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What are the functions of the structure of the power cable and its shielding layer

Update:2020-10-10
Abstract:

1. Classification The wire products used to transmit el […]

1. Classification
The wire products used to transmit electric (magnetic) energy, information and realize the conversion of electromagnetic energy are collectively referred to as wires and cables. According to different purposes, wires and cables can be divided into five categories:
Bare wires: products with only conductors without insulation, such as steel core aluminum stranded wire, aluminum stranded wire, and copper stranded wire. Products are mainly used in suburbs, rural areas, user main lines, switch cabinets, etc.
Winding wire (magnet wire): In the form of a winding, the magnetic line of force is cut in a magnetic field to induce current, or a wire that generates a magnetic field with current. It is mainly used in various motors, instruments and meters. Such as enameled wire.
Power cables: Cable products used to transmit and distribute high-power electrical energy in the backbone of the power system, such as cross-linked polyethylene insulated power cables. The products are mainly used in the transmission of strong electric energy in the power generation, distribution, transmission, transformation, and power supply lines, with large current (tens of amperes to several thousand amperes) and high voltage (220V to 500kV and above).
Communication cables and optical cables: cables and optical cables that transmit telephone, telegraph, television, radio, fax, data and other telecommunication information.
Wires and cables for electrical equipment: Wires and cables used to directly transmit electrical energy from the power distribution point of the power system to the power connection lines of various electrical equipment and appliances. Such as control cables, wiring wires, etc.

2. Use of wires and cables
Power system: The wire and cable products used in the power system mainly include overhead bare wires, busbars (bus bars), power cables (plastic cables, oil-paper cables (which are basically replaced by plastic power cables), rubber sheathed cables, and overhead insulated cables) , Branch cables, electromagnetic wires, and electrical equipment for electrical equipment, wires and cables.
Information transmission system: The wires and cables used in the information transmission system mainly include local telephone cables, television cables, electronic cables, radio frequency cables, optical cables, data cables, electromagnetic wires, power communications or other composite cables.
Mechanical equipment, instrumentation system: Except for overhead bare wires, almost all other products are used, but mainly power cables, electromagnetic wires, data cables, instrumentation cables, etc.

3. The basic structure of wire and cable
Conductor: An object that conducts current. The specifications of wires and cables are expressed by the cross-section of the conductor.
Insulation: The insulating material is wrapped on the outside of the conductor in different thicknesses according to the requirements of its withstand voltage.
Maintenance layer: the part that maintains the cable.

Why do cables need to be armored and stranded armored cables refer to cables with a metal material armored maintenance layer. The purpose of the cable plus the armored layer is to enhance the tensile strength, compressive strength and other mechanical maintenance to extend the service life, but also through Shielding maintenance improves cable anti-interference performance.

Commonly used armor materials include steel tape, steel wire, aluminum tape, aluminum tube, etc., among which the steel tape and steel wire armor layer has high magnetic permeability, has a good magnetic shielding effect, can be used for anti-low frequency interference, and can make the armor The cable is directly buried and laid without the need to pass through the pipe, and it is cheap and good-quality in practical applications.

Copper wires of different specifications and different numbers are twisted together in a certain arrangement sequence and stranding length, and then they become conductors with larger diameters. The conductors of this kind of stranded large-diameter stranding are better than single strands of the same diameter The copper wire is more flexible, the wire made has better bending performance, and it is not easy to break during the swing test. It is easier to meet the requirements for some wires that require softness (for example, medical-grade wires).

In terms of electrical performance: After the conductor is energized, it will generate heat due to the electrical energy consumed by the resistance. As the temperature rises, it will affect the performance and life of the insulation layer and the maintenance layer. In order to make the cable run efficiently, the conductor cross-section should be increased, but a large cross-section single wire It is inconvenient to bend and has poor flexibility, which is not conducive to production, transportation, installation and laying. From the mechanical performance, flexibility and reliability are required. If multiple single wires are twisted together, the contradiction can be solved.

4. The role of power cable shielding
a. Because the current through the power cable is relatively large, a magnetic field will be generated around the current. In order not to affect other components, the shielding layer can shield this electromagnetic field in the cable.
b. It can play a certain role in grounding maintenance. If the cable core is damaged, the leaked current can flow along the shielding layer like a grounding grid, playing a role in safety maintenance.
The above is all aspects of power cable knowledge compiled by Xiaobian Yinglian for everyone, and I hope to master it in the process of application.

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