JPS5919450B2 - How to judge the quality of non-linear resistors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for determining the quality of a nonlinear resistor used in an overvoltage protection device in an electrical system.

Overvoltage protection devices are used in electrical systems to protect the electrical system by removing overvoltages superimposed on normal voltages.

This overvoltage protection device uses a nonlinear resistor that exhibits substantially insulating properties at normal voltage and becomes relatively resistant when overvoltage is applied.

The non-linear resistor is made by firing a material made of silicon carbide (SiC) or zinc oxide (ZnO) mixed with a metal oxide.

That is, whether a nonlinear resistor made by pressing and molding a mixture of SiC or ZnO and a metal oxide, firing it, and further forming electrodes has predetermined electrical characteristics;
A pass/fail determination test is performed.

As this pass/fail determination inspection method, for example, a current of 1 mA or 1
Applied voltage V1 mA required to cause 0 mA to flow.

Measurement of VlomAl, that is, the value of the current flowing when a predetermined voltage, for example 4000V, is applied is performed.

These measurements are for inspecting the initial characteristics of the non-linear resistor, and in addition, measurements are also performed for inspecting the deterioration of the non-linear resistor over time or the characteristics after repeated application of overvoltage.

For example, apply 100 pulses of DC value 10.00OA, current waveform 10x20μ to a non-linear resistor at 30 second intervals.
After applying the voltage twice, tests were conducted to measure (1) 1mA and (2) 10mA.

However, once installed, overvoltage protection devices such as lightning arresters are used continuously for over 10 years.
There are strict requirements for long-term reliability of non-linear resistors, and non-linear resistors that do not have long-term durability are selected immediately after manufacturing.
There was a desire for a testing method that would eliminate this problem.

The present invention has been made in view of the above-mentioned needs, and provides a method for determining the quality of non-linear resistors that can easily select non-linear resistors that can be used for a long period of time.

Next, one embodiment of the present invention will be described with reference to the drawings.

Zinc oxide (ZnO) 86 moles, magnesium oxide (M
gO) 8 mol, bismuth oxide (Bi203) 2 mol, antimony oxide (5b203) 1.5 mol, cobalt oxide (Cod) 1.1 mol, chromium oxide (Cr2)
o3) o, 5 moles, manganese oxide (MnO) 0
．． Weigh and mix in a ratio of 5 moles and iron oxide (Be203) 0.4 moles.

For mixing, for example, a ball mill may be used, and the ball mill may be operated together with acetone for 24 hours.

The mixture is then dried and calcined in an electric furnace.

The calcination temperature is, for example, 800°C, and a suitable firing time is 2 hours.

When calcined, the oxide becomes lumpy, so it is crushed into fine particles.

An organic binder such as polyvinyl alcohol is mixed with the oxide before pulverization at a weight ratio of 1/100 to the oxide.

The mixed oxide is pulverized using, for example, an attritor.

The oxide is then placed in a granulator, such as a spray dryer, to form particles having a particle size of, for example, 100 to 300 microns.

This powdered oxide is pressed, for example, with a diameter of 100 mm.
Form into a disk shape with a thickness of 25 nm and a thickness of 25 mm.

This disk is placed in an electric furnace and fired at, for example, 1300° C. for 6 hours.

The disk after firing shrinks more than before firing, but has a nearly homogeneous composition and density.

After firing, the surface of the material is lightly polished.

After polishing, a coating of, for example, a ceramic composition is applied to the side surface of the disk, and then heated for two hours in an electric furnace at, for example, 1000° C. to form an insulating collar made of the ceramic composition.

Next, metal spraying, for example, aluminum on both sides of the disk,
Form an electrode.

A current of, for example, 50 KA and, for example, 15 m5 eC is applied to both end electrodes of the nonlinear resistor manufactured in this manner.

The current shock when applied may damage the non-linear resistor, burn out the electrodes, or otherwise alter the appearance.

Next, a visual inspection is conducted to exclude those that are significantly altered in quality, or those that are judged to be unsuitable as nonlinear resistors even if they are not significantly altered.

Next, V1r'r'IA of the non-linear resistor is measured using, for example, a V1mA measuring device, and the limit is set to, for example, 4500V, and only those with a value of 4500 or more are determined to be non-defective.

Measurement items are usually determined in accordance with the standards required for nonlinear resistors, such as not only V1 mA, but also voltage-temperature coefficient, maximum limiting voltage, etc.

Prior to pass/fail inspection, apply 50KA current for 15m5ec.
Figure 1 shows the life characteristics of a non-linear resistor that was certified as non-defective after applying the voltage.

In FIG. 1, a voltage of 4000 V is continuously applied to a nonlinear resistor for a long period of time, V and mA are measured every 500 hours, and the change ΔV1mAf time is displayed as a parameter.

In the figure, curve A shows the characteristics of the non-linear resistor manufactured by the manufacturing method of the present invention, and curve B shows the characteristics of the non-linear resistor manufactured by the conventional manufacturing method.

As is clear from FIG. 1, in the non-linear resistor to which the pass/fail determination method according to the present invention is applied, even if a voltage is applied for a long period of time, the change in, for example, VlmA is small.

This indicates that the nonlinear resistor of the present invention is suitable for overvoltage protection devices such as lightning arresters that are connected to an electrical system and voltage is continuously applied for a long period of 10 years or more. ing.

FIG. 2 shows the change in VlmA when a voltage is connected and applied for a long period of time, using as a parameter the time during which a current of 50 KA is applied prior to the quality determination test.

Figure 2 shows that after applying a current of 50 KA, a voltage of 4000 V is applied to a nonlinear resistor that has passed the pass/fail inspection.
After application for 0 hours, ■1 mA change ΔV1 mA is illustrated.

As shown in Figure 2, the current of 50 KA is
It was found that the non-linear resistors that were determined to be good after 0 m5ec was applied had small changes in characteristics after long-term energization, and could be used satisfactorily for earth arresters.

It was found that those in which the current was applied for less than 1 ms or for more than 21 H1 sec had poor characteristics, although they could not be used as lightning arresters.

As explained above, prior to the pass/fail inspection, 2m5e
Non-linear resistors with applied currents of c to 20 m5 ec are sufficient for use in lightning arresters.

It goes without saying that the effects of the present invention can be obtained even if the quality/failure discrimination test items are other than those of the above-mentioned embodiments.

Furthermore, the magnitude of the current applied prior to the pass/fail determination test is not limited to the above example, and may vary depending on the specifications required for the non-linear resistor used in the overvoltage protection device and the composition of the non-linear resistor. Of course, this is determined depending on the shape, size, etc.

Furthermore, the composition and mixing ratio of the non-linear resistor may be other than those in the above embodiments, and in that case, differences will occur in the electrical characteristics of the non-linear resistor. The degree of freedom is obtained.

The method of manufacturing the non-linear resistor is not limited to the above-mentioned embodiment, and it goes without saying that the same effect can be obtained even with other manufacturing methods.

[Brief explanation of drawings]

1 and 2 are curve diagrams for explaining the electrical characteristics of the nonlinear resistor according to the present invention.

Claims (1)

[Claims] 1. It is characterized by comprising a step of applying a current pulse having a duration of 2 to 20 m5eC to the non-linear resistor, and a step of performing a quality determination inspection by visual inspection of the non-linear resistor after applying the current pulse. A method for determining the quality of a nonlinear resistor.