POWER SWITCHING CONTROL DEVICE AND CLOSING CONTROL METHOD THEREOF

Abstract

 A power switching control device and a closing control method of the power switching control device that can suppress generation of a transient voltage or current that is possibly caused by a mismatch between a gap-voltage estimate value after interrupting a current and an actual gap voltage is obtained. It is estimated that a load-side voltage estimate value at the next closing is zero when a predetermined time determined based on an attenuation time constant of a residual voltage on a power transmission line (3) in advance passes since a current interruption time, and when the load-side voltage at and after the current interruption time is a direct-current signal and the load-side voltage shows a behavior of converging into zero at a speed equal to or higher than a constant speed at and after the current interruption time.

Description

Field

[0001] The present invention relates to a power switching control device and a closing control method thereof.

Background

[0002] It is known that an electric charge remains in sound phases after a current is interrupted in an accidental power interruption on a power transmission line. In this case, various voltages are generated on a load side (a transmission line side) of a circuit breaker depending on transmission line conditions. For example, in a case of the circuit breaker connected to a shunt-reactor-compensated power transmission line, an AC voltage having a constant frequency due to a reactor and the capacitive load of the power transmission line is generated on the load side of the circuit breaker, and in a case of the circuit breaker connected to a shunt-reactor-uncompensated power transmission line, a DC voltage in proportion to the power-supply side voltage of the circuit breaker during the interruption is generated on the load side of the circuit breaker.

[0003] A conventional power switching control device estimates a gap voltage at and after the present time as the difference between the power-supply side voltage at and after the present time that is obtained from the measured value of the power-supply side voltage and the load-side voltage at and after the present time that is obtained from the measured value of the load-side voltage. Furthermore, the conventional power switching control device controls the timing of closing the circuit breaker so that the circuit breaker can be closed at the timing when a gap-voltage estimate value is equal to a minimum value, thereby suppressing an overvoltage at the time of closing the circuit breaker (for example, Patent Literature 1).

Citation List

Patent Literature

[0004] Patent Literature 1: Japanese Patent No. 3986810

Summary

Technical Problem

[0005] The above conventional technique is adopted on the premise that the behavior of the load-side voltage does not change after interrupting a current. However, in a case where the power transmission line connected to the load side of the circuit breaker is the shunt-reactor-uncompensated power transmission line and the load-side voltage is measured by using a voltage measuring instrument such as a voltage transformer (VT) that discharges an electric charge, the electric charge remaining on the load side is discharged via the voltage measuring instrument. As a result, the load-side voltage rapidly attenuates to zero. Furthermore, whether the power transmission line connected to the load side of the circuit breaker is the shunt-reactor-compensated power transmission line or the shunt-reactor-uncompensated power transmission line, the electric charge remaining on the load side is discharged by the leakage resistance or the like of an insulator supporting the power transmission line as long as a sufficient time interval is secured from a previous interruption to the next closing similarly to a case, for example, of executing slow re-closing for which the time from the interruption to the closing is longer than a time specified in advance. Accordingly, the load-side voltage at the next closing attenuates over time and eventually becomes zero. Therefore, the conventional technique has the following problems. The gap-voltage estimate value does possibly not match an actual gap voltage, and it is impossible to suppress generation of a transient voltage or current at the time of closing the circuit breaker to a minimum.

[0006] The present invention has been achieved in view of the above problems, and an object of the present invention is to provide a power switching control device that can suppress generation of a transient voltage or current that is possibly caused by a mismatch between a gap-voltage estimate value after interrupting a current and an actual gap voltage.

Solution to Problem

[0007] In order to solve above-mentioned problems and achieve the object of the present invention, there is provided a power switching control device applied to a configuration of connecting a circuit breaker to a power transmission line between a power supply and a load, comprising: a voltage measurement unit that measures a power-supply side voltage and a load-side voltage of the circuit breaker; a gap-voltage estimation unit that estimates a power-supply-side voltage estimate value at and after a time when the circuit breaker interrupts a current based on the power-supply side voltage, that estimates a load-side voltage estimate value at and after the time when the circuit breaker interrupts the current based on the load-side voltage and a passage of time since the circuit breaker interrupts the current, and that calculates a circuit-breaker-gap-voltage estimate value at and after the time when the circuit breaker interrupts the current based on the power-supply-side voltage estimate value and the load-side voltage estimate value; a target closing-time detection unit that detects an optimum timing of closing the circuit breaker and outputs a target closing time based on the circuit-breaker-gap-voltage estimate value; and a closing control unit that controls the circuit breaker to be closed at the target closing time.

