A resonant network for suppressing circuit breaker transient recovery voltage

Abstract

The application discloses a resonance network for suppressing transient recovery voltage of a circuit breaker, and belongs to the technical field of high-voltage alternating-current circuit breaker breaking. The resonance network is composed of one metal oxide lightning arrester and N resonance branches with the same structure. The number N of the resonance branches and the resonance frequency of the resonance branches are obtained through an electromagnetic transient simulation model; the resonance frequency presents low impedance near the base frequency of the transient recovery voltage, provides a shunt and energy consumption path for high-frequency oscillation current, and actively suppresses the rising steepness and oscillation amplitude of the transient recovery voltage. The metal oxide lightning arrester serves as a backup protection and clamps the peak value of the transient recovery voltage when the suppression effect of the resonance branch is insufficient or abnormal. The resonance network can significantly suppress the rising rate and amplitude of the transient recovery voltage under high-voltage levels in the key period of dielectric strength recovery, effectively improves the breaking reliability of the vacuum circuit breaker, and has good working condition adaptability and system safety.

Description

Technical Field

[0001] This invention belongs to the field of high-voltage AC circuit breaker breaking technology, specifically relating to a resonant network for suppressing transient recovery voltage of circuit breakers. Background Technology

[0002] Vacuum AC circuit breakers have gained increasingly widespread application in power systems due to their outstanding advantages such as high breaking capacity, environmental friendliness, and low maintenance workload. However, with the increase in system voltage levels, the increase in system line length, and the increase in short-circuit capacity, the transient recovery voltage (TRV) problem faced by vacuum circuit breakers when interrupting short-circuit currents is becoming increasingly severe.

[0003] TRV is the high-frequency oscillating recovery voltage generated by the interaction between the power supply voltage and the distributed inductance and capacitance in the system at the moment when the circuit breaker interrupts the fault current, the contacts separate, and the current crosses zero to extinguish the arc. At high voltage levels of 126kV and above, this process typically contains multiple high-frequency oscillating components, with peak values ​​reaching nearly twice the system's rated voltage and rise rates as high as several kilovolts per microsecond. This poses a serious threat to the dielectric insulation recovery capability of vacuum circuit breakers, easily leading to re-breakdown or reignition, causing interruption failure and serious system accidents.

[0004] Currently, the main solutions to the high amplitude and high rise rate of transient response velocity (TRV) in high-voltage vacuum AC circuit breakers are still to improve insulation levels by optimizing the performance of the vacuum interrupter or to suppress TRV by using parallel capacitors, resistors, and metal oxide surge arresters. For example:

[0005] (1) Zhong Jianying, Sun Guanglei, Yang Baoxin, et al. published an article entitled “Research Status and Prospect of High Voltage Vacuum Circuit Breakers” in Volume 50, Issue 2 of High Voltage Technology in 2024. They pointed out that when the contact opening distance of a vacuum circuit breaker exceeds 10mm, it will exhibit a “saturation effect” of long vacuum gap insulation, and the insulation strength recovery will be significantly slowed down. The insulation strength can be improved by optimizing the shield structure and aging the arc extinguishing chamber, but the use of external circuits to suppress TRV was not considered to buy time for insulation strength recovery.

[0006] (2) The Chinese patent document CN101728825A, published on June 9, 2010, entitled "A Device for Limiting the Peak Value and Rise Rate of Transient Recovery Voltage of a Circuit Breaker", uses a method of connecting a capacitor and a metal oxide surge arrester in parallel across the circuit breaker to limit the TRV. However, its shortcomings are that the capacitor can only absorb energy, and a very large capacitor is required to absorb enough TRV energy at high voltage levels to slow down its rise rate; and since the capacitor does not consume energy, although it slows down the rise of TRV, it also makes its peak value higher. It can only rely on the frequent conduction of the metal oxide surge arrester to release huge amounts of energy to reduce the peak value of TRV. At the same time, due to the release of energy stored in the capacitor, the metal oxide surge arrester will be subjected to energy shocks far exceeding the design expectations, which greatly accelerates the deterioration rate of the metal oxide surge arrester varistor and limits the life of the device.

[0007] (3) Borghetti A, Napolitano F, Nucci CA, et al., published "Transient Recovery Voltages in Vacuum Circuit Breakers Generated by the Interruption of Inrush Currents of Large Motors" at the International Conference on Large Electric Systems in 2011. They attempted to connect RC buffer branches with various parameter combinations in parallel across the circuit breaker, demonstrating that it effectively suppressed the peak value and rate of rise of TRV at low voltage levels. However, at high voltage levels, the RC buffer branch has limited energy absorption and dissipation capabilities, often resulting in TRV becoming a slightly low-frequency but still high-amplitude oscillation. Furthermore, it did not consider the differences in suppression effects when facing multiple high-frequency oscillation components, thus failing to effectively limit TRV at high voltage levels.

