A circuit for suppressing overvoltage and overcurrent when circuit breaker is opened and reignited and capacitor is switched on and off

Abstract

The present invention belongs to the field of high-voltage protection of power systems, and discloses a circuit for suppressing circuit breaker opening, restrike and capacitor switching overvoltage and overcurrent, including an AC power supply, a circuit breaker S1, a protection circuit and a capacitor C1, wherein the protection circuit includes a switch device control module, a transformer, a variable resistor R1, a resistor R2, a resistor R3, a resistor R4, a switch device K1, a switch device K2, a switch device K3, a switch device K4, an auxiliary circuit breaker S2, a diode D1, a diode D2, a diode D3, a diode D4, a diode D5, a diode D6, a reactor L1 and a DC power supply DC. The protection circuit proposed in the present invention can suppress the closing inrush current and closing overvoltage in the process of switching capacitors by the circuit breaker, suppress the opening overvoltage and circuit breaker reignition in the opening process, and replace the discharge coil to discharge the parallel capacitor after the opening, so as to realize the full process protection of the circuit breaker switching parallel capacitor.

Description

Technical Field

[0001] The invention belongs to the field of high voltage protection of electric power systems, and in particular relates to a circuit for suppressing overvoltage and overcurrent during circuit breaker opening and restrike and capacitor switching. Background Art

[0002] Substations frequently use circuit breakers to switch parallel capacitors, which not only effectively improves the power factor of the power grid and reduces reactive power loss, but also significantly improves the quality of power, providing a strong guarantee for the safe, stable and efficient operation of the power system. Therefore, ensuring the safe, reliable and stable operation of parallel capacitor devices is of great significance to improving voltage quality and economic operation of substations.

[0003] Circuit breaker restrike overvoltage refers to the phenomenon that when the circuit breaker opens the circuit, the arc fails to be completely extinguished for some reason and then reignites, causing the voltage in the circuit to rise instantly. This overvoltage is potentially harmful to power equipment and systems, and may cause equipment damage, insulation breakdown, and even system accidents.

[0004] Capacitors will generate a large inrush current at the moment of closing. Currently, substations are mostly protected by installing series reactors, and at the moment of closing, a high overvoltage will appear on the series reactor. In recent years, due to the frequent switching of parallel capacitors, series reactor burnout accidents often occur in substations.

[0005] In order to release the residual pressure of the substation parallel capacitor as soon as possible after the switch is opened, most substations install discharge coils at both ends of the capacitor. Since overvoltage will be generated on the capacitor during the switching process, the discharge coil may be burned. In addition, the installation of the discharge coil makes the branch where the parallel capacitor group is located more complicated, which may increase the risk of resonant overvoltage.

[0006] The Chinese utility model patent CN204167900 U, published on February 18, 2015, "A parallel capacitor switch recovery overvoltage suppression circuit" reduces the recovery overvoltage at both ends of the circuit breaker by installing suppressors at both ends of the parallel capacitor, improves the reliability of the circuit breaker, and avoids the probability of the circuit breaker reigniting. The Chinese authorized invention patent CN111884233 B, published on January 30, 2024, "A parallel capacitor overcurrent and overvoltage suppression system" mainly realizes the phase selection control of the vacuum circuit breaker closing, suppressing the generation of overcurrent and overvoltage. The Chinese invention patent CN117013513A, published on November 7, 2023, "A combination switch for suppressing reignition overvoltage by series nonlinear resistors" limits the circuit breaker break voltage by adding nonlinear resistors, lightning arresters and auxiliary switches, thereby reducing the probability of two-phase, three-phase reignition and multiple reignition caused by single-phase reignition.

[0007] In summary, the prior art still has the following problems:

[0008] 1. Some protection circuits only consider a single link in the operation process, such as only considering the opening link or only considering the closing link, and cannot protect the entire operation process of the parallel capacitor;

[0009] 2. Most protection circuits do not take capacitor discharge into consideration, and do not consider the impact of the subsequent installation of a discharge coil on the original equipment. Summary of the invention

[0010] In view of the deficiencies of the prior art, the present invention provides a circuit for suppressing overvoltage and overcurrent during circuit breaker opening and restrike and capacitor switching, which solves the problem that the protection circuit in the prior art cannot protect all links of the operation process of the parallel capacitor.

