The invention is in the field of electronic components and is to be used in the construction of gas-filled surge arresters with at least two electrodes, in which an activating compound including a plurality of components is applied to at least one of the electrodes to ensure igniting properties.
In the case of surge arresters filled with an inert gas, the respectively required operating behavior, such as a static sparkover voltage (DC sparkover voltage), dynamic sparkover voltage (surge sparkover voltage), extinguishing voltage and glow voltage as well as a current-carrying capacity under alternating current and unipolar pulsed current, can be influenced by various measures. Those measures may be the structural layout of the electrodes, the type and pressure of the gas filling, the configuration of one or more ignition strips on an inner wall of a glass or ceramic insulator and the selection of the activating compound disposed on the active surfaces of the electrodes. For example, there is a known surge arrester which has two electrodes that are fitted at the ends into a hollow-cylindrical ceramic insulator and which has mutually facing electrode surfaces that are coated with an activating compound of aluminum and magnesium oxide. In that case, the activating compound is disposed in depressions in the electrode surface. Furthermore, a plurality of axially running ignition strips, which are constructed as so-called central ignition strips, are disposed on the inner wall of the insulator without directly joining the electrodes, in U.S. Pat. No. 4,266,260. In the case of surge arresters with two ceramic insulators and a third, annular central electrode, it is similarly known from U.S. Pat. No. 4,769,736 to also place the activating compound (in that case sodium silicate) in depressions in the central electrode.
The activating compounds used for gas-filled surge arresters frequently include a plurality of components. In the case of an activating compound including three components, there is a known composition which contains aluminum as a first component in an amount of approximately 25% by weight, a sodium bromide as a second component in an amount of approximately 50% by weight and a barium titanate as a third component in an amount of approximately 25% by weight. In that case, the gas filling contains not only an inert gas such as argon but also hydrogen in an amount of 5 to 20% by volume. Such an activating compound, according to German Patent DE 196 32 417 C1, is distinguished by a high adhesive strength over heavy-duty discharge gaps with low sparkover voltage.
With regard to high-voltage spark gaps it is also known in the case of a gas filling of pure nitrogen to use an activating compound which, apart from sodium or potassium silicate, additionally contains nickel. That structure, according to German Published, Non-Prosecuted Patent Application DE 37 23 571 A1, improves the long-term constancy of the ignition voltage.
It is accordingly an object of the invention to provide a gas-filled surge arrester with an activating compound formed of a plurality of components, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which, starting from a gas-filled surge arrester with at least two electrodes, with a hydrogen-containing gas filling and with an activating compound including a plurality of components, puts the components of the activating compound together in such a way that the surge arrester has a good current-carrying capacity under alternating current (test: 60 times 1A, 1 sec.) and under unipolar pulsed current (test: 1500 times 10A, wave {fraction (10/1000)} xcexcsec.) even at temperatures to xe2x88x9240xc2x0 C., while maintaining a low sparkover surge voltage (for example at 100 V/sec. lower than 550 V), a constant extinguishing voltage and a constant DC sparkover voltage.
With the foregoing and other objects in view there is provided, in accordance with the invention, a gas-filled surge arrester, comprising at least two electrodes; a hydrogen-containing gas filling; and an activating compound applied to at least one of the electrodes, the activating compound containing nickel powder in an amount of 30 to 35% by weight and potassium silicate in an amount of 25 to 35% by weight as basic components, sodium bromide in an amount of 15 to 20% by weight, and aluminum powder, sodium silicate and barium titanate as further components each in an amount of 5 to 10% by weight.
With such a combination of the components of the activating compound, the actual igniting and extinguishing properties of the surge arrester are essentially ensured by the potassium silicate component in combination with the hydrogen-containing gas filling, while the sodium bromide, barium titanate, sodium silicate and aluminum powder components stabilize the DC sparkover voltage and the nickel powder component guarantees the good extinguishing behavior before and after loading.
The novel electrode activating compound is suitable both for applying to the hollow-cylindrical central electrode of two-gap arresters and for applying to the end electrodes of two-gap and three-gap arresters.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a gas-filled surge arrester with an activating compound formed of a plurality of components, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.