JPS6238813B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuse, and particularly to a fuse having a fusible element (hereinafter referred to as a display fusible element) for indicating the operation of a small current rated fuse.

As shown in FIG. 1 of the accompanying drawings, _the conventional general structure of such a fuse is as follows. A copper inner terminal metal 4 is fixed to both terminal metals 1 and 1 _-1 by screws 3 respectively.
and 4 _-1 , a porcelain winding core 5 held at both ends by inner terminal metals 4 and 4 _-1 , and a winding core 5 made of porcelain, which is wound spirally on the outer peripheral surface of the winding core 5 and has both ends A silver main fusible element 6 connected to the inner terminal metals 4 and _4-1 , and a plastic display cover located at one end of the central hollow part of the winding core 5 and fixed to the terminal metal 1 on that side. 7, a plastic display rod 9 which is located inside the display cover 7 and is always urged to protrude by a pressure spring 8; A display fusible element 10 made of nichrome that is connected to both terminal metals 1 and 1 _-1 and acts to hold down the display rod 9 against the force of the push spring 8, and the outside except for the inside of the display cover 7. For example, the cavity in the cylinder 2 is filled with:
It is composed of an arc extinguishing agent 11 such as silica sand. However, the materials for each component mentioned above are merely those commonly used.

In addition, to explain the main fusible element 6 and the display fusible element 10, the main fusible element 6 is made by crushing a round wire-shaped one or punching a plate-shaped one as shown in FIG. As shown in Figure 2, the fuse is formed in such a way that parts with small cross-sectional areas are distributed over the entire length, and this is done to suppress the operating overvoltage by causing staggered firing when the fuse blows. It is. In addition, the display soluble element 10
A nichrome wire with a diameter of 0.1 to 0.3 mm is used, but this wire must have the tensile strength necessary to keep the indicator bar 9 in place at all times against the tension of the push spring 8. In addition, in order to prevent a situation in which the part in the arc extinguishing agent 11 melts first and the part holding the display rod 9 in the display cover 7 does not melt when melting, the display cover 7 is In some cases, the part that holds the display rod 9 inside is made thinner than the part in the arc extinguisher 11, but generally the space inside the display cover 7 is made thinner than the part in the arc extinguisher 11. Because they have poor thermal conductivity, they heat up when current flows and melt first, so they are often constructed with the same thickness without changing the thickness.

Since the conventional fuse is constructed as described above, in a normal state, current flows through one terminal metal 1, the inner terminal metal 4, the main fusible element 6, the other inner terminal metal _4-1 , and the terminal metal 1. The circuit passing through _-1 and the circuit passing through terminal metal 1, display fusible element 10 and the other terminal metal 1 _-1 flow in parallel, but normally the resistance of display fusible element 10 is the main fusible Since it is much higher than that of element 6, most of the current flows through the main fusible element 6.
flows. On the other hand, if the current becomes too large,
Since the main fusible element 6 melts first, and therefore the entire current is commutated to the display fusible element 10, the display fusible element 10 also melts, and as a result, the indicator rod 9 is unrestrained. Then, the tension of the push spring 8 causes the indicator bar 9 to protrude from the center hole of the terminal metal 1, thereby operating to indicate the operation of the fuse.

Conventional fuses are constructed and operate in this way, but the phenomenon during the arc after the fuse blows is as follows:
As shown in FIG. 3, it can be represented by an equivalent circuit.

In other words, the arc voltage v of the fuse is calculated by multiplying the combined resistance R _a · R _b /R _a +R _b of the arc resistance R _a of the main fusible element and the arc resistance R _b of the display fusible element by the passing current i. It is expressed by the first formula: v=R _a ·R _b /R _a +R _b ·i . Therefore, as can be seen from the above formula,
The arc voltage will be more influenced by the fusible element with lower arc resistance.

The maximum value of this arc voltage is called the operating overvoltage, and if it becomes excessive, the insulation of the circuit or equipment in which the fuse is used will be destroyed, so the upper limit is limited by the standards.

