Sintered body having non-linear resistance characteristics

Details Sintered body having non-linear resistance characteristics Sintered body having non-linear resistance characteristics

1999-05-24

2001-02-06

Easthom, Karl D. (Department: 2832)

Electrical resistors

Resistance value responsive to a condition

Current and/or voltage

C338S020000

Reexamination Certificate

active

06184771

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to sintered bodies which can be used in resistors having a nonlinear resistance (hereinafter “non-linear resistors”) and which include zinc oxide (ZnO) as their principal composition. In particular, the present invention relates to a non-linear resistor with superior non-linear current/voltage characteristics, and also with a greatly improved ability to withstand surge current.
DESCRIPTION OF THE RELATED ART
Generally, when abnormal voltage due to a lightning strike or lightning-like surge occurs in a power system, or when abnormal voltage due to the switching operation of an electronic equipment circuit (i.e., switching surge) occurs, a lightning arrester or a surge absorber is installed to protect the power system or the electronic equipment from the abnormal voltage. The lightning arrester or the surge absorber, which is composed of a non-linear resistor having a sintered body, on the one hand exhibits an insulating property under normal voltages, but exhibits a low resistance property when an abnormal voltage is applied. These lightning arresters or surge absorbers, are installed between a terminal of the equipment to be protected, or between the bus-line of the power system, and a ground. If abnormal voltage of a specified value or higher is generated by the lightning strike or the like, a discharge begins through the arrester and the abnormal voltage is limited by the discharge current flowing to the ground. Then, when the voltage returns to normal, the discharge immediately ceases, and the arrester returns to its former insulated state.
As disclosed in, for example, JAPANESE KOUKAI Patent PS 59-117202 Publication, the non-linear resistors that are part of the above-mentioned lightning arresters, etc., are produced by the following process. A raw material mixture is prepared by combining specified quantities of oxide powders such as Bi
2
O
3
, Sb
2
O
3
, Co
2
O
3
, MnO and Cr
2
O
3
, as auxiliary compositions, with zinc oxide (ZnO) powder, as the principal composition. After these raw material mixtures have been mixed together with water and an organic binder, a granulated powder is prepared using a spray drier or like. Then, after the granulated powder has been molded into a specified shape, a sintered body having non-linear property is produced by heating to remove the binder and sintering.
Then, as shown in
FIG. 1
, the essential components of a lightning arrester or the like are formed by forming a high-resistance layer (i.e., side insulating layer)
2
on the side surface of a sintered body
1
, which is the above-mentioned resistor, by coating and re-baking an insulating material to prevent creeping flash-over (see FIG.
2
). Then respective electrodes
3
are added after polishing the two end surfaces of the sintered body
1
.
In recent years, the production of equipment structures that are part of smaller and higher performance electrical transmission and conversion facilities has progressed in order to reduce transmission costs in power systems. In order to make transmission and conversion equipment smaller and of higher performance, it is desirable to reduce the requirement for dielectric strength by improving the current/voltage non-linear characteristics of non-linear resistors, which are construction components, and to reduce the residual voltage of lightning arresters.
In particular, with lightning arresters, there is a need for designing lightning arresters smaller by increasing the surge current withstand of the non-linear resistor on the one hand, and by reducing the dimensions, e.g., height, of the non-linear resistor. However, there is the problem that, with the non-linear resistor having the prior art composition, the current/voltage non-linear characteristics and surge current withstand are still insufficient.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a sintered composition which can be formed into a resistor having a non-linear resistance characteristic and overcomes the disadvantages of the related art described above.
It is a further object of the present invention provide a resistor having a non-linear resistance that has superior current/voltage non-linear characteristics and, at the same time, is capable of greatly improving the withstand-voltage property.
There has been provided according to one aspect of the present invention, a sintered body which includes: zinc oxide; and bismuth, cobalt, antimony, manganese and nickel expressed as Bi
2
O
3
, Co
2
O
3
, Sb
2
O
3
, MnO and NiO, and containing 0.05 to 10 mol % of Bi
2
O
3
, 0.05 to 10 mol % of Co
2
O
3
, 0.05 to 10 mol % of Sb
2
O
3
, 0.05 to 10 mol % of MnO and 0.05 to 10 mol % of NiO as auxiliary compositions. The content ratio of Bi
2
O
3
to NiO is in a mole ratio of 0.5 or more but 1.5 or less. The content ratio of MnO to Sb
2
O
3
is in a mole ratio of 1.0 or less. In a preferred embodiment, the sintered body has a non-linear electrical resistance characteristic.
According to another aspect of the invention, there has been provided a non-linear resistor which is formed from a sintered body. The non-linear resistor includes: zinc oxide as a principal composition; and bismuth, cobalt, antimony, manganese and nickel respectively converted to Bi
2
O
3
, Co
2
O
3
, Sb
2
O
3
, MnO and NiO, and containing 0.05 to 10.0 mol % of Bi
2
O
3
, 0.05 to 10 mol % of Co
2
O
3
, 0.05 to 10 mol % of Sb
2
O
3
, 0.05 to 10 mol % of MnO and 0.05 to 10 mol % of NiO as auxiliary compositions. The content ratio of Bi
2
O
3
to NiO is in a mole ratio of 0.5 or more but 1.5 or less. The content ratio of MnO to Sb
2
O
3
is in a mole ratio of 1.0 or less.
According to still another aspect of the invention, there has been provided a protection instrument, which protects electrical equipment from a abnormal voltage. The protection instrument includes: a first terminal connected to the electrical equipment; the non-linear resistor described above; and a second terminal connected between the non-linear resistor and a ground.
According to yet another aspect of the invention, there has been provided a method for manufacturing a sintered body described above, which includes: mixing to Bi
2
O
3
, NiO, Sb
2
O
3
, MnO, and Co
2
O
3
, as auxiliary compositions, with ZnO powder to obtain a mixture; reducing the viscosity of the mixture; spraying the mixture after reducing viscosity to obtain a granular powder; pressing the granular powder into a mold by pressure to form a molded body; heating the molded body to remove the binder; and sintering the molded body by sintering at a temperature higher than the temperature of removing the binder to obtain the sintered body.
In a preferred embodiment, the sintered body contains 0.5 to 500 ppm of aluminum, converted to Al
3+
, as an auxiliary composition. Moreover, it is also desirable that 10 to 1000 ppm of at least one or the other of boron and silver, converted respectively to B
3+
and Ag
+
, is contained as an auxiliary composition.
Also, the sintered body may preferably contain 0.01 to 1000 ppm of at least one of sodium, potassium, chlorine and calcium, converted respectively to Na
+
, K
+
, Cl
−
and Ca
2+
, as an auxiliary composition.


REFERENCES:
patent: 3899451 (1975-08-01), Ichinose et al.
patent: 4319215 (1982-03-01), Yamazaki et al.
patent: 4320379 (1982-03-01), Yodogawa
patent: 4460497 (1984-07-01), Gupta et al.
patent: 4527146 (1985-07-01), Kanai et al.
patent: 4719064 (1988-01-01), Nakata et al.
patent: 5143711 (1992-09-01), Kluge et al.
patent: 5231370 (1993-07-01), Arnold, Jr. et al.
patent: 5254816 (1993-10-01), Shutoh et al.
patent: 5422779 (1995-06-01), Borkowicz et al.
patent: 5569495 (1996-10-01), Evans et al.
patent: 5739742 (1998-04-01), Iga et al.
patent: 0241150 (1987-10-01), None
patent: 0 924 714 (1999-06-01), None
patent: 57-099708 (1982-06-01), None
patent: 59-117202 (1984-07-01), None

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