JP2003151802A - Current limiting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable current limiting device by stabilizing the current limiting pulse-height value and current feeding performance of the device by stabilizing contact resistances between electrodes and a PTC element after current limiting operations are performed. SOLUTION: On a PTC element excluding vicinities of connections with the electrodes, a portion where an electrical resistance value per unit length acting on an electric current is made higher than that acting on the electric current in the vicinities of the connections with the electrodes is provided. In addition, the current limiting device is constituted so that no arc is generated in the connections between the PTC element and electrodes.

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 that suppresses short circuit current.

[0002]

2. Description of the Related Art FIG. 11 shows, for example, JP-A-4-26600.
1 is a perspective view showing a conventional fault current limiter disclosed in Japanese Patent Publication No.
2 is a front view of the current limiting device shown in FIG. 11. 11 and 1
In reference numeral 2, 1 is, for example, PTC (positive tempe) obtained by kneading polyethylene with carbon black or metal particles.
2A, 2B are electrodes made of, for example, copper, 4 is a case made of an insulator made of, for example, epoxy resin, 5 is an elastic body, such as a leaf spring or a disc spring,
Alternatively, an organic elastic body is used. Electrodes 2A, 2B and P
The TC element 1 is pressed by the elastic body 5, and the electrodes 2A, 2B and P
The TC element 1 is electrically connected. Such a connection is called pressure welding. The electrodes 2A and 2B are electrically connected to electric wires (not shown).

Next, the operation of the conventional current limiting device will be described with reference to FIG. Normal load current is one electrode 2A, P
It flows through the TC element 1 and the other electrode 2B. When a normal load current is applied, the temperature rise of the PTC element 1 is kept low.

When a short circuit current flows, electrodes 2A, 2B and P
The PTC element 1 is heated by the contact resistance between the TC elements 1, the surface layer of the PTC element 1 transitions to a high resistance state, and a short circuit current is suppressed. The current suppressed by the PTC element 1 is cut off by a breaker (not shown). The surface portion of the PTC element 1 reaches the decomposition temperature of the polyethylene of the PTC element 1, and an arc is generated between the electrodes 2A, 2B and the PTC element 1 as shown in Japanese Patent Laid-Open No. 4-266001. To do. The arc is connected to one of the electrodes and the PTC element 1.
Between the electrodes 2A and 2B and the PTC element 1
Both can occur between.

When the PTC element 1 makes a transition to a high resistance state, an overvoltage is generated across the PTC element 1. In order to suppress this overvoltage, an arrester or a resistor may be connected to both ends of the PTC element 1.

The Joule integral value from the start of the short-circuit current to the time when an arc is generated between the PTC element and the electrode (a value obtained by time-integrating the square of the current flowing in the PTC element. As published on p.816 of the Society (published in 1988),
The Joule integral value is used as an index for starting the current limiting operation of the fuse. ) Is X, and the switch connected in series with the PTC element after the short-circuit current starts to flow is the PTC.
When the Joule integral value in the PTC element until the current limited by the element is cut off is Y, the electrodes 2A, 2
Since there is a contact resistance between B and the PTC element 1, X <Y in the conventional current limiting device, and an arc is generated between the electrodes 2A and 2B and the PTC element 1. When an arc occurs, the state of contact between the electrodes 2A, 2B and the PTC element 1 changes and does not return to the original state, so the contact resistance of the current limiting device that has once operated a current limiting operation increases, and after that, There was a problem that the flow peak value and current carrying performance changed.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and includes electrodes 2A, 2B and P
To prevent a phenomenon in which an arc is generated between the TC elements 1 and to stabilize the contact resistance between the electrodes 2A, 2B and the PTC element 1 after the current limiting operation to stabilize the current limiting peak value and the current carrying performance. Therefore, it is an object of the present invention to provide a highly reliable fault current limiter.

[0008]

In the fault current limiter according to the present invention, the electric resistance value per unit length acting on the electric current in the portion other than the connection portion between the PTC element and the electrode of the PTC element is PTC. Providing a portion higher than the electric resistance value per unit length that acts on the current in the vicinity of the connection portion with the element electrode,
In addition, the arc is not generated at the connecting portion between the PTC element and the electrode before the current limiting operation is started.

