Patent Description:
A direct-current circuit breaker forms a current zero point by superimposing an oscillating current on a direct current, and interrupts the direct current at the current zero point. As the direct-current circuit breaker, a direct-current circuit breaker of a forced-extinction type is known which includes a resonance circuit including a capacitor and a reactor and performs extinction by superimposing a resonance current generated by discharge of the capacitor on a direct current.

Patent Literature <NUM> discloses a direct-current circuit breaker including a lightning arrester for suppressing an overvoltage of a capacitor when interrupting a direct current.

Patent Literature <NUM> relates to a DC circuit breaker, provided with: a main circuit breaker inserted into a DC wire, a resonance circuit connected in parallel to the main circuit breaker, and a MOSA connected in parallel to the main circuit breaker through the resonance circuit; and a main circuit breaker inserted into a DC wire, a switch serially connected to the main circuit breaker, a resonance circuit connected in parallel to the main circuit breaker, and a MOSA connected in parallel to the main circuit breaker through the resonance circuit. The DC wire is a wire branching from the DC wire and returning to the DC wire. The switch is inserted on the upstream side of the DC wire.

Patent Literature <NUM> relates to a lightning arrester.

Non-Patent Literature <NUM> relates to a realization of heavy-duty zinc-oxide type lightning arrestors by parallel connection.

Non-Patent Literature <NUM> relates to surge arresters monitoring systems in AC-DC converter stations.

In a direct-current circuit breaker provided in a power system for high voltage direct current (HVDC) power transmission, energy processed by a lightning arrester may reach MJ order. Therefore, a lightning arrester including a plurality of columns connected in parallel to each other is used in the direct-current circuit breaker. Each of the plurality of columns is a stack of a plurality of nonlinear resistive elements. In the lightning arrester, when an anomaly occurs in at least one or some of the columns, an elevated temperature of the column in which the anomaly has occurred may lead to a failure, which is a state where it is difficult to perform a normal energy process. The conventional direct-current circuit breaker disclosed in Patent Literature <NUM> cannot obviate a failure of the lightning arrester, which is a problem.

The present disclosure has been made in view of the above, and an object thereof is to obtain a direct-current circuit breaker capable of obviating a failure of a lightning arrester.

According to the present disclosure, a direct-current circuit breaker as defined in independent claim <NUM> is provided. Further embodiments of the claimed invention are defined in the dependent claims. Although the claimed invention is only defined by the claims, the below embodiments, examples, and aspects are present for aiding in understanding the background and advantages of the claimed invention.

The direct-current circuit breaker according to the present disclosure achieves an effect that it is possible to obviate a failure of a lightning arrester.

Hereinafter, a direct-current circuit breaker according to each embodiment will be described in detail with reference to the drawings. The present disclosure is not limited to the embodiments.

<FIG> is a diagram illustrating a configuration of a direct-current circuit breaker according to a first embodiment. A direct-current circuit breaker <NUM> according to the first embodiment is a mechanical direct-current circuit breaker (DCCB) including mechanical components. The direct-current circuit breaker <NUM> is provided on a direct-current line <NUM> of a power system. In the first embodiment, the power system is a power system that performs HVDC power transmission. The direct-current circuit breaker <NUM> interrupts a direct current upon occurrence of an accident such as short-circuit or earth fault in the direct-current line <NUM>, thereby protecting the power system. The direct-current circuit breaker <NUM> interrupts the direct current at a current zero point formed by superimposing an oscillating current on a direct current flowing through the direct-current line <NUM>.

The direct-current circuit breaker <NUM> includes: a circuit breaker <NUM> provided on the direct-current line <NUM>; a capacitor <NUM>, a reactor <NUM> and a high-speed switch <NUM> that constitute a resonance circuit; a lightning arrester <NUM> for suppressing an overvoltage to a voltage level based on a withstand voltage specification of a DCCB; and a control circuit <NUM> that controls the entirety of the direct-current circuit breaker <NUM>. The capacitor <NUM>, the reactor <NUM>, and the high-speed switch <NUM> are connected in series to each other. The capacitor <NUM>, the reactor <NUM>, and the high-speed switch <NUM> are connected in parallel to the circuit breaker <NUM>. The lightning arrester <NUM> is connected in parallel with the capacitor <NUM> and the high-speed switch <NUM>.

