KR20060082363A - Ptc current limiting device having multi insulator - Google Patents

Abstract

The present invention relates to a PTC fault current limiter with multiple insulators. According to the present invention, a PTC fault current limiter for current-limiting current using PTC characteristics, the PTC element; Electrode portions disposed on both surfaces of the PTC element so as to interpose the PTC element; A first insulator provided around the PTC element to surround the PTC element; And a second insulator provided to surround the first insulator, wherein the first insulator is a fluid insulator. This effectively suppresses and eliminates arcs generated at the interface between the PTC element and the electrode when the overcurrent or short-circuit current is limited, as well as in the low voltage system. Therefore, the flashover between the electrodes can be prevented to prevent wear of the PTC element and to further extend the life of the PTC fault current limiter.

PTC, current limiter, arc, flashover

Description

PTC current limiting device having multi insulator

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 the structure of a fault current limiter having a conventional PTC characteristic.

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

3 is a sectional view schematically showing a multiple insulated fault current limiter according to another embodiment of the present invention.

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

10 ... PTC element 20 ... electrode part

21a, 21b ... Contact electrode 22a, 22b ... Current lead

30 ... first insulator 40 ... second insulator

50 ... coating layer

The present invention relates to a fault current limiter having a PTC characteristic, and more particularly to a PTC fault current limiter that minimizes arc extinguishing between electrodes and prevents flashover between electrodes. It is about.

In general, as a countermeasure against short-circuit currents in low and high voltage systems, circuit breakers are widely used. The current frequency of electricity is 60Hz, which is 16.7ms when one phase is converted into seconds. When defined as one cycle, the conventional breaker takes longer than several cycles to break, and there is no current limiting function for the expected fault current, resulting in a relatively long duration of the accident spread. In addition, the failure of short-circuit current interruption has a great effect on the surrounding power equipment and power system. Therefore, there is an increasing demand for current-limiting technology that can effectively limit the system short circuit current in a short time.

Among the current-limiting technologies described above, there is a current limiter, which limits and blocks overcurrent and short-circuit current generated in a 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.

In this regard, Japanese Patent Laid-Open No. 10-321413 discloses a current limiter using PTC. Referring to Fig. 1 showing this technique, a conventional current limiter using PTC is formed by mixing conductive particles and welding the PTC polymer element 1 having the PTC characteristic and the PTC polymer element 1 to be disposed on both surfaces. It consists of the 2nd electrode 3 arrange | positioned in the state electrically connected to the surface of the electrode 2 and the 1st electrode 2. As shown in FIG. At this time, the surface area of the PTC polymer element 1 is larger than the surface area of the first electrode 2, and the surface area 2 of the first electrode is greater than or equal to the surface area of the second electrode 3. Such a structure can prevent an internal short circuit accident occurring at both ends of the first electrode 2, reduce the change in the current limiter resistance before and after the operation of the current limiter, and can conduct a large load current. In addition, by providing a frame 4 made of an insulating member around the PTC polymer element 1 to increase the insulating distance, flashover between the first electrode 2 and the second electrode 3 is prevented.

However, when the current limiter is used for the purpose of limiting the short circuit current of 100 V or more and 10 kA or more, the time difference of the generated resistance and the nonlinearity due to the difference in the heat capacity of the first electrode 2 in contact with the PTC polymer element 1 Due to the property, a considerable resistance occurs at the contact interface between the PTC polymer element 1 and the first electrode 2 before the resistance due to the heat generation of the PTC polymer element 1. This causes heat stress to be concentrated, leading to arcing and significant noise. This arc decomposes and carbonizes the PTC polymer element 1, resulting in dielectric breakdown. In addition, the PTC material melts and vaporizes due to the heat generated by the arc and the PTC polymer element itself, so that the thickness of the PTC polymer element is continuously thinned and the first electrode is impregnated inside the PTC polymer element.

Accordingly, the current limiter according to the related art attempts to increase the contact pressure by using a pressurizing structure that adjusts the surface area of the first and second electrodes 2 and 3, but is generated at the interface with the actual PTC polymer element 1. Arc generation due to nonlinearity of resistance and electron repulsion force is inevitable, and it is not easy to avoid current flow deterioration and flashover between electrodes due to the generated arc.

