Discussion on thermal expansion and contraction of

2022-07-28
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Discussion on thermal expansion and contraction of power cable during wiring and Its Countermeasures; 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 will cause the displacement, sliding and even damage to cables and accessories. At present, the maximum cable section selected in China is 7 x 1600 mm=, so we must pay attention to the thermal expansion of large section cables

here is a simple analysis of the threat of cable thermal expansion to safe operation under various laying methods:

(1) when the cable is directly buried, the whole cable cannot be displaced due to the restriction of surrounding soil, so the wire core will generate a great thrust at the two ends of the road under the action of thermal mechanical force, causing end displacement, thus posing a great threat to the safety of cable accessories.

(2) when the pipe is laid, Because the cable is not subject to lateral constraints, the cable will produce bending deformation under the action of thermal mechanical expansion force; With the constant change of cable temperature, the bending deformation of the cable occurs repeatedly, causing the fatigue strain of the cable metal sheath

(3) firstly, during tunnel laying, the cable is generally placed on the support without rigid fixation, so the thermal expansion of the cable is large, and it is easy to slip when laying on the inclined plane; Serious displacement is easy to occur at the bend of the cable; With the constant change of cable temperature, the cable will appear repeatedly, which can realize accurate and continuous pressure control bending deformation, and make the cable metal sheath produce fatigue strain

(4) during shaft laying, the self weight and thermomechanical force of the cable may cause excessive strain to the metal sheath, thus shortening the service life of the cable

stretching speed: 100mm/min stretching to the breaking record tension (5) when laying municipal bridges, if the cables are laid in the drainage pipe in the bridge, there are the same problems as the drainage pipe laying; If the cable is laid in the box girder of the bridge, there will be the same problem as the tunnel laying. In addition, the cable laid on the bridge will also be affected by the bridge expansion and vibration, thus accelerating the damage of the cable metal sheath

corresponding countermeasures shall be taken against the above hazards from the design, production, cable route design, construction and other aspects of cables and accessories

(1) cables and accessories. In order to reduce the thermal expansion of large cross-section cables, the cable core should adopt split conductor, which can not only reduce the loss of the core, but also generate less thermal mechanical force per unit area than other types of conductors. Cable accessories must be designed to withstand the thermal mechanical force of the cable without damage

(2) at present, there are two kinds of cable metal sheath: aluminum sheath and aluminum alloy sheath, and their performances are quite different: compared with aluminum alloy sheath, aluminum sheath can improve the operation performance of the cable, so except for projects with particularly high anti-corrosion requirements, aluminum sheath is suitable for general cable metal sheath

(3) directly buried cables can be laid in a serpentine manner near the terminal, such as in the substation cable layer, to absorb deformation and reduce terminal thrust: rigid fixation shall be made at the support to prevent the terminal from being damaged due to cable displacement

(4) when laying large cross-section cables in a row, bentonite can be filled into the row of cables to prevent bending deformation of cables. Disturbing fixation can be made at the outlet of the drain pipe of the work well, and rigid fixation shall be made at 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 serpentine manner to absorb the deformation caused by thermal mechanical force. When laying on an inclined plane, the cables shall be fixed, and the cables on both sides of the joint shall also be rigidly fixed to protect the safety of the cable joint

(6) the large cross-section cable in the shaft can be laid in a serpentine manner with the help of a collet, and a suspension type fixing is made at the top of the shaft to absorb the deformation caused by thermal mechanical force

(7) the cables laid on municipal bridges must be aluminum sheathed to reduce the fatigue strain caused by bridge vibration on the cable metal sheath. The laying method can refer to the pipe or tunnel. It should be noted that while considering the thermal expansion of the cable, the expansion of the bridge should also be considered. Flexible fixation must be adopted at the bridge expansion joints and the upper and lower bridges, or bent frames that can make the cable expand and contract freely should be selected. (end)

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