Compensation device

Abstract

The charging current based on the cable charging capacity can be suitably compensated.SOLUTION: The compensation device includes an R-phase compensation reactor, one end of which is connected to the R-phase bus or an R-phase branch line led out from the R-phase bus, an R-phase resistor, one end of which is connected to the R-phase compensation reactor and the other end of which is connected to a reference voltage, an S-phase compensation reactor, one end of which is connected to the S-phase bus or an S-phase branch line led out from the S-phase bus, an S-phase resistor, one end of which is connected to the S-phase compensation reactor and the other end of which is connected to a reference voltage, a T-phase compensation reactor, one end of which is connected to the T-phase bus or a T-phase branch line led out from the T-phase bus, and a T-phase resistor, one end of which is connected to the T-phase compensation reactor and the other end of which is connected to a reference voltage; And interphase opening / closing units that substantially simultaneously short-circuit or open between the connection points.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a compensation device. [Background technology]

[0002] In recent years, renewable energy sources such as wind power and solar power are increasingly being connected to power networks (electrical grids). When connecting to power networks, most power generation companies use long-distance cables.

[0003] Since the charging current due to the cable charging capacity (ground capacitance) tends to be large in long-distance cables compared to overhead transmission lines, it is common to compensate for this charging current in some way. For example, Patent Document 1 discloses a technique for compensating for the charging current.

[0004] Fig. 3 shows an example of a conventional compensation method. Conventionally, the charging current of a long-distance cable has been compensated for by a positive-sequence compensation reactor connected between each transmission line. Furthermore, the charging current for the zero-sequence voltage in the event of a ground fault or the like has been compensated for by a zero-sequence compensation reactor, one end of which is connected to the neutral point of the transformer and the other end is grounded. For this reason, conventional compensation equipment generally uses two compensation reactors: a positive-sequence compensation reactor and a zero-sequence compensation reactor. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-209925 Summary of the Invention [Problem to be solved by the invention]

[0006] In the case of the method shown in Figure 3, in order to connect the zero-phase compensation reactor to the neutral point, the target transformer must have a neutral point. Therefore, in the case of equipment that does not have a neutral point, such as a delta connection, it is necessary to install a grounding transformer separate from the target equipment, which creates problems such as complex equipment and high costs.

[0007] Furthermore, in the system shown in Figure 3, when AC is applied to the cable charging capacitance and the positive-phase compensation reactor, the AC component is removed by the cable charging capacitance and the positive-phase compensation reactor in a transient state, leaving a DC component (which becomes a biased current), causing a zero-point shift phenomenon (hereinafter sometimes referred to as a zero miss) in which the zero point of the current passing through the circuit breaker shifts. When a zero miss occurs, the current passing through the circuit breaker does not cross zero, which hinders the circuit breaker from interrupting the current. In order for the circuit breaker to properly interrupt the current, additional measures must be taken to prevent the zero miss, which requires time and cost.

[0008] The present invention has been made in view of the above-mentioned points, and has an object to provide a technique that can suitably compensate for the charging current based on the cable charging capacity. [Means for solving the problem]

[0009] One aspect of the present invention is an inverter circuit including an R-phase compensating reactor having one end connected to an R-phase bus or an R-phase branch wire drawn from the R-phase bus, an R-phase resistor having one end connected to the R-phase compensating reactor and the other end connected to a reference voltage, an S-phase compensating reactor having one end connected to an S-phase bus or an S-phase branch wire drawn from the S-phase bus, an S-phase resistor having one end connected to the S-phase compensating reactor and the other end connected to a reference voltage, and a T-phase bus or the T-phase bus. a T-phase resistor having one end connected to the T-phase compensating reactor and the other end connected to a reference voltage; and inter-phase switches connected to a connection point between the R-phase compensating reactor and the R-phase resistor, a connection point between the S-phase compensating reactor and the S-phase resistor, and a connection point between the T-phase compensating reactor and the T-phase resistor, and for substantially simultaneously short-circuiting or opening each of the connection points.

[0010] In one aspect of the present invention, each of the interphase switching units short-circuits after a predetermined set time has elapsed since the magnitude of the current or voltage detected by the detection unit exceeded a predetermined threshold.