At the above-described current zero point formed by the oscillating current and the direct current canceling each other, the circuit breaker <NUM> interrupts the direct current. That is, the circuit breaker <NUM> interrupts the direct current by forced extinction. The circuit breaker <NUM> is a circuit breaker capable of performing high-speed current interruption, and is, for example, a vacuum circuit breaker (VCB). The capacitor <NUM> and the reactor <NUM> generate an oscillating current by discharging of the capacitor <NUM>. The high-speed switch <NUM> is a switch that performs closing for forming a current zero point.

The direct-current line <NUM> includes a current transformer <NUM> that detects an accident current which is a direct-current flowing when an accident occurs. The current transformer <NUM> outputs a detection result of the accident current to the control circuit <NUM>. A device other than the current transformer <NUM> may be used as the device that detects the accident current. The control circuit <NUM> outputs a command for an opening operation and a command for a closing operation to each of the circuit breaker <NUM> and the high-speed switch <NUM>. The control circuit <NUM> sends a signal indicating conditions of the direct-current circuit breaker <NUM> to a control panel which is a device outside the direct-current circuit breaker <NUM>. The control panel is not illustrated. The destination of the signal transmitted from the control circuit <NUM> may be a device other than the control panel.

When in a steady state, i.e., when the power system is in a steady state, the circuit breaker <NUM> is closed and the high-speed switch <NUM> is open. The capacitor <NUM> is charged by a direct-current voltage in the steady state, an external power supply, or the like. When an accident occurs, the circuit breaker <NUM> performs the opening operation and the high-speed switch <NUM> performs the closing operation. When the high-speed switch <NUM> is closed, electric charges from the capacitor <NUM> are discharged to a loop including the high-speed switch <NUM>, the capacitor <NUM>, the reactor <NUM>, and the circuit breaker <NUM>. When the electric charges are discharged from the capacitor <NUM>, an oscillating current that passes through the reactor <NUM>, the circuit breaker <NUM>, and the high-speed switch <NUM> flows from the capacitor <NUM>. As a result, the direct-current circuit breaker <NUM> superimposes, on an accident current at the circuit breaker <NUM>, the oscillating current in a direction opposite to the direction of the direct current, which is the accident current. When the current zero point is formed by superimposing the oscillating current on the accident current, the extinction of arc is completed in the circuit breaker <NUM> during the opening operation. The lightning arrester <NUM> suppresses an overvoltage generated after the extinction of arc by the circuit breaker <NUM>.

Next, a configuration of the lightning arrester <NUM> will be described. <FIG> is a side view of the lightning arrester included in the direct-current circuit breaker according to the first embodiment. <FIG> is a top view of the lightning arrester included in the direct-current circuit breaker according to the first embodiment. The lightning arrester <NUM> includes a plurality of columns <NUM> arranged in an array in a horizontal direction. In the example illustrated in <FIG>, the lightning arrester <NUM> includes <NUM> columns <NUM>. As the number of columns <NUM> constituting the lightning arrester <NUM>, any number thereof may be employed. The plurality of columns <NUM> are connected in parallel to each other.

An upper end of each of the plurality of columns <NUM> is attached to an upper plate <NUM>. A lower end of each of the plurality of columns <NUM> is attached to a lower plate <NUM>. The plurality of columns <NUM> in a state of being attached to the upper plate <NUM> and the lower plate <NUM> are supported by supports <NUM>. Below the plurality of columns <NUM> supported by the supports <NUM>, a space is provided which is capable of accommodating the column <NUM> separated from the upper plate <NUM> and the lower plate <NUM>.

<FIG> is a view illustrating a schematic configuration of the column constituting the lightning arrester illustrated in <FIG> and <FIG>. The column <NUM> includes: a stack of a plurality of nonlinear resistive elements <NUM>; a container <NUM> in which the stack is accommodated; an electrode <NUM> on a power supply side connected to an upper end of the stack; and an electrode <NUM> on a ground side connected to a lower end of the stack. The nonlinear resistive elements <NUM> are each a sintered body containing zinc oxide as a main component. The plurality of nonlinear resistive elements <NUM> constituting the stack are connected in series to each other. The container <NUM> is a container made of an insulating material, and is a porcelain hollow insulator or a polymer hollow insulator. <FIG> illustrates a cross section through each of the plurality of nonlinear resistive elements <NUM> of the column <NUM>.