In order to suppress this operating overvoltage, as described above, the main fusible element 6 is provided with a portion having a small cross-sectional area, and firing is performed at a different time.
Here, the thinner the fusible element is, the better the shearing performance of the fusible element is. Therefore, the main fusible element is designed to be as thin a wire as possible and to use a large number of them. By using a large number of thin wires, the contact between the fusible element and the arc extinguisher is improved, the energy processed by each fusible element is also reduced, and the fusible element The vapor content of the material is also small, and therefore the cross-sectional area of the arc is also small, resulting in high arc resistance.

On the other hand, for fusible elements of the same thickness, the smaller the fusing Jule integral, that is, the integral value of the square of the instantaneous value of the current flowing through the fuse during the fusing time, the better the fusing performance; , the arc resistance increases, but this is because the smaller the Joule integral for fusing, the easier it is to blow out, and therefore the energy required for processing is smaller.

In addition, in ordinary fuses, the display fusible element uses a thinner wire than the main fusible element and also uses a material with a smaller fusing integral, resulting in high shearing performance and high arc resistance. . As explained in the first equation above, this means that
In conventional fuses, the indicated fusible element has little effect on the operating overvoltage of the fuse, since the arc voltage is greatly influenced by the fusible element with lower arc resistance.

However, when the rated current of the fuse becomes a fuse with a very small capacity of about 1 ampere, the thickness of the displayed fusible element becomes equal to that of the main fusible element, and there is no large difference in the fusing integral. The influence of the display fusible elements on the insulation performance increases, and the operating overvoltage may also increase in some cases.
It will also be determined by the display fusible element rather than the primary fusible element.

In order to deal with such situations, it is important to suppress the operating overvoltage of display fusible elements.
To this end, as shown in FIGS. 4 and 5, in the past, about half of the display fusible element 20 on the opposite side from the display rod was made thicker, and the specific Joule integral, that is, the fusing Joule integral, was This part is made of a wire made of a material with a large value divided by the square of the minimum cross-sectional area of the fusible body, and a part 20 _-1 with a large fusing Joule integral is provided, so that the fusing Joule integral is larger than other parts. This caused a time lag.

However, in this case, the following problems may occur.

In other words, when the fault current is relatively large, the inflow energy is large, so the display fusible element 20 fires almost simultaneously over its entire length following the firing of the main fusible element, easily causing an accident. However, when the current is relatively small, the main fusible element 6 is provided with small cross-sectional areas distributed over its entire length as described above. , the display fusible elements 20 that were fired over almost the entire length but were subsequently fused were the fourth and fifth display fusible elements 20.
Only a small portion 20 _-2 of the fused Joule integral shown in the figure fires, and a large portion 20 _-1 of the fused Joule integral fires after a considerable delay. FIG. 6 shows the state at the time when only a small portion 20 _-2 of this fusible Joule integral is fired, and the portion indicated by a dotted line indicates the fusible element that has fired.

To explain the state at this point, point B where the display fusible element 20 is connected to the terminal metal 1 _-1 ,
The point C 1 at the tip of the large portion 20 _-1 of the fused Joule integral, which is the unfired part of the display fusible element _20, is at the same potential, and the point C ₁ and the main flux closest to this point C ₁ are at the same potential. A voltage between B and _D1 is applied to the point _D1 of the firing part of the melting element 6. For example, if the point _D1 of the arcing part is at the center of the main fusible element 6, a voltage that is 1/2 of the recovery voltage will be applied. Therefore, this voltage may destroy the insulation between point _C1 on the tip and point _D1 on the firing part, and in this case, the insulation between point A on terminal metal 1 and point D1 on the firing part may be broken. Re-ignition occurs in the main fusible element between point D ₁ of the arc and the arc diameter increases,
The shear cutting performance may deteriorate. To avoid this situation from occurring, point _C1 and point
_D1 , that is, between the main soluble element 6 and the display soluble element 20, it is necessary to increase the distance, but as a result, there is a drawback that the outer cylinder 2 becomes larger.

