JP5612879B2 - fuse - Google Patents

Description

  The present invention relates to a fuse used as an SPD (Surge Protective Device) separator.

In order to suppress overvoltage caused by lightning surge current flowing in the power supply system due to transient voltage fluctuations caused by lightning strikes, etc., and to protect devices connected to the power supply system, an SPD for surge protection is shown in FIG. As shown in FIG. 2, the power supply system is interposed between the ground point.
In addition, when a surge current exceeding the surge current capability flows through this SPD or when a short-circuit failure occurs due to secular change, the power supply to the electronic device is interrupted by the breaker inserted in series in the power supply system, Sometimes stopped.
For this reason, when the SPD is short-circuited, a fuse (see, for example, Patent Document 1) is connected in series with the SPD as a circuit breaker (SPD separator) for disconnecting the failed SPD from the power supply line.

JP-A-52-93950

However, when a fuse is used for the SPD separator, the conventional power fuse does not have a definition of an impulse current withstand capability against a surge.
For this reason, when a fuse having a fusing I ² t larger than the I ² t obtained from the lightning surge waveform is used, the rated current may be larger than the input breaker (breaker) for the electronic device that is the protection target device. It was.
Therefore, when a short-circuit failure occurs in the SPD and the current flowing through the fuse and the short-circuited SPD is larger than the rated current of the input breaker, the input breaker may be cut off first, thereby preventing protection coordination.

That is, from the Joule heat (RI ² t) generated in the fuse element to the arc extinguishing sand of the fuse element, in Patent Document 1, the heat radiation amount and heat radiation amount (Tout) to the high alumina ceramic sintered body are removed. Thermal energy (E (element)) is stored in the fuse. The accumulated thermal energy raises the temperature of the fuse element, the fuse element is melted by this heat, and the fuse is cut off, so that the SPD is separated from the system.
Here, when the fuse is interrupted when a large current is interrupted (within 10 ms), the heat transfer from the fuse element to the arc-extinguishing sand or the high alumina ceramic sintered body is difficult to be transmitted due to heat transfer by point contact. It becomes the heat insulation state, and heat generation proceeds.
For this reason, the interruption characteristic of the short-circuit current is evaluated by the square time integral value (melting I ² t) of the current flowing through the fuse before the fuse is interrupted. Equation (1) for obtaining the square time integral value of the current flowing through the fuse is shown below.

Also, the temperature rise of the fuse element due to lightning surge current can be considered as an adiabatic change because of a very short time phenomenon. For this reason, the heat energy applied to the fuse by the lightning surge is based on the square time integrated value (surge I ² t) of the current calculated from the time fluctuation curve of the surge current, which is obtained from the above equation (1). Therefore, the fusing I, which is a value obtained by integrating I ² t in the time from when the current starts to flow in the short-circuit breaking test of the fuse to just before the fuse blows and the arc is generated, than the surge I ² t. ^{by 2 t} is selected larger fuses, fuse as SPD separator is selected.
In general, the fuse element is composed only of a conductive metal, and the cross-sectional area of the conductor increases as the rated current of the fuse increases.
When the cross-sectional area of the fuse element is increased, the volume is increased, thereby increasing the heat capacity of the fuse element. Due to the increase in the heat capacity, the fuse blown I ² t increases.

In addition, power fuses have a large rated current and are generally used in circuits that have a very large short-circuit current in an abnormal state, such as in a low voltage distribution board adjacent to a transformer. For this reason, it is necessary to use a fuse with as small a fusing I ² t as possible and a high breaking speed.
Therefore, if a fuse with a large surge current resistance (surge I ² t) is selected from the power fuse, the rated current of the fuse will be large (melting I ² t will be large), and the rated current of the input breaker of the target device protected by the SPD Bigger than.
Therefore, when the SPD deteriorates and a short-circuit failure occurs, the input breaker of the protection target device is cut off before the fuse serving as the SPD separator, which causes a problem when supplying power to the device.

The present invention has been made in view of such circumstances, and a fuse having a low rated current and a low melting current as much as possible with respect to an overcurrent, as compared with a surge current withstand capability (surge I ² t) against an impulse surge current. The purpose is to provide.

