Electric circuit protection device and electric circuit protection method

Abstract

This electric circuit protection device comprises: a current interruption device including a conductor piece forming a part of an electric circuit and an igniter for cutting the conductor piece; and a current limiting element that is connected in series with the conductor piece of the current interruption device to form a part of the electric circuit, and that is connected in parallel with the igniter to exhibit a current limiting operation when an abnormal current flows, wherein the igniter has impedance higher than that of the current limiting element at a normal time, and when the current limiting element exhibits the current limiting operation, a current flows through the igniter, whereby the igniter is operated to interrupt a current flowing in the electric circuit.

Description

Electrical circuit protection device and electrical circuit protection method

[0001] The present invention relates to an electrical circuit protection device and an electrical circuit protection method.

[0002] An electric circuit may be provided with a circuit breaker that operates to immediately cut off electrical continuity in the event of an abnormality in a device that constitutes the electric circuit or in the system that the electric circuit is installed in. For example, in power systems such as power transmission and distribution networks, railway systems, and renewable energy power sources, circuit breakers are used that quickly and reliably cut off the power supply when an excessive abnormal current occurs due to a lightning strike, contact with a bird or animal, aging, or the like.

[0003] Patent Document 1 proposes a protective device including a circuit breaker between a first conductor and a second conductor, the circuit breaker receiving a trip signal to interrupt current in a power zone, and a control circuit sending the trip signal to the circuit breaker. The protective device further includes a fuse connected in series between the first conductor and the circuit breaker, so that current flows through the fuse to the power zone of the circuit breaker, and a control circuit connected between the fuse and the control zone of the circuit breaker.

[0004] US Patent Application Publication No. 2022 / 0013308

[0005] In Patent Document 1, the interruption operation is initiated by a change in the position of the piston over time. In this way, with a system in which the interruption is initiated by mechanical action, the start time after the occurrence of an abnormal current is delayed, and during this time, the abnormal overcurrent increases, which can prevent the power from being properly interrupted. Furthermore, in a configuration in which a trip signal is generated by a control circuit and sent to the circuit breaker to interrupt power, as in Patent Document 1, when an abnormal current occurs, it takes time for the trip signal to be generated and sent and for the circuit breaker to operate in response to this trip signal, which can increase damage caused by the abnormal current. Furthermore, when the control circuit has a complex configuration including sensors, etc., a failure of the control device can sometimes prevent the power from being interrupted, resulting in a problem of reduced reliability.

[0006] The technology of the present disclosure has been made in consideration of the above-mentioned circumstances, and its purpose is to provide a technology that quickly and automatically starts and reliably cuts off the power supply when an abnormal current occurs.

[0007] (Aspect 1) In order to solve the above problem, the electrical circuit protection device of the present disclosure comprises: a current interruption device including a conductor piece that forms part of an electrical circuit and an igniter for cutting the conductor piece; and a current limiting element that is connected in series with the conductor piece of the current interruption device to form part of the electrical circuit, and that is connected in parallel with the igniter to exert a current limiting effect when an abnormal current flows, wherein the igniter has a higher impedance than the current limiting element under normal conditions, and when the current limiting element exerts its current limiting effect, a current flows through the igniter, which activates the igniter and interrupts the current flowing in the electrical circuit.

[0008] (Aspect 2) In the electrical circuit protection device described in Aspect 1, the current-limiting element may be a current-limiting fuse that includes a fuse element that forms part of the electrical circuit, and that melts at least a portion of the fuse element when the abnormal current flows through the fuse element, thereby limiting the current flowing through the electrical circuit.

[0009] (Aspect 3) The electrical circuit protection device according to aspect 1 may further include a varistor connected in series with the igniter.

[0010] (Aspect 4) The electrical circuit protection device described in Aspect 1 may be configured such that the current flowing through the electrical circuit via the current-limiting element and the conductor piece is a direct current, and the direct current is interrupted by activation of the igniter.

[0011] (Aspect 5) The electrical circuit protection device according to Aspect 1 may further include a switching element connected in parallel with the current limiting element and the current interruption device and forming at least a part of a parallel path parallel to the current limiting element and the current interruption device, wherein the switching element closes the parallel path under normal conditions and opens the parallel path when an abnormal current occurs.

[0012] (Aspect 6) In the electrical circuit protection device described in Aspect 5, in the power path in which the current limiting element and the current interruption device are arranged in series, a linking contact that links with the opening and closing of the switching element may be provided in the range in which the parallel path is connected.

[0013] (Aspect 7) In the electrical circuit protection device according to any one of Aspects 1 to 6, the igniter may include an impedance element and an ignition unit that is activated by a current flowing through the impedance element.

[0014] (Aspect 8) The electrical circuit protection device described in Aspect 7 may be configured such that a first end of the current limiting element is connected to a first end of the impedance element, a second end of the current limiting element is connected to the conductor piece, a second end of the impedance element is connected to a first end of the ignition unit, and a second end of the ignition unit is connected between the second end of the current limiting element and the conductor piece.

[0015] (Aspect 9) The electric circuit protection device described in Aspect 8 may include: a first current limiting element as the current limiting element; a first impedance element as the impedance element; a second current limiting element connected between the conductor piece of the current interruption device and a second end of the first impedance element; and a second impedance element connected in parallel with the second current limiting element between the second end of the first impedance element and a first end of the ignition unit.

[0016] (Aspect 10) The electrical circuit protection device according to aspect 9 may further include a third current limiting element connected between the second impedance element and the first end of the ignition portion.

[0017] (Aspect 11) The electric circuit protection device according to any one of Aspects 2 to 4 may further include a switching element connected in parallel with the current limiting element and the current interruption device and forming at least a part of a parallel path parallel to the current limiting element and the current interruption device, wherein the switching element closes the parallel path under normal conditions and opens the parallel path when an abnormal current occurs.

[0018] (Aspect 12) In the electrical circuit protection device described in Aspect 11, in the power path in which the current limiting element and the current interruption device are arranged in series, a linking contact that links with the opening and closing of the switching element may be provided in the range in which the parallel path is connected.

[0019] (Aspect 13) The electric circuit protection device according to Aspect 8 may comprise: a first current limiting element as the current limiting element; a first impedance element as the impedance element; a second impedance element having a first end connected to a second end of the first impedance element; a second current limiting element having a first end connected to a second end of the second impedance element, the second end being an end opposite to the first end, and having a second end connected to the conductor piece; a first varistor connected in parallel with the second impedance element and the second current limiting element between the conductor piece and the second end of the first impedance element; and a second varistor having one end connected between the second end of the second impedance element and the first end of the second current limiting element, and the other end connected to the first end of the ignition unit.

[0020] (Aspect 14) In order to solve the above problem, the electric circuit protection method of the present disclosure is an electric circuit protection method performed by a current interruption device including a conductor piece forming part of an electric circuit and an igniter for cutting the conductor piece, and a current limiting element connected to the current interruption device, wherein the current limiting element, which is connected in series with the conductor piece of the current interruption device to form part of the electric circuit and is connected in parallel with the igniter, exerts a current limiting effect when an abnormal current flows, and the igniter, which has a higher impedance than the current limiting element under normal conditions, is activated by current flowing through the igniter when the current limiting element exerts its current limiting effect, thereby interrupting the current flowing in the electric circuit.

[0021] According to the present disclosure, it is possible to provide a technology that can be quickly and automatically started and reliably cut off the power supply when an abnormal current occurs.

[0022] FIG. 1 is a diagram illustrating the configuration of an electric circuit protection device according to a first embodiment. FIG. 1 is a diagram illustrating the configuration of an electric circuit protection device in which the ignition unit itself has a higher impedance than the current-limiting element under normal conditions. FIG. 2 is a diagram illustrating current and voltage waveforms when a 1.7 kV / 10 kA interruption test is performed on a current-limiting fuse alone. FIG. 3 is a diagram illustrating advantages and disadvantages of a current-limiting fuse and an interruption device. FIG. 4 is a diagram illustrating the principle of current limiting in a current-limiting fuse. FIG. 5 is a diagram illustrating the configuration of an interruption device. FIG. 6 is a top view of a conductor piece according to the first embodiment. FIG. 7 is a diagram illustrating the interruption principle of an interruption device. FIG. 8 is a schematic diagram illustrating a current waveform flowing in an electric circuit when an abnormal current is interrupted by a current-limiting fuse and an interruption device of a protection device. FIG. 9 is a schematic diagram illustrating the configuration of a test circuit. FIG. 10 is a diagram illustrating current and voltage waveforms when a 1.7 kV interruption test is performed. FIG. 11 is a diagram illustrating current and voltage waveforms when a 2.0 kV interruption test is performed. FIG. 12 is a diagram illustrating the configuration of an electric circuit protection device according to a second embodiment. FIG. 13 is a diagram illustrating current and voltage waveforms when an interruption is performed by the electric circuit protection device of the second embodiment. FIG. 14 is a diagram illustrating the configuration of an electric circuit protection device according to a third embodiment. FIG. 15 is a diagram illustrating an example of the rated voltage [V] and rated current [A] of a first current limiting element, a second current limiting element, and a third current limiting element. FIG. 1 is a diagram showing current and voltage waveforms at the time of interruption in the electric circuit protection device of the third embodiment. FIG. 2 is a diagram showing the configuration of the electric circuit protection device of the fourth embodiment. FIG. 3 is a diagram showing a modified example of the electric circuit protection device of the fourth embodiment. FIG. 4 is a diagram showing the configuration of the electric circuit protection device of the fifth embodiment. FIG. 5 is a diagram showing the interruption operation of the protection device of the fifth embodiment (part 1). FIG. 6 is a diagram showing the interruption operation of the protection device of the fifth embodiment (part 2). FIG. 7 is a schematic diagram showing the configuration of a test circuit of the fifth embodiment. FIG. 8 is a diagram showing the total voltage, total current, and pyroelectric voltage in a 600V interruption test. FIG. 9 is a diagram showing the second fuse current, ignition wire current, and pyroelectric voltage in a 600V interruption test. FIG. 10 is a diagram showing the total voltage, total current, and pyroelectric voltage in a 700V interruption test. FIG. 11 is a diagram showing the second fuse current, ignition wire current, and pyroelectric voltage in a 700V interruption test.