An object of the present invention is to obtain a fuse that eliminates such conventional drawbacks, and for this purpose, the display fusible element has a length approximately half of its total length not including its ends. It is characterized by having a larger fusing Joule integral in the part than in other parts.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings showing one embodiment thereof.

In FIG. 7, reference numeral 30 denotes a display fusible element, and a large portion 30 _-1 of the fused Joule integral is located at a position distant from the end of the display fusible element 30, for example.
In FIG. 7, it is provided approximately in the center with a length corresponding to about half of the total length. The other parts are the same as conventional fuses.

Since the fuse of the present invention is constructed in this way, in the event of a blowout caused by a relatively small fault current, the main fusible element 6 will blow out first as described above;
Subsequently, a small portion 30 _-2 of the fusible Joule integral of the display fusible element 30 is fused, and both of them are fired.
At this point, the main fusible element 6 fires over its entire length as described above, but the large portion 30 _-1 of the fusible Joule integral of the display fusible element 30 remains unfired. The point C ₂ which is the tip of the unfired portion, that is, the large portion 30 _-1 of the unfired Joule integral, and the point C ₃ which is the rear end are at the same potential. In this case, if the points of the main fusible element 6 closest to the point C ₂ at the tip and the point C ₃ at the rear end are defined as points D ₂ and D ₃ , respectively, the voltage between D ₂ and D ₃ is It extends between C ₂ and D ₂ and between C ₃ and D ₃ . For example, the distance between D ₂ and D ₃ is the total length of the main fusible element 6.
If the length is 1/2, then C ₂ − D ₂ and C ₃
A voltage of 1/4 of the circuit voltage is applied between -D and ₃ .

In this way, the voltage applied between the unfired part of the display fusible element and the fired part of the main fusible element is 1/2 compared to the case where the large part of the fusing integral is concentrated at the end. Therefore, dielectric breakdown is less likely to occur, and as a result, the shearing performance is improved and the outer cylinder can be made smaller.

The above embodiment shows a case where a large part of the fusible unit of the display fusible element is concentrated at a position away from the end of the fuse, but as shown in FIG. Needless to say, if it is provided in a similar manner, it will be even more effective.

As described above, according to the present invention, the voltage applied between the unfired portion of the display fusible element and the main fusible element is reduced, making it difficult for dielectric breakdown to occur and improving the insulation performance. This provides the effect of making the outer cylinder smaller.

[Brief explanation of the drawing]

Fig. 1 is a partially sectional front view showing the structure of a conventional fuse, Fig. 2 is a developed plan view of the main fusible element, and Fig. 3 is a partially sectional front view showing the structure of a conventional fuse.
The figure is an equivalent circuit diagram showing the phenomenon during arcing of a fuse, Figure 4 is a longitudinal sectional view showing the structure of another conventional fuse, Figure 5 is a developed view of the displayed fusible element, and Figure 6 is the operating state. 4 is a longitudinal sectional view of the fuse, FIG. 7 is a longitudinal sectional view of an embodiment of the present invention, and FIG.
The figure is a front view showing another example of the display soluble element. 6... Main soluble element; 10, 20, 30, 40...
...Fusible element for operation display; 20 _-1 , 30 _-1 , 40
_-1 ...large part of the fusing Joule integral; 20 _-2 ,
30 _-2 , 40 _-2 ... small part of the fused Joule integral.

Claims (1)

[Scope of Claims] 1. In a fuse having a fusible element for indicating operation that is electrically connected in parallel with the main fusible element, the fusible element for indicating operation has a length of about half of its total length. A fuse characterized in that the fuse has a larger portion of the fused Joule integral than other portions, and the larger portion of the fused Joule integral is located in a portion away from the end of the fusible element for displaying operation. . 2. The fuse according to claim 1, wherein a large part of the fused unit integral of the fusible element for displaying the operation is distributed at a plurality of locations.