Abstract:
Disclosed herein is a current circuit breaker that protects a semiconductor module by using fast switches to block a current. The current circuit breaker includes: a first switch configured to be opened upon a fault current being generated; a second switch connected to the first switch and configured to be opened after a predetermined period of time elapses since the first switch has been opened; a semiconductor module having an end connected to the first switch and another end connected to the second switch; a capacitor having a terminal connected to the second switch and the other terminal connected to the semiconductor module; and a surge arrester connected across the capacitor and configured to change its resistance according to a voltage across the capacitor to block the fault current.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2016-0041254, filed on Apr. 4, 2016, entitled “CURRENT CIRCUIT BREAKER”, which is hereby incorporated by reference in its entirety into this application. 
       BACKGROUND 
     1. Technical Field 
       [0002]    The present disclosure relates to a current circuit breaker. 
       2. Description of the Related Art 
       [0003]    A current circuit breaker refers to a device that opens/closes a load in a transmission/transformation system or an electric circuit, or interrupts current when an accident such as grounding or short-circuit occurs. If the blocking part of the current circuit breaker is made of an insulating material, a line in a normal use may be opened/closed manually. In addition, a current circuit breaker may open/close remotely by using an electric operation device or the like outside the metal case, and may interrupt a line automatically at the time of overload or short-circuit to thereby protect a power system and a load device. 
         [0004]      FIG. 1  is a view showing an existing current circuit breaker  10 . The operation of the current circuit breaker  10  will be described with reference to  FIG. 1 . When a steady-state current flows, a switch  12  is closed and the current flows through a power semiconductor  11  of a main circuit. In addition, when the steady-state current flows, a semiconductor module  13  is turned off, such that no current flows through the semiconductor module  13 . The semiconductor module  13  may be a combination of a plurality of power semiconductors  11 . 
         [0005]    When a high-voltage direct current transmission line or power line has to be repaired or replaced, or when a fault current flows therein, the semiconductor module  13  is turned on to interrupt the current. When the semiconductor module  13  is turned on, the power semiconductor  11  of the main circuit is turned off and the switch  12  is opened. 
         [0006]    When the switch  12  is opened, the fault current flows through the semiconductor module  13 , and then the semiconductor module  13  is turned off to block the fault current. 
         [0007]    Referring to  FIG. 1 , the existing current circuit breaker  10  requires the plurality of power semiconductors  11  for blocking current. Accordingly, there is a problem in that a lot of costs are incurred to block the current in the existing current circuit breaker  10 . In addition, there is another problem in that the existing current circuit breaker  10  has a large volume due to the plurality of power semiconductors  11 . In addition, there is yet another problem in that the existing current circuit breaker  10  requires a cooling device as the power semiconductors  11  generates heat. 
       SUMMARY 
       [0008]    It is an object of the present disclosure to provide a current circuit breaker that protects a semiconductor module by using fast switches to block a current. 
         [0009]    It is another object of the present disclosure to provide a current circuit breaker capable of reduce the number of power semiconductors by using a bypass circuit to block a current. 
         [0010]    It is yet another object of the present disclosure to provide a current circuit breaker capable of reducing the volume of the current circuit breaker and saving manufacturing cost by using a bypass circuit to block a current. 
         [0011]    It is still another object of the present disclosure to provide a current circuit breaker capable of suppressing heat generation by using a bypass circuit to block a current. 
         [0012]    In accordance with one aspect of the present disclosure, a current circuit breaker includes: a first switch configured to be opened upon a fault current being generated; a second switch connected to the first switch and configured to be opened after a predetermined period of time elapses since the first switch has been opened; a semiconductor module having an end connected to the first switch and another end connected to the second switch; a capacitor having a terminal connected to the second switch and the other terminal connected to the semiconductor module; and a surge arrester connected across the capacitor and configured to change its resistance according to a voltage across the capacitor to block the fault current. 
         [0013]    According to an exemplary embodiment of the present disclosure, the fast switches are used to block a current, and thus the semiconductor module can be protected. 
         [0014]    In addition, according to an exemplary embodiment of the present disclosure, the number of power semiconductors can be reduced by using a bypass circuit to block a current. 
         [0015]    In addition, according to the exemplary embodiment of the present disclosure, by utilizing the bypass circuit to block the current, the volume of the current circuit breaker can be reduced and the manufacturing cost can be reduced. 