[0011] In one aspect of the present invention, the set time is determined in accordance with information specifying the characteristics of the bus.

[0012] In one aspect of the present invention, the set time is set to be approximately 0.1 [s] or more and 10 [s] or less.

[0013] In addition, in one aspect of the present invention, the inverter further includes a detection unit that detects the magnitude of the current or voltage flowing in at least one of the R-phase busbar, S-phase busbar, T-phase busbar, R-phase branch line, S-phase branch line, and T-phase branch line, and each of the interphase switching units short-circuits after a predetermined set time has elapsed since the magnitude of the current or voltage detected by the detection unit exceeds a predetermined threshold value. [Effects of the Invention]

[0014] According to the present invention, the charging current based on the cable charging capacity can be suitably compensated. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 2 is a diagram illustrating an example of the configuration of a compensation device according to an embodiment. [Figure 2] FIG. 10 is a diagram showing a simulation result of zero miss when the compensation device according to the embodiment is used. [Figure 3] FIG. 1 is a diagram illustrating an example of a conventional compensation method. [Figure 4] FIG. 10 is a diagram showing the results of a zero-miss simulation when a conventional compensation facility is used. DETAILED DESCRIPTION OF THE INVENTION

[0016] [Embodiment] A compensation device according to the present embodiment will be described in detail below with reference to the accompanying drawings, showing preferred embodiments. In the drawings, identical or similar parts are designated by identical or similar reference numerals. Note that the present embodiment is not limited to these embodiments and includes various modifications or improvements. In other words, the components described below include those that can be easily imagined by a person skilled in the art and those that are substantially identical, and the components described below can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the components of the present embodiment may be made without departing from the spirit of the present invention.

[0017] Fig. 1 is a diagram illustrating an example of the configuration of a compensation device 40 according to an embodiment. Fig. 1 shows a portion of a three-phase power network 1 according to an embodiment. The three-phase power network 1 includes a three-phase power source 11 and a transformer 12 that transforms a three-phase voltage transmitted from the three-phase power source 11 via a three-phase bus 20. Three-phase buses 20, including an R-phase bus 20R, an S-phase bus 20S, and a T-phase bus 20T, are connected between the three-phase power source 11 and the transformer 12. The transformer 12 may be, for example, a load.

[0018] The bus bars 20 are long-distance transmission lines and may be, for example, long-distance cables or overhead transmission lines that transmit power over long distances. Each bus bar 20 has a cable charging capacity. Each bus bar 20 is also provided with a circuit breaker 13. An R-phase branch line 30R, an S-phase branch line 30S, and a T-phase branch line 30T are drawn out from the R-phase bus bar 20R, the S-phase bus bar 20S, and the T-phase bus bar 20T, respectively.

[0019] The compensation device 40 is provided on the bus 20 or the branch line 30 drawn from the bus 20. The compensation device 40 includes an R-phase compensating reactor 410R, an R-phase resistor 420R, an S-phase compensating reactor 410S, an S-phase resistor 420S, a T-phase compensating reactor 410T, a T-phase resistor 420T, each interphase switching unit 430, a control unit 440, and a detection unit 441. Each interphase switching unit 430 includes, for example, a first switch 431 and a second switch 432.

[0020] The R-phase compensating reactor 410R has one end connected to either the R-phase bus 20R or the R-phase branch line 30R, and the other end connected to an R-phase resistor 420R. The R-phase resistor 420R has one end connected to the R-phase compensating reactor 410R and the other end connected to a reference voltage. One end of a first switch 431 is connected to the connection point between the R-phase compensating reactor 410R and the R-phase resistor 420R (hereinafter, sometimes referred to as the R-phase connection point). The reference voltage may be 0 V (ground), a small voltage close to 0 V, or an arbitrary value determined by the designer of the compensating device 40. In the following description, connection to the reference voltage may be referred to as grounding.

[0021] The S-phase compensating reactor 410S has one end connected to either the S-phase bus 20S or the S-phase branch line 30S, and the other end connected to an S-phase resistor 420S. The S-phase resistor 420S has one end connected to the S-phase compensating reactor 410S and the other end connected to a reference voltage. The other end of the first switch 431 and one end of the second switch 432 are connected to the connection point (hereinafter sometimes referred to as the S-phase connection point) between the S-phase compensating reactor 410S and the S-phase resistor 420S.