Fuse of the present invention, a conductor is coated on the electrodes and the entire surface other than the end portion consisting of the conductor, the amount of heat generated in the conductor is constituted by a fuse element made of an insulator film for radiating the heat conduction, the The fuse element is divided into a plurality of pieces and connected in parallel, and the conductor of each of the divided fuse elements is coated with the insulator film, and the thickness of the insulator film is determined when a steady current is applied. The conductor has an equilibrium temperature that is lower than the conductor equilibrium temperature when the fuse element is not divided and the insulator film is not coated .

The fuse of the present invention comprises a conductor having a through hole parallel to the direction of a current flow path, and an insulator film that coats the entire surface including the inner surface of the through hole other than the end portion serving as an electrode of the conductor. It is comprised by the fuse element which becomes.

The fuse of the present invention includes a conductor made of a metal foam and an insulator film that is coated on the entire surface of the pores of the conductor other than an end portion that becomes an electrode of the conductor, and dissipates heat generated in the conductor by heat conduction. is constituted by a fuse element made of said fuse element is connected in parallel are divided into a plurality of, and divided the fuse element, each of the conductor are coated with the insulator film, the thickness of the insulating film The thickness of the conductor when the steady current is applied is lower than the temperature of the conductor when the fuse element is not divided and the insulator film is not coated. To do.

In the fuse of the present invention, the insulator film has a thickness from the outer peripheral surface of the conductor when the temperature of the conductor reaches a maximum when a surge current is applied with a prescribed surge waveform. It is less than the distance which the temperature gradient in the thickness direction to the outer peripheral surface of has arisen.

In the fuse of the present invention, the fuse element is divided into a plurality of pieces and connected in parallel, and the conductor of each of the divided fuse elements is coated with the insulator film, and the thickness of the insulator film is The balance temperature of the conductor when a steady current is applied is a thickness that is lower than the balance temperature of the conductor when the fuse element is not divided and the insulator film is not coated.

  The fuse of the present invention is characterized in that a plurality of fuse elements each having the insulator film coated on a conductor are connected in parallel.

As described above, according to the present invention, in the fuse configuration, the outer peripheral surface excluding the conductor electrode is coated with the insulator film that causes thermal conduction, and the insulator film is applied to the entire outer peripheral surface of the conductor. Since the heat dissipation effect by heat conduction is enhanced, it is possible to suppress a temperature rise due to a transient surge current in a lightning surge, and to improve the surge current withstand capability against the impulse current of the fuse.
As a result, the surge current withstand capability (melting I ² t) can be increased without greatly changing the rated current of the fuse, so that the rated current is smaller than the rated current of the input breaker of the target device protected by the SPD. In addition, it is possible to provide a fuse having a necessary surge current capability.

It is a figure which shows the structural example of the fuse by embodiment of this invention. Fuse element (a): Conventional fuse, (b): A graph showing a change in the maximum temperature of the conductor H after applying a surge current for the fuse of the present embodiment. It is a graph which shows the temperature distribution in the conductor H and insulator film C internal cross-section after progress for 20 microseconds after applying a surge current. It is a graph which shows a response | compatibility with the energizing current and the maximum temperature in each conductor H, after energizing for 2 seconds to the conductor H which coated the insulator film C of different thickness. It is a graph which shows the time change of the maximum temperature of the conductor H after surge current application. It is a graph which shows the change of the maximum temperature of the conductor H after applying a surge current to the conductor H of a different cross-sectional area each coated with the insulator film C to a thickness of 10 μm. It is a graph which shows the maximum temperature of the conductor H corresponding to the cross-sectional area of a conductor, when the same surge current (8/20 microseconds and peak current of 7500 kA / cm < ² >) per cross-sectional area of a conductor is sent through the conductor. It is a figure which shows the structural example of the fuse by other embodiment of this invention.

