Thermal scaling of power cables and Its Countermeasures

As the load current changes and the ambient temperature changes, the power cable will undergo thermal scaling. The great thermal mechanical force is generated due to the thermal expansion and contraction of the wire core. The larger the cable core section, the larger the thermal mechanical force is generated. At the same time, the wire core and metal jacket may also produce creep due to multiple cycles of thermal expansion and contraction. Thermal scaling poses a great threat to the operation of power cables, which may cause the operation of cables to shift, slide, or even damage the cables and accessories. Currently, the maximum Cable Section used in China is 7X1600mm =. Therefore, you must pay attention to the hot expansion of large-section cables.
The following is a brief analysis of the threats to secure operation caused by cable thermal scaling in various laying modes:
1) During direct buried laying, the whole cable cannot be displaced due to the limitations of surrounding soil, as a result, the wire core will generate a great thrust at the two ends of the line under the action of thermal mechanical force, causing the terminal displacement, thus posing a great threat to the safety of the Cable Accessories.
2) When the pipe is laid, the cable will produce bending deformation due to the lack of horizontal constraints under the thermal mechanical force; the cable will appear repeatedly as the temperature of the cable changes constantly, fatigue strain caused by Cable Metal Jacket
3) when laying a tunnel, the cables are generally placed on the bracket without rigid fixing. Therefore, the cable is hot scalable and prone to slide during inclined laying; severe displacement may occur at the bending position of the cable. As the temperature of the cable changes, bending deformation may occur repeatedly, resulting in fatigue strain on the Metal Sheath of the cable.
4) when the shaft is laid, the cable's self-weight and thermal mechanical force may cause excessive strain on the metal sheath, thus shortening the cable's service life.
5) when laying a municipal bridge, if the cable is laid in the tube inside the bridge, the problem is the same as that of laying the cable. If the cable is laid in the Box Girder of the bridge, in this case, the cable laying on the bridge will be affected by the scaling and vibration of the bridge, thus accelerating the damage of the Metal Jacket of the cable.
Corresponding countermeasures should be taken for the above hazards from the cable and accessories design, production, cable line design, construction and other aspects.
(1) cables and accessories. To reduce the thermal scaling of Large-section cables, split wires should be used for cable cores, which not only reduces the loss of wire cores, but also produces less thermal mechanical force per unit area than other cables. Cable Accessories must be designed to withstand the thermal mechanical power of cables without damage.
(2) There are two kinds of cable metal sheaths: aluminum sheaths and aluminum alloy sheaths. Their performances are quite different: Compared with aluminum sheaths, aluminum sheaths can improve the running performance of cables, therefore, except for projects with high anti-corrosion requirements, it is recommended to choose aluminum jacket for metal cable sheath.
(3) directly buried cables can be laid in the adjacent terminal, such as the substation cable layer, in a snake-like manner to absorb deformation and reduce the end thrust: rigid fixation should be performed at the bracket, to prevent terminal damage due to cable displacement.
(4) When laying a large cross-section cable, in order to prevent the cable from bending deformation, you can fill the discharge tube with cables with bentonite. Interference can be fixed at the outlet of the pipe discharge in the workwell, and rigid fixing is required on both sides of the cable joint to protect the safety of the cable joint.
(5) The cables in the tunnel can be laid in a snake-like manner to absorb the deformation caused by the thermal mechanical force. The cables must be fixed when the beam is laid, and the cables on both sides of the joints must also be rigid fixed, to protect the safety of cable connectors.
(6) The large cross-section cable in the shaft can be laid with the Chuck as a snake and suspended and fixed at the top of the shaft to absorb the deformation caused by the thermal mechanical force.
(7) Aluminum jacket must be used for cables laid for municipal bridges to reduce fatigue strain caused by Bridge Vibration on metal cable casings. For the laying method, refer to discharge pipes or tunnels, in addition to cable thermal scaling, the expansion of the bridge must be considered. Flexible and fixed measures must be taken at the expansion joints of the bridge, between the upper and lower bridges, or a rack capable of freely scaling the cable should be selected.