[0023] First Embodiment An electric circuit protection device according to an embodiment of the present disclosure will be described below with reference to the drawings. Note that each configuration and combination thereof in the embodiment is merely an example, and addition, omission, substitution, and other modifications of the configuration are possible as appropriate within the scope of the gist of the present disclosure. The present disclosure is not limited by the embodiment, but is limited only by the claims.

[0024] 1 is a diagram illustrating the configuration of an electric circuit protection device (hereinafter also simply referred to as a "protection device") 200 according to an embodiment. The protection device 200 is a device for preventing failure of a load 91, cables 92 and 93, etc. of the electric circuit 90 by interrupting the electric circuit 90 when an abnormality occurs in an electric circuit 90 included in, for example, an automobile, a home appliance, a solar power generation system, or a system including a battery (e.g., a lithium-ion battery) of the electric circuit 90. The protection device 200 may also be applied to power systems such as power transmission and distribution networks, railway systems, and renewable energy power sources.

[0025] The protection device 200 includes a current interruption device (hereinafter also referred to simply as the "interruption device") 1 including a conductor piece 50 constituting a part of the electrical circuit 90 and an igniter 20 for cutting off the conductor piece 50. The igniter 20 may include an impedance element 23 and an ignition unit (ignition) 21 activated by current flowing through the impedance element 23. The interruption device 1 of this embodiment is a so-called pyro-fuse (also referred to as a pyro-switch) that cuts off the conductor piece 50 by the combustion energy of the explosive when current is passed through the ignition unit 21, as described below. The protection device 200 also includes a current-limiting element 3 connected in series with the conductor piece 50 of the interruption device 1 and forming part of the electrical circuit 90. The current-limiting element 3 is an element that exerts a current-limiting effect when an abnormal current flows. Here, the current limiting action is the action of suppressing an abnormal current when it flows. For example, in the case of a current limiting fuse, the action is to increase the arc resistance (voltage) when the fuse element melts, thereby suppressing the short-circuit current to a small value and controlling the short-circuit current so that it does not reach its peak value.

[0026] 1 , the first end 301 of the current limiting element 3 is connected to the first end 231 of the impedance element 23, and the second end 302 of the current limiting element 3 is connected to the first end 501 of the conductor piece 50. The second end 232 of the impedance element 23 is connected to the first end 211 of the ignition unit 21. The second end 212 of the ignition unit 21 is connected to a point 921 between the second end 302 of the current limiting element 3 and the conductor piece 50.

[0027] A second end 502 of the conductor piece 50 in the circuit breaker 1 is connected to a load 91 via a cable 93. In the electric circuit 90, power is supplied from a power source via a cable 92 to the load 91 via the protection device 200. In this power supply path, the current limiting element 3 of the protection device 200 and the circuit breaker 1 are connected in series, and the current limiting element 3 is connected in parallel to the impedance element 23 and the ignition unit 21 of the igniter 20. In the electric circuit 90 configured as described above, the impedance of the impedance element 23 and the ignition unit 21 is set to be sufficiently higher than the impedance of the current limiting element 3 during steady operation (normal operation). Therefore, during steady operation, the current supplied from the power source flows to the load 91 via the current limiting element 3 and the conductor piece 50 of the circuit breaker 1, and almost no current flows through the impedance element 23 and the ignition unit 21. When an abnormal current occurs due to a lightning strike, a short circuit, or the like, causing the current limiting element 3 to perform a current limiting function, the impedance of the current limiting element 3 increases, causing a current to flow through the impedance element 23 and the ignition unit 21. As described below, the ignition unit 21 activates and cuts off the conductor piece 50. This allows the protection device 200 to prevent damage to the electric circuit 90 due to the abnormal current and protect the electric circuit 90. Note that, in this embodiment, steady-state operation refers to a state in which no abnormal current is occurring. In this embodiment, the current flowing through the electric circuit 90 via the current limiting element 3 and the conductor piece 50 is a direct current. However, the current flowing through the electric circuit 90 via the current limiting element 3 and the conductor piece 50 may be an alternating current.

[0028] In the example of FIG. 1 , igniter 20 includes impedance element 23 separate from ignition unit 21, but impedance element 23 may also be integrated into ignition unit 21 of igniter 20. Also, FIG. 2 is a diagram illustrating the configuration of electrical circuit protection device 200 in which ignition unit 21 itself has a higher impedance than current limiting element 3 under normal conditions. For example, ignition unit 21 may be configured as a discharge gap and have a higher impedance than current limiting element 3 under normal conditions. As long as ignition unit 21 itself has a higher impedance than current limiting element 3 connected in parallel in this way, it is not necessary to provide impedance element 23 separate from ignition unit 21 as shown in FIG. 1 .

[0029] <Current Limiting Element> Next, the current limiting element 3 will be described in detail. The current limiting element 3 of this embodiment is a so-called current limiting fuse. This current limiting element (hereinafter also referred to as a current limiting fuse) 3 includes a fuse element 32 (see FIG. 5 ) that forms part of an electric circuit. When an abnormal current (fault current) flows through the fuse element 32, at least a part of the fuse element 32 melts, limiting the current flowing through the electric circuit 90. Note that the current limiting element is not limited to a current limiting fuse, and may be any element that exhibits a current limiting effect when a current equal to or greater than a predetermined value flows, such as a current limiting breaker or a superconducting current limiter.

[0030] Figure 3 shows the current and voltage waveforms obtained when a 1.7kV / 10kA interruption test was conducted on a single current-limiting fuse 3 (DC rating 1.0kV / 50A). In Figure 3, an abnormal current occurred at t = 0ms, and when the current flowing through the fuse reached approximately 2300A, current-limiting fuse 3 arced and current limiting began. After t = 5ms, the current was limited to approximately 100A, but it was not possible to reduce the current to zero, and the current value began to rise. At t = 25ms, current-limiting fuse 3 exploded, resulting in an interruption failure.

[0031] As described above, the current-limiting fuse 3 can limit current even above its rated voltage, but may not be able to completely interrupt the current. On the other hand, the circuit breaker 1 physically breaks the conductor piece (metal plate) 50, which serves as the current path, and therefore excels in interrupting small currents. Therefore, in the present protection device 200, the current-limiting performance of the current-limiting fuse 3 and the circuit breaker 1 are connected in series to take advantage of their respective interrupting capabilities. In this DC circuit breaker with current-limiting function (protection device 200) that combines the current-limiting fuse 3 and the circuit breaker 1, the circuit breaker 1 cuts off the current path in a voltage range that exceeds the rated voltage of the current-limiting fuse 3 and cannot be interrupted by the fuse alone. Figure 4 shows the advantages and disadvantages of the current-limiting fuse 3 and the circuit breaker 1. In Figure 4, excellent current limiting or interrupting capabilities are indicated by a "◯" and poor current limiting or interrupting capabilities are indicated by a "X." When the current-limiting fuse 3 and the circuit breaker 1 are used alone as shown in Figure 4, there are advantages and disadvantages, but when the current-limiting fuse 3 and the circuit breaker 1 are used together, the disadvantages of each are complemented, resulting in a configuration in which only the advantages of both are realized.

[0032] <Current-limiting principle of current-limiting fuse> Fig. 5 is a diagram showing the principle of current-limiting in the current-limiting fuse 3. States (A) to (C) in Fig. 5 show the state transitions when the current-limiting fuse 3 is activated by an abnormal current. The current-limiting fuse 3 has a metal fuse element 32 that passes current inside a housing 31, and arc-extinguishing sand (mainly SiO ２ When an abnormal current occurs, the current-limiting fuse 3 operates in the following order (i) to (iii).

[0033] (i) State (A): The load current in normal operation is passed through the fuse element 32. Since the resistance value of the fuse element 32 is on the order of several milliohms, it can be considered that there is almost no loss in normal operation.

[0034] (ii) State (B) When a fault current occurs and the energy injected into the fuse element 32 exceeds a threshold, the narrow portion 321 of the fuse element 32 melts and an arc occurs (ignition).

[0035] (iii) State (C): Most of the energy of the generated arc is consumed in evaporating the arc-extinguishing sand 33. At this time, the arc voltage exceeds the power supply voltage, thereby limiting the abnormal current.

[0036] <Shutoff device> Fig. 6 is a diagram showing the configuration of the shutoff device 1, and is a vertical cross-sectional view taken along the height direction (the direction in which an accommodation space 13, which will be described later, extends) of the shutoff device 1. Fig. 6 shows the state before the shutoff device 1 is activated.

