JPH11243001A - Current limiter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a current-limiter in which a PTC polymer is not easily damaged in the event of a short circuit. SOLUTION: In a current limiter having a PTC polymer 1, a pair of electrodes 2 and 3 which are electrically brought into contact with the PTC polymer 1, and means 9, 10, 11, and 12 for applying pressure to the electrodes and the PTC polymer, a sharp edge 2A around the electrodes 2 and 3 are removed and a stress applied on the PTC polymer 1 is reduced so as to allow the PTC polymer 1 to be not easily damaged. This arrangement lowers a concentrated stress applied to the PTC polymer 1 in the event of a short circuit. Thus, it is possible to obtain the current limiter which protects the PTC polymer 1 from damage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current limiting device used for limiting, for example, a short-circuit current or an overcurrent by using a conductive polymer (hereinafter referred to as a PTC polymer) having a positive temperature coefficient of resistance. It is about.

[0002]

2. Description of the Related Art FIG. 5 shows, for example, Japanese Patent Application No. 8-223945.
1 is a side view showing a conventional current limiter shown in FIG. In FIG. 5, 1 is a plate-like PTC polymer having PTC (positive temperature resistance coefficient) characteristics, 2 and 3 are a pair of plate-like electrodes,
The PTC polymer 1 and the electrodes 2, 3 are in electrical contact. As shown in FIG. 6, the resistivity of the PTC polymer 1 is low up to the transition start temperature T1, and increases rapidly after exceeding the transition start temperature T1. Some PTC polymers gradually increase above the transition end temperature T2, but gradually decrease. In one example of a PTC polymer, T1 is 125 ° C., T2
Is 135 ° C., and the resistivity at T2 is 1000 times the resistivity at T1.

FIG. 7 shows a top view of the electrodes 2 and 3 in FIG. 8 shows a cross section taken along line AA of FIG. In FIG. 8, reference numeral 2A denotes an edge portion formed on the electrode 2, and the edge 2A contacts the PTC polymer 1. Electrode 2 and PT
FIG. 9 shows a perspective view of the C polymer 1. In the conventional current limiter, as shown in FIG. 9, the edge portion (periphery 2A) of the electrode 2
Are pressed against the PTC polymer 1.

Reference numeral 4 denotes an interface between the PTC polymer 1 and the electrodes 2 and 3, and a contact resistance exists at an interface between the PTC polymer 1 and the electrodes 2 and 3. The PTC polymer 1 may be pressed against the electrodes 2 and 3 or may be thermally fused. When thermally fused, the contact resistance at the interface between the PTC polymer 1 and the electrodes 2, 3 is reduced. A pair of terminal plates 6 and 7 are provided outside the electrodes 2 and 3, and the terminal plates 6 and 7 are respectively connected to the external electric wires 1.
3, 14 are connected. The terminal plates 6, 7 may be integrated with the electrodes 2, 3, or the terminal plates 6, 7 may also serve as the electrodes 2, 3. Reference numeral 8 denotes an elastic body, for example, a leaf spring, a disc spring, or the like is used. The elastic body 8 includes terminal plates 6 and 7, electrodes 2, 3, P
TC polymer 1 is being pressed. 9 and 10 are a pair of insulating plates, the insulating plates 9 and 10 are provided with holes 9a and 10a, respectively, the holes 9a and 10a are provided with screws 11 therethrough, and the screws 11 are tightened with nuts 12, The elastic body 8 is compressed.

The electric current flows through one of the electric wires 13, one of the terminal plates 6,
It flows via one electrode 2, the PTC polymer 1, the other electrode 3, the other terminal plate 7, and the other electric wire 14.

Next, the operation will be described. The load current flows through the PTC polymer 1 via the electrodes 2 and 3. When a load current flows, the temperature of the PTC polymer 1 rises due to Joule heating, but the temperature of the PTC polymer 1 is lower than the transition start temperature T1 due to a small current flow. When a short-circuit current or an overcurrent flows, the temperature rise of the PTC polymer 1 increases, the temperature of the PTC polymer 1 becomes higher than the transition start temperature T1, and the resistivity of the PTC polymer 1 sharply increases. Therefore, short-circuit current or overcurrent is suppressed. The suppressed current is cut off by a switch (not shown). When the current is cut off and the heat input to the current limiter disappears and the temperature of the PTC polymer 1 falls below the transition start temperature T1, the load current can be re-energized.

[0007]

In the conventional current limiter, as shown in FIG. 5, the edge (periphery 2A) of the electrode 2 is PT
Since it is pressed by C polymer 1, PTC polymer 1
Intense strong stress acts on the electrode peripheral contact portion. When a short-circuit current flows, an electromagnetic force is generated on the electrodes and the terminal plate, and the element further receives mechanical stress due to the electromagnetic force. This mechanical stress also gives intensive strong stress to the contact portion of the PTC polymer 1 around the electrode. These stresses combine with the problem that the PTC polymer is easily damaged during the current limiting operation.

An object of the present invention is to provide a current limiter in which the PTC polymer 1 is hardly damaged.

[0009]

According to the present invention, there is provided a current limiter having a PTC polymer, a pair of electrodes in contact with the PTC polymer, and a means for pressurizing the electrode and the PTC polymer. The edge is removed by processing the periphery of the electrode on the side that contacts the PTC polymer.

The current limiting device according to the present invention may be one in which the peripheral edge of the electrode is C-chamfered to remove the edge.

[0011] The current limiter according to the present invention may be one in which the edge is removed by performing R chamfering on the periphery of the electrode.

The current limiter according to the present invention may be one in which the edge is removed by pressing the periphery of the electrode.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In FIG. 1, 1
Is a plate-like PTC polymer having PTC characteristics, 2 and 3 are a pair of plate-like electrodes, and the PTC polymer 1 and the electrodes 2 and 3 are electrically contacted. FIG. 2 shows a cross-sectional view of the electrodes 2 and 3. As shown in FIG. 6, the resistivity of the PTC polymer is low up to the transition start temperature T1, and increases sharply when it exceeds the transition start temperature T1. Some PTC polymers gradually increase above the transition end temperature T2, but gradually decrease.
In one example of a PTC polymer, T1 is 125 ° C. and T2 is 1
35 ° C. and the resistivity at T2 is 1000 times the resistivity at T1.

Reference numeral 4 denotes an interface between the PTC polymer 1 and the electrodes 2 and 3, and a contact resistance exists at an interface between the PTC polymer 1 and the electrodes 2 and 3. The PTC polymer 1 may be pressed against the electrodes 2 and 3 or may be thermally fused. When thermally fused, the contact resistance at the interface between the PTC polymer 1 and the electrodes 2, 3 is reduced. A pair of terminal plates 6 and 7 are provided outside the electrodes 2 and 3, and the terminal plates 6 and 7 are respectively connected to the external electric wires 1.
3, 14 are connected. The terminal plates 6, 7 may be integrated with the electrodes 2, 3, or the terminal plates 6, 7 may also serve as the electrodes 2, 3. Reference numeral 8 denotes an elastic body, for example, a leaf spring, a disc spring, or the like is used. The elastic body 8 includes terminal plates 6 and 7, electrodes 2, 3, P
TC polymer 1 is being pressed. 9 and 10 are a pair of insulating plates, the insulating plates 9 and 10 are provided with holes 9a and 10a, respectively, the holes 9a and 10a are provided with screws 11 therethrough, and the screws 11 are tightened with nuts 12, The elastic body 8 is compressed.

The electric current flows through one of the electric wires 13, one of the terminal plates 6,
It flows via one electrode 2, the PTC polymer 1, the other electrode 3, the other terminal plate 7, and the other electric wire 14.

Next, the operation will be described. The load current flows through the PTC polymer 1 via the electrodes 2 and 3. When a load current flows, the temperature of the PTC polymer 1 rises due to Joule heating, but the temperature of the PTC polymer 1 is lower than the transition start temperature T1 due to a small current flow. When the short-circuit current or the overcurrent flows, the temperature rise of the PTC polymer 1 increases, the temperature of the PTC polymer 1 becomes higher than the transition start temperature T1, and the resistivity of the PTC polymer 1 sharply increases. Therefore, short-circuit current or overcurrent is suppressed. The suppressed current is cut off by a switch (not shown). When the current is cut off and the heat input to the current limiter stops, and the temperature of the PTC polymer 1 falls below the transition start temperature T1, the load current can be re-energized.

In this embodiment, as shown in FIGS. 1 and 2, the edges of the electrodes 2 and 3 which are in contact with the PTC polymer 1 are chamfered to remove sharp edges. In the event of a short circuit, the concentrated stress acting on the PTC polymer 1 can be reduced. As a result, the number of times the PTC polymer 1 can withstand the current limiting operation is 1.5 to 2 times. Therefore, it is possible to obtain a current limiter in which the PTC polymer 1 is hardly damaged at the time of a short circuit accident. In the present embodiment, since the processing of the peripheral edge 2A of the electrodes 2 and 3 is C chamfering, there is an advantage that the processing is easy.

Embodiment 2 FIG. Next, a second embodiment will be described. FIG. 3 shows a sectional view of the electrodes 2 and 3 in this embodiment. In this embodiment, as shown in FIG. 3, the peripheral edges 2A of the electrodes 2 and 3 are subjected to R chamfering to remove sharp edges. In the embodiment, the concentrated stress acting on the PTC polymer 1 at the time of a short circuit accident is greatly reduced.
The TC polymer 1 can be harder to break. Thereby, the number of times that the PTC polymer 1 can withstand the current limiting operation is 2 to 2.5.
Doubled.

Embodiment 3 In this embodiment, the electrodes 2 and 3 are manufactured by press working. FIG. 4 is a cross-sectional view of an electrode manufactured by press working. The electrode shown in FIG.
Are pressed in the directions from A to B shown in FIG.
In this embodiment, since the electrodes 2 and 3 are manufactured by press working, there is an advantage that manufacturing is easy. Since the cross-section of the pressed electrode is as shown in FIG. 4, the surface C of the electrodes 2, 3 from which the sharp edges are removed is brought into contact with the PTC polymer, so that the PTC polymer 1
Since the concentrated stress acting on the PTC polymer 1 is reduced, the PTC polymer 1 can be harder to break. Thereby, the life of PTC polymer 1 was 1.5 to 2 times.

[0020]

According to the current limiting device according to the present invention, the PTC
In a current limiter having a polymer, a pair of electrodes in contact with the PTC polymer, and a means for pressurizing the electrodes and the PTC polymer, an edge of a peripheral edge of the electrode in contact with the PTC polymer was removed. At this time, the concentrated stress acting on the PTC polymer 1 can be reduced. Therefore, it is possible to obtain a current limiter in which the PTC polymer 1 is hardly damaged at the time of a short circuit accident.

Further, according to the present invention, the periphery of the electrode is C
Since the edges are removed by chamfering, the concentrated stress acting on the PTC polymer 1 at the time of a short circuit accident can be reduced. Therefore, it is possible to obtain a current limiter in which the PTC polymer 1 is hardly damaged at the time of a short circuit accident.

Further, according to the present invention, the peripheral edge of the electrode is formed by R
Since the edges are removed by chamfering, the concentrated stress acting on the PTC polymer 1 at the time of a short circuit accident can be reduced. Therefore, it is possible to obtain a current limiter in which the PTC polymer 1 is hardly damaged at the time of a short circuit accident.

According to the present invention, the peripheral edge of the electrode is pressed to remove the peripheral edge, and the surface of the electrode from which the sharp edge has been removed is brought into contact with the PTC polymer. Sometimes, the concentrated stress acting on the PTC polymer 1 can be reduced. Therefore, when a short circuit occurs,
A current limiter in which the polymer 1 is hard to break can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a current limiter according to the present invention.

FIG. 2 is a sectional view showing an electrode of the current limiter of FIG. 1;

FIG. 3 is a sectional view showing an electrode according to another embodiment of the current limiter of the present invention.

FIG. 4 is a cross-sectional view showing an electrode of another embodiment of the current limiter according to the present invention.

FIG. 5 is a cross-sectional view of a conventional current limiter.

FIG. 6 is a view showing PTC characteristics of a PTC polymer.

FIG. 7 is a top view showing electrodes of a conventional current limiter.

FIG. 8 is a sectional view of an electrode of a conventional current limiter.

FIG. 9 is a perspective view of a PTC polymer and an electrode of a conventional current limiter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 PTC polymer, 2 electrodes, 3 electrodes, 6 terminal boards, 7 terminal boards, 8 elastic bodies, 11 screws, 12 nuts, 13 electric wires, 14 electric wires

Continuing from the front page (72) Inventor Itsuo Nishiyama 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsui Electric Co., Ltd. (72) Inventor Hideo Horibe 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Inside (72) Inventor Kenichi Nishina 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsui Electric Co., Ltd. (72) Inventor Shiro Murata 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation (72) Inventor: Manabu Sogabe 2-3-2 Marunouchi, Chiyoda-ku, Tokyo, Japan Mitsui Electric Corporation (72) Inventor Masahiro Ishikawa 2-3-2, Marunouchi, Chiyoda-ku, Tokyo, Mitsubishi Electric Corporation

Claims (4)

[Claims] In a current limiter having a PTC polymer, a pair of electrodes in contact with the PTC polymer, and a means for pressurizing the electrode and the PTC polymer, a peripheral edge of an electrode in contact with the PTC polymer is processed. Current limiter characterized by removing edges. 2. The current limiter according to claim 1, wherein the processing is C chamfering. 3. The current limiter according to claim 1, wherein the processing is an R chamfering processing. 4. The current limiter according to claim 1, wherein the working is a press working.