KR100734668B1 - PTC current limiting device - Google Patents

Abstract

The present invention relates to a PTC fault current limiter provided with protection means for the PTC element. According to the present invention, a PTC fault current limiter for current-limiting current using PTC characteristics, the PTC element; A pair of electrodes impregnated in the PTC element; And a pair of current leads connected to the electrodes to energize the electrodes with a circuit. Impregnating the electrode into the PTC element prevents separation between the PTC element and the electrode due to the electromagnetic repulsion force generated between the electrodes by the initial overcurrent before the current-limiting action and the repulsive force caused by the magnetic field induced by the electrode, Concentration of the electric field can be alleviated to prevent burnout of the PTC element.

PTC, fault current limiter, electric field, PTC polymer, electrode

Description

PTC current limiter {PTC current limiting device}

The following drawings attached to this specification are illustrative of preferred embodiments of the present invention, and together with the detailed description of the invention to serve to further understand the technical spirit of the present invention, the present invention is a matter described in such drawings It should not be construed as limited to.

1 is a cross-sectional view showing a PTC fault current limiter according to the prior art.

2 is a cross-sectional view showing the flow of current in a PTC fault current limiter according to the prior art.

3 is a cross-sectional view showing the state of the electric field formed after the current-limiting action in the PTC current-limiter according to the prior art.

4 is a sectional view showing a PTC fault current limiter according to a preferred embodiment of the present invention.

Fig. 5 is a sectional view showing a PTC fault current limiter according to another embodiment of the present invention.

6 is a cross-sectional view showing the state of the electric field formed after the current-limiting action in the PTC current-limiter of FIG.

Fig. 7 is a sectional view showing a PTC fault current limiter according to another embodiment of the present invention.

Fig. 8 is a sectional view showing a PTC fault current limiter according to still another embodiment of the present invention.

Fig. 9 is a sectional view showing a PTC fault current limiter according to still another embodiment of the present invention.

Fig. 10 is a sectional view showing a PTC fault current limiter according to still another embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

10, 13 ... PTC elements 20a, 20b, 21a, 21b, 22a, 22b, 25a, 25b ... electrodes

23a, 23b ... auxiliary electrode 24a, 24b ... main electrode

30, 31a, 31b ... current lead 11 ... first PTC element layer

12 ... second PTC element layer

The present invention relates to a PTC limiter, and more particularly, to a PTC limiter that can be used without damaging the PTC element when an accident current flows in the current limiter using the PTC element.

In general, as a countermeasure against short-circuit currents in low and high voltage systems, circuit breakers and current limiters are widely used.

The current limiter is to limit and cut off the overcurrent and the short circuit current generated in the power system. In general, the function can be achieved by using a positive temperature coefficient (PTC) element.

A material having PTC characteristics has a low resistance at room temperature, and thus allows a good current to pass through. However, if the ambient temperature rises or a current exceeding the allowable value is generated and heats itself, the resistance may increase rapidly by several hundred times or more, thereby limiting the current. Therefore, in the case of constructing a circuit element using this, it is possible to protect various circuits when the temperature rises.

1 is a cross-sectional view showing a PTC fault current limiter according to the prior art. Referring to FIG. 1, the PTC fault current limiter according to the prior art is a PTC element 1 having a current-limiting function, electrodes 2a and 2b provided to interpose the PTC element 1, and current leads connected to the electrodes 2a and 2b. (3a, 3b). When a steady current is applied from the power system through the current leads 3a and 3b, the current proceeds through the current limiter. If an overcurrent is applied due to an accident such as a short circuit, the PTC element 1 generates heat, thereby causing a rapid increase in resistance. Thus, the PTC fault current limiter limits the overcurrent.

The PTC fault current limiter according to the prior art is applied with an initial overcurrent of 1 kA or more before the current limiting action. This initial overcurrent flows to the PTC element 1 through the electrodes 2a and 2b, at which time the current is concentrated at the interface between the PTC element 1 and the electrode. Then, a contact repulsion force is generated between the electrodes 2a and 2b and the fine contacts of the PTC element 1. Therefore, there is a problem in that repulsive force acts on the joint surfaces of the electrodes 2a and 2b and the PTC element 1 and separation and breakage of the PTC joint surfaces occur.

On the other hand, referring to Figure 2, the PTC fault current limiter according to the prior art, the current flowing in both electrodes (2a, 2b) immediately before the current limiting action of the PTC current limiter flows in parallel to each other in the opposite direction. When a current is applied, a magnetic field is generated by the current flowing through the electrodes 2a and 2b. The parallel flowing currents are reversed, and thus a magnetic field acting as a repulsive force is generated. The repulsive force separates the PTC element 1 and the electrodes 2a and 2b and can damage the PTC element 1.