In addition, although the insulation member 4 provided at both ends of the PTC polymer element 1 proposed by the prior art is positive in terms of securing an insulation distance, the arc generated in the PTC polymer element 1 and the first electrode 2 It cannot be removed at source, and it is difficult to anticipate the noise mitigation caused by blocking.

For the same reason, the current limiter is capable of limiting noise and no arc current in a low current region, but arc generation is inevitable in a high-current large-capacity structure, resulting in deterioration and life reduction of the PTC device due to the arc.

The present invention has been made to solve the above problems, PTC limiter that can effectively suppress and remove the arc generated when limiting the over-current or short-circuit current in the high-pressure system as well as in the low-voltage system, and prevent the flashover between the electrodes The purpose is to provide.

PTC fault current limiter according to the present invention for achieving the above object, PTC current limiter for limiting the current by using the PTC characteristics, PTC element; Electrode portions disposed on both surfaces of the PTC element so as to interpose the PTC element; A first insulator provided around the PTC element to surround the PTC element; And a second insulator provided to surround the first insulator, wherein the first insulator is a fluid insulator.

Preferably, the PTC device may be composed of a polymer having PTC properties.

According to the present invention, the electrode unit comprises a contact electrode provided to directly contact the PTC element; And a current lead connected to the contact electrode to energize the contact electrode with the circuit.

According to the present invention, the flowable insulator is preferably at least one selected from the group consisting of vacuum, gas and oil.

More preferably, the vacuum has a vacuum degree of 10 ^-3 torr or more, the gas is 1 bar or more SF _6, N ₂ or a mixture thereof, and the oil is an insulating oil having a cooling performance.

Preferably, the PTC device or a coating layer interposed between the electrode portion and the first insulator may be further included.

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 present specification and claims should not be construed as being limited to the common or dictionary meanings, 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.

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

Referring to FIG. 2, the PTC fault current limiter according to the present invention includes a PTC element 10, an electrode portion 20 in contact with the PTC element, an insulator provided to surround the PTC element 10 and the electrode portion 20.

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.

Although the physical properties of the PTC device 10 vary depending on the current value to be limited, in the present embodiment, the specific resistance is 100 Ωm or less at 25 ° C., and the specific resistance is 25 at the switching temperature at which Joule heat is generated due to the current supply. It is preferable to be 10 ⁵ times or more of the specific resistance in ° C. It also needs to be able to withstand voltages of 100V AC or higher while maintaining electrical and thermal stability, and to prevent flashovers when overvoltages of 30kV or more are applied per cm. In addition, the PTC element 10 should not be tripped when energizing the current before and after the 1A, so that the constant current, for example, 1A before and after the current is supplied to the circuit. In addition, when the overcurrent more than 10 times the normal operating current is energized, the resistance rises within 1/2 cycle to limit the overcurrent, and the operation time is shortened as the short circuit current increases. It is desirable to be manufactured so that it can be reduced to its previous state within a short time.

The PTC element 10 may be formed in a circular or polygonal shape, and the area and thickness thereof are preferably designed in consideration of the conditions of use of the PTC element 10, that is, the constant current, the overcurrent to be limited, the operation time, and the like. .

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 conductive particles are impregnated in a crystalline or semi-crystalline polymer having an amorphous region and a crystalline region. 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 particles is shifted and the connection state is sporadically disconnected, thereby rapidly increasing the overall resistance of the device.

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.

The PTC fault current limiter according to the present embodiment includes an electrode portion 20 provided to contact the PTC element 10. Preferably, the electrode portion 20 includes contact electrodes 21a and 21b in contact with the PTC element 10 and current leads 22a and 22b for energizing the contact electrodes 21a and 21b to the circuit.

The contact electrodes 21a and 21b may be made of copper foil or other metal based elements. In addition, the contact electrodes 21a and 21b may be installed in the form of reducing contact resistance as much as possible, such as, for example, lamination or free contact, but are preferably installed on at least one surface of the PTC element 10.

