WO2015099467A1

WO2015099467A1 - Dc circuit breaker for breaking bidirectional fault current using single circuit

Info

Publication number: WO2015099467A1
Application number: PCT/KR2014/012856
Authority: WO
Inventors: 김남경; 정영환; 황휘동
Original assignee: 주식회사 효성
Priority date: 2013-12-26
Filing date: 2014-12-24
Publication date: 2015-07-02
Also published as: KR101522411B1

Abstract

The present invention relates to a DC circuit breaker for breaking fault current on a DC line. The present invention comprises: a main switch which is opened when a fault occurs on a DC line so as to break current on the DC line; first and second switching devices which are connected in parallel with the main switch and connected in series with each other in opposite directions; third and fourth switching devices which are connected in parallel with the main switch and connected in series with each other in opposite directions, wherein the third and fourth switching devices are positioned in the opposite direction to the first and second switching devices and connected in series with each other; an L/C circuit which is connected between the middle point of the first and second switching devices and the middle point of the third and fourth switching devices and which includes a capacitor and a reactor connected in series with each other to generate LC resonance; and a fifth switching device which is connected in parallel with the L/C circuit and is switched to reverse the polarity of charge voltage in the capacitor by generating LC resonance in the L/C circuit.

Description

DC circuit breaker that blocks bidirectional fault currents in a single circuit

The present invention relates to a direct current (DC) circuit breaker, and in particular, when a failure occurs on one side or the other side of a direct current (DC) line for power transmission or distribution, the bidirectional fault current is blocked by a single circuit to block the bidirectional fault current flowing in the DC line. Relates to a DC circuit breaker.

In general, a high voltage DC circuit breaker is a switching device capable of blocking a current flowing through a high voltage transmission line of about 50 mA or more, such as a high voltage direct current (HVDC) transmission system. That is, the high voltage DC circuit breaker is installed on the DC line and serves to block the fault current from being provided to the faulted side when a fault occurs on one side or the other. Of course, the present invention can also be applied to a medium voltage DC power distribution system having a DC voltage level of about 1 to 50 mA.

In the case of such a high voltage DC circuit breaker, if a fault current occurs in the system, the main switch installed in the DC line is opened to isolate the fault circuit and cut off the fault current. However, since there is no zero point in the DC line, the arc generated between the terminals of the main switch is not extinguished when the main switch is opened, and the fault current flows continuously through this arc to prevent fault current. There is a problem.

Japanese Patent Laid-Open Publication No. 1984-068128 shown in FIG. 1 uses an arc generated during the switching operation of the main switch CB in a high voltage DC circuit breaker to block the fault current Idc to cut off the fault current Idc. The technique of superimposing the arc by creating a zero current at the main switch CB by superimposing a resonant current Ip by the L / C circuit on the DC current I _DC flowing in the current (Idc = I _DC + Ip). To provide. That is, when a failure occurs, the main switch CB is opened and the resonant current Ip is superimposed on the DC current I _DC while being injected through the arc, and injected into the main switch CB. The resonance current Ip becomes a vibrating current due to the resonance, and the vibration current Ip gradually increases along the main switch CB. Thus, the arc of the main switch CB is extinguished when the negative resonant current -Ip becomes larger than I _DC and the fault current Idc becomes a zero current.

However, in this prior art, since the resonant current (Ip) larger than the DC current (I _DC ) must overlap, the circuit rating must be more than twice the rated current, and in order to generate such a large resonant current (Ip) Since the resonance must be made, there is a problem that the blocking speed becomes slow. In addition, such a conventional DC circuit breaker has a problem that it is impossible to block the bidirectional fault current.

SUMMARY OF THE INVENTION An object of the present invention is to provide a DC circuit breaker for blocking bidirectional fault currents in a single circuit to completely block a fault current in the main switch even when a plurality of resonance currents are not applied to the main switch in the DC breaker.

In addition, the present invention provides a DC circuit breaker to block the bidirectional fault current in a single circuit to cut the fault current through the arc by artificially creating a current zero to remove the arc generated in the main switch when the main switch is blocked in the DC breaker Has a different purpose.

In addition, another object of the present invention is to provide a DC circuit breaker for blocking a bidirectional fault current in a single circuit to block a fault current in both directions in a high voltage DC line.

