Cut-off device system

Abstract

To properly cut off a current in a system interconnection in the event of an accident.SOLUTION: A cut-off device system (9) in a power system (100) including a shunt reactor (7) includes a target cut-off device (4) connected in series with the shunt reactor, and a capacity device (8) that is connected in parallel with the shunt reactor and has, among multiple phases, a reactor (82) and a capacitor (83) which are connected in series with each other.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a circuit breaker system. [Background technology]

[0002] Trading of electricity through grid interconnection has become common. When an accident such as a short circuit or a ground fault occurs in a grid-connected power system, it is necessary to quickly cut off the fault area in order to limit the area of ​​the fault.

[0003] In cable-based grid interconnection, shunt reactors are generally used to mitigate voltage fluctuations in the grid interconnection. When an accident occurs in a power grid equipped with a shunt reactor, a current that is a combination of the charging current of the power transmission cable and the current through the shunt reactor flows through the circuit breaker. As a result, a direct current is applied to the circuit breaker, causing a zero-point transition phenomenon in which the current does not cross zero, and the circuit breaker cannot interrupt the current even when it is opened.

[0004] In response to this, Patent Document 1 discloses a technology in which a capacitor is connected in series to a shunt reactor to cause the current applied to the shunt reactor to cross zero by resonating the current flowing through the power grid. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 5-22458 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the conventional technology described above, the voltage between the terminals of the capacitor increases due to AC vibrations that occur during an accident, so it is necessary to increase the withstand voltage of the capacitor, which is costly.

[0007] An object of one aspect of the present invention is to provide a circuit breaker system that appropriately interrupts current in the event of an accident in a grid-connected system. [Means for solving the problem]

[0008] In order to solve the above problems, a circuit breaker system according to one embodiment of the present invention is a circuit breaker system in a power system, and includes a circuit breaker, a shunt reactor connected in series to the circuit breaker, and a capacitance device connected in parallel to the shunt reactor and having a reactor and a capacitor connected in series to each other. Effect of the Invention

[0009] According to one aspect of the present invention, current can be appropriately interrupted in the event of an accident. [Brief description of the drawings]

[0010] [Figure 1] 1 is a circuit diagram showing a configuration of a main part of a power system according to a first embodiment. [Diagram 2] 3 is a tri-line diagram showing details of a capacitance device 8 according to the first embodiment. FIG. [Diagram 3] 1 is a graph showing current fluctuations at various parts before and after an accident occurs. [Figure 4] This is the frequency-impedance characteristic of the capacitance device as seen from the target circuit breaker side. [Diagram 5] FIG. 11 is a circuit diagram showing the configuration of a main part of a power system according to a second embodiment. [Figure 6] FIG. 11 is a circuit diagram showing the configuration of a main part of a power system according to a third embodiment. [Figure 7] FIG. 11 is a tri-line diagram showing details of a capacitance device 8 according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] [Embodiment 1] Hereinafter, an embodiment according to one aspect of the present invention (hereinafter, also referred to as "the present embodiment") will be described with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference characters and their description will not be repeated.

[0012] (Circuit configuration) 1 is a circuit diagram showing a configuration of a main part of a power system 100 according to the first embodiment. The power system 100 includes a three-phase power source 1, which supplies power to the power system 100. The power system 100 is connected to a transmission line 5 via a target circuit breaker 4 in a lower system of the three-phase power source 1. A load and a power generation facility are connected in parallel to the lower system of the transmission line 5.

[0013] A shunt reactor 7 is connected in a star configuration to one of the loads in the power system 100. That is, the shunt reactor 7 is connected in series to the target circuit breaker 4. A shunt reactor circuit breaker 6 is connected between the transmission line 5 and the shunt reactor 7. Note that the symbol S in FIG. 1 is a symbol representing a star connection. That is, FIG. 1 shows that the shunt reactor 7 is connected in a star connection. The same applies to similar symbols not bearing the symbol S in FIG. 1 and the subsequent drawings.

[0014] 2 is a three-wire diagram showing the details of the capacitance device 8 according to the first embodiment. The capacitance device 8 is connected in parallel to the shunt reactor 7 upstream of the transmission line 5. The capacitance device 8 is a circuit in which a capacitance device circuit breaker 81, a reactor 82, and a capacitor 83 are connected in series to each other. The capacitance device 8 is connected in star configuration to the power system 100. The reactor 82 also plays a role in suppressing an inrush current to the capacitor 83. The shunt reactor 7 and the capacitance device 8 are arranged at different locations.