[0037] The circuit breaker 1 includes a housing 10 as an outer shell member, an igniter 20, a projectile 40, a conductor piece 50, a coolant material 60, etc. The housing 10 has an accommodating space 13 extending in one direction from a first end 11 on the upper end side to a second end 12 on the lower end side. The accommodating space 13 is a linear space that allows the projectile 40 to move, and extends along the vertical direction of the circuit breaker 1. As shown in Fig. 6 , the projectile 40 is accommodated in the accommodating space 13 formed inside the housing 10. However, in this specification, the vertical direction of the circuit breaker 1 merely indicates the relative positional relationship of each element in the circuit breaker 1 for the convenience of explaining the embodiment.

[0038] [Housing] The housing 10 includes a housing body 100, a top holder 110, and a bottom container 120. The top holder 110 and the bottom container 120 are coupled to the housing body 100, thereby forming the housing 10 as a single unit.

[0039] The housing body 100 has, for example, a generally rectangular prism-shaped outer shape. However, the shape of the housing body 100 is not particularly limited. A hollow portion is formed in the housing body 100 so as to extend vertically through the housing body 100, and this hollow portion forms a part of the storage space 13. The housing body 100 also has an upper surface 101 to which a flange portion 111 of the top holder 110 is fixed, and a lower surface 102 to which a flange portion 121 of the bottom container 120 is fixed. In this embodiment, a cylindrical upper cylindrical wall 103 extends upward from the outer periphery of the upper surface 101 of the housing body 100. In this embodiment, the upper cylindrical wall 103 has, for example, a rectangular prism shape, but may have other shapes. A cylindrical lower cylindrical wall 104 extends downward from the outer periphery of the lower surface 102 of the housing body 100. In this embodiment, the lower tube wall 104 has, for example, a rectangular cylindrical shape, but may have other shapes. Furthermore, a cylindrical mounting portion 106 is provided on the lower surface 102 of the housing main body 100, extending downward from the lower surface 102 around the periphery of the hollow portion. In this embodiment, the mounting portion 106 is formed cylindrically to fit the hollow portion, but may have other shapes. The housing main body 100 configured as described above can be formed from an insulating material such as a synthetic resin. For example, the housing main body 100 may be formed from nylon, a type of polyamide synthetic resin.

[0040] [Top Holder] Next, the top holder 110 will be described. The top holder 110 is, for example, a cylinder member having a stepped cylindrical shape and a hollow interior. The top holder 110 is configured to include a small-diameter cylinder portion 112 located on the upper side (first end 11 side), a large-diameter cylinder portion 113 located on the lower side, a connection portion 114 connecting these, and a flange portion 111 extending outward from the lower end of the large-diameter cylinder portion 113. For example, the small-diameter cylinder portion 112 and the large-diameter cylinder portion 113 are arranged coaxially, and the large-diameter cylinder portion 113 has a larger diameter (inner diameter) than the small-diameter cylinder portion 112.

[0041] The flange portion 111 of the top holder 110 has a generally rectangular outline that fits inside the upper cylindrical wall 103 of the housing main body 100. The flange portion 111 may be disposed inside the upper cylindrical wall 103 and fastened to the upper surface 101 of the housing main body 100 using screws or the like, or may be fixed with rivets or the like. The top holder 110 may be joined to the housing main body 100 with a sealant applied between the upper surface 101 of the housing main body 100 and the lower surface of the flange portion 111 of the top holder 110. This can improve the airtightness of the storage space 13 formed in the housing 10. Alternatively, instead of or in addition to a sealant, an O-ring may be interposed between the upper surface 101 of the housing main body 100 and the flange portion 111 of the top holder 110 to improve the airtightness of the storage space 13.

[0042] The cavity formed inside the small-diameter cylinder portion 112 of the top holder 110 functions as an accommodating space that accommodates a portion of the igniter 20, as shown in FIG. 6 . Furthermore, the cavity formed inside the large-diameter cylinder portion 113 of the top holder 110 communicates with the cavity of the housing main body 100 located below, and forms a portion of the accommodating space 13. The top holder 110 configured as described above can be formed from an appropriate metal member, such as stainless steel or aluminum, which has excellent strength and durability. However, the material from which the top holder 110 is formed is not particularly limited. Furthermore, the above-described embodiment of the shape of the top holder 110 is merely an example, and other shapes may be adopted.

[0043] [Bottom Container] Next, the bottom container 120 will be described. The bottom container 120 in this embodiment is a form of outer shell container. The bottom container 120 has a generally hollow, bottomed cylindrical shape and includes a side wall 122, a bottom wall 123 connected to the lower end of the side wall 122, and a flange 121 connected to the upper end of the side wall 122. The side wall 122 has, for example, a cylindrical shape, and the flange 121 extends outward from the upper end of the side wall 122. The flange 121 of the bottom container 120 has a generally rectangular outline that fits inside the lower tube wall 104 of the housing main body 100. The flange 121 may be disposed inside the lower tube wall 104 and fastened to the lower surface 102 of the housing main body 100 using screws or the like, or may be fixed by rivets or the like. Here, the bottom container 120 may be coupled to the housing body 100 with a sealant applied between the lower surface 102 of the housing body 100 and the upper surface of the flange portion 121 of the bottom container 120. This can improve the airtightness of the receiving space 13 formed in the housing 10. Also, instead of or in addition to the sealant, an O-ring may be interposed between the lower surface 102 of the housing body 100 and the flange portion 121 of the bottom container 120 to improve the airtightness of the receiving space 13.

[0044] The above-described shape of the bottom container 120 is merely an example, and other shapes may be adopted. The cavity formed inside the bottom container 120 communicates with the housing main body 100 located above and forms part of the storage space 13. The bottom container 120 configured as described above can be formed from an appropriate metal member, such as stainless steel or aluminum, which has excellent strength and durability. By forming the bottom container 120 from a metal member, the bottom container 120 achieves compactness while maintaining rigidity to withstand pressure during operation. The bottom container 120 is not limited to being made of metal. For example, the bottom container 120 may be formed from a synthetic resin or a composite material in which carbon fiber or glass fiber is added to a synthetic resin.

[0045] As described above, the housing 10 in this embodiment is configured to include the housing main body 100, the top holder 110, and the bottom container 120, which are assembled together, and an accommodating space 13 is formed inside the housing 10, extending from the first end 11 to the second end 12. The accommodating space 13 accommodates the igniter 20, the projectile 40, the cut portion 53 of the conductor piece 50, the coolant material 60, and the like, which will be described in detail below.

[0046] The housing 10 is assembled together such that the flange portion 111 of the top holder 110 and the flange portion 121 of the bottom container 120 sandwich the housing main body 100 and are fastened together by metal bolts 130. Note that the fastening of the housing 10 is not limited to the bolts 130 and may be performed using other fasteners. In this case, the fasteners may be made of metal.

[0047] [Igniter] Next, the igniter 20 will be described. The igniter 20 is an electric igniter including an ignition unit 21 containing an ignition charge, an igniter body 22 that holds the ignition unit 21, and an impedance element 23 connected to the ignition unit 21 via a cable. The igniter body 22 is surrounded by, for example, insulating resin. Furthermore, the ignition unit 21 has electrical ends (211 and 212 in FIG. 1 ) that are exposed to the outside through the igniter body 22 as a pair of conductive pins. One of the conductive pins (first end 211) is connected to the impedance element 23 via a cable 291, and the other (second end 212) is connected to a point 921 between the current limiting element 3 and the conductor piece 50 via a cable 292.

[0048] The igniter main body 22 includes a generally cylindrical main body portion 226 housed inside the small-diameter cylinder portion 112 of the top holder 110, and a connector portion 225 located at an upper portion of the main body portion 226. The igniter main body 22 is fixed to the small-diameter cylinder portion 112, for example, by press-fitting the main body portion 226 into the inner circumferential surface of the small-diameter cylinder portion 112. Furthermore, a constricted portion, whose outer circumferential surface is recessed compared to other portions, is formed in an annular shape along the circumferential direction of the main body portion 226 at an axially intermediate portion of the main body portion 226, and an O-ring 223 is fitted into this constricted portion. The O-ring 223 is made of, for example, rubber (e.g., silicone rubber) or synthetic resin, and functions to increase the airtightness between the inner circumferential surface of the small-diameter cylinder portion 112 and the main body portion 226.

[0049] Connector portion 225 of igniter 20 is disposed so as to protrude to the outside through opening 112A formed at the upper end of small-diameter cylinder portion 112. Connector portion 225 has, for example, a cylindrical shape that covers the side of the conductive pin, and is configured so as to be connectable to a connector on the power supply side.

[0050] As shown in FIG. 6 , the ignition unit 21 of the igniter 20 is disposed so as to face the accommodation space 13 of the housing 10 (more specifically, the hollow portion formed inside the large-diameter cylinder portion 113). The ignition unit 21 is configured, for example, as an igniter cup in which an ignition charge is accommodated. For example, the ignition charge is accommodated in the igniter cup of the ignition unit 21 while in contact with a bridge wire (resistor) that connects the base ends of a pair of conductive pins. As the ignition charge, for example, ZPP (zirconium potassium perchlorate), ZWPP (zirconium tungsten potassium perchlorate), THPP (titanium hydride potassium perchlorate), lead tricinate, etc. may be used.