<First Embodiment>
Hereinafter, a fuse according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a conceptual diagram showing a configuration example of a fuse (SPD separator) according to an embodiment of the present invention. This embodiment is used as a separator that disconnects the failed SPD from the power supply system when the SPD fails.
As shown in FIG. 1 (b), the fuse of this embodiment is composed of a fuse element G. The fuse element G is a fusible conductor H (FIG. 1 (a)) and a fusible body. It is comprised from the insulator film C which consists of an insulating substance with good heat conductivity closely contacted (contacted on the whole surface) except for the electrode surfaces D1 and D2 of the conductor H. . As shown in FIG. 1C, the electrode surfaces D1 and D2 are connected in series with the SPD and are interposed between the power supply system and the grounding point. Here, the conductor H may be not only a rectangular parallelepiped shape as shown in FIG. In the case of a cylinder, both bottom surfaces of the cylinder are used as electrodes.
Here, a metal such as copper is used for the conductor H, and the insulating material of the insulator film C is silicon dioxide (SiO ₂ ), alumina-based aluminum oxide (Al ₂ O ₂ ), titania-based titanium oxide (TiO). ₂ ), zirconia-based (ZrO ₂ ), tungsten carbide (WC), or the like can be used.
Hereinafter, the insulating material adhered to the adherend surface will be described as the insulator film C. The insulator film C is formed, for example, by bringing an insulating substance into close contact with the adherend surface by coating.

Further, by forming the insulator film C, the cross-sectional area of the conductor H is set to a smaller value than the conventional conductor cross-sectional area of the fuse element having the same rated current.
That is, by forming the insulator film C on the adherend surface of the conductor H (entire surface other than the electrode formation surface), the amount of heat generated by the transient current fluctuation generated by the lightning surge can be reduced from the conductor H to the insulator film. C can be dissipated by heat conduction with a shorter response time than heat radiation or heat transfer.
Thereby, in this embodiment, the temperature rise by transient surge currents, such as a lightning surge of the conductor H, can be reduced, and when the fuse has the same surge current withstand capability, the cross-sectional area of the conductor H is changed to the conventional fuse. High surge current withstand characteristics can be obtained even if it is set smaller than the above. That is, the rated current can be reduced.
As a result, according to the present embodiment, when the SPD has a short-circuit failure, the SPD that has failed due to this failure current can be quickly and reliably cut off from the power supply, and the fuse blown I ² t can be set large. It becomes possible to set smaller than the rated current of the input breaker of the target device protected by the SPD.

Next, the setting of the thickness formed by the insulator film C in this embodiment will be described. A temperature gradient in the insulator film C is generated by the amount of heat generated by the above-described lightning surge. This temperature gradient changes depending on characteristics such as thermal conductivity, specific heat, density, and the like depending on the materials of the conductor H and the insulator film C, and the amount of heat generated by a lightning surge.
Therefore, the condition for the thickness of the insulator film C necessary for heat dissipation is set by the following equation (2).

When the rated surge current (peak current 7500 kA / cm ² , 8/20 μs: rated peak surge current) is flowed according to the above-described unsteady heat conduction equation, the temperature of the conductor H is calculated, and when this temperature becomes maximum Then, a temperature gradient generated in the thickness direction from the outer peripheral surface of the conductor H to the outer peripheral surface of the insulator film C inside the insulator film C in the vicinity of the adherend surface of the conductor H is obtained. Then, the thickness of the insulator film C is set to be equal to or shorter than the distance where the temperature gradient is generated. As a result, the amount of heat can be effectively radiated to the outside from the outer peripheral surface of the insulator film C, and the temperature rise of the conductor H can be controlled under transient heat generation due to a lightning surge current.

Next, the setting of the thickness of the insulator film C necessary for the conductor H to be melted by the overcurrent that flows when the SPD is short-circuited and operates as an SPD separator will be described.
From the Joule heat generated in the conductor H, the surface radiant heat radiated from the outer peripheral surface of the conductor H, and the balance condition of the surface radiant heat, the maximum temperature of the fuse due to overcurrent is calculated by the following equation (3). Then, the thickness of the insulator film C is set so that the maximum temperature of the fuse due to overcurrent does not decrease by 20% or more when the insulator film C is formed compared to the case without the insulator film C.

