JPH0129770Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an opening device for disconnecting the arrester from the ground when the varistor element deteriorates or short-circuits for some reason in a gear press surge arrester using a varistor element whose main component is zinc oxide. .

In recent years, varistor elements containing zinc oxide as a main component have been widely used as gear press arresters due to their excellent voltage-current characteristics and large lightning surge absorption ability. As an example of the characteristics of this varistor element, it has an extremely high impedance to a voltage within a normal rated value, that is, it operates as an insulator, and its leakage current is so small that it can be ignored.

However, if a varistor element with a small leakage current is subjected to multiple surges or a surge that significantly exceeds its rating, its voltage-current characteristics will deteriorate and a large leakage current will flow even at a normal applied voltage. This large leakage current causes heat generation in the varistor element, and if this heat generation continues, the varistor element undergoes thermal runaway, leading to short-circuit destruction. Then, due to this short circuit breakdown, a ground fault current flows and an abnormality occurs.
This can have a significant impact on the power grid, such as by activating the fuse or breaker of the power supply to which the lightning arrester is connected.

For this reason, when the temperature of the varistor element rises above the specified value due to leakage current or flow into the varistor element, or when the varistor element is short-circuited and destroyed, a release device built into the arrester disconnects the arrester from the ground. This prevents ground fault abnormalities from spreading to the grid. FIG. 1 shows a conventional example of a lightning arrester equipped with an opening device. In FIG. 1, a varistor element 2 having a disc-like or cylindrical shape and having electrodes on both end faces is housed in a hollow exterior case 1 which is usually made of epoxy resin or insulator. A charging side electrode 3 is arranged on the upper end surface of the varistor element 2 and is pressed into contact with the varistor element 2 by a spring (not shown). Further, on the lower end surface of the varistor element 2, a ground electrode 4 is arranged which is thermally coupled to the varistor element 2 and supported by the bottom of the hollow exterior case 1 having a hole. The upper end of a metal rod 5 passing through a hole in the bottom of the hollow exterior case 1 is fixed to the ground side electrode 4 by soldering 6 of a low melting point alloy (melting point of 130°C to 190°C), and the center of the metal rod 5 is connected to a fuse. 7, and a metal cap 8 is electrically and mechanically connected to the lower end of the metal rod 5 by soldering or caulking 9. cap 8
Inside, the aforementioned metal rod 5 and fuse 7 are housed, as well as a coiled spring 10. This spring 10 is stored in the cap 8 while being slightly compressed by the supporting force of the soldering 6, the fuse 7, and the soldering or caulking 9.
It serves as a separation spring that separates the cap 8 when the solder joint 6 melts or the fuse 7 melts. Both ends of the winding start and winding end of the spring 10 are short-circuiting bars 1 made of flexible copper plates or the like.
1 is shorted by 1. The upper end of the spring 10 and the upper end of the cap 8 come into contact with a terminal 12 embedded in the hollow exterior case 1 together with a shorting bar 11, and the tip of this terminal 12 serves as a terminal portion 13 for external extraction.

The lightning arrester having such a structure is connected by wiring the terminal drawn out from the charging side electrode 3 to a power line, and wiring the terminal portion 13 to a ground line or another power line. When a surge current flows into this lightning arrester, the inflow path includes the charging side electrode 3, the varistor element 2, the grounding side electrode 4, the metal rod 5 including the fuse 7, the cap 8, the shorting bar 11, and the terminal 1.
2. The terminal section 13 is in this order.

When the varistor element 2 in such a lightning arrester deteriorates, the varistor element 2 generates heat due to leakage current, and when the temperature of the solder 6 reaches the melting point or higher due to this heat generation, the spring 10 pulls away the ground side electrode. The metal rod 5 is separated from the metal rod 4. In addition, if the varistor element 2 immediately becomes short-circuited,
Due to the inflow of short circuit current, fuse 7 is blown before soldering 6 is melted. In this case as well, the separation is performed by the separation force of the spring, and also by the increase in internal pressure caused by the arc caused by fusing.