<FIG> is a diagram for explaining a process of energy performed by the lightning arrester illustrated in <FIG> and <FIG>. Current ICB is a current flowing through the circuit breaker <NUM>. Voltage VCB is a voltage applied to the circuit breaker <NUM>. Energy E is energy processed by the lightning arrester <NUM>. In <FIG>, respective changes in current ICB, voltage VCB, and energy E after the occurrence of an accident are indicated by graphs. In the graph of current ICB, a broken line indicates a current waveform in a case where the circuit breaker <NUM> is assumed to be in a closed state. Such a current waveform is a current waveform obtained by combining a direct current and a resonance current.

After the occurrence of the accident at time t<NUM>, an accident current larger than a current in the steady state flows through the direct-current line <NUM>, and thereby current ICB increases. The circuit breaker <NUM> performs the opening operation at any time between time t<NUM> and time t<NUM>. At time t<NUM>, the high-speed switch <NUM> performs the closing operation. The direct-current circuit breaker <NUM> forms a current zero point by superimposing, on the accident current, an oscillating current generated in the resonance circuit by the high-speed switch <NUM> being closed. As a result, the direct-current circuit breaker <NUM> forcibly interrupts the accident current.

By forcibly interrupting the accident current, electromagnetic energy remains in the system, the electromagnetic energy being expressed as <NUM>/<NUM>×LI<NUM> where L denotes inductance and I denotes current. The lightning arrester <NUM> starts processing energy from time t<NUM> when voltage VCB has risen to a certain voltage value. The lightning arrester <NUM> processes energy from time t<NUM> to time t<NUM>, and thereby the lightning arrester <NUM> suppresses an increase in voltage VCB.

The lightning arrester <NUM> is designed such that a current uniformly flows to each column <NUM> in a period in which energy is processed. However, currents flowing through the columns <NUM> may vary due to a difference in characteristics such as impedance unique to each column <NUM>. As the number of columns <NUM> constituting the lightning arrester <NUM> increases, there is a higher possibility that the column <NUM> in which a magnitude of a current flowing therethrough is different from magnitudes of currents flowing through other columns <NUM> is included in the plurality of columns <NUM>. Therefore, as the number of columns <NUM> increases, there is a higher probability that the variation in the currents flowing through the columns <NUM> increases.

When the currents flowing through the plurality of columns <NUM> become nonuniform, a temperature in the column <NUM> through which a large current flows rises to be higher than temperatures in other columns <NUM>. If a current is continued to be concentrated on one or some of the columns <NUM>, an anomaly that temperatures of the columns <NUM> exceed an allowable temperature may lead to a failure of the lightning arrester <NUM>. Here, the allowable temperature is a maximum value of a temperature at which the column <NUM> can maintain a state in which energy is normally processed.

In the first embodiment, the direct-current circuit breaker <NUM> monitors an anomaly in each of the plurality of columns <NUM> by measuring a temperature in each of the plurality of columns <NUM>. When an anomaly occurs in one or some columns <NUM> out of the plurality of columns <NUM>, the direct-current circuit breaker <NUM> locks the operations of the circuit breaker <NUM> and the high-speed switch <NUM>, and thereby the direct-current circuit breaker <NUM> is stopped operating. In addition, the direct-current circuit breaker <NUM> physically separates the column <NUM> in which the anomaly has occurred from other columns <NUM>. As a result, the direct-current circuit breaker <NUM> obviates a failure of the lightning arrester <NUM> in a case where an anomaly has occurred in one or some columns <NUM> out of the plurality of columns <NUM>.

