With the change of the load current and the change of the ambient temperature, thermal expansion and contraction of the cable for power mining occurs, in which a very large thermo-mechanical force is generated due to thermal expansion and contraction of the core, and the larger the cross-section of the cable core, the resulting thermal mechanical force. The larger the wire, the same time, the core and the metal sheath will also creep due to the multiple cycles of thermal expansion and contraction. Thermal expansion poses a great threat to the operation of the power cable, causing displacement, slipping, and even damage to cables and accessories. At present, the largest cable cross section that has been selected in China is 7×1600 mm=, so the thermal expansion of large-section cables must be considered.
Here is a brief analysis of the threats to the safe operation of cable thermal expansion under various laying methods:
(1) When burying directly, the cable is restricted by the surrounding soil, and the entire cable cannot be displaced. As a result, the core will generate a large thrust at the two ends of the line under the effect of thermomechanical force, causing the end displacement. As a result, the safety of the cable attachment poses a great threat.
(2) When the pipe is laid, the cable will not be laterally constrained. Under the effect of thermo-mechanical force, the cable will be bent and deformed. With the continuous change of the cable temperature, the bending deformation will occur repeatedly, causing fatigue strain on the metal sheath of the cable. (3) When laying the tunnel, the cables are generally placed on the bracket and are not rigidly fixed. Therefore, the thermal expansion of the cable is large, and slipping occurs easily when the cable is laid on the inclined plane; serious displacement occurs easily at the bent position of the cable; the cable follows the cable. Constant changes in temperature, but also repeated bending deformation, so that the cable metal sheath fatigue strain.
(4) When the shaft is laid, the weight of the cable and the thermomechanical force may cause excessive strain on the metal sheath, thereby shortening the service life of the cable.
(5) When the municipal bridge is laid, if the cable is laid in the inner pipe of the bridge, there is the same problem as the laying of the pipe; if the cable is laid in the box girder of the bridge, the same problem as the laying of the tunnel exists, except for the laying of the The cables on the bridge will also be affected by the expansion and contraction of the bridge, which will accelerate the damage of the metal sheath of the cable.
The corresponding countermeasures for the above hazards must be taken from the aspects of the design and production of cables and accessories, cable circuit design and construction.
(1) Cables and accessories. In order to reduce the thermal expansion of large-section cables, split conductors should be used for the cable cores, which can not only reduce the loss of the cores, but also generate smaller thermo-mechanical forces per unit area than other forms of wires. The cable accessory design must take into account the thermal mechanical resistance of the cable without damage.
(2) There are two types of cable sheathing: aluminum sheath and aluminum alloy sheath. Their properties are quite different: Aluminum sheath can improve the running performance of the cable compared with the aluminum alloy sheath. High engineering, general cable metal jacket to choose aluminum jacket is appropriate.
(3) Directly laid cables can be laid in the serpentine shape near the terminal, such as the substation cable layer, to absorb deformation and reduce the end thrust: they should be rigidly fixed at the bracket to prevent the terminal from being damaged due to cable displacement. .
(4) When laying large-section cable in the row pipe, in order to prevent the cable from being bent and deformed, bentonite can be filled into the pipe lined with the cable. The work pipe outlet can be disturbed and fixed at the outlet of the pipe. The two sides of the cable connector must be rigidly fixed to protect the safety of the cable connector.
(5) The cable in the tunnel can be laid in a serpentine shape to absorb the deformation caused by the thermo-mechanical forces. The cable must be fixed when laying on the slope, and the cables on both sides of the joint must also be rigidly fixed to protect the safety of the cable joint.
(6) Large cross-section cables in the shaft can be serpentine-shaped with the aid of a clamp and suspended at the top of the shaft to absorb the deformation caused by thermomechanical forces.
