Thirty cable common problem knowledge popularization（2）
6. What regulations should be followed when selecting the cross-section of power cables?
Answer: The selection of power cables should follow the following principles:
(1) The rated voltage of the cable must be greater than or equal to the rated voltage of the power supply system at the installation point;
(2) The continuous allowable current of the cable should be equal to or greater than the maximum continuous current of the power supply load;
(3) The wire core cross-section must meet the stability requirements of the power supply system during short circuit;
(4) Check whether the voltage drop meets the requirements based on the cable length;
(5) The minimum short-circuit current at the end of the line should enable the protective device to operate reliably.
7. What are the advantages of cross-linked polyethylene cables and oil-paper cables?
Answer: (1) Easy to install because it allows a small minimum bending radius and is lightweight;
(2) Not affected by line differences;
(3) Good thermal performance, allowing high operating temperature and large transmission capacity;
(4) The cable accessories are simple and all are dry structures;
(5) Operation and maintenance are simple and there is no oil leakage problem;
(6) The price is lower;
(7) High reliability and low failure rate;
(8) Few manufacturing steps, simple process, and significant economic benefits.
8. What are the requirements for clamps for fixing AC single-core cables? Why?
Answer: The clamp should have no iron parts to form a closed magnetic circuit. This is because when the cable core passes current, magnetic lines of force are generated around it. The magnetic lines of force are proportional to the current passing through the core. If magnetically conductive materials such as iron parts are used, according to It can be seen from electromagnetic induction that eddy currents will be generated in the iron parts to cause the cable to heat up and even burn the cable. Therefore, iron parts cannot be used as fixed fixtures for single-core AC cables.
9. What are the biggest features and advantages of heat shrinkable cable head accessories?
Answer: The biggest feature of heat shrink accessories is that they use stress tubes instead of traditional stress cones. It not only simplifies the construction process, but also reduces the size of the joint terminals. It is easy to install, saves time and labor, has superior performance, and saves metal. Heat-shrinkable cable accessories are both potted and dry-packed, combining the advantages of both types of accessories.
10. What inspections should be carried out before laying cables?
Answer: (1) The brackets should be complete and the paint should be complete.
(2) The cable model, voltage, and specifications comply with the design.
(3) The cable insulation is good. When there is doubt about the sealing of oil-paper cables, moisture judgment should be made; directly buried cables and small bottom cables should pass the DC withstand voltage test; oil samples of oil-filled cables should pass the test.
(4) The oil pressure of oil-filled cables should not be lower than 1.47MPa.