In addition, after a current-limiting action, when an accidental high voltage is applied to both ends of the electrodes 2a and 2b, an electric field formed from the electrodes 2a and 2b toward the PTC element 1 is concentrated at the edge of the electrode as shown in FIG. It proceeds through the end of the PTC element 1 interposed between the electrodes 2a and 2b. As a result, the electric field is densely formed. Therefore, arcs are more likely to occur, resulting in burnout of the PTC element 1.

The present invention has been made to solve the above problems, PTC PTC current limiter, PTC current limiting to prevent the occurrence of the repulsive force by the magnetic field induced to the electrode and the electromagnetic repulsion force generated on the joint surface by the initial overcurrent before the current-limiting action The purpose is to provide a group.

In addition, an object of the present invention is to provide a PTC fault current limiter which can prevent separation of the PTC element and the electrode despite the repulsive force as described above.

Moreover, an object of this invention is to provide the PTC fault current limiter which relieves concentration of the electric field which arises in the edge part of an electrode immediately after a current-limiting action.

PTC fault current limiter according to the present invention for achieving the above object, PTC current limiter using a PTC characteristic to limit the current, PTC element having a PTC characteristic that the resistance increases when the temperature rises; A pair of electrodes impregnated at a predetermined distance in the PTC element; And a pair of current leads connected to the electrode and extending out of the PTC element to energize the electrode with an external circuit. By impregnating the electrode in the PTC element in this manner, the electrode is not separated and damaged despite the repulsive force due to the electromagnetic repulsion force or the magnetic field.

According to the present invention, it is preferable that the electrode is rounded at a corner with a predetermined curvature. Therefore, it is possible to reduce the concentration of the electric field at the edge of the electrode to prevent arc and flashover.

According to another embodiment of the present invention, the pair of current leads are preferably arranged alternately. In this case, the direction of the current flowing through the two electrodes becomes the same direction, and the attraction force acts, thereby preventing the repulsive force of the electrode due to the overcurrent.

According to another aspect of the present invention, a PTC fault current limiter for current-limiting current using a PTC characteristic, comprising: a first PTC element layer; A pair of auxiliary electrodes provided with surface irregularities and provided to interpose the first PTC device layer; A pair of main electrodes connected to the auxiliary electrode; A pair of current leads connected to the main electrode to conduct electricity with the circuit; And a second PTC device layer provided to surround the first PTC device layer, the auxiliary electrode, and the main electrode.

According to still another aspect of the present invention, a PTC current limiter for current-limiting current using PTC characteristics, comprising: a pair of electrodes provided to surround one electrode with another; A PTC element interposed between the pair of electrodes; And a pair of current leads connected to the electrodes for conducting the electrodes to the circuit.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms or words used in the specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

4 is a cross-sectional view schematically showing a PTC fault current limiter according to a preferred embodiment of the present invention.

Referring to FIG. 4, the PTC fault current limiter according to the present embodiment includes a PTC element 10, electrodes 20a and 20b impregnated in the PTC element 10, and current leads 30 connected to the electrodes 20a and 20b. Include.

As described above, the PTC element 10 is an element that suppresses overcurrent in the power system by rapidly increasing the electrical resistance at a specific temperature value as the ambient temperature rises. The PTC element 10 may use an element having proper physical properties according to the use environment, such as a rated voltage and a fault current to be cut off. In this embodiment, the resistivity is 100 Ωm or less at 25 ° C., and Joule heat is generated due to current supply. At the switching temperature, an element having a specific resistance of 105 times or more of the specific resistance at 25 ° C is used. However, it is a matter of course that the present invention is not limited to a PTC device having such a resistance characteristic.

According to the present embodiment, the PTC element 10 is preferably made of a polymer having PTC characteristics. The PTC polymer has a configuration in which a conductive filler is mixed with a crystalline or semicrystalline polymer having an amorphous region and a crystalline region. Alternatively, the polymer may be prepared by dissolving in a solvent and adding and mixing a conductive filler.

Preferably, an inorganic additive may be further added to the PTC polymer to further improve low resistance at room temperature and high resistance at high temperature. More preferably, antioxidants may be further added to prevent oxidation of the PTC polymer.