[0022] The T-phase compensating reactor 410T has one end connected to either the T-phase bus 20T or the T-phase branch 30T, and the other end connected to a T-phase resistor 420T. The T-phase resistor 420T has one end connected to the T-phase compensating reactor 410T and the other end connected to a reference voltage. The other end of the second switch 432 is connected to the connection point (hereinafter sometimes referred to as the T-phase connection point) between the T-phase compensating reactor 410T and the T-phase resistor 420T. In the following description, when referring to either the bus 20 or the branch 30, it may be simply referred to as the transmission line.

[0023] Each interphase switch 430 is connected between the R-phase connection point, the S-phase connection point, and the T-phase connection point. Each interphase switch 430 may connect the R-phase connection point, the S-phase connection point, and the T-phase connection point using, for example, a first switch 431 and a second switch 432. Each interphase switch 430 may further include a third switch (not shown) having one end connected to the R-phase connection point and the other end connected to the T-phase connection point, thereby connecting the phase connection point, the S-phase connection point, and the T-phase connection point. Each interphase switch 430 may be configured by connecting three switches between the R-phase connection point, the S-phase connection point, and the T-phase connection point like a star connection.

[0024] Each interphase switching unit 430 mutually short-circuits or opens the R-phase connection point, the S-phase connection point, and the T-phase connection point approximately simultaneously. Specifically, the first switch 431 and the second switch 432 included in each interphase switching unit 430 short-circuit or open the R-phase connection point, the S-phase connection point, and the T-phase connection point approximately simultaneously. The range of approximately simultaneously may be simultaneous, or there may be a time lag that allows the compensation device 40 to perform its function.

[0025] When a transient state occurs and a transient current flows through the circuit breaker 13, each interphase switching unit 430 opens the R-phase connection point, the S-phase connection point, and the T-phase connection point. The transient current is a current that flows through the circuit breaker 13 in a transient state. The transient current is generated in a transient state, for example, when the circuit breaker 13 is closed.

[0026] When each interphase switch 430 is open, the R-phase compensating reactor 410R connected to the R-phase transmission line is grounded via an R-phase resistor 420R. The S-phase compensating reactor 410S connected to the S-phase transmission line is grounded via an S-phase resistor 420S. The T-phase compensating reactor 410T connected to the T-phase transmission line is grounded via a T-phase resistor 420T. In this case, the R-phase compensating reactor 410R, the S-phase compensating reactor 410S, and the T-phase compensating reactor 410T function as positive-phase compensation reactors having damping resistances.

[0027] When each interphase switch 430 is open, the R-phase resistor 420R, the S-phase resistor 420S, and the T-phase resistor 420T function as damping resistors. The R-phase resistor 420R, the S-phase resistor 420S, and the T-phase resistor 420T convert a portion of the transient current passing through the circuit breaker 13 into thermal energy and consume it during a transient state. This shortens the time it takes for the transient state to subside, quickly ending a zero-phase error. Resistor 420 is sufficiently small compared to the reactance of the compensating reactor 410 to ensure the zero-phase compensation rate of the compensating reactor. For example, the resistance value of resistor 420 is preferably several percent to several tens of percent of the reactance of the compensating reactor 410.

[0028] When the transient state at the time of closing the circuit breaker 13 ends, each interphase switch 430 quickly short-circuits the R-phase connection point, the S-phase connection point, and the T-phase connection point. When each interphase switch 430 is short-circuited, the R-phase compensation reactor 410R connected to the R-phase transmission line, the S-phase compensation reactor 410S connected to the S-phase transmission line, and the T-phase compensation reactor 410T connected to the T-phase transmission line are connected via the first switch 431 and the second switch 432. The contact resistances of the first switch 431 and the second switch 432 included in each interphase switch 430 are sufficiently small compared with the resistances of the R-phase resistor 420R, the S-phase resistor 420S, and the T-phase resistor 420T. Therefore, the R-phase connection point, the S-phase connection point, and the T-phase connection point are short-circuited, and almost no current flows through the R-phase resistor 420R, the S-phase resistor 420S, and the T-phase resistor 420T. In this case, the R-phase compensating reactor 410R, the S-phase compensating reactor 410S, and the T-phase compensating reactor 410T function as positive-phase compensating reactors without damping resistors that compensate for the charging current based on the three-phase cable charging capacity, preventing power loss due to normal reactor current. At the same time, the R-phase compensating reactor 410R, the S-phase compensating reactor 410S, and the T-phase compensating reactor 410T also function as zero-phase compensating reactors with damping resistors. Regarding transient currents that occur during a ground fault, the zero-phase damping resistors quickly converge the transient current, quickly ending zero-phase faults during a ground fault.