Now, the lightning arrester opening device having the structure and function as described above has the following drawbacks.
This is because due to the rapid cooling effect of rainwater, etc., the air inside the cap 8 sucks water droplets adhering to the edges of the cap 8 into the cap 8, and these water droplets are further absorbed into the cap 8.
A metal rod 5 is placed inside a saucer-shaped container as shown in Figure 2.
The cap 8 has a semi-tight structure with the hole 14 closed.
It may accumulate inside. Then, these water droplets cause corrosion to the fuse 7 or the solder joint 6 made of a low melting point alloy, making it impossible to expect a long service life.

SUMMARY OF THE INVENTION In view of the above-mentioned drawbacks, the present invention aims to provide a lightning arrester opening device that prevents water from accumulating inside the cap without affecting the opening characteristics.

The basic idea of the present invention to achieve this purpose is to provide ventilation holes at the bottom and top of the cap.

An embodiment of the present invention will now be described with reference to FIGS. 3a and 3b. In FIG. 3, the same parts as in FIG. 2 are given the same reference numerals, and FIG. 1 is also referred to for convenience of explanation. FIG. 3 shows the cap 8 included in the opening device of this embodiment. The bottom part 8a of the cap 8, which has a hole 14 in the center through which the metal rod 5 is passed and connected, has three small holes 15 around the hole 14.
is formed. This small hole 15 is a ventilation hole and is used to allow water droplets generated inside the cap 8 to fall. Therefore, the number of small holes 15 is not limited to three, but one or more is sufficient. The size of the small hole 15 is, for example, 16 mm if the inner diameter of the cap 8 is 16 mm.
In this case, the diameter can be exemplified as approximately 2 mm.

On the other hand, a slit 16 is provided at the upper edge of the cap 8. This slit 16 is a ventilation hole, and the number thereof may be one or more, and the size thereof may be, for example, a square hole with a side of 2 mm.

In this way, a small hole 15 and a slit 1 are formed in the bottom 8a and the upper end (or the upper end) of the cap 8.
This ventilation hole prevents water droplets from being sucked in due to temperature changes, and water droplets that have entered for some reason fall through the small hole 15, and furthermore, the moisture inside the cap 8 flows through the small hole 15 and It is vaporized through ventilation between the slits 16.

It has also been found that the presence of the small holes 15 and slits 16 has little effect on the operation of the opening device. When the fuse 7 blows, the internal pressure of the cap 8 rises shockingly due to the arc gas, but since the time is within several milliseconds, the internal pressure rises through the small hole 15 or the slit 1 during that time.
The amount that escapes to the outside through 6 is small and has almost no effect on the pulling force of cap 8. In other words, the size is such that it does not affect the internal impact pressure.
It is necessary to make small holes 15 and slits 16 depending on the number of pieces. By the way, the current-time characteristics of the fuse 7 with a structure of a 16 mm diameter cap 8, three 2 mm diameter small holes 15, and a 2 mm slit 16 were compared with a conventional structure product over a short circuit current of 600 A to 12,000 A. As a result of the measurement, the difference was within the error range of the characteristics of the opening device.

In the above-described embodiment, the small hole 15 was formed as a circular hole and the slit 16 was formed as a square hole, but the shape is not particularly limited.

As explained in the embodiments above, in this invention, by providing ventilation holes at the bottom and top of the cap, it is possible to prevent water droplets from accumulating inside the cap while maintaining the operating characteristics of the opening device. It was possible to prevent corrosion of fuses, soldering, etc.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of an example of a conventional surge arrester equipped with an opening device, Fig. 2 is an example of a conventional cap, Fig. 2a is a half-cut sectional view, Fig. 2b is a bottom view, and Fig. 3 is an example of a conventional cap. FIG. 3a is a half-cut sectional view, and FIG. 3b is a bottom view of an embodiment of the lightning arrester opening device according to the present invention. In the drawing, 5 is a metal rod, 6 is soldering, 7 is a fuse, 8 is a cap, 8a is a bottom, 10 is a spring, 15 is a small hole, and 16 is a slit.

Claims (1)

[Scope of utility model registration request] The base end of a metal rod having a fuse in the middle is connected to one of the electrodes connected to both ends of the zinc oxide varistor element using a low melting point alloy, and the base end is pulled in the direction to break the connection and the fuses. A lightning arrester is provided with a cap in which a coil spring is placed through the metal rod by applying a force, and the center of the bottom is engaged with the tip of the metal rod to house the metal rod and the coil spring. A lightning arrester opening device characterized by having a ventilation hole in the upper end and the upper end.