The Basic Structure of Power Cables
The conductor is extruded and covered with an insulating layer, such as an overhead insulated cable, or several-core stranded (corresponding to the phase, neutral and ground wires of the power system), such as an overhead insulated cable with more than two cores, or an additional sheath, such as plastic/ Rubber sheathed wire and cable. The main process technologies include drawing, stranding, insulation extrusion (wrapping), cable formation, armoring and sheath extrusion, etc. The different process combinations of various products have certain differences.
What is the use of power cable?
Power cables are cables used to transmit and distribute electrical energy. Power cables are often used in urban underground power grids, power station outgoing lines, internal power supply in industrial and mining enterprises, and underwater transmission lines across the river.
The basic structure of a power cable is composed of four parts: core (conductor), insulating layer, shielding layer and protective layer.
The core is the conductive part of the power cable, used to transmit electrical energy, and is the main part of the power cable.
2,. Insulation Layer
Insulation layer is to electrically isolate the core from the earth and the cores of different phases from each other to ensure the transmission of electric energy. It is an indispensable part of the power cable structure.
3. Shielding Layer
15kV above power cables generally have conductor shielding layer and insulation shielding layer.
The role of the protective layer is to protect the power cable from the intrusion of external impurities and moisture, and to prevent the power cable from being directly damaged by external forces.
Part A : Conductor
A conductor is a path for supplying load current. Its main technical indicators and requirements:
- Conductor cross-section and DC resistance: As current passes through the conductor, heat will be generated due to the resistance of the conductor. Therefore, the appropriate conductor cross-section should be selected according to the amount of current delivered, and the DC resistance should meet the specified value to meet the heat of the cable during operation. Stability requirements.
- 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 are local burrs, the electric field strength 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 as possible without burrs, so as to improve the electric field distribution on the conductor surface.
Part B: Metal Shield
The role of metal shielding:
- The low-voltage electrode that forms the working electric field will also form a strong electric field when there are local burrs. Therefore, we must also try to make the surface of the conductor as smooth and round as possible without burrs.
- Provide a path for capacitance current and fault current, so there are certain cross-sectional requirements.
Part C: 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 increase the electric strength of the insulating surface.
- Instead of the conductor, a smooth and round surface is formed, which greatly improves the surface electric field distribution.
- At the same time, it can be in close contact with the insulation, which overcomes the weakness of the insulation and metal that cannot be in close contact with the air gap, and shields the air gap from the working field. This technique is also commonly used in accessory production.
Part D: Insulation
Insulation is the key structure to reliably isolate the high-voltage electrode from the ground electrode.
- 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 completes the power transmission task.
- It can withstand the thermal action of the heating conductor and maintain the proper electrical 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 performances of insulation.
Part E :Protective Layer
The sheath is an important guarantee for the protection of the insulation and the normal and reliable operation of the entire cable.
The corresponding protective layer structure is designed for various environmental conditions. Mainly mechanical protection (vertical and radial external forces), waterproof, fireproof, anti-corrosion, anti-biological, etc. Various combinations can be made as required.