More preferably, the contact areas of the contact electrodes 21a and 21b are determined so as not to cause flashover between the contact electrodes 21a and 21b during operation of the PTC element 10 in consideration of the area and thickness of the PTC element 10.

The current leads 22a and 22b are connected to the contact electrodes 21a and 21b to energize the contact electrodes 21a and 21b with the power system. The current leads 22a and 22b are manufactured by using a metal-based material, and the size of the current leads 22a and 22b is preferably calculated by calculating a current carrying capacity so as not to exceed the temperature allowed for system current.

More preferably, the current limiter may be provided with a connection electrode (not shown) interposed between the contact electrodes 21a and 21b and the current leads 22a and 22b. The connection electrode is made of metal such as gold, silver, etc., which has a relatively low resistance, and serves to smoothly conduct electricity from the power system to the current limiter.

According to the present embodiment, the PTC device 10 includes an insulator provided around the PTC element 10. The insulator includes a first insulator 30 composed of a flowable insulator and a second insulator 40 provided to surround the first insulator 30.

The first insulator 30 may be configured to surround the PTC element 10, all of the contact electrodes 21a and 21b, and some or all of the current leads 22a and 22b. As a result, the function of preventing arcing and flashover can be more effectively exerted as the first insulator 30 will be described later.

The first insulator 30 is configured to directly surround the PTC element 10 to remove arcs and noise generated between the PTC element 10 and the contact electrodes 21a and 21b. When the PTC element 10 is operated due to overcurrent, an arc is instantaneously generated between the interfaces with the contact electrodes 21a and 21b, and the PTC element 10 is liable to burn 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. At this time, the first insulator 30 instantly absorbs and dissipates the instantaneous impact energy and the initial arc generated at the interface between the PTC device 10 and the contact electrodes 21a and 21b during the operation of the PTC device 10. Therefore, arc and noise are hardly generated. In addition, since it is made of a flowable insulator, a space that cannot be completely contacted between the PTC element 10 and the contact electrodes 21a and 21b can be hermetically sealed, thereby reducing the occurrence of an arc.

In addition, the first insulator 30 ensures an insulating distance between the contact electrodes 21a and 21b at both ends. As described above, an arc occurs instantaneously between the contact electrodes 21a and 21b of the PTC element 10 and the interface between the PTC element 10 and the interface when the current limiting operation of the PTC element 10 occurs. The flashover is generated between the contact electrodes 21a and 21b at both ends. Therefore, it is important to secure an insulation distance where no flashover occurs. The first insulator 30 is configured to surround the PTC element 10, all of the contact electrodes 21a and 21b, and some or all of the current leads 22a and 22b. The insulation distance is secured at both ends of the PTC element 10. That is, considerable dielectric strength can be secured around the contact electrodes 21a and 21b, thereby preventing flashover.

In addition, the PTC device 10 may be cooled to a normal temperature state in a fast time after the operation of limiting current by the first insulator 30.

Specifically, the flowable insulator constituting the first insulator 30 may be made of a vacuum. More specifically, the vacuum is a vacuum layer having a vacuum degree of 10 ⁻³ torr or more. Vacuum has a dielectric strength 10 times higher than that of general air, and in the vacuum state, since there is no medium that can transfer energy, it can prevent the breakdown of the insulation. Therefore, when the first insulator 30 is configured as a vacuum, a high dielectric strength in vacuum can be realized, and the arc can be extinguished by using the arc rapidly extinguished in a vacuum, and the insulator can be made lighter.

Alternatively, the flowable insulator constituting the first insulator 30 may be made of gas. Preferably the gas may be composed of more than 1 bar SF ₆ gas or N ₂ gas.

The SF ₆ gas is an inert gas, which is odorless, harmless, non-toxic, non-flammable, and non-explosive, has a low dielectric loss and leakage loss, and is a thermally stable gas. The dielectric strength is 89 kV / cm, which is considerably higher than atmospheric pressure air having an dielectric strength of 30 kV / cm. In addition, it has a low dielectric constant compared to liquid and solid insulators, and thus has a low charging current.

