JPH07114161B2 - Oxide resistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is a resistor suitable for absorbing switching surges such as circuit breakers, which has zinc oxide, aluminum oxide, and magnesium oxide as basic components and other components as other components. Relative density including oxide
It relates to a linear resistor using a 70 to 90% sintered body.

[Conventional technology]

A linear resistor has a voltage-current characteristic according to Ohm's law, and is approximately represented by I (current) = {V (voltage) / C (constant)} ^α , and α (linearity index) is 1.3 or less. It has been found that a positive temperature coefficient of resistance has a great effect on absorbing a surge generated when a circuit breaker or the like is opened or closed.

A typical example of such a linear resistor is an aluminum oxide-viscosity-carbon system in which the resistance value is controlled by the carbon content. The outline of the manufacturing method of this linear resistor is mainly composed of aluminum oxide and carbon, to which viscosity and a low melting point oxide are added as a sintering aid and sufficiently mixed. The mixed powder is granulated, molded and fired by adding an appropriate binder such as water or an aqueous solution of polyvinyl alcohol. In order to prevent the carbon powder from being oxidized, firing should be performed in an electric furnace in a reducing atmosphere at 1000-1500 ° C.
The resistance value is controlled by the content of carbon powder, that is, the contact area between carbon powder and the adhesion between carbon powder, and the like.

[Problems to be solved by the invention]

The resistor obtained by the above conventional technique has the following drawbacks. First, the relative density of the sintered body is low at 50 to 60%, which suppresses the resistance value.The adhesion between carbon powder and carbon powder is poor, so contact between carbon powder and carbon powder during discharge surge absorption. discharged at the surface, it discharging capability is small, and the second temperature coefficient of resistance -9 × 10 ^-2 Ω / ℃ negative (20 to 250 [° C.) and absorbs the discharge surge in larger temperature rises the resistance The value drops,
When the voltage is constant, there is a drawback that the current further increases due to a rapid increase in the current, resulting in a thermal runaway state. For this reason, when the carbon powder dispersible resistor is used, the shape of the resistor is made large and the absorbed energy per unit volume is made small. However, according to this method, a container such as an insulator for accommodating the resistor becomes large in size, resulting in a high price. In addition, since devices such as circuit breakers become large,
This causes problems such as a large installation area.

An object of the present invention is to provide an oxide resistor having a high discharge surge resistance and a positive temperature coefficient of resistance.

[Means for solving problems]

The present invention comprises a sintered body having a molar ratio of 0.5 to 30% aluminum oxide, 5 to 40% magnesium oxide and the balance zinc oxide, and a relative density of 70 to 90%. It is an oxide resistor characterized in that electrodes are provided on the upper and lower end faces, and further, in a molar ratio, aluminum oxide 0.5
~ 30%, magnesium oxide 5-40%, antimony oxide,
One or more selected from silicon oxide and lithium oxide 0.01 to
An oxide resistor having 30% and the balance zinc oxide, and comprising a sintered body having a relative density of 70 to 90%, wherein electrodes are provided on the upper and lower end surfaces of the sintered body. By providing a high discharge surge withstand capability and a positive temperature coefficient of resistance, and by gradually cooling at a cooling rate of 150 ° C / h or less after firing, the linearity of voltage-current characteristics can be improved. It was done. The structure of an oxide linear resistor having a voltage-current characteristic linearity index of 1.3 or less is shown in FIG. Further, as shown in FIG. 8, it goes without saying that a hole may be provided near the center of the obtained oxide linear resistor.

As a result of various studies by the inventors, when the relative density of the obtained sintered body is 70% or less, and the discharge surge withstand capacity is 90% or more, the discharge surge withstand capacity of the conventional carbon dispersion type resistor is 400 J / cm ^{3 or} more. As with the discharge surge resistance, the temperature coefficient of resistance becomes negative when the relative density of the obtained sintered body is 90% or more, as in the case of the conventional carbon dispersion type resistor.
On the other hand, the linearity of the voltage-current characteristic depends on the cooling rate after firing.
It was found that the linearity index α becomes larger than the target value of 1.3 at 0 ° C / h, and it becomes unsuitable as a resistor for a circuit breaker.

