows: when the current increases, the arc resistance decreases, and the arc voltage drop decreases instead, indicating that its equivalent resistance decreases with increasing current; when the current decreases, the arc voltage increases. Typically, the arc voltage between circuit breaker contacts is similar to the arc voltage of the switch, making it difficult to transfer the short-circuit current to the transfer and energy dissipation units. By adding a capacitor C to the output terminal of the bridge rectifier element D1, the short-circuit current charges the capacitor C. This process reduces the current in the working branch. Due to the negative resistance characteristic of the arc, the reduced current causes the arc voltage to rise. When the arc voltage on the circuit breaker DL1 exceeds the voltage drop U of the fast-breaking element T1, which is already in the conducting state... T When the value is [value missing], the fast-breaking element T2 is in the open state. Therefore, the short-circuit current in the working branch will be transferred to the fast-breaking element T1. Since the equivalent resistance of the fast-breaking element T1 is extremely small, approximately R[value missing], [resistance missing]. T=0.003Ω, so the circuit breaker DL1 will break under near-arc-free conditions. After the circuit breaker DL1 breaks, the relay protection device will activate the fast-breaking element T1 for rapid breaking, with an opening time of approximately t1≈10~20μs. Let t2 be the time to fully charge the capacitor C. When t2≥t1, the fast-breaking element T1 can also achieve arc-free breaking. After the capacitor C is fully charged, the current is forced to the branch formed by the voltage equalization unit. The resistor R1 in this branch can not only be used for voltage division, but also for current limiting. At this time, the main circuit breaker DL can also be easily broken. Example: Assume the main circuit has a rated voltage of 500kV, the working branch consists of 10 disconnecting switches, and the voltage equalization unit consists of 15 resistors R1 connected in series. Assume R1 is a high-resistance resistor, R1 = 20kΩ. When circuit breaker DL1 opens, the current shifts and flows through the fast-opening unit. The voltage across each fast-opening unit is equal to the voltage across resistor R1. At this time, the current flowing through the fast-opening unit is... This is already an order of magnitude reduction of 180,000 times compared to the initial short-circuit current of 30kA.

[0010] Preferably, the resistors R1 and / or R2 of the voltage equalization unit are electro-phase change energy-absorbing resistors. The electro-phase change pulse absorbing material is typically made of a high dielectric constant material, such as titanate. Appropriate insulating and electrode materials are selected to ensure the performance of the electro-phase change pulse absorber. Electrode plates made of metallic materials are connected to electrode leads to introduce charge into the phase change material. The liquid phase change material mixture and the electrode plates are then encapsulated as an electro-phase change resistor. This absorber device can absorb more than 95% of the pulse energy, thereby protecting the overvoltage level on the power-generating equipment and limiting it within the equipment's insulation withstand safety range.

[0011] Preferably, the fast-breaking unit further includes a bridge rectifier element D2. The input terminal of the bridge rectifier element D2 is connected in parallel with the fast-breaking element T1, and the output terminal is connected in parallel with the capacitor C. The function of the bridge rectifier element D2 is to isolate the capacitor C during the discharge process of the fast-breaking element T1 when it breaks, preventing the capacitor C from reverse charging the breaking electrode of the fast-breaking element T1, thereby improving the breaking effect of the fast-breaking element. At the same time, when the fast-breaking element T2 is turned on and the resistor R2 discharges to the capacitor C, it ensures that the current does not affect the voltage at the port of the fast-breaking element T1 and is not reverse fed back, thus ensuring the safety of the port of the fast-breaking element T1.

[0012] Preferably, the fast switching elements T1 and T2 are IGBT, IEGT, or IGCT elements, which have the function of turning off the circuit within 10 to 20 μs.

[0013] Compared with existing technologies, the beneficial effects of this invention are as follows: This technology first achieves voltage division and equalization of the DC rated voltage through a multi-resistor series voltage equalization circuit connected in series and parallel to each circuit breaker. When a circuit breaker trips, the short-circuit current it generates is quickly transferred to the fast-breaking unit. The capacitor C in this unit effectively reduces the current amplitude flowing through the fast-breaking element by absorbing current energy, enabling it to complete the breaking under near-arc-free conditions. After the capacitor is fully charged, the residual current is forced to the voltage equalization circuit. With the help of the high-resistance current-limiting effect of the resistor series structure in this circuit, the short-circuit current is significantly suppressed. Finally, the subsequent main circuit breaker can easily and safely complete the breaking at an extremely low current level. The overall process is: voltage division → current transfer → capacitor energy absorption and current reduction → fast-switching arc-free breaking → current limiting → easy breaking of the main circuit breaker. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the 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.

[0015] Figure 1 This is a circuit diagram of a DC circuit breaker scheme in the prior art;

[0016] Figure 2 This is a schematic diagram of the DC circuit breaker principle of the present invention;

[0017] Figure 3 This is a schematic diagram of embodiment 3 of the DC circuit breaker of the present invention.

[0018] Figure 4 This is a structural diagram showing the change of the electro-phase change liquid medium of the energy-absorbing resistor of the electro-phase change material of the present invention with the applied electric field. Detailed Implementation

[0019] 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, and 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.

[0020] Example 1: As Figure 2As shown, during normal operation of the DC system, all circuit breakers DL1 connected in series on the working branch are in the closed state, the fast-breaking element T1 in the fast-breaking unit is also in the conducting state, and the fast-breaking element T2 is in the open state. The fast-breaking element can be IGBT, IEGT, or IGCT. Due to the large voltage drop of power electronic devices, for example, when the IGBT element has a conduction current of 1.5kA, the voltage drop VCE = 7~10V, Z = 10 / 1500 = 0.00667Ω. If there are 15 IGBTs connected in series, the total voltage drop will be... Given UT = 15 × 10 = 150V, under high current, the high-voltage arc when the circuit breaker contacts break is in a plasma state, with a very low arc voltage, typically UDLH = 50~200V. Since UDLH ≈ UT, i.e., Z1 ≈ ZT, the short-circuit current cannot be transferred from the working branch to the branch composed of the fast-breaking unit, which will cause breaking failure. Therefore, a bridge rectifier element D1 is added in the design. The output terminal of the bridge rectifier element D1 is connected to a large energy storage capacitor C. When the arc voltage on the circuit breaker DL1 exceeds 50V, the charging current I... C When the current flows from the bridge rectifier element D1 to C, according to the negative resistance characteristics of the arc plasma, the current I1 on the circuit breaker DL1 will decrease, and the arc voltage of the plasma inside the circuit breaker DL1 will increase. When the arc voltage UDLH > the voltage drop of the UT tube, the current will turn to the fast-breaking branch I4, and at this time the circuit breaker DL1 can be opened, completing a key step in the current transfer of the DC circuit breaker.

[0021] The bridge rectifier element D1 can isolate the circuit breaker DL1 during the breaking and transfer process in the fast breaking unit and working branch to prevent mutual back charging. It also uses m series resistors R1 connected in parallel with the circuit breaker D1 to form the independence of a transfer breaking unit, so as to ensure that the fast breaking element T1 operates in a controllable voltage and current environment and within a safe range. At the same time, it also prevents the charge stored in the capacitor C in the next stage from being fed back into the main circuit.

[0022] In actual design, the capacity of the energy storage capacitor is calculated according to... C represents the capacitance, U represents the capacitor voltage, and t2 represents the time it takes for the capacitor to fully charge. If the IGBT's switching time is t1 seconds, then t2 = 10t1 is used for calculation. If t1 = 15–20 μs, then t2 = 150 μs is used. In this way, the fast-switching element T1 can be switched off before the capacitor is fully charged, thus achieving the switching objective without an electric arc.

