Electricity: conductors and insulators – Conduits – cables or conductors – Combined
Reexamination Certificate
1999-12-13
2001-08-28
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Conduits, cables or conductors
Combined
C174S08400S, C174S07400A
Reexamination Certificate
active
06281442
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to a cable fitting for the protection of a cable connection in a medium voltage technology, wherein strippable cable conductors are connected to a conductive connecting element. The protection of the cable connection is accomplished by a field controlling or shielding element covering the set off edges of the cable conductive layers, a shrinkable inner insulation tube, sleeve or hose disposed on the field controlling element, a shrinkable outer insulation hose, sleeve or tube, a conductive layer and a shrinkable protective hose, sleeve or tube that completely covers the arrangement are arranged lying on top of one another from inside to outside over the joint.
Cable sleeves are notoriously known for the connection of two cables in the medium voltage region. The conductors that are to be connected are respectively contacted with a press or screw connector and are covered with means for controlling the electrical field. Shrinkable insulation hoses or tube are arranged over this means. U.S. Pat. No. 4,383,131, which claims priority from the same British Application as German 29 37 253-C2, discloses such an arrangement. The electrical field control or shield occurs with the help of a heat shrinkable field control tube or shielding sleeve. The outside diameter of this field control tube is smaller than the inside diameter of a shrinkable insulation tube that is to be arranged thereover. Thus, the field control tube or shielding tube overlaps the outside conductor layers of each cable and is not interrupted in its course across the joint. The heat shrinkable insulation tubes that are to be arranged over the field control tube are initially arranged in one another and respectively shrunken following one another onto the field control tube or sleeve, which has already been shrunken on the connection. In order to avoid the individual sleeves getting mixed up or mistaken, these are correspondingly designated or other measures have to be taken, such as diameters that are different from each other, for example. This requires a considerable manufacturing, installation and time outlay. Thus, the field control tubes, for example, are always manufactured smaller in the outside diameter than the insulating tubes or sleeves which are to be arranged thereover. As a result of this pre-customizing, it is then possible to preclude an incorrect insulation in this manner. However, the geometrical adaptation of the tubes and customizing are involved regarding the manufacturing. Potentially, a limitation concerning the shrinking region must be accepted due to the different diameters of the individual sleeves, since the outermost sleeve must be shrunken significantly more than the sleeve that lies inside. Besides, it is disadvantageous that cavities may be formed at the junctions given the utilization of these tubes or sleeves, and these cavities can lead to a partial discharge at the outer conductive layer edges of the cable. An additional band that preferably exhibits field controlling or shielding properties as well was previously utilized at these locations in order to solve such problems. Electrically conductive lacquers, with which the cavities are filled, are also utilized in order to force a defined electrical potential at the described locations and prevent partial discharges therewith.
European 0 681 010-A2 discloses a method for manufacturing a field controlling or shielding layer for medium voltage fittings. This field controlling layer is a liquid polymer with conductive additives of granulated silicon carbide. The mix recipe contains a halogen-free solvent that evaporates after application onto the medium voltage fitting. Such field controlling sealing compounds meet all the required criteria for field controlling layers given medium voltage fittings. Moreover, different exemplary embodiments for the field controlling layer that satisfy the environmental conditions regarding solvents are specified therein, whereby the required electrical conditions are adhered to.
SUMMARY OF THE INVENTION
The present invention is based on an object of designing a cable fitting for the protection of a cable connection in the medium voltage technology, wherein the problems of the electrical field control in conjunction with an appropriate insulation manufacture are solved in a simple and time-saving manner. In particular, the partial discharge intensity is to be kept as small as possible by avoiding cavities in the joint region and by avoiding partial discharge from the beginning. Besides, the invention is based on the object of facilitating the installation with the help of the cable fitting and improving the manufacture of the product. This object is inventively achieved with a cable fitting having a field controlling or shielding element arranged as a coating on the inside surface of a shrinkable inner insulation tube or sleeve and the field controlling or shielding element can be deformed at least during the step of installing.
One clear advantage of the inventive cable fitting is that a separate sleeve that was previously the separate field controlling or shielding element is no longer necessary given the overall arrangement. Given the installation, this means that the working steps can be saved, namely the arrangement of the shrinking procedure of the separate field controlling or shielding sleeve. Furthermore, given the adaptation of the diameter, it is advantageous that there is one fewer sleeve, so that the gradation of the diameter of the sleeves which are to be shrunken on top of one another can be better fashioned. This has the result that a larger region of the cable diameter can be covered with one type of cable fitting. In addition, the tendency to form a cavity is avoided by the deformability of the field controlling or shielding element that is applied as a coating, so that partial discharges are no longer possible. Thus, for example, a field control layer or, respectively, a field controlling compound that at preferably does not contain halogen-containing solvents is applied as a field controlling element on the inside surface of the insulating tube or sleeve as a coating. Thereby, the coating of the semiconductive field controlling element must cover the joint of both cables to the extent that the field controlling element is in touch with the outer conductive layers of both cables after the installation.
The field controlling or shielding element contains, for example, a viscous, highly sticky polymer at room temperature, a highly volatile solvent at room temperature, an electrically conductive additive of granulated silicon carbonate, various additives and antioxidant agents that serve the purpose of making the element softer. The solvent is halogen-free and exhibits an evaporation factor of <10 with reference to ester. Ethylene-propylene-dienterpolymer (EPDM), for example, is appropriate as the polymer. The following solvents can be utilized, for example: Isopropanol, 2-butanone, ethylacetate, petroleum-benzine 60-80, n-hexane, cyclohexane and others. Chlorinated aliphatic hydrocarbons, chlorinated cycloaliphatic compounds, for example, are potential additional additives. Commercially-obtainable phenolic and/or aminic compounds are added as antioxidant agents.
Generally, such field shielding or controlling elements are continuously applied as a coating; however, an annular interruption is possible in the region of the press or screw connector. The materials of the applied insulation hoses exhibit properties resistant to creep current and erosion, whereby the specific volume resistivity is ≧10
10
&OHgr;cm. The insulation tubes or sleeves can be supplied as endless tubes, so that the respectively required length can be cut at the installation location. In general, however, it is expedient to precut manufacture expandates, i.e., expanded, shrinkable insulation tubes or sleeves, the field controlling element being then inserted as a coating at the factory in this insulation tube or sleeve. The thickness of the coating of
Nino Adolfo
Reichard Dean A.
RXS Kabelgarnituren GmbH
Schiff & Hardin & Waite
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