Introduction to basic knowledge of wires and cables
Introduction to basic knowledge of wires and cables:
The conductor is the path that provides the load current. The main technical indexes and requirements are as follows:
1) Conductor section and DC resistance: as the current passes through the conductor, heat will be generated due to the resistance of the conductor. Therefore, it is necessary to select the appropriate conductor section according to the delivered electric flow, and its DC resistance shall meet the specified value to meet the requirements of thermal stability during cable operation.
2) Conductor structure: the conductor is also the high-voltage electrode when the cable is working, and its surface electric field strength will be greater if there are local burr. Therefore, one of the main technical problems to be solved in the design and production as well as in the use department is to try to make the conductor surface as smooth and round as possible without burr, so as to improve the electric field distribution on the conductor surface.
Function of metal shielding:
1) The low-voltage electrode which forms the working electric field will also form the situation of strong electric field when there are local burr. Therefore, we should try to make the conductor surface as smooth and round as possible without burr.
2) It provides the path of capacitance current and fault current, so it also has certain section requirements.
Semi conductive shielding layer
Semi conductive shielding layer is an important technical measure to improve the distribution of electric field on the surface of metal electrode and improve the electrical strength of insulation surface.
1) Firstly, a smooth and round surface is formed instead of the conductor, which greatly improves the surface electric field distribution,
2) At the same time, it can make close contact with the insulation, which overcomes the weakness of the air gap caused by the close contact between the insulation and the metal, and shields the air gap outside the working field strength.
Insulation is the key structure to separate the high voltage electrode from the ground electrode reliably.
1) It bears the long-term action of working voltage and various over-voltage, so its electrical strength and long-term stability is an important part to ensure that the whole cable completes the transmission task.
2) It can withstand the thermal action of the heating conductor and keep the 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 the various properties of insulation.
The protective layer is an important guarantee to protect the insulation and the normal and reliable operation of the whole cable.
The corresponding protective layer structure is designed for various environmental conditions. It is mainly mechanical protection (vertical and radial external force), waterproof, fireproof, anti-corrosion, anti biological, etc. Various combinations can be made as needed.
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