[0023] Under the impact of a short-circuit current, after the DL1 contacts of each circuit breaker complete the opening distance within 3-5 ms, the relay protection is activated to initiate the breaking action of the fast-breaking element T1 in the fast-breaking unit. Since a large-capacity capacitor C is connected in parallel across the current-carrying electrodes of the fast-breaking element T1, when the fast-breaking element T1 breaks, the short-circuit current originally flowing through the fast-breaking unit will be redirected and charge the capacitor C. (See...) Figure 3 In the design, the breaking time t1 of the fast-breaking element T1 should be 10 to 100 times smaller than the time t2 for fully charging capacitor C. That is, when capacitor C is large enough, the contacts of the fast-breaking element T1 can reliably break the circuit without an electric arc. After capacitor C is fully charged, the short-circuit current re-selects a path and flows through the branch composed of the voltage equalization unit, i.e., A→R1-1→R1-2→R1-m→B. In this way, the current in the DC circuit can be reduced from the initial short-circuit current value of 30kA to 0.2~0.3A after passing through each of the series R1s (m). At this time, the final main circuit breaker DL can perform the final breaking under a small current. This circuit realizes the process of transferring the current to the energy storage capacitor C under a large short-circuit current in the DC circuit, achieving arc-free breaking, current limiting by resistors, and then complete breaking under a small current. After the entire DC circuit is disconnected, the fast-start element T2 is turned on, and the capacitor C is quickly discharged by the resistor R2. The discharge time is controlled within tens of seconds or within the time required for reclosing, so that the capacitor C can continue to be charged when the circuit is interrupted again.

[0024] In Example 2, compared to Example 1, the resistors R1 and / or R2 of the voltage equalization unit are electro-phase change energy-absorbing resistors. These resistors are R / C elements with high dielectric constants, capable of absorbing DC impulse wave voltage energy. The parameters of the electro-phase change energy-absorbing resistor consist of two parts: resistance value and equivalent capacitance value. The resistance is typically 20~25KΩ, and the capacitance value is C=100 uF~500 uF. It is a dispersion system composed of dielectric particles with high dielectric constants, such as calcium titanate, and a polar molecular liquid insulating liquid. Figure 4As shown, without an external electric field, the electrorheological fluid is liquid with a viscosity similar to oil (typically about 0.1 dyn·s / cm2). When an external electric field is applied, its apparent viscosity increases with the increase of the electric field. When the electric field is sufficiently large (e.g., greater than 1000 V / mm), the material transforms into a solid-like substance, undergoing a phase transition, resulting in increased viscosity. The electric field causes the material to deform and perform work, thereby absorbing the energy of a DC shock wave voltage. This liquid-solid transition is reversible, with a transition time (or response time) typically on the order of micro-nanoseconds, and the material can recover to its original state after the pulse. The energy absorbed by this phase-change resistor is A = ΔP·V, where P is the pressure and V is the volume of the container. In this design, the volume of the container V ≥ 0.5 m3, which can absorb more than 95% of the DC shock wave voltage energy, thereby protecting the overvoltage level at the upper end of the equipment and limiting it within the safe range of low-voltage equipment.

[0025] Example 3, compared to Examples 1 and 2, as follows: Figure 3 As shown, the fast interruption unit also includes a bridge rectifier element D2. The input terminal of the bridge rectifier element D2 is connected in parallel with the fast interruption element T1, and the output terminal is connected in parallel with the capacitor C. The function of the bridge rectifier element D2 is to isolate the capacitor C during the discharge process of the fast interruption element T1, preventing the capacitor C from recharging the interruption electrode of the fast interruption element T1, thereby improving the interruption effect of the fast interruption element. At the same time, when the fast interruption element T2 is turned on and the resistor R2 discharges to the capacitor C, it ensures that the current does not affect the voltage at the port of the fast interruption element T1 and is not reverse fed back, thus ensuring the safety of the port of the fast interruption element T1.

[0026] For the working branch circuit breaker DL1, a 25-50kV vacuum circuit breaker can be selected, such as DT 24-40.5kV / 3150A, manufactured by Baoji Baoguang Vacuum Electric Co., Ltd., or an SF6 circuit breaker can be selected, manufactured by Henan Pinggao Electric Co., Ltd.