DC circuit breaker for blocking bidirectional fault current in a single circuit according to the present invention,

In the DC circuit breaker for blocking the current flowing in the DC line,

A main switch installed at the DC line and opened when a failure occurs at one side or the other side of the DC line to cut off the current of the DC line; First and second switching elements connected in parallel to the main switch 110 and connected in series in opposite directions; Third and fourth switching devices connected in parallel to the main switch and connected in series in opposite directions to each other and disposed in opposite directions to the first and second switching devices and connected in series to each other; An L / C circuit comprising a capacitor and a reactor connected between an intermediate point of the first and second switching elements and an intermediate point of the third and fourth switching elements and connected in series with each other to generate an LC resonance; And a fifth switching element connected in parallel to the L / C circuit to switch to generate LC resonance in the L / C circuit to invert the polarity of the charging voltage in the capacitor.

In the present invention, it further comprises a charging resistor provided between the LC circuit and the ground for voltage charging of the capacitor in a steady state.

In the present invention, each of the first to fifth switching elements includes a power semiconductor switch that can be turned on or turned on / off.

In the present invention, the first and fourth switching elements are connected to both ends of the L / C circuit and the main switch one by one along the first closed circuit formed between the L / C circuit and the main switch. Make sure to turn on.

In the present invention, the second and the third switching device, the current in the second direction along the second closed circuit formed between the L / C circuit and the main switch one by one connected to each end of the L / C circuit and the main switch Make sure to turn on.

In the present invention, the fifth switching device maintains the OFF state in the normal state and is switched to the ON state when the main switch is opened to reverse the polarity of the voltage charged in the capacitor.

In the present invention, when the main switch is opened, the main switch is supplied by supplying current to the main switch through the first and fourth switching elements or the second and third switching elements by the polarity inverted voltage at the capacitor. Extinguish the arc that occurred.

In the present invention, when an arc occurs when the main switch is opened, the first and fourth switching devices are turned on while the second and third switching devices are turned off. Arc is generated in the main switch by the current is supplied to the main switch through the first and fourth switching elements by the polarity inverted voltage in the capacitor and becomes a zero current in the main switch by the supplied current. Ensure that SO is called.

In the present invention, the current supplied to the main switch is opposite in direction to the fault current sustained through the arc in the main switch and is larger in magnitude.

In the present invention, when an arc occurs when the main switch is opened, the second and third switching devices are turned on while the first and fourth switching devices are turned off. Arc is generated in the main switch by the current is supplied to the main switch through the second and third switching elements by the polarity inverted voltage in the capacitor and becomes a zero current in the main switch by the supplied current Ensure that SO is called.

According to the present invention, when an arc occurs during the switching operation of the main switch in the DC circuit breaker, the arc can be extinguished quickly so that the fault current can be completely blocked.

In addition, in the DC circuit breaker according to the present invention, by using a plurality of semiconductor switching elements as a bridge circuit, a fault current in both directions can be blocked in a high voltage DC line.

In addition, according to the present invention, since the DC circuit breaker charges the capacitor using the current flowing through the DC line in the normal state, a separate charging circuit is not required, thereby reducing the cost of constructing the circuit.

1 is a block diagram of a conventional DC circuit breaker.

2 is a block diagram of a DC circuit breaker for blocking a bidirectional fault current in a single circuit according to an embodiment of the present invention.

Figure 3 is a schematic diagram showing the current flow in the DC circuit breaker blocking the bidirectional fault current in a single circuit in a steady state according to an embodiment of the present invention.

Figure 4 is a schematic diagram showing a fault current blocking process in the DC circuit breaker to block the bidirectional fault current in a single circuit when a fault occurs on one side of the DC line according to the present invention.

5 is a schematic diagram showing a fault current blocking process in a DC circuit breaker for blocking bidirectional fault currents in a single circuit when a fault occurs on the other side of the high voltage DC line according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the description of the present invention, detailed descriptions of well-known functions or configurations will be omitted when it is determined that the detailed descriptions may unnecessarily obscure the subject matter of the present invention.

2, the DC circuit breaker 100 according to the embodiment of the present invention includes a main switch 110 installed between one side A and the other side B of the DC line 10. The main switch 110 basically serves to block the DC line 10 in order to prevent a fault current from flowing into a circuit in which a fault occurs when a fault occurs in one side A or the other side B. To this end, the main switch 110 is closed in the normal state and is opened when a failure occurs. The main switch 110 is controlled by the control signal of the control unit (not shown).

