Electrical cable, in particular for medium- or high-voltage power transmission or distribution, having a metal shield and a semiconductive water-blocking expanded layer. This layer exerts three main functions, the first one is to elastically and uniformly absorb radial forces of expansion and contraction of the cable coating layers due to thermal cycles of the cable during use, thus preventing deformations or breakages in the metal shield, the second one is to ensure electrical continuity between the cable core and the metal shield, the third one is to effectively avoid penetration and propagation of moisture and/or water along the cable core due, e.g., to possible ruptures in the metal shield. The third function is obtained by including in the expanded layer a water-swellable material.

Electrical cable having a semiconductive water-blocking expanded layer

A cable and termination for high voltage and high frequency current carrying applications includes an inner conductor having a sheath of braided metallic wire and a cylindrical core of flexible material extending within the sheath and supporting the sheath to prevent reduction in diameter of the sheath in response to tensile forces applied to the cable. The core includes one or more wire filaments connected to bear a portion of tensile forces applied to the cable. The inner conductor is encased in an outer insulation assembly which includes a conducting layer, spaced from the sheath and connected for ground return. The cable includes a termination assembly having a socket, connected to the sheath and wire filaments, for receiving an inner conductor of a complementary termination assembly. The socket includes a shank portion for receiving the pin of a complimentary termination assembly and which is fitted within the outer insulation assembly, and a bell portion which abuts the outer insulation assembly and is attached to the metallic wire sheath.

Cable and termination for high voltage and high frequency applications

A rubber or plastic insulated power cable having water impervious layers on the center conductor and cable insulation core. The layers completely prevent water infiltration into the insulation for a long time period and eliminate dielectric deterioration of the insulation by water trees.

Water impervious rubber or plastic insulated power cable

A high voltage electrical power cable with a longitudinally folded, smooth or corrugated, metal strip around a plurality of layers around the conductor and a water swellable material at least at the adjacent edges of the strip. Preferably, the water swellable material is included with a polymeric material which is flowable at a temperature at least as low as 100° C., the polymeric material has a 100 gram needle penetration value in the range from 50-100 tenths of a millimeter at 25° C. and the water swellable material has a particle size not greater than 200 microns.

Power cable with metallic shielding tape and water swellable powder

The water tree is one of the key factors leading to the insulation property deterioration in cross-linked polyethylene (XLPE) cables. An accelerated ageing experiment has been performed to produce water trees with the purpose of ageing the full-size XLPE cable under the high-frequency electric field. Based on Polarization and Depolarization Current (PDC) method, the diagnostic tests are employed to evaluate the ageing extent of the cable subjected to water tree at different ageing time. Results show that the average length of water trees is proportional to the ageing time, and thus the experiment is effective to accelerate the growth of water trees. Furthermore, such various diagnostic indicators as the I∗t∼lnt curves, the loss factor at different frequency, have their rules to assess the ageing condition of the cable with the duration of ageing time. Therefore, information obtained from PDC current can be used for determining the ageing extent of the cables.

Condition assessment of XLPE insulated cables based on polarization/depolarization current method

This cable for high-voltage, alternating current power transmission cables not only reduces the access of moisture into the cable but reduces access of moisture to the inner face of the insulation to such an extent as to make the cable highly resistant to the formation of electrochemical trees in the solid extruded insulation of the cable. A compressible layer of closed cell, foamed plastic is extruded over the outside surface of the insulation; and a metallic shield fits tightly around the compressible layer, the metallic shield being a longitudinally folded tape with a lap seam which is preferably bonded to prevent ingress of air or other fluid into the cable. If the conductor is stranded, sealant is used to prevent ingress of moisture, or of air, and the humidity it contains into the cable at cable ends.