Here, the thickness of the insulator film C is set so that the maximum temperature of the fuse due to overcurrent is not reduced by 20% or more when the insulator film C is formed compared to the case without the insulator film C. The reason is as follows.
That is, fuses are roughly classified into type A and type B fuses. According to the standard (JIS C 8352), the A type is 1.35 times the rated current and the B type is cut off when 1.6 times the current flows. Therefore, by changing the type A fuse to the type B fuse without changing the rated current, the magnitude of the fusible breaking current is 1.18 (1.6 / 1.35) in order to improve the surge current withstand capability. ) Must be within double. For this purpose, it is necessary that the maximum temperature of the fuse due to overcurrent should not be lowered by 20% or more when the insulator film C is formed compared to the case where the insulator film C is not provided.

  In the above equation (3), Δd that does not decrease the equilibrium temperature by 20% or more is obtained with respect to the equilibrium temperature T when Δd = 0 (when the thickness of the insulator film C is 0, that is, Δm = 0). Thus, when the SPD is short-circuited, the thickness of the insulator film C that does not impair the overcurrent cutoff characteristic for the fuse to function as an SPD separator is set as Δd.

Next, in the present embodiment, a case where copper is used as the conductor H and SiO ₂ is used as the material of the insulator film C will be described.
FIG. 2 shows the maximum temperature of the conductor H on the vertical axis when the same surge current (peak current 7500 kA / cm ² , 8/20 μs) per cross-sectional area of the conductor H is applied to the conductor H having the same cross-sectional area. Shows the elapsed time from the start of surge application, and the conventional fuse (no insulator film) and the fuse of this embodiment (the fuse element G in the fuse of the present invention: the insulator film C having a thickness of 100 μm on the conductor H). The change of the maximum temperature of the conductor H in coating) is shown. The cross section of the conductor H is square, and its cross sectional area is 10000 (= 100 × 100) μm ² .
As can be seen from FIG. 2, by coating the conductor H with the insulator film C, the maximum temperature due to heat generated by the surge current of the conductor H can be reduced.

Next, FIG. 3 shows the temperature at the cross section of the conductor H and the insulator film C (cross section taken along the cut surface S in FIG. 1B) after applying a surge current to the fuse according to the present embodiment after 20 μs has elapsed. Distribution is shown. The vertical axis represents temperature, and the horizontal axis represents the distance from the center of the fuse element G. In this case, the fuse element has a structure in which a conductor H having a cross-sectional area of 10000 μm ² is coated with an insulating film C having a thickness of 100 μm.
As can be seen from FIG. 3, the temperature gradient (temperature boundary layer) of the inner cross section of the insulator film C occurs from the position in contact with the outer peripheral surface of the conductor H to a distance of 15 μm. Therefore, when the insulator film C is SiO _2, relative to the contact surface of the conductor H, thickness of coating the insulator film C, by a 15μm or 15μm or less, the effect of the maximum temperature of the conductor H Can be reduced. In other words, in the present embodiment, the thickness of the insulator film C is set at a distance where a temperature gradient is generated or less than that in consideration of heat dissipation characteristics.

Next, FIG. 4 shows five types of fuse elements in which the same conductor H (φ100 μm) is coated with an insulator film C having five different thicknesses (0 μm, 5 μm, 10 μm, 15 μm, and 30 μm). It is a figure which shows the relationship of the equilibrium temperature T 'of the conductor H after energizing for 2 seconds (it is assumed that it is sufficient time for temperature to be balanced) calculated by the formula. The vertical axis represents the equilibrium temperature T ′, and the horizontal axis represents the current value for energizing the fuse element.
As can be seen from FIG. 4, by coating the conductor H with the insulator film C, the overall cross-sectional area including the conductor H and the insulator film C is increased, that is, the heat dissipation area is increased. It can be seen that the maximum temperature decreases and the maximum temperature decreases. This decrease in the maximum temperature not only increases the surge current withstand capability, but also increases the overcurrent rated current at the same time.
For this reason, as already explained, in order to keep the decrease in the maximum temperature when coated with the insulator film C within 20% as compared with the case where the insulator film C is not coated, the result of FIG. It can be seen that the thickness needs to be within 10 μm.

