Introduction: With the change of load current and ambient temperature, the power cable will undergo thermal expansion, which is caused by the thermal expansion and cold contraction of the wire core, resulting in a very large thermal mechanical force, the larger the cable core section, the greater the thermal mechanical force generated;
At the same time, the wire core and metal sheath will creep due to multiple cycles of thermal expansion and cold contraction.
Thermal expansion poses a great threat to the operation of power cables, which may cause displacement, slide, or even damage to cables and accessories.
At present, the maximum cable cross section selected in China is 7X1600mm=, so we must pay attention to the thermal expansion of large cross section cable.
1. With the change of load current and ambient temperature, the power cable will undergo thermal expansion, which is caused by the thermal expansion and cold contraction of the wire core, resulting in a very large thermal mechanical force. The larger the cable core section, the greater the thermal mechanical force generated;
At the same time, the wire core and metal sheath will creep due to multiple cycles of thermal expansion and cold contraction.
Thermal expansion poses a great threat to the operation of power cables, which may cause displacement, slide, or even damage to cables and accessories.
At present, the maximum cable cross section selected in China is 7X1600mm=, so we must pay attention to the thermal expansion of large cross section cable.
Threats to safe operation brought by thermal expansion of cables under various laying methods are briefly analyzed:
(1) When directly buried, the cable is limited by the surrounding soil, so the whole cable cannot produce displacement. Therefore, the core of the line will generate great thrust at the two ends of the line under the action of thermal-mechanical force, resulting in displacement of the ends, thus posing a great threat to the safety of cable accessories.
(2) The cable will bend and deform under the action of thermal-mechanical force because it is not subject to lateral constraints in the process of pipe-laying;
With the constant change of cable temperature, bending deformation appears repeatedly, which causes fatigue strain of cable metal sheath.
(3) When laying tunnels, cables are generally placed on brackets and not rigidly fixed, so the thermal expansion of cables is large, and it is easy to slide down when laying on inclined surfaces;
Serious displacement is easy to occur at the bending point of the cable.
With the constant change of cable temperature, there will be repeated bending deformation, so that the cable metal sheath fatigue strain.
(4) When laying the shaft, the dead weight and thermal-mechanical force of the cable may cause excessive strain of the metal sheath, thus shortening the service life of the cable.
If (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 are the same problems as the tunnel laying, except that the cable laid on the bridge will also be affected by the expansion and vibration of the bridge, thus accelerating the damage of the cable metal sheath.
The above hazards should be taken the corresponding countermeasures must be from the cable and accessories design, production, cable line design, construction and other aspects.
(1) Cables and accessories.
In order to reduce the thermal expansion of the large cross-section cable, the cable core should be split conductor, which can not only reduce the loss of the wire core, but also produce less thermal mechanical force per unit area than other forms of wire.
Cable accessories must be designed to withstand the thermo-mechanical force of the cable without damage.
(2) there are two kinds of cable metal sheath aluminum sheath and aluminum alloy sheath, their performance is very different: aluminum sheath and aluminum alloy sheath compared to improve the operation performance of the cable, so in addition to the anti-corrosion requirements of particularly high engineering, the general cable metal sheath to choose aluminum sheath is appropriate.
(3) Directly buried cables can be laid near the terminal, such as in the cable layer of a substation, in a snake shape to absorb deformation and reduce thrust at the end: rigid fixation should be made at the bracket to prevent damage to the terminal due to cable displacement.
(4) When laying large cross-section cables in the row, bentonite can be filled into the row with cables in order to prevent bending deformation of the cables.
It can be disturbed fixed at the drainage outlet of the working shaft, and the two sides of the cable joint should be rigid fixed to protect the safety of the cable joint.
(5) The cable in the tunnel can be laid in a serpentine shape to absorb the deformation brought by the thermal mechanical force. When laying on the inclined surface, the cable should be fixed, and the cable on both sides of the joint should also be rigid-fixed to protect the safety of the cable joint.
(6) The large-section cable in the shaft can be laid in a serpentine shape with the help of the chuck, and the hanging fixed on the top of the shaft to absorb the deformation brought by the 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.