JPH09102402A - Surge absorber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surge absorber which can prevent damages such as smoke or heat caused by the breakage of surge absorbing element and gives no serious influence on the periphery parts. SOLUTION: Electrodes are formed on both surfaces of a varister element, and lead wires 2 and 3 are connected thereto, then the outer surface of the varistor element is coated with an epoxy resin, so as to form a surge absorbing element 1. The element 1 is housed inside an aluminum case 4 and the case 4 is sealed with a synthetic rubber 5. The lead wires 2 and 3 are inserted into through holes formed in the rubber 5 and drawn outside the case 4, and the element 1 is also held thereby.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surge absorber for protecting semiconductor devices and electronic devices from abnormal voltage such as lightning surge voltage.

[0002]

2. Description of the Related Art A conventional surge absorber is one in which lead wires are connected to a varistor element having electrodes on both sides and coated with an insulating resin.

Further, the recent mainstream power transmission and distribution system for general houses is a single-phase three-wire system capable of simultaneously supplying AC100V and AC200V with the reduction of power transmission and distribution costs and the spread of AC200V electric equipment which is advantageous in terms of electric power. ing.

FIG. 8 shows a distribution diagram of the single-phase three-wire system. The distribution line b (neutral line) is grounded, and AC 100V is supplied between the distribution line a and the distribution line b, AC 100V between the distribution line b and the distribution line c, and AC 200V is supplied between the distribution line a and the distribution line c. And
AC100V and AC200V are supplied simultaneously and with half the number of wires. Further, the three distribution lines a, b, c wired in the house are wired by the electrician for each house.

[0005]

If the wiring of the single-phase three-wire system is erroneously wired, AC200V is applied to the electric equipment for AC100V, the connection of the distribution line b is insufficient, or the phase is lost. AC connected with
An overvoltage in the range of AC100 to AC200V is applied between the distribution line a and the distribution line b or between the distribution line b and the distribution line c depending on the impedance balance of the electric device for 100V.

At this time, in the electric equipment for AC100V using the above-mentioned conventional surge absorber, AC200V is erroneously applied to the AC100V line, or AC is generated due to a neutral wire missing accident.
When the voltage of the 100V line rises, the surge absorber may be destroyed, and if smoke or heat is generated, there is a risk of affecting peripheral parts.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a surge absorber which prevents damage due to smoke generation and heat generation in the unlikely event that the surge absorbing element is broken, and does not exert a great influence on peripheral parts.

[0008]

In order to achieve this object, a surge absorber according to the present invention comprises a case having an opening,
A surge absorbing element housed in this case, an insulator for sealing the opening of the case, and a lead wire electrically connected to the surge absorbing element and penetrating the insulator to be drawn out of the case. The surge absorbing element is a varistor element having a pair of electrodes on the surface, and the outer periphery of the varistor element is coated with an insulating resin. This can prevent the influence of the destruction of the surge absorbing element.

[0009]

According to the first aspect of the present invention, when the surge absorbing element is broken, scattering of fragments, smoke and ignition are physically blocked from exerting effects outside the case. be able to. As a result, it is possible to prevent adverse effects on the parts around the surge absorber.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a surge absorber in one embodiment.

Electrodes are formed on both sides of a general disk type varistor element (element diameter of about 10 mm, varistor voltage V _{1 mA} is 220 V), and after connecting the lead wires 2 and 3, the exterior is coated with epoxy resin and surged. The absorption element 1 is formed. The surge absorbing element 1 is housed inside an aluminum case 4, and an opening of the aluminum case 4 is sealed with a synthetic rubber 5 which is an insulator. Further, the synthetic rubber 5 has through holes formed at the same intervals as the lead wires 2 and 3, and the lead wires 2 and 3 are inserted into the through holes to connect the lead wires 2 and 3 to the outside of the aluminum case 4. The surge absorbing element 1 is held while being pulled out. As shown in FIG. 1, the synthetic rubber 5 or the surge absorbing element 1 is positioned in the upper recess 6 formed by caulking the aluminum case 4, and the aluminum case 4 and the synthetic rubber 5 are caulked and mechanically joined. And keeps confidentiality. Further, on the upper surface of the aluminum case 4, a groove 8 is formed by pressing from one point as a center point toward the outer periphery of the aluminum case 4 as shown in FIGS. A pressure valve 7 having an explosion-proof mechanism with a range of 0.5 to 2.0 MPa is provided.