When a certain amount of current is supplied to the PTC polymer and Joule heat is generated, the PTC polymer is changed from a room temperature state to a high temperature state. As the temperature increases, the polymer is accompanied by volume expansion as the crystal region becomes amorphous, whereby the position of the conductive filler is shifted and the connection state is sporadically disconnected, thereby rapidly increasing the overall resistance of the device.

The PTC fault current limiter according to the present embodiment includes a pair of electrodes 20a and 20b impregnated in the PTC element 10 prepared as described above. The electrodes 20a and 20b are made of a metal-based material such as copper foil, but fine surface roughness is preferably formed. The surface unevenness is for the electrode 20 to be impregnated in the PTC element 10 to reduce the contact resistance at the interface in contact with the PTC element 10 to conduct a larger load current.

The surface irregularities may be generated by surface treatment of a metal surface, for example, by electroplating or etching. However, the present invention is not limited thereto, and the method of forming the surface irregularities may be employed by various modifications by those skilled in the art.

Preferably, the pair of electrodes 20a and 20b are disposed to face each other. In addition, the electrodes 20a and 20b may be constituted by copper foils of multiple layers having different resistances, thereby making the current limiting of the PTC current limiter more effective.

On the other hand, the electrodes 20a and 20b may be impregnated into the PTC device 10 in various ways. For example, the prepared PTC polymer may be pulverized and then subjected to high temperature press molding to include the electrodes 20a and 20b having surface irregularities, so that the electrodes 20a and 20b may be impregnated into the PTC device.

Alternatively, the prepared PTC polymer may be injection molded to include the electrodes 20a and 20b having surface irregularities, so that the electrodes 20a and 20b may be impregnated into the PTC device.

As another alternative, the polymer may be dissolved in a solvent and then mixed with a conductive filler and an additive to prepare a PTC polymer, and the surface irregularities may be formed to be impregnated by molding the prepared electrode.

In general, when the portion of the PTC element 10a interposed between the electrodes due to overcurrent acts as a current, an arc occurs instantaneously between the interfaces with the electrodes 20a and 20b, and the PTC element 10 is likely to be burned out due to the arc. . Therefore, if the original performance of the PTC element 10 is not exhibited, and the above process is repeated, the performance is further lowered, making it impossible to use. However, the PTC device 10 formed by wrapping and molding the electrodes 20a and 20b as in the present invention may have instantaneous impact energy generated at the interface between the PTC device 10 and the electrodes 20a and 20b during the operation of the PTC device 10. Instantly absorbs the initial arc and extinguishes it. Therefore, arc and noise are hardly generated.

In addition, when the initial overcurrent before the current-limiting action of the current limiter is applied to the current limiter, an electron repulsion force is generated at the junction between the electrodes 20a and 20b and the PTC element 10 and between the two electrodes 20a and 20b. At this time, since the electrodes 20a and 20b are impregnated in the PTC element 10 as described above, the electrodes 20a and 20b generated due to the repulsive force of the bonding surface between the electrodes 20a and 20b and the PTC element 10. And separation and separation of the PTC element 10 can be prevented.

According to the present embodiment, the PTC fault current limiter includes a current lead 30 connected to the electrodes 20a and 20b to energize the circuit. The current lead 30 is manufactured by using a metal-based material, and it is preferable to determine the size by calculating the current carrying capacity so as not to exceed the temperature allowed for system current.

Figure 5 shows a PTC fault current limiter according to another embodiment of the present invention. In FIG. 5, the same reference numerals as in the above-described drawings indicate the same members having the same functions, and thus detailed description thereof will be omitted.

Referring to FIG. 5, the PTC fault current limiter according to the present embodiment includes electrodes 21a and 21b having edges 21 'rounded at corners with a predetermined curvature. Preferably, the curvature may be manufactured to have a radius of 1 mm or more, but the present invention is not limited to this value. The rounded electrodes 21a and 21b relax the concentration of the electric field at the corners.

6 is a view illustrating a state in which an electric field is formed in the PTC fault current limiter of FIG. 5. Hereinafter, FIG. 6 will be described with reference to FIG. 3. In FIG. 3, the electric field is concentrated at the angled edges of the electrodes 2a and 2b after the current-limiting action. The electric field is concentrated through the PTC element 1 interposed only between the electrodes 2. However, in FIG. 6, the edges of the electrodes 21a and 21b have rounded ends 21 ′, and the electric field is evenly distributed at the rounded corners. Further, a gentler electric field is formed through the PTC elements 10 surrounding the electrodes 21a and 21b and their surroundings. Therefore, it is possible to prevent burnout of the PTC element 10 due to arc and flashover due to the concentrated electric field.

