1. Eddy current problems caused by high current power cables
During the construction of power cables, there are steel supports, steel protective pipes, and cable clamps and overhead laying. Any steel (iron) closed loop formed around the power cable may form eddy currents, especially in high current power cable systems, where the eddy currents are larger. During the construction of power cables, measures must be taken to prevent the formation of steel (iron) closed loops around the cables and prevent the occurrence of eddy currents caused by the cables.
2. Mechanical damage caused by turning of power cables
Due to the large outer diameter of power cables, it is difficult to transport and lay them, and the requirements for turning radius of power cables are also relatively strict. During the construction of power cables, if the turning angle is too large, it may cause mechanical damage to the inside of the conductor, and the mechanical damage may be reduced by the insulation strength of the cable until a fault occurs. During the construction, a cable head fault was found. During the production of the cable head, the three cable heads were of the same length, and when connected to the equipment, due to terrain constraints, the middle phase cable head was too long and became arched, causing damage and discharge at the root of the cable head. After that, measures were taken to appropriately shorten the connection length of the middle phase cable head during the connection of the equipment, so that the three-phase cable head would not be subjected to external forces. Practice has proven that the operation effect is good. It can be seen that during cable construction, it is necessary to minimize the torsion on the cable. When the cable is turned and the cable is reserved, the cable should be kept in natural bending to prevent internal mechanical damage.
3. It's a moisture proof problem for power cables
Operating experience has shown that most of the failures of medium and low voltage power cables are caused by cable intermediate joints and terminal heads, while most of the failures of intermediate joints and terminal heads are caused by poor sealing and moisture intrusion, resulting in a decrease in insulation strength. Medium and low voltage power cable networks mostly use dendritic power supply, with a large number of cable terminal heads, Therefore, properly sealing the cable terminal and intermediate joint is one of the important measures to ensure the safe and reliable operation of the cable.
4. It is the grounding problem of medium and low voltage power cables
In public medium and low voltage power cable networks, because three-phase loads are not equal, if a cable with a metal protective layer is used, the grounding of the metal protective layer must be considered, and the normal induced voltage at any point of the metal protective layer that is not grounded must not be greater than 100 V. I believe that in medium and low voltage cable networks, all cable joints should be provided with grounding electrodes (grids), and the metal protective layer should be reliably grounded.