The nonlinear resistor 120 is connected to the main switch 110 in parallel to prevent excessive voltage above the rated voltage from being applied to both ends of the DC circuit breaker 100 when the main switch 110 is opened. When both ends of the DC circuit breaker 100 over a predetermined reference value is automatically turned on (ON) to consume a high voltage. In one example, the nonlinear resistor 120 may be implemented as, for example, a varistor.

In this embodiment, since a high voltage is applied to the DC line 10, a large current flows through the main switch 110. Therefore, when a failure occurs, an arc occurs between the switch terminals of the main switch 110 when the main switch 110 is opened, and the DC fault current continues to flow in the DC line 10 through the arc. Therefore, in the present invention, an additional device or circuit is needed to completely extinguish the fault current by extinguishing such an arc.

Specifically, the first and

second switching elements

140 and 150 connected in series in opposite directions are connected to the main switch 110 in parallel. In addition, the third and

fourth switching devices

160 and 170 connected in series in opposite directions are connected to the main switch 110 in parallel. Thus, the series connection pairs of the first and

second switching elements

140 and 150 are connected in parallel to the series connection pairs of the third and

fourth switching elements

160 and 170. In this case, the first and

second switching devices

140 and 150 are installed in opposite directions to the third and

fourth switching devices

160 and 170, respectively.

In addition, a capacitor 131 connected in series with each other to generate LC resonance between the midpoint N1 of the first and

second switching devices

140 and 150 and the midpoint N2 of the third and

fourth switching devices

160 and 170. And a L / C circuit 130 including a reactor 132. In the L / C circuit 130, the capacitor 131 and the reactor 132 are configured in series and a voltage is charged to the capacitor 131 by a current supplied to the L / C circuit 130 in a normal state. When generated, current is transmitted to the main switch 110 by the voltage charged in the capacitor 131. A fifth switching device 180 is connected in parallel to the L / C circuit 130. The switching device 180 generates LC resonance in the L / C circuit 130 to generate a charge voltage of the capacitor 131. Switch to reverse polarity. Although not shown in the drawings, the operation (on / off) of the first to fifth switching devices 140 to 180 is controlled by a controller (not shown). In the present embodiment, the first to fifth switching elements 140 to 180 may be implemented as turn-on controllable elements, for example, thyristors, or the like, or turn-on / As a turn-off controllable element, for example, it may be implemented with GTO, IGCT, IGBT, or the like.

The first and

fourth switching elements

140 and 170 are connected to each of both ends of the L / C circuit 130 and the main switch 110 to form a first closed circuit between the L / C circuit 130 and the main switch 110. Do it. As a result, the first and

fourth switching devices

140 and 170 are switched so that current flows in the first direction along the first closed circuit by the voltage charged in the capacitor 131 of the L / C circuit 130. In addition, the second and

third switching devices

150 and 160 are connected to both ends of the L / C circuit 130 and the main switch 110, respectively, and are formed between the L / C circuit 130 and the main switch 110. As a result, the second and

third switching devices

150 and 160 are switched such that current flows in the second direction along the second closed circuit by the voltage charged in the capacitor 131 of the L / C circuit 130. Here, the first closed circuit is different from the second closed circuit, and the first direction and the second direction mean the direction of the current, and indicate current flow in different directions.

In the present embodiment, the first and

fourth switching elements

140 and 170 are installed in the same direction so that current flows in the first direction when turned on, and the second and

third switching elements

150 and 160 are turned on when the second and

third switching elements

150 and 160 are turned on. Are installed in the same direction so that current flows in the direction. At this time, the current flowing in the first direction or the second direction is the voltage (+ Vc) initially charged in the capacitor 131 of the L / C circuit 130 is the polarity inversion by the fifth switching element 180 for polarity inversion Voltage (-Vc). This current is provided to the main switch 110 in the first or second direction to extinguish the arc generated in the main switch 110 when the main switch 110 is opened.

To this end, the current must be supplied to the main switch 110 in a direction opposite to the current flowing through the arc generated in the main switch 110. Therefore, the first direction or the second direction is determined by the direction of the current flowing through the arc in the main switch 110. That is, the first and

fourth switching devices

140 and 170 are turned on to flow current in the first direction, and the second and

third switching devices

150 and 160 are turned on to flow current in the second direction. Of course, the turn-on / turn-off of the first and

fourth switching elements

140 and 170 and the second and

third switching elements

150 and 160 may be implemented in reverse.

