JPH0522362B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to an improved zinc oxide type arrester element.

The voltage-current characteristics of a conventional zinc oxide type lightning arrester element are conceptually shown in FIG. This device is characterized by excellent voltage-current nonlinearity. Conventionally, the composition of the element was mainly devised to reduce the leakage current Ia when the normal ground voltage was applied and the voltage between the element electrodes (hereinafter referred to as limiting voltage) when the lightning current Ic was applied. Improvements have been made over time.

In addition, aretas (surge arresters) using the above elements have excellent protection characteristics against lightning current, so
It is sometimes used in conventional lightning arresters by removing the gap. In this case, the current Ia in FIG. 1 will always flow through the element. FIG. 2 conceptually shows the change in leakage current flowing through the element over time when a voltage is constantly applied. C shows a pattern in which the element breaks down as the leakage current increases, while D shows a stable pattern in which the leakage current does not increase with respect to energization. Conventionally, efforts have been made to obtain a stable pattern D mainly through reheating treatment. It is believed that the internal structure of the device, especially the bismuth oxide crystal phase, changes due to the reheating treatment (for example, Japanese Patent Application Laid-open No. 131094/1983,
JP-A No. 52-53295 and JP-A No. 52-87695; however, no data directly indicating this is described). Bismuth oxide forms a grain boundary layer between the zinc oxide grains in the device's microstructure, and can be considered as a constituent phase that plays an important role in the voltage-current nonlinearity characteristics of the device. Therefore, how bismuth oxide is manufactured and controlled has extremely important implications for the various characteristics of the device.

When the crystal phase of bismuth oxide is a gamma (r) phase, the above-mentioned charging characteristics and device characteristics after lightning current are more stable than when other crystal phases are used. However, the leakage current Ia shown in Fig. 1 increases with the growth of the γ phase, and the ratio of the starting voltage to the limiting voltage (hereinafter referred to as limiting voltage ratio) increases, resulting in poor protection characteristics. It was hot.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and the crystal phase of bismuth oxide in the zinc oxide type lightning arrester element contains a γ phase, and the amount of bismuth oxide is entirely in the γ phase. By controlling the amount of boric acid to be 20 to 80% of the temperature at the time of aging, and by controlling the amount of boric acid added in the range of 0.001 to 0.01 mol%, the limiting voltage ratio and leakage current are small, and it can be used under heavy duty conditions. The purpose of this invention is to provide a zinc oxide type lightning arrester element with stable charging characteristics under the following conditions.

This invention provides a zinc oxide type lightning arrester element containing at least bismuth oxide and boric acid as additives, in which 20 to 80% of the crystal phase of the bismuth oxide is gamma bismuth oxide, and the amount of the boric acid added is 0.001 to 0.01 mol. % zinc oxide type lightning arrester element.

In order to obtain γ-Bi ₂ O ₃ , additives, firing and atmospheric conditions, reheating, etc. may be factors, but in the embodiments of the present invention, reheating will be explained as a factor.

The present invention will be explained below based on examples.

Example 1 Zinc oxide (ZnO) is the main component, and additives include bismuth oxide (Bi ₂ O ₃ ) in an amount of 0.1 to 2 mol%, respectively.
Antimony oxide (Sb ₂ O ₃ ), cobalt oxide (CoO), manganese oxide (MnO), chromium oxide (C ₂ O ₃ ), silicon oxide (SiO ₂ ), and each
0.001 to 0.01 mol% of boric acid (H ₃ BO ₃ ) and aluminum nitrate (Al(NO ₃ ) ₃ ).9H ₂ O) were selected, crushed, mixed, granulated, molded, and then fired at 1200°C.

450 to 700 of these samples (size 508φ x 25)
After being reheated for 2 hours at °C, electrodes were attached, and the limiting voltage ratio, leakage current, and charging characteristics were examined.

FIG. 3 shows the change in limiting voltage ratio due to reheating. The limiting voltage ratio becomes the minimum during reheating treatment at 450-500°C, and becomes a very large value at 700°C.