[0029] As described above, the compensation device 40 according to the embodiment includes an R-phase compensating reactor 410R having one end connected to the R-phase bus 20R or the R-phase branch line 30R drawn from the R-phase bus 20R, an R-phase resistor 420R having one end connected to the R-phase compensating reactor 410R and the other end connected to a reference voltage, an S-phase compensating reactor 410S having one end connected to the S-phase bus 20S or the S-phase branch line 30S drawn from the S-phase bus 20S, an S-phase resistor 420S having one end connected to the S-phase compensating reactor 410S and the other end connected to a reference voltage, and a T-phase The compensation device 40 according to the embodiment includes a T-phase compensating reactor 410T having one end connected to a bus 20T or a T-phase branch 30T drawn from the T-phase bus 20T, a T-phase resistor 420T having one end connected to the T-phase compensating reactor 410T and the other end connected to a reference voltage, and interphase switches 430 connected to an R-phase connection point between the R-phase compensating reactor 410R and the R-phase resistor 420R, an S-phase compensating reactor 410S and the S-phase resistor 420S, and a connection point between the T-phase compensating reactor 410T and the T-phase resistor 420T, and short-circuiting or opening the connection points approximately simultaneously. The compensation device 40 according to the embodiment can use the three-phase compensating reactor 410 to function both as a positive-phase compensating reactor that compensates for a positive-phase charging current and as a zero-phase compensating reactor that compensates for a zero-phase charging current. Furthermore, with the compensator 40, in addition to the positive-phase compensation reactor, there is no need for a separate neutral reactor (zero-phase compensation reactor) or a grounding transformer for obtaining the neutral point, reducing the cost required for compensating for the charging current. Furthermore, with the compensator 40, the equipment configuration is simple and no complex control is required, reducing the costs required for installation and maintenance.

[0030] Conventional compensation equipment requires the introduction of a circuit breaker 13 with a resistor closing method or closing phase control to address zero misses during closing of the circuit breaker 13 or zero misses during a ground fault, resulting in significant equipment costs. The compensation device 40 of this embodiment can quickly resolve zero misses during closing or zero misses during a ground fault, eliminating the need to take measures such as installing additional zero miss countermeasure equipment. Therefore, the compensation device 40 can reduce the cost required for zero miss countermeasures. As described above, the compensation device 40 can perform the three roles of positive-phase compensation, zero-phase compensation, and zero miss countermeasures with a single piece of equipment.

[0031] The control unit 440 controls the timing of short-circuiting or opening each inter-phase switching unit 430. Specifically, the control unit 440 basically opens the inter-phase switching units 430 immediately after applying a voltage to the compensation equipment, and then shorts the inter-phase switching units 430 after the transient phenomenon that occurs when the voltage is applied has subsided. The control unit 440 may be realized, for example, by using a computer and software including a central processing unit (CPU) and memory, or may be realized by using an electronic circuit as necessary. Furthermore, the control unit 440 does not have to be a functional unit separate and independent from each inter-phase switching unit 430, and may be a function included in each inter-phase switching unit 430.

