A composite sintered oxide resistor comprising crystal grains of zinc oxide and crystal grains of a zinc oxide compound of other metal or semi-metal element than zinc, and a grain boundary layer having an electric resistance equal to or lower than that of the crystal grains of zinc oxide between the individual crystal grains and which has a very large withstanding capacity against switch surge, a small non-linear coefficient of voltage in the voltage-current characteristics, a positive, smaller resistance-temperature coefficient, and a small percent change in resistivity after heat treatment at 500.degree. C. in the atmosphere.
An electrically resistive body best suited for providing varistors of high surge withstanding capability and high nonlinearity coefficient over a wide range of current magnitudes. The resistive body is composed of a major proportion of metallic oxides including zinc oxide, bismuth trioxide, antimony trioxide, cobaltous oxide, magnesium oxide, manganous oxide, and boric oxide. To these major ingredients there are added minor proportions of boric oxide and aluminum oxide, or of boric oxide and spinel. For the fabrication of such resistive bodies, the mixture of the noted ingredients in finely divided form are molded into desired shape and size, and the moldings are sintered.
A compact power circuit breaker having a large breaking capacity and stable breaking performance by using a compact closing resistor unit having high performance. The power circuit breaker includes a main switch arranged in a current path, an auxiliary switch connected to the current path parallel with respect to the main switch and turned on prior to an ON state of the main switch, and a closing resistor unit connected in series with the auxiliary switch and incorporated with a resistor having a sintered body consisting of a Zn--Ti--Co--O--based oxide and having metal components consisting of titanium calculated as titanium oxide (TiO.sub.2) in an amount of 0.5 to 25 mol %, cobalt calculated as cobalt oxide (CoO) in an amount of 0.5 to 30 mol %, and Zn as substantially the balance.
A substation includes standard arresters installed near a bushing of a power transmission line entrance and at a connecting bus of a transformer and one or more high voltage arresters having a discharge voltage 10 to 30% higher than a standard arrester. Each high voltage arrester uses zinc oxide elements and is disposed on a line side of a line entrance breaker and/or near an open end of a double main bus in the substation.
According to this invention, there is disclosed a compact power circuit breaker having a large breaking capacity and stable breaking performance due to a compact closing resistor unit having high performance. The power circuit breaker includes a main switching mechanism having an arc extinguishing function, an auxiliary switching mechanism parallelly connected to the main switching mechanism and having an arc extinguishing function, and a closing resistor unit connected in series with the auxiliary switching mechanism and incorporated with a resistor containing zinc oxide (ZnO) as a main component and titanium figured out as titanium oxide (TiO.sub.2) in an amount of 0.5 to 25 mol% and nickel figured out as nickel oxide (NiO) in an amount of 0.5 to 30 mol. % as sub-components.
Disclosed is a power resistor which has a large heat capacity per unit volume and an appropriate and stable electrical resistance, and in which the resistance changes little with time due to surge absorption. This power resistor includes a sintered body containing aluminum oxide and carbon, and a pair of electrodes formed on the two opposing surfaces of the sintered body. This sintered body consists of first regions containing a small amount of carbon or not containing carbon and second regions containing a larger amount of carbon than in the first regions and so arranged as to be connected to the electrodes.