<FIG> is a block diagram illustrating the control circuit included in the direct-current circuit breaker according to the first embodiment. <FIG> illustrates components of the control circuit <NUM> and components connected to the control circuit <NUM>. The direct-current circuit breaker <NUM> includes: a detector <NUM> that detects a temperature of each column <NUM> provided in the lightning arrester <NUM>; and a separator <NUM>. The separator <NUM> is a mechanism for separating one or some columns <NUM> in which an anomaly has occurred from other columns <NUM>. In <FIG>, illustrations of the detector <NUM> and the separator <NUM> are omitted.

The detector <NUM> includes, for example, a contact type temperature sensor attached to each of the plurality of columns <NUM>. The temperature sensor is attached to the container <NUM>. The detector <NUM> may be a non-contact type temperature sensor such as a radiation thermometer or an infrared thermography device.

The control circuit <NUM> includes: an operation processor <NUM> that controls an opening operation and a closing operation by each of the circuit breaker <NUM> and the high-speed switch <NUM>; a monitor <NUM> that monitors the presence or absence of an anomaly in each of the plurality of columns <NUM>; and a lock processor <NUM> that locks the operations of the circuit breaker <NUM> and the high-speed switch <NUM> controlled by the operation processor <NUM> in a case where an anomaly has occurred in at least one or some columns <NUM> out of the plurality of columns <NUM>. In the first embodiment, the monitor <NUM> determines that an anomaly has occurred in one or some columns <NUM> having a temperature rise exceeding the allowable temperature out of the plurality of columns <NUM>. The control circuit <NUM> further includes a communicator <NUM> that communicates with a device outside the direct-current circuit breaker <NUM>.

The detection result of the accident current obtained by the current transformer <NUM> is input to the operation processor <NUM>. When a current exceeding a threshold which is a criterion for determination of accident current is detected in the current transformer <NUM>, the operation processor <NUM> outputs a command for an opening operation to the circuit breaker <NUM> and outputs a command for a closing operation to the high-speed switch <NUM>. The operation processor <NUM> instructs the communicator <NUM> to notify that the operation for interruption has been performed. The communicator <NUM> transmits, to the control panel, a signal indicating that the direct-current circuit breaker <NUM> has performed the operation for interruption.

Detection results of temperatures obtained by the detector <NUM> are input to the monitor <NUM>. The monitor <NUM> determines whether there is the column <NUM> of which temperature has exceeded a preset allowable temperature in the plurality of columns <NUM> on the basis of the detection result of the temperature of each column <NUM>. In a case where there is the column <NUM> of which temperature has exceeded the allowable temperature, the monitor <NUM> determines that an anomaly has occurred in the column <NUM>. When it is determined that there is the column <NUM> in which an anomaly has occurred, the monitor <NUM> outputs, to the lock processor <NUM>, information indicating the column <NUM> in which the anomaly has occurred together with a determination result indicating that the anomaly has occurred.

When the determination result indicating that the anomaly has occurred is input from the monitor <NUM>, the lock processor <NUM> outputs a command for locking the operations of the circuit breaker <NUM> and the high-speed switch <NUM> to the operation processor <NUM>. The operation processor <NUM> stops the control of the circuit breaker <NUM> and the high-speed switch <NUM> in accordance with the command from the lock processor <NUM>. The direct-current circuit breaker <NUM> locks the operation for interruption by maintaining the circuit breaker <NUM> in the closed state and maintaining the high-speed switch <NUM> in the open state until the lock by the lock processor <NUM> is unlocked. The lock processor <NUM> instructs the communicator <NUM> to notify that the direct-current circuit breaker <NUM> has locked the operation for interruption. The communicator <NUM> transmits, to the control panel, a signal indicating that the direct-current circuit breaker <NUM> has locked the operation for interruption. While the direct-current circuit breaker <NUM> locks the operation for interruption, the power system is protected by a protection means other than the direct-current circuit breaker <NUM>.

The lock processor <NUM> outputs information indicating the column <NUM> in which the anomaly has occurred to the separator <NUM>. The separator <NUM> separates the column <NUM> in which the anomaly has occurred from other columns <NUM> on the basis of the information from the lock processor <NUM>.

<FIG> is a view for explaining an operation of the direct-current circuit breaker in a case where an anomaly has occurred in one or some of the plurality of columns constituting the lightning arrester illustrated in <FIG> and <FIG>. In the example illustrated in <FIG>, it is assumed that an anomaly has occurred in a column 20a which is one of the plurality of columns <NUM>.