[0032] For example, the control unit 440 may open the resistor 420 when the current or voltage detected by the detection unit 441 falls below a predetermined threshold, and may short the resistor 420 after a set time has elapsed since the current or voltage detected by the detection unit 441 exceeded the predetermined threshold. The set time is a time predetermined by the designer or user of the compensation device 40. The set time is, for example, a time period long enough to prevent the resistor 420 from being destroyed based on the withstand voltage of the resistor 420 and to sufficiently resolve zero error. If the interphase switching unit 430 remains open after the transient state ends, the resistor 420 will consume power not only due to the transient current but also due to the normal compensation current. The compensation device 40 according to the embodiment includes a control unit 440 that shorts the resistor 420 after a predetermined set time has elapsed since the current or voltage detected by the detection unit 441 exceeded the predetermined threshold, thereby preventing unnecessary power consumption due to the normal compensation current. Furthermore, by switching from open to short circuit after the set time has elapsed, the compensation device 40 does not require a complex configuration or control. This reduces the costs required for designing and maintaining the compensator 40. Note that when the magnitude of the current or voltage detected by the detector 441 falls below a predetermined threshold, this means that no voltage is being applied. The predetermined threshold for detecting that no voltage is being applied may be, for example, a value that is sufficiently lower than the normal operating voltage and higher than the induced voltage on an adjacent line.

[0033] The set time may be determined by information specifying the properties of the bus bar 20, such as the magnitude of the cable charging capacity of the bus bar 20 or the length of the bus bar 20. The larger the cable charging capacity of the bus bar 20, the larger the generated charging current, and the smaller the cable charging capacity of the bus bar 20, the smaller the generated charging current. Furthermore, the longer the bus bar 20, the larger the generated charging current, and the shorter the bus bar 20, the smaller the generated charging current. By determining the set time in accordance with the properties of the bus bar 20, the compensator 40 can switch each inter-phase switch 430 between open and short circuit at an appropriate timing.

[0034] Furthermore, the set time may be, for example, a length of time predetermined by the designer of the compensator 40. In this case, the set time may be, for example, approximately 0.1 seconds or more and 10 seconds or less. When the set time is approximately 0.1 seconds or more and 10 seconds or less, the compensator 40 can eliminate zero misses while reducing the possibility of the resistor 420 being damaged. Furthermore, by not changing the set time for each bus 20, the effort required for preparation when installing the compensator 40 can be reduced.

[0035] The control unit 440 acquires information regarding the timing of opening or shorting each interphase switching unit 430. The timing of opening each interphase switching unit 430 is sufficient as long as it is in an open state immediately after voltage application to the compensator. Therefore, the interphase switching unit 430 may be opened before or immediately after voltage application. If the interphase switching unit 430 is opened before voltage application, the information regarding the timing of opening may be, for example, information regarding the current or voltage detected by the detection unit, and the interphase switching unit 430 may be opened when the magnitude of the current or voltage detected by the detection unit 441 falls below a predetermined threshold. If the interphase switching unit 430 is opened immediately after voltage application, the information regarding the timing of opening may be, for example, information indicating the occurrence of a transient current or information indicating that the circuit breaker 13 has been closed. The control unit 440 may determine whether a transient current has occurred by, for example, acquiring the magnitude of the current or voltage detected by the detection unit 441. The detection unit 441 acquires the magnitude of the current or voltage flowing through at least one of the transmission lines, the R-phase bus 20R, the S-phase bus 20S, the T-phase bus 20T, the R-phase branch 30R, the S-phase branch 30S, and the T-phase branch 30T. 1 shows an example in which the detection unit 441 is a current sensor that detects the current in the T-phase branch wire 30T based on changes in a magnetic field. The control unit 440 determines that a transient current has occurred when the magnitude of the current or voltage detected by the detection unit 441 exceeds a predetermined threshold, and opens each interphase switch 430. This allows the compensator 40 to appropriately converge the transient current in response to the occurrence of the transient current and quickly resolve the zero error. Note that the control unit 440 may open each interphase switch 430, for example, when it receives information indicating that the circuit breaker 13 has been closed from a control unit (not shown) that controls the circuit breaker 13.

[0036] The above-described control unit 440 has been described as an example in which it controls each interphase switch 430 to short-circuit after a set time has elapsed. However, this embodiment is not limited to this example. The control unit 440 may short-circuit each interphase switch 430 when the transient current is eliminated. The control unit 440 may short-circuit each interphase switch 430 when, for example, the current or voltage detected by the detection unit 441 falls below a predetermined threshold. The control unit 440 may have separate thresholds for determining whether a transient current is present and for determining whether a transient current is absent.