Solid dielectric cable resistant to electrochemical trees

A joint structure for covering a joint between cables is provided in which an insulation structure extends over and beyond cut back ends of insulation layers of the cables, but terminates at a distance ahead of cut back ends of insulation shield layers of the cables. The insulation structure of the joint structure includes a multi-layered, heat shrinkable tube with its ends beveled or "feathered". In assembling the joint, the tube is positioned to overlie the cable conductors and the insulation layers of the cables and is shrunk thereover so as to terminate at a distance from the cut back ends of the insulation shield layers of the cables. The heat shrinkable tube can be manufactured with feathered edges, so that no additional time or labor is required to shape the sleeve when the joint is assembled. The joint structure also includes a semiconductive conductor shield member applied in successive convoluted layers over the exposed conductors of the joint prior to application of the heat shrunk tube. The conductor shield member is an elongated strip formed with a narrowed forward portion and a somewhat wider rear portion, which is feathered along either longitudinal edge and overlaps the cable insulation layers. The conductor shield member is constructed to be pre-curled so as to speed assembly of the joint. A termination of a single conductor is also disclosed.

Electrical cable joint and electrical cable termination and methods of making same

This invention relates to stress control cones for terminations of high-voltage power transmission cables. Such cones are used beyond the end of the cable insulation shielding, and for the purpose of providing thicker insulation for reducing the stress at and beyond the unshielded insulation on a high-voltage power cable. This invention builds up greater thickness of insulation beyond the end of the cable insulation shield, preferably by wrapping the cable with layers of insulating tapes that are then heated and fused to one another and to the outside surface of the cable insulation. The hot build-up of additional insulation is fused, or brought to incipient fusion, to merge the build-up to the cable insulation and the build-up layers to one another, instead of using preformed stress relief cones which are unsuitable for very high voltage. The build-up material is shaped to the most effective contour by the application of force from hydraulically-operated molding shapes made of metal and forced against the build-up by hydraulic motors attached to portable shaping apparatus.

Apparatus for molding stress control cones insitu on the terminations of insulated high voltage power cables

Long lengths of a heat-shrinkable sleeve for use in splicing electrical cables and the like are manufactured by providing an elongated impermeable core having a smooth outer surface, extruding an elongated sleeve around and in contact with the core, the sleeve having a smooth inner surface conforming to the outer surface of the core, and effecting an initial expansion of a portion of the sleeve to a larger diameter in an expansion zone so that the sleeve separates from the core and leaves a space between the sleeve and core. A fluid is introduced into the space under pressure via a fitting at the downstream end of the sleeve while continuously advancing the sleeve and core through the expansion zone. To begin the process, a permeable core is used, and the sleeve is extruded around and in contact with the permeable core. A fluid is introduced under pressure from a fitting upstream or downstream of the expansion zone through the permeable core to the inside of the sleeve in the expansion zone, and the leading end of the impermeable core is welded to amd trailing end of the permeable core at a location upstream of the expansion zone. The sleeve has a composite structure comprising an inner compound and an outer compound, the inner and outer compounds having different characteristics. In a first crosshead, the inner compound an a thin layer of outer compound are applied, and the balance of the outer compound is applied around the sleeve in a second crosshead. Between the two crossheads, liquid nitrogen cools and stabilizes the inchoate sleeve.

Apparatus and method for manufacturing heat-shrinkable sleeve using solid core

For extra high voltage power cables this invention provides insulation consisting of synthetic plastic material with paper bonded to both sides to form a laminated strip. In place of the porous paper previously used, this invention uses very thin paper such as ''''capacitor tissue''''; space for the thermal expansion of the synthetic and passages for the removal of moisture and the introduction of oil are obtained by embossing the strip. To prevent locking of overlying strips when bending the cable, the embossing is preferably embossed with a random pattern, or plain unembossed strips are wrapped alternately between embossed strips. The invention includes the novel strip, cable made with the strip and the method of making the strip.

Carlos Katz

Papers

Solid dielectric cable resistant to electrochemical trees

Electrical cable joint and electrical cable termination and methods of making same

Apparatus for molding stress control cones insitu on the terminations of insulated high voltage power cables

Apparatus and method for manufacturing heat-shrinkable sleeve using solid core

Extra high voltage cables