JPS6214922B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nonlinear resistor, and more particularly to a method for manufacturing a nonlinear resistor used in an overvoltage protection device in an electrical system.

Overvoltage protection devices are used in electrical systems to protect the electrical system by removing overvoltages superimposed on normal voltages.

This overvoltage protection device uses a non-linear resistor that exhibits almost insulating properties at normal voltage and has a relatively low resistance value when overvoltage is applied.

Non-linear resistors are made by mixing silicon carbide (SiC) or zinc oxide (ZnO) with metals and oxides, then firing the molded material.

For example, ZnO 76 mol%, magnesium oxide (MgO) 16 mol%, bismuth oxide (Bi ₂ O ₃ ), antimony oxide (Sb ₂ O ₃ ), cobalt oxide (CoO), manganese oxide (MnO), chromium oxide (Cr ₂ O) ₃ ), iron oxide (Fe ₂ O ₃ ) from 0.05 to 3.5 mol% each, total 8
mole %, weigh and mix.

Press and mold the mixture at 1200℃ to 1300℃
Baked for 8 hours at a temperature of ℃, diameter 60mm, thickness 5mm
A disc-shaped non-linear resistor material is made, and electrodes are formed by metal spraying to create a non-linear resistor.

The nonlinear resistor manufactured in this manner has a drawback that it is hygroscopic and absorbs water in the atmosphere, resulting in deterioration of electrical characteristics. Particularly when used in overvoltage protection devices such as lightning arresters, lightning arresters are installed outdoors in locations with poor weather conditions and are continuously connected to the electrical system for over 20 years, so trace amounts of moisture that enter the lightning arrester are It is necessary to avoid deterioration of the electrical characteristics of the nonlinear resistor due to Therefore, there has been a need for a method of manufacturing a nonlinear resistor with improved hygroscopicity.

The present invention was made in view of the above-mentioned needs, and provides a method for manufacturing a nonlinear resistor that can improve moisture absorption.

Next, embodiments of the present invention will be described with reference to the drawings.

For example, 80 mol% ZnO and at least one metal oxide, such as 14 mol% MgO, 2 mol% Bi ₂ O ₃ , 1.5 mol % Sb ₂ O ₃ , 1.1 mol % CoO, 0.5 mol % Cr ₂ O ₃
mol%, MnO 0.5 mol%, and Fe ₂ O ₃ 0.4 mol% are weighed and mixed.

For mixing, for example, the oxide and deionized water may be placed in a ball mill and the ball mill may be operated for 24 hours.

The mixture is then dried and calcined in an electric furnace. The appropriate calcination temperature is, for example, 900°C for 2 hours.

When calcined, the oxide becomes lumpy, so it is crushed into fine particles.

An organic binder such as polyvinyl alcohol is added to the oxide before crushing in a weight ratio of 100 to the oxide.
Mix 1/2.

The mixed oxide is pulverized using a ball mill. The finely divided metal oxide and polyvinyl alcohol are substantially homogeneously mixed.

The mixture is then placed in a granulating device, such as a spray dryer, to form spherical agglomerates having a particle size of, for example, 100 to 300 microns.

This powdered mixture is pressed through a press, e.g.
Form into a disk of 100mm and 25mm thick.

This molded product is placed in an electric furnace and fired. The firing temperature is, for example, 1300° C., and the firing time is, for example, 6 hours.
Note that the characteristics of the nonlinear resistor obtained by firing are best when the firing temperature is 1000°C to 1400°C.
If the firing temperature changes, the characteristics of the nonlinear resistor, for example, the voltage V _{1 mA} that causes a current of 1 mA to flow through the nonlinear resistor, will change. There are advantages that can be obtained by simply changing the structure without changing the composition of the nonlinear resistor or other manufacturing processes.

Although the disc-shaped fired product after firing shrinks more than before firing, it has a substantially homogeneous composition and density.

After firing, the surface of the sample is lightly polished to make it smooth.

A diamond grindstone is most desirable for polishing, but other polishing devices may also be used. During polishing, polishing oil is poured into the fired product to remove polished powder and cool the fired product.

When the surface smoothness and dimensions of the fired product reach standard values, polishing is stopped and cleaning is performed using trichlorotrifluoroethane.

The cleaning method may be to simply immerse the fired product in a trichlorotrifluoroethane solution, but an ultrasonic cleaning method is preferable in order to shorten the cleaning time. Although the cleaning time varies depending on the cleaning method, it is, for example, 30 minutes in the case of an ultrasonic cleaning method.

After applying mud of a ceramic composition, for example, to the side surface of the polished and cleaned disk-shaped fired body,
The ceramic composition is heated, for example, in a furnace at 1000° C. for 2 hours, to fuse the ceramic composition to the surface of the disc.

Next, electrodes are formed on both surfaces of the disk-shaped fired body by metal spraying, for example, aluminum.

The electrical characteristics of the nonlinear resistor manufactured in this manner are shown in the figure. The figure illustrates the change in V ₁ mA _, ΔV _{1 mA} , when the nonlinear resistor is left in a constant temperature bath at a humidity of 90% or more and a temperature of 75 to 90° C. for a long period of time. In the figure, curve A is the electrical characteristic of a non-linear resistor manufactured by the manufacturing method of the present invention, and curve B is the electrical characteristic of a non-linear resistor manufactured by the conventional manufacturing method. V _{1 mA} refers to the voltage when a current of 1 mA flows.

As is clear from the figure, the change in V _{1 mA} of the nonlinear resistor manufactured by the manufacturing method of the present invention is significantly improved compared to the conventional one. It was confirmed that it is sufficient and can be practically used in lightning arresters.

In the above example, ZnO is the main component,
MgO, _Bi2O3 , _Sb2O3 , _CoO , _{Cr2O3 , MnO} ,
Although we have described a nonlinear resistor doped with Fe ₂ O ₃ , other metal oxides include nickel oxide (NiO), silicon dioxide (SiO ₂ ), boron oxide (B ₂ O ₃ ), and silver oxide ( AgO), titanium oxide (TiO ₂ ),
Aluminum oxide (Al ₂ O ₃ ) can also be used. In this case, the electrical and mechanical properties of the non-linear resistor will vary depending on the type and amount of metal oxide added, but the non-linear resistor should be selected according to the electrical system or equipment to be protected. This is an advantage because you can choose.

The apparatus and manufacturing method used in the manufacturing method of the present invention are not limited to the above-mentioned embodiments, and it goes without saying that the effects of the present invention can be obtained even if other methods and apparatuses are used.

[Brief explanation of the drawing]

The figure is a curve diagram showing the characteristics of a nonlinear resistor manufactured using the manufacturing method of the present invention.

Claims (1)

[Claims] 1. A step of mixing zinc oxide and at least one metal oxide, and a step of molding the mixture,
a step of firing the molded product at a temperature of 1000°C to 1400°C; a step of polishing the fired product using polishing oil; a step of cleaning the fired product using trichlorotrifluoroethane; and a step of cleaning the fired product using trichlorotrifluoroethane. 1. A method for manufacturing a nonlinear resistor, comprising the steps of: forming an electrode;