[0008] (4) Technical report published by ENSPEC POWER in 2022:

[0009] The paper, "Optimizing Application of MV Surge Arresters in Resistor-Capacitor (RC) Snubbers," effectively suppresses peak voltage (TRV) by connecting a gapped metal oxide surge arrester in parallel with an RC snubber circuit across the circuit breaker. However, this method relies on the frequent operation of the metal oxide surge arrester to limit the peak value. At high voltage levels, TRV energy increases exponentially, posing a dual challenge to the energy withstand capability and lifespan of the metal oxide surge arrester.

[0010] In summary, the existing technology has the following problems:

[0011] (1) There are physical limits to simply relying on optimizing the insulation performance of the vacuum interrupter, making it difficult to match the high amplitude and high rise rate of TRV at high voltage levels.

[0012] (2) Traditional single capacitor or RC snubber circuits have limited ability to absorb and dissipate energy at high voltage levels, making it difficult to effectively suppress the amplitude and rise rate of multi-frequency TRV at the same time.

[0013] (3) Traditional methods for suppressing TRV rely on metal oxide surge arresters to limit peak values. Metal oxide surge arresters have a short lifespan due to frequent exposure to excessive energy surges. Summary of the Invention

[0014] The technical problem to be solved by this invention is the deficiency pointed out in the background art. This invention proposes a resonant network for suppressing transient recovery voltage of circuit breakers. It adopts a composite protection mechanism of "active frequency selective damping + peak clamping". By configuring a resonant branch with a specific resonant frequency, a low impedance path is formed at the main frequency component of the transient recovery voltage. The current that generates transient recovery voltage flowing through the line is actively guided into the resonant branch, thereby suppressing the peak value and rise rate of the transient recovery voltage. At the same time, a metal oxide surge arrester is used as backup protection to limit the high peak value of the transient recovery voltage in possible abnormal situations.

[0015] The technical solution of the present invention is as follows.

[0016] A resonant network for suppressing transient recovery voltage of a circuit breaker is provided, wherein the resonant network is connected in parallel across the circuit breaker; the resonant network consists of a metal oxide surge arrester and N resonant branches with identical structures connected in parallel with the metal oxide surge arrester, wherein the resonant branches consist of capacitors, resistors and inductors connected in series.

[0017] Let any one of the N resonant branches be denoted as the i-th resonant branch, i = 1, 2, ..., N; the number of resonant branches N and the resonant frequency f of the i-th resonant branch are... i Determined using the following method:

[0018] In the electromagnetic transient simulation program, an electromagnetic transient simulation model including a circuit breaker is established;

[0019] The circuit breaker is set to open at the moment the short-circuit current crosses zero. An electromagnetic transient simulation model is used to obtain the voltage across the circuit breaker over time from this moment onwards, thus obtaining the time-domain waveform of the transient recovery voltage. The peak voltage value u of this transient recovery voltage time-domain waveform is then obtained. cPerform a Fast Fourier Transform on the time-domain waveform of the transient recovery voltage to obtain the spectrum of the transient recovery voltage. The horizontal axis of the spectrum is the frequency f, and the vertical axis is the voltage amplitude |U(f)|. The voltage amplitude |U(f)| represents the voltage amplitude of the sinusoidal component with frequency f in the time-domain waveform of the transient recovery voltage.

[0020] In the spectrum of the transient recovery voltage, search for a value that satisfies |U(f)|≥0.2u c The candidate frequencies obtained satisfy |U(f)|≥0.2u c The number of candidate frequencies is M, and the candidate frequencies are sorted according to the magnitude of their corresponding voltage amplitudes |U(f)|, in the order of f. hj j=1,2,…,M;

[0021] From M candidate frequencies, N dominant frequencies are obtained, where N ≤ M. The dominant frequency corresponding to the i-th resonant branch is denoted as the dominant frequency f. mi resonant frequency f i Satisfied with: .

[0022] Preferably, the dominant frequency f mi The search process is as follows:

[0023] For each candidate frequency f hj Given its value range A j A j =[0.8f hj , 1.2f hj ], in the value interval A j Find the candidate frequency corresponding to the maximum voltage amplitude |U(f)|, denoted as f. hj;

[0024] All f The hj values ​​are merged into a set, and the repetitive frequency values ​​are removed to obtain N different frequency values;

[0025] Arrange these N frequency values ​​in descending order according to their corresponding voltage amplitudes |U(f)|, and denote them as the dominant frequencies f. mi , i=1,2,…,N.