Advantageous Effects of Invention

[0008] According to the present invention, it is possible to suppress generation of a transient voltage or current that is possibly caused by a mismatch between a gap-voltage estimate value after interrupting a current and an actual gap voltage.

Brief Description of Drawings

[0009] 

FIG. 1 is a configuration example of a power switching control device according to a first embodiment.

FIGS. 2 depict an example of a behavior of voltages and a current of respective parts before and after interrupting the current on a shunt-reactor-compensated power transmission line.

FIGS. 3 depict an example of a behavior of voltages and a current of respective parts before and after interrupting the current on a shunt-reactor-uncompensated power transmission line.

FIG. 4 is a flowchart of an example of processes performed by the power switching control device according to the first embodiment.

FIG. 5 is a flowchart of an example of processes performed by a power switching control device according to a second embodiment.

Description of Embodiments

[0010] A power switching control device and a closing control method thereof according to embodiments of the present invention will be explained below in detail with reference to the accompanying drawings. The present invention is not limited to the embodiments.

First embodiment.

[0011] FIG. 1 is a configuration example of a power switching control device according to a first embodiment. In FIG. 1, a circuit breaker 2 is connected between a power-supply-side main circuit 1 on a left-side of Fig. 1 and a no-load power transmission line 3 on a right-side thereof. A voltage measurement unit 6 that includes a power-supply-side voltage measurement unit 4 measuring a power-supply side voltage of the circuit breaker 2 and a load-side voltage measurement unit 5 measuring a load-side voltage of the circuit breaker 2 is connected to both ends of the circuit breaker 2. An auxiliary switch 7 interlocking with movable contacts of the circuit breaker 2 is connected to the circuit breaker 2. An open/closed-state detection unit 10 detecting whether the auxiliary switch 7 is in an open state or a closed state is connected to the auxiliary switch 7. In the example shown in FIG. 1, only one phase among phases R, S, and T is shown for the brevity of explanations.

[0012] In the example shown in FIG. 1, the power transmission line 3 is a shunt-reactor-compensated power transmission line or a shunt-reactor-uncompensated power transmission line. If the power transmission line 3 is the shunt-reactor-compensated power transmission line, an AC voltage having a constant frequency due to a reactor on a load side of the circuit breaker 2 and an electrostatic capacity of the power transmission line 3 is generated. If the power transmission line is the shunt-reactor-uncompensated power transmission line, a DC voltage in proportion to a power-supply side voltage at a time of interrupting a current is generated on the load side of the circuit breaker 2.

[0013] For example, the power switching control device according to the first embodiment is constituted by a computer and the like, and includes a gap-voltage estimation unit 11, a target-closing-time detection unit 12, and a closing control unit 13. In the example shown in FIG. 1, it is described that the power switching control device does not include the voltage measurement unit 6, the auxiliary switch 7, and the open/closed-state detection unit 10. Alternatively, the power switching control device can be configured to include these constituent elements.

[0014] The gap-voltage estimation unit 11 continuously estimates instantaneous values of a gap voltage based on the power-supply side voltage output from the power-supply-side voltage measurement unit 4, the load-side voltage output from the load-side voltage measurement unit 5, and an open/closed-state detection signal output from the open/closed-state detection unit 10, and outputs the instantaneous values of the gap voltage to the target-closing-time detection unit 12.

[0015] The target-closing-time detection unit 12 detects an optimum closing timing when the circuit breaker 2 can be closed next time based on a circuit-breaker-gap-voltage estimate value, and outputs a target closing time.

[0016] When a closing command is input, the closing control unit 13 controls the circuit breaker 2 to be closed at the target closing time output from the target-closing-time detection unit 12.

[0017] A method of suppressing the generation of a transient voltage or current by the power switching control device according to the first embodiment is explained next with reference to FIGS. 2 and 3.

[0018] FIGS. 2 depict an example of a behavior of voltages and a current of respective parts before and after interrupting the current on the shunt-reactor-compensated power transmission line. FIG. 2(a) depicts a waveform of a main circuit current in one phase. FIG. 2(b) depicts a waveform of the power-supply side voltage in the phase and FIG. 2(c) depicts a waveform of the load-side voltage in the phase. FIG. 2(d) depicts a waveform of the circuit-breaker gap voltage in the phase obtained by subtracting the load-side voltage shown in FIG. 2(c) from the power-supply side voltage shown in FIG. 2(b).