If the grooves 8 are evenly provided from the center of the upper surface of the aluminum case 4 toward the outer periphery, stress is more likely to be concentrated and the operating pressure can be lowered.
The higher the distance from the center, the higher. However, the operating pressure is groove 8
Is determined by the position of the central point forming the groove, the depth of the groove 8 and the number of grooves. Further, as can be seen from the drawing, the groove 8 is preferably provided so as not to penetrate the aluminum case 4 in order to prevent the entry of foreign matter. Further, by narrowing the shape of the groove 8 downward as shown in FIG. 5, stress is likely to be concentrated and the operating pressure can be lowered.

When the above surge absorber is used as a measure against surge between single-phase three-wire AC100V lines, if the surge absorber is destroyed by (1) AC200V erroneous application, (2) neutral wire is missing. A case of being destroyed by an accident will be described with reference to the drawings.

(1) In case of damage due to erroneous application of AC200V FIG. 6 shows the most general circuit configuration as a countermeasure against surge between lines of AC100V line, which is a test circuit of this embodiment. Reference numeral 31 is a glass tube type current fuse as an overcurrent protection device, and 32 is a sample surge absorber.

When AC 200 V is applied between the lines in FIG. 6, the varistor element is destroyed by overvoltage and is in a short-circuit state of low resistance. The glass tube type current fuse 31 is blown by the short-circuit current, and the current is cut off to suppress damage after the varistor element is destroyed. Therefore, the breakdown status of the varistor element is as follows.
Is greatly affected by the breaking characteristics, especially the breaking time. Therefore, it is important to select the rated current value of the glass tube type current fuse 31. The rated current value of the glass tube type current fuse 31 is determined to some extent based on the surge absorption performance of the varistor element, the shape and the state of destruction at the time of destruction. In the case of the disk type varistor element with an element diameter of 10 mm used in this example, It is common to use a rated current value of 7 A or less. In consideration of the above points, if the glass tube current fuse 31 having a rated current value of 7 A or more is used by mistake,
Assuming a case where the glass tube type current fuse 31 malfunctions, the rated current value of the glass tube type current fuse 31 is changed, and a breakdown situation comparison when AC200V is applied and destroyed is compared with the surge absorber of this embodiment. The case was applied and the case where a conventional general disc type varistor element was applied. Table 1 is a summary of the above experimental results.

[0016]

[Table 1]

According to (Table 1), the conventional surge absorber is
When the rated current value of the glass tube type current fuse 31 was 7 A or less, the exterior resin was slightly discolored and deformed, and some smoke and heat were generated. Glass tube type current fuse 3
When the rated current value of No. 1 was more than 7 A, there was a high risk of destruction because fragments of the surge absorber were scattered, a large amount of smoke, abnormal heat generation and ignition were observed.

On the other hand, in the surge absorber of this embodiment, when the rated current value of the glass tube type current fuse 31 is 7 A or less, no abnormality such as discoloration or deformation in appearance is observed, and when it is larger than 7 A. Scattering of debris from the surge absorber,
There was no abnormal appearance such as smoke or fire.

As described above, in the surge absorber of this embodiment, the surge absorbing element is casing with the aluminum case 4 and the synthetic rubber 5 even when the protective effect of the overcurrent protection device is not sufficiently exerted when the surge absorbing element is destroyed. Therefore, it is possible to suppress the scattering of debris due to the destruction of the surge absorbing element 1, heat generation, and the like, and further suppress or prevent the adverse effect of heat generation on the peripheral members.