[0051] When the igniter 20 is activated, an operating current for igniting the ignition charge is supplied from a power source to the conductive pin, causing the bridge wire in the ignition portion 21 to heat up, igniting and burning the ignition charge in the igniter cup and generating combustion products such as combustion gas. Instead of the bridge wire, a discharge gap may be provided between the base ends of a pair of conductive pins, and when an operating voltage is supplied to the conductive pins, a discharge occurs in the discharge gap, igniting the ignition charge in the igniter cup. As the ignition charge in the igniter cup of the ignition portion 21 burns, the pressure in the igniter cup increases, causing the cleavage surface 21A of the igniter cup to cleave, and the combustion products are released from the igniter cup into the accommodating space 13. More specifically, the combustion products from the igniter cup are released into a recess 411 in a piston portion 41 (described later) of the projectile 40 disposed in the accommodating space 13.

[0052] [Projectile] Next, the projectile 40 will be described. The projectile 40 is formed of an insulating material such as synthetic resin, and includes a piston portion 41 and a rod portion 42 connected to the piston portion 41. The piston portion 41 has a roughly cylindrical shape and an outer diameter that roughly corresponds to the inner diameter of the large-diameter cylinder portion 113 in the top holder 110. For example, the diameter of the piston portion 41 may be slightly smaller than the inner diameter of the large-diameter cylinder portion 113. The shape of the projectile 40 can be changed as appropriate depending on the shape of the housing 10, etc.

[0053] Furthermore, a recess 411 having, for example, a cylindrical shape is formed on the upper surface of the piston portion 41, and this recess 411 receives the ignition portion 21. The bottom surface of the recess 411 is formed as a pressure-receiving surface 411A that receives energy from the igniter 20 when the igniter 20 is activated. Furthermore, a constricted portion, whose outer peripheral surface is recessed compared to other portions, is formed in an annular shape along the circumferential direction of the piston portion 41 in the axial middle portion of the piston portion 41, and an O-ring 43 is fitted into this constricted portion. The O-ring 43 is made of, for example, rubber (e.g., silicone rubber) or synthetic resin, and functions to increase the airtightness between the inner peripheral surface of the large-diameter cylinder portion 113 and the piston portion 41.

[0054] The rod portion 42 of the projectile 40 is, for example, a rod-shaped member having an outer circumferential surface with a smaller diameter than the piston portion 41 and is integrally connected to the lower end side of the piston portion 41. The lower end surface of the rod portion 42 is formed as a cutting surface 421 for cutting the cut portion 53 from the conductor piece 50 when the interrupter 1 is activated. Note that, although the rod portion 42 in this embodiment has a generally cylindrical shape, its shape is not particularly limited and may be changed depending on the shape and size of the cut portion 53 to be cut from the conductor piece 50 when the interrupter 1 is activated. The rod portion 42 may have a columnar shape, such as a cylindrical column or a rectangular column. Note that, in the initial position of the projectile 40 shown in FIG. 6 , the tip end region of the rod portion 42 of the projectile 40, including the cutting surface 421, is positioned in the hollow portion of the housing main body 100 (forming part of the accommodating space 13). The diameter of the rod portion 42 is, for example, slightly smaller than the inner diameter of the inner surface of the housing main body 100, and is configured so that the outer surface of the rod portion 42 is guided along the inner surface when the projectile 40 is launched.

[0055] As will be described in detail later, when the igniter 20 is activated, the projectile 40 configured as described above is launched from the initial position shown in FIG. 6 and moves at high speed toward the second end 12 (downward) along the accommodation space 13 due to the energy from the igniter 20 being received by the upper surface of the piston portion 41, including the pressure-receiving surface 411A. Specifically, as shown in FIG. 6 , the piston portion 41 of the projectile 40 is accommodated inside the large-diameter cylinder portion 113 of the top holder 110 and is capable of sliding axially along the inner wall surface of the large-diameter cylinder portion 113. In this embodiment, the piston portion 41 of the projectile 40 has a generally cylindrical shape, but the shape is not particularly limited. The outer shape of the piston portion 41 can be an appropriate shape and size depending on the shape and size of the inner wall surface of the large-diameter cylinder portion 113.

[0056] [Conductor Piece] Next, the conductor piece 50 will be described. FIG. 7 is a top view of the conductor piece 50 according to the embodiment. The conductor piece 50 is a conductive metal body that constitutes part of the components of the circuit breaker 1 and forms part of a predetermined electric circuit when the circuit breaker 1 is attached to the electric circuit, and is sometimes called a bus bar. The conductor piece 50 can be formed of a metal such as copper (Cu). However, the conductor piece 50 may be formed of a metal other than copper, or may be formed of an alloy of copper and another metal. Examples of metals other than copper contained in the conductor piece 50 include manganese (Mn), nickel (Ni), platinum (Pt), etc.

[0057] In one embodiment shown in FIG. 7 , the conductor piece 50 is formed as an elongated flat piece overall, including a first connecting end 51 and a second connecting end 52 at both ends, and a cuttable portion 53 located in the middle. The first connecting end 51 and the second connecting end 52 of the conductor piece 50 are provided with connection holes 51A and 52A, respectively. These connection holes 51A and 52A are used to connect to other conductors (e.g., lead wires) in an electrical circuit. Note that the connection holes 51A and 52A of the conductor piece 50 are not shown in FIG. 6 . The cuttable portion 53 of the conductor piece 50 is positioned across the housing space 13 and is a portion that is forcibly and physically cut by the rod portion 42 of the projectile 40 in the event of an abnormality, such as an excessive current, occurring in the electrical circuit to which the circuit breaker 1 is applied. Slits 54 are formed at both ends of the cuttable portion 53 of the conductor piece 50 to facilitate cutting.

[0058] Here, the conductor piece 50 can have various shapes, and its shape is not particularly limited. In the example shown in FIG. 7 , the surfaces of the first connection end 51, the second connection end 52, and the cut portion 53 form the same plane, but this is not limited thereto. For example, the cut portion 53 of the conductor piece 50 may be connected perpendicular to the first connection end 51 and the second connection end 52 or at an angle to them. The planar shape of the cut portion 53 of the conductor piece 50 is also not particularly limited. Of course, the shapes of the first connection end 51 and the second connection end 52 of the conductor piece 50 are also not particularly limited. Furthermore, the notches 54 of the conductor piece 50 can be omitted as appropriate. In this embodiment, the cut portion 53 is cut at two locations where the notches 54 are formed, separating it from the first connection end 51 and the second connection end 52. However, the cut portion (also referred to as the cut portion) 53 is not limited thereto. It may also be configured such that the rod portion 42 cuts near the center and bends the cut ends toward the bottom container 120 to separate them.

[0059] Here, a pair of conductor piece retaining holes 105A, 105B are formed in the housing main body 100 according to the embodiment. The pair of conductor piece retaining holes 105A, 105B extend in a cross-sectional direction perpendicular to the up-down direction (axial direction) of the housing main body 100. More specifically, the pair of conductor piece retaining holes 105A, 105B extend in a straight line across the hollow portion (accommodation space 13) of the housing main body 100. The conductor piece 50 configured as described above is retained in the housing main body 100 by being inserted into the pair of conductor piece retaining holes 105A, 105B formed in the housing main body 100. In the example shown in FIG. 6 , the first connecting end 51 of the conductor piece 50 is retained by being inserted into the conductor piece retaining hole 105A, and the second connecting end 52 is retained by being inserted into the conductor piece retaining hole 105B. In this state, the cut portion 53 of the conductor piece 50 is positioned in the hollow portion (accommodation space 13) of the housing main body 100. As described above, the conductor piece 50 attached to the housing main body 100 is held in an orientation perpendicular to the extension direction (axial direction) of the accommodation space 13, with the cut portion 53 crossing the accommodation space 13. Note that the symbol L1 shown in FIG. 7 indicates the outer circumferential position of the rod portion 42 located above the conductor piece 50 when attached to the housing main body 100 of the circuit breaker 1. In this embodiment, the conductor piece 50 is installed so that the outer circumferential position L1 of the rod portion 42 roughly overlaps the positions of the notches 54 located at both ends of the cut portion 53. In this embodiment, for example, because the cross-sectional area of ​​the accommodation space 13 is larger than the cross-sectional area of ​​the cut portion 53, gaps are formed on the sides of the cut portion 53.

[0060] [Coolant Material] Next, the coolant material 60 disposed in the accommodation space 13 of the housing 10 will be described. Here, as shown in FIG. 6 , before activation of the circuit breaker 1 (igniter 20), the cut-off portion 53 of the conductor piece 50 held in the pair of conductor piece holding holes 105A, 105B in the housing main body 100 is horizontally disposed across the accommodation space 13 of the housing 10. Hereinafter, within the accommodation space 13 of the housing 10, the region (space) on the side where the projectile 40 is disposed across the cut-off portion 53 of the conductor piece 50 will be referred to as the "projectile initial placement region AR1," and the region (space) located on the opposite side of the projectile 40 will be referred to as the "arc-extinguishing region AR2." As described above, because a gap is formed on the side of the cut-off portion 53 disposed across the accommodation space 13 before activation, the projectile initial placement region AR1 and the arc-extinguishing region AR2 are not completely isolated by the cut-off portion 53, but are instead connected to each other. Of course, depending on the shape and size of the cut portion 53, the projectile initial placement area AR1 and the arc extinguishing area AR2 may be completely isolated by the cut portion 53.

