A circuit for suppressing overvoltage when switching parallel capacitors in an SF6 circuit breaker.

Abstract

This invention provides a suppression circuit for overvoltage when SF6 circuit breakers switch parallel capacitors, belonging to the field of overvoltage technology in electrical engineering. The suppression circuit consists of a load switch, a resistor, and a capacitor connected in series. The opening and closing of the load switch controls the switching on and off of the suppression circuit. The opening and closing of the load switch is linked to the opening and closing of the SF6 circuit breaker (QF), thus suppressing the overvoltage when the SF6 circuit breaker switches parallel capacitors, thereby solving the problem of equipment damage caused by overvoltage when the SF6 circuit breaker switches parallel capacitor banks. Furthermore, the resistor and capacitor in the suppression circuit of this invention can be integrated into the porcelain bushing of the current transformer or the lower porcelain bushing of the circuit breaker, transforming the theoretical method of the suppression circuit into two field application measures. In field use, only the original current transformer or circuit breaker needs to be replaced, making on-site installation convenient and construction efficient.

Description

Technical Field

[0001] This invention belongs to the field of overvoltage technology in electrical engineering, specifically relating to a circuit for suppressing overvoltage when switching parallel capacitors in an SF6 circuit breaker. Background Technology

[0002] Parallel capacitor banks are crucial equipment for regulating reactive power in power systems. In substations, parallel capacitor banks are connected to the low-voltage busbar in the form of parallel capacitor bank bays. Circuit breakers (mostly SF6 pole-mounted circuit breakers) configured in these bays are used to connect and disconnect the parallel capacitor banks and their series reactors. Statistics on the causes of parallel capacitor failures in recent years show that overvoltage accidents caused by switching parallel capacitor banks account for approximately 70%-80% of all overvoltage accidents in the entire power system. Furthermore, an analysis by a power company suggests a strong correlation between the failure rate of parallel capacitor banks and the frequency of their switching.

[0003] Due to the lack of effective measures to suppress overvoltage during circuit breaker switching of parallel capacitor banks, and pressured by safety concerns regarding the failure rate of circuit breaker switching of parallel capacitor banks, especially the prominent failure rate of the originally maintenance-free dry-type air-core reactors in the parallel capacitor bank bays, many substations have abandoned the use of dry-type air-core reactors and reverted to oil-immersed series reactors. This alleviated the predicament of the high failure rate of dry-type air-core reactors for a certain period. However, besides increasing the equipment maintenance workload of substation technicians, this measure, in terms of the fundamental nature of the high equipment failure rate, still did not fundamentally solve the problem of equipment damage caused by overvoltage during SF6 circuit breaker switching of parallel capacitor banks. Furthermore, even though the failure rate of oil-immersed series reactors is lower than that of dry-type air-core reactors for a certain period, the threat of overvoltage and failure of parallel capacitors and current transformers in this bay still exists.

[0004] Therefore, it is necessary to propose a suppression circuit for overvoltage when SF6 circuit breakers switch parallel capacitors and a suppression device or apparatus that meets the requirements of field use, so as to solve the problem of equipment damage caused by overvoltage when SF6 circuit breakers switch parallel capacitor banks. Summary of the Invention

[0005] This invention provides a suppression circuit for overvoltage when an SF6 circuit breaker switches parallel capacitors. Its purpose is to suppress the occurrence and development of overvoltage when the SF6 circuit breaker switches parallel capacitors, reduce the overvoltage impact of the operation overvoltage on the equipment insulation, and solve the technical problem of equipment damage caused by overvoltage when the SF6 circuit breaker switches parallel capacitor banks.

[0006] To achieve the objective of this invention, a circuit for suppressing overvoltage during SF6 circuit breaker switching of parallel capacitors is employed. The switching refers to the operation of opening or closing the SF6 circuit breaker to connect or disconnect a group of parallel capacitors C. The parallel capacitors C belong to a parallel capacitor bank interval, which also includes a disconnecting switch QS1, an SF6 circuit breaker QF, a current transformer CT, and a series reactor L. D The disconnecting switch QS2 and surge arrester MOA are connected in the following manner: the first end of the disconnecting switch QS1 is connected to the low-voltage busbar M of the main transformer in the substation, and its end is connected in series with the SF6 circuit breaker QF, current transformer CT, series reactor LD, parallel capacitor C and disconnecting switch QS2 in sequence. The first end of the surge arrester MOA is connected to the series reactor L. D The parallel capacitor bank C is connected to the ground at its end; the low-voltage side bus M is the bus connected to the low-voltage side of the main transformer of the substation, and multiple other electrical equipment bays are connected in parallel on the bus M.