(2) Destruction due to a neutral wire missing accident In the case of a neutral wire missing accident, the line voltage of the AC100V line may rise in the range of 100 to 200V. When the voltage across the varistor element rises above the maximum allowable circuit voltage, the varistor element is destroyed. After the breakdown, the short-circuit current is limited by the impedance of the electrical equipment connected between the lines, so it is expected that the overcurrent protection device will not operate or that it will take a long time to operate. Therefore, a short-circuit current will continue to flow through the varistor element after destruction, and it is expected that there will be a high risk of destruction such as a large amount of smoke emission, abnormal heat generation of the element, and ignition.

In FIG. 7, 43 is a variable AC power supply, and the applied voltage is AC1 assuming that the line voltage rises above the maximum allowable circuit voltage of the varistor element due to the accidental loss of the neutral line.
It was set to 80V. 41 is a 3 A glass tube type current fuse,
42 is a resistive load that limits the short-circuit current, and 44 is a test surge absorber. The reason why the glass tube type current fuse 41 having a rated current value of 3 A is selected here is to minimize the heat generation when the varistor element is broken and to maximize the surge absorption performance of the varistor element. The setting of short circuit current is
Assuming a case where the glass tube type current fuse 41 having a rated current value of 3 A does not melt, it is set to 4.8 A. This current of 4.8 A means that the 3 A glass tube current fuse 41 is
It is a current that operates within the time. That is, in the case of the 3 A glass tube type current fuse 41, a short circuit current of 4.8 A may continuously flow for a maximum of 1 hour. Actually, the glass tube type current fuse 41 of 3 A operates in about several seconds to several tens of seconds.

Therefore, in this test, in order to reproduce the case where the glass tube type current fuse 41 is not blown, the glass tube type current fuse 41 is not inserted and the terminals of the current fuse are short-circuited to generate a current of 4.8A. Surge absorber for test 4
4 was continuously energized for 1 hour. Surge absorber for test 4
In order to observe the damage situation around the temperature rise after destruction of No. 4, the test sample was mounted on the substrate. The test results conducted under the above test conditions are shown in (Table 2).

[0023]

[Table 2]

According to (Table 2), in the case of the conventional surge absorber, after the varistor element was destroyed by overvoltage, the element temperature rapidly rose, and the exterior resin was deformed and a large amount of smoke was generated. The surface temperature of the varistor element is about 600 ~ about 5 minutes after destruction.
It reached 700 ° C. and was stable at that temperature until 1 hour later. Further, the substrate around the varistor element was burned out in a wide range.

On the other hand, in the surge absorber of the embodiment, after the varistor element is destroyed, the temperature of the surface of the aluminum case 4 slightly rises until the pressure valve 7 which is the explosion-proof mechanism operates.
No remarkable change or abnormality was found in the appearance. After a lapse of a certain period of time, the pressure valve 7 on the upper part of the aluminum case 4 was operated, and smoke was generated from the crack generated. However, the amount of smoke generated at this time was much smaller than that of the conventional example. The temperature rise of the surface of the aluminum case 4 was stable at about 250 to 300 ° C., and the substrate was discolored in an extremely narrow area around the surge absorber.

As described above, in the surge absorber according to the present embodiment, even if the varistor element is destroyed due to the accidental loss of the neutral line and the short-circuit current is continuously supplied after the destruction, smoke is temporarily generated due to the destruction of the varistor element. Therefore, the amount of smoke emitted to the outside of the aluminum case 4 after the operation of the pressure valve 7 can be suppressed.

Regarding the heat generated when the varistor element is destroyed, the temperature rise on the surface of the surge absorber can be suppressed by the heat insulating effect of the air between the varistor element and the aluminum case 4 and the heat radiating effect of the aluminum case 4. Aluminum case 4
Pressure valve 7 operates at a fixed time after the varistor element is destroyed,
Effectively limit the temperature rise at the time of destruction of the surge absorption element and the pressure rise inside the aluminum case 4 due to the generation of combustion gas,
Explosion can be prevented, and appearance change at the time of destruction can be suppressed by only a slight deformation of the aluminum case 4.