[0026] Preferably, the parameters of the i-th resonant branch include the inductance value L. i Capacitance value C i and resistance value R i It shall be determined in the following manner;

[0027] Step 3.1, capacitance value C i The determination

[0028] Given a minimum capacitance value Cmin ;

[0029] The capacitance value C is determined as follows: i Design: When i=1, the capacitance value C1 satisfies C1≥10C min When i≥2, the capacitance value C i The value is in [C min 10C min Select within the interval;

[0030] Step 3.2, inductance value L i Design

[0031] According to the dominant frequency f mi And the capacitance value C determined in step 3.1 i Using the formula The inductance value L was calculated. i ;

[0032] Step 3.3, resistance value R i The determination

[0033] N resonant branches are connected in parallel across the circuit breaker in the electromagnetic transient simulation model, and simulation and calculation are performed simultaneously to obtain the resistance value R. i Specifically:

[0034] First, the damping coefficient is given in the following manner. The range of values ​​for:

[0035] Given minimum damping coefficient and maximum damping coefficient ;

[0036] When i=1, the damping coefficient The range of values ​​for is [ ,3 When i≥2, the damping coefficient The range of values ​​is [3 , ];

[0037] Secondly, calculate the minimum resistance value R. i,min and maximum resistance value R i,max The calculation formulas are as follows:

[0038] When i=1,

[0039] , ;

[0040] When i≥2

[0041] , ;

[0042] Determine the resistance value R i The scanning range is [ R i,min , R i,max ];

[0043] Then, at the resistance value R i Scan range [R] i,min R i,max [Set K numbers with equal spacing] The discrete resistance values ​​distributed across the range are used as scanning points, and any one of these scanning points is denoted as the j-th scanning point, with the discrete resistance value at that point denoted as . , =R i,min +(j-1) j=1,2,…,K;

[0044] The K discrete resistance values ​​of the i-th branch are combined into a resistance parameter vector R. Ai R Ai =(R i,1 , R i,2 ,…,R i,j ,…, R i,K ); and the resistance parameter vector R Ai Each discrete resistance value in Substituting the i-th resonant branch, simulation and calculation are performed in the electromagnetic transient simulation model to obtain the corresponding transient recovery voltage time-domain waveform and peak value. The discrete resistance value corresponding to the transient recovery voltage with the smallest peak value is selected as the resistance value R. i .

[0045] Preferably, the parameters of the metal oxide surge arrester are the continuous operating voltage U of the metal oxide surge arrester in the system. c and residual voltage U of metal oxide surge arrester res Its configuration simultaneously satisfies:

[0046] ;

[0047] Among them, U m U is the highest voltage when the system is operating normally. drm This represents the peak value of the dielectric recovery strength of the circuit breaker.

[0048] The system in question is the power system in which the circuit breaker is located.

[0049] Preferably, the minimum capacitance value C min =0.1μF; the minimum damping coefficient min=0.2, the maximum damping coefficient max =2.0.

[0050] Preferably, the electromagnetic transient simulation model is a simulation model established in an electromagnetic transient simulation program that includes power supply, grounding impedance, line equivalent impedance, circuit breaker and frequency modulation branch.

[0051] The topology of the electromagnetic transient simulation model is as follows: it consists of a power supply grounding impedance, a three-phase power supply, a three-phase line impedance, a three-phase circuit breaker, and three identical frequency modulation branches. One end of the power supply grounding impedance is grounded, and the other end is connected to the three-phase power supply. Each phase of the three-phase power supply is connected to a frequency modulation branch through the line impedance. The frequency modulation branch consists of a first frequency modulation resistor, a first frequency modulation capacitor, a second frequency modulation resistor, a second frequency modulation capacitor, a second frequency modulation inductor, and a time delay capacitor. The first frequency modulation resistor and the first frequency modulation capacitor are connected in series and then in parallel across the circuit breaker. The second frequency modulation resistor, the second frequency modulation capacitor, and the second frequency modulation inductor are connected in series and then in parallel across the circuit breaker. The time delay capacitor is connected separately in parallel across the circuit breaker.

[0052] Compared with the prior art, the beneficial effects of the present invention include:

[0053] (1) This invention adopts a composite protection mechanism of "active frequency selective damping + peak clamping". The resonant network realizes dual effective control of the rise steepness and peak value of the transient recovery voltage, and the metal oxide surge arrester limits the peak value of the high transient recovery voltage in possible abnormal situations, thus ensuring the reliability of the device. The composite protection mechanism formed by the two together ensures that the transient recovery voltage is always lower than the dielectric recovery strength, providing a strong guarantee for the breaking of vacuum AC circuit breakers at high voltage levels.

[0054] (2) The present invention adopts a parallel structure of multiple sets of resonant branches with different resonant frequencies to form a multi-frequency parallel resonant network. In view of the characteristics of transient recovery voltage with two or more high amplitude main frequency components under high voltage level, it provides multiple shunt and energy dissipation branches of specific frequency currents, so as to effectively suppress the high voltage transient recovery voltage with wide bandwidth and multiple main frequencies, avoid the problem of large difference in effect of traditional single parameter resonant branch under different working conditions, and significantly improve the adaptability of the device under different working conditions.

