Some customers in the design of low medium voltage power cable process, the actual load flow and theoretical load of power cable in the understanding of the misunderstanding, often think that cable selection as long as the actual operating capacity to meet the equipment can be, and often ignore the actual laying conditions on the actual operation of the cable load flow correction,
For the occurrence of cable accidents buried hidden dangers. A new silicon industry company, the plant's internal transmission of more than 50 10kV power cable, all alone into the thick white PVC plastic pipe, no gap between the arbitrary stacking 5 layers, and then directly buried laying, the depth of soil buried about 1 meters, the number of cables laid on each layer of 10, The distribution section of the whole cable pipe is arranged in rectangular way, the total length of cable line is about 1 kilometers. There are two cable wells in the middle of the cable joint, which is convenient for the maintenance of cable lines. These cables in the continuous power operation of 1 days or so, from the cable wellhead out of the unpleasant due to the thermal decomposition of the cable's Coke paste flavor, less than a week there will be a cable has occurred a heat breakdown. The end result is that the entire 10kV power cable line is not working properly. The above problem is the lack of scientific understanding of the actual operation of the cable, which leads to the typical case of cable accident. Various models of low and medium voltage power cables have a theoretical calculation of the load flow, however, for the actual laying environment of power cable, it is necessary to fully consider the thermal resistance correction coefficient of the actual use of the laying environment, and correct the actual load flow of the cable, which must be considered fully in the design stage before the cable selection and construction. Otherwise, once the cable construction is completed, there will be no remedy, resulting in a huge loss of power economy. Multi-cable into PVC plastic pipe, no gap at random laying directly buried, each cable's environmental resistance coefficient than cable directly buried laying way greatly increased. In the actual power operation of the cable, the medium around each cable inside the pipe is mainly plastic pipes and adjacent cables, rather than pure soil, its thermal resistance will be far greater than the soil, and the heat generated by the cable in the operation of the plastic pipe and the surrounding cable heating, At this time, the actual installation of cable is not pure directly buried, the actual operation of the allowable load flow will be greatly reduced, cable thermal breakdown of the occurrence potential in the inevitable.
Therefore, for the initial design of the cable laying project, the actual thermal resistance after the cable laying must be fully taken into account, and the correction design should be carried out in time, otherwise the economic loss is enormous. When more than one cable with no gap between the arbitrary stacking laying directly buried, when one of the cable failure may be adjacent to one or more cables will be burned, resulting in the spread and expansion of the accident. At the same time will cause a thermal breakdown of the accident occurred.
The number of direct buried cable is too much for the actual repair and excavation of cable line fault, because of the number of cables, the excavation process caused by the damage of the cable machinery will also be greatly increased, while in the excavation of faulty cables, adjacent cables may be in power, personnel electric shock accidents and two accidents caused by the scope of the blackout is likely to expand. For multiple cables at the same time buried directly, the number of the best can be controlled under 6, the laying process as far as possible, to give the cable enough heat dissipation space, in the cable selection, to its surrounding soil or sand to fully consider the thermal performance, resistance coefficient of correction, to ensure the normal safe use of cables, So that its useful life can be fully realized.