[0015] Here, reactor 82 and capacitor 83 are connected between a plurality of phases. As shown in Fig. 2, a certain reactor, a certain capacitor, another capacitor, and another reactor are connected in this order between different phases (for example, a first phase and a second phase). The reactor and the capacitor are each one element of reactor 82 and capacitor 83, which have a plurality of elements.

[0016] The capacitance device 8 does not necessarily have to include the capacitance device circuit breaker 81. The capacitance device 8 has three phases connected in a star connection. The target circuit breaker 4 and the capacitance device 8 are also collectively referred to as a circuit breaker system 9. In the circuit breaker system 9, the target circuit breaker 4 is a circuit breaker used to break the power system 100.

[0017] (Operation in the event of an accident) The following describes the operation when an accident, for example a short circuit accident, occurs at a location P above the target circuit breaker 4 in Fig. 1. The accident is not limited to a short circuit accident, but may be a ground fault accident. Fig. 3 is a graph showing the current fluctuations in each part before and after the accident occurs. Fig. 3 shows a graph 400 of the current flowing into the target circuit breaker 4, a graph 600 of the current flowing into the shunt reactor circuit breaker 6, and a graph 800 of the current flowing into the capacitance device circuit breaker 81. In each of the graphs 400, 600, and 800, the horizontal axis represents time and the vertical axis represents current.

[0018] 3, before the occurrence of a short-circuit accident, the three-phase AC current is measured in graphs 600 and 800. Note that, as shown in graph 400, the current flowing into the target circuit breaker 4 is zero before the occurrence of a short-circuit accident. This is because the sum of the fundamental wave reactive powers from the three-phase power source 1 in the shunt reactor 7, the capacitance device 8, and the transmission line 5 is set to be 0 [Mvar].

[0019] After that, at time T1, a short circuit occurs at a location P above the target circuit breaker 4. As a result, the waveforms of the graphs 400, 600, and 800 change. In the graph 600, the shunt reactor 7 acts to cause a continuous current to flow from before the accident, resulting in a direct current. In the graph 800, the reactor 82 and the capacitor 83 in the capacitance device 8 resonate with each other. The resonant frequency of the capacitance device 8 is higher than the commercial frequency of the three-phase power source 1.

[0020] The circuit breaker system 9 detects the accident and attempts to shut off the target circuit breaker 4. However, the target circuit breaker 4 will be subject to currents flowing through the devices on the load side, i.e., the shunt reactor circuit breaker 6, the capacitance device circuit breaker 81, and downstream loads (including the current flowing through the power transmission line 5) of the three-phase power source 1, which are not shown.

[0021] The target circuit breaker 4 opens over a period of time that is the combined total of the circuit breaker's relay time or the time it takes for a signal to be transmitted from the upper system, plus the opening time of the circuit breaker itself. Until the target circuit breaker 4 opens, as shown in graph 400, the inflow current of the target circuit breaker 4 oscillates at a frequency higher than the commercial frequency. Note that this oscillation gradually attenuates due to losses occurring in the load-side equipment. Note that the zero-point evaluation time of the target circuit breaker 4 begins after the target circuit breaker 4 physically opens.

[0022] After that, at time T2, with the contacts of the target circuit breaker 4 sufficiently open, the target circuit breaker 4 is tripped when the current flowing into the target circuit breaker 4 crosses zero. This timing is, for example, about 61 milliseconds after the occurrence of the short circuit accident.

[0023] After time T2, the target circuit breaker 4 is tripped. As a result, the current that had been flowing into the target circuit breaker 4 flows back between the load side devices. This causes current oscillations in each load side device. This oscillation is gradually attenuated by the resistance of each device.

[0024] (Mechanism of accident occurrence) Here, a description will be given of the resonance occurring in the capacitance device 8. In the capacitance device 8, a reactor 82 having an inductance L and a capacitor 83 having a capacitance C are connected in series. Therefore, the resonance frequency fr in the capacitance device 8 can be expressed by the following equation.

[0025]

number

[0026] Furthermore, the current resonates in the capacitance device 8, and the amplitude of the current in this resonance can be set to a value larger than the DC current generated in the shunt reactor 7. As a result, the current in the target circuit breaker 4 can be made to cross zero by superimposing the current due to resonance on the DC current generated in the shunt reactor 7.

[0027] In order to make the capacitance device 8 function as a capacitance device, the resonant frequency fr of the capacitance device 8 is higher than the commercial frequency. When the resonant frequency is higher than the commercial frequency, the current can be made to cross zero appropriately within the zero point evaluation time of the target circuit breaker 4. Therefore, the current can be interrupted by the target circuit breaker 4.