[0007] The suppression circuit for overvoltage of the SF6 circuit breaker switching parallel capacitor is referred to as the suppression circuit. The suppression circuit is composed of a load switch QL, a resistor QR, and a capacitor QC connected in series. The suppression circuit is added as a new branch and connected in parallel in the above-mentioned parallel capacitor bank interval. Its connection method is as follows: the first end of the load switch QL is connected between the SF6 circuit breaker QF and the current transformer CT, and the end of the capacitor QC is grounded.

[0008] When the SF6 circuit breaker QF needs to be closed, the load switch QL closes first, and then the SF6 circuit breaker QF closes. That is, during the closing process of the SF6 circuit breaker QF, the resistor QR and capacitor QC in the suppression circuit are in the working state. When the SF6 circuit breaker QF needs to be opened, the SF6 circuit breaker QF opens first, and then the load switch QL opens. That is, during the opening process of the SF6 circuit breaker QF, the load switch QL is still in the closed state, and the resistor QR and capacitor QC in the suppression circuit are still connected to the parallel capacitor bank at intervals, that is, in the working state.

[0009] Preferably, the outermost layer of the current transformer (CT) is a porcelain bushing, and the suppression circuit is integrated in the porcelain bushing of the current transformer (CT). The current transformer (CT) with the above-mentioned suppression circuit integrated is referred to as a capacitive current transformer.

[0010] Preferably, the SF6 circuit breaker QF is a column-type circuit breaker, consisting of upper and lower sections. The suppression circuit is integrated in the lower section cavity of the column-type circuit breaker, and the SF6 circuit breaker QF with the above-mentioned suppression circuit integrated is referred to as the suppression circuit breaker.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0012] 1. This invention proposes a suppression circuit for overvoltage when switching parallel capacitors in an SF6 circuit breaker. The suppression circuit utilizes a load switch QL linked to the SF6 circuit breaker QF for opening and closing. During the opening and closing process of the SF6 circuit breaker QF, a resistor QR and a capacitor QC are connected. These connected resistors and capacitors can alter the high-frequency oscillation parameters of the transient electrical circuit during the switching process, reducing the amplitude and steepness of the switching overvoltage, and lowering the oscillation frequency of the switching overvoltage. This effectively suppresses the occurrence and development of overvoltage, ultimately solving the problem of equipment damage caused by overvoltage when switching parallel capacitor banks in an SF6 circuit breaker.

[0013] 2. This invention also proposes an implementation method for suppressing overvoltage of SF6 circuit breaker switching parallel capacitors, that is, a method for implementing suppression equipment that can meet the needs of field use; specifically, it proposes two methods: a capacitive current transformer and a suppression circuit breaker. Based on the traditional structure of current transformers and circuit breakers, electrical components such as resistors QR and capacitors QC in the suppression circuit are integrated into the porcelain bushing of the current transformer or the lower porcelain bushing of the circuit breaker. This transforms the circuit theory method into a field application measure, and while specifying the suppression theory method, it also provides the implementation means, thereby improving the practical value of the suppression circuit.

[0014] 3. This invention proposes two implementation methods for suppression devices that can meet on-site requirements. Both the described capacitive current transformer and a suppression circuit breaker integrate the suppression circuit with the current transformer or circuit breaker. Without altering the key structure of the original current transformer or circuit breaker, the suppression circuit is added, achieving integration. Because no additional electrical equipment or devices are added, during substation renovation, only the original current transformer or circuit breaker needs to be replaced with a capacitive current transformer or suppression circuit breaker. There is no need to consider issues such as installation location and electrical distance caused by adding equipment; thus, this method is convenient and efficient in construction. Attached Figure Description

[0015] Figure 1 This is a wiring diagram for a circuit that suppresses overvoltage when switching parallel capacitors in an SF6 circuit breaker.

[0016] Figure 2 This is an equivalent circuit diagram for switching a 66kV parallel capacitor bank in a 500kV substation.

[0017] Figure 3 This is a waveform diagram of the voltage at the beginning of the series reactor when the SF6 circuit breaker without suppression circuit is opened.

[0018] Figure 4 This is a waveform diagram of the voltage at the beginning of the series reactor when the SF6 circuit breaker with suppression circuit is tripped. Specific implementation methods

[0019] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0020] This invention provides a circuit for suppressing overvoltage when switching parallel capacitors using an SF6 circuit breaker. The switching refers to the operation of opening or closing the SF6 circuit breaker to connect or disconnect a group of parallel capacitors C.

