Insulating component for high-voltage equipment

An insulating component for use in high-voltage switching equipment, especially gas-insulated switching gear. A nozzle made of an insulating material is used in a power switch. Portions of the surface of the nozzle subject to high dielectric stresses in use are provided with increased surface roughness in the form of grooves. These grooves may be cut by a lathe.

FIELD OF THE INVENTION 
The present invention relates to an insulating component for use in 
high-voltage switching equipment, and more particularly for use in a 
gas-insulated switch gear. 
BACKGROUND INFORMATION 
An insulating component is described, for example, in Germany Patent No. 26 
26 855. These insulating components are used, for example, as spacers or 
nozzles for the feeding of insulating gas in electric high-voltage 
switches, particularly high-voltage power switches. 
Such components are used as supports for busbar conductors or leadthroughs 
in, for example, encapsulated high-voltage switchgear. They may, for 
example, consist of cast resin, an epoxy resin, polytetrafluoroethylene 
("PTFE"), a ceramic, or porcelain. 
Under high dielectric stresses, such as in the case of high electrical 
field strengths, particularly if the field strength has a component 
tangential to the surface of the insulating component, there is an 
increased probability of displacement currents on the surface of the 
insulating component, which may also lead to electric arcing. 
In accordance with the related art, a poorly conductive fabric is embedded 
in the region of the surface of the component in order to discharge 
surface charges. 
While this certainly increases the conductivity of the component, it also 
contributes a substantial expense to the cost of the manufacture of the 
component. Different structural materials are combined with each other and 
there is the danger that a part of the fabric is not firmly bound to the 
component and extends into a dielectrically highly stressed region of the 
high-voltage equipment. 
It is known from German Patent No. 30 47 761 to embed in an insulating 
component a mineral filler the particles of which lie freely on the 
surface of the component and prevent the formation of carbon-containing, 
and partially electrically conductive, tracks on the surface upon 
discharges. Such an insulating component is difficult to manufacture. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide an insulating component 
of the aforementioned type which permanently withstands high dielectric 
stresses and is economical to manufacture. 
The object of the present invention is achieved by providing the surface of 
the component with sharp-edged grooves or ridges with a depth of roughness 
of at least 100 .mu.m in at least one region which is particularly 
strongly stressed dielectrically. 
One advantageous embodiment of the invention provides that at least one 
particularly dielectrically stressed region of the surface has a depth of 
roughness of at least 200 .mu.m. 
As a result of the depth of roughness, no displacement currents which could 
give rise to electric arcing can occur on the surface of the component. 
In a cross section of the component, the latter has, in the region of its 
surface, sharp-edged elevations or recesses due to its surface structure. 
This structure leads to an improved dielectric strength since high 
electric field strengths occur on the tips and edges, which lead to the 
emission of surface charges and thus limit the potential of surface 
charges. 
No additional material other than that of which the component is made of is 
necessary in order to achieve this result. 
Another exemplary advantageous embodiment of the invention provides that 
the grooves or ridges are produced by machining. 
In that case, the component, after it has been formed by casting, sintering 
or extrusion, can be worked further by lathe-cutting or milling in the 
dielectrically particularly stressed region. 
A groove-depth more than 200 .mu.m has been found to be particularly 
advantageous. 
In the case of a component with rotational symmetry, the grooves may 
advantageously be concentric to each other or arranged in the form of a 
spiral. 
This is particularly advantageous when the component is part of an 
insulating material nozzle for a high-voltage power switch. Since such a 
power switch is frequently designed with rotational symmetry, the regions 
which are particularly highly stressed dielectrically also exhibit 
rotational symmetry and can be provided with said grooves by suitable 
machining (turning). 
The grooves or ridges may advantageously have a rectangular or saw-tooth 
cross section. Such a profile is simple to produce by turning on a lathe 
or milling. 
The present invention furthermore refers to a method of producing an 
insulating component for high-voltage equipment in which the component, 
after it has been formed, is provided, in at least one dielectrically 
particularly highly stressed region of its surface, with grooves by 
machining or is worked in such a manner that ridges remain. 
However, it is also possible for the component to be produced by a casting 
process and for the casting to have, in its dielectrically particularly 
strongly stressed region, grooves or ridges which produce corresponding 
complementary structures on the surface of the component. 
After it has been formed, an insulating component frequently has a surface 
of uniform quality and can then be worked by the method of the present 
invention in the dielectrically particularly strongly stressed regions of 
its surface. 
For example, it is also possible for a region of the surface to be provided 
with roughness using an embossing tool.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows a power switch in its "on" position. Two arc contact pieces 1 
and 2, as well as two continuous-current contact pieces 3 and 4 lie 
opposite each other and are in contact with each other when the switch is 
turned on. Electric connections of the switch are designated 11, 12 and 
are shown merely diagrammatically. 
In order to turn the switch off, the displaceable arc-contact piece 1 as 
well as the continuous-current contact piece 3 which is connected to it 
using a compression cylinder 5 are moved to the left in FIG. 1. This is 
done by a switch drive, not shown in detail. 
At the same time, arc-extinguishing gas is compressed within a compression 
chamber 6. 
After the separation of the two arc contact pieces 1 and 2 from each other, 
an arc is produced between them, with the arc heating the extinguishing 
gas within the region of the arc chamber 7. From arc chamber 7, the hot 
arc-extinguishing gas flows into heating chamber 8, where it is 
temporarily stored for the subsequent blowing-out of the arc. 
After the displaceable arc contact piece 1 has separated from the 
stationary arc contact piece 2, the insulating material nozzle 9, which is 
made of PTFE, also separates from the stationary arc contact piece 2. The 
insulating material nozzle 9 is connected to the compression cylinder 5 in 
the region of the continuous-current contact 3. 
After the insulating material nozzle 9 has separated from the stationary 
arc contact piece 2, end face 10 of the insulating material nozzle is 
dielectrically stressed by the electric field between arc contact pieces 1 
and 2. In this region, substantially concentric grooves (FIG. 2) of a 
width and depth of about 1 mm are produced by machining (for instance by 
cutting a spiral groove in the end surface), whereby a ridge of 
rectangular cross section having a width of about 1 mm is produced between 
the grooves. 
An arrangement in accordance with the present invention is dielectrically 
safer than a component provided with an overall better surface quality 
produced by manufacture. 
FIG. 3 shows a double-nozzle switch with two fixed nozzle-shaped contact 
pieces 13 and 14 which are conductively connected to each other by a 
bridging switch piece 15 when the switch is turned on. A compression 
device for an arc-extinguishing gas, consisting of a stationary 
compression piston 16 and a movable compression cylinder 17, is provided. 
When the switch is turned off, the compression cylinder is pulled back to 
such an extent that its bottom 18 is located in the separation gap between 
the stationary contact pieces 13, 14 and is exposed there to the 
electrical field. Bottom 18 has, on its side facing the switch path when 
it is turned-off, a structure of saw-tooth shape in cross section, which 
permits a discharge of surface charges.