Alternatively, the electrode may be configured in the form of a sphere substantially as shown in FIG. The electrodes 22a and 22b configured in the substantially spherical shape can further alleviate an electric field formed around the electrode. Meanwhile, in FIG. 7, the same reference numerals as in the above-described drawing indicate the same members having the same function.

8 is a cross-sectional view showing a PTC fault current limiter according to another embodiment of the present invention. In FIG. 8, the same reference numerals as in the previous drawings indicate the same members having the same functions, and thus, detailed description thereof will be omitted.

Referring to FIG. 8, the PTC fault current limiter according to the present embodiment is arranged with a pair of current leads 31 a and 31 b connected to the electrodes 21 a and 21 b. That is, one current lead 31a is connected to one end of one electrode 21a and the other current lead 31b is connected to the other end of the other electrode 21b. As such, when the connection positions of the current leads are staggered, the direction of the current is formed differently from the prior art, so that no repulsive force is generated.

Hereinafter, the mechanism in which the occurrence of the repulsive force is suppressed in the embodiment of FIG. 8 will be described with reference to FIG. 2. In the PTC current limiter of FIGS. 2 and 8, current leads through which current flows are called first current leads 3a and 30a, and current leads through which current flows out are referred to as second current leads 3b and 30b. Assume that the electrodes connected to 3a and 30a are first electrodes 2a and 21a and the electrodes connected to second current leads 3b and 30b are second electrodes 2b and 21b. In FIG. 2, when a current is applied to the first current lead 3a, the current flows in the direction in which the current is diffused to the peripheral portion of the first electrode 2a as shown by the arrow of FIG. 2. In addition, in the second electrode 2b, current flows in the direction in which the current collects in the center as shown by the arrow of FIG. Therefore, in the areas 4 and 5 indicated by the dotted lines, the direction of the current is reversed, and the magnetic field induced by the current acts as a repulsive force. Meanwhile, in the PTC current limiter of FIG. 8, the current flowing through the first electrode 21a flows from the one end to which the first current lead 30a is connected to the opposite end, and the current flowing through the second electrode 21b passes through the second current lead ( 30b) flows from the unconnected end toward the second current lead 30b. Therefore, the current flowing through the first and second electrodes 21a and 21b in the region 40 indicated by the dotted line at 8 is in the same direction, and the magnetic field induced by the current acts as an attractive force. Accordingly, separation or breakage between the PTC element 10 and the electrodes 21a and 21b is prevented.

9 is a cross-sectional view showing a PTC fault current limiter according to another embodiment of the present invention. In FIG. 9, the same reference numerals as in the above-described drawings indicate the same members having the same function and detailed description thereof will be omitted.

Referring to FIG. 9, the PTC fault current limiter according to the present embodiment includes the auxiliary electrodes 23a and 23b and the main electrodes 24a and 24b electrically connected to the auxiliary electrodes 23a and 23b.

The auxiliary electrodes 23a and 23b are made of copper foil having fine surface irregularities and the like to reduce contact resistance at the interface with the PTC element 10 so as to conduct a larger load current. The surface irregularities may be formed by, for example, electroplating or etching.

The main electrodes 24a and 24b use a metal material having a lower resistance than the auxiliary electrodes 23a and 23b to more effectively conduct electricity.

The PTC fault current limiter according to the present embodiment includes a first PTC element layer 11 and a second PTC element layer 12 provided to be interposed between the auxiliary electrodes 23a and 23b.

The first PTC element layer 11 is interposed between the electrodes to act as a current-limiting function when an overcurrent is energized due to an accident or the like.

Meanwhile, the second PTC device layer 12 is provided to surround the first PTC device layer 11, the auxiliary electrodes 23a and 23b, and the main electrodes 24a and 24b. As described above, the second PTC device layer 120 relaxes the concentration of the electric field formed in the electrode and prevents the electrode from being separated by the repulsive force generated at the interface between the electrode and the first PTC device layer 11.

Preferably, the second PTC device layer 12 may be configured to have the same resistivity or greater than the first PTC device layer 11. When the specific resistance of the second PTC element layer 12 is smaller than that of the first PTC element layer 11, the current-limiting action of the first PTC element layer 11 becomes insignificant, and the effect of mitigating concentration of the electric field formed in the electrode periphery is reduced. Can not be exercised properly. Therefore, it is preferable to use a less conductive filler or reduce the amount thereof so that the specific resistance of the second PTC device layer 12 is equal to or higher than that of the first PTC device layer 11.