Furthermore, in the DC circuit breaker 100 according to the present embodiment, the charging resistor R is connected between the contact of the L / C circuit 130 and the first bidirectional switching element 140 and the ground GND. Through the charging resistor R, the capacitor 131 of the L / C circuit 130 is initially charged by the DC voltage Vc.

Figure 3 is a schematic diagram showing the current flow in the DC circuit breaker for blocking the bidirectional fault current in a single circuit in a steady state according to an embodiment of the present invention.

In FIG. 3, (a) illustrates a case where current is supplied from one side A to the other side B, and (b) illustrates a case where current is supplied from the other side B to one side A. As shown in FIG. In the normal state, the main switch 110 is closed, the first and

fourth switching elements

140 and 170 are turned on and conducting, and the second and

third switching elements

150 and 160 are turned off to turn off the current. Does not flow Therefore, the current supplied from one side A flows through the first switching element 140, the L / C circuit 130, the fourth switching element 170, and the charging resistor Rc, thereby allowing the L / C circuit ( The capacitor 131 of 130 is charged with the DC voltage + Vc. Hereinafter, for convenience of description, as shown in FIG. 3A, when the power is supplied from N1 to N2, the voltage charged in the capacitor 131 is represented by + Vc, and the polarity reversed voltage is -Vc. It is written as.

Furthermore, in the case of (b), since the main switch 110 is closed in the normal state, the current supplied from the other side B passes through the main switch 110 to one side A along the DC line 10. Delivered. At this time, the second and

fourth switching elements

150 and 170 are turned on and conducting, and the first and

third switching elements

140 and 160 are turned off to not flow current. Therefore, the current supplied from the other side B flows through the second switching element 150, the L / C circuit 130, the fourth switching element 170, and the charging resistor Rc, thereby providing the L / C circuit 130. DC capacitor + Vc is charged in the capacitor 131 of the N-axis.

As described above, in the steady state, the control unit turns on the first, second, and

fourth switching elements

140, 150, and 170, and the capacitor of the L / C circuit 130 by the current supplied from one side A or the other side B. 131 is charged to + Vc.

4 is a schematic view showing a fault current blocking process when a fault occurs in the other side (B) of the DC circuit breaker for blocking a bidirectional fault current in a single circuit according to an embodiment of the present invention, Figure 5 is according to another embodiment of the present invention This is a schematic diagram showing the fault current blocking process when a fault occurs at one side (A) of the DC circuit breaker that blocks the bidirectional fault current in a single circuit.

First, the DC voltage of + Vc is charged in the capacitor 131 in the normal state as shown in FIG. 3. If a failure occurs in the B side in this state, as shown in Figure 4, the control unit detects the failure to open the main switch 110 that was closed. At this time, an arc is generated between the switch terminals of the main switch 110 when the main switch 110 is opened, and the fault current continuously flows from the A side to the B side through the arc.

In addition, with the opening of the main switch 110, the first to fourth switching devices 140 to 170 are turned off and the fifth switching device 180 is turned on. When the fifth switching device 180 is turned on, LC resonance occurs in the L / C circuit 130 through the fifth switching device 180 and the voltage initially charged in the capacitor 131 (+). Vc) is reversed in polarity and charged to -Vc. That is, the voltage (-Vc) polarized inverted at the voltage (+ Vc) initially charged in the capacitor 131 by LC resonance in the L / C circuit 130 through the fifth switching element 180 is a capacitor. Is recharged in 131.

Subsequently, the first and

fourth switching devices

140 and 170 are turned on in the state in which the second and

third switching devices

150 and 160 are turned off to be charged by the voltage (-Vc) charged in the capacitor 131. Current flows in the first direction through the fourth switching device 170, the main switch 110, and the first switching device 140. By the current supplied in this way, the current in the main switch 110 becomes 0 (zero) and the arc is extinguished. As described above, the current supplied to the main switch 110 in the first direction is opposite in direction to the fault current sustained through the arc in the main switch 110 and is larger in size. To this end, the charging capacity of the capacitor can be determined.

Subsequently, when the arc generated in the main switch 110 is completely extinguished and the fault current is blocked by the main switch 110, the voltage on the A side is increased rapidly compared to the B side. The voltage on the A side thus increased is consumed in the nonlinear resistor 120 connected in parallel to the main switch 110. At the same time, the fifth switching device 180 is turned off again, and current flows through the first switching device 140, the L / C circuit 130, the fourth switching device 170, and the charging resistor Rc. The capacitor 131 of the L / C circuit 130 is again recharged with a DC voltage of + Vc.

