JP2816258B2 - Method of manufacturing voltage non-linear resistor and lightning arrester - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises ZnO as a main component,
The present invention relates to a method for producing a voltage non-linear resistor having excellent life characteristics including a metal oxide such as Bi ₂ O ₃ , and an arrester using the voltage non-linear resistor.

[0002]

2. Description of the Related Art Non-linear resistors (Z
An nO element) has excellent nonlinearity and is widely used as an arrester element. In particular, the ZnO element used for the gapless surge arrester is always in the charged state, so a small leakage current is generated in the element, and the leakage current gradually increases due to the long-term application of electricity, causing the element to generate heat and run away. May cause phenomena. In order to prevent thermal runaway of the element (improve the service life), it is important to reduce the increase rate of the leakage current. For this reason, as a method for obtaining a long-life element which does not deteriorate in its characteristics due to constant application of power to the ZnO element, Japanese Patent Application Laid-Open No.
According to JP-A-159303, a ZnO element sintered at a high temperature of 1050 to 1300 ° C is reheated to 500 to 700 ° C, held for one or two hours, and then cooled at a rate of 100 to 300 ° C / h.
A method of preventing the deterioration of the characteristics of the element by a single heat treatment after sintering, which is to re-cool to room temperature at the same time, is disclosed. According to JP-A-58-200508, ZnO
And a composition containing at least Bi ₂ O ₃ and
A ZnO element sintered at a high temperature of 50 to 1300 ° C.
After reheating to 0 to 950 ° C and holding for one or two hours, the temperature was lowered to 300 ° C or less at a rate of 300 ° C / h, and then 500 to 500 ° C again.
After heating to 700 ° C and holding for one or two hours,
There is disclosed a method of re-cooling to room temperature at 150 ° C./h, that is, a method of preventing the property deterioration of the element by performing a heat treatment twice after sintering.

[0003]

The ZnO element is a ZnO element.
The particles have a structure in which a high-resistance boundary layer mainly composed of Bi ₂ O ₃ surrounds the periphery of the particles, and the resistance of the boundary layer shows nonlinearity with respect to voltage.

In general, the voltage-current characteristics of a ZnO element are approximately expressed by the following equation.

[0005]

I = KV ^α (Equation 1)

Where I is a current, V is a voltage, K is a constant, α
Represents a non-linear coefficient. Α of the ZnO element is in the order of 10 to 70.

The leakage current flowing in the ZnO element in the always-on state is smaller as α is larger. Therefore, it is desirable that α is large. In addition, in order to suppress an increase in leakage current due to long-term application of electricity, the heat treatment of the sintered ZnO element
It is known that it is effective to generate a γ-type Bi ₂ O ₃ phase in an nO element.

However, in this prior art, sintered ZnO
In one heat treatment of heating the element at 500 to 700 ° C,
Even though the γ-type Bi ₂ O ₃ is generated in the ZnO element and the characteristic deterioration can be prevented, there is a problem that the voltage-current characteristic of the element is poor.

On the other hand, when the sintered ZnO element is heat-treated twice to extend the life of the ZnO element, the first heat treatment is performed in the first heat treatment.
When γ-type Bi ₂ O ₃ is not generated in the nO element, there is a problem that the application life property of the ZnO element is not improved even if the heat treatment is performed twice. For example, Bi ₂ is mainly composed of ZnO.
Even with a composition containing O ₃ , Sb ₂ O ₃ , MnCO ₃ , Cr
₂ O ₃ , Co ₂ O ₃ , SiO ₂ , NiO, B ₂ O ₃ , Al (N
In a composition containing various kinds of metal oxides such as O ₃ ) ₃ ,
In the first heat treatment step of the sintered ZnO element, when the temperature decreasing rate is set to 300 ° C./h as disclosed in the related art, γ-type Bi ₂ O ₃ may not be easily generated in the ZnO element.

For these reasons, the prior art is insufficient in reliability, especially for a multi-component ZnO element or the like used at a high charging rate in a DC system.

An object of the present invention is to provide a method for manufacturing a ZnO element which is highly reliable and does not deteriorate its characteristics even when power is applied for a long time, and a lightning arrester.