Further, a portion having a higher current density than the current density at the connection portion with the electrode is provided in the portion other than the connection portion with the electrode of the PTC element. In addition, the cross-section reduced portion with respect to the current is formed by providing a notch in a portion other than the connection portion with the electrode of the PTC element. Further, a notch is provided so that the current path in the cross-section reduction portion is plural. Furthermore, the notch is filled with an electrical insulator. Also, a resistor is inserted in the notch. Further, the cross-sectional area of the cross-section reduced portion with respect to the current is one half or less of the total area of the portion where the current flows from the electrode to the PTC element. Further, the electrodes are heat-sealed to the PTC element.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1. 1 is a front view showing a structure of a current limiting device according to a first embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a plate-shaped PTC element in which, for example, polyethylene is mixed with carbon black or metal particles, and a cut-out portion 1B is formed by providing a notch 1A. The PTC element 1 may have other shapes such as a columnar shape and a prismatic shape. A perspective view of the PTC element 1 is shown in FIG. The electrodes 2A and 2B are electrodes made of, for example, copper. Reference numeral 4 is an insulating case made of resin, for example, and 5 is an elastic body such as a leaf spring, a disc spring or an organic elastic body. The electrodes 2A, 2B and the PTC element 1 are pressed against each other by being pressed by the elastic body 5. The electrodes 2A, 2B may be provided on the side of the PTC element 1 as shown in the perspective view of FIG. 3 or 4, and the electrodes 2A, 2B may be pressed against the PTC element 1 by the elastic body 5.

In these current limiting devices, when a short-circuit accident occurs, the cross-sectional reduced portion 1B of the PTC element 1 has a higher current density than other portions, especially the connection portion with the electrode, so that the cross-sectional reduced portion 1B is heated strongly. The transition to the high resistance state occurs and the short-circuit current is suppressed. The current suppressed by the PTC element 1 is cut off by a breaker (not shown). Section reduction section 1B
May be provided in a portion other than the electrode connection portion of the PTC element. That is, the time until the current limiting operation starts, for example, 1 m
It suffices that the reduced cross-section portion 1B and the electrode connection portion are separated by a distance that is hardly transmitted to the connection portion with the electrode in about s. Since this distance is very small, the reduced cross section 1B
The effect of the present invention can be obtained if it is provided in a portion other than the electrode connecting portion of the PTC element.

In the conventional fault current limiter as shown in FIG. 11 which does not have the cross-sectional reduction portion 1B, when the cross-sectional area is the same as the cross-sectional area of the portion other than the cross-sectional reduction portion 1B of FIG. The Joule integral value until the arc is generated between the PTC element and the electrode (the value obtained by time-integrating the square of the current flowing through the PTC element) is defined as X, and the fault current limiter according to the first embodiment of the present invention in FIG. In the case where the switch connected in series with the PTC element is P
PT until the current limited by the TC element is cut off
If the Joule integral value in the C element is Y, in the first embodiment, the PTC element 1 is provided with the reduced cross section, so that Y <X is satisfied in the present invention. That is, according to the current limiting device of the first embodiment of the present invention, the current limiting operation is started before the arc is generated, and eventually the arc is not generated.

As described above, according to the current limiter of the first embodiment of the present invention, the PTC element 1 is provided by providing the reduced section in a portion other than the connection portion with the electrode of the PTC element 1.
The portion where the electric resistance value per unit length acting on the electric current is higher than the electric resistance value per unit length acting on the electric current in the vicinity of the connecting portion with the electrode of the PTC element, in a portion other than the connecting portion with the electrode of By providing it, it is possible to prevent the phenomenon of generating an arc between the PTC element and the electrode. As a result, PTC
Since it is possible to obtain a fault current limiter with stable contact resistance between the element and the electrode, it is possible to obtain a fault current limiter with stable current limiting performance and current-carrying performance.

Further, in the conventional current limiting device, it is necessary to increase the cross-sectional area of the PTC element 1 in advance in order to ensure the current carrying performance after the current limiting operation. As a result, the peak value of the current limiting during the current limiting operation for the first time becomes high, so that there is a problem that the element is easily damaged during the first current limiting. Even if the element is not damaged during the initial current limiting operation, the thermal and mechanical stress acting on the PTC element 1 is high due to the high peak current limiting crest value, and the limit until the PTC element 1 is damaged. There was a problem that the number of flow operations was small. In the present invention, since the contact resistance is stable and it is not necessary to increase the cross-sectional area of the PTC element 1 in advance, the first current limiting peak value should be the same as the current limiting peak value during the second current limiting operation. You can As a result, it is possible to prevent the PTC element 1 from being damaged during the current limiting operation.