FIG. 4 shows the change in leakage current due to reheating.
The measurement conditions were an element ambient temperature of 40° C. and an applied voltage of 70% of the voltage generated between the element electrodes (hereinafter referred to as starting voltage) when /mA was applied to the element. When the reheating temperature is 450-500°C, the leakage current is minimum, and at 700°C it becomes very large.

FIG. 5 shows changes in charging characteristics due to reheating.
Here, the charging characteristics are 35% (curve E), 55% (curve F), and
This refers to the leakage current characteristics of an element when an applied voltage of 80% (curve G) is applied. The vertical axis of Figure 5 shows the leakage current I for 1 hour after energization and the leakage current for 40 hours after energization as a guide to show the tendency of increase/decrease in leakage current.
It shows the value of _{the ratio I 40 /} I ₁ (hereinafter referred to as leakage current ratio). If this value is smaller than 1.0 or close to 1.0, it means that the leakage current does not increase, and it can be said that the charging characteristics are stable.

When the applied voltage is small, as shown by curve E in FIG. 5, it is stable regardless of the reheating process. However, when the applied voltage is increased (curve F,
G), without reheating, the leakage current ratio is 1.0.
It is not possible to maintain a value close to . Under conditions where the applied voltage is 80% of the starting voltage, which is a critical condition for the device, reheating is necessary as shown in curve G.
The leakage current ratio in the range of 500 to 600℃ is
It is close to 1.0, and in this case it can be said that the element charging characteristics are stable.

After completing the electrical test, the central part of the element was cut out, and the resulting powder was subjected to X-ray diffraction measurements.

FIG. 6 shows the powder X-ray diffraction pattern of the element before reheating, and FIG. 7 shows the powder X-ray diffraction pattern of the element after reheating at 700°C. The diffraction peaks appearing in Figures 6 and 7 are
It can be identified that the substances are ZnO, Zn ₇ Sb ₂ O ₁₂ , Zn ₂ SiO ₄ and Bi ₂ O ₃ . Also noteworthy is the 6th
A comparison between the figure and FIG. 7 shows that only Bi ₂ O ₃ undergoes phase transformation upon reheating. That is, the crystal phase of Bi ₂ O ₃ before reheating was β phase, but
After reheating at 700°C, it was observed that the phase transformed to the γ phase.

As seen in Figures 6 and 7, β-
Since the strongest peaks of Bi ₂ O ₃ and γ-Bi ₂ O ₃ overlap at 2θ≈28°, the transformation of bismuth oxide due to reheating treatment was quantitatively investigated using the peak appearing at 2θ = 32 to 34°. In other words, we focused on the peak due to (400) for β-Bi ₂ O ₃ and the peak due to (321) for γ-Bi ₂ O ₃ , and calculated the overall value that appeared above the background on the recording paper on which these peaks were measured. Cut out the
This was weighed on a balance, and the weight is shown in FIG. 8 as equivalent to the peak integrated intensity. Curve H in the figure is β-
Curve I shows the peak integrated intensity equivalent of Bi ₂ O ₃ (400), and curve I shows the peak integrated intensity equivalent of γ-Bi ₂ O ₃ (321).

From Figure 8, from about 450℃, the γ- of β-Bi ₂ O ₃
It can be seen that the transformation to Bi ₂ O ₃ begins and almost completely completes the conversion to γ-Bi ₂ O ₃ at about 650°C. The ratio of the peak integrated intensity equivalent value of γ-Bi ₂ O ₃ at each heating temperature to the equivalent value of the peak integrated intensity of γ-Bi ₂ O ₃ at 700°C, when bismuth oxide has completely converted to γ-Bi ₂ O ₃ , is calculated. It is shown in FIG. That is, FIG. 9 shows the conversion rate to bismuth oxide γ phase by reheating treatment.

Comparing and examining the limiting voltage ratio (Figure 3), leakage current (Figure 4), charging characteristics (Figure 5), and conversion rate of bismuth oxide to γ phase (Figure 9), it was found that bismuth oxide When 20 to 80% of these are γ-Bi ₂ O _three- phase, it is possible to keep the charging characteristics of the device stable under heavy duty conditions without worsening the limiting voltage ratio or leakage current. It is.

