SUPERCONDUCTOR SWITCH

Technical Field

[1] The present invention relates to a superconductor switch, and more particularly, to a superconductor switch that operates in response to a magnetic field generated in a superconductor module when a fault current such as an over-current is applied to the superconductor module so as to protect an electric system from the fault current.

[2]

Background Art

[3] In an electric system, a fault current limiter (FCL) is used to limit a fault current caused by a malfunction or an accident so as to protect components such as a bus bar, an insulator, a circuit breaker, and a load component from mechanical, thermal, and electrical stresses. Although a fault current caused by a malfunction increases in an electric system, it is difficult to develop an electric device configured to remove the fault current. Therefore, there is an increasing need for an FCL capable of controlling a fault current such as an over-current.

[4] The discovery of a high-temperature superconductor has made it possible to develop an FCL using nonlinear characteristics of a new device and has facilitated the development of a high-temperature superconducting fault current limiter using liquid nitrogen as a refrigerant. A superconducting material has high-nonlinear-resistance characteristics, and thus the superconducting material can be used to form an FCL. Various FCLs have been developed using superconducting properties. Particularly, much research has been conducted on a high-speed FCL that can sensitively react to rapid current variations.

[5]

Disclosure of Invention Technical Problem

[6] An aspect of the present invention provides a superconductor switch that can be switched in response to a magnetic field induced at a superconductor module by a fault current applied to the superconductor module so as to rapidly block the fault current and protect an electric system from the fault current.

[7]

Technical Solution

[8] According to an aspect of the present invention, there is provided a superconductor switch including: a superconductor module including first and second superconductor wires non-inductively wound in a hollow shape in a state where one end of the first su- perconductor wire and one end of the second superconductor wire are connected to a first terminal, the first and second superconductor wires having different critical characteristics; and an actuator configured to mechanically response to a magnetic field induced at a hollow part of the superconductor module for being switched between a second terminal and the other end of the first superconductor wire and the other end of the second superconductor wire, wherein if an over-current is applied to the first terminal, a magnetic field is induced at the hollow part of the superconductor module.

[9] The actuator may include: a first plate facing the hollow part of the superconductor module to receive a repulsive force caused by a magnetic field generated at the hollow part; and a second plate switching between the second terminal and the other ends of the first and second superconductor wires.

[10] The superconductor switch may further include a latch unit configured to maintain a state of the actuator for a predetermined time.

[11] The latch unit may include: an electromagnet including a first pole connected to a first coil power source and a second pole; a control switch disposed between the second pole of the electromagnet and a second coil power source; and a recovery circuit configured to operate the control switch by detecting a magnetic field generated at the hollow part of the superconductor module.

[12] The recovery circuit may short the control switch after a predetermined time from a detection of a magnetic field at the hollow part of the superconductor module.

[13] The electromagnet may fix the actuator by generating a magnetic field in response to a current applied from the first coil power source, and the magnetic field generated at the electromagnet may be removed by a current applied from the second coil power source so that the actuator returns to an original position.

[14] The superconductor module may further include a bobbin around which the first and second superconductor wires are wound.

[15] The superconductor module may have a pancake shape in which the first and second superconductor wires are spirally wound and stacked.

[16] The first and second superconductor wires of the superconductor module may be wound in a solenoid shape.

[17]

Advantageous Effects

[18] According to the present invention, the superconductor switch can be switched in response to a magnetic field induced at the superconductor module by a fault current applied to the superconductor module, so as to rapidly block the fault current and protect an electric system from the fault current.

[19] Brief Description of Drawings

[20] FIG. 1 is a diagram illustrating a superconductor switch according to an embodiment of the present invention.

[21] FIG. 2 is a circuit diagram of the superconductor switch of FIG. 1.

[22] FIG. 3 is a diagram illustrating a superconductor switch according to another embodiment of the present invention.

[23] FIGS. 4 through 6 are views for explaining operations of a latch unit illustrated in

FIG. 3.

