China Zhenglan Cable Technology Co., Ltd Company News

Dear Customer Thanks for visiting our website. Due to China's National Day Holiday is coming, we will be on holiday from 1st(Tuesday) to 7th(Monday). Work resume from 8th(Tuesday). During holiday, we will have limited access to email and may reply you late. Kindly ask for your understanding. Zhenglan Cable Technology Co., Ltd September 30th, 2024

Dear Customers   Here comes Chinese traditional Mid Autumn Day festival. Kindly note we will be on a 3-day Mid-Autumn Day holiday from September 15th(Sunday) to September 17th(Tuesday). Work resume from Wednesday.    During holiday, work will stop temporarily. For all the messages you left, we wonnot be cable to reply untill after holiday. Thanks for your kind understanding. Once come back, we will contact you at our first time.   Hope everyone will have a good time.    Zhenglan Cable Technology Co., Ltd  

Shielded cable has the word "shielded" in it. As the name implies, it is a cable with the ability to resist external electromagnetic interference formed by adding a shielding layer to the transmission cable. The so-called "shielding" in the cable structure is also a measure to improve the distribution of the electric field. The cable conductor is made of multiple strands of wires twisted together. It is easy to form an air gap between it and the insulation layer. The surface of the conductor is not smooth, which will cause electric field concentration. 1. Cable shielding layer 1). Add a shielding layer of semi-conductive material on the surface of the conductor. It has the same potential as the shielded conductor and has good contact with the insulation layer, thereby avoiding local discharge between the conductor and the insulation layer. This layer of shielding is also called the inner shielding layer. There may also be gaps at the contact between the insulation surface and the sheath. When the cable is bent, the insulation surface of the oil-paper cable is prone to cracks. These are factors that cause local discharge. 2). Add a shielding layer of semi-conductive material on the surface of the insulation layer. It has good contact with the shielded insulation layer and has the same potential as the metal sheath, thereby avoiding local discharge between the insulation layer and the sheath. To make the conductive core and the insulating electric field uniform, medium and high voltage power cables of 6kV and above generally have conductor shielding layers and insulating shielding layers, and some low voltage cables do not have shielding layers. There are two types of shielding layers: semi-conductive shielding and metal shielding. 2. Shielded cable The shielding layer of this type of cable is mostly made of metal wires woven into a mesh or metal film, and there are many different ways of single shielding and multi-shielding. Single shielding refers to a single shielding net or shielding film, which can wrap one or more wires. Multi-shielding means multiple shielding nets and shielding films are in one cable. Some are used to isolate electromagnetic interference between wires, and some are double-layer shielding to enhance the shielding effect. The mechanism of shielding is to ground the shielding layer to isolate the induced interference voltage of the external connection to the wire. 1). Semi-conductive shielding The semi-conductive shielding layer is usually set on the outer surface of the conductive core and the outer surface of the insulating layer, respectively called the inner semi-conductive shielding layer and the outer semi-conductive shielding layer. The semi-conductive shielding layer is composed of a semi-conductive material with very low resistivity and thin thickness. The inner semi-conductive shielding layer is to even out the electric field on the outer surface of the core, and avoid partial discharge between the conductor and the insulation due to the uneven surface of the conductor and the air gap caused by the twisting of the core. The outer semi-conductive shielding layer is in good contact with the outer surface of the insulation layer, and is at the same potential as the metal sheath, avoiding partial discharge with the metal sheath due to defects such as cracks on the cable insulation surface. 2). Metal shielding For medium and low voltage power cables without metal sheaths, in addition to the semi-conductive shielding layer, a metal shielding layer must be added. The metal shielding layer is usually wrapped with 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 will be generated around the current. In order not to affect other components, the shielding layer can be added to shield this electromagnetic field in the cable. Moreover, the cable shielding layer can play a certain role in grounding protection. If the cable core is damaged, the leaked current can flow along the shielding layer like the grounding grid, playing a role in safety protection. It can be seen that the role of the cable shielding layer is still very large.

The selection of power cables should follow the following principles: 1. Rated voltage: Select appropriate wires and cables according to the voltage level of the place of use, and ensure that the rated voltage of the cable is not lower than the actual use voltage. 2. Current capacity: Select appropriate wire and cable cross-section according to the load current to ensure that the cable will not overheat under the maximum load, and the voltage drop is within an acceptable range. 3. Safety requirements: According to safety requirements, non-flammable cables, flame-retardant cables, halogen-free flame-retardant cables, fire-resistant cables, etc. can be selected. 4. Mechanical strength: When it is necessary to withstand mechanical tension, pressure and large-span creep resistance, reinforced cables such as copper wire or steel belt armored structural cables can be selected. 5. Economy: Under high load conditions, select according to economic current density, considering that power loss and capital investment should be within the most reasonable range. 6. Laying conditions: Select the model and specification of the cable according to the cable laying environment and laying method to ensure that the cable can adapt to specific laying conditions. 7. Environmental factors: Calculate the resistance and voltage drop of the cable considering the cable laying length and laying method, and select the flame retardant grade of the cable according to the safety requirements of the power system. 8. Comprehensive considerations: When selecting power cables, it is also necessary to comprehensively consider various factors such as purpose, voltage, environment, etc., and more accurately select the appropriate cable for a specific application through example calculations. Through the above principles, it can be ensured that the selection of power cables not only meets the actual use needs, but also has safety and economy.

