Coated electrical cables fulfill the function of providing electrical or mechanical protection to the cable, such as insulation, semi-conducting, metallic screen, filler, seat, armor, or cover.
In this post, we tell you everything you need to know about the different coatings and insulation processes of a Medium Voltage cable
To achieve this, an insulating coating is placed on the conductor to prevent current leakage, extending the life of the cable. Isolates are classified into two large groups:
- The most common thermoplastic insulations are PVC, Z1, PE, Polyurethane, Teftel, Teflon, etc.
- The most common thermostable insulations are EPR, XLPE, EVA, SI, PCP, or SBR, among others.
– Semiconductor. Semiconductive insulation is achieved through low electrical resistance extruded layers of insulation-related materials. That is, if these are thermostable, the semiconductor layers will also be.
Its use is fundamentally applied to Medium and High Voltage cables in two layers. The first, directly on the conductor; the second, between the insulation and the screen.
– Metallic screen. The screens isolate the signals that circulate through the cable from possible external interference. In addition, they also shield power to prevent them from interfering with adjacent signal circuits.
– Filling. The filler is material that occupies the empty spaces that remain in the wiring of the insulated conductors. The padding can be a textile or plastic material.
– Seat. If the cable is designed with metallic armor, it has an extruded layer, placed on the filler that protects the insulation from possible interactions with the metallic masses.
– Armors. They are responsible for protecting the cable from external aggressions, such as blows, rodent attacks, traction, etc. They are usually made with steel, and aluminum and can be made of strips, crowns of threads, or braid of threads.
– Cover. These are cables with an outer polymer coating to protect themselves. The jacket isolates the inside of the cable from external elements that can alter its electrical properties, such as humidity, and protects it from shocks.
Medium Voltage cables have an insulation process divided into 7 stages:
1- Input power. The input coils feed the line continuously through an input accumulator.
2- Accumulation of the driver. Make input splices without stopping the line.
3- Polymer feeding + triple extrusion + thickness control. Feeding is done in a clean and closed circuit, which ensures the purity of the materials from start to finish.
The extrusion is carried out with a triple-layer head, which allows perfect contact between the semiconductors and the insulation and the total absence of foreign elements between them. Compared to the other types of extrusion, triple extrusion eliminates the possibility of moisture/dust particles entering any of the three layers.
4- Crosslinked. The cross-linking of the insulation and the semiconductors is carried out in a nitrogen atmosphere, eliminating the risk of water absorption, through nine independent temperature zones, allowing the perfect adjustment of the crosslinking progression to the characteristics of each material.
5- Cooling and 6. Cable return. The final route of the catenary tube focuses on controlled cooling of the already crosslinked cable to achieve the optimum temperature.
7- Collection and tests. Once the insulated cable is obtained, it is collected on double reels with an automatic distributor through an auxiliary pulling caterpillar, ensuring perfect spooling, turn by turn, and without excessive tension. Once collected, the cable is subjected to exhaustive tests in the laboratory. Which its subsequent operation at full capacity is verified.
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