Based on the power cable of thermal expansion and Countermeasures - China TDM Over IP Device
Changes with the load current and ambient temperature changes, power Cable Thermal expansion occurs, in which the core of the thermal expansion and contraction due to line generated a very large thermal mechanical force, the greater the cable core cross section, the heat generated by the greater mechanical strength; the same time line will be for the core and metal sheath repeated expansion and contraction Cycle , And creep. Thermal expansion of the power cable to run a great threat to run the cable will cause displacement, slip, or even damage to cables and accessories. Currently the largest cable cross section have been selected for the 7X 1600 mm =, so must pay attention to the thermal expansion large section cable problem.
Now under way on a variety of cable laying the safe operation of thermal expansion of the threat posed to make a brief analysis:
(1 direct arrangement, the cable due to restrictions by the surrounding soil, the whole cable can not generate displacement, so cores will be hot under the action of mechanical forces in the line of the two ends with great thrust, causing the end of displacement, the safety of the cable accessories to the threat posed.
(2) irresolute pipe laying, cable lateral restraint for not being in the heat under the effect of mechanical deformation of cable will produce; cable with the cable temperature changing, repeated bending of the cable metal sheath fatigue strain.
(3) the laying of the tunnel, the cables are generally on the scaffold, without rigid fixation, so the thermal expansion larger cable, laying prone in the slope slip phenomenon; easy to bend in the cable serious displacement; cable With the temperature changing cables, but also repeated bending of the cable metal sheath fatigue strain.
(4) shaft installed, the cable weight and thermal mechanical force has the potential to generate excessive strain metal sheath, thus shortening the life of the cable.
(5) municipal bridge laying, cable laying, if ranked in the bridge tube, and pipe laying, then there exists the same problem; if cable laid in the box girder bridge, then there is the laying of the same problems with the tunnel, except for the laying of cables on the bridge will be a bridge stretching vibration, thus speeding up the cable metal sheath damage.
These hazards, take appropriate measures to cables and accessories from the design, manufacture, cabling design and construction of several aspects.
(1) cables and accessories. To reduce the large cross-section of thermal expansion cable, cable core wire split should be adopted, not only can reduce the loss of the core line, and the heat produced per unit area than other forms of mechanical strength also leads to small. Cable Accessories Cable design must take into account the thermal withstand mechanical forces without damage.
(2) cable metal sheath present Aluminum Aluminum sheath and jacket are two very different to their performance: aluminum sheath, compared with aluminum sheath cable can improve operating performance, so except Antisepsis Particularly demanding project, the general cable metal sheath to select suitable aluminum sheath.
(3) direct burial cable near the terminal, such as in substations cable layer, can be used for snake lay, to absorb the deformation, reducing the end of the thrust: The stent should be rigidly fixed to prevent the terminal for cable displacement damage.
(4) a large section of pipe laying cable, in order to prevent the cables for bending the cable can apply a fill tube row Bentonite . Work well in the exit row of tubes can be used for immunity fixed on both sides of the cable connector required for rigid fixation, in order to protect the security of cable joints.
(5) tunnels snake laying cable in order to absorb the heat caused by mechanical deformation, the slope required for laying a fixed, rigid joints on both sides of cable should also be fixed to protect the security of cable joints.
(6) the large cross-section shaft with chuck for snake cables can be laid, and hanging in the shaft to the top so fixed, to absorb mechanical forces caused by thermal deformation.
(7) municipal bridge cable from aluminum sheathing must be selected to reduce vibration on the cable metal sheath bridge the fatigue caused by strain, laying method can refer to row tube or tunnel, should be noted that, in considering the thermal expansion cable the same time, need to consider the expansion bridge in the bridge expansion joints, upper and lower fixed bridge Department must adopt flexible or retractable cable can use bent.
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