The manufacturing sequence of the PTC fault current limiter according to the present embodiment is as follows. First, the first PTC element layer 11 is prepared. Subsequently, auxiliary electrodes 23a and 23b having surface irregularities are prepared and attached to the first PTC element layer 11 to form a plate shape, and the main electrodes 24a and 24b are electrically connected on the auxiliary electrodes 23a and 23b. Connect with In addition, a current lead 30 is connected to the main electrodes 24a and 24b. Thereafter, the second PTC device manufactured to have the same or higher resistivity than the first PTC device layer 11 is molded to mold the first PTC device layer 11, the auxiliary electrodes 23a and 23b, and the main electrodes 24a and 24b. The second PTC device layer 12 is formed so as to surround the film.

Although not shown, the current leads 30 may be alternately arranged in the embodiment of FIG. 9 as in the embodiment of FIG. 8.

10 is a cross-sectional view showing a PTC fault current limiter according to another embodiment of the present invention. In FIG. 10, the same reference numerals as used in the drawings illustrated above indicate the same members having the same functions, and a detailed description thereof will be omitted.

Referring to FIG. 10, the PTC fault current limiter according to the present embodiment includes a pair of electrodes 25a and 25b configured to surround one electrode 25b around another electrode 25a. In addition, a PTC element 13 is interposed between the pair of electrodes 25a and 25b. The current then flows as indicated by the arrows in FIG. 10. That is, the pair of electrodes 25a and 25b have a symmetrical structure, so that the electric field is not concentrated in a part of the region, and the repulsive force between the electrodes in the direction of the current does not occur.

Although not shown, the second PTC device layer surrounding the electrodes 25a and 25b may be provided similarly to the embodiment of FIG. 10. Furthermore, a modification of the form in which FIG. 7 and FIG. 10 are combined is also possible. That is, in the structure shown in FIG. 7, the shapes and structures of the electrodes 22a and 22b may be replaced with the structures and shapes of the electrodes 25a and 25b shown in FIG. 10.

As described above, although the present invention has been described by way of limited embodiments and drawings, the present invention is not limited thereto and is intended by those skilled in the art to which the present invention pertains. Of course, various modifications and variations are possible within the scope of equivalents of the claims to be described.

As described above, the PTC fault current limiter according to the preferred embodiment of the present invention prevents the generation of the electromagnetic repulsive force generated at the joint surface by the initial overcurrent and the repulsive force caused by the magnetic field induced by the electrode before the current limiting action. Separation or breakage of the electrode can be prevented.

In addition, the concentration of the electric field generated at the corners of the electrode immediately after the current-limiting action can be alleviated to prevent flashover and burnout of the PTC element and to extend the life of the PTC current limiter.

Claims (11)

In the PTC fault current limiter which current-limits current using the PTC characteristic, PTC element having a PTC characteristic that the resistance increases when the temperature rises; A pair of electrodes impregnated at a predetermined distance in the PTC element; And And a pair of current leads connected to the electrode and extending out of the PTC element to energize the electrode with an external circuit. The method of claim 1, The PTC fault current limiter, characterized in that the PTC element is composed of a polymer having a PTC characteristic. The method of claim 1, The electrode is a PTC fault current limiter, characterized in that the corner is rounded with a predetermined curvature. The method according to any one of claims 1 to 3, And the pair of current leads are staggered from each other. The method according to claim 1 or 2, The pair of electrodes PTC limiter, characterized in that any one electrode is provided to surround the other electrode. The method according to claim 1 or 2, The pair of electrodes is PTC limiter, characterized in that made of a spherical shape. In the PTC fault current limiter which current-limits current using the PTC characteristic, A first PTC device layer; A pair of auxiliary electrodes provided with surface irregularities and provided to interpose the first PTC device layer; A pair of main electrodes formed on the auxiliary electrode; A pair of current leads connected to the main electrode to energize the main electrode with an external circuit; And And a second PTC device layer formed to surround the first PTC device layer, the auxiliary electrode, and the main electrode. The method of claim 7, wherein And said main electrode of said one phase is rounded with corners having a predetermined curvature. The method according to claim 7 or 8, And the pair of current leads are staggered from each other. In the PTC fault current limiter which current-limits current using the PTC characteristic, A pair of electrodes provided such that one electrode surrounds the other electrode; A PTC element interposed between the pair of electrodes; And And a pair of current leads connected to the electrodes for energizing the electrodes with an external circuit. delete

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