Electricity: conductors and insulators – Conduits – cables or conductors – Combined
Patent
1996-10-08
1998-05-26
Kincaid, Kristine L.
Electricity: conductors and insulators
Conduits, cables or conductors
Combined
174 74A, 174 84R, 174DIG8, H02G 15184
Patent
active
057569363
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention refers to a cylindrical radially shrinkable sleeve for enclosing a connection or an end termination of an electrical cable.
BACKGROUND OF THE INVENTION
When making cable splices or cable end terminations, it is necessary to expose the conductor of the cable or the cable core. It is common to use radially shrinkable sleeves to enclose a connection or an end termination of an electrical cable. These sleeves consist either of a heat-shrinkable material or of elastic material. In the latter case, they are mechanically retained in an expanded state, usually by a removable core. When the core is removed, the sleeve engages the cable connection or the cable end termination under pressure.
Examples of mechanical support cores are disclosed in DE 37 15 915 and EP 0 379 056. The latter publication also discloses a sleeve composed of two layers, with the outer layer having a residual deformation smaller than that of the radially innermost sleeve after the installation of the sleeve. The layers can be manufactured by co-extrusion.
Known shrinkable sleeves for the use in the medium voltage range normally have a three-layer structure for electrophysical reasons. The inner layer is provided with field controlling properties. This layer can extend throuhout the length of the sleeve as proposed by EP 0 079 118 or, alternatively, consists of three spaced portions, namely a central electrode and two electrodes at the ends as known from DE 39 43 296. The electrodes provide for a uniform distribution of the electrical field in the connection area of the cable conductors and at the ends in the transition area to the cable insulation as well. A second layer, which normally has a larger thickness, serves for insulation purposes, and so it is manufactured from suitable insulation material. An outer layer of semi-conductive material serves for the necessary shielding effect.
Sleeves having cylindrical layers can be molded by extrusion or injection molding. In the latter method, the layers are molded by successive injection molding and adhered to each other thereby. Co-extrusion of the sleeve according to the DE 39 43 296 is not possible Rather, the electrodes have to be manufactured by injection molding.
From U.S. Pat. No. 4,390,745, a cylindrical sleeve has become known composed of two separate sleeve portions of heat-shrinkable material. The first or inner sleeve portion has an insulating layer, a dielectric portion at least at one extremity of the sleeve, and a conductive portion spaced from the dielectric portion provided at the inner side of the insulating layer. The second or outer sleeve portion includes an insulating layer and a semi-conductive layer provided at the outer side thereof. The dielectric layer at the inner side and the conductive portion are provided to effect a refractive field control, i.e., to make the field distribution relatively uniform in order to build up electrophysical conditions similar to that of the cable.
The semi-conductive inner layer or the electrodes of the sleeve according to DE 39 43 296 consist of a suitable field controlling material which according to U.S. Pat. No. 34 12 029 may include a permanent flexible dielectric basic material into which a finely divided effective substance is mixed which may consist of dustfine particles of an electrically polarizable material of low electrical conductivity. For example, carbon black may he used as effective substance. Further, an additional effective substance is used which is metallic conductive. As to this, microspheres having a diameter of at least 2 .mu.m are proposed. The microspheres are at least surface-conductive and may for example consist of aluminum. With such a field controlling material, a relative dielectric constant .epsilon..sub.r of 30 to 300 is achieved. Such a field controlling material, therefore, is particularly suited for sleeves which are used with high voltage cables.
U.S. Pat. No. 4,547,312 discloses an elastomeric electrically conductive mass which is composed of an elastomer and m
REFERENCES:
patent: 3585274 (1971-06-01), Tomaszewski et al.
patent: 3670091 (1972-06-01), Frantz et al.
patent: 3816639 (1974-06-01), Anderson et al.
patent: 4304616 (1981-12-01), Richardson
patent: 4412029 (1983-10-01), Kehr et al.
patent: 4579882 (1986-04-01), Kambe et al.
Chamberlain Craig
Hellbusch Dieter
Knorr Winfried H.
Krabs Raymond A.W.
Muenchow Burkhard
Kincaid Kristine L.
McNutt Matthew B.
Minnesota Mining and Manufacturing Company
Nguyen Chau N.
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