         [0016]    In addition, according to an exemplary embodiment of the present disclosure, heat generation can be suppressed by using the bypass circuit to block a current. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0017]      FIG. 1  is a view showing an existing current circuit breaker; 
           [0018]      FIG. 2  is a diagram of a current circuit breaker according to an exemplary embodiment of the present disclosure; 
           [0019]      FIG. 3  is a diagram showing a first switch and a stroke according to an exemplary embodiment of the present disclosure; 
           [0020]      FIG. 4  is a diagram showing the second switch opened by the control unit when the first switch is completely opened; 
           [0021]      FIG. 5  is a diagram showing the current circuit breaker according to an exemplary embodiment of the present disclosure when a steady-state current is flowing in the main circuit; 
           [0022]      FIG. 6  is a diagram showing the current circuit breaker according to an exemplary embodiment of the present disclosure when a fault current is flowing in the main circuit; 
           [0023]      FIG. 7  is a diagram showing the current circuit breaker according to the exemplary embodiment of the present disclosure when a fault current flows in a second switch and a semiconductor module; 
           [0024]      FIG. 8  is a diagram showing the current circuit breaker according to an exemplary embodiment of the present disclosure when a fault current is flowing in a capacitor; 
           [0025]      FIG. 9  is a diagram showing the current circuit breaker according to an exemplary embodiment of the present disclosure when a fault current is flowing in a surge arrester; and 
           [0026]      FIG. 10  is a graph showing the magnitude of a fault current according to an exemplary embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    The above objects, features and advantages will become apparent from the detailed description with reference to the accompanying drawings. Embodiments are described in sufficient detail to enable those skilled in the art in the art to easily practice the technical idea of the present disclosure. Detailed descriptions of well known functions or configurations may be omitted in order not to unnecessarily obscure the gist of the present disclosure. Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Throughout the drawings, like reference numerals refer to like elements. 
         [0028]      FIG. 2  is a diagram of a current circuit breaker  100  according to an exemplary embodiment of the present disclosure. Referring to  FIG. 2 , the current circuit breaker  100  according to the exemplary embodiment may include a first switch  110 , a second switch  120 , a semiconductor module  130 , a capacitor  140 , a surge arrester  150 , and a control unit  160 . The current circuit breaker  100  shown in  FIG. 2  is merely an exemplary embodiment of the present disclosure, and the elements are not limited to those shown in  FIG. 2 . Some elements may be added, modified or eliminated as desired.  FIG. 3  is a diagram showing the first switch  110  and a stroke  111  according to an exemplary embodiment of the present disclosure.  FIG. 4  is a diagram showing the second switch opened by the control unit when the first switch is completely opened. Hereinafter, the current circuit breaker  100  according to the exemplary embodiment of the present disclosure will be described in detail with reference to  FIGS. 2 to 4 . 
         [0029]    When a fault current is generated, the first switch  100  may be opened. The first switch  110  may be a fast switch and may open or short the terminals of a main circuit  170  depending on whether a fault current flows or a steady-state current flows. That is, the first switch  110  is opened when a fault current flows in the main circuit  170  and is closed when a steady-state current flows in the main circuit  170 . The fault current is generated when a high-voltage direct current transmission line or power line is repaired or replaced and may have a value larger than the steady-state current. 
         [0030]    The second switch  120  may be connected to the first switch  110 . The second switch  120  may be a fast switch. The second switch  120  and the first switch  110  may be of the same type. The second switch  120  may be opened after a predetermined period of time has elapsed since the first switch  110  is opened. The predetermined period of time may be set by a user or set by the control unit automatically. 
         [0031]    For example, the second switch  120  may be opened to block fault current when the semiconductor module  130  is turned on. That is, when the fault current flows through the main circuit  170 , the first switch  110  is opened, and the semiconductor module  130  is turned on. When the semiconductor module  130  is turned on, the fault current flows through the semiconductor module  130 . Meanwhile, the second switch  120  is opened such that the fault current flowing through a bypass circuit can be blocked. After the second switch  120  is opened, the semiconductor module  130  is turned off, which will be described in detail below. 
         [0032]    The predetermined period of time may be in proportion to the stroke  111  of the first switch  110 . The stroke  111  refers to a distance by which the first switch  110  moves. In  FIG. 3 , it refers to the distance  111 . For example, the longer the stroke  111  of the first switch  110  is, the later the second switch  120  may be opened since the first switch  110  is opened. In addition, the shorter the stroke  111  of the first switch  110  is, the earlier the second switch  120  may be opened since the first switch  110  is opened. 
