JPS6293904A - Manufacture of zinc oxide type arrestor device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing a zinc oxide type lightning arrester element.

More specifically, the present invention relates to a method of manufacturing a zinc oxide type lightning arrester element whose charging characteristics are stable even when used at a high charging rate.

[Prior Art] Zinc oxide type lightning arrester elements (hereinafter sometimes simply referred to as "elements") are characterized by their excellent voltage and current characteristics, as conceptually shown by curve (A) in Figure 2. - Current non-linearity.

Conventionally, the electrical characteristics of lightning arrester elements have been improved mainly by modifying the composition of the element to improve the normal voltage to ground (Va), leakage current (Ia) when applied, lightning current (Ie), and between the element electrodes when energized. This is done so that the voltage (Vf) (hereinafter referred to as "limited voltage") is reduced.

Further, since a lightning arrester using a zinc oxide type lightning arrester element has excellent protection characteristics against lightning current, it is sometimes used without the gap used in a conventional type lightning arrester. In that case, the leakage current (I
a) always flows through the element. FIG. 3 conceptually shows the change over time in the leakage current flowing through the element (electrification characteristics) when the element is constantly energized. In FIG. 3, curve (C) shows a pattern in which the leakage current increases with time, heat generation increases, and the element eventually breaks down. On the other hand, the curve (D
) indicates a stable pattern in which the leakage current does not increase over time with respect to power application.

In the normally used oxidized boat type surge arrester element containing bismuth oxide, grains of about 10 am in size mainly composed of zinc oxide and a grain boundary layer mainly composed of bismuth oxide that fills in between the grains are used. It has an internal structure characterized by being formed.

The fact that this grain boundary layer mainly composed of bismuth oxide plays an important role in the voltage-current nonlinearity of the device is shown in, for example, the Japanese Journal of Applied Physics (Japanese Journal of Applied Physics).
Applied Physics) 10, p. 736, 1971.

In addition, if the crystal phase of bismuth oxide that forms the grain boundary layer is made into a gamma (γ) type, the leakage current during voltage application has a stable tendency that does not increase with the application time, as shown by curve (D) in Figure 3. ) can also be shown, for example, in the Japanese Journal of Applied Physics.
al of Applied Physics) 15
．． It is widely known from pages 1847 and 1976.

Regarding the distribution of γ-type bismuth oxide, it is particularly clear that when the transformation rate of bismuth oxide to γ-type bismuth oxide is set to 10 to 90% and the distribution of γ-type bismuth oxide in the device is made uniform, the charging characteristics of the cables are improved. It is shown in Japanese Patent Application No. 59-34526.

In this way, it can be said that improving the charging characteristics of an element, or more broadly improving the electrical characteristics of an element, depends on grain boundary control in the internal structure of the element. Since the properties of the grain boundary layer are influenced by the manufacturing conditions of the zinc oxide type element, especially the heat treatment conditions, setting the manufacturing conditions of the element is an important factor for grain boundary control.

Figure 4 shows an example of the device manufacturing method published in Japanese Patent Application Laid-open No. 58-20.
The heat treatment process disclosed in Publication No. 0508 is shown.

This figure shows the heat treatment process of the sintered zinc oxide type element. The process is divided into two stages, and since the melting temperature of bismuth oxide is about 850°C, the bismuth oxide is melted in the heat treatment in the first stage. It is believed that bismuth oxide is transformed into the γ type by the second heat treatment. In addition, for a holding time of 1 to 2 hours, bismuth oxide is melted,
This is considered to be the time required to sufficiently generate γ-type bismuth oxide.

[Problems to be Solved by the Invention] However, raising the holding temperature to a temperature at which bismuth oxide melts in the first stage of the heat treatment process causes bismuth oxide to evaporate and reduce the amount of oxidation within the element. There is a problem in that the distribution of bismuth becomes non-uniform, changing the characteristics of the device and making it unstable.

In addition, the condition of holding time 1 to 2 hours is, for example, a diameter of 1 to 2 hours.
As shown in Japanese Patent Application No. 60-86763, this is insufficient for doll elements such as 106a and 401r1m in thickness.

The present invention has been made in order to eliminate the drawbacks of the conventional manufacturing method as described above, and provides a method for manufacturing a zinc oxide type lightning arrester element that has stable charging characteristics even when used at a high charging rate. The purpose is to

Means for Solving Problem F] The method for manufacturing a zinc oxide lightning arrester element of the present invention involves maintaining the element in a temperature range lower than the melting temperature of bismuth oxide, which is one of the elements constituting the element, for 4 hours or more. This method is characterized by including a step of repeating the treatment one or more times.

[Function] The bismuth oxide crystal phase within the device manufactured by the manufacturing method of the present invention transforms into the γ type almost uniformly within the device. This γ-type bismuth oxide exhibits a stable tendency in which the leakage current does not increase with respect to the application time when a voltage is applied. Therefore, the leakage current in any part of the element remains stable for a long time e1 without increasing.

U example] An embodiment of the present invention will be described below.

The main component is zinc oxide, and each additive is 0.1~
2 mol% bismuth oxide, antimony oxide, cobalt oxide, manganese oxide, chromium oxide, silicon oxide, and 0.001 to 0.1 mol% each of boric acid and aluminum nitrate were selected, crushed, mixed, granulated, and molded. After, 12
It was fired at 00°C to obtain an element with a diameter of 106M and a thickness of 40M.