[0021] Figure 1 This is a wiring diagram for a circuit that suppresses overvoltage when an SF6 circuit breaker switches parallel capacitors. Figure 1 As can be seen, the parallel capacitor C belongs to the parallel capacitor bank interval, which also includes the disconnecting switch QS1, the SF6 circuit breaker QF, the current transformer CT, and the series reactor L. D The disconnecting switch QS2 and surge arrester MOA are connected in the following manner: the first end of the disconnecting switch QS1 is connected to the busbar M on the low-voltage side of the main transformer of the substation, and its end is connected to the SF6 circuit breaker QF, the current transformer CT, and the series reactor L. D The parallel capacitor C and the disconnecting switch QS2 are connected in series in sequence, and the first end of the surge arrester MOA is connected to the series reactor L. D The parallel capacitor bank C is connected to the ground at its end; the low-voltage side bus M is the bus connected to the low-voltage side of the main transformer of the substation, and multiple other electrical equipment bays are connected in parallel on the bus M.

[0022] The suppression circuit for overvoltage of the SF6 circuit breaker switching parallel capacitor is referred to as the suppression circuit. The suppression circuit is composed of a load switch QL, a resistor QR, and a capacitor QC connected in series. The suppression circuit is added as a new branch and connected in parallel in the above-mentioned parallel capacitor bank interval. Its connection method is as follows: the first end of the load switch QL is connected between the SF6 circuit breaker QF and the current transformer CT, and the end of the capacitor QC is grounded.

[0023] When the SF6 circuit breaker QF needs to be closed, the load switch QL closes first, and then the SF6 circuit breaker QF closes. That is, during the closing process of the SF6 circuit breaker QF, the resistor QR and capacitor QC in the suppression circuit are in the working state. When the SF6 circuit breaker QF needs to be opened, the SF6 circuit breaker QF opens first, and then the load switch QL opens. That is, during the opening process of the SF6 circuit breaker QF, the load switch QL is still in the closed state, and the resistor QR and capacitor QC in the suppression circuit are still connected to the parallel capacitor bank at intervals, that is, in the working state.

[0024] In this embodiment, the SF6 circuit breaker QF is a column-type circuit breaker, consisting of upper and lower sections. The suppression circuit is integrated into the lower section of the column-type circuit breaker, and the SF6 circuit breaker QF with integrated control circuit is referred to as the suppression circuit breaker. Specifically, in this embodiment, the voltage level on the low-voltage side of the 500kV substation is 66kV or 35kV. The SF6 circuit breaker QF for this voltage level is a column-type circuit breaker, which consists of upper and lower sections. Figure 1 In this circuit, the SF6 circuit breaker QF and the suppression circuit are integrated into one unit, which together constitute the suppression circuit breaker. Its circuit diagram is shown below. Figure 1 The block diagram is shown in the figure.

[0025] The suppression circuit can also be integrated using another method. In this embodiment, the outermost layer of the current transformer (CT) is a porcelain bushing, and the suppression circuit is integrated into the porcelain bushing of the current transformer (CT). The current transformer (CT) with the integrated control circuit is referred to as a capacitive current transformer.

[0026] To demonstrate the beneficial effects of this invention, it was tested. During the testing, it was conducted according to… Figure 1 The main wiring diagram is shown, and the calculated parameters for each electrical device in the substation are shown in Table 1. Among them, QR = 100Ω, and capacitor QC = 64nF.

[0027] Without the addition of a suppression circuit, the equivalent circuit diagram for switching a 66kV parallel capacitor bank in a 500kV substation is as follows: Figure 2 As shown. During the switching process, the parallel capacitor banks intermittently form an equivalent circuit for switching a 66kV parallel capacitor bank in a 500kV substation. Figure 2 In this circuit, the equivalent circuit includes the equivalent inductance L of the series reactor and the capacitance C of the series reactor to ground. L Equivalent capacitance C of the capacitor bank ∑ Switch K, equivalent power supply G, and equivalent inductor L on the power supply side G .

[0028] The switch K is the equivalent switching element of the SF6 circuit breaker QF during the transient process of opening or closing. The start time of this transient process is t = t0. When opening, the SF6 circuit breaker QF begins to change from the closed state to the open state at t = t0. When closing, the SF6 circuit breaker QF begins to change from the open state to the closed state at t = t0.

[0029] The equivalent power source G is a finite power source seen from the bus M into the main transformer T. This power source is a 66kV sinusoidal power source, which is equal to the operating voltage of the bus M. At time t = t0, the voltage amplitude of the equivalent power source G is denoted as U0.

[0030] The equivalent inductance L on the power supply side GTo take into account the transformer short-circuit voltage percentage, the equivalent inductance of the station service transformer, the main transformer T and the connecting leads between the bus M and the busbar.

[0031] The equivalent inductance L of the series reactor is the series reactor L D The inductance value, the capacitance C of the series reactor to ground L For the series reactor L during transient process D The capacitance to ground.

[0032] The equivalent capacitance C of the capacitor bank ∑ It is the equivalent capacitance of the parallel capacitor bank C during the transient process. ∑ It is the parallel capacitor bank C, and the neutral point capacitance to ground of the parallel capacitor bank C. CN The capacitance C to ground after being connected in series and then in parallel with the capacitor bank C The equivalent capacitance of the three.

