Abb Research Ltd.

Abb Schweiz Ag

Asea Brown Boveri Ag

Michael Hagemeister

Felix Greuter

Reto Kessler

Wolfgang Kluge

Hansjoerg Gramespacher

Lise Donzel

Petra Kluge-Weiss

Bernhard Richter

Oliver Beck

Stephan Hoffarth

Ren&eacute; Rudolph

Claus Christian Sch&uuml;ler

The present invention relates to a varistor material for a surge arrester with target switching field strength ranging from 250 to 400 V/mm comprising ZnO forming a ZnO phase and Bi expressed as BiOforming an intergranular bismuth oxide phase, said varistor material further comprising a spinel phase, characterized in that the amount of a pyrochlore phase comprised in the varistor material is such, that the ratio of the pyrochlore phase to the spinel phase is less than 0.15:1.

High field strength varistor material

The invention relates to a nonlinear electrical material with improved microvaristor filler (), to devices and electrical apparatuses comprising such nonlinear electrical material and to a production method thereof. According to invention, the filler () comprises larger spherical particles () and smaller irregular particles () that are arranged interstitially and provide non-point-like and/or multiple contact areas () owing to their irregular outer shape comprising edges and faces. Embodiments, among other things, relate to: spherical particles () being calcinated and broken-up to retain their original shape; irregular, spikly shaped, particles () obtained by calcinating or sintering and crushing or fracturing granules or blocks; and addition of a third filler fraction. Advantages, among others, are: higher filler contents, more and more durable inter-particle contacts (), enlarged effective micro-contact area, and improved electrical performance of the nonlinear electrical material.

Nonlinear electrical material for high and medium voltage applications

The manufacturing method for an electroceramic component (), for example a varistor (), comprises a laser irradiation of a part () of the surface of an electroceramic body () before a metallization () is applied to the part () of the surface. By means of the laser irradiation it is possible to produce a micro-roughness and/or a chemical modification of the surface which permits good adhesion of the metallization, and it is possible to reduce or eliminate areas of unevenness or waviness of that part () of the surface of the electroceramic body () which is to be metallized. In addition, improved transverse conductivity can be produced, by virtue of which a low contact resistance and a very homogeneous current distribution is achieved, in particular near to the metallization (). In addition it is possible to remove residues which originate in particular from a sinter support or from the application of a passivation layer. After the laser irradiation, the electroceramic body advantageously has a border () which adjoins the part () of the surface and which is not laser-irradiated. The laser beam can advantageously be pulsed and focused.

Laser-irradiated metallized electroceramic

The surrounding body () serves to surround the end, a branching or a connecting point of a high-voltage cable. It has an element () with a nonlinear current-voltage characteristic line, which serves to control the electric field in the surrounding area. The field control element () contains a polymer and a filler embedded in the polymer und containing microvaristors, as well as at least a hollow body section extending along an axis () and designed flat, with an axially symmetrical inner surface conductive by deforming the surrounding body () to an outer surface of the cable. To ensure good field control in cables, which are operated at high voltages, the inner surface of the hollow body section is designed as a variation of the outer surface of the cable and in such a way that the field control in the surrounding area is achieved by altering the number of microvaristors per surface unit as a result of expansion and/or shrinking of the hollow body section after deforming.

Surrounding body for a high voltage cable and cable element, which is provided with such a surrounding body

Surge arrester

Method for producing a varistor based on a metal oxide and a varistor produced using this method

The resistor is designed in the form of a column and has a cylindrical resistor body which is arranged between two planar electrodes, aligned parallel, and is made of a ceramic material. The resistor is preferably a varistor on a metal-oxide base, and is then used as a voltage-limiting element in an overvoltage suppressor. The strength of the ceramic material and the length of the resistor are chosen to be as great as possible. However, the length of the resistor is at most sufficiently large that damage to the ceramic resistor body caused by thermally produced pressure waves is avoided when the resistor is loaded in an electrical field of given magnitude with at least one highly energetic current pulse of defined amplitude, form and duration.

Resistor which is designed in the form of a column and is resistant to high current in particular a varistor on a metal-oxide base, and method for producing such a resistor

Growing community of inventors

Zurich, Switzerland

Michael Hagemeister