[24]

[25] DESCRIPTION OF THE SYMBOLS IN MAIN PORTIONS OF THE

DRAWINGS>

[26] 110: Superconductor module 120: Actuator

[27] 330: Latch unit

[28]

Best Mode for Carrying out the Invention

[29] Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[30] FIG. 1 is a diagram illustrating a superconductor switch according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of the superconductor switch of FIG. 1.

[31] In the current embodiment, a superconductor switch 100 may include a superconductor module 110 and an actuator 120.

[32] In the superconductor module 110, first and second superconductor wires 111 and

112 having different critical characteristics may be non-inductively wound in a hollow cylindrical shape. The first superconductor wire 111 and the second superconductor wire 112 may be formed of different materials. In the current embodiment, silver may be used as a stabilizing material for the first superconductor wire, and stainless steel may be used for a stabilizing material for the second superconductor wire. Materials having different specific resistances may be used as stabilizing materials for the first and second superconductor wires.

[33] The first and second superconductor wires 111 and 112 may be non-inductively wound around a hollow bobbin 113. That is, when there are normal currents through the first and second superconductor wires 111 and 112, magnetic fields induced in the hollow part of the bobbin 113 by the first and second superconductor wires 111 and 112 may be offset by each other.

[34] The first and second superconductor wires 111 and 112 may be wound in a pancake shape in which spiral wires are stacked, or a solenoid shape in which wires are wound in opposite directions. In the current embodiment, the first and second superconductor wires 111 and 112 may be spirally wound in opposite directions to form a stacked pancake shape.

[35] One end of the first superconductor wire 111 and one end of the second superconductor wire 112 may be connected to a first terminal 101. A power source may be connected to the first terminal 101 to apply a normal current to the first and second superconductor wires 111 and 112 through the first terminal 101.

[36] The actuator 120 may be switched between a second terminal and the other ends of the first and second superconductor wires 111 and 112 in mechanical response to a magnetic field induced in the hollow part of the superconductor module.

[37] In the current embodiment, the actuator 120 may includes a first plate 121 configured to face the hollow part of the superconductor module and be repelled by a magnetic field generated in the hollow part, and a second terminal 122 configured to be switched between the second terminal 102 and the other end of the first superconductor wire and the other end of the second superconductor wire.

[38] The first and second plates 121 and 122 of the actuator 120 may be formed of an electrically conductive material, and a connection structure between the first and second plates 121 and 122 may be formed of a light material that does not conduct a current easily. In the current embodiment, the actuator 120 may further include a third plate 123.

[39] The superconductor switch 100 may operate as follows. If there is a current through the first superconductor wire 111 in the winding direction of the first superconductor wire 111, a magnetic field may be formed in the hollow part (H) of the bobbin 113 in the downward direction by the right hand rule. If there is a current through the second superconductor wire 112 in the winding direction of the second superconductor wire 112, a magnetic field may be formed in the hollow part (H) of the bobbin 113 in the upward direction by the right hand rule.

[40] In the current embodiment, if there is a normal current through the first terminal 101 connected to ends of the first and second superconductor wires 111 and 112, magnetic fields formed in the hollow part (H) of the bobbin by the first and second superconductor wires 111 and 112 may be offset by each other. At this time, the other ends of the first and second superconductor wires may be connected to the second terminal 102 by the second plate 122 of the actuator 120. In this case, the impedance component of the superconductor module 110 is very low, and thus the normal current can flow from the first terminal 101 to the second terminal 102 through the superconductor module 110.

[41] If there is an over-current through the first terminal 101, the amounts of currents passing through the first and second superconductor wires 111 and 112 may become different, and in this case, the first and second superconductor wires 111 and 112 may become inductive.