The N ₂ gas is a nonflammable gas similar to SF ₆ gas as a main component of air, and can be easily obtained from the surroundings and is economical.

More preferably, the gas may be composed of a SF ₆ -N ₂ mixed gas of 1 bar or more. As a main component of air, N ₂ gas with low boiling point, low cost, and excellent chemical stability such as non-toxicity and non-combustibility, mixed with SF ₆ has less deterioration of dielectric strength due to the presence of foreign substances or roughness of electrode surface. It can be used as an economical insulating gas in terms of cost and low cost.

Alternatively, the flowable insulator constituting the first insulator 30 may be made of oil.

Preferably, the oil does not contain impurities, and may be an insulating oil having cooling performance. For example, the oil may be composed of mineral oil mainly composed of hydrocarbons of leadene, paraffinic, and aromatic hydrocarbons. The cooling performance means that the insulating oil has a performance capable of returning to a normal state within 3 minutes after the operation of the PTC element 10.

Although specific examples of the flowable insulator have been disclosed herein, the present invention is not limited thereto, and it should be understood that various modifications may be employed.

The PTC fault current limiter according to the present embodiment includes a second insulator 40 provided to surround the first insulator 30. The second insulator 40 serves as a case to maintain and support the shape of the first insulator 30 that can expand during the current-limiting operation. In addition, the first insulator 30 is protected from an external environment such as light, humidity, and contaminants. Therefore, the first insulator 30 is preferably configured to be completely airtight from the outside.

The second insulator 40 may be made of an insulating material such as polyethylene, polypropylene, or bakelite. However, the present invention is not limited thereto, and various modifications may be employed by those skilled in the art within the scope for achieving the object of the present invention.

3 is a cross-sectional view schematically showing a multiple insulated fault current limiter according to another embodiment of the present invention. In FIG. 3, 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. 3, the PTC fault current limiter according to the present embodiment further includes a PTC element 10 and a coating layer 50 interposed between the electrode part 20 and the first insulator 30.

When molding the PTC device 10 with the first insulator 30, bubbles may be generated at the contact interface thereof. Then, when the PTC device 10 operates, insulation breakdown may proceed along the bubble, so that the function of the first insulator 30 may not be properly exhibited. In this case, when the coating layer 50 is provided at the interface, the first insulator 30 may be more closely adhered to the surface of the PTC device 10, and thus the action of the PTC current limiter becomes more effective.

Preferably, the coating layer 50 may be made by applying epoxy or silicone rubber. However, the present invention is not limited thereto, and various modifications may be employed by those skilled in the art within the scope for achieving the object of the present invention.

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 with multiple insulators according to the present invention effectively suppresses and eliminates arcs generated at the interface between the PTC element and the electrode when the overcurrent or short-circuit current is limited, not only in a low voltage system but also in a high voltage system. can do. This prevents flashover between the electrodes, thereby preventing wear of the PTC element and further extending the life of the PTC fault current limiter.

Claims (8)

In the PTC fault current limiter which current-limits current using the PTC characteristic, PTC device; Electrode portions disposed on both surfaces of the PTC element so as to interpose the PTC element; A first insulator provided around the PTC element to surround the PTC element; And And a second insulator provided to surround the first insulator. And the first insulator is a flow insulator. 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, wherein the electrode unit, A contact electrode provided to directly contact the PTC device; And And a current lead connected to the contact electrode to energize the contact electrode with the circuit. The method according to any one of claims 1 to 3, The flowable insulator is PTC limiter, characterized in that any one or more selected from the group consisting of vacuum, gas and oil. The method of claim 4, wherein PTC vacuum limiter, characterized in that the vacuum has a degree of vacuum of 10 ^-3 torr or more. The method of claim 4, wherein PTC gas limiter, characterized in that the gas is 1 bar or more SF _6, N ₂ or a mixture thereof. The method of claim 4, wherein PTC oil limiter, characterized in that the oil is an insulating oil having a cooling performance. The method according to any one of claims 1 to 3, PTC limiter, characterized in that it further comprises a coating layer interposed between the PTC element or the electrode portion and the first insulator.

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