Brief Introduction: With the change of load current and environmental temperature, the power cable will have thermal expansion, and the thermal mechanical force will be very large due to the thermal expansion and cold contraction of the cable core. The larger the section of the cable core is, the larger the thermal mechanical force will be. At the same time, the core and the metal sheath will creep due to multiple cycles of thermal expansion and cold contraction. Thermal stretching poses a great threat to the operation of power cables, causing them to move, slide, and even damage the cables and accessories. At present, the maximum cable section selected in China is 7X1600mm=, so it is necessary to pay attention to the thermal expansion of large-section cable.
1.With the change of load current and environmental temperature, thermal expansion and contraction of power cable will occur, in which a very large thermal mechanical force will be generated due to thermal expansion and cold contraction of the cable core. At the same time, the core and the metal sheath will creep due to multiple cycles of thermal expansion and cold contraction. Thermal stretching poses a great threat to the operation of power cables, causing them to move, slide, and even damage the cables and accessories. At present, the maximum cable section selected in China is 7X1600mm=, so it is necessary to pay attention to the thermal expansion of large-section cable.
This paper makes a simple analysis of the threats to safe operation brought by thermal expansion of cables under various laying methods:
(1) During direct buried laying, due to the limitation of surrounding soil, the whole cable cannot produce displacement, so the wire core will produce a great thrust at the two ends of the line under the action of thermal mechanical force, causing the end displacement, and thus posing a great threat to the safety of cable accessories.
(2) During haik laying, the cable will be bent and deformed under the effect of thermal mechanical force due to the absence of transverse constraints; With the constant change of cable temperature, bending deformation occurs repeatedly, which causes fatigue strain of cable metal sheath.
(3) During tunnel laying, the cables are generally placed on the supports without rigid fixation. Therefore, the thermal expansion of the cables is relatively large, and it is easy to slip down during the inclined surface laying; Severe displacement is easy to occur at the bending of the cable. With the constant change of cable temperature, the cable will repeatedly appear bending deformation, which will make the cable metal sheath fatigue strain.
(4) During the laying in the shaft, the dead weight and thermal mechanical force of the cable may cause excessive strain to the metal sheath, thus shortening the service life of the cable.
(5) the municipal bridge installation, cable laying within the bridge in the exhaust pipe, the Bi Hume brachial ou Qian Zhao zhe scoffs nai shi? If the cable is laid in the box girder of the bridge, there will be the same problems as the tunnel laying, except that the cable laid on the bridge will also be affected by the bridge stretching and vibration, thus accelerating the damage of the cable metal sheath.
The corresponding countermeasures should be taken from the design and production of cables and accessories, cable line design, construction and other aspects.
(1) Cables and accessories. In order to reduce the thermal expansion of large section cable, the cable core should be split conductor, which can not only reduce the loss of cable core, but also produce less thermal mechanical force per unit area than other types of wire. Cable accessories must be designed to withstand the thermal and mechanical forces of the cable without damage.
(2) There are two kinds of cable sheath: aluminum sheath and aluminum alloy sheath. Their performance is quite different: compared with aluminum alloy sheath, aluminum sheath can improve the running performance of the cable. Therefore, except for projects with high anti-corrosion requirements, aluminum sheath is the best choice for general cable metal sheath.
(3) Cables buried directly near terminals, such as substation cable layer, can be servially laid to absorb deformation and reduce terminal thrust: Rigid fixation should be made at the bracket to prevent terminal damage due to cable displacement.
(4) When laying large-section cable in the drainage pipe, bentonite can be filled to the drainage pipe with cable to prevent bending deformation of the cable. In order to protect the safety of the cable joint, disturbing fixation can be made at the outlet of the drainage pipe of the working well and rigid fixation should be made at both sides of the cable joint.
(5) The cables in the tunnel can be laid serpentine to absorb deformation caused by thermal mechanical force. The cables should be fixed when laying on the inclined surface, and the cables on both sides of the joints should also be fixed rigid to protect the safety of the cable joints.
(6) The large-section cables in the shaft can be serpentine laying with the help of collet and mounted on the top of the shaft to absorb the deformation caused by thermal mechanical force.
(7) municipal bridge laying cable must choose aluminum sheath, in order to reduce the vibration of cable bridge fatigue strain caused by metal sheath, laying mode can reference line or tunnel, it is important to note that in the consideration of cable thermal expansion at the same time, also take into account the scale of the bridge, the bridge expansion joint, up and down QiaoLiangChu must adopt flexible fixed, or choose can make cable retractile bent.