The effect of the surge absorber of the present embodiment has been described above when it is destroyed by the overvoltage due to the AC200 erroneous application and the neutral wire missing accident in the countermeasure against the surge between the lines. It is effective even when the surge absorbing element is destroyed due to a cause other than the example such as destruction due to deterioration, and the same effect can be obtained when applied between the line and the ground. In addition, the effect of suppressing the temperature rise at the time of destruction of this example product is that the entire circuit board is coated or potted with a moisture resistant resin such as urethane as in a washing machine, a dishwasher, etc. Is especially useful when implemented in a covered
Smoke absorption of the moisture-resistant resin due to abnormal heat generation after destruction of the surge absorber,
The safety of the product can be significantly improved by significantly suppressing / preventing the burning situation such as ignition.

Although the aluminum case 4 is used in this embodiment, the same effect can be obtained by using any metal such as copper as long as it has a heat radiation effect, malleability and workability. I think that the.

The aluminum case 4 is preferably as large as possible so as not to come into contact with the surge absorbing element 1.

The synthetic rubber 5 is preferably butyl rubber, ethylene propylene rubber or the like having heat resistance and solvent resistance.

Further, it is preferable that the case and the synthetic rubber 5 have the same coefficient of thermal expansion. Further, as shown in FIG. 1, by providing the convex portion 9 between the lead wires 2 and 3 on the surface of the synthetic rubber 5, the insulation distance on the surface of the synthetic rubber 5 between the lead wires 2 and 3 can be increased. In addition, the groove 10 is provided between the convex
By providing the above, when the surge absorber is soldered to the substrate, the groove 10 serves as an escape path for the flux gas and the solderability can be improved.

[0033]

As described above, according to the present invention, it is possible to physically block the influence of scattering of fragments when the surge absorber is broken, smoke, and ignition from the outside of the case. As a result, it is possible to prevent adverse effects on the parts around the surge absorber and significantly improve the safety of the product.

[Brief description of the drawings]

FIG. 1 is a sectional view of a surge absorber according to an embodiment of the present invention.

FIG. 2 is a top view of an aluminum case according to an embodiment of the present invention.

FIG. 3 is a top view of an aluminum case according to another embodiment of the present invention.

FIG. 4 is a sectional view of an aluminum case according to still another embodiment of the present invention.

FIG. 5 is a sectional view of an aluminum case according to still another embodiment of the present invention.

FIG. 6 is a test circuit diagram according to an embodiment of the present invention.

FIG. 7 is a test circuit diagram according to another embodiment of the present invention.

[Fig. 8] Wiring diagram of general single-phase three-wire system

[Explanation of symbols]

 1 Surge absorbing element 2 Lead wire 3 Lead wire 4 Aluminum case 5 Synthetic rubber 7 Pressure valve 8 Groove 9 Convex part 10 Groove

Claims (6)

[Claims] 1. A case having an opening, a surge absorbing element housed in the case, an insulator for sealing the opening of the case, and an insulator electrically connected to the surge absorbing element. Surge absorber having a lead wire penetrating through and extending to the outside of the case. 2. The surge absorber according to claim 1, wherein the surge absorbing element is a varistor element having a pair of electrodes on its surface, the outer periphery of which is coated with an insulating resin. 3. An explosion-proof valve is provided on the upper surface of the case.
The surge absorber according to the above. 4. The surge absorber according to claim 2, wherein the explosion-proof valve comprises a groove provided from an upper surface of the case toward an outer circumference of the case. 5. The surge absorber according to claim 1, wherein a protrusion is provided between the lead wires of the insulator. 6. The surge absorber according to claim 3, wherein a groove is provided between the convex portions.