[0011] To achieve the above object, the present invention provides the following technical solutions:

[0012] A circuit for suppressing overvoltage and overcurrent when a circuit breaker is opened and reignited and when a capacitor is switched on and off, comprising an AC power supply, a circuit breaker S1, a protection circuit and a capacitor C1, wherein the protection circuit comprises a switch device control module, a transformer, a variable resistor R1, a resistor R2, a resistor R3, a resistor R4, a switch device K1, a switch device K2, a switch device K3, a switch device K4, an auxiliary circuit breaker S2, a diode D1, a diode D2, a diode D3, a diode D4, a diode D5, a diode D6, a reactor L1 and a DC power supply DC; the switch device K1, the switch device K2, the switch device K3 and the switch device K4 are all insulated gate bipolar transistors; one end of the circuit breaker S1 is connected to the AC power supply, one end of the primary winding of the transformer is connected to the other end of the circuit breaker S1, the other end of the primary winding of the transformer is respectively connected to one end of the capacitor C1, the anode of the diode D5 and one end of the resistor R2, and one end of the secondary winding of the transformer is respectively connected to one end of the auxiliary circuit breaker S2, one end of the capacitor C2 and one end of the reactor L1 The other end of the secondary winding of the transformer is respectively connected to the other end of the variable resistor R1, the other end of the capacitor C2, the emitter of the switch device K3, the collector of the switch device K2, the anode of the diode D3 and the cathode of the diode D2; the other end of the auxiliary circuit breaker S2 is connected to one end of the variable resistor R1, the other end of the reactor L1 is respectively connected to the emitter of the switch device K1, the collector of the switch device K4, the anode of the diode D1 and the cathode of the diode D4; the positive electrode of the DC power supply DC is respectively connected to the collector of the switch device K1, the collector of the switch device K3, the cathode of the diode D1 and the cathode of the diode D3, and the negative electrode of the DC power supply DC is respectively connected to the cathode of the diode D5 and the cathode of the diode D6; the other end of the resistor R2 is respectively connected to one end of the resistor R3, the emitter of the switch device K2, the emitter of the switch device K4, the anode of the diode D2 and the anode of the diode D4; one end of the resistor R4 is respectively connected to the anode of the diode D6 and the other end of the resistor R3; the other end of the resistor R4 is connected to the other end of the capacitor C1.

[0013] As a further solution of the present invention: the protection circuit has four working modes, namely: mode 1: closing inrush current and closing overvoltage suppression; mode 2: low impedance; mode 3: restrike and overvoltage suppression and capacitor discharge; mode 4: capacitor discharge; the four working modes correspond to different processes of circuit breaker switching capacitor, that is, mode 1 and mode 2 correspond to circuit breaker closing and capacitor steady-state operation respectively; mode 3 corresponds to circuit breaker opening and capacitor discharge; mode 4 corresponds to capacitor discharge;

[0014] The closing time of the circuit breaker S1 is ta, and the opening time is tb; t1, t2 and t3 are three time periods set by the protection circuit respectively, t1 is the duration of the resistance change of the variable resistor R1, t2 is the duration of the high-frequency PWM wave control signal output by the switch device control module before the circuit breaker S1 is opened, and t3 is the duration of the high-frequency PWM wave control signal output by the switch device control module after the circuit breaker S1 is opened; ta, tb, t1 and t2 meet the condition (ta+t1)<(tb-t2); t is any time during the circuit breaker switching capacitor and the capacitor operation process;

[0015] The operation process of the protection circuit has the following six stages:

[0016] Phase 1, 0≤t<ta: the protection device works in mode 1, that is, before closing, the variable resistor R1 works in a high impedance state, the switch devices K1, K2, K3, and K4 are turned off, and the auxiliary circuit breaker S2 is kept in a closed state;

[0017] Phase 2, ta≤t<(ta+t1): the protection device transitions from mode 1 to mode 2. At t=ta, the circuit breaker S1 is closed; ta<t<(ta+t1), the resistance of the variable resistor R1 decreases to a low impedance state within t1.

