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We are surrounded by electrical cables. We have become so used to it that we hardly notice them. However, if we didn’t have them, daily tasks such as switching on a light in a room, using a lift, or turning on a computer wouldn’t be possible.
The cables come in different types and sizes, which makes it possible to supply electricity to a lamp, or make a wind-turbine work. The technology needed to ensure an electrical cable stays in good working condition for several years without problems involves complicated manufacturing processes which require highly qualified staff.
Cable coatings provide an electrical cable with electrical or mechanical protection. The most important ones are insulation, semiconductor, metal screen, filling, seating, armour and outer sheath.
Types of Cable coating
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Different insulation materials may be used depending on the characteristics of the cable required. The quality of an insulation material depends on two basic characteristics: its insulation capacity and its heat resistance. The material’s insulation capacity and its thickness determine the cable’s maximum service voltage.
Insulation material with a high heat resistance allows the conductor to transmit more power than the same cross-section with insulation with lower heat resistance.
In the insulation, an insulating coating is placed on the conductor to prevent current leakage. Environmental and climatic conditions or contact with aggressive agents, as well as lack of care in the installation, handling and maintenance, are the main causes that limit the life of a cable.
Insulations are classified into two large groups: thermoplastics and thermosetting.
The most common thermoplastic insulations in the manufacture of electrical cables are PVC (Polyvinyl chloride), Z1 (Polyolefins), PE (Linear polyethene), Polyurethane (PU), Teftel, Teflon (fluorinated), etc.
The most common thermosetting insulations are EPR (Ethylene Propylene), XLPE (Crosslinked Polyethylene), EVA (Ethyl Vinyl Acetate), SI (Silicone), PCP (Neoprene), SBR (Natural Rubber), etc.
PVC and Polyethylene are used as insulation and as a protective cover for electrical cables, due to their high resistance to impact and abrasion.
Semiconductors are formed through extruded layers of reduced electrical resistance from materials similar to insulation. If these are thermally stable, the semiconductor layers will also be thermally stable.
They are mainly applicable to medium and high voltage cables in two layers: the first one, directly on the conductor. The second, between the insulation and the screen.
At Top Cable, the production process of the semiconductor layers and the insulation is carried out by the “triple extrusion” process, which is the most advanced technology at present. The extrusion is carried out by means of a triple-layer head. This brings the semiconductors and the insulation into direct contact and guarantees the absence of foreign elements. In this way, defects in the internal semiconductor are avoided, which could degenerate into partial discharges and reduction of the cable’s life span.
The electrical protection, also called “screen”, isolate the signals circulating in the cable from possible external interference. They also shield the power cables to prevent them from interfering with adjacent signal circuits.
The filler is the mass of material whose function is to occupy the empty spaces left in the wiring of the insulated conductors. These fillers can be textile or plastic material.
Cables designed with metal reinforcements have an extruded layer which, when placed over the filling, protects the insulation from possible interactions with the metal masses.
The mechanical protection, called “armour”, protect the cable from external aggressions, such as blows, rodent attack, traction. The armour is made of steel or aluminium and can be can come in the form of metal strips, wires or braids.
COVER (OUTER SHEATH)
Cables are usually provided with an outer polymer coating for protection. This is called the “outer sheath”.
This outer sheath isolates the inside of the cable from external elements that could alter its electrical properties, such as moisture. It also protects them from mechanical aggression, which may occur during the cable installation.
As with the insulation, the outer-sheath can be made from a thermoplastic or a thermosetting plastic. The sheath may be made from different materials depending on the required protection level, the final flexibility of the cable, the work environment, etc.
To correctly identify the cable, it is marked with the most relevant data: manufacturer, commercial and cable name, number of conductors, section, CPR construction standard, CE marking and other data of interest, such as product certification and meter-by-meter marking, which facilitates stock control.
In order to guarantee the high quality required by Top Cable’s customers, the cables undergo extensive quality control checks in our laboratories, therefore ensuring that all the cables are free from defects and are ready to be sold.