With respect to the column 20a in which the anomaly has occurred, the separator <NUM> detaches an upper end of the column 20a from the upper plate <NUM> and detaches a lower end of the column 20a from the lower plate <NUM>. When the column 20a is detached from the upper plate <NUM> and the lower plate <NUM>, the column 20a drops downward by gravity. The column 20a in which the anomaly has occurred drops downward, thereby being physically separated from other columns <NUM>. The column 20a is electrically insulated from other columns <NUM> by being physically separated from other columns <NUM>. The method of separating the column 20a from other columns <NUM> by the separator <NUM> is not limited to the method described in the first embodiment. The separator <NUM> may separate the column 20a from other columns <NUM> by a method other than the method in which the column 20a is dropped.

The monitor <NUM> continues to acquire the detection result of the temperature of each column <NUM> other than the column 20a thus separated. The monitor <NUM> determines whether the temperature of each column <NUM> other than the column 20a out of the plurality of columns <NUM> has decreased to a reference temperature. The reference temperature is a temperature set in advance as a reference for restart of the operation by the direct-current circuit breaker <NUM>. The lock processor <NUM> unlocks the operations of the circuit breaker <NUM> and the high-speed switch <NUM> in a case where the temperature of each column <NUM> has decreased to the reference temperature.

After the column 20a is separated from other columns <NUM>, the column 20a is collected by an operator. The lightning arrester <NUM> is replenished with a new column <NUM>, which is a substitute for the column 20a in which the anomaly has occurred, by the operator. The direct-current circuit breaker <NUM> may include a mechanism for making replenishment of the new column <NUM>. In that case, the replenishment of the new column <NUM> is automatically performed by the mechanism regardless of the operator. The lock processor <NUM> may unlock the lock after it is confirmed that the temperature of each column <NUM> has decreased to the reference temperature and after the replenishment of the column <NUM> has been performed. The lock processor <NUM> may unlock the lock when it is confirmed that the temperature of each column <NUM> has decreased to the reference temperature regardless whether the replenishment of the column <NUM> has been performed or not.

<FIG> is a flowchart illustrating an operation procedure of the direct-current circuit breaker according to the first embodiment. In step S1, the detector <NUM> measures the temperature of each column <NUM> constituting the lightning arrester <NUM>. In step S2, the monitor <NUM> determines whether there is the column <NUM> of which temperature has exceeded the allowable temperature. If there is no column <NUM> of which temperature has exceeded the allowable temperature (step S2, No), the direct-current circuit breaker <NUM> returns the procedure to step S1.

If there is the column <NUM> of which temperature has exceeded the allowable temperature (step S2, Yes), in step S3, the lock processor <NUM> locks the operations of the circuit breaker <NUM> and the high-speed switch <NUM> controlled by the operation processor <NUM>. That is, the lock processor <NUM> locks the operation for interruption by the direct-current circuit breaker <NUM>. In step S4, the separator <NUM> separates the column <NUM> in which the anomaly has occurred.

In step S5, the monitor <NUM> determines whether the temperature of each column <NUM> other than the column <NUM> in which the anomaly has occurred is equal to or lower than the reference temperature. If the temperature of each column <NUM> is not equal to or lower than the reference temperature (step S5, No), the direct-current circuit breaker <NUM> returns the procedure to step S5. If the temperature of each column <NUM> is equal to or lower than the reference temperature (step S5, Yes), in step S6, the lock processor <NUM> unlocks the operation for interruption by the direct-current circuit breaker <NUM>. As a result, the direct-current circuit breaker <NUM> terminates the operation in accordance with the procedure illustrated in <FIG>.

Note that the monitor <NUM> is not limited to those monitoring the presence or absence of an anomaly on the basis of a temperature detected by the detector <NUM>. The monitor <NUM> may monitor the presence or absence of an anomaly on the basis of a detection result of a current flowing through each of the plurality of columns <NUM>. In that case, as the detector <NUM>, an ammeter that detects a current flowing through each of the plurality of columns <NUM> is used. For each column <NUM>, the monitor <NUM> calculates a difference between a current flowing through the column <NUM> and a current flowing through another column <NUM>. The monitor <NUM> determines that an anomaly that a current is concentrated has occurred in the column <NUM> in which the calculated difference is larger than a threshold set in advance.