[0019] FIGS. 3 depict an example of a behavior of voltages and a current of respective parts before and after interrupting the current on the shunt-reactor-uncompensated power transmission line. FIG. 3(a) depicts a waveform of the main circuit current in each phase. FIG. 3(b) depicts a waveform of the power-supply side voltage in each phase and FIG. 3(c) depicts a waveform of the load-side voltage in each phase. FIG. 3(d) depicts a waveform of the circuit-breaker gap voltage in each phase obtained by subtracting the load-side voltage shown in FIG. 3(c) from the power-supply side voltage shown in FIG. 3(b). FIG. 3(e) depicts a waveform of the load-side voltage when a voltage measuring instrument such as a voltage transformer (hereinafter, "VT") that discharges an electric charge is used as the load-side voltage measurement unit 5.

[0020] As shown in FIG. 2(c), when the current is interrupted at a time T on the shunt-reactor-compensated power transmission line, the waveform of the load-side voltage changes to a waveform of the AC voltage having the constant frequency due to the reactor and the capacitive load of the power transmission line.

[0021] As shown in FIG. 3(c), when the current is interrupted at the time T on the shunt-reactor-uncompensated power transmission line, the waveform of the load-side voltage changes to a waveform of the DC voltage in proportion to the power-supply side voltage at the time of an interruption.

[0022] As shown in FIG. 2(c), for example, when timings when the load-side voltage is equal to or higher than a predetermined positive-electrode-side threshold (80% of a maximum value of the power-supply side voltage, for example) and timings when the load-side voltage is equal to or lower than a negative-electrode-side threshold equal to the positive-electrode-side threshold are respectively detected at least once within a certain time (100 milliseconds, for example) at and after a current interruption time T, it is possible to determine that the load-side voltage is an AC wave signal. In this case, it is possible to determine that the power transmission line 3 connected to the load side of the circuit breaker 2 is the shunt-reactor-compensated power transmission line. In other cases, the load-side voltage is determined to be a DC signal. In this case, it is determined that the power transmission line 3 connected to the load side of the circuit breaker 2 is the shunt-reactor-uncompensated power transmission line. Alternatively, it is possible to determine that the load-side voltage is an AC waveform signal and that the power transmission line 3 connected to the load side of the circuit breaker 2 is the shunt-reactor-compensated power transmission line when, for example, zero points in a constant cycle are generated on the load-side voltage within the certain time at and after the circuit interruption time T.

[0023] As in a case of executing slow re-closing for which a time from the current interruption of the circuit breaker 2 to the closing of the circuit breaker 2 is longer than a a time specified in advance (by 3 or more seconds, for example), when a sufficient time interval is secured from the current interruption time T to the next closing, the load-side voltage (that is, a residual voltage) attenuates by a time constant or the like that is determined by the electrostatic capacity of the power transmission line 3 and a leakage resistance of an insulator supporting the power transmission line 3 and eventually converges into zero over time. Therefore, when a time from the current interruption time is counted and a predetermined time determined, for example, based on an attenuation time constant of the residual voltage on the power transmission line 3 estimated by a prior calculation or the like, then it is determined that the slow re-closing is executed, and it is estimated that the load-side voltage estimate value at the time of closing the circuit breaker 2 is zero. On the other hand, if the predetermined time does not pass since the current interruption time T, it is determined that fast re-closing is executed and the load-side voltage estimate value at and after the present time is calculated using data by as much as the certain time since the current interruption time T. The present invention is not limited to the method of calculating the load-side voltage estimate value adopted in this case.