The oxide linear resistor of the present invention can be obtained by a general ceramic manufacturing method. That is, zinc oxide 5 to 40 mol% magnesium oxide, aluminum oxide 0.5 to 30 mol% as a basic component, more preferably, antimony oxide,
One or more components selected from silicon oxide and lithium oxide should be used.
Add 01 to 30 mol% and mix well, add water and binder such as polyvinyl alcohol as a target layer to granulate, and mold using a mold. The molded body was placed in the atmosphere using an electric furnace.
After firing at a temperature of 00 to 1500 ° C, it is cooled at a cooling rate of 150 ° C / h or less. The cooling after firing here has an effect on the linearity of the voltage-current characteristics of the obtained resistor, as described above. In addition, the obtained sintered body should have a relative density of 70 to 90% so that the optimum mixing ratio of the above-mentioned basic components of zinc oxide, magnesium oxide, and aluminum oxide and other components of antimony oxide, lithium oxide, and silicon oxide are different. It is important to select the optimum addition amount and the optimum firing temperature corresponding to it. This is because the relative density affects the discharge surge withstand capacity and the temperature coefficient of resistance. Furthermore, in the obtained sintered body, ZnAl ₂ O ₄ , MgAl having higher resistance than ZnO crystal grains
₂ O ₄ , Zn ₂ SiO ₄ , MgSiO ₄ , ZnnSb ₂ O ₁₂ , Li ₂ SiO ₄ and other crystal grains are generated, and between each crystal grain, at least, a grain boundary having a higher resistance than the ZnO crystal grain. That is, no phase is formed. Therefore, addition of bismuth oxide or the like is not desirable because it forms a high resistance layer in the grain boundary phase or the like. The thus-sintered sintered body has its both end surfaces polished to form electrodes, and the electrodes are formed by electrospraying or baking.
The obtained resistor may be provided with a high resistance ceramic layer or a glass layer on the side surface of the resistor in order to prevent creeping discharge during use. Although the obtained resistor exhibits linearity in voltage-current characteristics, it is effective to destroy the high resistance portion (particularly, the grain boundary layer) when it exhibits nonlinearity.

〔Example〕

[Example 1] 3400 g of zinc oxide (ZnO), 101 g of magnesium oxide (MgO),
510 g of aluminum oxide (Al ₂ O ₃ ) is mixed in a wet ball mill for 15 hours. After the mixed powder is dried, 5 Wt% polyvinyl alcohol aqueous solution is added to the dry raw material powder at 7 Wt% for granulation. The granulated powder is molded into a size of 50 mm x 15 mm using a mold. Molded body is held at 1300 ℃ in air for 3 hours, then at 70 ℃ / h
Cooled to 100 ° C. The relative density of the obtained sintered body is 85%
It was.

Separately, AGF-72 glass powder (PbO-Al ₂ O ₃ -SiO ₂ system) of low melting point crystallized glass manufactured by Iwaki Glass Co., Ltd. was suspended in an ethyl cellulose butyl carbitol solution, and the sintered body was fired. It was brush-painted on the side surface of the so as to have a thickness of 50 to 300 μm. The glass powder-coated sintered body was heat-treated in the air at 500 ° C. for 30 hours to bake the glass. Both ends of the glass-formed sinter were polished with a lap master by about 0.5 mm and washed with trichlorethylene. The cleaned sintered body was used as a resistor by forming an Al electrode by electrospraying. Comparison of the discharge surge resistance, the resistance temperature coefficient, the resistance value change rate before and after heat treatment at 500 ° C. in air, and the linearity index α of the voltage-current characteristics of the product of the present invention and the conventional product (carbon dispersion type resistor) is shown in Table 1. Becomes

It can be seen that the product of the present invention has a larger discharge surge resistance than the conventional product, a positive temperature coefficient of resistance, a small change in resistance value before and after heat treatment at 500 ° C. in air, and a linearity index close to 1.

Example 2 In order to obtain a resistor having a resistivity of 500 to 600 Ω · cm and a relative density of the sintered body of 60 to 98%, zinc oxide (ZnO) was mixed with magnesium oxide (MgO) 5 to 40 mol% and oxidized. Aluminum (Al ₂ O ₃ )
0.5 to 30 mol%, and antimony oxide (Sb
0.01 to 30 mol% of one component selected from ₂ O ₃ ), silicon oxide (SiO ₂ ) and lithium oxide (Li ₂ O) was added, and the blending amount was accurately weighed. The weighed raw material powder was the same as in Example 1,
After mixing, granulating, and molding, the firing temperature was changed to 1200 to 1400 ° C, and the mixture was held for 3 hours and fired in the atmosphere. The cooling rate after firing is
It was 133 ° C / h. Both end faces of the obtained sintered body were polished by a lap master by about 0.5 mm and ultrasonically cleaned in trichloroethylene. An Al sprayed electrode was formed on the polished surface of the washed sintered body to form a resistor. Fig. 1 shows the relationship between the relative density of the sintered body of the obtained resistor, the resistivity, the discharge surge withstand capacity, and the resistance temperature coefficient.

From FIG. 1, it can be seen that the discharge surge resistance and the temperature coefficient of resistance of the resistor are significantly affected by the relative density of the sintered body. In other words, the discharge surge withstand capability is defined as 70% of the relative density of the sintered body.
% Or less and 90% or more, it becomes 400 J / cm ³ or less and becomes smaller than the conventional product (carbon dispersion type resistor). On the other hand, the temperature coefficient of resistance becomes negative when the relative density of the sintered body is about 95% or more, which is not preferable as a resistor for a circuit breaker.