Further, in the current limiting device of the present invention, the PTC element 1
Since no arc is generated between the electrodes and electrodes 2A and 2B, PT
C element 1 is not damaged. Therefore, even if the current limiting operation is repeated, it is possible to make the PTC element 1 less likely to be damaged.

Further, in the first embodiment, the PTC element 1
An inexpensive current limiting device can be obtained because of the simple structure in which the cross-sectional reduced portion is provided.

Embodiment 2. FIG. 5 shows a front view of the configuration of the current limiting device according to the second embodiment of the present invention. The second embodiment is characterized in that, as shown in FIG. 5, the notch 1A is provided so that a plurality of cross-section reduction portions 1B are provided in parallel with the current.

With such a configuration, the cross-sectional reduction section 1
Since there are a plurality of Bs in parallel with the current, the current distribution in the portion where the cross section of the PTC element 1 is not reduced can be made uniform, so that the energization performance can be improved.

Embodiment 3. FIG. 6 shows a front view of the configuration of the current limiting device according to the third embodiment of the present invention. In the third embodiment, as shown in FIG. 6, an electrical insulator 6 is provided in a notch formed to provide the cross-sectional reduced portion 1B.

If the notch for forming the reduced cross section 1A has a space like the current limiting device according to the second embodiment, it is easily damaged when bending stress acts on the PTC element 1. In the fault current limiter according to the form 3, the cross-sectional reduction section 1
An electrical insulator 6 is formed in the notch formed to provide A.
Since the PTC element is reinforced due to the provision of the above, it is possible to obtain a highly reliable current limiting device that is not easily damaged.

Fourth Embodiment FIG. 7 shows a front view of the configuration of the current limiting device according to the fourth embodiment of the present invention. In the fourth embodiment, as shown in FIG. 7, the resistor 7 is provided in the notch formed to provide the cross-sectional reduced portion 1B.

In the conventional fault current limiter, resistors are connected to both ends of the electrodes 2A and 2B through electric wires in order to suppress overvoltage during the current limiting operation. In such a connection method, the inductance of the resistance circuit becomes large, so that the overvoltage cannot be significantly reduced. As a result, the energy injected into the current limiting device during the current limiting operation becomes large, and the current limiting device is easily damaged.

In the fourth embodiment, since the resistor 7 is provided in the notch formed to provide the reduced cross section 1B, it is not necessary to connect a resistor to the outside, so that the inductance of the resistor circuit is remarkably increased. Since it can be reduced, the energy injected into the current limiting device during the current limiting operation becomes small, and the current limiting device is less likely to be damaged.

Embodiment 5. FIG. 8 shows a sectional view of the configuration of the current limiting device according to the fifth embodiment of the present invention. In FIG.
Reference numeral 1 denotes a columnar PTC element in which carbon black or metal particles are kneaded in polyethylene, for example, with a cutout 1A.
The cross-sectional reduced portion 1B is formed by forming the. The electrodes 2A and 2B are circular electrodes made of, for example, copper. Reference numeral 4 is a cylindrical electrical insulating container made of, for example, an epoxy resin. Reference numeral 5 denotes a circular elastic body, for example, an organic elastic body is used. Reference numeral 8 is a circular end plate, and the elastic body 5 is compressed by the end plate 8, and the electrodes 2A, 2B and the PTC element 1 are pressed against each other.

In order to obtain the structure shown in FIG. 8, for example, the following manufacturing method is adopted. The electrode 2B and the case 4 are sealed by adhering the electrode 2B and the case 4, and the PTC element 1, the upper electrode 2A, and the organic elastic body 5 are inserted. In this state, the organic elastic body 5 is in a state in which a part thereof protrudes from the upper surface of the cylindrical electrically insulating container 4.
Next, the end plate 8 is pressed, and the end plate 8 and the cylindrical electrically insulating container 4 are bonded with an adhesive. The organic elastic body 5 is elastically deformed by being pressed by the end plate 8, and the organic elastic body 5 is pressed against the upper terminal 2A, the cylindrical electrically insulating container 4, and the end plate 8 to push the PTC element 1 Seal it.