[0055] (3) This invention proposes a differentiated design strategy based on the damping coefficient. The damping range is set between 0.2 and 2.0, which can ensure that the resonant branch can fully consume energy without generating violent oscillations, and also ensure that it can fully absorb energy without shunting too little current and causing the capacitor to charge too slowly. At the same time, a low damping coefficient (0.2~0.6) is used in combination with a large capacitor value (≥1μF) for the first resonant branch with the highest amplitude to prioritize the rapid throughput of instantaneous high-power energy; for the secondary frequency components, a medium-high damping coefficient (0.6~2.0) is used in combination with a small capacitor value to prioritize the rapid decay of energy, effectively balancing the contradiction between the TRV suppression effect of the device and the cost of the device.

[0056] (4) The modular structure and robust design constructed in this invention allow the number of multiple resonant branches to be flexibly configured according to the actual transient recovery voltage spectrum characteristics of the system, avoiding over-design. The resonant branches exhibit a high impedance characteristic of more than 1000Ω at power frequency, and the leakage current is much less than 1mA under normal power frequency conditions, so they hardly draw energy from the system. When the transient recovery voltage characteristics deviate from the design value, the resonant network only shows that the suppression effect is enhanced or weakened, and will not produce a counter-effect such as increasing the peak value of the transient recovery voltage or increasing the rise rate. Even if a single branch fails, the remaining branches can still maintain part of the suppression function, which has high robustness. Attached Figure Description

[0057] Figure 1 This is a topology diagram of a resonant network used to suppress transient recovery voltage of a circuit breaker in an embodiment of the present invention.

[0058] Figure 2 This is a schematic waveform diagram showing the dielectric recovery strength and transient recovery voltage between the contacts during the short-circuit current interruption process of a circuit breaker.

[0059] Figure 3 This is a schematic diagram comparing the transient recovery voltage waveforms before and after adding the resonant network of this invention when the circuit breaker interrupts the short-circuit current under a given condition.

[0060] Figure 4 A comparison of transient recovery voltage waveforms when a metal oxide surge arrester is used alone as a transient recovery voltage suppression measure under a given condition.

[0061] Figure 5 This is a comparison of transient recovery voltage waveforms before and after adding a resonant network under a non-standard transient recovery voltage condition.

[0062] Figure 6 The topology diagram of the electromagnetic transient simulation model established for this invention. Detailed Implementation

[0063] The present invention will now be described in more detail with reference to the accompanying drawings and embodiments.

[0064] Figure 1 This is a topology diagram of a resonant network used to suppress transient recovery voltage of a circuit breaker in an embodiment of the present invention. Figure 1 The surge arrester in the figure is a metal oxide surge arrester. As can be seen from the figure, the present invention provides a resonant network for suppressing transient recovery voltage of a circuit breaker, which is connected in parallel across the circuit breaker. The resonant network consists of a metal oxide surge arrester and N resonant branches with identical structures connected in parallel with the metal oxide surge arrester. The resonant branches are composed of capacitors, resistors, and inductors connected in series.

[0065] Let any one of the N resonant branches be denoted as the i-th resonant branch, i = 1, 2, ..., N; the number of resonant branches N and the resonant frequency f of the i-th resonant branch are... i Determined using the following method:

[0066] In the electromagnetic transient simulation program, an electromagnetic transient simulation model including a circuit breaker is established;

[0067] The circuit breaker is set to open at the moment the short-circuit current crosses zero. An electromagnetic transient simulation model is used to obtain the voltage across the circuit breaker over time from this moment onwards, thus obtaining the time-domain waveform of the transient recovery voltage. The peak voltage value u of this transient recovery voltage time-domain waveform is then obtained. c Perform a Fast Fourier Transform on the time-domain waveform of the transient recovery voltage to obtain the spectrum of the transient recovery voltage. The horizontal axis of the spectrum is the frequency f, and the vertical axis is the voltage amplitude |U(f)|. The voltage amplitude |U(f)| represents the voltage amplitude of the sinusoidal component with frequency f in the time-domain waveform of the transient recovery voltage.

[0068] In the spectrum of the transient recovery voltage, search for a value that satisfies |U(f)|≥0.2u c The candidate frequencies obtained satisfy |U(f)|≥0.2u c The number of candidate frequencies is M, and the candidate frequencies are sorted according to the magnitude of their corresponding voltage amplitudes |U(f)|, in the order of f. hj j=1,2,…,M;

[0069] From M candidate frequencies, N dominant frequencies are obtained, where N ≤ M. The dominant frequency corresponding to the i-th resonant branch is denoted as the dominant frequency f. mi resonant frequency f i Satisfied with: .

[0070] In this embodiment, the dominant frequency f mi The search process is as follows:

[0071] For each candidate frequency f hj Given its value range Aj A j =[0.8f hj , 1.2f hj ], in the value interval A j Find the candidate frequency corresponding to the maximum voltage amplitude |U(f)|, denoted as f. hj;

[0072] All f The hj values ​​are merged into a set, and the repetitive frequency values ​​are removed to obtain N different frequency values;

[0073] Arrange these N frequency values ​​in descending order according to their corresponding voltage amplitudes |U(f)|, and denote them as the dominant frequencies f. mi , i=1,2,…,N.