[0018] Stage 3, (ta+t1)≤t<(tb-t2): the protection device works in mode 2;

[0019] Phase 4, (tb-t2)≤t<tb: the protection device works in the transition state from mode 2 to mode 3, at t=(tb-t2), the auxiliary circuit breaker S2 is opened; (tb-t2)<t<tb, the switching devices K1, K2, K3, and K4 are in the high-frequency switching state, and the switching device control module outputs a high-frequency PWM wave control signal to control the on and off, the circuit breaker S1 is not opened, and the capacitor is discharged at the same time;

[0020] Stage 5, tb≤t<(tb+t3): The protection device works in mode 3, at t=tb, the circuit breaker S1 is opened; tb<t<(tb+t3), the switching devices K1, K2, K3, and K4 are in a high-frequency switching state, and the switching device control module outputs a high-frequency PWM wave control signal to control the on and off, suppressing the circuit breaker from reigniting, and the capacitor is discharged at the same time;

[0021] Stage six, t≥(tb+t3): the protection device operates in mode four. At t=(tb+t3), the switching devices are switched to the following states: K1 is off, K2 is off, K3 is off, and K4 is off; when t>(tb+t3), the capacitor is discharged.

[0022] As a further solution of the present invention: the function of the switch device control module is to control the module to output a continuous on / off signal or a high-frequency PWM wave control signal to control the on / off of the switch device K1, the switch device K2, the switch device K3 and the switch device K4;

[0023] The transformer primary voltage is U4, the power supply to ground voltage is U1, the capacitor C1 voltage to ground is U2, U3=U1-U2, when PWM control method is adopted, the carrier is a triangle wave, the modulation wave is Um=N×U3, negative feedback control is adopted, the given value is U3, and the error input is , the controlled quantity is N;

[0024] The transformation ratio between the primary side and the secondary side of the transformer is k:1, and the resistance values ​​of resistors R2, R3 and R4 are r2, r3 and r4 respectively, and r2=r3<r4.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention can replace the series reactor, discharge coil, etc. in the reactive power compensation capacitor group, completely solve the problem of burning of the series reactor and discharge coil due to overvoltage, realize the protection function and reduce the investment of the corresponding primary equipment.

[0027] 2. The present invention can protect the closing, opening and discharging links of the parallel capacitor, thus avoiding the problem that the traditional protection device can only protect a single link.

[0028] 3. The present invention can simultaneously suppress the closing inrush current and closing overvoltage during the closing stage, solving the problem that the traditional protection device can only suppress the inrush current or overvoltage.

[0029] 4. The present invention utilizes the residual voltage after the parallel capacitor is disconnected to suppress the reignition of the circuit breaker, rationally utilizes the excess electric energy of the capacitor, and saves energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without creative work. Among them:

[0031] Figure 1 is a circuit diagram of the present invention;

[0032] Figure 2 It is a circuit diagram of Mode 1 and Mode 2 of the present invention;

[0033] Figure 3 It is a circuit diagram of mode 3 of the present invention;

[0034] Figure 4 1 is a circuit diagram of mode 4 of the present invention;

[0035] Figure 5 It is a simulation circuit diagram using traditional protection methods;

[0036] Figure 6 It is a simulation circuit diagram using the protection method of the present invention;

[0037] Figure 7 It is the simulated current waveform of the circuit breaker when using the traditional protection circuit;

[0038] Figure 8 It is the simulated current waveform of the circuit breaker when the protection circuit of the present invention is adopted;

[0039] Fig. 9 It is the simulated voltage waveform of the circuit breaker when using the traditional protection circuit;

[0040] Fig.10 It is the simulated voltage waveform of the circuit breaker when the protection circuit of the present invention is adopted;

[0041] Fig.11 It is the simulated voltage waveform at the capacitor end when using the traditional protection circuit;

[0042] Fig.12 It is a simulated voltage waveform at the capacitor terminal when the protection circuit of the present invention is adopted. DETAILED DESCRIPTION