These samples were held at a holding temperature of 500 to 6
00℃, holding time 5 hours, temperature increase/decrease rate 100℃/11r
Heat treatment was performed once. Here, the samples are divided into two groups, the first group is left as is, and the second group is again subjected to a second heat treatment at a holding temperature of 5oo = eoo
The heating time was 5 hours, and the cooling rate was 100°C/Hr. The surfaces of the devices in both groups were polished, electrodes were provided, and their voltage-current characteristics were measured.

In that case, the starting voltage of the element is 3.4x 10-5 A
The voltage between the north and south poles of the device was taken as the voltage when a current of /c,j was applied to the device.

Next, in order to examine the charging characteristics of these devices, we maintained the ambient temperature of the devices at 130°C and applied a voltage to the devices at a charging rate (ratio to the starting voltage) of 80%. Changes over time were measured over 40 hours.

Table 1 shows the measured charging characteristics of the elements subjected to various heat treatments.

Table 1 In Table 1, the numerical value is the ratio of the leakage current after 40 hours (■@) to the leakage current after 1 hour (1+) I ao / I
Indicates +. The larger this value is, the more the leakage current tends to increase, and the charging characteristics become worse. The thermal runaway of the device without heat treatment is due to the change in leakage current over time, as shown in Figure 3 (
This shows that the shape is C). It can be seen that by the first heat treatment, the element approached the shape shown in FIG. 3(D) in which thermal runaway did not occur. It can be seen that the charging characteristics become more stable after the second heat treatment.

After measuring the charging characteristics, the distribution of γ-type bismuth oxide (γ-Bi2o3) from the periphery to the center of the device was analyzed by X-ray diffraction.

In the element containing zinc oxide type M71 with the formulation of this example, beta (β) type and γ type bismuth oxide phases are produced.

The respective strongest peaks are located near an X-ray diffraction angle 2θ of 28° and overlap.

Therefore, in order to detect the γ-Bi2O3 phase, 2θ is 33,
We focused on the (321) peak seen near 0''.

FIG. 5 shows the transformation rate (1) determined from the peak intensity of γ-Bi2O3 for the sample that was not heat-treated, and the transformation rate determined from the peak intensity for the sample that was heat-treated once at 500°C. g rate (2:
J, heat treated at 500°C and then a second heat treatment at 600°C as (3), heat treated once at 600°C as (4), and the results of analysis using X-ray diffraction method. show. From Figure 5, 7-Bi2O3 was not generated in the case that was not heat-treated at 500°C.
When heat-treated once, γ-Bi2O3 is produced, but it is seen that more is produced at the periphery of the element than at the center.

When heat treatment is performed twice (500℃→600℃), γ-B
It can be seen that i2O3 is generated uniformly within the element. 60
It can be seen that in the case of the sample heat-treated at 0° C., the production of γ-Bi2O3 progresses, but its distribution begins to become somewhat non-uniform.

Therefore, it can be seen that multiple heat treatments are effective as a means to uniformly generate γ-type oxidized sulfur by heat treatment.

The data from this XPJ diffraction analysis are shown in Table 1. J.I.
When compared with the data representing the electrical properties, γ-Bi2O
It can be seen that the more uniformly 3 is generated within the element, the better the 3-electrical characteristics of the element.

Also, from Figure 5, the effect of the first heat treatment at 600°C and the effect of the second heat treatment at 600°C are as follows:
You can see that they are different. The transformation rate of bismuth oxide to the γ type is higher in the case of the one subjected to the first heat treatment at 600°C.

[Effects of the Invention] As described above, according to the present invention, 7-Bi2030
This has the effect that it is possible to manufacture an element with uniform distribution and stable charging characteristics.

[Brief explanation of drawings]

Fig. 1 is a conceptual diagram showing the heat treatment process according to an embodiment of the present invention, Fig. 2 is a conceptual diagram showing the voltage-current characteristics of a zinc oxide type arrester element, and Fig. 3 is a conceptual diagram showing the voltage-current characteristics of a zinc oxide type arrester element. FIG. 4 is a conceptual diagram showing an example of the heat treatment process according to the prior art; FIG. 5 is a diagram showing the distribution of γ-Bi2O3 in the zinc oxide type lightning arrester element manufactured according to the present invention. .

Claims (5)

[Claims] (1) In the process of firing and then heat-treating the raw material molded product of zinc oxide type lightning arrester element containing bismuth oxide, the fired raw material molded product is held at a holding temperature lower than the melting temperature of bismuth oxide for 4 hours or more. A method for manufacturing a zinc oxide type lightning arrester element, the method comprising at least one zinc oxide type lightning arrester element. (2) The method for manufacturing a zinc oxide type lightning arrester element according to claim 1, wherein the holding temperature is within a temperature range of 500 to 600°C. (3) The method for manufacturing a zinc oxide type lightning arrester element according to claim 1, wherein the number of steps of holding the raw material molded product fired at the holding temperature for 4 hours or more is 2. (4) The first holding temperature is within the temperature range of 500 to 600°C, the second holding temperature is within the temperature range of 500 to 600°C, and the second holding temperature is the same as the first holding temperature. Claim 1, which is a temperature higher than the holding temperature of
A method for manufacturing a zinc oxide type lightning arrester element as described in . (5) The first holding temperature is within the temperature range of 500 to 600°C, the second holding temperature is within the temperature range of 500 to 600°C, and the second holding temperature is the same as the first holding temperature. Claim 1, which is a temperature lower than the holding temperature of
A method for manufacturing a zinc oxide type lightning arrester element as described in .