[0024] Furthermore, in a case where the power transmission line 3 is the shunt-reactor-uncompensated power transmission line and where the voltage measuring instrument such as the VT that discharges an electric charge is used as the load-side voltage measurement unit 5, as shown in FIG. 3(e), the electric charge remaining on the load side is rapidly discharged because of saturation of an iron core of the VT after interrupting the current. Accordingly, the load-side voltage actually output from a secondary side of the load-side voltage measurement unit 5 converges into zero in several hundreds of milliseconds after the current interruption. Generally, a time interval since the circuit breaker 2 interrupts the current until the circuit breaker 2 is closed next time is about 0.3 second to about 1.0 second even in the case of the fast re-closing. Therefore, the load-side voltage attenuates to nearly zero by the time of closing the circuit breaker 2 next time as a result of discharging the electric current by the VT. Therefore, when the power transmission line 3 is the shunt-reactor-uncompensated power transmission line and the load-side voltage shows a behavior of converging into zero at a speed equal to or higher than a constant speed (100 milliseconds, for example) after the current interruption time T, then it is determined that the load-side voltage measurement unit 5 is the voltage measuring instrument such as the VT that discharges an electric charge, and the load-side voltage estimate value at the time of closing the circuit breaker 2 next time is estimated as zero. On the other hand, when the load-side voltage does not show the behavior of converging into zero at the speed equal to or higher than the constant speed after the current interruption time T, then it is determined that the load-side voltage measurement unit 5 is not the voltage measuring instrument such as the VT (such as a capacitive voltage transformer) that discharges an electric charge, and the load-side voltage estimate value at and after the present time is calculated using the data by as much as the certain time since the current interruption time T. The present invention is not limited to the method of calculating the load-side voltage estimate value adopted in this case.

[0025] That is, the power switching control device according to the first embodiment estimates that the load-side voltage estimate value at the next closing is zero when the predetermined time determined based on the attenuation time constant of a residual voltage on the power transmission line 3 in advance passes since the current interruption time T, and when the load-side voltage at and after the current interruption time T is a DC signal and the load-side voltage shows the behavior of converging into zero at the speed equal to or higher than the constant speed at and after the current interruption time T. The power switching control device according to the first embodiment can thereby more accurately estimate the gap voltage at and after the present time and suppress generation of a transient voltage or current that is possibly caused by a mismatch between the gap-voltage estimate value and the actual gap voltage in a case of a slow re-closing operation or even in a case where the power transmission line 3 is the shunt-reactor-uncompensated power transmission line and where the load-side voltage measurement unit 5 is the voltage measuring instrument such as the VT that discharges an electric charge.

[0026] An operation performed by the power switching control device according to the first embodiment is explained next with reference to FIGS. 1 to 4. FIG. 4 is a flowchart of an example of processes performed by the power switching control device according to the first embodiment.

[0027] First, the gap-voltage estimation unit 11 converts an analog signal of the power-supply side voltage input from the power-supply-side voltage measurement unit 4 into a digital signal, discretizes the digital signal at a predetermined sampling interval, and stores therein the power-supply-side voltage signal by as much as a certain time (Step ST101). In addition, the gap-voltage estimation unit 11 converts an analog signal of the load-side voltage input from the load-side voltage measurement unit 5 into a digital signal, discretizes the digital signal at a predetermined sampling interval, and stores therein the load-side voltage signal by as much as the certain time (Step ST201).

[0028] Next, the gap-voltage estimation unit 11 detects and stores therein a plurality of zero-point times when a sign of the power-supply-side voltage signal changes from minus to plus or from plus to minus (Step ST102). In addition, the gap-voltage estimation unit 11 detects and stores therein a plurality of zero-point times when a sign of the load-side voltage signal changes from minus to plus or from plus to minus (Step ST202).

[0029] The gap-voltage estimation unit 11 always stores therein the power-supply-side voltage signal before the certain time since the present time, the load-side voltage signal before the certain time since the present time, the zero-point times of the power-supply-side voltage signal, and the zero-point times of the load-side voltage signal as data. When detecting that the auxiliary switch 7 changes from the closed state to the open state, the gap-voltage estimation unit 11 determines that the circuit breaker 2 interrupts the current and stops storing therein the above data at a time point when the certain time passes since the current interruption time T. That is, the gap-voltage estimation unit 11 calculates the power-supply-side voltage estimate value and the load-side voltage estimate value at and after the present time using the data by as much as the certain time since the current interruption in subsequent processing steps.

[0030] Next, the gap-voltage estimation unit 11 determines whether the power-supply-side voltage signal is an AC waveform signal (Step ST103). In addition, the gap-voltage estimation unit 11 determines whether the load-side voltage signal is the AC waveform signal (Step ST203). A process of calculating the load-side voltage estimate value is explained first.

