General knowledge about wire and cable construction(2)


1. In the installation of single-core wires, why is it […]

1. In the installation of single-core wires, why is it necessary to install a return line parallel to the cable after one end of the single-core cable sheath is grounded?
In a power line with one end of the metal sheath of the cable grounded, in order to ensure that the voltage induced in the sheath is not higher than the allowed voltage, a conductor laid in parallel along the cable line must be installed, and both ends of the conductor Ground. This type of conductor is called a return wire. If there is a single-phase grounding problem, the short-circuit current when it is grounded can flow back into the power system through the return line. The magnetic flux generated by the grounding current through the return line cancels out some of the cable conductor ground current Magnetic flux, thereby reducing the induced voltage of the sheath in the event of a short circuit fault.
2. Which aspects should be considered when selecting the cross section of a power cable?
(1) Working current allowed for long-term cable operation under normal environment;
(2) the stability of the cable if short-circuit conditions are encountered;
(3) The voltage drop on the line cannot exceed the allowable working range.
3.What are the advantages of power cables and overhead lines?
(1) The operation is stable, because the power cable is buried in the ground or other hidden places, and is generally not damaged by external forces. The probability of cable problems is relatively small, the power supply is safe, and it will not cause harm to people;
(2) The maintenance workload is small, and frequent inspections are not required;
(3) No need to erect poles;
(4) It helps to improve the power factor.