[0028] Fig. 4 shows the frequency-impedance characteristics of the capacitance device 8 as viewed from the target circuit breaker 4 side. In Fig. 4, the horizontal axis is frequency and the vertical axis is impedance. As shown in Fig. 4, it can be seen that a resonance point occurs at a frequency of about 200 [Hz]. This is because Fig. 4 was designed based on equation 1 so that the resonance frequency is higher than the commercial frequency, about four times the commercial frequency.

[0029] (Design of Capacitive Device 8) In order for the circuit breaker system 9 to operate as desired, it is necessary to appropriately design the installation capacity of the capacitance device 8 with respect to the lagging reactive power. Design guidelines for the installation capacity of the capacitance device 8 will be described below.

[0030] The capacity of the shunt reactor 7 is Q L [Mvar], line voltage in V l [kV], the direct current I generated in the shunt reactor 7 when a three-phase short circuit occurs Ldc1 [A] can be expressed by the following formula.

[0031]

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[0032]

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[0033]

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[0034]

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[0035]

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[0036]

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[0037]

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[0038]

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[0039] In addition, since the capacitance device 8 is provided in parallel with the shunt reactor 7, the function of the shunt reactor 7 is not impaired even during maintenance of the capacitance device 8. Therefore, a stable power system 100 can be realized.

[0040] [Embodiment 2] Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals are given to members having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0041] 5 is a circuit diagram showing the configuration of a main part of a power system 101 according to the second embodiment. The power system 101 is the same as the power system 100 except that a shunt reactor breaker 6 and a shunt reactor 7 are connected upstream to a transmission line 5. That is, while the capacity device 8 and the shunt reactor 7 are arranged at different locations in the first embodiment, the capacity device 8 and the shunt reactor 7 are arranged at the same location in the second embodiment.

[0042] Even in this case, the capacitance device 8 can generate a high frequency wave in the current flowing into the target circuit breaker 4. Therefore, the target circuit breaker 4 can interrupt the current.

[0043] [Embodiment 3] Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals are given to members having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0044] FIG. 6 is a circuit diagram showing the configuration of a main part of a power system 102 according to the third embodiment. The power system 102 differs from the power system 100 in that the power system 102 has a three-phase three-winding transformer 3 on the secondary side of the power transmission line 5. Furthermore, a second target circuit breaker 41 is connected to the tertiary side of the three-phase three-winding transformer 3. A shunt reactor 7 and a capacitance device 8 are connected in parallel to the secondary side of the second target circuit breaker 41. In this embodiment, the target circuit breaker 4 is also referred to as a first target circuit breaker 4. The first target circuit breaker 4, the second target circuit breaker 41, and the capacitance device 8 are collectively referred to as a circuit breaker system 9a. The shunt reactor 7 and the capacitance device 8 are arranged at the same base.

[0045] Even in this case, the capacitance device 8 can generate a high frequency wave in the current flowing into the first target circuit breaker 4 and the second target circuit breaker 41. Therefore, the first target circuit breaker 4 and the second target circuit breaker 41 can interrupt the current.

[0046] Here, in the power system 102, unlike the power system 100, the shunt reactor 7 and the capacitance device 8 are connected to the location indicated by symbol P, which is higher than the first target circuit breaker 4 where the accident occurred, via the three-phase three-winding transformer 3. In other words, the first target circuit breaker 4 and the second target circuit breaker 41 do not directly share the bus wiring of the transmission line 5. However, the circuit breaker system 9a operates normally like the circuit breaker system 9, and can interrupt the current by opening the first target circuit breaker 4 and the second target circuit breaker 41.

[0047] Although the third embodiment has been described with respect to the three-phase three-winding transformer 3, it may be a three-phase two-winding transformer. In this case, a shunt reactor 7 and a capacitance device 8 are connected in parallel to the secondary side of the three-phase two-winding transformer.

[0048] [Modifications] In the first to third embodiments, the capacitance device 8 is connected to the power grid in a star configuration, but may be connected to the power grid in a delta configuration. Fig. 7 is a three-wire diagram showing the details of the capacitance device 8 according to a modification. In this modification, the capacitance device 8 is connected in a delta configuration instead of in a star configuration.

[0049] That is, as shown in Fig. 7, a certain reactor, a certain capacitor, and another reactor are connected in this order between different phases (for example, the first phase and the second phase). The reactor and the capacitor are each one element of a reactor 82 and a capacitor 83, each of which has a plurality of elements.