[0043] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] Example 1

[0045] See also Figure 1As shown, the present invention provides a circuit breaker opening and restrike and capacitor switching overvoltage and overcurrent suppression circuit, including an AC power supply, a circuit breaker S1, a protection circuit and a capacitor C1, wherein the protection circuit includes a switch device control module, a transformer, a variable resistor R1, a resistor R2, a resistor R3, a resistor R4, a switch device K1, a switch device K2, a switch device K3, a switch device K4, an auxiliary circuit breaker S2, a diode D1, a diode D2, a diode D3, a diode D4, a diode D5, a diode D6, a reactor L1 and a DC power supply DC; the switch device K1, the switch device K2, the switch device K3 and the switch device K4 are all insulated gate bipolar transistors; one end of the circuit breaker S1 is connected to the AC power supply, one end of the primary winding of the transformer is connected to the other end of the circuit breaker S1, the other end of the primary winding of the transformer is respectively connected to one end of the capacitor C1, the anode of the diode D5 and one end of the resistor R2, and one end of the secondary winding of the transformer is respectively connected to one end of the auxiliary circuit breaker S2, one end of the capacitor C2 and the reactor. The auxiliary circuit breaker S2 is connected to one end of the variable resistor R1, and the other end of the secondary winding of the transformer is respectively connected to the other end of the variable resistor R1, the other end of the capacitor C2, the emitter of the switch device K3, the collector of the switch device K2, the anode of the diode D3 and the cathode of the diode D2; the other end of the auxiliary circuit breaker S2 is connected to one end of the variable resistor R1, and the other end of the reactor L1 is respectively connected to the emitter of the switch device K1, the collector of the switch device K4, the anode of the diode D1 and the cathode of the diode D4; the positive electrode of the direct current power supply DC is respectively connected to the collector of the switch device K1, the collector of the switch device K3, the cathode of the diode D1 and the cathode of the diode D3, and the negative electrode of the direct current power supply DC is respectively connected to the cathode of the diode D5 and the cathode of the diode D6; the other end of the resistor R2 is respectively connected to one end of the resistor R3, the emitter of the switch device K2, the emitter of the switch device K4, the anode of the diode D2 and the anode of the diode D4; one end of the resistor R4 is respectively connected to the anode of the diode D6 and the other end of the resistor R3; the other end of the resistor R4 is connected to the other end of the capacitor C1.

[0046] like Figure 2-4 As shown, the protection circuit has four working modes, namely: Mode 1: Closing inrush current and closing overvoltage suppression; Mode 2: Low impedance; Mode 3: Restiring and overvoltage suppression and capacitor discharge; Mode 4: Capacitor discharge. The four working modes correspond to different processes of circuit breaker switching capacitors, that is, Mode 1 and Mode 2 correspond to circuit breaker closing and capacitor steady-state operation respectively; Mode 3 corresponds to circuit breaker opening and capacitor discharge; Mode 4 corresponds to capacitor discharge;

[0047] The closing time of the circuit breaker S1 is ta, and the opening time is tb; t1, t2 and t3 are three time periods set by the protection circuit respectively, t1 is the duration of the resistance change of the variable resistor R1, t2 is the duration of the high-frequency PWM wave control signal output by the switch device control module before the circuit breaker S1 is opened, and t3 is the duration of the high-frequency PWM wave control signal output by the switch device control module after the circuit breaker S1 is opened; ta, tb, t1 and t2 meet the condition (ta+t1)<(tb-t2); t is any time during the circuit breaker switching capacitor and the capacitor operation process;

[0048] The operation process of the protection circuit has the following six stages:

[0049] Phase 1, 0≤t<ta: the protection device works in mode 1, that is, before closing, the variable resistor R1 works in a high impedance state, the switch devices K1, K2, K3, and K4 are turned off, and the auxiliary circuit breaker S2 is kept in a closed state;

[0050] Phase 2, ta≤t<(ta+t1): the protection device transitions from mode 1 to mode 2. At t=ta, the circuit breaker S1 is closed; ta<t<(ta+t1), the resistance of the variable resistor R1 decreases to a low impedance state within t1.

[0051] Phase 3, (ta+t1)≤t<(tb-t2): The protection device works in mode 2, such as Figure 2 As shown;

[0052] Phase 4, (tb-t2)≤t<tb: the protection device works in the transition state from mode 2 to mode 3, at t=(tb-t2), the auxiliary circuit breaker S2 is opened; (tb-t2)<t<tb, the switching devices K1, K2, K3, and K4 are in the high-frequency switching state, and the switching device control module outputs a high-frequency PWM wave control signal to control the on and off, the circuit breaker S1 is not opened, and the capacitor is discharged at the same time;

[0053] Phase 5, tb≤t<(tb+t3): The protection device works in mode 3, at t=tb, the circuit breaker S1 is open; tb<t<(tb+t3), the switch devices K1, K2, K3, K4 are in a high-frequency switching state, and the switch device control module outputs a high-frequency PWM wave control signal to control the on and off, inhibiting the circuit breaker from reigniting, and at the same time the capacitor is discharged, such as Figure 3 As shown;

[0054] Stage 6, t≥(tb+t3): The protection device works in mode 4. At t=(tb+t3), the switch devices are switched to the following states: K1 is off, K2 is off, K3 is off, and K4 is off. When t>(tb+t3), the capacitor is discharged. Figure 4 shown.

[0055] Preferably, the function of the switch device control module is to control the module to output a continuous on / off signal or a high-frequency PWM wave control signal to control the on / off of the switch device K1, the switch device K2, the switch device K3 and the switch device K4;

[0056] like Figure 3 As shown, the transformer primary voltage is U4, the power supply to ground voltage is U1, the capacitor C1 voltage to ground is U2, U3=U1-U2, when PWM control method is adopted, the carrier is a triangle wave, the modulation wave is Um=N×U3, negative feedback control is adopted, the given value is U3, and the error input is , the controlled quantity is N;

[0057] The transformation ratio between the primary side and the secondary side of the transformer is k:1, and the resistance values ​​of resistors R2, R3 and R4 are r2, r3 and r4 respectively, and r2=r3<r4.

[0058] Example 2

[0059] Specifically, the present invention provides ta=0.5s, tb=1.0s, t1=0.1s, t2=0.01s, t3=0.5s, r2=1000Ω, r3=1000Ω, r4=8000Ω, K:1=40:1, C2=1μF, DC power supply DC is 3kV, variable resistor R1 has a resistance of r1, high impedance state r1=10Ω, low impedance state r1=0, transition state r1=(1000×t2-1200×t+360)Ω;

[0060] The conventional protection circuit and the protection circuit of the present invention are simulated and analyzed respectively, including: simulation of the voltage, current and capacitor terminal voltage of the three-phase circuit breaker, wherein the effective value of the three-phase power line voltage used is 66kV and the equivalent internal resistance of each phase is 1Ω, the three-phase capacitors Ca, Cb and Cc are all 40μF, and the neutral point to ground capacitance Co is 50pF;

[0061] Figure 5 This is a simulation circuit diagram of a traditional protection circuit. The series reactors La1, Lb1 and Lc1 used are all 30mH, the equivalent resistances Ra, Rb and Rc of the discharge coil used are all 8000Ω, and the equivalent inductances La2, Lb2 and Lc2 are all 50mH. Figure 6 This is a simulation circuit diagram of the protection circuit of the present invention. From the simulation results in the attached figure, it can be seen that the protection circuit of the present invention can protect the closing, opening and discharging links of the parallel capacitor compared with the traditional protection circuit, solving the problem that the traditional protection device cannot protect all links of the operation process of the parallel capacitor.

[0062] Example 3

[0063] Figure 7 is the circuit breaker current waveform when the traditional protection circuit is used in the embodiment of the present invention, Figure 8 1 is a circuit breaker current waveform when the protection circuit of the present invention is adopted in an embodiment of the present invention; the horizontal axis t is any time, and the vertical axis is the circuit breaker current; it can be seen from the figure that when the present invention is used for protection, compared with the traditional protection method, the closing inrush current suppression effect is obvious, and the closing current rises steadily.

[0064] Example 4

[0065] Fig. 9 is the voltage waveform of the circuit breaker when the traditional protection circuit is used in the embodiment of the present invention, Fig.10 3 is a waveform of circuit breaker break voltage when the protection circuit of the present invention is adopted in an embodiment of the present invention. The horizontal axis t is any time, and the vertical axis is the circuit breaker break voltage. It can be seen from the figure that when the present invention is used for protection, compared with the traditional protection method, when the insulation strength of the circuit breaker is restored after the opening, the circuit breaker break voltage is suppressed at a lower level, indicating that the present invention has a better circuit breaker reignition suppression effect.

[0066] Example 5

[0067] Fig.11 is the voltage waveform of the capacitor terminal when the conventional protection circuit is used in the embodiment of the present invention, Fig.12 3 is the voltage waveform of the capacitor terminal when the protection circuit of the present invention is adopted in the embodiment of the present invention. The horizontal axis t is any time, and the vertical axis is the voltage of the capacitor terminal. It can be seen from the figure that when the present invention is used for protection, compared with the traditional protection method, the closing overvoltage and the opening overvoltage of the capacitor terminal are suppressed, which shows that the present invention has a better overvoltage suppression effect.