[0031] When the load-side voltage signal is the AC waveform signal (YES at Step ST203), the gap-voltage estimation unit 11 determines that the power transmission line 3 is the shunt-reactor-compensated power transmission line, and determines whether the predetermined time passes since the current interruption time T (Step S204). When the predetermined time does not pass since the current interruption time T (NO at Step S204), the gap-voltage estimation unit 11 determines that the fast re-closing is executed, determines that an attenuation due to the leakage resistance or the like does not occur to the load-side voltage, obtains a frequency, a phase, and an amplitude of the load-side voltage, and calculates the load-side voltage estimate value at and after the present time (Step S205). When the predetermined time passes since the current interruption time T (YES at Step ST204), the gap-voltage estimation unit 11 determines that the slow re-closing is executed and estimates the load-side voltage estimate value as zero (Step ST206).

[0032] An example of a method of calculating the load-side voltage estimate value at and after the present time at Step S205 is explained. As for the frequency of the load-side voltage signal, for example, it suffices to obtain an average value of a plurality of zero-point time intervals of the load-side voltage signal stored at Step ST202, to multiply a reciprocal of the average value of the zero-point time intervals by 1/2, and to set a resultant value as the frequency of the load-side voltage signal. As for the phase of the load-side voltage signal, a value of the latest zero-point time when the load-side voltage changes from the minus sign to the plus sign among a plurality of zero-point times stored at Step ST202 is stored as the time of a phase of 0 degree. In addition, a value of the latest zero-point time when the load-side voltage signal changes from the plus sign to the minus sign is stored as a phase of 180 degrees. As for the amplitude of the load-side voltage signal, a maximum value and a minimum value of a plurality of load-side voltage signals obtained for a period, for example, from the current interruption time T to the present time are stored, and an average of absolute values of the stored maximum and minimum values is set as the amplitude of the load-side voltage signal. Alternatively, the amplitude of the load-side voltage signal can be obtained by integrating the load-side voltage signals by a cycle to obtain an effective value and by multiplying the effective value by √2. If the above calculated values are used, the load-side voltage signal can be approximated as expressed by "voltage value = amplitude × sin(2π × frequency ×t)", with t=0 as the time corresponding to the phase of 0 degree. This value obtained by the equation is assumed as the load-side-voltage estimate value at and after the present time at step STP205.

[0033] Referring back to the flowchart shown in FIG. 4, when the load-side voltage signal is not the AC waveform signal (that is, a DC signal) (NO at Step ST203), the gap-voltage estimation unit 11 determines that the power transmission line 3 is the shunt-reactor-uncompensated power transmission line, and determines whether the load-side voltage shows the behavior of converging into zero at the speed equal to or higher than the constant speed at and after the current interruption time T (Step ST207).

[0034] When the load-side voltage shows the behavior of converging into zero at the speed equal to or higher than the constant speed at and after the current interruption time T (YES at Step ST207), the gap-voltage estimation unit 11 determines that the load-side voltage measurement unit 5 is the voltage measuring instrument such as the VT that discharges an electric charge, and estimates the load-side voltage estimate value as zero (Step ST206). When the load-side voltage does not show the behavior of converging into zero at the speed equal to or higher than the constant speed at and after the current interruption time T (NO at Step ST207), the gap-voltage estimation unit 11 determines that the load-side voltage measurement unit 5 is not the voltage measuring instrument such as the VT (such as a capacitive voltage transformer) that discharges an electric charge, and determines whether the predetermined time passed since the current interruption time T (Step ST208). When the predetermined time does not pass since the current interruption time T (NO at Step S208), the gap-voltage estimation unit 11 determines that the fast re-closing is executed, determines that the attenuation due to the leakage resistance or the like does not occur to the load-side voltage, calculates a time average value of the load-side voltage signals, for example, as the amplitude of a DC signal, and sets this value as the load-side voltage estimate value at and after the present time (Step ST209). When the predetermined time passes since the current interruption time T (YES at Step ST208), the gap-voltage estimation unit 11 determines that the slow re-closing is executed and estimates the load-side voltage estimate value as zero (Step ST206).

[0035] A process of calculating the power-supply-side voltage estimate value is explained next. When the load-side voltage signal is the AC waveform signal (YES at Step ST103), the gap-voltage estimation unit 11 obtains a frequency, a phase, and an amplitude of the power-supply-side voltage and calculates the power-supply-side voltage estimate value at and after the present time (Step ST105). Because a method of calculating the power-supply-side voltage estimate value at Step ST105 is identical to the method of calculating the load-side voltage estimate value at Step ST205, the calculation method is not described herein.

[0036] When the power-supply-side voltage signal is not the AC waveform signal (that is, a DC signal) (NO at Step ST103), the gap-voltage estimation unit 11 calculates a time average value of the load-side voltage signals, for example, as the amplitude of the DC signal, and sets this value as the power-supply-side voltage estimate value at and after the present time (Step ST109).