The direct-current circuit breaker <NUM> according to the first embodiment is not limited to a mechanical direct-current circuit breaker. The direct-current circuit breaker <NUM> may be a hybrid direct-current circuit breaker constituted by combining a mechanical component and a semiconductor component.

According to the first embodiment, the direct-current circuit breaker <NUM> includes: the monitor <NUM> that monitors the presence or absence of an anomaly in each of the plurality of columns <NUM>; and the lock processor <NUM> that locks the operations of the circuit breaker <NUM> and the high-speed switch <NUM> controlled by the operation processor <NUM>. The monitor <NUM> determines that an anomaly has occurred in one or some columns <NUM> having a temperature rise exceeding the allowable temperature out of the plurality of columns <NUM>. In a case where there is a temperature rise exceeding the allowable temperature due to current concentration in one or some columns <NUM>, the direct-current circuit breaker <NUM> obviates a failure of the lightning arrester <NUM> by locking the operation for interruption. As a result, the direct-current circuit breaker <NUM> achieves an effect that it is possible to obviate a failure of the lightning arrester <NUM>.

<FIG> is a view for explaining an operation by the direct-current circuit breaker according to a second embodiment. The direct-current circuit breaker <NUM> according to the second embodiment has a configuration similar to that of the direct-current circuit breaker <NUM> according to the first embodiment. The direct-current circuit breaker <NUM> according to the second embodiment locks the operation for interruption in a case where there is an anomaly that an overall temperature of the plurality of columns <NUM> constituting the lightning arrester <NUM> rises. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and configurations different from those in the first embodiment will mainly be described.

In the direct-current circuit breaker <NUM>, when a current uniformly flows through each of the plurality of columns <NUM>, an overall temperature of the plurality of columns <NUM> may uniformly rise. As the number of columns <NUM> connected in parallel to each other in the lightning arrester <NUM> is increased with respect to energy assumed to be processed in the lightning arrester <NUM>, the number of columns <NUM> through which a current flows increases, and thereby it is possible to reduce the rising of the overall temperature of the plurality of columns <NUM>. However, while it is possible to reduce the rising of the overall temperature of the plurality of columns <NUM> by increasing the number of columns <NUM> to be larger than the number thereof required with respect to the energy assumed to be processed, the increase in the number of columns <NUM> provided in the lightning arrester <NUM> leads to an increase in size of the lightning arrester <NUM>. In the second embodiment, when the overall temperature of the plurality of columns <NUM> rises, the direct-current circuit breaker <NUM> locks the operations of the circuit breaker <NUM> and the high-speed switch <NUM>, and thereby the direct-current circuit breaker <NUM> is stopped operating. As a result, the direct-current circuit breaker <NUM> obviates a failure of the lightning arrester <NUM> due to the rising of the overall temperature of the plurality of columns <NUM>. In addition, the direct-current circuit breaker <NUM> may not increase the number of columns <NUM> to be larger than the number thereof required with respect to the energy assumed to be processed.

The monitor <NUM> determines whether the overall temperature of the plurality of columns <NUM> has risen to a first reference temperature on the basis of the detection result of the temperature of each column <NUM>. The first reference temperature is a temperature set in advance as a reference for interruption of the operation of the direct-current circuit breaker <NUM>, and is a temperature lower than the allowable temperature. When the overall temperature of the plurality of columns <NUM> exceeds the first reference temperature, the monitor <NUM> determines that an anomaly that the overall temperature of the plurality of columns <NUM> rises has occurred. That is, the monitor <NUM> determines that there is an anomaly in the entirety of the plurality of columns <NUM>. The monitor <NUM> outputs the determination result to the lock processor <NUM>.