[0061] The arc-extinguishing area AR2 of the accommodation space 13 is an area (space) for receiving the cut portion 53 cut by the rod portion 42 of the projectile 40 fired when the circuit breaker 1 (igniter 20) is activated. A coolant material 60 is disposed in this arc-extinguishing area AR2 as an arc-extinguishing material. The coolant material 60 is a coolant that absorbs and cools the arc and the thermal energy of the cut portion 53 that are generated when the projectile 40 cuts the cut portion 53 of the conductor piece 50, thereby suppressing the generation of an arc when the current is interrupted or extinguishing (extinguishing) any arc that occurs.

[0062] Arc-extinguishing area AR2 in circuit breaker 1 is a space for receiving cut portion 53 that has been cut from first connection end 51 and second connection end 52 of conductor piece 50 by projectile 40, and also serves as a space for effectively extinguishing the arc that is generated when projectile 40 cuts cut portion 53. In order to effectively extinguish the arc that is generated when cut portion 53 is cut from conductor piece 50, coolant material 60 is disposed in arc-extinguishing area AR2 as an arc-extinguishing material.

[0063] In one embodiment, the coolant material 60 is solid. In another embodiment, the coolant material 60 is formed from a shape-retaining material. The shape-retaining material here refers to a material that maintains a certain shape when no external force is applied and maintains its integrity (does not break apart) even if it is deformed when an external force is applied. For example, a fibrous material formed into a desired shape can be used as the shape-retaining material. In this embodiment, the coolant material 60 is formed from metal fibers, which are shape-retaining materials. Examples of metal fibers that form the coolant material 60 include at least one of steel wool and copper wool. However, the above-described embodiments of the coolant material 60 are merely examples and are not intended to be limiting. For example, the coolant material 60 may be formed from conductive materials other than metal fibers, such as carbon fibers or resin materials mixed with conductive fillers.

[0064] The coolant material 60 is formed, for example, in a generally disk shape and is placed at the bottom of the bottom container 120 .

[0065] <Operation of Circuit Breaker> Figure 8 is a diagram showing the interruption principle of the circuit breaker 1. States (A) to (D) in Figure 8 show the states when an abnormal current occurs and the circuit breaker 1 interrupts the electric circuit 90. When interrupting an abnormal current, the circuit breaker 1 operates in the following order (i) to (iv).

[0066] (i) State (A): A load current under normal conditions is passed through the conductor piece 50. Since the resistance value of the conductor piece 50 is on the order of several mΩ, it can be considered that there is almost no loss.

[0067] (ii) State (B) When an abnormal current occurs and an operating current flows through the ignition portion 21 of the igniter 20 of the circuit breaker 1, the bridge wire (resistor) 215 in the ignition portion 21 generates heat.

[0068] (iii) State (C) When the bridge wire 215 of the igniter 20 generates heat, the ignition charge filled around it ignites and burns, generating products including combustion gas. Here, the ignition part 21 of the igniter 20 is arranged so that the cleavage surface 21A faces the pressure-receiving surface 411A of the projectile 40. Therefore, the pressure (combustion energy) of the combustion gas released from the cleavage surface 21A of the ignition part 21 is transmitted to the pressure-receiving surface 411A of the piston part 41. As a result, the projectile 40 is pushed downward with great force, and the conductor piece 50 is cut by the lower end surface of the rod part 42.

[0069] (iv) State (D): The cut portion 53, cut from the conductor piece 50 by the projectile 40, is received in the arc-extinguishing area AR2, where the coolant material 60 is located. In the circuit breaker 1, the coolant material 60 is located in the arc-extinguishing area AR2. Therefore, the cut portion 53 received in the arc-extinguishing area AR2 is rapidly cooled by the coolant material 60. Even if an arc occurs at the cut portion, the coolant material 60 absorbs the arc energy, enabling the arc to be quickly and effectively extinguished. As a result, the first connection end 51 and the second connection end 52, located at both ends of the conductor piece 50, are electrically disconnected, and the predetermined electrical circuit to which the circuit breaker 1 is applied is forcibly interrupted.

[0070] <Current-Limiting Fuse and Circuit Breaker Principle> Figure 9 is a schematic diagram showing the current waveform flowing through the electrical circuit 90 when the current-limiting fuse 3 and circuit breaker 1 of the protection device 200 interrupt an abnormal current. The horizontal axis of Figure 9 represents time, and the vertical axis represents current value. An abnormal current occurs at timing A in Figure 9, and current limiting is performed by the current-limiting fuse 3 of the protection device 200 at timings B-C. While current limiting is performed by the current-limiting fuse 3, the impedance of the current-limiting fuse 3 increases, causing current to flow through the impedance element 23 and the ignition unit 21, which had previously received almost no current from the power source. This current heats the bridge wire 215 (Figure 8) of the ignition unit 21, igniting and burning the explosives around it and activating the circuit breaker 1 as described above. In Figure 9, the circuit breaker 1 begins operation at timing C, and circuit breaker 1 is completed at timing D.

[0071] In Figure 9, the dashed line indicates the case of a single current-limiting fuse. In the example of Figure 9, the power supply voltage is greater than the potential difference generated across the current-limiting fuse 3, so after the current-limiting fuse 3 limits the current at timing B-C, it is unable to completely cut off the current and is damaged at timing E, as described above.

[0072] <Interruption Test> Figure 10 is a schematic diagram showing the configuration of the test circuit. In this test, a capacitor bank was charged by a rectifier and used as a 1.7 kV and 2.0 kV DC power supply 95. The DC power supply 95 has a built-in closing machine and backup circuit breaker. In this test, current-limiting fuses 3 with DC ratings of 1.0 kV / 50 A and 1.5 kV / 200 A were used. The configuration of the protection device 200 is the same as that shown in Figure 1.

[0073] The DC rating of the circuit breaker (pyrofuse) 1 is 100V / 200A, with a maximum interrupting current of 3000A. The ignition unit 21 of the circuit breaker 1 operates when an inflow current of, for example, 1.75A continues for 0.5ms or more. The ignition unit 21 also operates when an inflow current of 1.2A continues for 2.0ms or more. Since the circuit breaker 1 preferably operates in the low-current region where the current-limiting speed of the current-limiting fuse 3 is slow, the current flowing through the ignition unit 21 is adjusted by the resistance value of the impedance element 23. If the resistance value of the impedance element 23 is too high, the current flowing through the ignition unit 21 will be too low, resulting in insufficient heat generation in the bridge wire, preventing the ignition charge from igniting and preventing the circuit breaker 1 from operating. On the other hand, if the ignition wire resistance is too low, the current will be too high, causing the circuit breaker 1 to operate faster than necessary. In this test, the impedance of the impedance element 23 was changed to adjust the current value flowing through the ignition unit 21, and the circuit breaker 1 was operated in the low current region.

[0074] [Test 1] In the test circuit of Figure 10, current-limiting fuse 3 (DC rating 1.0 kV / 50 A) and interrupter 1 (DC rating 100 V / 200 A) were connected in series, and an interruption test was conducted at 1.7 kV / 10 kA. The total voltage was measured at measurement point D1, the total current at measurement point D2, the voltage across the pyroelectric element at measurement point D3, and the ignition wire current at measurement point D4. Ignition wire 953 is a wiring that connects impedance element 23 and ignition unit 21 in parallel with current-limiting fuse 3. The resistance of impedance element 23 was 1400 Ω, and the resistance of the bridge wire in ignition unit 21 was 2 Ω.

[0075] Figure 11 shows the current and voltage waveforms from a 1.7 kV / 10 kA interruption test. As shown in Figure 11, an abnormal current occurs at t = 0 ms, and current-limiting fuse 3 arcs at approximately 2300 A, initiating current limiting. At the time of fuse arcing, an arc voltage is generated in current-limiting fuse 3, and current simultaneously flows through ignition element 21. Approximately t = 1 ms later, when the current flowing through current-limiting fuse 3 and interrupter 1 is limited to 1400 A, interrupter 1 operates, rupturing conductor piece 50 and generating an arc discharge within the pyroelectric element, generating voltage across both ends of the pyroelectric element. At approximately t = 9.5 ms, the current drops to zero as the pyroelectric element completes its operation, completing the interruption. After that, interrupter 1 takes over the entire power supply voltage, and the ignition line current gradually converges to zero.

[0076] [Test 2] In the test circuit shown in Figure 10, a current-limiting fuse 3 (DC rating: 1.5 kV / 200 A) and a circuit breaker 1 (DC rating: 100 V / 200 A) were connected in series, and a 2.0 kV / 10 kA interruption test was conducted. Test 2 was conducted in the same manner as Test 1, except that the applied voltage was changed to 2.0 kV and the resistance of the impedance element 23 to 2000 Ω. Figure 12 shows the current and voltage waveforms of the 2.0 kV / 10 kA interruption test. As shown in Figure 12, an abnormal current occurred at t = 0 ms, and the current-limiting fuse 3 arced at approximately 5100 A, initiating current limiting. At the fuse arcing timing, an arc voltage was generated in the current-limiting fuse 3, and simultaneously, current flowed through the ignition element 21. After approximately t=2.5ms, when the current flowing through the current-limiting fuse 3 and circuit breaker 1 was limited to 2200A, circuit breaker 1 operated, causing an arc to occur due to the rupture of conductor piece 50, generating a voltage across the pyroelectric. At approximately t=7.5ms, the pyroelectric operation was completed, and the current became zero, indicating that the circuit breaker was complete. After that, the circuit breaker took on the entire power supply voltage, and the ignition wire current gradually converged to zero.