Example 2 Zinc oxide (ZnO) is the main component, and additives include 0.5 mol% each of bismuth oxide (Bi ₂ O ₃ ), cobalt oxide (CoO), manganese oxide (MnO), and chromium oxide (Cr ₂ O ₃ ). , respectively 1.0 mol% antimony oxide (Sb ₂ O ₃ ), silicon oxide (SiO ₂ ), 0.005 mol% aluminum nitrate (Al(NO ₃ ).9H ₂ O) and 0 mol% 0.005 mol% or 1 mol %. % of boric acid (H ₃ BO ₃ ), grind them, mix them,
After granulation and molding, it was fired at 1200°C.

Next, from these samples, elements that were heat-treated at a temperature of 550°C and elements that were not heat-treated were prepared.

As a result of examining the crystal phase of Bi ₂ O ₃ by X-ray diffraction, it was found that the element without heat treatment was β-Bi ₂ O ₃ .
On the other hand, the heat-treated device has γ−Bi ₂ O ₃
The conversion rate was approximately 50%.

Next, the limiting voltage ratio, leakage current, and charging characteristics of the heat-treated elements were investigated. As an index representing the charging characteristics, FIG. 10 shows the relationship between the amount of boric acid added and the leakage current ratio. When H ₂ BO ₃ was 0 mol %, the limiting voltage ratio and leakage current were the smallest and good characteristics were obtained, but as shown in Figure 10, the charging characteristics deteriorated the most and the characteristics was bad. When H ₂ BO ₃ is 0.005 mol %, the limiting voltage ratio and leakage current are almost the same as when H ₂ BO ₃ is 0 mol %, and the characteristics are good, and there is no deterioration in the charging characteristics and the results are good. It was hot. That is, the value of the leakage current ratio was approximately 1. When H ₂ BO ₃ was 1 mol %, the limiting voltage ratio and leakage current were very large (that is, the characteristics were very poor), and therefore the charging characteristics were also unstable.

On the other hand, all the elements that were not heat-treated had a large leakage current when energized, and the deterioration was large.

In the above example, the optimal amount of γ-Bi ₂ O ₃ produced was controlled by reheating, but any method that can control the amount of γ-Bi ₂ O ₃ produced may be used, for example, by changing the firing atmosphere or the element. It may be a method of devising the composition of.

As described above, according to the present invention, bismuth oxide in a zinc oxide type lightning arrester element is controlled so that its crystal phase is γ phase and its amount is 20 to 80% of the total bismuth oxide, and boric acid Add amount of
By setting it in the range of 0.001 to 0.01 mol%,
This has the effect of keeping the element charging characteristics stable under severe conditions without worsening the limiting voltage ratio or leakage current.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the voltage-current characteristics of a conventional zinc oxide type arrester element, Fig. 2 is a diagram conceptually showing the charging characteristics of the element in Fig. 1, and Fig. 3 is a diagram showing a reproduction of the element according to the embodiment. Diagram showing changes in limiting voltage ratio due to heating,
Figure 4 is a diagram showing the change in leakage current due to reheating of the element according to the example, Figure 5 is a diagram showing the charging characteristics due to reheating of the element according to the example, and Figure 6 is a diagram showing the change in leakage current due to reheating of the element according to the example. Figure 7 shows the X-ray diffraction pattern of the element according to the example. Figure 7 shows the X-ray diffraction pattern of the element according to the example which was reheated at 700°C. Figure 8 shows the Bi ₂ O ₃ peak intensity due to reheating. Figure 9 shows the change in γ of bismuth oxide due to reheating treatment.
FIG. 10 is a diagram showing the conversion rate to the phase, and FIG. 10 is a diagram showing the change in leakage current ratio due to the addition of boric acid.

Claims (1)

[Claims] 1. In a zinc oxide type lightning arrester element containing at least bismuth oxide and boric acid as additives, 20 to 80% of the crystal phase of the bismuth oxide is gamma bismuth oxide, and the amount of the boric acid added is 0.001 to 80%.
A zinc oxide type lightning arrester element characterized by containing 0.01 mol%.