[0012]

Above object In order to achieve the above, ZnO as a main component, other Bi ₂ O _3, various kinds of metal oxides _{(e.g., Sb 2 O 3, MnCO 3} , Co 2 O 3, Cr 2 O ₃ , Si
ZnO containing O ₂ , NiO, B ₂ O ₃ , Al (NO ₃ ) ₃ etc.
The raw materials of the element are mixed and molded, and the molded body is 1050 to 130.
A step of sintering at 0 ° C., and thereafter,
The temperature is then lowered to 900 to 950 ° C., held for 1 to 3 hours, and then subjected to a first heat treatment for lowering the temperature to 300 ° C. or less, and again to 650 to 900 ° C. And a step of performing a second heat treatment of re-cooling to room temperature after holding for 3 to 3 hours. In the first and second heat treatment steps, the rate of temperature decrease after holding at a high temperature is 100 ° C.
/ H and 150 ° C / h or less.

Still another object is achieved by a lightning arrester having electrodes formed on an end surface excluding an outer peripheral surface of a disk-shaped or cylindrical ZnO element manufactured by the above-described manufacturing method, and placing the electrodes in an insulator tube.

[0014]

According to the present invention, the sintering and heat treatment patterns shown in FIG. 1 are used.

A molded body obtained by mixing and molding a raw material containing ZnO as a main component and a metal oxide such as Bi ₂ O ₃ is first formed by:
Sinter at 050-1300 ° C. for 1-2 hours. The rate of temperature rise / fall in this sintering step is set to 300 ° C./h or less at which the ZnO element does not thermally break. At the end of sintering, the temperature is lowered to 300 ° C. or lower and cooled to stabilize the crystal and grain boundary structure of the device. After the temperature is lowered to 300 ° C. or lower, the heat treatment step is started with the holding time T or immediately.

In the first heat treatment step, the sintered ZnO element is
The temperature was raised to 900 to 950 ° C., and heat treatment was performed for 1 to 3 hours to dissolve Bi ₂ O ₃ in the ZnO element.
γ-type Bi ₂ O ₃ is generated in the nO element. Γ-type Bi element
_The generation of ₂ O ₃ improves the life characteristics of the device. The reason is not always clear, but is presumed as follows. (1) The characteristic deterioration of the ZnO element due to long-term power
The same characteristic degradation occurs when the O element is heat-treated in nitrogen gas, and the characteristics return to the original property when the ZnO element with the deteriorated characteristic is heat-treated in air.
It is considered that oxygen ions existing on the surface of the crystal particles and the like dissipated to the outside due to heat generation of the element at the time of application of electric power, and as a result, the electrostatic potential of the boundary layer was reduced (the varistor voltage was reduced). (2) γ-type Bi ₂ O ₃ is generally composed of α-type Bi ₂ O ₃ and β-type B
Compared to i ₂ O ₃ and δ-type Bi ₂ O ₃ , it has an effect of preventing diffusion of oxygen passing through the boundary layer of the ZnO crystal because of its high crystallinity, few internal defects, and large volume. For this reason,
The movement of oxygen ions present on the surface of the ZnO particles is prevented, the dissipation of oxygen to the outside is reduced, and the ZnO element becomes stable against application of electricity.

The temperature reduction rate of the ZnO element in the first heat treatment step is 1 because the ZnO element generates γ-Bi ₂ O _3.
The temperature is set to 00 ° C / h or less. When the temperature exceeds 100 ° C / h, γ-type Bi
₂ O ₃ is not generated. In the first heat treatment, Bi ₂ O ₃
Has the effect of reducing voids in the sintered body, preventing a reduction in the varistor voltage, and preventing deterioration of the characteristics of the ZnO element. At 900 ° C or lower, Bi at the grain boundary of ZnO element
_{The 2} O ₃ layer is not sufficiently dissolved, and even if the subsequent heat treatment is adjusted, γ
No formation of type Bi ₂ O ₃ is observed. Above 950 ° C, Zn
The thermal activation of the O crystal becomes too high, so that the dissolution of the Bi ₂ O ₃ layer does not stay in the grain boundary region, and the oxygen ions adsorbed on the ZnO grain boundaries are easily dissipated, which is not desirable. When the heat treatment time is one hour or less, the effect of maintaining the temperature is small, and when the heat treatment time is three hours or more, a problem of activation of the ZnO crystal occurs.

