Electricity: conductors and insulators – Insulators – With insulator-supporting or attaching means
Reexamination Certificate
2001-06-04
2003-03-18
Dinkins, Anthony (Department: 2831)
Electricity: conductors and insulators
Insulators
With insulator-supporting or attaching means
C174S1400CR, C174S209000, C174S211000, C427S058000
Reexamination Certificate
active
06534721
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a hollow high-voltage insulator, which has an insulating body, with a hollow support element made of a thermosetting composition, and a potential control device. The invention also relates to a process for producing a hollow insulator of this type.
A hollow insulator of the foregoing type is used to allow current or voltage on high-voltage-carrying parts to be reliably measured by means of measuring transducers. A hollow insulator of this type is also used for example to allow high voltages to be conducted into a transformer. In the first case, the measuring transducer is arranged in the hollow space of the hollow insulator, one side of the measuring transducer being connected to the high-voltage-carrying part and the other side of the measuring transducer being connected to a measuring instrument or to ground. In the second case, a current conductor is for example led from a high-voltage-carrying line via the hollow space of the hollow insulator into the transformer.
The support element of the hollow insulator may be provided on its outer side with a cladding comprising shields. Silicone rubber has proven to be a successful material for the shields. The cladding of silicone rubber is thereby case solidly bonded to the thermosetting composition of the support element. This is also referred to as a composite insulator.
The thermosetting composition of the support element is decisive for the mechanical stability of the hollow insulator. A thermosetting composition is understood as meaning a highly polymeric material which is closely crosslinked up to the decomposition temperature and at lower temperatures is energy-elastic, and even at high temperatures does not have viscous flow. The glass transition temperature of a thermosetting composition always lies above 50° C.
Examples of thermosetting compositions are phenolics, aminoplastics, epoxy resins acrylic, and alkyd resins, as well as unsaturated polyester resins.
When using a hollow conductor for measuring or leading through high voltages or currents, there are inevitably very short distances between the parts being insulated, which are at very different potentials. Regions with critical field strengths are formed, at which flashovers or discharges can easily take place and can lead to the destruction of the hollow insulator or the device on which the hollow insulator is arranged. To avoid such phenomena, it is known from HÜTTE, Taschenbücher der Technik [technology pocket books], Springer Verlag Berlin, Electrische Energietechnik [electrical power engineering), volume 2: Geräte [devices], 29th edition 1978, section 2.1.3.6, to design leading-through current conductors or lead-throughs in general as what are known as capacitor bushings with potential control. In that case, an insulating body made of hard paper, soft paper or casting resin, which contains concentrically arranged cylindrical conductive coverings, is applied directly to the current conductor to be led through. The conductive coverings become shorter from the inside outward and control the potential distribution between the conductor and ground.
Reference is had, in this context, to European published patent applications EP 0 029 164 A1 and EP 0 032 690 A2, which disclose high-voltage lead-throughs of this type with capacitive potential control inserts.
It has also been known for controlling the potential of lead-throughs in the interior of a hollow insulator to provide control electrodes which are electrically bonded to the fittings by which the hollow insulator is fastened. The potential distribution between the led-through conductor and ground can also be controlled in this way.
If capacitor bushings with control inserts are used, the control electrodes must be disadvantageously applied directly to the conductor in a complex and expensive process. Such a process is not required when a current conductor is led through a hollow insulator. However, for controlling the potential, the control electrodes must then be subsequently arranged in the interior of the hollow insulator, involving additional installation effort. This disadvantageously increases the production costs for a hollow insulator. Moreover, both configurations for potential controllers, or generally for potential control device, disadvantageously require additional installation space.
German patent No. DE 32 08 358 C2 also discloses a casting resin insulator in which capacitive field control inserts are cast into the casting resin body of the insulator as potential control device. For this purpose, first of all a preform with successively step-shaped transitional regions is cast. After removal from the casting mold, its circumferential surface is provided with an electrically conductive covering and subsequently, in a second casting operation, is encapsulated with an outer casting resin sheath. Since it is necessary to work with two casting molds and, moreover, many separate working steps are required, the process described is complex and cost-intensive, with the result that the casting resin insulator obtained in this way is disadvantageously very expensive.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a hollow insulator and a production method which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this general kind, and wherein the hollow insulator can be produced in a particularly simple and low-cost process and the corresponding fabrication method is appropriately configured.
With the above and other objects in view there is provided, in accordance with the invention, a hollow high-voltage insulator, comprising:
an insulating body with a hollow support element made of a thermosetting composition, and a potential control device encapsulated with the thermosetting composition of the support element;
the potential control device being at least partially encoiled with fibers, and the support element built up by alternating insertion of the potential control device, coiling on of the fibers, and simultaneous or subsequent application of the thermosetting composition.
In other words, the potential control device is encapsulated with the thermosetting composition of the support element and at least partially encoiled with fibers.
The invention is in this respect based on the fact that the support element of a composite insulator is produced by curing a blank of the still soft thermosetting compositions. This is because it was recognized that, in this way, the potential control device can be arranged in the hollow insulator by being processed simultaneously with the soft thermosetting composition to form the blank. The joint processing takes place in this case by building up the blank layer by layer by alternating insertion of the potential control device, coiling with fibers and simultaneous or subsequent application of the thermosetting composition. It is also referred to as the filament-winding process. After the curing of the thermosetting composition, which, as known, takes place by a heat treatment, the potential control device is cast, i.e. solidly bonded, with the thermosetting composition of the support element. The support element is at the same time reinforced with fibers.
Neither the complex application of the potential control device to the conductor to be led through nor an additional installation effort for the potential control device to be subsequently introduced into the interior of the hollow insulator is required according to this novel invention. The invention combines the installation of the potential control device and the production of the support element into a single operation. Furthermore, no additional space in the interior of the hollow insulator is taken up by the potential control device encapsulated with the thermosetting composition of the support element.
The use of a thermosetting composition reinforced with glass fibers has been found to be particularly advantageous for the mechanical stabilit
Dinkins Anthony
Mayback Gregory L.
Siemens Aktiengesellschaft
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