Further, as shown in FIG. 9, the cylindrical electrically insulating container 4 and the electrodes 2A and 2B can be adhered and sealed. In this case, when the electrodes 2A, 2B are pressed against the PTC element 1 at the time of bonding, the electrodes 2A, 2B and the PTC element can be electrically connected to each other.

In the fifth embodiment, as described above, the P
The TC element 1 is characterized by being cut off from the outside air. PT
The C element 1 is easily deteriorated when it absorbs moisture, and is easily deteriorated when it reacts with an atmospheric gas such as hydrogen sulfide. Since the PTC element 1 is provided inside the case 4 and the PTC element 1 is shielded from the outside air, it is possible to obtain a current limiting device which is less likely to deteriorate.

In the first to fifth embodiments so far, the end surface of the PTC element may be metallized by metal vapor deposition or the like. Since the end face of the PTC element is metallized, the contact resistance between the PTC element 1 and the electrodes 2A and 2B is greatly reduced. As a result, the phenomenon that an arc is generated between the PTC element and the electrode can be more reliably prevented.

Alternatively, the electrodes may be roughened and heat-bonded or pressure-contacted to the PTC element. As a result, the contact resistance between the PTC element 1 and the electrodes 2A, 2B is remarkably reduced, so that P
The phenomenon that an arc is generated between the TC element and the electrode can be prevented more reliably.

Sixth Embodiment In the current limiting device according to the sixth embodiment of the present invention, the cross-sectional area of the cross-sectional reduced portion of the PTC element is 1/2 of the area of the connecting portion between the electrode and the PTC element, that is, the total area of the portion where the current flows from the electrode to the PTC element. It is characterized by the following. Here, in the case of the current limiting device shown in FIG. 1, the area of the connecting portion between the electrode and the PTC element, that is, the total area of the portion where the current flows into the PTC element, means the electrode 2A and the PTC element.
This means the area of the connecting portion with the element 1, and in the case of the current limiting device shown in FIG. 3, it means the total area of the connecting portions of the two electrodes 2A and the PTC element. As a result, the density of the current flowing in the contact portion between the electrode and the PTC element can be reduced to ½ or less of the current density in the cross-sectional reduction portion of the PTC element, so that a short-circuit current starts flowing between the PTC element and the electrode. The Joule integral value (value obtained by time-integrating the square of the current flowing through the PTC element) until the arc is generated can be reduced to 1/4 or less. As a result, the phenomenon in which an arc is generated between the PTC element and the electrode can be very reliably prevented.

Embodiment 7. FIG. 10 shows a front view of the configuration of the current limiting device according to the seventh embodiment of the present invention. In the above-described embodiments, the PTC element is provided with the reduced cross section so that the current limiting operation can be performed without generating an arc. However, as shown in FIG. By providing the high layer 10, it is possible to prevent arc generation. In this case, before the arc is generated between the PTC element and the electrode, the layer 10 having a high room temperature resistivity in the PTC element suppresses the short circuit current, and the suppressed current is P
It is cut off by a switch connected in series with the TC element. Therefore, the phenomenon that an arc is generated between the PTC element and the electrode is prevented.

PTC having a layer having a high room temperature resistivity
The element is manufactured as follows, for example. First, two PTC elements with low room temperature resistivity and P with high room temperature resistivity
Two PTs with low room temperature resistivity that make one TC element
A PTC element having a high room temperature resistivity is provided between the C elements. The current limiting device of the present embodiment can be manufactured by providing these between the roughened electrodes and heat-sealing them.

[0033]

According to the current limiter of the present invention, the PT
In the part other than the connection part between the C element and the electrode of the PTC element,
By providing a portion where the electric resistance value per unit length that acts on the current is higher than the electric resistance value per unit length that acts on the current in the vicinity of the connection portion with the electrode of the PTC element, and before starting the current limiting operation Since the arc is not generated at the connecting portion between the PTC element and the electrode, it is possible to obtain the current limiter with stable contact resistance between the PTC element and the electrode.
It is possible to provide a highly reliable current limiter with stable current limiting performance and current carrying performance.

Further, since a portion having a higher current density than the current density at the connection portion with the electrode is provided in the portion other than the connection portion with the electrode of the PTC element, the structure between the PTC element and the electrode is simple with a simple structure. A current limiting device with stable contact resistance can be obtained.

Further, since the cross-sectional reduced portion for the current is formed by providing the notch in the portion other than the connection portion with the electrode of the PTC element, the portion having a high current density can be formed with a simple structure.

Further, since the notches are provided so that the current paths in the reduced cross section are plural, the current distribution can be made uniform in the non-reduced portion of the PTC element.
The energization performance can be improved.

Furthermore, since the notch is filled with an electric insulator, the PTC element is reinforced, and it is possible to obtain a highly reliable element that is less likely to be damaged.

Since a resistor is inserted in the notch,
The energy injected into the current limiting device during the current limiting operation becomes small, and it is possible to obtain a highly reliable device that is not easily damaged.

Further, since the cross-sectional area of the cross-section reduced portion with respect to the current is set to ½ or less of the total area of the portion where the current flows from the electrode to the PTC element, it is possible to more reliably prevent the arc from occurring. We can provide more reliable products.

Further, since the electrode is heat-sealed to the PTC element, the contact resistance between the PTC element and the electrode is remarkably reduced,
The phenomenon that an arc is generated between the PTC element and the electrode can be more surely prevented, and a more reliable device can be provided.

[Brief description of drawings]

FIG. 1 is a front view showing a current limiting device according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing a PTC element according to Embodiment 1 of the present invention.

FIG. 3 is a perspective view showing an example of the electrode section according to the first embodiment of the present invention.

FIG. 4 is a perspective view showing another example of the electrode section according to the first embodiment of the present invention.

FIG. 5 is a front view showing a current limiting device according to a second embodiment of the present invention.

FIG. 6 is a front view showing a current limiting device according to a third embodiment of the present invention.

FIG. 7 is a front view showing a current limiting device according to a fourth embodiment of the present invention.

FIG. 8 is a sectional view showing a current limiting device according to a fifth embodiment of the present invention.

FIG. 9 is a sectional view showing another example of the current limiting device according to the fifth embodiment of the present invention.

FIG. 10 is a front view showing a current limiting device according to a seventh embodiment of the present invention.

FIG. 11 is a perspective view showing a conventional current limiting device.

FIG. 12 is a front view showing a PTC element of a conventional current limiting device.

[Explanation of symbols]

1 PTC element, 1A notch, 1B cross-section reduction part,
2A, 2B electrodes 6 electrical insulators, 7 resistors

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Katsuhiko Fukuhara             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. F term (reference) 5E034 AA07 AB00 BB05 CB01 DA07

Claims (8)

[Claims] 1. A current limiting device comprising a PTC element and electrodes provided at both ends of the PTC element for flowing a current through the PTC element, wherein a portion other than a connection portion of the PTC element with the electrode is provided. The portion is provided with a portion where the electric resistance value per unit length acting on the current is higher than the electric resistance value per unit length acting on the current in the vicinity of the connection portion of the PTC element with the electrode, and A current limiting device characterized in that an arc does not occur at a connecting portion between the PTC element and the electrode before the flow operation is started. 2. A current limiter comprising a PTC element and electrodes provided at both ends of the PTC element for passing a current through the PTC element, wherein a part other than a connection part of the PTC element with the electrode is provided. A current limiting device characterized in that a portion having a current density higher than a current density at a connection portion with the electrode is provided in the portion. 3. The fault current limiter according to claim 2, wherein a cut-out portion is formed in a portion other than the portion of the PTC element other than the connection portion with the electrode to form a cross-sectional reduction portion for the electric current. 4. The fault current limiter according to claim 3, wherein the cutout is provided so that a plurality of current paths are provided in the reduced section. 5. The fault current limiter according to claim 3, wherein the notch is filled with an electric insulator. 6. The fault current limiter according to claim 3, wherein a resistor is inserted in the notch. 7. The cross-sectional area of the reduced cross section with respect to the current is set to ½ or less of the total area of the portion where the current flows from the electrode to the PTC element. Current limiter. 8. The fault current limiter according to claim 1, wherein the electrode is heat-sealed to the PTC element.