[0077] [Test Results] In Test 1, the sum of the rated voltages of the current-limiting fuse 3 with a DC rating of 1.0 kV / 50 A and the circuit breaker 1 with a DC rating of 100 V / 200 A was 1.1 kV, but successful circuit breaking was achieved under the condition of 1.7 kV / 10 kA, which is 600 V higher than this value.

[0078] In Test 2, the sum of the rated voltages of the 1.5 kV / 200 A DC fuse and the 100 V / 200 A DC circuit breaker 1 was 1.6 kV. However, successful circuit breaking was achieved even at 2.0 kV / 10 kA, 400 V higher than this value. This is because the fuse and circuit breaker are combined to create a circuit breaking method that complements each other's shortcomings. Although a current-limiting fuse alone can limit current even at voltages higher than its rated voltage, it is unable to fully interrupt the current, wasting its current-limiting performance. Therefore, by connecting a circuit breaker (pyrofuse) 1, which is good at interrupting small currents, in series with the current-limiting fuse 3, it became possible to interrupt at a voltage higher than the sum of their rated voltages.

[0079] <Effects of the Embodiment> (1) The protection device 200 of the present embodiment includes a circuit breaker 1 including a conductor piece 50 that forms part of an electric circuit 90 and an igniter 20 for cutting off the conductor piece 50, and a current limiting element 3 that is connected in series with the conductor piece 50 of the circuit breaker 1 and forms part of the electric circuit. The current limiting element 3 is connected in parallel with the igniter 20 and exhibits a current limiting effect when an abnormal current flows. In addition, in the protection device 200, the igniter 20 has a higher impedance than the current limiting element 3 under normal conditions. When the current limiting element 3 exhibits a current limiting effect, a current flows through the igniter 20, which activates the igniter 20 and interrupts the current flowing in the electric circuit 90. As a result, the protection device 200 of the present embodiment can quickly limit the current using the current limiting element 3 and cut off the circuit using the circuit breaker 1 when an abnormal current occurs, thereby accurately interrupting the power supply. In particular, in this embodiment, when an abnormal current occurs, the current limiting element exerts its current limiting effect due to this abnormal current, and current flows to the ignition unit 21 of the circuit breaker 1 connected in parallel, activating the circuit breaker 1, so that the abnormal current can be interrupted without using a sensor or processor. In other words, the electrical circuit protection device 200 of this embodiment can operate sensorlessly and fully automatically.

[0080] (2) In the protection device 200 of this embodiment, the current-limiting element 3 is a current-limiting fuse. The current-limiting fuse includes a fuse element 32 that forms part of the electric circuit 90, and when an abnormal current flows through the fuse element 32, at least a portion of the fuse element 32 melts to limit the current flowing through the electric circuit 90. This allows the protection device 200 of this embodiment to cut off power when an abnormal current occurs before the abnormal current reaches its peak.

[0081] (3) In the protection device 200 of this embodiment, the current flowing through the electric circuit 90 via the current limiting element 3 and the conductor piece 50 is a direct current, and the direct current is cut off by the activation of the igniter 20. As a result, the protection device 200 of this embodiment can accurately cut off the power supply when an abnormal current occurs in the DC electric circuit.

[0082] <Second embodiment> Figure 13 is a diagram showing the configuration of an electric circuit protection device 200A according to a second embodiment. This embodiment differs from the first embodiment in that it is provided with a varistor 80 connected in series with the igniter 20, but the other configurations are the same. For this reason, the same elements are given the same reference numerals, and repeated explanations will be omitted.

[0083] In the aforementioned electric circuit protection device 200, current may continue to flow through the ignition wire 953 after the operation of the interrupter 1 is completed. The electric circuit protection device 200A is an example of a configuration for interrupting this possible follow-on current through the ignition wire 953. As shown in FIG. 13 , the resistance value of the varistor 80 changes depending on the voltage applied to the varistor itself; when the applied voltage is low, the resistance value becomes high, and when the applied voltage is high, the resistance value becomes low. Utilizing this characteristic, the protection device 200A of this embodiment can interrupt the follow-on current of the ignition wire current (i.e., the current flowing through the ignition unit 21). FIG. 14 is a diagram showing current and voltage waveforms during interruption by the electric circuit protection device 200A of the second embodiment. At around time 2.4 ms, the current (ignition wire current) C1 flowing through the ignition wire converges to 0 A, interrupting the follow-on current.

[0084] 15 is a diagram showing the configuration of an electric circuit protection device 200B according to a third embodiment. This embodiment is different from the first embodiment in that a second current limiting element 3B and a second impedance element 23B are connected in parallel between the impedance element 23 and the ignition unit 21, but the other configurations are the same. For this reason, the same elements are denoted by the same reference numerals, and a repeated description will be omitted.

[0085] The protection device 200B of this embodiment uses the current limiting element 3 as a first current limiting element and further includes a second current limiting element 3B and a third current limiting element 3C. The second current limiting element 3B and the third current limiting element 3C are the same as the first current limiting element and are current-limiting fuses in this embodiment. The protection device 200B of this embodiment uses the impedance element 23 as a first impedance element and further includes a second impedance element 23B.

[0086] 15 , in the protection device 200B of this embodiment, a second current limiting element 3B is connected between the conductor piece 50 of the circuit breaker 1 and the second end 232 of the first impedance element 23. Then, a second impedance element 23B is connected in parallel with the second current limiting element 3B between the second end 232 of the first impedance element 23 and the first end 211 of the ignition unit 21. Furthermore, the protection device 200B of this embodiment includes a third current limiting element 3C connected between the second impedance element 23B and the first end 211 of the ignition unit 21.

[0087] In the protection device 200B, the impedances of the first impedance element 23, the second impedance element 23B, and the ignition unit 21 are set sufficiently higher than the impedance of the first current limiting element 3 during steady operation (normal operation). Therefore, during steady operation, current supplied from the power source flows to the load 91 via the current limiting element 3 and the conductor piece 50 of the circuit breaker 1, with almost no current flowing through the impedance element 23. When an abnormal current occurs due to a lightning strike, a short circuit, or the like, and the first current limiting element 3 performs a current limiting function, the impedance of the first current limiting element 3 increases, causing current to flow through the first impedance element 23. Here, because the impedances of the second impedance element 23B and the ignition unit 21 are set higher than the impedance of the second current limiting element 3B, the current through the first impedance element 23 flows to the second current limiting element 3B. When this current causes the second current limiting element 3B to perform a current limiting function, the impedance of the second current limiting element 3B increases. As a result, the current passing through the first impedance element 23 flows to the ignition unit 21 via the second impedance element 23B and the third current limiting element 3C, and the ignition unit 21 is activated by this current.

[0088] As described above, the protection device 200B of this embodiment includes multiple current-limiting elements 3, 3B, and 3C. Because it takes time for the current-limiting elements 3 and 3B to exert their current-limiting effect, the time until the ignition unit 21 is activated can be adjusted. The reason for delaying the rise of the current passing through the ignition wire relative to the current-limiting start time is to limit the abnormal current to the limit of the current-limiting performance by the current-limiting fuse 3 and to interrupt the current limited to that limit by the circuit breaker 1. This maximizes the current-limiting performance of the current-limiting fuse 3 and the current-interrupting performance that can be interrupted by the circuit breaker 1, enabling a higher current to be interrupted. Furthermore, after the operation of the circuit breaker 1 is completed, the current that may continue to flow through the ignition wire 953 can be interrupted by the second current-limiting element 3B and the third current-limiting element 3C.

[0089] Next, a method for selecting each element in this embodiment will be described. First, the current value Ia of the operating current input to the ignition unit 21 and the time Δt0 from when the operating current of this current value Ia is input to the ignition unit 21 until the ignition unit 21 activates are determined. Based on this time Δt0, the time Δta from when the first current limiting element 3 arcs until the third current limiting element starts to conduct is determined. Furthermore, the resistance value R1 of the first impedance element 23 is determined so that the second current limiting element 3B can pass a current that can be interrupted within the time Δta. The resistance value R2 of the second impedance element 23B is determined so that the operating current of the current value Ia can pass through the ignition unit 21. Then, the third current limiting element 3C is selected so that it will not blow out until the ignition unit 21 activates.

[0090] 16 is a diagram showing an example of the rated voltages and rated currents of the first current limiting element 3, the second current limiting element 3B, and the third current limiting element 3C. For example, the current value Ia of the operating current input to the ignition unit 21 is set to 1.2 A, and the time Δt0 from when this operating current is input to the ignition unit 21 until the ignition unit 21 activates is set to 5 to 6 ms. Next, the resistance value R1 of the first impedance element 23 is set to 300 Ω so that the second current limiting element 3B can pass a current (2 A) that it can interrupt in 5 ms. The resistance value R2 of the second impedance element 23B is set to 100 Ω so that the ignition unit 21 can pass a 1.2 A operating current. The third current limiting element 3C is then selected so that it will not blow out until the ignition unit 21 activates.