Here, the DC circuit breaker 100 of the present invention is characterized in that the operation of reclosing the main switch 110 is possible. That is, when the failure of the B side is removed after the opening of the main switch 110, the control unit may close the main switch 110 to form a closed in the DC line (10). When closing the main switch 110 to form a closed, if the B-side failure is not eliminated to repeat the above process. This reclosing is possible because the capacitor 131 remains charged at + Vc in the L / C circuit 130 after the arc is extinguished in the main switch 110.

As described above, the DC circuit breaker 100 for blocking the bidirectional fault current in a single circuit according to the present invention is a voltage (+) initially charged in the capacitor 131 by LC resonance in the L / C circuit 130 By supplying a current to the main switch 110 by using the voltage (-Vc) inverted polarity at Vc) to achieve a zero current to the main switch 110 to arc the arc to completely block the fault current flowing through the arc Do it.

On the other hand, when a failure occurs in the A side, as shown in Figure 5, the control unit detects the failure to open the main switch 110. When the main switch 110 is opened, an arc occurs between the switching terminals of the main switch 110 so that a fault current continuously flows from the B side to the A side.

In addition, with the opening of the main switch 110, the first to fourth switching devices 140 to 170 are turned off and the fifth switching device 180 is turned on. When the fifth switching device 180 is turned on, LC resonance occurs in the L / C circuit 130 through the fifth switching device 180, and the + Vc voltage initially charged in the capacitor 131 is Polarity reversal occurs, charging to -Vc voltage. That is, in the L / C circuit 130, the voltage is generated in the LC resonance through the fifth switching device 180 and becomes the voltage (-Vc) polarized inverted from the voltage (+ Vc) initially charged in the capacitor 131. Recharged at 131.

Thereafter, the second and

third switching devices

150 and 160 are turned on while the first and

fourth switching devices

140 and 170 are turned off to the voltage (-Vc) charged in the capacitor 131. As a result, current flows in the second direction through the third switching device 160, the main switch 110, and the second switching device 150. By the current supplied in this way, the current in the main switch 110 becomes 0 (zero) and the arc is extinguished. As described above, the current supplied to the main switch 110 in the second direction is opposite in direction to the fault current sustained through the arc in the main switch 110 and is larger in size. To this end, the charging capacity of the capacitor can be determined.

Subsequently, when the arc generated in the main switch 110 is completely extinguished and the fault current is blocked by the main switch 110, the voltage on the A side is increased rapidly compared to the B side. The voltage on the A side thus increased is consumed in the nonlinear resistor 120 connected in parallel to the main switch 110. At the same time, the fifth switching device 180 is turned off again, and current flows through the second switching device 150, the L / C circuit 130, the fourth switching device 170, and the charging resistor Rc. The capacitor 131 of the L / C circuit 130 is again recharged with a DC voltage of + Vc.

Here, also in FIG. 5, the DC circuit breaker 100 of the present invention may operate to reclose the main switch 110. That is, when the A side fault is removed after the opening of the main switch 110, the control unit may close the main switch 110 to form a closure in the DC line 10. At this time, in the case of closing the main switch 110 to form a closed, if the A-side failure is not removed to repeat the above process. This reclosing is possible because the capacitor 131 remains charged at + Vc in the L / C circuit 130 after the arc is extinguished in the main switch 110.

As described above, in the DC circuit breaker 100 for blocking the bidirectional fault current in a single circuit according to the present invention, the current caused by the LC resonance is not the main switch CB as shown in FIG. The device 180 is characterized in that it is made. Therefore, the current oscillation due to the LC resonance is not increased as in the prior art, but in the present invention, the LC resonance needs to be performed only once so that the polarity of the voltage of the capacitor 131 of the L / C circuit 130 is reversed by the LC resonance. . This causes the blocking speed to increase compared to the prior art. In addition, in the prior art, the arc is extinguished at the time when the magnitude of the fault current is increased by continuously increasing the magnitude of the resonance current through LC resonance. However, in the present invention, unlike the prior art, the capacitor 131 determined according to the capacity of the capacitor 131 By injecting the current in the opposite direction to the fault current flowing in the main switch 110 by the charging voltage of the main to the main switch 110 to make a zero current arc arc arc.