[0074] In this embodiment, taking the expected transient recovery voltage specified in GB / T 1984-2024 under the T100 test mode of 126kV, first polarity factor of 1.3 as an example, the electromagnetic transient simulation program PSCAD / EMTDC is used to establish a system simulation model (hereinafter referred to as the transient recovery voltage simulation model). Figure 6 This is a topology diagram of the electromagnetic transient simulation model established in this invention. The electromagnetic transient simulation model is a simulation model established in the electromagnetic transient simulation program, which includes power supply, grounding impedance, line equivalent impedance, circuit breaker, and frequency modulation branch.

[0075] Depend on Figure 6 As can be seen, the topology of this electromagnetic transient simulation model is as follows: it consists of a power supply grounding impedance, a three-phase power supply, a three-phase line impedance, a three-phase circuit breaker, and three identical frequency modulation branches. One end of the power supply grounding impedance is grounded, and the other end is connected to each of the three-phase power supplies. Each phase of the three-phase power supply is connected to a frequency modulation branch through the line impedance. The frequency modulation branch consists of a first frequency modulation resistor, a first frequency modulation capacitor, a second frequency modulation resistor, a second frequency modulation capacitor, a second frequency modulation inductor, and a time delay capacitor. The first frequency modulation resistor and the first frequency modulation capacitor are connected in series and then in parallel across the circuit breaker. The second frequency modulation resistor, the second frequency modulation capacitor, and the second frequency modulation inductor are connected in series and then in parallel across the circuit breaker. The time delay capacitor is connected separately in parallel across the circuit breaker.

[0076] exist Figure 6 In the diagram, L0 is the power supply grounding impedance, and R... line and L line These are the equivalent resistance and reactance of the line in the line impedance, S. A S B S C The circuit breakers for the three-phase branches A, B, and C are respectively, R T1 For the first frequency modulation resistor, C T1 For the first frequency modulation capacitor, RT2 For the second frequency modulation resistor, C T2 For the second frequency modulation capacitor, L T2 For the second frequency modulation inductor, C d This is a time delay capacitor.

[0077] By adjusting the component parameters in the frequency modulation branch of the simulation model, a transient recovery voltage meeting the national standard is generated under this operating condition. After performing a Fast Fourier Transform on this transient recovery voltage, its spectrum is obtained. From this spectrum, two candidate frequencies f can be obtained, with voltage amplitudes |U(f)| greater than 0.2 times the peak value of the transient recovery voltage, and sorted in descending order of their corresponding |U(f)|. h1 f h2 f h1 ≈500Hz, f h2 ≈2kHz, the dominant frequency is f. m1 ≈500Hz, f m2 ≈2kHz.

[0078] Therefore, in this embodiment, N=2, and two resonant branches are set, with the resonant frequencies of the two resonant branches set to f1=500Hz and f2=2kHz respectively.

[0079] In this embodiment, the parameters of the i-th resonant branch include the inductance value L. i Capacitance value C i and resistance value R i It shall be determined in the following manner;

[0080] Step 3.1, capacitance value C i The determination

[0081] Given a minimum capacitance value C min ;

[0082] The capacitance value C is determined as follows: i Design: When i=1, the capacitance value C1 satisfies C1≥10C min When i≥2, the capacitance value C i The value is in [C min 10C min Select within the interval;

[0083] Step 3.2, inductance value L i Design

[0084] According to the dominant frequency f mi And the capacitance value C determined in step 3.1 i Using the formula The inductance value L was calculated. i .

[0085] Step 3.3, resistance value Ri The determination

[0086] N resonant branches are connected in parallel across the circuit breaker in the electromagnetic transient simulation model, and simulation and calculation are performed simultaneously to obtain the resistance value R. i Specifically:

[0087] First, the damping coefficient is given in the following manner. The range of values ​​for:

[0088] Given minimum damping coefficient and maximum damping coefficient ;

[0089] When i=1, the damping coefficient The range of values ​​for is [ ,3 When i≥2, the damping coefficient The range of values ​​is [3 , ];

[0090] Secondly, calculate the minimum resistance value R. i,min and maximum resistance value R i,max The calculation formulas are as follows:

[0091] When i=1,

[0092] , ;

[0093] When i≥2

[0094] , ;

[0095] Determine the resistance value R i The scanning range is [ R i,min , R i,max ].

[0096] Then, at the resistance value R i Scan range [R] i,min R i,max [Set K numbers with equal spacing] The discrete resistance values ​​distributed across the range are used as scanning points, and any one of these scanning points is denoted as the j-th scanning point, with the discrete resistance value at that point denoted as . , =R i,min +(j-1) j=1,2,…,K;

[0097] The K discrete resistance values ​​of the i-th branch are combined into a resistance parameter vector R. Ai R Ai =(R i,1 , R i,2 ,…,R i,j ,…, R i,K ); and the resistance parameter vector R Ai Each discrete resistance value in Substituting the i-th resonant branch, simulation and calculation are performed in the electromagnetic transient simulation model to obtain the corresponding transient recovery voltage time-domain waveform and peak value. The discrete resistance value corresponding to the transient recovery voltage with the smallest peak value is selected as the resistance value R. i .