Next, as a second heat treatment, after the temperature drop in the first heat treatment reaches 300 ° C. or less, the temperature is raised to 650 to 900 ° C. for an appropriate holding time T or immediately, and the temperature is lowered by one to three times. Hold for a while to cool.

By this second heat treatment, the remaining Bi ₂ O ₃ that could not be transformed into γ-type Bi ₂ O ₃ by the first heat treatment is transformed into γ-type Bi ₂ O ₃ , and the particles in the grain boundary layer are transformed. Regulate growth.
At this time, when the temperature is 650 to 900 ° C., Bi ₂ O ₃ is γ-type B
This is the temperature required to change to i ₂ O ₃ , and the holding time for one to three hours at that time is determined for the same reason as described above. The rate of temperature decrease in the second heat treatment is set to 150 ° C./h or less. This is effective in improving the characteristics of the ZnO element by removing the thermal distortion of the element.

It is also effective to repeat the same heat treatment as the second heat treatment several times.

[0021]

【Example】

<Example 1> ZnO9 having a purity of 99% or more as a starting material
4-95 mol%, Bi ₂ O ₃ 0.1-1 mol%, Sb ₂ O ₃
0.8-1.2 mol%, MnCO ₃ 0.8-1.2 mol%, C
o ₂ O ₃ 0.8 to 1.2 mol%, Cr ₂ O ₃ 0.1 to 1.0 mol%, SiO ₂ 1.0 to 1.5 mol%, NiO 0.5 to 1.0 mol%
Mol%, B ₂ O ₃ 0.1~0.15 mol%, Al (NO _{3) 3}
A predetermined amount of each powder was weighed so as to be 0.005 to 0.009 mol%, and after mixing, granulation and pressure molding, 119
Sintered at 0 ° C. for about 4 h. The shape and dimensions of the sintered ZnO element are φ90 × 20t. At this time, the temperature was raised and lowered at a rate of about 70 ° C./h, and the temperature was lowered to room temperature and cooled. next,
After heating the sintered body to 950 ° C. and holding for 2 hours,
Each sintered body cooled to room temperature at a cooling rate of about 300 ° C./h and about 300 ° C./h is again heated to 700 ° C. and maintained for 2 hours, and then cooled to room temperature at a cooling rate of about 70 ° C./h. Heat treatments were performed. An electrode was attached to the thus obtained sintered body to produce a ZnO element.

A DC voltage was applied to the fabricated ZnO element and the element that was not subjected to heat treatment after sintering. FIG. 2 shows the change with time of the leakage current flowing in the ZnO element at this time. The power application conditions were set to an ambient temperature of 115 ° C. and a power application rate (= applied voltage / voltage when 1 mA flows through the ZnO element) = 0.85.

In FIG. 2, in the element not subjected to the heat treatment (characteristic A), the leakage current has a large change with time and causes a thermal runaway phenomenon in a short time. In the first heat treatment step, the device (characteristic B) obtained by the conventional heat treatment method in which the temperature was lowered at a rate of 300 ° C./h exceeding 100 ° C./h was about 30 hours.
Heat runaway in a short time. The device (characteristic C) obtained by the heat treatment method of the present invention has almost no increase in leakage current due to long-time application of electricity, and has achieved a long life. Note that, for the element at the stage where the first heat treatment was performed, γ was determined by X-ray diffraction.
Type Bi ₂ O ₃ results of examining the presence or absence of generation, the device according to the conventional heat treatment method without the generation of γ-type Bi ₂ O _3, in the device according to the heat treatment method of the present invention is produced reliably γ-type Bi ₂ O ₃ It was confirmed that.

Embodiment 2 Of the first and second heat treatment steps shown in Embodiment 1, the heating temperature in the first heat treatment step was changed to 750, 800, 900, 950, 1000 ° C.
ZnO obtained by heat treatment twice at a temperature lowering rate of 70 ° C./h
An electrode was formed on the sintered body, and a DC voltage was applied under the same conditions as in Example 1. FIG. 3 shows the change with time of the leakage current flowing in the ZnO element at this time.

