JPS5967606A - Method of producing nonlinear resistor - 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 [Technical Field of the Invention] The present invention relates to a method of manufacturing a nonlinear resistor used particularly in an overvoltage protection device in an electrical system.

[Technical background and problems of the invention]

In electrical systems, overvoltage protection devices such as surge absorbers and lightning arresters are used to remove normal voltage (double overvoltage) and protect electrical systems and electrical equipment.

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.

The non-linear resistor is made by pressing and molding a material made of silicon carbide (8iC) or zinc oxide (ZnO) mixed with a metal oxide, and firing the material.

ZnO-based non-linear resistors have sharp non-linear characteristics in small current ranges and have a sharp rise up to large current ranges, so overvoltage protection devices using SiC-based non-linear resistors are recommended. You can make a better overvoltage protection device than this.

However, in the conventional ZnO-based nonlinear resistor, the leakage magnetic current increases greatly with respect to the constantly applied voltage, and the width pressure drop due to the impact current increases. Therefore, it is unsuitable for an overvoltage protection device that is subjected to lightning pulses or voltage surge pulses over a long period of time, and there has been a demand for a nonlinear resistor that has stable electrical characteristics over a long period of time, that is, has long life characteristics.

[Purpose of the invention]

The present invention was made in view of the above-mentioned needs, and an object of the present invention is to provide a method for manufacturing a nonlinear resistor having stable electrical characteristics over a long period of time, that is, long life characteristics.

[Summary of the invention]

In order to achieve such an object, the present invention provides a method for manufacturing a non-linear resistor in which a metal oxide containing zinc oxide as a main component is mixed and molded, and then fired. Electrical aging is performed, and the aging for a certain period of time is characterized by a constant value after the initial leakage current of the nonlinear resistor decreases.

[Embodiments of the invention]

Hereinafter, the present invention will be explained based on examples.

The main component is zinc oxide (ZnO) powder (bismuth dioxide ("yes) + antimony oxide (sb, Os),
Chromium oxide (Crtos), cobalt oxide (C00)
and powder of manganese oxide (MnO), etc., each at 0.0
It is added in a range of 1 to 60 moles and mixed in a ball mill. At this time, the oxide and an organic binder such as polyvinyl alcohol are mixed simultaneously. The mixture thus prepared is placed in a dry granulation device, such as a spray dryer, to form spherical aggregates. This powdered mixture is pressed,
For example, it is formed into a disk having a diameter of IQQ7M and a thickness of 25ia. Thereafter, the sintered body is sintered at 1000 to 1400°C, and the surface of the obtained sintered body is polished, and then an aluminum electrode is sprayed to form a nonlinear resistor. For example, the non-linear resistor formed in this way has an ambient temperature of 90'G and a duty ratio of 71% (ratio of applied voltage peak value to varistor Ichikawa V, mA) of 85%.
Temperature and pressure stress for a certain period of time,
Perform charging aging. The temperature and voltage stress application time (electrification time) are determined by measuring the change in leakage current of the nonlinear resistor. Figure 1 shows the change in the leakage current of the non-linear resistor in the above example.The temperature and the time for which voltage stress is applied (electrification time) are such that the leakage current, once reduced, remains approximately constant. Time B (approximately 24 hours) until reaching point A is desirable.

The conditions for applying this temperature and voltage stress, that is, the ambient temperature and charge rate, vary depending on the composition and formation method of the nonlinear resistor. It is desirable to use conditions that give a constant value after the leakage current decreases. Therefore, the conditions of ambient temperature and charging rate are not limited to those in the above embodiments.

Also, the time to apply temperature and voltage stress (power application time)
Of course, the present invention is not limited to the above-mentioned embodiments1). ' Figure 2 shows the life characteristics of the non-linear resistor of the present invention and the conventional one, and shows the change in leakage current of the non-linear resistor when an ambient temperature of 110°C and a charge rate of 95% are applied. It is something. The solid line C shows the characteristics of the conventional non-linear resistor, and the vertical line C shows the characteristics of the non-linear resistor according to the present invention.

Table 1 shows the nonlinearity of the nonlinear resistors of the present invention and the conventional nonlinear resistor. V. KA/v11nA
, v, ■lA/V(,,, mA + vo,, mA/
V0. . , mA is the ratio of the voltages when the respective electric currents t are applied to the in-phase (the smaller the value), the better the nonlinearity is.

As is clear from FIG. 2 and Table 1, the nonlinear resistor of the present invention, that is, subjected to energized aging, has significantly improved life characteristics and nonlinearity compared to conventional nonlinear resistors. . As described above, the nonlinear resistor according to the present invention satisfies the characteristics required of a nonlinear resistor for gearless lightning arrester G4.

The reason why such excellent characteristics as in the present invention can be obtained can be explained by the conduction mechanism of the ZnO-based nonlinear resistor in a low electric field region of about the normal ground voltage. The conduction mechanism is dominated by the Schottky effect of the barrier on the reverse bias side, in which two Schottky's are formed in the grain boundary layer region of the ZnO particles.

The current density (J) is calculated by the following formula: It is shown that the leakage current depends on the barrier height φ, the electric field strength E (proportional to the charging rate), and the ambient temperature T, and the increase in leakage current under a constant magnetic field and ambient temperature, that is, the charging degradation shorty
This shows that this occurs due to deformation of the barrier. Therefore, by increasing the height of the barrier to reduce leakage current at normal operating voltage and reducing Joule heat generated within the nonlinear resistor during normal operation, the life characteristics are improved.

Figure 3 shows the second embodiment (ambient temperature 90'G, charge rate 85
%, which shows the change in the barrier height φ of the nonlinear resistor when electricity is applied for a certain period of time and temperature and voltage stress are applied.

As is clear from FIG. 3, in the present invention, that is, in the non-linear resistor subjected to energized aging, the barrier height φ is increased, so that the life characteristics and non-linearity are significantly improved.

The apparatus used in the manufacturing method of the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various types of apparatus can be applied as long as they can be used in the manufacturing method of the present invention.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a nonlinear resistor with stable electrical characteristics over a long period of time, that is, with excellent life characteristics.

[Brief explanation of drawings]

Figures 1 and 2 are characteristic diagrams showing the degree of change in leakage current versus energization time of a nonlinear resistor according to an embodiment of the present invention, and Figure 3 is a characteristic diagram showing the degree of change in leakage current versus energization time of a nonlinear resistor according to an embodiment of the present invention. FIG. 3 is a characteristic diagram showing the degree of change in the height of a barrier versus the energization time of a linear resistor. (7317) Kensuke Chika, Patent Attorney Nori
(1 other person) 25- Charge ■%PJ'j CH) Secret room investigation CH)

Claims (1)

[Claims] 1. In a method for manufacturing a non-linear resistor in which a metal oxide containing zinc oxide as a main component is mixed and molded and then fired, the fired non-linear resistor I is subjected to ν→1,000- for a certain period of time. 1. A method for manufacturing a non-linear resistor, characterized in that aging by applying electricity for a certain period of time is carried out until the non-linear resistance is maintained at a constant value.