[0098] In this embodiment, the minimum capacitance value C min =0.1μF; the minimum damping coefficient min =0.2, the maximum damping coefficient max =2.0.

[0099] In this embodiment, the resonant frequency of the first resonant branch is 500Hz. A low-impedance path needs to be formed for the component of the transient recovery voltage with an oscillation frequency near 500Hz to absorb the main energy. Therefore, a large capacitance value C1 is required to absorb more energy. When C1 ≥ 10C... min That is, C1 is selected within the range of C1≥1μF; the resonant frequency of the second resonant branch is 2kHz, and the energy of the component with the oscillation frequency near 2kHz in the corresponding transient recovery voltage is relatively low, so a smaller capacitance value C2 can be set to meet the requirements, while effectively reducing cost and volume.

[0100] In this embodiment, referring to the commonly used preferred capacitor number system E6 proposed in the relevant standard IEC 60063 formulated by the International Electrotechnical Commission, the E6 number system takes values ​​of 1.0, 1.5, 2.2, 3.3, 4.7, and 6.8 multiplied by decimal multiples. At the same time, considering the balance between the increased energy absorption capacity as the capacitance increases and the increased size and cost, C1=3.3μF and C2=0.68μF are selected. The corresponding inductance values ​​are selected through calculation as L1=30.7mH and L2=9.3mH.

[0101] In this embodiment, the damping coefficient of each resonant branch essentially reflects the relative ratio between the energy dissipation rate of the resistor and the energy exchange rate of the inductor-capacitor circuit. A larger damping coefficient means that the resistor dissipates energy faster, and a smaller damping coefficient means that the branch has a stronger energy storage capacity. Prioritizing the absorption of higher energy components and prioritizing the consumption of lower energy components, the damping coefficients of the first resonant branch are calculated based on the minimum and maximum damping coefficients. The range of values ​​for ζ1 is [0.2, 0.6], and for ζ2 is [0.6, 2.0]. Further calculations show that the range of values ​​for R1 is approximately [40Ω, 120Ω], and for R2 is approximately [140Ω, 470Ω].

[0102] In this embodiment, two resonant branches are connected in parallel across the circuit breaker in the aforementioned transient recovery voltage simulation model, and the determined capacitor and inductor values ​​are filled in. The Multiple Run component in PSCAD / EMTDC is selected, and the values ​​of R1 and R2 are set as variables as inputs to Multiple Run. The iteration of R1 starts at 40Ω and ends at 120Ω; the iteration of R2 starts at 140Ω and ends at 470Ω, with a step size of 10Ω for both. The absolute value of the transient recovery voltage peak across the circuit breaker is used as the output of Multiple Run. Simulation is performed, and after the iteration is complete, the combination of R1 and R2 resistance values ​​corresponding to the lowest absolute value of the transient recovery voltage peak is found from the simulation results: R1 = 50Ω and R2 = 250Ω.

[0103] In this embodiment, the parameter of the metal oxide surge arrester is the continuous operating voltage U of the metal oxide surge arrester in the system. c and residual voltage U of metal oxide surge arrester res Its configuration simultaneously satisfies:

[0104] ;

[0105] Among them, U m U is the highest voltage when the system is operating normally. drm This refers to the dielectric recovery strength of the circuit breaker at the peak of the transient recovery voltage.

[0106] The system in question is the power system in which the circuit breaker is located.

[0107] In this embodiment, the highest voltage during normal system operation is the three-phase power line voltage of 126kV, and the continuous operating voltage U of the metal oxide surge arrester is... c Then set it to U c =1.1×126kV / √3≈80kV, ensuring that the metal oxide surge arrester will not malfunction during normal system operation; assuming the dielectric recovery strength of the circuit breaker at the peak transient recovery voltage is 165kV, then the residual voltage U of the metal oxide surge arrester is...res Set in U res =0.9×165kV≈148kV, ensuring that when a fault such as an abnormality in the resonant branch causes the transient recovery voltage to exceed the dielectric recovery strength, the transient recovery voltage is clamped to a safe value.

[0108] To demonstrate the beneficial effects of the present invention, a simulation was performed.

[0109] Figure 2 This diagram illustrates the dielectric recovery strength and transient recovery voltage between the contacts during the short-circuit current interruption process of a circuit breaker. The dashed line represents the dielectric recovery strength curve of the gap after the circuit breaker contacts separate; it monotonically increases with time and gradually approaches saturation, reflecting the dynamic process of insulation performance recovery of the vacuum dielectric after the current crosses zero. The solid line represents the actual transient recovery voltage waveform, which exhibits high-frequency oscillation characteristics, rapidly rising to its peak value in the initial stage after the current crosses zero. Ideally, under the condition of successful interruption, the instantaneous value of the actual transient recovery voltage should always be lower than the dielectric recovery strength at the same moment throughout the entire transient recovery process. Figure 2 The solid line must always be below the dashed line. If the rise steepness of the transient recovery voltage is too large or the peak value is too high, i.e., the peak value of the solid line exceeds the dielectric recovery strength shown by the dashed line, electrical breakdown will occur between the breaks, leading to interruption failure and potentially causing a serious accident.

[0110] Figure 3 This diagram illustrates a comparison of transient recovery voltage waveforms before and after incorporating the resonant network of this invention when the circuit breaker interrupts the short-circuit current under a given condition. The given condition is: initial polarity factor of 1.3, equipment rated voltage of 126kV, and end-fault short-circuit interruption current of 100%. The solid line in the diagram represents the actual transient recovery voltage waveform without the resonant network, while the dashed line represents the transient recovery voltage waveform with the resonant network. The comparison shows that the device of this invention significantly suppresses transient recovery voltage: the peak value of the transient recovery voltage decreases from 187kV to 144kV, a reduction of 43kV, or 23%; the rise of the transient recovery voltage slows significantly after approximately 30μs, and the peak value and rise rate of the transient recovery voltage are significantly suppressed during the critical dielectric recovery period after the current crosses zero.

[0111] Figure 4 This is a comparison of transient recovery voltage waveforms when a metal oxide surge arrester is used alone as a transient recovery voltage suppression measure under a given state. The given state and... Figure 2The waveforms are identical. The solid line in the figure represents the actual transient recovery voltage waveform without the resonant network, while the dashed line represents the transient recovery voltage waveform after a metal oxide surge arrester is connected in parallel across the circuit breaker. From the waveform comparison, it can be observed that the metal oxide surge arrester exhibits high impedance characteristics in the initial stage of the transient recovery voltage rise. At this time, the dashed line and the solid line basically coincide, indicating that the metal oxide surge arrester does not significantly affect the initial rise of the transient recovery voltage. When the transient recovery voltage rises to the operating threshold of the metal oxide surge arrester (approximately 148kV), the metal oxide surge arrester quickly enters a low-impedance conduction state, clamping the subsequent voltage peak near this threshold.

[0112] Figure 5 This figure shows a comparison of transient recovery voltage waveforms before and after the addition of a resonant network under a non-standard transient recovery voltage condition. The dotted lines in the figure represent... Figure 2 The transient recovery voltage envelope, plotted according to the expected transient recovery voltage value given by the national standard under the same conditions, represents a transient recovery voltage under a non-standard operating condition that may occur in reality. Its rise rate and peak value are lower compared to the transient recovery voltage under the standard operating condition. The dashed line represents the transient recovery voltage after adding a resonant network under this non-standard operating condition. As can be seen from the figure, after adding a resonant network under the non-standard operating condition, the peak transient recovery voltage is further reduced from approximately 155 kV to approximately 130 kV, a reduction of approximately 16%, still showing a good suppression effect.

Claims

1. A resonant network for suppressing transient recovery voltage of a circuit breaker, the resonant network being connected in parallel across the circuit breaker; characterized in that, The resonant network consists of a metal oxide surge arrester and N resonant branches with the same structure connected in parallel with the metal oxide surge arrester. The resonant branches are composed of capacitors, resistors and inductors connected in series. Let any one of the N resonant branches be denoted as the i-th resonant branch, i = 1, 2, ..., N; the number of resonant branches N and the resonant frequency f of the i-th resonant branch are... i Determined using the following method: In the electromagnetic transient simulation program, an electromagnetic transient simulation model including a circuit breaker is established; The circuit breaker is set to open at the moment the short-circuit current crosses zero. An electromagnetic transient simulation model is used to obtain the voltage across the circuit breaker over time from this moment onwards, thus obtaining the time-domain waveform of the transient recovery voltage. The peak voltage value u of this transient recovery voltage time-domain waveform is then obtained. c Perform a Fast Fourier Transform on the time-domain waveform of the transient recovery voltage to obtain the spectrum of the transient recovery voltage. The horizontal axis of the spectrum is the frequency f, and the vertical axis is the voltage amplitude |U(f)|. The voltage amplitude |U(f)| represents the voltage amplitude of the sinusoidal component with frequency f in the time-domain waveform of the transient recovery voltage. In the spectrum of the transient recovery voltage, search for a value that satisfies |U(f)|≥0.2u c The candidate frequencies obtained satisfy |U(f)|≥0.2u c The number of candidate frequencies is M, and the candidate frequencies are sorted according to the magnitude of their corresponding voltage amplitudes |U(f)|, in the order of f. hj j=1,2,…,M; From M candidate frequencies, N dominant frequencies are obtained, where N ≤ M. The dominant frequency corresponding to the i-th resonant branch is denoted as the dominant frequency f. mi resonant frequency f i Satisfied with: .