In the production of wires and cables, the phenomenon of low insulation resistance is often encountered. There are many factors that affect the insulation resistance value of cables. In fact, there are four main factors that have a great influence on the insulation resistance coefficient. 1. The influence of temperature As the temperature increases, the insulation resistance coefficient decreases. This is due to the increase in thermal motion, the increase in ion generation and migration. Under the action of voltage, the conduction current formed by ion movement increases, and the insulation resistance decreases. Theory and practice show that the insulation resistance coefficient decreases exponentially with the increase in temperature, and the conductivity increases exponentially with the increase in temperature. 2. The influence of electric field strength When the electric field strength is in a relatively low range, the mobility of ions increases in a proportional relationship with the increase in electric field strength. Ionic current and electric field strength follow Ohm's law. When the electric field strength is relatively high, as the electric field strength increases, the mobility of ions gradually changes from a linear relationship to an exponential relationship. When the electric field strength is close to breakdown, a large amount of electron migration occurs, thereby greatly reducing the insulation resistance coefficient. The withstand voltage test voltage of various wire and cable products specified in the standard is in the stage where the ion mobility increases proportionally with the electric field strength, so the influence of the electric field strength on the insulation resistance coefficient cannot be reflected. When the sample is subjected to a breakdown test, the influence of the electric field on the insulation resistance coefficient is clearly reflected. 3. The influence of humidity Due to the high conductivity of water, the size of water molecules is much smaller than that of polymer molecules. Under the action of heat, the polymer macromolecules and the constituent chain segments move relatively, so that water molecules can easily penetrate into the polymer, increase the conductive ions in the polymer, and reduce the insulation resistance. The standard specifies immersion tests for various wires and cables. For example, before measuring the insulation resistance, the rubber specimen is immersed in water for 24 hours. The purpose is to meet the influence of moisture and water on electrical properties during use. Insulation resistance is one of the main electrical properties of insulating materials and an important indicator of wire and cable products or materials. Generally, the insulation resistance is required to be not less than a certain value. If the insulation resistance value is too low, the leakage current along the wire and cable line will inevitably increase, resulting in a waste of electrical energy. At the same time, the electrical energy will be converted into thermal energy, preparing for thermal breakdown and increasing the possibility of thermal breakdown. 4. Influence of material purity Impurities are mixed into the material, increasing the conductive particles in the material and reducing the insulation resistance. Therefore, the insulation resistance of a certain rubber and plastic material will reflect the purity of the material and verify whether it meets the standard. During the production of wires and cables, the process does not strictly follow the operating procedures, mixed impurities and materials bubble due to moisture, insulation core deviation or outer diameter size is smaller than the standard, insulation delamination or cracks, insulation scratches, etc. , will reduce the insulation resistance of the product. Therefore, in order to check the insulation resistance, it is necessary to check whether there are any problems in the process operation. During the use of wires and cables, measuring the changes in insulation resistance can also check the insulation damage and prevent accidents.

There are many types of wire and cable products, and their application range is very wide. If they are not stored properly, it will affect the life and safety of the cables, and even cause unnecessary disasters. Therefore, how to store them is an issue that needs attention. 1. When storing wires and cables, avoid water sources, and do not contact acids, alkalis and mineral oils. The outer skin of the wires is mostly plastic. Contact with corrosive liquids will cause the outer skin of the wires to swell, accelerate the damage of the outer skin and cause leakage, which is very dangerous. 2. Wires and cables cannot be exposed to the sun or in an ultra-high temperature environment for a long time, otherwise it will cause cracks or peeling on the outer sheath of the cable. 3. In the environment where wires and cables are stored, it is strictly forbidden to have gases that are harmful to cables, such as corrosive gases and flammable and explosive gases. 4. Wires and cables should be stored regularly, according to specifications and production time. The storage period is limited to the product's factory date, and generally should not exceed one and a half years. 5. Long-term storage of wires and cables will be affected by extrusion pressure, which may cause deformation of the sheath and cable. The cables should be rolled regularly. After rolling, the cables should be checked to see if they are intact to avoid damage that affects subsequent safe use. (Cable reels are not allowed to be laid flat) 6. The transportation of wires and cables is also the key to the storage and protection of wires. It is strictly forbidden to throw cable reels from high places during transportation, which may cause cracks in insulation and sheath, and damage the conductivity and mechanical properties of the cables.