[42] When over-currents pass through the first and second superconductor wires 111 and

112, the first and second superconductor wires 111 and 112 change with different speeds from a superconductive state to a normal conductive state. In addition, the first and second superconductor wires 111 and 112 have different specific resistances. Therefore, the impedance component of the superconductor module 110 may increase when over-currents flow through the first and second superconductor wires 111 and 112. That is, at the moment when an over-current passes, the resistance of the second superconductor wire 112 is first increased because a super- normal conductor transition occurs first at the second superconductor wire 112 having a lower n-value (a characteristic value of a superconductor related with the speed of superconductor-normal conductor transition), and thus most of the over-current passes through the first superconductor wire 111. Then, a super- normal conductor transition occurs also at the first superconductor wire 111, and the over-current is distributed to the first and second superconductor wires 111 and 112 according to the normal conductivities of the first and second superconductor wires 111 and 112. Therefore, the first and second superconductor wires 111 and 112 become inductive.

[43] At this time, since the strengths of magnetic fields generated by the first and second superconductor wires 111 and 112 become different, a magnetic field can be formed in the hollow part of the superconductor module 110.

[44] In response to the magnetic field formed in the hollow part of the superconductor module 110, an electromagnetic field is induced at the first plate 121 of the actuator, and thus the first plate 121 is repelled away from the superconductor module 110. Thus, the actuator 120 is moved upward, that is, the second plate 122 of the actuator 120 is lifted. As a result, the other ends of the first and second superconductor wires 111 and 112 can be disconnected from the second terminal 102.

[45] In this way, when a normal current is applied, the superconductor switch of the current embodiment can be turned on because magnetic fields of the superconductor module are offset by each other, and when a fault current is applied, the superconductor switch can be turned off because a magnetic field is induced at the superconductor module. In addition, since the superconductor switch operates using an electromagnetic repulsive force generated by a rapid magnetic field variation when a fault current is applied to the superconductor switch, the switching operation of the superconductor switch can be rapid.

[46] FIG. 3 is a diagram illustrating a superconductor switch according to another embodiment of the present invention.

[47] In the current embodiment, a superconductor switch 300 may include a super- conductor module 310, an actuator 320, and a latch unit 330.

[48] In the superconductor module 310, first and second superconductor wires 311 and

312 having different critical characteristics may be non-inductively wound in a hollow cylindrical shape. The first superconductor wire 311 and the second superconductor wire 312 may be formed of different materials. In the current embodiment, the first superconductor wire may be formed of silver, and the second superconductor wire may be formed of stainless steel.

[49] The first and second superconductor wires 311 and 312 may be non-inductively wound around a hollow bobbin 313. That is, when there are normal currents through the first and second superconductor wires 311 and 312, magnetic fields induced in the hollow part of the bobbin 313 by the first and second superconductor wires 311 and 312 may be offset by each other.

[50] The first and second superconductor wires 311 and 312 may be wound in a pancake shape in which spiral wires are stacked, or a solenoid shape in which wires are wound in opposite directions. In the current embodiment, the first and second superconductor wires 311 and 312 may be spirally wound in opposite directions to form a stacked pancake shape.

[51] One end of the first superconductor wire 311 and one end of the second superconductor wire 312 may be connected to a first terminal 301. A power source may be connected to the first terminal 301 to apply a normal current to the first and second superconductor wires 311 and 312 through the first terminal 301.

[52] The actuator 320 may be switched between a second terminal and the other end of the first superconductor 311 wire and the other end of the second superconductor wire 312 in mechanical response to a magnetic field induced in the hollow part of the superconductor module.

[53] In the current embodiment, the actuator 320 may includes a first plate 321 configured to face the hollow part of the superconductor module and be repelled by a magnetic field generated in the hollow part, and a second terminal 322 configured to be switched between the second terminal 302 and the other ends of the first and second superconductor wires 311 and 312.

[54] The first and second plates 321 and 322 of the actuator 320 may be formed of an electrically conductive material, and a connection structure between the first and second plates 321 and 322 may be formed of a light material that does not conduct a current easily.

[55] In the current embodiment, the actuator 320 may further include a third plate 323 disposed between first and second poles of an electromagnet 331 of the latch unit.