[0091] 17 is a diagram showing current and voltage waveforms during interruption in the electric circuit protection device 200B of the third embodiment. In the protection device 200 without the second current limiting element 3B, the third current limiting element 3C, and the second impedance element 23B, the time from arcing of the current limiting element 3 to activation of the ignition unit 21 was approximately 0.6 to 1.4 ms, whereas in the protection device 200B of this embodiment, this time was extended to 5 ms. This allows the protection device 200B of this embodiment to maximize the current-limiting performance of the current-limiting fuse 3 and the current interruption performance of the interrupting device 1, thereby enabling higher current interruption. While this embodiment illustrates an example in which the current-limiting fuse 3C is provided, this is not limiting, and the current-limiting fuse 3C may be omitted.

[0092] <Fourth embodiment> Figure 18 is a diagram showing the configuration of an electric circuit protection device 200C according to a fourth embodiment. This embodiment differs from the first embodiment in that it includes a switching element 7 connected in parallel with the current limiting element 3 and the circuit breaker 1, but the other configurations are the same. For this reason, the same elements are given the same reference numerals, and repeated description will be omitted. Note that the other configurations are not limited to those of the first embodiment, and may be the same as those of the second to third embodiments.

[0093] 18 , the protection device 200C of this embodiment includes a switching element 7 connected in parallel with the current limiting element 3 and the circuit breaker 1. The switching element 7 forms at least a part of a parallel path 955 that is parallel to the main path 954 in which the current limiting element 3 and the circuit breaker 1 are provided.

[0094] The switching element 7 is configured to close the parallel path 955 when no abnormal current is occurring (normal operation) and pass at least a portion of the power supplied from the power source to the load 91 through the parallel path 955. When an abnormal current is occurring (abnormal operation), the switching element 7 opens the parallel path 955. At this time, the impedance of the switching element 7 increases, and all of the abnormal current is diverted to the main path 954. As a result, the current limiting element 3 and the circuit breaker 1 interrupt the electric circuit 90 and protect the electric circuit 90, as in the above-described embodiment.

[0095] The switching element 7 is, for example, a switch whose opening and closing is controlled by a control circuit. The switching element 7 may also be a current interruption device (for example, a pyro-fuse) whose operation is controlled by a control circuit. The switching element 7 is not limited to a device controlled by a control circuit, but may also be a switch that is set to a closed state under normal conditions and that, when an overcurrent (abnormal current) occurs, opens the parallel path 955 by electromagnetic repulsion or the like caused by the overcurrent. The main path 954 and the parallel path 955 may each be provided with a device similar to the protection devices 200 to 200B of the first to third embodiments.

[0096] In this way, by providing a parallel path 955 in parallel with the main path 954 and dividing the current supplied from the power source to the load 91 between the main path 954 and the parallel path 955, it is possible to increase the power supplied to the load 91 under normal conditions even with a current limiting element 3 or a circuit breaker 1 having a small rated capacity.

[0097] Fig. 19 is a diagram showing a modified example of an electric circuit protection device 200C according to the fourth embodiment. The electric circuit protection device 200C of Fig. 19 differs from that of Fig. 18 in that a linking contact 71 that links the opening and closing of the switching element 7 is provided in the power path in which the current limiting element 3 and the circuit breaker 1 are provided in series. The other configuration is the same as that of the fourth embodiment described above, and therefore the same reference numerals are used and repeated description will be omitted.

[0098] The switching element 7 is a switch including a contact 72 provided in the parallel path 955 and a linking contact 71 that opens and closes in linkage with the contact 72. The linking contact 71 is provided between the connection part 96 of the main path 954 and the parallel path 955 and the current limiting element 3. However, the linking contact 71 may be provided at another location on the power path in which the current limiting element 3 and the circuit breaker 1 are provided, as long as it is within the range in which the parallel path 955 is connected in parallel, that is, on the power path in which the current limiting element 3 and the circuit breaker 1 are provided and between the connection part 96 and the connection part 97.

[0099] Under normal conditions, the switching element 7 closes the contact 72 of the parallel path 955 and opens the linking contact 71 of the main path 954, thereby supplying power normally supplied from the power source to the load 91 via the parallel path 955. When an abnormal current occurs, the switching element 7 opens the contact 72 of the parallel path 955 and closes the linking contact 71 of the main path 954, thereby diverting all of the abnormal current to the main path 954. As a result, the current limiting element 3 and the circuit breaker 1 break the electric circuit 90 and protect the electric circuit 90, as in the above-described embodiment. In this way, the protection device 200C of this modified example can switch the current flow path from the normal state when an abnormal current occurs, thereby accurately breaking the abnormal current.

[0100] Although the embodiments of the electrical circuit protection device according to the present disclosure have been described above, each aspect disclosed herein can be combined with any other feature disclosed herein.

[0101] Fifth Embodiment FIG. 20 is a diagram showing the configuration of an electric circuit protection device 200D according to a fifth embodiment. In the electric circuit protection device 200D of this embodiment, the igniter 20 includes an ignition line circuit including a first impedance element 24, a second impedance element 25, and a second current limiting element 3B connected in series, and a first varistor 81 connected in parallel with the second impedance element 25 and the second current limiting element 3B. The ignition line circuit of the igniter 20 also includes a second varistor 82 connected in parallel with the second current limiting element 3B. This embodiment differs from the third embodiment in the configuration of the ignition line circuit, but the other configurations are the same. Therefore, in this embodiment, the same elements are denoted by the same reference numerals, and a repeated description will be omitted. The first current limiting element 3B is also referred to as a first current limiting fuse, and the second current limiting element 3B is also referred to as a second current limiting fuse 3B.

[0102] 20 , in the protection device 200D, the first end 301 of the first current-limiting fuse 3 is connected to the first end 241 of the first impedance element 24. Furthermore, the second end 242 of the first impedance element 24 is connected to the first end 251 of the second impedance element 25 and the first end 811 of the first varistor 81. The second end 812 of the first varistor 81 is connected to a point 921 between the second end 302 of the first current-limiting fuse 3 and the conductor piece 50.

[0103] The second end 252 of the second impedance element 25 is connected to the first end 821 of the second varistor 82 and the first end 3B1 of the second current-limiting fuse 3B. The second end 822 of the second varistor 82 is connected to the first end 211 of the ignition unit 21. The second end 3B2 of the second current-limiting fuse 3B is connected to a connection point 921 between the second end 302 of the first current-limiting fuse 3 and the conductor piece 50.

[0104] 21 to 23 are diagrams illustrating the interruption operation of the protection device 200D. (1) in FIG. 21 illustrates steady-state operation (normal). In the ignition line circuit including the first impedance element 24, the second impedance element 25, the second current-limiting fuse 3B, the first varistor 81, the second varistor 82, and the ignition unit 21, the impedance from the first end 241 of the first impedance element 24 to the connection point 921 is set sufficiently higher than the impedance of the first current-limiting fuse 3 during steady-state operation (normal). Therefore, during steady-state operation, the current supplied from the power source flows to the load 91 via the first current-limiting fuse 3 and the conductor piece 50 of the interrupter 1, with almost no current flowing through the first impedance element 24. In other words, the shaded portion in (1) in FIG. 21 is in the OFF state.

[0105] 21 (2) shows the case where an abnormal current occurs (when an accident occurs) due to a lightning strike, a short circuit, etc. As shown in (2), when an abnormal current flows through the first current-limiting fuse 3, the first current-limiting fuse 3 exerts a current-limiting effect.

[0106] 22(3) shows a state in which the first current-limiting fuse 3 has blown and is performing a current-limiting function. In this case, the impedance of the first current-limiting fuse 3 increases, causing a current to flow toward the first impedance element 24. The current passing through the first impedance element 24 flows to the connection point 921 via the second impedance element 25 and the second current-limiting fuse 3B.

[0107] Here, by using the first varistor 81 as a constant voltage source, a constant current is set to flow through the second impedance element 25 and the second current-limiting fuse 3B. Because a constant current flows through the second current-limiting fuse 3B, the time until it blows or cuts off can be set arbitrarily based on its fusing characteristics. Therefore, the circuit can be designed so that the time until the second current-limiting fuse 3B blows or cuts off is long enough for the first current-limiting fuse 3B to fully limit the current, and so that current begins to flow to the ignition unit 21 after the second current-limiting fuse 3B blows or cuts off. By connecting the second current-limiting fuse 3B in parallel with the second varistor 82 and the ignition unit 21, it is possible to prevent current from flowing to the ignition unit 21 until the second current-limiting fuse 3B blows or cuts off ( FIG. 22 (4)) and the second varistor 82 becomes conductive.

[0108] (5) in Figure 23 shows the state in which the second current-limiting fuse 3B has interrupted the current. When the second current-limiting fuse 3B enters the interrupted state, the limiting voltage of the first varistor 81 is applied to the second varistor 82. When the voltage applied to the second varistor 82 exceeds the varistor voltage at this time, the second varistor 82 becomes conductive and current flows to the ignition unit 21. When this current activates the ignition unit 21, the circuit breaker 1 cuts off the conductor piece 50 as described above. (6) in Figure 23 shows the state in which the circuit breaker 1 has operated and the interruption of the current flowing in the electric circuit 90 has been completed.