[0050] Even in the case of delta connection, as in the case of star connection, by providing a capacitance device 8 in parallel with the shunt reactor 7, it is possible to add a high frequency current to the inflow current of the target circuit breaker 4. This causes the inflow current of the target circuit breaker 4 to cross zero, and when the target circuit breaker 4 is opened, it becomes possible to cut off the current.

[0051] In addition, since the capacitance device 8 is provided in parallel with the shunt reactor 7, the function of the shunt reactor 7 is not impaired even during maintenance of the capacitance device 8. Therefore, a stable power system 100 can be realized.

[0052] 〔summary〕 A circuit breaker system according to a first aspect of the present invention is a circuit breaker system in a power system equipped with a shunt reactor, comprising a circuit breaker connected in series to the shunt reactor, and a capacitance device connected in parallel to the shunt reactor and having a reactor and a capacitor connected in series to each other.

[0053] According to the above configuration, the shunt reactor can be kept connected to the power system even when maintenance is being performed on the capacitance device.

[0054] A second aspect of the present invention relates to a breaker system according to the first aspect, wherein the reactor and the capacitor are connected between a plurality of phases in the power system.

[0055] According to the above configuration, each element of the reactor and the capacitor can be connected between a plurality of phases.

[0056] A circuit breaker system according to a third aspect of the present invention is in the first or second aspect, wherein the power system is a three-phase power system.

[0057] According to the above configuration, the capacitance device can be connected to a three-phase power system.

[0058] A fourth aspect of the present invention relates to a breaker system in any one of the first to third aspects, wherein the shunt reactor and the capacitance device are disposed at different locations.

[0059] According to the above configuration, the arrangement of the capacitance device is not particularly limited.

[0060] A circuit breaker system according to a fifth aspect of the present invention is in any one of the first to third aspects, wherein the capacitance device and the circuit breaker may be arranged at the same site.

[0061] According to the above configuration, the arrangement of the capacitance device is not particularly limited.

[0062] A sixth aspect of the present invention relates to a circuit breaker system in any one of the first to fifth aspects, wherein the shunt reactor and the capacitance device may be connected to a secondary side of a transformer connected in series to the circuit breaker.

[0063] According to the above configuration, the capacitance device and the circuit breaker may be connected via a transformer.

[0064] A circuit breaker system according to a seventh aspect of the present invention is any one of the first to sixth aspects, in which a current resonates in the capacitance device, and the amplitude of the current at the resonance may be set to a value larger than a DC current generated in a shunt reactor.

[0065] According to the above configuration, the amplitude of the current supplied from the capacitance device becomes larger than the DC current generated in the shunt reactor, so that the current in the breaker can cross zero.

[0066] In the breaker system according to an eighth aspect of the present invention, in any one of the first to seventh aspects, the capacitive device may be connected in a star configuration to the power system.

[0067] A ninth aspect of the present invention relates to a circuit breaker system in any one of the first to seventh aspects, wherein the capacitive device is connected in a delta configuration to the power grid.

[0068] [Additional Notes] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0069] 1 3 phase power supply 3. Three-phase, three-winding transformer 4. Target circuit breaker 5. Power Lines 6. Shunt reactor circuit breaker 7 Shunt reactor 8 capacity device 9, 9a Circuit Breaker System 81 Capacitive device circuit breaker 82 Reactor 83 Capacitor 100, 101, 102 Power system

Claims

1. A circuit breaker system in an electric power system having a shunt reactor, a circuit breaker connected in series to the shunt reactor; a capacitive device connected in parallel to the shunt reactor and having a reactor and a capacitor connected in series to each other.

2. The breaker system according to claim 1 , wherein the reactor and the capacitor are connected between a plurality of phases in the power system.

3. The circuit breaker system of claim 1 , wherein the power system is a three-phase power system.

4. The circuit breaker system of claim 1 , wherein the shunt reactor and the capacitive device are located at different sites.

5. The circuit breaker system of claim 1 , wherein the capacitive device and the circuit breaker are located at the same site.

6. The circuit breaker system of claim 1 , wherein the shunt reactor and the capacitive device are connected to a secondary side of a transformer connected in series to the circuit breaker.

7. A current resonates in the capacitive device; The circuit breaker system according to claim 1 , wherein an amplitude of the current at the resonance is set to a value larger than a DC current generated in a shunt reactor.

8. The circuit breaker system of claim 1 , wherein the capacitive devices are connected to the power grid in a star configuration.

9. The circuit breaker system of claim 1 , wherein the capacitive devices are delta-wired to the power grid.

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