Next, FIG. 5 shows three types of fuse elements having the same insulator film C thickness (SiO ₂ thickness is 10 μm) and different square conductor cross-sectional areas (10000 μm ² , 2500 μm ² , 100 μm ² ). When equal surge current (peak current 7500 kA / cm ² , 8/20 μs) is applied per cross-sectional area of the conductor H, the maximum temperature of the conductor H is shown on the vertical axis, and the elapsed time after the start of surge current application is shown on the horizontal axis. .
As can be seen from FIG. 5, as the insulator film C is coated and the cross-sectional area of the conductor H is reduced, the rate of heat radiation from the conductor H to the insulator film C increases and the temperature rise of the conductor H is suppressed. It can be seen that the maximum temperature decreases.

Next, FIG. 6 shows the case where different surge currents are applied to two types of fuse elements in which two types of conductors having a square cross section and different cross sectional areas are coated with a 10 μm insulator film C. The maximum temperature of the conductor H is the elapsed time after the start of application of the horizontal axis surge current. From this result, when the insulator films C are equal and the maximum temperature of the conductor H is the same, the fuse element G having a conductor cross section of 100 μm ² is about 1.3 times as large as the fuse element G having a conductor cross section of 10000 μm ^2. It can be seen that it is possible to flow a surge current.

As a result, the conductor H is coated and formed in close contact with the insulator film C, and a fuse is formed by connecting a plurality of fuse elements G each having a conductor H having a small cross-sectional area in parallel. It has become possible to increase the permissible surge current tolerance. Thus, in the present embodiment, with a fuse having the same rated current, it is possible to increase the surge current resistance per cross-sectional area by reducing the conductor cross-sectional area of the fuse element.
In addition, with the same surge fuse, the conductor cross-sectional area of the fuse element can be reduced as compared with the conventional fuse. Therefore, according to the present embodiment, a fuse having both a large surge current resistance and a small rated current is provided. Can be realized.

Next, FIG. 7 shows a case where the same surge current (7500 kA / cm ² ) per conductor cross-sectional area of the fuse element is applied to the fuse element having the same insulator film C thickness (10 μm). Maximum temperature is shown on the horizontal axis.
As can be seen from this figure, when the surge current resistance is increased, if the cross-sectional area is 10000 μm ² or more, the cross-sectional area is 10000 μm in the present embodiment, assuming that there is almost no difference from the case where the insulator film is not coated. The cross-sectional area of the conductor H was reduced to 400 μm ² so as to be 80% or less of the maximum temperature of the ^second conductor H.

Therefore, when the thickness of the insulator film C is the same, reducing the conductor cross-sectional area of the fuse element further promotes heat dissipation from the conductor H, and can increase the surge current resistance.
However, since the rated current that defines the overcurrent increases in order to operate as an SPD separator when the SPD is short-circuited, the thickness of the insulator film C satisfies the conditions of the expressions (2) and (3). The thickness needs to be satisfied.
That is, by dividing into a plurality of fuse elements G without changing the cross-sectional area of the entire conductor, the insulator film C can more absorb the amount of heat generated by the conductor H, increasing the surge current withstand capability, The thickness of the insulator film C can be effectively optimized while satisfying the conditions of the equations (2) and (3) in the direction of decreasing the rated current.

As described above, according to this embodiment, the insulating film C is brought into close contact with the conductor H, thereby improving the heat dissipation characteristics due to heat conduction from the conductor H to the insulating film C, and transients caused by lightning surges and the like. Therefore, it is possible to reduce the temperature rise of the conductor H due to the surge current flowing in an automatic manner, and it is possible to improve the surge current resistance of the fuse.
Further, according to the present embodiment, the thickness of the insulator film C is calculated using the equation (3) from the unsteady thermal analysis of the equation (2) and the equilibrium condition of Joule heat and heat transfer due to overcurrent and heat dissipation due to radiation. By using this calculation method, the surge current withstand capability can be improved without increasing the rated current of the fuse so much.

