The role of the shield of the power cable

2021-05-02

1, because the Power Cable through the current is relatively large, the current around the magnetic field will be generated, in order not to affect Other components, so add shielding layer can shield this electromagnetic field in the cable.

2, can play a certain degree of grounding protection, if there is damage inside the cable core, leakage of current can be along the shielding of laminar flow such as grounding network, play a role in security protection.

Wire and cable classification application and basic structure 1. Classification Wire products used to transfer electrical (magnetic) energy, information and realize electromagnetic energy conversion are collectively referred to as wire and cable. According to different uses, wire and cable can be divided into five categories:

Bare wires: Products that have conductors but no insulating layer, such as ACSR, Al-strand, and Cu-strand. Products are mainly used in suburbs, rural areas, user main lines, switchgear, etc.

Winding wire (magnet wire): In the form of windings in the magnetic field cutting magnetic line induced current, or through the current generated by the magnetic field of the wire, mainly for a variety of motors, instruments and meters. Such as enameled wire.

Power cable: A cable product that is used to transmit and distribute high-power electrical energy in the backbone of a power system, such as cross-linked polyethylene insulated power cables. The products are mainly used in the transmission of electricity, electricity, electricity, electricity, electricity, and electricity in high-voltage transmission lines, with large currents (tens of amps to several thousand amps) and high voltages (220 V to 500 kV and above).

Communication cables and optical cables: cables, optical cables, etc. that transmit telephone, telegraph, television, radio, fax, data, and other telecommunication information. Wire and cable for electrical equipment: Wires and cables used to transmit power directly from the power distribution point of the power system to the power supply connection lines of various electrical equipment and appliances. Such as control cables, cloth wires, etc.

2. Application of Wire and Cable Power System: The wire and cable products used in the power system mainly include bare overhead wires, busbars (bus bars), power cables (plastic cables, oil-paper cables (substituted by plastic power cables), and rubber bushings. Cables, overhead insulated cables), branch cables, electromagnetic wires, and electrical equipment.

Information transmission system: Wire and cable used for information transmission system mainly includes local Telephone Cable, television cable, electronic cable, radio frequency cable, Optical Cable, Data Cable, magnet wire, power communication or other composite cables.

Mechanical equipment, instrumentation systems: Except for overhead bare wires, almost all other products have applications, but mainly power cables, electromagnetic wires, data cables, instrumentation cables, etc.

3, the basic structure of the wire and cable Conductor: the object of conduction current, wire and cable specifications are represented by the cross section of the conductor.

Insulation: The insulation material is coated with a different thickness on the outside of the conductor according to the requirements of its withstand voltage level.

Protective layer: The part that protects the cable.

Why should cables be armored and twisted? Armored cable means a cable with a metal armored protective layer. The purpose of the cable plus the armored layer is not only to enhance the mechanical protection such as tensile strength and compressive strength, but also to extend the service life. Shield protection improves cable interference performance.

The commonly used armouring materials include steel belts, steel wires, aluminum belts, and aluminum tubes. Among them, steel belts and wire armored layers have a high magnetic permeability and have a good magnetic shielding effect. They can be used for anti-low frequency interference and enable The cable is laid directly buried to avoid wearing the tube and it is cheap and practical.

Different sizes of copper wires are twisted together according to a certain arrangement order and twisting distance, and they become larger diameter conductors. Such twisted large-diameter stranded conductors are larger than the same diameter. The copper wire is more flexible, and the wire bending performance is good. It is not easy to break when the swing test is performed. It is easier to meet the requirements for some soft wire materials (such as medical grade wires).

According to the electrical performance, after the conductor is energized, the resistor will generate heat due to power consumption. As the temperature rises, the performance life of the insulating layer and the protective layer material will be affected. In order to make the cable run efficiently, the conductor cross section should be increased, but the large cross-section single conductor Inconvenient to bend, poor flexibility, it is not conducive to the production of transport and installation laying. From the mechanical properties and requirements of flexibility, reliability, multiple single twisted twisted together, you can solve the problem.

Video surveillance line organization structure: PVC PVC sheath, copper wire braided shield, solid polyethylene insulation, copper core conductor braided mesh is made of fine copper wire braided, confining electrical signals in a closed space. At the same time, it is possible to prevent the ingress of external signals and enhance the cable strength. The braided net can be divided into 64 series, 96 series and 128 series according to the different specifications of the monitoring line. The more the number, the stronger the transmission performance and the shielding performance. Copper clad aluminum, copper, and oxygen-free copper are common. However, in the purchase of surveillance video cable, can not blindly choose the high-definition surveillance video cable, in general, the distance is closer, do not use so high selection of lines, generally 75-396 series can generally transmit 150 meters Above, so small projects: small offices, convenience stores and other places use the 75-3 video line on the line, generally used to 128 braided nets are the transmission distance, interference strong project.

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