(7) Aluminium sheathing must be used for cables laid on municipal bridges to reduce the fatigue strain caused by bridge vibrations on the metal sheathing of cables. The laying method can refer to the pipe or tunnel. Note that while considering the thermal expansion of cables, It is also necessary to consider the expansion and contraction of the bridge. Flexible expansion must be taken at the expansion joint of the bridge and at the upper and lower bridges, or a flexible rack that allows the cable to flex freely can be used.
Here is a brief analysis of the threats to the safe operation of cable thermal expansion under various laying methods:
(1) When burying directly, the cable is restricted by the surrounding soil, and the entire cable cannot be displaced. As a result, the core will generate a large thrust at the two ends of the line under the effect of thermomechanical force, causing the end displacement. As a result, the safety of the cable attachment poses a great threat.
(2) When the pipe is laid, the cable will not be laterally constrained. Under the effect of thermo-mechanical force, the cable will be bent and deformed. With the continuous change of the cable temperature, the bending deformation will occur repeatedly, causing fatigue strain on the metal sheath of the cable. (3) When laying the tunnel, the cables are generally placed on the bracket and are not rigidly fixed. Therefore, the thermal expansion of the cable is large, and slipping occurs easily when the cable is laid on the inclined plane; serious displacement occurs easily at the bent position of the cable; the cable follows the cable. Constant changes in temperature, but also repeated bending deformation, so that the cable metal sheath fatigue strain.
(4) When the shaft is laid, the weight of the cable and the thermomechanical force may cause excessive strain on the metal sheath, thereby shortening the service life of the cable.
(5) When the municipal bridge is laid, if the cable is laid in the inner pipe of the bridge, there is the same problem as the laying of the pipe; if the cable is laid in the box girder of the bridge, the same problem as the laying of the tunnel exists, except for the laying of the The cables on the bridge will also be affected by the expansion and contraction of the bridge, which will accelerate the damage of the metal sheath of the cable.
The corresponding countermeasures for the above hazards must be taken from the aspects of the design and production of cables and accessories, cable circuit design and construction.
(1) Cables and accessories. In order to reduce the thermal expansion of large-section cables, split conductors should be used for the cable cores, which can not only reduce the loss of the cores, but also generate smaller thermo-mechanical forces per unit area than other forms of wires. The cable accessory design must take into account the thermal mechanical resistance of the cable without damage.
(2) There are two types of cable sheathing: aluminum sheath and aluminum alloy sheath. Their properties are quite different: Aluminum sheath can improve the running performance of the cable compared with the aluminum alloy sheath. High engineering, general cable metal jacket to choose aluminum jacket is appropriate.
(3) Directly laid cables can be laid in the serpentine shape near the terminal, such as the substation cable layer, to absorb deformation and reduce the end thrust: they should be rigidly fixed at the bracket to prevent the terminal from being damaged due to cable displacement. .
(4) When laying large-section cable in the row pipe, in order to prevent the cable from being bent and deformed, bentonite can be filled into the pipe lined with the cable. The work pipe outlet can be disturbed and fixed at the outlet of the pipe. The two sides of the cable connector must be rigidly fixed to protect the safety of the cable connector.
(5) The cable in the tunnel can be laid in a serpentine shape to absorb the deformation caused by the thermo-mechanical forces. The cable must be fixed when laying on the slope, and the cables on both sides of the joint must also be rigidly fixed to protect the safety of the cable joint.
(6) Large cross-section cables in the shaft can be serpentine-shaped with the aid of a clamp and suspended at the top of the shaft to absorb the deformation caused by thermomechanical forces.
(7) Aluminium sheathing must be used for cables laid on municipal bridges to reduce the fatigue strain caused by bridge vibrations on the metal sheathing of cables. The laying method can refer to the pipe or tunnel. Note that while considering the thermal expansion of cables, It is also necessary to consider the expansion and contraction of the bridge. Flexible expansion must be taken at the expansion joint of the bridge and at the upper and lower bridges, or a flexible rack that allows the cable to flex freely can be used.