Surge suppressor having looped clamping elements

The surge arrester contains two connection fittings (1, 2) which are spaced apart from one another along an axis and between which at least one cylindrical varistor element (7) is arranged. The connection fittings (1, 2) and the at least one varistor element (7) are clamped with one another, accompanied by the formation of contact force, to form a mechanically stable active part of the surge arrester. The active part is surrounded by a cast housing (12) made from insulating material. The clamping of the active part is achieved by at least two loops (5) respectively acting independently of one another on the connection fittings (1, 2). The loops (5) are arranged at a distance from the at least one varistor element (7). The connection fittings (1, 2) contain bearing areas which correspond respectively to the number of the loops (5) and are distributed uniformly about the axis azimuthally and on which a loop end is respectively supported. Despite its simple design, the surge arrester has good mechanical and electrical characteristics and can be produced in a particularly cost-effective way.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention pertains to a surge arrester having looped clamping elements. 
2. Discussion of Background 
The invention refers in this connection to a prior art such as emerges, for 
example, from EP 0,335,480 B1. A surge arrester described in this prior 
art contains a plurality of nonlinear resistor elements with varistor 
behavior, which are stacked one above another and arranged between two 
power connection fittings. A winding led around the resistor elements and 
a portion of the connection fittings and made from nonconductive material 
clamps the connection fittings and the resistor elements while forming a 
force which acts in an axial manner. This force is required to form a 
current path, which must conduct high currents briefly given the occurence 
of surge. A cast housing made from a weather-resistant plastic surrounds 
the resistor elements, the winding and the predominant portion of the 
connection fittings. 
The production of such a surge arrester is expensive, since the resistor 
elements are accommodated in a plastic tube and since the application of 
the winding is, in addition, relatively complicated. 
SUMMARY OF THE INVENTION 
Accordingly, one object of this invention is to provide a novel surge 
arrester which despite a simple design has good mechanical and electrical 
characteristics, and which can be produced in a particularly 
cost-effective way. 
By comparison with comparable surge arresters according to the prior art, 
the surge arrester according to the invention is distinguished in that 
despite excellent mechanical and electrical characteristics it is of 
simple design and therefore can be produced in a particularly economic 
way. All that is required for its assembly is a prefabricated template 
which temporarily guarantees axial guidance in which the connection 
fittings and the at least one varistor element are firstly stacked and 
thereafter connected to form the mechanically stable active part of the 
surge arrester by fitting the loops and forming a bias. Since in this case 
the loops are fitted at a distance from the at least one varistor element, 
during the subsequent production of the cast housing the active part can 
be extrusion coated very reliably in a manner free from gaps and shrink 
holes. The surge arrester according to-the invention therefore has not 
only good mechanical, but also good electrical characteristics. 
The loops can already be prefabricated and then require during assembly 
only to be pushed onto the bearing areas of the connection fittings. Loops 
which are particularly stable and yet of small dimensions contain a tape 
which is wound in the shape of a loop and is advantageously embedded in a 
plastic matrix. The mechanical stability of the active part can then be 
achieved by subsequently clamping the elements stacked in the template 
during assembly, for example by means of a clamping device provided in one 
of the two connection fittings, or else by means of spring elements which 
are installed in the stack arranged in the template and are biased during 
fitting of the loops accompanied by the formation of the desired contact 
force and thus also of the required mechanical stability. 
An additional clamping device or additional spring elements can be saved if 
the loops are formed in each case by an elastically deformable tape, for 
example made from glass fibers. The tape is then wound around the 
connection fittings with the bias prescribed by the contact force 
accompanied by the formation of the contact force and thus also of the 
mechanical stability of the active part, and herewith supported on each 
case one of the bearing areas of each of the two connection fittings. 
The wound tape should expediently be embedded in a plastic matrix, which is 
formed by the curing of curable plastic after the loops have been placed 
on the bearing areas. The tape is advantageously impregnated with a 
pregelled, for example epoxy-based plastic (prepreg) which is cured after 
the winding executed under bias. Since such a tape has good adhesive 
properties, fastening devices for the tape end are eliminated when it is 
used. 
The bearing areas on the connection fittings should preferably have a 
section with a semicircular surface profile of the largest possible circle 
diameter, since then the clamping force exerted by the tape is absorbed 
particularly uniformly by the connection fittings and is transmitted as a 
homogeneously acting contact force to the at least one varistor element. 
The bearing areas can be arranged on projections or in recesses of the 
connection fittings which are constructed as shoulder and as groove, 
respectively. The construction as groove is particularly advantageous in 
this case, since a groove can be shaped without difficulty in a 
conventionally employed, cylindrical connection fitting and simultaneously 
guarantees a particularly secure support for the assigned loop. 
Two bearing areas arranged diametrically relative to one another and on 
which one of two loops is respectively supported generally suffice on each 
connection fitting for good mechanical stability of the active part. 
Additional stability is achieved by using three bearing areas, arranged 
offset azimuthally about the axis by approximately 120.degree., on which 
one of three possibly further improved slightly by four or more bearing 
areas per connection fitting, but this does not cause additional outlay on 
production. 
It is expedient to provide at least one current transfer element which can 
be deformed with the formation of the contact force in the current path 
between the connection fittings. This guarantees particularly reliable 
contacting and thus a good current carrying capacity of the current 
transfer between two varistor elements or the connection fitting and a 
varistor element or a pressure plate possibly provided in the current 
path. It has proved to be very favorable for the current transfer element 
to be constructed as a disk and to have grooves which are guided 
concentrically about the axis and shaped in end faces of the disk. A 
current transfer element constructed in this way specifically seals the 
current transfer zones in the active part against the penetration of 
liquid insulating material during casting of the housing of the surge 
arrester. 