[0033] Table 1 Calculation parameters for electrical equipment

[0034]

[0035] In the verification, the overvoltage at the beginning of the 66kV parallel capacitor bank in a 500kV substation was calculated before and after the addition of the suppression circuit, with the end closest to transformer T as the beginning. The waveform characteristics such as amplitude and frequency of the overvoltage waveform were compared.

[0036] Figure 3 This is a waveform diagram of the voltage at the beginning of the series reactor when an SF6 circuit breaker without suppression circuit is tripped. Figure 4 The diagram shows the voltage waveform at the beginning of the series reactor when the SF6 circuit breaker without suppression circuit is tripped, where Ua, Ub, and Uc are the three-phase voltage waveforms at the beginning of the series reactor.

[0037] Figure 3 and 4 In the graph, the horizontal axis represents time, with the unit being seconds, denoted as Time (sec); the vertical axis represents voltage, with the unit being kilovolts, denoted as Voltage (kV). Figure 3 and 4 In the figure, the start time of the transient process is t = 1 (sec) when the circuit is opened, that is, when the circuit is opened at t = 1 second. Therefore, the horizontal axis in the figure starts from 0.99s. Before t = 1 second, the voltage at the beginning of the series reactor is a sine wave of 66kV.

[0038] From the diagram, we can see that: Figure 3 In the test, the maximum amplitude of phases a, b, and c is 120.31kV; the voltage waveform exhibits obvious high-frequency oscillation, with a voltage frequency of approximately 444.44Hz. Figure 4The maximum amplitude of phases a, b, and c is 74.16 kV. After the SF6 circuit breaker QF is tripped, the oscillation only lasts for a short time before starting to decay until the value gradually decreases to 0. Comparison shows that the maximum amplitude of phases a, b, and c is reduced by 38.36%, and the oscillation process is basically completely suppressed, indicating that the suppression circuit has a significant suppression effect.

Claims

1. A circuit for suppressing overvoltage when an SF6 circuit breaker switches a parallel capacitor, characterized in that, The switching refers to the operation of opening or closing an SF6 circuit breaker to connect or disconnect a group of parallel capacitors C; the parallel capacitors C belong to a parallel capacitor bank interval, which also includes a disconnecting switch QS1, an SF6 circuit breaker QF, a current transformer CT, and a series reactor L. D The disconnecting switch QS2 and surge arrester MOA are connected in the following manner: the first end of the disconnecting switch QS1 is connected to the busbar M on the low-voltage side of the main transformer of the substation, and its end is connected to the SF6 circuit breaker QF, the current transformer CT, and the series reactor L. D The parallel capacitor C and the disconnecting switch QS2 are connected in series in sequence, and the first end of the surge arrester MOA is connected to the series reactor L. D The parallel capacitor bank C is connected to the ground at its end; the low-voltage side bus M is the bus connected to the low-voltage side of the main transformer of the substation, and multiple other electrical equipment bays are connected in parallel on the bus M. The suppression circuit for overvoltage of the SF6 circuit breaker switching parallel capacitor is referred to as the suppression circuit. The suppression circuit is composed of a load switch QL, a resistor QR, and a capacitor QC connected in series. The suppression circuit is added as a new branch and connected in parallel in the above-mentioned parallel capacitor bank interval. Its connection method is as follows: the first end of the load switch QL is connected between the SF6 circuit breaker QF and the current transformer CT, and the end of the capacitor QC is grounded. When the SF6 circuit breaker QF needs to be closed, the load switch QL closes first, and then the SF6 circuit breaker QF closes. That is, during the closing process of the SF6 circuit breaker QF, the resistor QR and capacitor QC in the suppression circuit are in the working state. When the SF6 circuit breaker QF needs to be opened, the SF6 circuit breaker QF opens first, and then the load switch QL opens. That is, during the opening process of the SF6 circuit breaker QF, the load switch QL is still in the closed state, and the resistor QR and capacitor QC in the suppression circuit are still connected to the parallel capacitor bank at intervals, that is, in the working state.

2. The overvoltage suppression circuit for switching parallel capacitors in an SF6 circuit breaker according to claim 1, characterized in that, The outermost layer of the current transformer (CT) is a porcelain bushing. The suppression circuit is integrated in the porcelain bushing of the current transformer (CT), and the current transformer (CT) with the above-mentioned suppression circuit integrated is referred to as a capacitive current transformer.

3. The overvoltage suppression circuit for switching parallel capacitors in an SF6 circuit breaker according to claim 1, characterized in that, The SF6 circuit breaker QF is a column-type circuit breaker, consisting of upper and lower sections. The suppression circuit is integrated in the lower section cavity of the column-type circuit breaker, and the SF6 circuit breaker QF with the above-mentioned suppression circuit integrated is referred to as the suppression circuit breaker.

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