[0037] The gap-voltage estimation unit 11 calculates an absolute value of the gap-voltage estimate value for the certain time since the present time using the power-supply-side voltage estimate value and the load-side voltage estimate value (Step ST310).

[0038] The target-closing-time detection unit 12 estimates the target closing time for the certain time since the present time so that the circuit breaker 2 can be closed at a timing when the absolute value of the gap-voltage estimate value becomes smaller based on the absolute value of the gap-voltage estimate value input from the gap-voltage estimation unit 11 (Step ST311). The present invention is not limited to this method of estimating the target closing time.

[0039] The target-closing-time detection unit 12 assumes that a latest estimation result of the target closing time is correct, deletes the target closing time estimated in a previous process, rewrites the target closing time estimated in the previous process to the target closing time estimated in the present process, and updates and outputs the target closing time (Step ST312).

[0040] When a closing command 15 is input, the closing control unit 13 controls the circuit breaker 2 to be closed at the target closing time obtained by the target-closing-time detection unit 12 (step ST313).

[0041] As described above, the power switching control device according to the first embodiment estimates that the load-side voltage estimate value at the next closing is zero when the predetermined time determined based on the attenuation time constant of a residual voltage on the power transmission line in advance passes since the current interruption time, and when the load-side voltage at and after the current interruption time is a DC signal and the load-side voltage shows the behavior of converging into zero at the speed equal to or higher than the constant speed at and after the current interruption time. The power switching control device according to the first embodiment can thereby more accurately estimate the gap voltage at and after the present time and suppress the generation of the transient voltage or current that is possibly caused by a mismatch between the gap-voltage estimate value and the actual gap voltage after the current interruption in the case of the slow re-closing operation or even in the case where the power transmission line 3 is the shunt-reactor-uncompensated power transmission line and where the load-side voltage measurement unit 5 is the voltage measuring instrument such as the VT that discharges an electric charge.

Second embodiment.

[0042] FIG. 5 is a flowchart of an example of processes performed by a power switching control device according to a second embodiment. Because configurations of a power switching control device according to the second embodiment are identical to those described in the first embodiment and shown in FIG. 1, explanations thereof will be omitted. In addition, in the flowchart of FIG. 5, processes identical or equivalent to those shown in FIG. 4 and described in the first embodiment are denoted by same step numbers and detailed explanations thereof will be omitted.

[0043] In the flowchart of the first embodiment shown in FIG. 4, the process of determining whether the predetermined time passes since the current interruption time T (that is, whether the slow re-closing is executed) (Step ST204 or ST208) is carried out in each of the case where the load-side voltage signal is an AC waveform signal and the case where the load-side signal is a DC signal. In the second embodiment, before the process of determining whether the load-side voltage is the AC waveform signal (Step ST203a), a process of determining whether the predetermined time passes since the current interruption time T is performed (Step ST204a), as shown in FIG. 5. When the predetermined time passes since the current interruption time T (that is, the slow re-closing is executed) (YES at Step ST204a), the gap-voltage estimation unit 11 estimates the load-side voltage estimate value as zero (Step ST206) whether the load-side voltage signal is the AC waveform signal or the DC signal. Therefore, in the second embodiment, the number of processing steps can be decreased as compared with that in the first embodiment.

[0044] As described above, the power switching control device according to the second embodiment performs the process of determining whether the predetermined time passes since the circuit breaker is closed before the process of determining whether the load-side voltage signal is the AC waveform signal, and estimates the load-side voltage estimate value as zero whether the load-side voltage signal is the AC waveform signal or the DC signal. Therefore, in addition to effects of the first embodiment, it is possible to decrease the number of processing steps as compared with that in the first embodiment.

[0045] In the embodiments described above, it has been explained that it is determined whether the load-side voltage signal is the AC waveform signal or the DC signal and determined whether the power transmission line is the shunt-reactor-compensated power transmission line or the shunt-reactor-uncompensated power transmission line. Alternatively, if it is already known that the power transmission line is the shunt-reactor-compensated power transmission line or the shunt-reactor-uncompensated power transmission line, the power switching control device can be configured to select one of these options using a switch or the like.