[0109] As described above, the protection device 200D of this embodiment includes the current-limiting element 3B, and because it takes time for the current-limiting element 3B to fuse and break, it is possible to adjust the time until the ignition unit 21 is activated. For example, by delaying the rise of the current passing through the ignition wire relative to the current-limiting start time of the first current-limiting fuse 3, the current-limiting fuse 3 limits the abnormal current to the limit of its current-limiting performance, and the current limited to that limit is then broken by the circuit breaker 1. This makes it possible to make the most of the current-limiting performance of the current-limiting fuse 3 and the current-breaking performance that can be broken by the circuit breaker 1, thereby making it possible to break a higher current.

[0110] <Interruption Test> Figure 24 is a schematic diagram showing the configuration of a test circuit. In this test, a capacitor bank was charged by a rectifier and used as a 600V and 700V DC power supply 95. The DC power supply 95 includes a closing device and a backup circuit breaker. In this test, the rated voltage of the first current-limiting fuse 3 is 600V, and the rated voltage and rated current of the second current-limiting fuse 3B are 250V and 250mA, respectively. The rated voltage of the interrupter 1 is 100V. The impedance of the first impedance element 24 is 149Ω, the impedance of the second impedance element 25 is 129Ω, the varistor voltage of the first varistor 81 is 200V, and the varistor voltage of the second varistor 82 is 47V. The configuration of the protection device 200D is the same as that shown in Figure 20.

[0111] [Test 1] In the test circuit of Figure 24, an interruption test was performed by applying 600 V to the series-connected first current-limiting fuse 3 and interrupter 1. The total voltage was measured at measurement point M1, the voltage across both ends of interrupter 1 (pyro voltage) at measurement point M2, the total current at measurement point M3, the current flowing through second current-limiting fuse 3B (second fuse current) at measurement point M4, and the ignition wire current at measurement point M5.

[0112] Figure 25 shows the total voltage, total current, and pyroelectric voltage in a 600V interruption test, and Figure 26 shows the second fuse current, ignition wire current, and pyroelectric voltage in a 600V interruption test. In Figures 25 and 26, an abnormal current occurs at t = 0 ms, first current-limiting fuse 3 arcs at t = 1.2 ms, and current begins to flow through second current-limiting fuse 3B. Then, second current-limiting fuse 3B enters an interrupted state at t = 5.4 ms, and circuit breaker 1 operates around t = 6.1 ms, completing the interruption.

[0113] [Test 2] In the test circuit shown in Figure 24, an interruption test was conducted by applying 700 V to the first current-limiting fuse 3 and circuit breaker 1 connected in series. Other than this voltage, the conditions were the same as those in Test 1. Figure 27 shows the total voltage, total current, and pyroelectric voltage in the 700 V interruption test, and Figure 28 shows the second fuse current, ignition wire current, and pyroelectric voltage in the 700 V interruption test. In Figures 27 and 28, an abnormal current occurs at t = 0 ms, the first current-limiting fuse 3 arcs at t = 1.2 ms, and current begins to flow through the second current-limiting fuse 3B. Then, the second current-limiting fuse 3B enters an interruption state at t = 5.4 ms, and the circuit breaker 1 operates around t = 6.1 ms, completing the interruption.

[0114] As described above, the protection device 200D of this embodiment can interrupt the current at a predetermined timing when an abnormal current occurs. Furthermore, the protection device 200D of this embodiment can operate the circuit breaker 1 at the same predetermined timing even when the voltage applied to the protection device 200D changes. This is because the first varistor 81 keeps the voltage applied to the second current-limiting fuse 3B and the current flowing through the second current-limiting fuse 3B constant regardless of the test voltage, thereby stabilizing the timing at which the second current-limiting fuse 3B enters an interrupted state and supplies the ignition wire current regardless of the test voltage. For example, if an impedance element is used instead of a varistor to adjust the time until the ignition unit 21 is activated, a change in the voltage applied to the protection device would also change the voltage applied to the second current-limiting fuse 3B, changing the timing at which the circuit breaker 1 operates. Therefore, in a configuration using an impedance element, the value of the impedance element must be designed according to the voltage applied to the protection device, which may reduce robustness against the test voltage. In contrast, the protection device 200D of this embodiment can operate the circuit breaker 1 at the same predetermined timing even when the voltage applied to the protection device 200D changes, thereby improving robustness against test voltages. In other words, the range of voltages that the protection device 200D can handle can be expanded.

[0115] 1: Breaker device 3, 3B, 3C: Current limiting element (current limiting fuse) 7: Switching element 10: Housing 11: First end 12: Second end 13: Storage space 20: Igniter 21: Ignition portion 21A: Cleavage surface 22: Igniter body 23, 23B: Impedance element 24: First impedance element 25: Second impedance element 31: Housing 32: Fuse element 33: Arc-extinguishing sand 40: Projectile 41: Piston portion 42: Rod portion 50: Conductor piece 60: Coolant material 71: Linking contact 72: Contact 80: Varistor 81: First varistor 82: Second varistor 90: Electrical circuit 91: Load 100: Housing body 200, 200A, 200B, 200C, 200D: Electrical circuit protection device

Claims

1. An electric circuit protection device comprising: a current interruption device having a conductor piece that forms part of an electric circuit and an igniter for cutting off the conductor piece; and a current limiting element that is connected in series with the conductor piece of the current interruption device to form part of the electric circuit, and is connected in parallel with the igniter to exert a current limiting effect when an abnormal current flows, wherein the igniter has a higher impedance than the current limiting element under normal conditions, and when the current limiting element exerts its current limiting effect, a current flows through the igniter, which activates the igniter and cuts off the current flowing in the electric circuit.

2. The electrical circuit protection device according to claim 1, wherein the current-limiting element is a current-limiting fuse that includes a fuse element that forms part of the electrical circuit, and that melts at least a portion of the fuse element when the abnormal current flows through the fuse element, thereby limiting the current flowing through the electrical circuit.

3. The electrical circuit protection device of claim 1 further comprising a varistor connected in series with said igniter.

4. The electric circuit protection device according to claim 1, wherein the current flowing through the electric circuit via the current-limiting element and the conductor piece is a direct current, and the direct current is interrupted by the activation of the igniter.

5. The electric circuit protection device according to claim 1, further comprising a switching element connected in parallel with the current limiting element and the current interrupting device and forming at least a part of a parallel path parallel to the current limiting element and the current interrupting device, wherein the switching element closes the parallel path under normal conditions and opens the parallel path when an abnormal current occurs.

6. An electric circuit protection device as claimed in claim 5, wherein a linking contact that links the switching of the switching element is provided in the range where the parallel path is connected in the power path in which the current limiting element and the current interruption device are connected in series.

7. An electric circuit protection device according to any one of claims 1 to 6, wherein the igniter comprises an impedance element and an ignition unit that is activated by a current flowing through the impedance element.

8. The electric circuit protection device according to claim 7, wherein a first end of the current limiting element is connected to a first end of the impedance element, a second end of the current limiting element is connected to the conductor piece, a second end of the impedance element is connected to a first end of the ignition unit, and a second end of the ignition unit is connected between the second end of the current limiting element and the conductor piece.

9. The electric circuit protection device according to claim 8, wherein the current limiting element is a first current limiting element, the impedance element is a first impedance element, a second current limiting element is connected between the conductor piece of the current interruption device and a second end of the first impedance element, and a second impedance element is connected in parallel with the second current limiting element between the second end of the first impedance element and the first end of the ignition part.

10. The electrical circuit protection device of claim 9, further comprising a third current limiting element connected between said second impedance element and the first end of said ignition portion.

11. An electric circuit protection device as claimed in any one of claims 2 to 4, further comprising a switching element connected in parallel with the current limiting element and the current interruption device and forming at least a part of a parallel path parallel to the current limiting element and the current interruption device, wherein the switching element closes the parallel path under normal conditions and opens the parallel path when an abnormal current occurs.

12. The electric circuit protection device according to claim 11, wherein a linking contact that links the switching of the switching element is provided in the range where the parallel path is connected in the power path in which the current limiting element and the current interruption device are connected in series.

13. The electric circuit protection device according to claim 8, comprising: the current limiting element is a first current limiting element; the impedance element is a first impedance element; a second impedance element having a first end connected to the second end of the first impedance element; a second current limiting element having a first end connected to a second end of the second impedance element opposite the first end and a second end connected to the conductor piece; a first varistor connected in parallel with the second impedance element and the second current limiting element between the conductor piece and the second end of the first impedance element; and a second varistor having one end connected between the second end of the second impedance element and the first end of the second current limiting element and the other end connected to the first end of the ignition section.

14. An electric circuit protection method implemented by a current interruption device having a conductor piece that forms part of an electric circuit and an igniter for cutting the conductor piece, and a current limiting element connected to the current interruption device, wherein the current limiting element, which is connected in series with the conductor piece of the current interruption device to form part of the electric circuit and is connected in parallel with the igniter, exerts a current limiting effect when an abnormal current flows, and the igniter, which has a higher impedance than the current limiting element under normal conditions, is activated by current flowing through the igniter when the current limiting element exerts its current limiting effect, thereby interrupting the current flowing in the electric circuit.

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