Components of power cables
Power cables are widely used in life. In order to help you better understand the structure of power cables, Zhengzhou Jinshui Cable Group will introduce you to the main 4 components of cables.
Power cable, a cable used to transmit and distribute electrical energy, is an insulated wire composed of one or more mutually insulated conductive cores placed in a sealed sheath. It is often used in urban underground power grids, outgoing lines of power stations, internal power supply of industrial and mining enterprises, and underwater transmission lines crossing rivers and seas. In power lines, the proportion of cables is gradually increasing. Power cable is a cable product used to transmit and distribute high-power electrical energy in the main line of the power system, including 1-500KV and above various voltage levels and various insulation power cables.
Components of power cables
1. Insulation layer: The insulating material used for the cable should have high insulation resistance, high breakdown electric field strength, low dielectric loss and low dielectric constant. Commonly used insulating materials in cables are oil-impregnated paper, polyvinyl chloride, polyethylene, cross-linked polyethylene, rubber, etc. Cables are often classified by insulating materials, such as oil-impregnated paper insulated cables, PVC cables, XLPE cables, etc.
2. Sealing sheath: protect the insulated core from mechanical, moisture, moisture, chemicals, light, etc. damage. For insulation susceptible to moisture, lead or aluminum extruded sealing sheaths are generally used.
3. Protective cover: used to protect the sealing sheath from mechanical damage. Generally, galvanized steel tape, steel wire or copper tape, copper wire, etc. are used as armor to wrap around the sheath (called armored cable), and the armor layer also plays the role of electric field shielding and preventing external electromagnetic interference.
4. Conductive core: Made of high conductivity material (copper or aluminum). According to the requirements for the flexibility of the cable under the conditions of laying and use, each core may be stranded by a single wire or multiple wires.
The basic structure of power cable line
1. Conductor: It is the path that provides the load current. Its main technical indicators and requirements:
(1) Conductor cross-section and DC resistance: As the current passes through the conductor, heat will be generated due to the resistance of the conductor. Therefore, an appropriate conductor cross-section should be selected according to the amount of conveying current, and its DC resistance should meet the specified value to meet the requirements of the cable during operation. Thermal stability requirements.
(2) Conductor structure: The conductor is also the high-voltage electrode when the cable is working, and its surface electric field strength is the largest. If there is a local burr, the electric field strength there will be greater. Therefore, one of the main technical problems to be solved in the design and production and when the user department makes the conductor connection of the joint is to try to make the conductor surface as smooth and round as possible without burrs, so as to improve the electric field distribution on the conductor surface.
2. Metal shield
The role of metal shielding:
(1) The low-voltage electrode that forms the working electric field will also have a large electric field intensity when there are local burrs. Therefore, it is also necessary to try to make the conductor surface as smooth and round as possible without burrs.
(2) Provide the path of capacitive current and fault current, so there are also certain cross-sectional requirements.
3. Semi-conductive shielding layer
Semi-conductive shielding layer is an important technical measure used in medium and high voltage cables to improve the electric field distribution on the surface of the metal electrode and at the same time improve the electrical strength of the insulating surface.
(1) First, instead of the conductor, a smooth and round surface is formed, which greatly improves the surface electric field distribution,
(2) At the same time, it can be in close contact with the insulation, overcoming the weakness of the insulation and the metal that cannot be in close contact with the air gap, and the air gap is shielded from the working field strength. This technique is also commonly used in accessory production.
Insulation is the key structure to reliably isolate the high voltage electrode from the ground electrode.
(1) It can withstand the long-term effects of working voltage and various overvoltages, so its electrical strength and long-term stability are the most important parts to ensure that the entire cable can complete the power transmission task.
(2) It can withstand the thermal action of the heating conductor and maintain the proper electric strength.
The progress of cable technology is mainly determined by the progress of insulation technology. From production to operation, most of the test and measurement items are aimed at monitoring various properties of insulation.
5. Protective layer
The sheath is an important guarantee for the protection of insulation and the normal and reliable operation of the entire cable.
Corresponding sheathing structures are designed for various environmental conditions. Mainly mechanical protection (longitudinal and radial external force), waterproof, fireproof, anti-corrosion, anti-biological and so on. Various combinations are possible as required.
The above contents are the main components of power cables. When choosing power cables, you must pay attention to choosing national standard cables, and refuse to choose cables that are fake and have potential safety hazards.