[0068] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A circuit for suppressing overvoltage and overcurrent when a circuit breaker is opened and reignited and a capacitor is switched on and off, comprising an AC power supply, a circuit breaker S1, a protection circuit and a capacitor C1, characterized in that: The protection circuit includes a switch device control module, a transformer, a variable resistor R1, a resistor R2, a resistor R3, a resistor R4, a switch device K1, a switch device K2, a switch device K3, a switch device K4, an auxiliary circuit breaker S2, a diode D1, a diode D2, a diode D3, a diode D4, a diode D5, a diode D6, a reactor L1 and a DC power supply DC; the switch device K1, the switch device K2, the switch device K3 and the switch device K4 are all insulated gate bipolar transistors; one end of the circuit breaker S1 is connected to an AC power supply, and one end of the transformer One end of the secondary winding is connected to the other end of the circuit breaker S1, and the other end of the primary winding of the transformer is respectively connected to one end of the capacitor C1, the anode of the diode D5 and one end of the resistor R2. One end of the secondary winding of the transformer is respectively connected to one end of the auxiliary circuit breaker S2, one end of the capacitor C2 and one end of the reactor L1. The other end of the secondary winding of the transformer is respectively connected to the other end of the variable resistor R1, the other end of the capacitor C2, the emitter of the switch device K3, the collector of the switch device K2, the anode of the diode D3 and the cathode of the diode D2; the other end of the auxiliary circuit breaker S2 is connected to the variable resistor R 1, the other end of the reactor L1 is respectively connected to the emitter of the switching device K1, the collector of the switching device K4, the anode of the diode D1 and the cathode of the diode D4; the positive electrode of the DC power supply DC is respectively connected to the collector of the switching device K1, the collector of the switching device K3, the cathode of the diode D1 and the cathode of the diode D3, and the negative electrode of the DC power supply DC is respectively connected to the cathode of the diode D5 and the cathode of the diode D6; the other end of the resistor R2 is respectively connected to one end of the resistor R3, the emitter of the switching device K2, the emitter of the switching device K4, the anode of the diode D2 and the cathode of the diode D4 anode of the variable resistor R1; one end of the resistor R4 is respectively connected to the anode of the diode D6 and the other end of the resistor R3; the other end of the resistor R4 is connected to the other end of the capacitor C1, the closing time of the circuit breaker S1 is ta, and the opening time is tb; t1, t2 and t3 are three time periods set by the protection circuit, t1 is the duration of the resistance change of the variable resistor R1, t2 is the duration of the high-frequency PWM wave control signal output by the switch device control module before the circuit breaker S1 is opened, and t3 is the duration of the high-frequency PWM wave control signal output by the switch device control module after the circuit breaker S1 is opened; ta, tb, t1 and t2 satisfy the condition (ta+t1)<(tb-t2).

2. A circuit for suppressing overvoltage and overcurrent during circuit breaker opening and restrike and capacitor switching according to claim 1, characterized in that: The protection circuit has four working modes, namely: Mode 1: Closing inrush current and closing overvoltage suppression; Mode 2: Low impedance; Mode 3: Restiring and overvoltage suppression and capacitor discharge; Mode 4: Capacitor discharge; The four working modes correspond to different processes of circuit breaker switching capacitors, that is, Mode 1 and Mode 2 correspond to circuit breaker closing and capacitor steady-state operation respectively; Mode 3 corresponds to circuit breaker opening and capacitor discharge; Mode four corresponds to capacitor discharge.

3. A circuit for suppressing overvoltage and overcurrent during circuit breaker opening and restrike and capacitor switching according to claim 2, characterized in that: The function of the switch device control module is to control the module to output a continuous on / off signal or a high-frequency PWM wave control signal to control the on / off of the switch device K1, the switch device K2, the switch device K3 and the switch device K4; The transformer primary voltage is U4, the power supply to ground voltage is U1, the capacitor C1 voltage to ground is U2, U3=U1-U2, when PWM control method is adopted, the carrier is a triangle wave, the modulation wave is Um=N×U3, negative feedback control is adopted, the given value is U3, and the error input is , the controlled quantity is N; The transformation ratio between the primary side and the secondary side of the transformer is k:1, and the resistance values ​​of resistors R2, R3 and R4 are r2, r3 and r4 respectively, and r2=r3<r4.

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