         [0033]    One end of the semiconductor module  130  may be connected to the first switch  110  and the other end thereof may be connected to the second switch  120 . The semiconductor module  130  may be turned on when the first switch  110  is opened and the second switch  120  is closed to allow the fault current to flow, and may include at least one diode and at least one transistor. In addition, the semiconductor module  130  may be turned off after the second switch  120  is opened to allow the fault current to flow to the capacitor  140 . The capacitor may be, but is not limited to, a MOSFET, a BJT, an IGBT, etc. 
         [0034]    According to an exemplary embodiment of the present disclosure, the semiconductor module  130  may include a first diode  131  and a second diode  133  opposed to each other. In addition, the semiconductor module  130  may include a first transistor  132  connected across the first diode  131  in the opposite direction, and a second transistor  134  connected across the second diode  133  in the opposite direction. The configuration of the semiconductor module  130  shown in  FIG. 2  is for controlling a fault current flowing in two directions. 
         [0035]    For example, when a fault current flows from left to right, the fault current flows through the second switch  120 , the first transistor  132  and the second diode  133 . On the other hand, when a fault current flows from right to left, the fault current flows through the second transistor  134 , the first diode  131  and the second switch  120 . 
         [0036]    The bypass circuit includes the second switch  120  and the semiconductor module  130 . According to the exemplary embodiment of the present disclosure, the bypass circuit is used to block current to thereby reduce the number of power semiconductors. In addition, according to the exemplary embodiment of the present disclosure, by utilizing the bypass circuit to block the current, the volume of the current circuit breaker  100  can be reduced and the manufacturing cost can be reduced. 
         [0037]    One terminal of the  140  may be connected to the second switch  120  and the other terminal thereof may be connected to the semiconductor module  130 . According to an exemplary embodiment of the present disclosure, when the second switch  120  is opened and the semiconductor module  130  is turned off, a fault current may flow in the capacitor  140 . In addition, when the semiconductor module  130  is turned off and the second switch  120  is opened, a fault current may flow in the capacitor  140 . When a fault current flows in the capacitor  140 , the capacitor  140  may be charged with the fault current. When the capacitor  140  is charged, the voltage across the capacitor  140  may have a certain value, e.g., 100 V. 
         [0038]    The surge arrester  150  may be connected across the capacitor  140  and may block a fault current by changing the resistance according to the voltage across the capacitor  140 . 
         [0039]    The resistance of the surge arrester  150  becomes infinite (∞) when the voltage applied across it is below a predetermined level, and becomes zero when the voltage applied across it is above the predetermined value. By utilizing such feature, a fault current can be blocked. 
         [0040]    For example, the surge arrester  150  may increase the resistance if the voltage across the capacitor  140  is below a predetermined value to thereby open the terminals of the capacitor  140 . In addition, the surge arrester  150  may decrease the resistance if the voltage across the capacitor  140  is above a predetermined value to thereby short the terminals of the capacitor  140 . The predetermined value may be 100 V. When the terminals of the capacitor  140  are open, a fault current does not flow through the surge arrester  150 . When the terminals of the capacitor  140  are shorted, a fault current flows through the surge arrester  150 . 
         [0041]    The control unit  160  determines whether a fault current is generated. If it is determined that a fault current is generated, the control unit  160  may generate a control signal to open the first or second switch. The control unit  160  may determine whether is a fault current flows or a steady-state current flows based on the magnitude of the current flowing in the main circuit  170 . For example, if the magnitude of a current is constant, the current is determined as a steady-state current. If the magnitude of a current is increasing, the current is determined as a fault current. In addition, the control unit  160  may generate a control signal to open or close the first switch  110  and the second switch  120 , and may turn on or turn off the semiconductor module  130 . 
         [0042]    The current circuit breaker  100  according to an exemplary embodiment of the present disclosure may further include a sensor  410  to detect if the first switch  110  is open. The control unit  160  may receive a signal from the sensor  410  which indicates that the first switch  110  is completely open and then generate a control signal to open the second switch  120 . The signal indicating that the first switch  110  is completely open is generated when the stroke  11  shown in  FIG. 3  is the maximum. Referring to  FIG. 4 , the control unit  160  may generate the control signal after the first switch  110  is completely open to open the second switch  120 . By doing so, the control unit  160  may control the open time of the first switch  110  and the open time of the second switch  120 . 