When the determination result indicating that the anomaly has occurred in the entirety of the plurality of columns <NUM> is input from the monitor <NUM>, the lock processor <NUM> outputs a command for locking the operations of the circuit breaker <NUM> and the high-speed switch <NUM> to the operation processor <NUM>. The operation processor <NUM> stops the control of the circuit breaker <NUM> and the high-speed switch <NUM> in accordance with the command from the lock processor <NUM>. The direct-current circuit breaker <NUM> locks the operation for interruption by maintaining the circuit breaker <NUM> in the closed state and maintaining the high-speed switch <NUM> in the open state until the lock by the lock processor <NUM> is unlocked. The lock processor <NUM> instructs the communicator <NUM> to notify that the direct-current circuit breaker <NUM> has locked the operation for interruption. The communicator <NUM> transmits, to the control panel, a signal indicating that the direct-current circuit breaker <NUM> has locked the operation for interruption. While the direct-current circuit breaker <NUM> locks the operation for interruption, the power system is protected by a protection means other than the direct-current circuit breaker <NUM>.

In the second embodiment, the direct-current circuit breaker <NUM> does not separate the column <NUM> and waits until the temperature of the plurality of columns <NUM> as a whole decreases. The monitor <NUM> continues to acquire the detection result of the temperature of each of the plurality of columns <NUM>. The monitor <NUM> determines whether the temperature of each of the plurality of columns <NUM> has decreased to a second reference temperature. The second reference temperature is a temperature set in advance as a reference for restart of the operation by the direct-current circuit breaker <NUM>. The second reference temperature is the same as the reference temperature in the first embodiment. The lock processor <NUM> unlocks the operations of the circuit breaker <NUM> and the high-speed switch <NUM> in a case where the temperature of each column <NUM> has decreased to the second reference temperature.

<FIG> is a flowchart illustrating an operation procedure of the direct-current circuit breaker according to the second embodiment. In step S11, the detector <NUM> measures the temperature of each column <NUM> constituting the lightning arrester <NUM>. In step S12, the monitor <NUM> determines whether the overall temperature of the plurality of columns <NUM> has exceeded the first reference temperature. If the overall temperature of the plurality of columns <NUM> does not exceed the first reference temperature (step S12, No), the direct-current circuit breaker <NUM> returns the procedure to step S11.

If the overall temperature of the plurality of columns <NUM> has exceeded the first reference temperature (step S12, Yes), in step S13, the lock processor <NUM> locks the operations of the circuit breaker <NUM> and the high-speed switch <NUM> controlled by the operation processor <NUM>. That is, the lock processor <NUM> locks the operation for interruption by the direct-current circuit breaker <NUM>.

In step S14, the monitor <NUM> determines whether the temperature of each of the plurality of columns <NUM> is equal to or lower than the second reference temperature. If the temperature of each of the plurality of columns <NUM> is not equal to or lower than the second reference temperature (step S14, No), the direct-current circuit breaker <NUM> returns the procedure to step S14. If the temperature of each of the plurality of columns <NUM> is equal to or lower than the second reference temperature (step S14, Yes), in step S15, the lock processor <NUM> unlocks the operation for interruption by the direct-current circuit breaker <NUM>. As a result, the direct-current circuit breaker <NUM> terminates the operation in accordance with the procedure illustrated in <FIG>.

The direct-current circuit breaker <NUM> according to the second embodiment may also perform an operation similar to that in the first embodiment in a case where there is an anomaly in one or some of the plurality of columns <NUM>. In the direct-current circuit breaker <NUM> according to the second embodiment, the separator <NUM> may be omitted in a case where an operation similar to that in the first embodiment is not performed. The direct-current circuit breaker <NUM> according to the second embodiment may be either a mechanical direct-current circuit breaker or a hybrid direct-current circuit breaker.

According to the second embodiment, the direct-current circuit breaker <NUM> determines that there is an anomaly in the entirety of the plurality of columns <NUM> in a case where the overall temperature of the plurality of columns <NUM> has risen to the first reference temperature. When the direct-current circuit breaker <NUM> continually performs the interruption operation and thereby the overall temperature of the plurality of columns <NUM> rises above the first reference temperature, the direct-current circuit breaker <NUM> can lock the operation for interruption. As a result, the direct-current circuit breaker <NUM> can obviate a failure of the lightning arrester <NUM> due to the rising of the overall temperature of the plurality of columns <NUM>. Furthermore, in the direct-current circuit breaker <NUM>, there is no need to increase the number of columns <NUM> with respect to the energy assumed to be processed, and therefore it is possible to suppress an increase in size of the lightning arrester <NUM>.