[56] The latch unit 330 may include the electromagnet 331, a control switch 332, and a recovery circuit 333. The electromagnet 331 has first and second poles, and a first coil power source is connected to the first pole of the electromagnet 331. The control switch 332 is disposed between the second pole of the electromagnet 331 and a second coil power source. The recovery circuit 333 detects a magnetic field generated in the hollow part of the superconductor module 310 and operates the control switch 332.

[57] Coils may be wound around the first and second poles 33 Ia and 33 Ib of the electromagnet 331. The first pole 331a may be connected to the first coil power source. If a current is applied from the first coil power source, a magnetic field is generated at the first pole 331a of the electromagnet, and another magnetic field may be generated at the second pole 331b in response to the magnetic field generated at the first pole 331a.

[58] The control switch 332 is disposed between the second pole 331b of the electromagnet and the second coil power source to allow a current from the second coil power source to the second pole 331b.

[59] The recovery circuit 333 may operate the control switch 332 by detecting a magnetic field generated in the hollow part of the superconductor module 310. The recovery circuit 333 may short the control switch after a predetermined time from a detection of a magnetic field at the hollow part of the superconductor module.

[60] The superconductor switch 300 may operate as follows. If there is a current passing through the first superconductor wire 311 in the winding direction of the first superconductor wire 311, a magnetic field may be formed in the hollow part of the bobbin 313 in the downward direction by the right hand rule. If there is a current passing through the second superconductor wire 312 in the winding direction of the second superconductor wire 312, a magnetic field may be formed in the hollow part of the bobbin 313 in the upward direction by the right hand rule.

[61] In the current embodiment, if there is a normal current passing through the first terminal 301 connected to one end of the first superconductor wire and one end of the second superconductor wire, magnetic fields formed in the hollow part of the bobbin by the first and second superconductor wires 311 and 312 may be offset by each other. At this time, the other end of the first superconductor wire and the other end of the second superconductor wire may be connected to the second terminal 102 by the second plate 322 of the actuator 320. In this case, the impedance component of the superconductor module 310 is very low, and thus the normal current can flow from the first terminal 301 to the second terminal 302 through the superconductor module 310.

[62] If an over-current is applied to the first terminal 301, the amounts of currents passing through the first and second superconductor wires 311 and 312 may become different, and in this case, the first and second superconductor wires 311 and 312 may become inductive.

[63] When over-currents pass through the first and second superconductor wires 311 and

312, the first and second superconductor wires 311 and 312 change with different speeds from a superconductive state to a normal conductive state. In addition, the first and second superconductor wires 311 and 312 have different specific resistances. Therefore, the impedance component of the superconductor module 310 may increase when over-currents flow through the first and second superconductor wires 311 and 312. That is, at the moment when an over-current passes, the resistance of the second superconductor wire 312 is first increased because a super- normal conductor transition occurs first at the second superconductor wire 312 having a lower n-value, and thus most of the over-current passes through the first superconductor wire 311. Then, a super-normal conductor transition occurs also at the first superconductor wire 311, and the over-current is distributed to the first and second superconductor wires 311 and 312 according to the normal conductivities of the first and second superconductor wires 311 and 312. Therefore, the first and second superconductor wires 311 and 312 become inductive.

[64] At this time, since the strengths of magnetic fields generated by the first and second superconductor wires 311 and 312 become different, a magnetic field can be formed in the hollow part of the superconductor module 310.

[65] In response to the magnetic field formed in the hollow part of the superconductor module 310, an electromagnetic field is induced at the first plate 321 of the actuator, and thus the first plate 321 is repelled away from the superconductor module 310. Thus, the actuator 320 is moved upward, that is, the second plate 322 of the actuator 320 is lifted. As a result, the other ends of the first and second superconductor wires 311 and 312 can be disconnected from the second terminal 302.

[66] An operation of the latch unit 330 in the case of a normal current, and an operation of the latch unit 330 in the case of a fault current will now be described with reference to FIGS. 4 through 6.

