China Zhenglan Cable Technology Co., Ltd Company News

Power cables are widely used to transmit and distribute electric energy. They are often used in urban underground power grids, outgoing lines of power stations, internal power supply of industrial and mining enterprises, and underwater transmission lines across rivers and seas. The main lines in the power system are generally power cables used to transmit and distribute high-power electric energy, including 1-500kv and above voltage levels. Therefore, the quality of cable products is very important, and the quality and thickness of cable sheath are equally important. What effect does the thickness of cable sheath have on the cable? 1. Affect the service life of power cables The first is the environment. After the construction of power cables, they are basically buried in the ground, immersed in water, in the open air or in an environment prone to corrosion, plus the corrosion of external media for a long time, the insulation level and mechanical level of the thinnest point of the cable sheath will decline. In case of line grounding fault, the thinnest point of cable sheath may be broken down, increasing the hidden danger of safety accidents. The other is the internal consumption of heat energy generated by cables. The cable will produce a lot of heat energy in the process of transmitting electric energy, which is a consumption of the sheath. If the thickness of the cable sheath is not enough, the copper core of the conductor will directly melt the sheath material after heating, which will cause circuit failures and other related safety problems. 2. Impact on Construction According to the current requirements, more and more environmental requirements require that the outer diameter of high-voltage cable products must be small, and it is necessary to consider leaving gaps in the laying process, so as to dissipate the heat generated by the cable after it is powered on. The thickness of the sheath is too thick, which will increase the difficulty of laying, so the thickness of the cable sheath must strictly comply with the relevant national standards, otherwise it cannot protect the cable conductor.

Precautions 1、 Observe the appearance of the wire. The insulation (sheath) layer of qualified products is soft, tough and flexible, and the surface layer is tight, smooth and free of roughness. If the plastic wrapping the wire is easy to peel off, there is a problem of insufficient plastic strength. 2、 It depends on the cross-section of the wire. The surface of copper core or aluminum core of qualified products should have metallic luster. Copper with black surface or aluminum with white surface indicates that it has been oxidized. 3、 Pay attention to check the quality certificate when purchasing wires. If the quality of the wire is qualified, the wire quality should also be tested, and there will be no big problem.

4. Wire and cable with unqualified conductor resistance Conductor resistance is an important indicator for evaluating the compatibility of wire and cable conductor materials and cross-sections. When the conductor resistance exceeds the standard, the loss of the current passing through the line is increased, and the heating of the wire and cable is aggravated. The main reason for the unqualified conductor resistance is that some companies shrink the copper material, which accounts for 80% of the raw material cost, in order to reduce the cost, reduce the cross-sectional area of the conductor or use recycled copper with too high impurities, which causes the conductor resistance of the wire and cable to seriously exceed the standard. , In the process of use, in addition to easily causing fire, it will also accelerate the aging of the insulating layer covering the wire.

The metal shielding methods of medium-voltage XLPE insulated power cables are mainly composed of copper tape overlap wrapping shielding and sparse copper wire shielding. According to the GB/T12706-2008 standard for cables with rated voltage from 6kV to 35kV, the average overlap ratio of copper tape in the copper tape shielding method is not less than 15% of the width of the copper tape (nominal value), and the minimum value is not less than 5%. The thickness of copper tape for single-core cables is ≥ 0. 12mm, the average thickness of multi-core cables is ≥ 0. 10mm, and the minimum thickness of copper tape is not less than 90% of the nominal value. The copper wire shield consists of loosely wound soft copper wires, the surface of which should be fastened by reversely wound copper wires or copper tapes, and the average gap between adjacent copper wires should not be greater than 4mm. The shielding on the cable structure is a measure to improve the distribution of the electric field. The role of the metal shielding mainly has the following aspects: 1. When the cable is normally energized, the metal shielding layer passes the capacitive current, and when the short-circuit fault occurs, the short-circuit current passes. 2. The electromagnetic field caused when the cable is energized is shielded in the insulated core to reduce electromagnetic interference to the outside world, and the metal shielding layer also limits the impact of the external electromagnetic field on the interior. 3. The power station protection system requires the outer metal shield to have better lightning protection properties. 4. Homogenize the electric field to prevent axial discharge. Since the semi-conductive layer has a certain resistance, when the metal shielding layer is poorly grounded, the cable will discharge along the surface due to uneven potential distribution in the cable axis.

3. Wire and cable with aging insulation layer   The unqualified tensile strength and elongation of the insulating sheath before aging directly greatly shortens the working life of the wire and cable, and the insulator is easily broken during construction or in a long-term energized and high-temperature environment, resulting in live conductors. If exposed, there is a risk of short circuit that can cause electric shock. The main reasons for its failure are: first, the use of recycled materials for production to reduce product costs; second, small enterprises that do not have production qualifications cut corners for profit.

2. Wires and cables with unqualified structural dimensions The main problem of the structure size is the thickness of the sheath and the thickness of the insulation. When the sheath and insulation thickness of the cable do not meet the standard, the electrical strength of the wire and cable will be seriously reduced, resulting in a shortened service life of the wire and cable. and cables may break, insulation may not work properly, resulting in electrical shorts and fires.