Next, a hardware configuration of the control circuit <NUM> included in the direct-current circuit breaker <NUM> according to the first and second embodiments will be described. A function of the control circuit <NUM> is realized using a processing circuitry. The processing circuitry is a processor that executes a program stored in a memory. The processing circuitry may be dedicated hardware mounted on the direct-current circuit breaker <NUM>.

<FIG> is a first diagram illustrating an example of a hardware configuration of the control circuit included in the direct-current circuit breaker according to the first or second embodiment. <FIG> illustrates a hardware configuration in a case where the function of the control circuit <NUM> is realized by using hardware that executes a program. A processor <NUM>, a memory <NUM>, and an interface <NUM> are connected to each other via a bus.

The processor <NUM> is a central processing unit (CPU), a processing device, an arithmetic device, a microprocessor, a microcomputer, or a digital signal processor (DSP). Functions of the operation processor <NUM>, the monitor <NUM>, and the lock processor <NUM> are realized by the processor <NUM>, and software, firmware, or a combination of software and firmware. The software or the firmware is written as a program and stored in the memory <NUM> as a built-in memory. The memory <NUM> is a nonvolatile or volatile semiconductor memory, and is a random access memory (RAM), a read only memory (ROM), a flash memory, an erasable programmable read only memory (EPROM), or an electrically erasable programmable read only memory (EEPROM (registered trademark)).

The interface <NUM> is responsible for signal input and signal output. The communicator <NUM> is realized by using the interface <NUM>. The interface <NUM> outputs a command to each of the circuit breaker <NUM> and the high-speed switch <NUM>. A signal indicating a detection result of a direct current obtained by the current transformer <NUM> is input to the interface <NUM>.

<FIG> is a second diagram illustrating an example of the hardware configuration of the control circuit included in the direct-current circuit breaker according to the first or second embodiment. <FIG> illustrates a hardware configuration in a case where the function of the control circuit <NUM> is realized by using dedicated hardware. The control circuit <NUM> includes a processing circuitry <NUM> that executes various processes and the interface <NUM> similar to that in <FIG>. The processing circuitry <NUM> and the interface <NUM> are connected to each other via a bus.

The processing circuitry <NUM> as dedicated hardware is a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or a combination thereof. The function of the control circuit <NUM> is realized by using the processing circuitry <NUM>.

The configurations described in the embodiments above are merely examples of the content of the present disclosure. The configurations of the respective embodiments can be combined with other known technology. The configurations of the respective embodiments may be appropriately combined. Part of the configurations of the respective embodiments can be omitted or modified without departing from the gist of the present disclosure.

Claim 1:
A direct-current circuit breaker (<NUM>) including a circuit breaker (<NUM>) adapted to interrupt a direct current flowing through a direct-current line (<NUM>), the direct-current circuit breaker (<NUM>) comprising:
a resonant circuit including a capacitor (<NUM>), a reactor (<NUM>), and a switch (<NUM>) connected in series to each other;
a lightning arrester (<NUM>); and
an operation processor (<NUM>) adapted to control an opening operation and a closing operation by each of the circuit breaker (<NUM>) and the switch (<NUM>),
characterized in that the lightning arrester (<NUM>) includes a plurality of columns (<NUM>) each including a stack of a plurality of nonlinear resistive elements (<NUM>), the lightning arrester (<NUM>) being connected in parallel to the capacitor (<NUM>),
wherein the direct-current circuit breaker (<NUM>) further comprises:
a monitor (<NUM>) adapted to monitor presence or absence of an anomaly in each of the plurality of columns (<NUM>); and
a lock processor (<NUM>) adapted to:
lock operations of the circuit breaker (<NUM>) and the switch (<NUM>) controlled by the operation processor (<NUM>) in a case where there is an anomaly in at least one or some columns (20a) out of the plurality of columns (<NUM>); and
unlock the operations of the circuit breaker (<NUM>) and the switch (<NUM>) after the anomaly is resolved.