[67]

[68] FIGS. 4 through 6 are views for explaining operations of the latch unit illustrated in

FIG. 3.

[69] FIG. 4 is a view for explaining an operation of the latch unit when a normal current is applied to the superconductor module. Referring to FIG. 4, a coil is wound around the first pole 431a of the electromagnet 431, and a first coil power source is connected to the coil for applying a current to the coil. A coil is wound around the second pole 431b of the electromagnet; however, since a control switch is opened, there is no current from a second power source to the second pole 431b.

[70] Since there is a current from the first coil power source to the first pole 431a, a magnetic field is generated at the electromagnet. The direction of the magnetic field at the first and second poles is indicated by arrows ® and ®. Therefore, the third plate 423 of the actuator disposed between the first and second poles 431a and 431b may be attracted by the first pole 431a and brought into contact with the first pole 431a.

[71] FIG. 5 is a view for explaining an operation of the latch unit when a fault current is applied to the superconductor module. Referring to FIG. 5, the coil is wound around the first pole 431a of an electromagnet 431, and a current can be applied to the coil from the first coil power source connected to the coil. Although the coil is wound around the second pole 431b of the electromagnet, since the control switch is opened, there is no current from the second power source to the second pole 431b.

[72] In the current embodiment, when a fault current is applied to the superconductor module, a magnetic field may be formed in the hollow part of the superconductor module to apply a repulsive force © to the first plate of the actuator and thus move the third plate 423 of the actuator. At this time, the third plate can be moved when the repulsive force acting on the actuator from the superconductor module © is greater than an attractive magnetic force ® acting on the third plate 423 from the first pole of the electromagnet. As the third plate 423 approaches the second pole 431b, the third plate 423 receives an electromagnetic force from the second pole 431b as well as the repulsive force ©, and thus the third plate 423 can be brought into contact with the second pole 431b. If this condition continues without any change, the contact between the third plate 423 and the second pole 431b is stably maintained, and thus the other ends of the first and second superconductor wires are not connected to the second terminal by the second plate of the actuator.

[73] FIG. 6 is a view for explaining an operation of the latch unit when the superconductor module returns to a normal state after a fault current is applied to the superconductor module. Referring to FIG. 6, the coil is wound around the first pole 431a of an electromagnet 431, and a current can be applied to the coil from the first coil power source connected to the coil. The coil is wound around the second pole 431b of the electromagnet, and the control switch is turned on (shorted). Therefore, there can be a current from the second power source to the second pole 431b.

[74] In the current embodiment, the recovery circuit may turn on the control switch for a predetermined time after a predetermined time from a detection of a magnetic field variation at the superconductor module, so as to connect the second coil power source to the second pole 431b of the electromagnet. The recovery circuit may be connected to a hall sensor disposed at the superconductor module to detect a magnetic field variation at the superconductor module.

[75] While a current flows from the second power source to the second pole 431b, a magnetic field ® generated at the second pole 431b may be offset by a magnetic field © generated at the first pole 431a, and thus magnetic flux may disappear in the electromagnet. As the magnetic flux varies, a repulsive force © may be induced and applied to the third plate 423. By the inductive repulsive force ©, the third plate 423 is moved toward the first pole 431a. Therefore, in a normal state, the first and second superconductor wires can be connected to the second terminal by the second plate of the actuator.

[76] According to the above-described embodiments of the present invention, when a normal current is applied, the superconductor switch can be turned on because magnetic fields of the superconductor module are offset by each other, and when a fault current is applied, the superconductor switch can be turned off by a magnetic field induced at the superconductor module. In addition, the superconductor switch is operated by using an electromagnetic repulsive force generated by a rapid magnetic field variation caused by a fault current applied to the superconductor switch, and the superconductor switch can rapidly return to a normal state owing to the latch unit. Therefore, high-speed switching is possible.

[77] While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.

[78]

[79]