[0046] Furthermore, it has been described that it is determined whether the load-side voltage falls at the speed equal to or higher than the constant speed at and after a current interruption time and determined whether the load-side voltage measurement unit is the voltage measuring instrument that discharges an electric charge such as the VT. Alternatively, if it is already known whether the load-side voltage measurement unit is the voltage measuring instrument that discharges an electric charge such as the VT, the power switching control device can be configured to select one of these options using a switch or the like.

[0047] The configuration described in the above embodiments is only an example of the configuration of the present invention, and it is possible to combine the configuration with other publicly-known techniques, and it is needless to mention that the present invention can be configured while modifying it without departing from the scope of the invention, such as omitting a part of the configuration.

Reference Signs List

[0048] 

1

main circuit

2

circuit breaker

3

power transmission line

4

power-supply-side voltage measurement unit

5

load-side voltage measurement unit

6

voltage measurement unit

7

auxiliary switch

10

open/closed-state detection unit

11

gap-voltage estimation unit

12

target-closing-time detection unit

13

closing control unit

Claims

1. A power switching control device applied to a configuration of connecting a circuit breaker to a power transmission line between a power supply and a load, comprising:

a voltage measurement unit that measures a power-supply side voltage and a load-side voltage of the circuit breaker;

a gap-voltage estimation unit that estimates a power-supply-side voltage estimate value at and after a time when the circuit breaker interrupts a current based on the power-supply side voltage, that estimates a load-side voltage estimate value at and after the time when the circuit breaker interrupts the current based on the load-side voltage and a passage of time since the circuit breaker interrupts the current, and that calculates a circuit-breaker-gap-voltage estimate value at and after the time when the circuit breaker interrupts the current based on the power-supply-side voltage estimate value and the load-side voltage estimate value;

a target closing-time detection unit that detects an optimum timing of closing the circuit breaker and outputs a target closing time based on the circuit-breaker-gap-voltage estimate value; and

a closing control unit that controls the circuit breaker to be closed at the target closing time.

2. The power switching control device according to claim 1, wherein the gap-voltage estimation unit estimates the load-side voltage estimate value as zero when a predetermined time determined based on an attenuation time constant of a residual voltage on the power transmission line in advance passes, when estimating the load-side voltage estimate value.

3. The power switching control device according to claim 1, wherein the gap-voltage estimation unit estimates the load-side voltage estimate value as zero when the load-side voltage within a certain time after the time when the circuit breaker interrupts the current is a direct-current voltage and when the load-side voltage shows a behavior of converging into zero at a speed equal to or higher than a constant speed, when estimating the load-side voltage estimate value.

4. The power switching control device according to claim 1, wherein the gap-voltage estimation unit estimates the load-side voltage estimate value as zero when it is already known that the load-side voltage within a certain time after the time when the circuit breaker interrupts the current is a direct-current voltage and when the load-side voltage shows a behavior of converging into zero at a speed equal to or higher than a constant speed when estimating the load-side voltage estimate value.

5. The power switching control device according to claim 1, wherein the gap-voltage estimation unit estimates the load-side voltage estimate value as zero when the load-side voltage shows a behavior of converging into zero at a speed equal to or higher than a constant speed within the certain time.

6. A closing control method of a power switching control device applied to a configuration of connecting a circuit breaker to a power transmission line between a power supply and a load, the closing control method comprising:

a first step of determining whether the load-side voltage within a certain time after a time when the circuit breaker interrupts a current is an alternating-current voltage or a direct-current voltage;

a second step of determining whether a predetermined time determined based on an attenuation time constant of a residual voltage on the power transmission line in advance passes when it is determined at the first step that the load-side voltage is the alternating-current voltage;

a third step of estimating the load-side voltage estimate value as zero when it is determined at the second step that the predetermined time passes;

a fourth step of estimating a power-supply-side voltage estimate value at and after the time when the circuit breaker interrupts the current;

a fifth step of calculating a circuit-breaker-gap-voltage estimate value at and after the time when the circuit breaker interrupts the current based on the power-supply-side voltage estimate value and the load-side voltage estimate value;

a sixth step of detecting optimum timing of closing the circuit breaker and outputting a target closing time based on the circuit-breaker-gap-voltage estimate value; and

a seventh step of controlling the circuit breaker to be closed at the target closing time.

