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Power cable wiring of thermal expansion and its countermeasure

Information Source:Henan Huadong Cable Co., Ltd  Release date:2014-02-27

With the load current changes and the change of environmental temperature, power cable may occur due to thermal expansion and contraction, the wire core expansion and contraction due to thermal mechanical force is very large, the larger section of cable core, thermal mechanical force generated is larger; at the same time line core and metal sheath and also because of heat expansion and cold contraction multiple cycle, and creep. The thermal expansion of the power cable operation posed a great threat, will cause the operation of cable displacement, slide, or even damaged cables and accessories. The largest cable section currently has chosen 7 X 1600 mm=, we must pay attention to thermal expansion problem of large section cable.

Is to make a brief analysis on the retractable cable thermal laying way brings to the safe operation of the threat:

(1) buried laying, cable because of the surrounding soil, the whole cable can not produce displacement, so the core in the heat under the action of mechanical force in the two end of the line to produce great thrust, cause end displacement, thus security of cable accessories pose a great threat to.

(2) that the pipe laying, cable was not subject to lateral restraint, the thermal mechanical force of cable will produce bending deformation; cable with constant changes of cable temperature, bending deformation occurs repeatedly, the cable metal sheath fatigue strain

(3) when laying the cable tunnel, are usually placed on the bracket, not rigidly fixed, so the cable thermal expansion is large, easy to slip in the inclined plane laying; easy to appear serious displacement at the bend cable; cable with constant changes of cable temperature, will be repeated bending deformation, so that the cable metal sheath fatigue strain.

(4) shaft installation, gravity and thermal mechanical cable metal sheath may make excessive strain, so as to shorten the service life of the cable.

(5) the municipal bridge laying, if the cable laying in the bridge pipe, and pipe laying there is the same problem; if the cable laying in the bridge box girder, are the same and tunnel laying of cable, except external set on the bridge also affected the bridge expansion, vibration thus, accelerated damage cable metal sheath.

Take corresponding countermeasures must be from the design, cable and accessories production should be the harm, cable design, several aspects of construction etc..

(1) cables and accessories. In order to reduce the thermal expansion of large cross section cable, cable core conductor loss should be adopted, not only can reduce the wire core, and thermal mechanical force on unit area than other forms lead to small also. Design of cable accessories must consider the thermal mechanical stress can withstand without damage to the cable.

(2) with an aluminum sheath and aluminum alloy sheath two kinds of current cable metal sheath, their performance differences: compared with aluminum sheath and the aluminum alloy sheath can improve the running performance of cable, so in addition to anticorrosion requirements are particularly high engineering, metal sheath for general cable aluminum sheath is suitable to choose.

(3) direct buried cable near the terminal, such as substation cable layer, can make the snake laying, to absorb the deformation, reducing end thrust: as rigidly fixed on the support, in order to prevent the terminal from being damaged due to cable displacement.

(4) pipe laying of large cross section cable, bending deformation of bentonite row tube is filled with a cable to the application in order to prevent the cable. In the exhaust pipe outlet for rejection fixed shaft, both sides of the cable connector should be rigidly fixed, in order to protect the safety of cable joint.

(5) the tunnel cable can be deformed to absorb the snake laying, caused by the thermal mechanical stress in the slope, when laying the cable should be fixed, both sides of the joint cable also need rigid fixation, in order to protect the safety of cable joint.

(6) large section cable shaft with chuck as the snake laying in shaft, and top mounted fixed, to absorb the heat deformation caused by mechanical force.

(7) the municipal bridge cable laying must be selected aluminium sheath, in order to reduce the fatigue strain of cable metal sheath caused by vibration of bridges, laying mode may refer to the row tube or tunnel, the need to pay attention to is, in considering the cable thermal expansion at the same time, also need to consider the expansion of bridge, the bridge expansion joint, upper and lower bridge must take flexible fixation, or choose to bent the cable telescopic.

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