The heating temperature of the element in the first heat treatment step is 7
In the case of 50 and 1000 ° C., the characteristics A and B in FIG.
As shown in the figure, a thermal runaway phenomenon occurred in a short time. The reason is that Bi ₂ O ₃ contained in the ZnO element at 750 ° C.
Was determined not to be dissolved, and that γ-type Bi ₂ O ₃ was not generated in the ZnO element at 1000 ° C.

When the heating temperatures are 800, 900 and 950 ° C., as shown by characteristics C, D and E in FIG.
Although the leakage current is larger at 00 and 900 ° C. than at 950 ° C., in both cases, the leakage current is hardly increased due to long-time application of electricity, and the life of the element is extended. Therefore, the heating temperature is more preferably between 800 and 950 ° C.
Is preferably between 900 and 950 ° C. <Example 3> In the first and second heat treatment steps shown in Example 1,
In the first heat treatment step, the cooling rate was set to 70 ° C./h,
In the second heat treatment step, the heating temperature is set to 600, 650, 7
An electrode was formed on the ZnO sintered body obtained by performing the heat treatment twice at 50, 900 and 950 ° C., and a DC voltage was applied under the same conditions as in Example 1. FIG. 4 shows the change with time of the leakage current flowing through the ZnO element at this time.

When the heating temperature in the second heat treatment step was 600 or 950 ° C., as shown by the characteristics A and E in FIG. 4, the leakage current was large, and both of them performed thermal runaway in a short time. On the other hand, heating temperatures of 650, 750 and 900 ° C.
As shown in characteristics B, C, and D, the element heated in step (1) has a long life because there is no large difference in leakage current and there is almost no increase in leakage current due to long-time application of electricity. . For this reason, the heating temperature of the element by the second heat treatment is desirably 650 to 900 ° C.

Example 4 Twenty-two elements (elements having the characteristic C in FIG. 4) manufactured in Example 3 were stacked and housed in an insulator tube to manufacture a lightning arrester for 125 kV DC shown in FIG. Based on the life characteristics of the element, this arrester is guaranteed for a life of 100 years under actual use conditions.

[0029]

As described above, according to the present invention, it is possible to obtain an excellent charging life property.
By using a voltage non-linear resistor and its resistor,
Therefore, a lightning arrester having a long life can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a sintering and heat treatment pattern according to the present invention.

FIG. 2 is an explanatory view showing the life characteristics of the device according to the present invention together with those of the conventional method.

FIG. 3 is a life characteristic diagram of an element when the heating temperature of the first heat treatment in the present invention is changed.

FIG. 4 is a life characteristic diagram of the element when the heating temperature of the second heat treatment in the present invention is changed.

FIG. 5 is a perspective view showing the structure of an arrester using a voltage non-linear resistor according to the method of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Voltage non-linear resistor, 2 ... Insulator tube, 3 ... Shield, 4
... insulation base.

Continued on the front page (72) Inventor Ken Takahashi 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd.Hitachi Research Laboratory (72) Inventor Tetsuo Nakazawa 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Hitachi, Ltd. Inventor Takeo Yamazaki 1-1-1, Kokubuncho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd.Kokubu Plant (72) Inventor Shingo Shirakawa 1-1-1, Kokubuncho, Hitachi City, Ibaraki Prefecture Hitachi Kokubu, Ltd. In-plant (56) References JP-A-54-61214 (JP, A) JP-A-1-313902 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01C 7/10

Claims (2)

(57) [Claims] 1. A step of mixing and molding raw materials containing ZnO as a main component and Bi ₂ O ₃ as an essential component to obtain a molded body. After the molded body is held at a temperature of 1050 to 1300 ° C. for a certain time, A step of cooling to a temperature of 300 ° C. or lower to obtain a sintered body; holding the sintered body at a temperature of 900 to 950 ° C. for 1 to 3 hours; A first heat treatment step, after the first heat treatment step, after further holding at a temperature of 650 to 900 ° C. for 1 to 3 hours, cooling to a room temperature at a temperature lowering rate of 150 ° C./h or less, Performing a heat treatment including at least two heat treatment steps of the above. 2. A disk-shaped or cylindrical voltage non-linear resistor manufactured by using the manufacturing method according to claim 1 having electrodes formed on an end surface excluding an outer peripheral surface, and formed in an insulator tube. A surge arrester characterized by the following.