Preferred exemplary embodiments of the invention and the further advantages 
which can be achieved therewith are explained in more detail below with 
the aid of drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, wherein like reference numerals designate 
identical or corresponding parts throughout the several views, the 
essentially cylindrically symmetrically constructed surge arrester 
represented in FIGS. 1 to 3 has two connection fittings 1, 2 which 
preferably consist of aluminum and are spaced apart from one another along 
the cylinder axis. The connection fitting 1 is provided with a fastening 
device (not represented) for an electric conductor. Provided in the ground 
connection fitting 2 is an axially aligned threaded bore 3 in which a 
clamping bolt 4 can be displaceably guided in the axial direction. 5 
denotes two loops made from a wound, glass fiber reinforced tape embedded 
in a plastic matrix. The loops are guided with their ends in grooves 6 
which are shaped into the connection fittings 1 and 2. The grooves 6 
respectively form in the base of the groove bearing areas with a section 
having a semicircular surface profile which are adjoined respectively by 
two axially extending sections (FIG. 2). 
Cylindrical varistor elements 7 made from nonlinear resistance material, 
for example based on metal oxide such as, in particular, ZnO are arranged 
between the connection fittings 1, 2. A disk-shaped pressure plate 8 made 
from aluminum is inserted in a cutout of the connection fittings 1. 
Arranged between this plate and the adjacent varistor element 7, between 
adjacent varistor elements 7 and between a further pressure plate 9 made 
from aluminum and a further varistor element 7 are current transfer 
elements which are respectively constructed as disk 10 having grooves 
which are guided concentrically about the axis and shaped in the two end 
faces of the disk. The disks 10 are advantageously formed from 
soft-annealed aluminum. 
The connection fittings 1, 2 are partly surrounded, and the varistor 
elements 7, the pressure plates 8, 9 and the loops 5 are completely 
surrounded by a cast housing 12 provided with shields 11 and made from 
insulating material. 
In order to produce this surge arrester, the connection fitting 2 and the 
pressure plate 9 are sequentially, and the disks 10 and the varistor 
elements 7, the pressure plate 8 and the connection fitting 1 are 
alternately packed one above another in a template. The grooves 6 of the 
two connection fittings 1, 2 are aligned in this case such that they are 
flush with one another (FIG. 1). Two prefabricated loops 5, which 
preferably respectively consist of a wound, tapeshaped prepreg which has 
been cured after winding, are then suspended in the mutually flush grooves 
6, and by turning the clamping bolt 4 force is exerted on the pressure 
plate 9 and thus, via the self-clamping loops 5, also on all the remaining 
parts of the active part of the arrester. 
Instead of two prefabricated loops, it is also possible to use two loops 
which are formed during the production of the surge arrester. In order to 
form these loops, two tapes to which a biasing force is respectively 
applied are wound around the two connection fittings 1, 2 and laid down on 
the bearing areas of the two flush grooves 6. In this case, the two 
connection fittings 1, 2 are permanently clamped to one another 
accompanied by the formation of contact force, and a mechanically stable 
active part of the surge arrester to be produced is thereby formed. This 
biasing is generally already completely adequate for a good mechanical 
strength of the active part of the arrester. In the case of the use of 
tapes of adequate elasticity such as is already possessed, for example, by 
tapes made from glass fibers, the active part of the arrester can 
therefore consist only of the two connection fittings 1, 2, the at least 
one varistor element 7 and the loops 5. 
These tapes are preferably prepregs, in particular based on glass fibers 
and epoxy. Prepregs have a good adhesion effect. Loops wound from the 
biased prepregs are therefore stable after being wound even without an 
additional fastening device, and can now be cured at raised temperatures. 
The loops 5, which effect the contact force and thus also the mechanical 
stability of the active part and which consist of the wound tape and a 
cured plastic matrix which embeds the tape are now formed in the process. 
In addition to a good contacting of the individual parts located in the 
current path between the two connection fittings, by virtue of the 
clamping of the two connection fittings 1, 2 the use of the disks 10 
simultaneously also achieves a close fit of the grooves of the disks 10 
with the end faces of the varistor elements 7 and of the connection 
fittings 1, 2 as well as of the pressure plates 8, 9 possibly provided. 
During subsequent extrusion coating of the active part of the arrester by 
means of insulating material, preferably based on silicone, the 
penetration of liquid insulating material between the parts located 
individually in the current path is thus largely avoided. In accordance 
with exemplary embodiments, such as those shown FIGS. 4 and 6, the loops 5 
are fitted at a distance from the varistor elements 7, such that during 
subsequent production of the cast housing, the active part can be 
extrusion coated very reliably in a manner free from gaps and shrink 
holes. 
As may be seen from FIG. 4, instead of two grooves the connection fittings 
can also have two projections constructed as shoulders 13. Such 
projections can easily be shaped into the connection fittings 1, 2, and 
facilitate the application of the loops 5. 
It may be seen from FIGS. 5 and 6 that the connection fittings can also 
possibly have three grooves 6 or shoulders 13 respectively arranged offset 
by 120.degree.. The mechanical stability of the active parts of the 
arrester can be additionally increased in conjunction with prescribed 
contact force by the installation of such connection fittings 1, 2. 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein.