What is the shielded cable?

Shielded cable is a cable with the ability to resist external electromagnetic interference formed by adding a shielding layer to the transmission cable. The structural shielding of the cable is also a common measure to improve the electric field distribution. The conductor of the cable is generally formed by twisting multiple wires. Due to the gap with the insulating layer, the electric field will be concentrated. If a shielding layer made of semiconductor material is added to the surface of the conductor, it will become equipotential with the conductor and have good contact with the insulating layer, thereby effectively avoiding the discharge between the conductor and the insulator. The semiconductor material is called the inner shield.

On the surface of the insulating layer, because it is not only intact, but also has gaps, when the cable is bent, it will cause the surface to crack and discharge. A shielding layer of semi-conductive material is added to the surface of the insulating layer, which is in good contact with the shielded insulating layer, and is equipotential with the metal sheath to avoid partial discharge between the insulating layer and the sheath.

Understand the cable shielding layer, what is a shielded cable? The shielding layer of this type of cable is generally made of metal wires woven into a net and a metal film, and can be divided into single shielding or multi-shielding. Single shielding refers to a single shielding net or shielding film, in which one or more wires can be wound, multi-shielding refers to multiple shielding nets, the shielding films are all in one cable, and some are designed as double-layer shielding to prevent electromagnetic interference , And some are designed to enhance the shielding effect.

There is also a semiconductor shield. The so-called semi-conductive shielding layer is the outer surface of the conductive core and the outer surface of the insulating layer, which are called the inner semi-conductive shielding layer and the outer semi-conductive shielding layer, respectively. The semiconductor shielding layer is made of a low-resistivity, thin-thickness semiconductor material. The inner semi-conductive shielding layer is designed to equalize the electric field on the outer surface of the core, and avoid the air gap caused by the uneven surface of the conductor and the distortion of the core from causing partial discharge of the conductor and insulation. The outer semi-conductive shielding layer is in good contact with the outer surface of the insulating layer, and has the same potential as the metal sheath, avoiding partial discharges with the metal sheath due to defects such as cracks on the cable insulation surface.

For medium and low voltage power cables without metal sheath, in addition to the semi-conductive shielding layer, a metal shielding layer should also be added. The metal shielding layer is usually made of copper tape or copper wire, and mainly plays the role of shielding the electric field. Because the current passing through the power cable is relatively large, a magnetic field is generated around the current. In order not to affect other components, the electromagnetic field in the cable can be shielded by adding a shielding layer. And the cable shielding layer can play a certain role in grounding protection. If the cable core is damaged, the leakage current can flow into the grounding grid along the shielding layer, which plays a role of safety protection. It can be seen that the role of the cable shielding layer is still great.