Although the present invention described above has been described in detail through the preferred embodiments, the present invention is not limited to the content of these embodiments. Those skilled in the art to which the present invention pertains, although not shown in the embodiments, can be imitated or improved for various inventions within the scope of the appended claims, all of which fall within the technical scope of the present invention. Belonging will be too self-evident. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

Claims

In the DC circuit breaker to block the bidirectional fault current in a single circuit to block the current flowing on the DC line,

A main switch (110) installed on the DC line and opened when a failure occurs on one side or the other side of the DC line to cut off the current of the DC line;

First and second switching devices 140 and 150 connected in parallel to the main switch 110 and connected in series in opposite directions;

Third and fourth switching devices 160 and 170 connected in parallel to the main switch 110 and connected in series in opposite directions, respectively, arranged in opposite directions to the first and second switching devices 140 and 150 and connected in series to each other;

A capacitor connected between an intermediate point N1 of the first and second switching elements 140 and 150 and an intermediate point N2 of the third and fourth switching elements 160 and 170 and connected in series with each other to generate an LC resonance. L / C circuit 130 including 131 and reactor 132; And

A fifth switching device 180 connected in parallel to the L / C circuit 130 to generate LC resonance in the L / C circuit 130 to switch to invert the polarity of the charging voltage in the capacitor 131. ; DC circuit breaker for blocking bidirectional fault current in a single circuit comprising a.
The method of claim 1,

DC circuit breaker for blocking a bidirectional fault current in a single circuit further comprising a charge resistor (Rc) is installed between the LC circuit 130 and the ground (GND) for the voltage charging of the capacitor (131) in the normal state.
The method according to claim 1 or 2, wherein the first to fifth switching elements (140 to 180),

A DC circuit breaker that blocks bidirectional fault currents in a single circuit, each of which includes a power semiconductor switch that can be turned on or turned on / off.
The method of claim 3, wherein the first and fourth switching elements (140, 170),

One end of each of the L / C circuit 130 and the main switch 110 is connected to conduct current in a first direction along a first closed circuit formed between the L / C circuit 130 and the main switch 110. DC circuit breaker that blocks bidirectional fault currents in a single circuit.
The method of claim 3, wherein the second and third switching device (150, 160),

One end of each of the L / C circuit 130 and the main switch 110 is connected to conduct current in the second direction along a second closed circuit formed between the L / C circuit 130 and the main switch 110. DC circuit breaker that blocks bidirectional fault currents in a single circuit.
The method of claim 3,

The fifth switching device 180 maintains an OFF state in a normal state, and is switched to an ON state when the main switch 110 is opened to change the polarity of the voltage charged in the capacitor 131. DC circuit breaker that blocks bidirectional fault currents with a single circuit that inverts.
The method of claim 6,

When the main switch 110 is opened, current is supplied through the first and fourth switching elements 140 and 170 or the second and third switching elements 150 and 160 by the polarity inverted voltage of the capacitor 131. DC circuit breaker for supplying to the (110) to block the bidirectional fault current in a single circuit to extinguish the arc generated in the main switch 110.
The method of claim 6,

If an arc occurs when the main switch 110 is opened,

The first and fourth switching devices 140 and 170 are turned on while the second and third switching devices 150 and 160 are turned off, so that a current is generated by the polarity inverted voltage in the capacitor 131. The main switch 110 is supplied to the main switch 110 through the first and fourth switching elements 140 and 170 and becomes zero current in the main switch 110 by the supplied current, which occurs in the main switch 110. DC circuit breaker that cuts bidirectional fault currents in a single circuit to ensure that arcs are extinguished.
The method of claim 8,

The current supplied to the main switch 110 is a DC circuit breaker to block the bidirectional fault current in a single circuit of the opposite direction and larger in magnitude and the direction of the fault current persisted through the arc in the main switch (110).
The method of claim 6,

If an arc occurs when the main switch 110 is opened,

The second and third switching devices 150 and 160 are turned on while the first and fourth switching devices 140 and 170 are turned off, so that a current is generated by the voltage reversed in polarity in the capacitor 131. The main switch 110 is supplied to the main switch 110 through the second and third switching elements 150 and 160 and becomes a zero current in the main switch 110 by the supplied current to occur in the main switch 110. DC circuit breaker that cuts bidirectional fault currents in a single circuit to ensure that arcs are extinguished.
The method of claim 10,

The current supplied to the main switch 110 is a DC circuit breaker to block the bidirectional fault current in a single circuit of the opposite direction and larger in magnitude and the direction of the fault current persisted through the arc in the main switch (110).