2. The resonant network for suppressing transient recovery voltage of a circuit breaker according to claim 1, characterized in that, The dominant frequency f mi The search process is as follows: For each candidate frequency f hj Given its value range A j A j =[0.8f hj , 1.2f hj ], in the value interval A j Find the candidate frequency corresponding to the maximum voltage amplitude |U(f)|, denoted as f. hj; All f The hj values ​​are merged into a set, and the repetitive frequency values ​​are removed to obtain N different frequency values; Arrange these N frequency values ​​in descending order according to their corresponding voltage amplitudes |U(f)|, and denote them as the dominant frequencies f. mi , i=1,2,…,N.

3. A resonant network for suppressing transient recovery voltage of a circuit breaker according to claim 1, characterized in that, The parameters of the i-th resonant branch include the inductance value L. i Capacitance value C i and resistance value R i It shall be determined in the following manner; Step 3.1, capacitance value C i The determination Given a minimum capacitance value C min ; The capacitance value C is determined as follows: i Design: When i=1, the capacitance value C1 satisfies C1≥10C min When i≥2, the capacitance value C i The value is in [C min 10C min Select within the interval; Step 3.2, inductance value L i Design According to the dominant frequency f mi And the capacitance value C determined in step 3.1 i Using the formula The inductance value L was calculated. i ; Step 3.3, resistance value R i The determination N resonant branches are connected in parallel across the circuit breaker in the electromagnetic transient simulation model, and simulation and calculation are performed simultaneously to obtain the resistance value R. i Specifically: First, the damping coefficient is given in the following manner. The range of values ​​for: Given minimum damping coefficient and maximum damping coefficient ; When i=1, the damping coefficient The range of values ​​for is [ ,3 When i≥2, the damping coefficient The range of values ​​is [3]. , ]; Secondly, calculate the minimum resistance value R. i,min and maximum resistance value R i,max The calculation formulas are as follows: When i=1 ， ； When i≥2 ， ； Determine the resistance value R i The scanning range is [ R i,min , R i,max ]; Then, at the resistance value R i Scan range [R] i,min R i,max [Set K numbers at equal intervals] The discrete resistance values ​​distributed across the range are used as scanning points, and any one of these scanning points is denoted as the j-th scanning point, with the discrete resistance value at that point denoted as . , =R i,min +(j-1) j=1,2,…,K; The K discrete resistance values ​​of the i-th branch are combined into a resistance parameter vector R. Ai R Ai =(R i,1 , R i,2 ,…, R i,j ,…,R i,K ); and the resistance parameter vector R Ai Each discrete resistance value in Substituting the i-th resonant branch, simulation and calculation are performed in the electromagnetic transient simulation model to obtain the corresponding transient recovery voltage time-domain waveform and peak value. The discrete resistance value corresponding to the transient recovery voltage with the smallest peak value is selected as the resistance value R. i .

4. A resonant network for suppressing transient recovery voltage of a circuit breaker according to claim 1, characterized in that, The parameters of the metal oxide surge arrester are the continuous operating voltage U of the metal oxide surge arrester in the system. c and residual voltage U of metal oxide surge arrester res Its configuration simultaneously satisfies: Among them, U m U is the highest voltage when the system is operating normally. drm This represents the peak value of the dielectric recovery strength of the circuit breaker. The system in question is the power system in which the circuit breaker is located.

5. A resonant network for suppressing transient recovery voltage of a circuit breaker according to claim 3, characterized in that, The minimum capacitance value C min =0.1μF; the minimum damping coefficient min =0.2, the maximum damping coefficient max =2.

0.

6. A resonant network for suppressing transient recovery voltage of a circuit breaker according to claim 1, characterized in that, The electromagnetic transient simulation model is a simulation model established in the electromagnetic transient simulation program that includes power supply, grounding impedance, line equivalent impedance, circuit breaker and frequency modulation branch. The topology of the electromagnetic transient simulation model is as follows: it consists of a power supply grounding impedance, a three-phase power supply, a three-phase line impedance, a three-phase circuit breaker, and three identical frequency modulation branches. One end of the power supply grounding impedance is grounded, and the other end is connected to the three-phase power supply. Each phase of the three-phase power supply is connected to a frequency modulation branch through the line impedance. The frequency modulation branch consists of a first frequency modulation resistor, a first frequency modulation capacitor, a second frequency modulation resistor, a second frequency modulation capacitor, a second frequency modulation inductor, and a time delay capacitor. The first frequency modulation resistor and the first frequency modulation capacitor are connected in series and then in parallel across the circuit breaker. The second frequency modulation resistor, the second frequency modulation capacitor, and the second frequency modulation inductor are connected in series and then in parallel across the circuit breaker. The time delay capacitor is connected separately in parallel across the circuit breaker.

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