From these facts, it is particularly desirable for the blocking resistor to have a relative density of the sintered body of 70 to 90%.

[Example 3] Zinc oxide (ZnO) 4880 g, magnesium oxide (MgO) 400 g,
Aluminum oxide (Al ₂ O ₃ ) 2550g, Silicon oxide (SiO ₂ ) 300
g and lithium oxide (Li ₂ O) 2 g are mixed in a wet ball mill for 15 hours. The mixed raw material powder was the same as in Examples 1 and 2,
Granulate, shape and fire. The firing method is 1350 ° C for 3 hours, and then the cooling rate is 17 ° C / hr, 30 ° C / hr, 60 ° C / hr, 13
The temperature was changed to 3 ° C / hr, 200 ° C / hr and 300 ° C / hr. The relative density of the obtained sintered body was 80 to 85%. Both ends of the fired sintered body are polished by a lap master by about 0.5 mm,
Ultrasonic cleaning was performed in trilol ethylene. An Al sprayed electrode was formed on the polished surface of the cleaned sintered body to form a resistor. The resistivity of the obtained resistor was 450 to 500 Ω · cm. The relationship between the cooling rate after firing of the obtained resistor and the linearity index α of the voltage-current characteristic, the discharge surge withstand capability and the temperature coefficient of resistance is described in the second section.
Shown in the figure.

From Fig. 2, the linear index α of the resistor becomes larger as the cooling rate after firing becomes faster, and it is necessary to set the cooling rate to about 150 ° C / hr or less to achieve the target value of 1.3 or less. .
The discharge surge resistance tends to decrease as the cooling rate increases, but the maximum cooling rate is 300 ° C / hr.
However, it is about 750 J / cm ³ and 400 J / c of the conventional product (carbon dispersion type resistor).
Greater than m ³ . On the other hand, the temperature coefficients of resistance are all positive.

From these facts, what is particularly desirable as the circuit breaker resistor is to set the cooling rate after firing to 150 ° C./hr or less.

[Embodiment 4] FIGS. 3 and 4 show that the oxide resistor of the present invention obtained in Embodiments 1 to 3 is filled with SF ₆ gas to absorb a surge generated when the breaker for power transmission is closed. An example of application to a neutral point grounding resistor (NGR) of a transformer for call transmission of resistors is shown. The cylindrical oxide resistor 4 shown in FIG. 8 is used by being incorporated into the closing resistor 6 of FIG. 3 and the NGR of FIG. 4 through the insulating rod 5. In FIGS. 3 and 4, 7 is a capacitor, 8 is a cutoff portion, 9 is a bushing, 10 is a tank, and 11 is a ground terminal.

5 and 6 show the closing resistors of the circuit breaker using the oxide resistor of the present invention and the conventional resistor.
This is a comparison of NGR.

〔The invention's effect〕

The oxide linear resistor according to the present invention is about 2.3 times larger than the conventional resistor (carbon dispersion type resistor), the linearity of the voltage-current characteristic is excellent, the temperature coefficient of resistance is positive and small,
And since the change in resistance value after heat treatment at 500 ° C is also small,
The area occupied by the resistors of conventional circuit breakers can be halved.

[Brief description of drawings]

FIG. 1 is a function diagram of relative density and resistivity, discharge surge withstand capacity and resistance temperature coefficient of a sintered body of an oxide resistor according to an embodiment of the present invention, and FIG. 2 is firing of the oxide resistor of the present invention. The relationship between the cooling rate and the linearity index α of the voltage-current characteristic, the discharge surge withstanding capability, and the temperature coefficient of resistance, which are shown in FIGS. 3 and 4, in which the oxide resistor of the present invention is used as a circuit breaker and transformer FIGS. 5, 5 and 6 are examples of application to a neutral grounding resistor for a circuit breaker and a neutral point when the oxide resistor of the present invention is used and when a conventional resistor is used. FIGS. 7 and 8 are cross-sectional views of an oxide resistor according to an embodiment of the present invention, in which ground resistors are compared. 1 ... Sintered body.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shinichi Owada 1-1-1 Kokubun-cho, Hitachi-shi, Ibaraki Inside the Kokubun factory of Hitachi, Ltd. (56) Reference JP-A-57-53906 (JP, A) Kaisho 56-126902 (JP, A)

Claims (2)

[Claims] 1. A molar ratio of aluminum oxide 0.5 to 30%,
Having 5-40% magnesium oxide and the balance zinc oxide,
An oxide resistor comprising a sintered body having a relative density of 70 to 90%, wherein electrodes are provided on upper and lower end surfaces of the sintered body. 2. A molar ratio of aluminum oxide 0.5 to 30%,
A sintered body having 5 to 40% magnesium oxide, 0.01 to 30% of at least one selected from antimony oxide, silicon oxide and lithium oxide and the balance zinc oxide, and having a relative density of 70 to 90%, An oxide resistor, wherein electrodes are provided on upper and lower end surfaces of the sintered body.