[0037] FIG. 4 is a diagram showing the results of a zero miss simulation when a conventional compensation facility is used. The compensation facility in FIG. 4 has a compensation rate of 95%. FIG. 2 is a diagram showing the results of a zero miss simulation when a compensation device 40 according to the embodiment is used. FIGS. 2 and 4 show the time change in the current passing through the circuit breaker when a zero miss occurs. In FIGS. 2 and 4, the simulation was performed with a frequency of 50 Hz.

[0038] Figure 4(A) shows the zero-point error condition when a circuit breaker is closed when using conventional compensation equipment. In Figure 4(A), the R-phase, S-phase, and T-phase currents are biased, with the R-phase current always being positive and the S-phase and T-phase currents always being negative. This condition continues until the transient state ends, and the R-phase, S-phase, and T-phase currents do not pass 0 A even after 0.5 seconds. This prevents the circuit breaker from interrupting the current. Figure 4(B) shows the zero-point error condition when a line-to-ground fault occurs when using conventional compensation equipment. In Figure 4(B), a zero-point error occurs in the healthy S-phase and T-phase currents, and, as in Figure 4(A), they do not pass 0 A even after 0.5 seconds.

[0039] FIG. 2(A) shows the state of a zero miss when a circuit breaker is closed when the compensation device 40 according to the embodiment is used. In FIG. 2(A), it can be seen that the DC components of the R-phase current, S-phase current, and T-phase current are consumed, and the zero miss is resolved in a short time of about 0.1 [s]. FIG. 2(B) shows the state of a zero miss when a single-phase to ground fault occurs when the compensation device 40 according to the embodiment is used. In FIG. 2(B), it can be seen that the DC components of the S-phase current and T-phase current, which are healthy phases, are consumed, and the zero miss is resolved in a short time of about 0.1 [s], as in FIG. 2(A).

[0040] Although one embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to the above, and various design modifications can be made without departing from the spirit of the present invention. Furthermore, the configurations described in the above-described embodiments and examples can be combined. [Explanation of symbols]

[0041] 1... three-phase power network, 11... three-phase power source, 12... transformer, 13... circuit breaker, 20... busbar, 30... branch line, 40... compensation device, 410... compensation reactor, 420... resistor, 430... inter-phase switching unit, 431... first switch, 432... second switch, 440... control unit, 441... detection unit

Claims

1. an R-phase compensating reactor having one end connected to an R-phase bus or an R-phase branch wire drawn from the R-phase bus; an R-phase resistor having one end connected to the R-phase compensating reactor and the other end connected to a reference voltage; an S-phase compensating reactor having one end connected to an S-phase bus or an S-phase branch line drawn from the S-phase bus; an S-phase resistor having one end connected to the S-phase compensating reactor and the other end connected to a reference voltage; a T-phase compensating reactor having one end connected to a T-phase bus or a T-phase branch line drawn from the T-phase bus; a T-phase resistor having one end connected to the T-phase compensating reactor and the other end connected to a reference voltage; interphase switching units connected to a connection point between the R-phase compensating reactor and the R-phase resistor, a connection point between the S-phase compensating reactor and the S-phase resistor, and a connection point between the T-phase compensating reactor and the T-phase resistor, and which substantially simultaneously short-circuit or open the respective connection points; A compensation device comprising:

2. Each of the inter-phase switching units is short-circuited after a predetermined set time has elapsed since the magnitude of the current or voltage detected by the detection unit exceeded a predetermined threshold. The compensation device of claim 1 .

3. the set time is determined in accordance with information specifying the characteristics of the bus; The compensation device of claim 2 .

4. The set time is set to approximately 0.1 [s] or more and 10 [s] or less. The compensation device of claim 2 .

5. a detection unit that detects the magnitude of a current or a voltage flowing through at least one of the R-phase bus bar, the S-phase bus bar, the T-phase bus bar, the R-phase branch line, the S-phase branch line, and the T-phase branch line; Each of the inter-phase switches short-circuits after a predetermined set time has elapsed since the magnitude of the current or voltage detected by the detector exceeded a predetermined threshold. A compensation device according to any one of claims 2 to 4.

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