7. A closing control method of a power switching control device applied to a configuration of connecting a circuit breaker to a power transmission line between a power supply and a load, the closing control method comprising:

a first step of determining whether the load-side voltage within a certain time after a time when the circuit breaker interrupts a current is an alternating-current voltage or a direct-current voltage;

a second step of determining whether the load-side voltage shows a behavior of converging into zero at a speed equal to or higher than a constant speed when it is determined at the first step that the load-side voltage is the direct-current voltage;

a third step of estimating the load-side voltage estimate value as zero when it is determined at the second step that the load-side voltage shows the behavior of converging into zero at the speed equal to or higher than the constant speed;

a fourth step of estimating a power-supply-side voltage estimate value at and after the time when the circuit breaker interrupts the current;

a fifth step of calculating a circuit-breaker-gap-voltage estimate value at and after the time when the circuit breaker interrupts the current based on the power-supply-side voltage estimate value and the load-side voltage estimate value;

a sixth step of detecting optimum timing of closing the circuit breaker and outputting a target closing time based on the circuit-breaker-gap-voltage estimate value; and

a seventh step of controlling the circuit breaker to be closed at the target closing time.

8. A closing control method of a power switching control device applied to a configuration of connecting a circuit breaker to a power transmission line between a power supply and a load, the closing control method comprising:

a first step of determining whether the load-side voltage within a certain time after a time when the circuit breaker interrupts a current is an alternating-current voltage or a direct-current voltage;

a second step of determining whether the load-side voltage shows a behavior of converging into zero at a speed equal to or higher than a constant speed when it is determined at the first step that the load-side voltage is the direct-current voltage;

a third step of determining whether a predetermined time determined based on an attenuation time constant of a residual voltage on the power transmission line in advance passes when it is determined at the second step that the load-side voltage does not show the behavior of converging into zero at the speed equal to or higher than the constant speed;

a fourth step of estimating the load-side voltage estimate value as zero when it is determined at the third step that the predetermined time passes;

a fifth step of estimating a power-supply-side voltage estimate value at and after the time when the circuit breaker interrupts the current;

a sixth step of calculating a circuit-breaker-gap-voltage estimate value at and after the time when the circuit breaker interrupts the current based on the power-supply-side voltage estimate value and the load-side voltage estimate value;

a seventh step of detecting optimum timing of closing the circuit breaker and outputting a target closing time based on the circuit-breaker-gap-voltage estimate value; and

an eighth step of controlling the circuit breaker to be closed at the target closing time.

9. A closing control method of a power switching control device applied to a configuration of connecting a circuit breaker to a power transmission line between a power supply and a load, the closing control method comprising:

a first step of determining whether a predetermined time determined based on an attenuation time constant of a residual voltage on the power transmission line in advance passes;

a second step of estimating the load-side voltage estimate value as zero when it is determined at the first step that the predetermined time passes;

a third step of estimating a power-supply-side voltage estimate value at and after a time when the circuit breaker interrupts the current;

a fourth step of calculating a circuit-breaker-gap-voltage estimate value at and after the time when the circuit breaker interrupts the current based on the power-supply-side voltage estimate value and the load-side voltage estimate value;

a fifth step of detecting optimum timing of closing the circuit breaker and outputting a target closing time based on the circuit-breaker-gap-voltage estimate value; and

a sixth step of controlling the circuit breaker to be closed at the target closing time.

10. A closing control method of a power switching control device applied to a configuration of connecting a circuit breaker to a power transmission line between a power supply and a load, the closing control method comprising:

a first step of determining whether a predetermined time determined based on an attenuation time constant of a residual voltage on the power transmission line in advance passes;

a second step of determining whether the load-side voltage within a certain time after a time when the circuit breaker interrupts a current is an alternating-current voltage or a direct-current voltage when it is determined at the first step that the predetermined time does not pass;

a third step of determining whether the load-side voltage shows a behavior of converging into zero at a speed equal to or higher than a constant speed when it is determined at the second step that the load-side voltage is the direct-current voltage;

a fourth step of estimating the load-side voltage estimate value as zero when it is determined at the third step that the load-side voltage shows the behavior of converging into zero at the speed equal to or higher than the constant speed;

a fifth step of estimating a power-supply-side voltage estimate value at and after the time when the circuit breaker interrupts the current;

a sixth step of calculating a circuit-breaker-gap-voltage estimate value at and after the time when the circuit breaker interrupts the current based on the power-supply-side voltage estimate value and the load-side voltage estimate value;

a seventh step of detecting optimum timing of closing the circuit breaker and outputting a target closing time based on the circuit-breaker-gap-voltage estimate value; and

an eighth step of controlling the circuit breaker to be closed at the target closing time.

Drawing