Next, FIG. 8 is a diagram illustrating a configuration example of another embodiment of the fuse element G. In this figure, the conductor H shown in FIG. 1 (a) is a cube, but as shown in FIG. 8 (a), a metal foam is formed inside the conductor H, and the pores in the metal are A through-hole P having a diameter L is formed with the half length of the diameter as the cavity already described. Then, as shown in FIG. 8B, the fuse element G may be configured by adhering the insulating film C to the entire outer peripheral surface of the conductor H including the inner surface of the through hole P. The fuse composed of the fuse element G is used as an SPD separator as in FIG.
As shown in FIG. 8, the through hole P has a hole having a diameter L in a plane perpendicular to the penetrating direction and is formed from the electrode D1 toward the electrode D2 (parallel to the direction of the current flow path). Has been. Further, this hole may be formed as a square whose cross section is L with the length of each side.
In addition, when the cross section of the through hole P in a plane perpendicular to the penetrating direction is a circle, the thickness of the insulator film C in which the radius L / 2 of the through hole P is set in accordance with the conditions described above. The insulating film C is filled in the through hole P.
When the cross section in the plane perpendicular to the penetrating direction is a square, L / 2, which is half the length L of one side, is the same as the thickness of the insulator film C set in accordance with the conditions described above. A numerical value is used, and the insulating film C is filled in the through hole P.

Further, the conductor H is a foam metal formed of a metal such as copper or aluminum, and the length of half the diameter of the pores in the metal is the same as the thickness of the insulator film C set in accordance with the conditions already described. It may be formed by filling the insulator film C (so as to cover the entire surface of the foam metal, that is, the entire inside of the pores).
Even when the through hole P is formed in the conductor H described above or when the conductor H is a foam metal, the insulator film C is not formed on the electrode.

Further, according to the present embodiment, the insulator film C is brought into close contact with the conductor H to form the fuse element G, and a plurality of fuse elements G are connected in parallel to form a fuse. It is possible to form a fuse with a higher surge current withstand without changing the total cross-sectional area of the conductor as compared with the case of a single conductor.
Further, according to the present embodiment, by using the fuse formed as described above as the SPD separator, the conductor cross-sectional area of the conductor H is not changed, the value of the fusing I ² t is increased, and the surge current withstand capability is increased. It is possible to increase the rated current of the fuse as compared with the input breaker by providing the fuse with a surge current withstand capability as in the prior art.

C ... Insulator film D1, D2 ... Electrode surface G ... Fuse element H ... Conductor P ... Through-hole

Claims (5)

Conductors,
It is coated on the entire surface other than the end portion that becomes the electrode of the conductor, and is composed of a fuse element including an insulator film that dissipates heat generated by the conductor by heat conduction ,
The fuse element is divided into a plurality of pieces and connected in parallel, and the conductor of each of the divided fuse elements is coated with the insulator film, and the thickness of the insulator film is applied with a steady current. The fuse is characterized in that the equilibrium temperature of the conductor is lower than the equilibrium temperature of the conductor when the fuse element is not divided and the insulator film is not coated . A conductor having a through hole parallel to the direction of the current flow path;
A fuse comprising: a fuse element comprising: an insulating film that coats the entire surface including the inner surface of the through-hole other than the end portion serving as an electrode of the conductor. The fuse element is divided into a plurality of pieces and connected in parallel, and the conductor of each of the divided fuse elements is coated with the insulator film, and the thickness of the insulator film is applied with a steady current. 3. The fuse according to claim 2 , wherein an equilibrium temperature of the conductor is lower than an equilibrium temperature of the conductor when the fuse element is not divided and the insulator film is not coated. . A conductor made of foam metal;
The entire surface of the pores of the conductor other than the end portion serving as the electrode of the conductor is coated, and is constituted by a fuse element including an insulating film that dissipates heat generated by the conductor by heat conduction ,
The fuse element is divided into a plurality of pieces and connected in parallel, and the conductor of each of the divided fuse elements is coated with the insulator film, and the thickness of the insulator film is applied with a steady current. The fuse is characterized in that the equilibrium temperature of the conductor is lower than the equilibrium temperature of the conductor when the fuse element is not divided and the insulator film is not coated . The thickness from the outer peripheral surface of the conductor to the outer peripheral surface of the insulator film when the temperature of the conductor becomes maximum when a surge current is applied with a prescribed surge waveform. The fuse according to any one of claims 1 to 4, wherein the fuse is equal to or shorter than a distance at which a temperature gradient in the vertical direction is generated.

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