[0027] The voltage equalization unit uses high-impedance resistors R1 to R1.n, which can be liquid-phase high-resistance resistors made of electro-phase change material. The equivalent resistance is R = 20 to 30 kΩ and the equivalent capacitance is C = 50 to 200 nF. This resistor has the function of quickly absorbing the energy of steep wave pulses. The manufacturer is Wenzhou Leixingtai Technology Co., Ltd.

[0028] The bridge rectifier element D1 in the transfer and energy dissipation unit is a high-performance bridge rectifier that can withstand high voltage and high current. The commonly used model is D1800N48T.VF, with parameters of U=5.5kV, rated current I=1.8kA, and surge current withstand value of 25kA. In actual engineering, multiple parallel circuits are used to achieve the requirement of no heat generation and no abnormal faults under 3kA of working branch.

[0029] The fast-start unit's switching elements T1 and T2 are IGBTs, IEGTs, IGCTs, or other transistors, capable of turning off the circuit within 10–20 μs. A typical model is ST3000GXH.24A, with a voltage of 4.5 kV and a current of I=3 kA. In practice, it operates in parallel with 2–3 groups of IGBT elements. The manufacturer is Toshiba Electric Corporation.

[0030] The function of capacitor C is to absorb the current value of the arc voltage drop generated by the short-circuit current I1 on the circuit breaker DL1, and to store the charge when the breaking element T1 breaks. The voltage value of the DC capacitor is Ue=5kV, and the capacitor C=5000uF. The commonly used model is HZMJ-5kV-2000uF, and multiple units are operated in parallel. The manufacturer is Wuhezhong Xingye Electric Co., Ltd.

[0031] The electro-phase change material discharge resistor R2 is a phase change low-resistance capacitor that has both resistance and capacitance properties. It is usually selected with an equivalent resistance of R=1~5Ω and an equivalent capacitance of C=1~100uF. It is made of a combination of a liquid with a high dielectric constant and a composite material with a high dielectric constant. It has the characteristic of rapidly absorbing the energy of interference wavefront pulses, and has a low heat generation level after energy absorption, which helps to reduce the requirements of the overall turn-off and reclosing time of the switch.

[0032] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0033] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A high-voltage DC circuit breaker, characterized in that, It includes working branches, equalizing units, transfer and energy dissipation units, and fast disconnection units; The working branch consists of n circuit breakers DL1 connected in series, and connected in series with the main circuit breaker DL. The voltage equalization unit includes m series-connected resistors R1, and each voltage equalization unit is connected in parallel to both ends of each circuit breaker DL1. The transfer and energy dissipation unit includes a bridge rectifier element D1, and the input terminal of each bridge rectifier element D1 is connected in parallel to the two ends of the resistor R1 of the voltage equalization unit. The fast interruption unit includes fast interruption element T1, fast interruption element T2, resistor R2, and capacitor C. Fast interruption element T1 is connected in parallel with the output terminal of bridge rectifier element D1. Capacitor C is connected in parallel with fast interruption element T1. Fast interruption element T2 is connected in series with resistor R2 and then in parallel with capacitor C. The control terminals of fast interruption elements T1 and T2 are connected to the interruption signal controller.

2. The high-voltage DC circuit breaker according to claim 1, characterized in that, The resistors R1 and / or R2 of the voltage equalization unit are electro-induced phase change energy-absorbing resistors, which are R / C elements with high dielectric constants.

3. The high-voltage DC circuit breaker according to claim 1, characterized in that, The fast interruption unit also includes a bridge rectifier element D2, the input terminal of which is connected in parallel with the fast interruption element T1, and the output terminal of which is connected in parallel with the capacitor C.

4. The high-voltage DC circuit breaker according to claim 1, characterized in that, The fast-interrupting elements T1 and T2 are IGBTs, IEGTs, or IGCTs.

Images