         [0043]      FIG. 5  is a diagram showing the current circuit breaker  100  according to an exemplary embodiment of the present disclosure when a steady-state current is flowing in the main circuit  170 .  FIG. 6  is a diagram showing the current circuit breaker  100  according to the exemplary embodiment of the present disclosure when a fault current is flowing in the main circuit  170 . 
         [0044]      FIG. 7  is a diagram showing the current circuit breaker  100  according to the exemplary embodiment of the present disclosure when a fault current flows in the second switch  120  and the semiconductor module  130 .  FIG. 8  is a diagram showing the current circuit breaker  100  according to the exemplary embodiment of the present disclosure when a fault current is flowing in the capacitor  140 . 
         [0045]      FIG. 9  is a diagram showing the current circuit breaker  100  according to the exemplary embodiment of the present disclosure when a fault current is flowing in the surge arrester  150 .  FIG. 10  is a graph showing the magnitude of a fault current according to an exemplary embodiment of the present disclosure. Hereinafter, a process of blocking a current by the current circuit breaker  100  according to an exemplary embodiment of the present disclosure will be described in detail with reference to  FIGS. 5 to 10 . 
         [0046]    Referring to  FIGS. 5, 6 and 10 , the first switch  110  is closed, and a steady-state current flows in the main circuit  170  via the first switch  110 . The control unit  160  may monitor continuously the magnitude of the current flowing in the main circuit  170  to determine whether the current is a fault current or a steady-state current. If it is determined that the current is a fault current, the control unit  160  may open the first switch  110 . The control unit  160  may determine whether the current is a fault current or a steady-state current based on the magnitude of the current. In the example shown in  FIG. 10 , the magnitude of the current is constant until time t0 and increases after time t0, and thus it may be determined that a fault current is generated. 
         [0047]    If it is determined that a fault current is generated, the first switch  110  is opened, and then the semiconductor module  130  is turned on. When the semiconductor module  130  is turned on, the fault current may pass through the bypass circuit. It to be noted that even though the first switch  110  is open after it is determined that the fault current is generated, the entire fault current does not flow through the bypass circuit. Specifically, an arc current flows in the main circuit  170  and the fault current except the arc component flows in the bypass circuit. Referring to  FIG. 10 , a curve  930  indicates the magnitude of the arc current flowing in the main circuit  170 , a curve  940  indicates the magnitude of the current flowing in the bypass circuit, and a curve  950  indicates the magnitude of the fault current. As can be seen from the graph, the arc current in the main circuit  170  decreases while the current flowing in the bypass circuit increases from time t1 to time t2. 
         [0048]    Subsequently, the second switch  120  is opened, and then the semiconductor module  130  is turned off. When the second switch  120  is opened and the semiconductor module  130  is turned off, a fault current flows in the capacitor  140 . The fault current flowing in the capacitor  140  charges the capacitor  140 , and the voltage across the charged capacitor  140  may remain constant. Referring to  FIGS. 8 and 10 , the fault current flowing through the capacitor  140 . The magnitude of the fault current at this time is indicated by the curve  960 . 
         [0049]    After the capacitor  140  is charged, the voltage across the capacitor  140  is applied across the surge arrester  150 . When the voltage across the capacitor  140  is applied, the resistance of the surge arrester  150  may become zero. When the resistance of the surge arrester  150  becomes zero, the terminals of the surge arrester  150  are shorted, such that all the fault current flows through it. When a certain amount of the fault current exits through the surge arrester, the voltage across the arrester decreases, and thus the resistance of the arrester becomes infinite (∞). As a result, the fault current no longer can flow through the arrester  150  and thus is blocked. 
         [0050]    According to an exemplary embodiment of the present disclosure, the fast switches are used to block a current, and thus the semiconductor module can be protected. In addition, according to an exemplary embodiment of the present disclosure, the number of power semiconductors can be reduced by using a bypass circuit to block a current. 
         [0051]    In addition, according to the exemplary embodiment of the present disclosure, by utilizing the bypass circuit to block the current, the volume of the current circuit breaker can be reduced and the manufacturing cost can be reduced. In addition, according to an exemplary embodiment of the present disclosure, heat generation can be suppressed by using the bypass circuit to block a current. 
         [0052]    The present disclosure described above may be variously substituted, altered, and modified by those skilled in the art to which the present invention pertains without departing from the scope and sprit of the present disclosure. Therefore, the present disclosure is not limited to the above-mentioned exemplary embodiments and the accompanying drawings.