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Power engineering construction company to introduce the common situation of cable laying

2020-12-28 00:00:00
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The operation quality, safety and reliability of power supply system in power engineering are not only related to the quality of the wires and cables, but also to the construction quality of cable accessories and lines. This paper will introduce the common situation of cable laying in power engineering.

1. Laying mode of cable

The laying methods of cables are as follows: direct laying, pipe laying, shallow groove laying, cable trench laying, cable tunnel laying and overhead laying.

There are advantages and disadvantages in several ways. Generally, urban development planning, the number of density cable lines and the influence of surrounding environment of existing buildings should be considered. Compared with each other in technology, the cable tunnel and cable trench laying method of Guizhou power project are convenient for the construction, maintenance and maintenance of cables. In some developed countries, public tunnels have been considered in urban planning and construction. The practice shows that the utility tunnel has good operation effect, which greatly reduces the repeated investment times and the phenomenon of repeatedly excavating the pavement. However, the initial investment of the project is huge, and the construction materials cost. In China, due to the limitation of various factors, this laying method is very rare.

In contrast, direct buried laying and shallow groove laying are economical laying methods. Direct buried cables are economical and widely used for power laying. They are used in places where the suburban and vehicle are not frequently used, but it is not conducive to the maintenance and maintenance of cables. In case of cable failure, even if the fault point is detected by the tester, it is very inconvenient to excavate the cable trench again. Therefore, the selection of cable laying mode should be determined according to the engineering conditions, environmental characteristics, cable type and quantity, and in accordance with the requirements of operation reliability, easy maintenance and reasonable technology and economy.

2. Cable selection

The common power cables are oil immersed cable, PVC insulated cable, cross-linked polyethylene cable, etc. according to the different use situation, they are also extended into different types of special cables. At present, with the continuous improvement of production technology and production technology, cross linked polyethylene cable has become a widely used cable product. In cable selection, it is necessary to select according to the different environment and conditions used and in combination with specific conditions, so as to minimize the crossing of various railway, highway and communication cables. If direct buried and shallow groove laying is adopted, consideration should be given to make the cable selection possible Use steel armored cable.

3. Selection of cable cross section

The choice of cable cross-section area is related to the investment, the loss of the line and the quality of voltage, the service life of the cable, etc. If the selected cross-section area is small, it will lead to the voltage quality reduction and the line loss too large, then the initial investment will be too high. Therefore, according to the load prediction results, the appropriate cross-section area should be selected to make the power cable meet the requirements of cable core temperature and voltage drop under the working current and the thermal stability requirements under the action of short-circuit current. Because of the high difficulty and low accuracy of load forecasting. Therefore, when selecting the cable cross-section area, it is necessary to meet the requirements of technical guidelines for urban medium and low voltage distribution network transformation and urban power network planning guidelines.

When selecting power cable in three-phase four wire low-voltage power grid, the selection of zero line cross-section area should be considered. In public low-voltage network, due to the influence of user factors, the three-phase load balance is difficult to control. In order to improve the voltage quality and reduce line loss, the cross-sectional area of the zero line should be the same as that of the phase line.

4. Cable network and automation

With the continuous promotion and use of power cables in distribution network, distribution network can be divided into cable network and overhead network (including overhead and cable hybrid network). The implementation and supplementary opinions on technical guidelines for the transformation of medium and low voltage distribution network in cities also put forward specific requirements for the automation of cable distribution network. Therefore, when the regional network of distribution network adopts cable network, new technology and equipment shall be adopted according to the requirements of distribution automation. If conditions are available, the pilot work of automation shall be considered. If the conditions are not mature, sufficient space shall be considered to lay the foundation for realizing the automation scheme when selecting the supporting equipment.

5. Precautions for power cable construction

1. Eddy current caused by high current power cable

In the construction of power cables, there are steel supports, some adopt steel protective pipes, and cable cards and overhead laying are used. For those with steel (iron) closed loop around power cables, eddy current may be formed, especially in large current power cable system. In the construction of power cable, measures must be taken to prevent the steel (iron) closed loop around the cable, so as to prevent the occurrence of eddy current phenomenon caused by the cable.

2. Mechanical damage caused by turning of power cable

Because of the large outer diameter of power cable, it is difficult to transport and lay, and the requirements of turning radius of Guizhou power cable are also strict. In the construction of power cable, if the turning angle is too large, Guizhou electric power project may cause mechanical damage to the conductor, while the mechanical damage will decrease due to the cable insulation strength until the failure occurs. In the construction, it is found that the cable head fault is once. During the cable head production, the length of three cable heads is the same. When connecting with the equipment, due to the limitation of terrain, the cable head of the middle phase is too long and becomes arch shape, and the root of the cable head is damaged and discharged. After that, the measures are taken to shorten the connection length of the middle phase cable head properly in the connection of the equipment, so that the three-phase cable head is not subjected to external force. The practice proves that the operation effect is good. Thus, the cable construction process should minimize the torque on the cable, and when the cable turns and reserves the cable, it is necessary to make the cable in natural bending, and prevent the internal mechanical damage.

3. Moisture proof of power cable

The operation experience shows that the fault of medium and low voltage power cable is mostly the middle connector and terminal head fault, while the failure of the intermediate connector and terminal head is mainly caused by poor sealing and moisture intrusion, which results in the decrease of insulation strength. The branch power supply is used in the medium and low voltage power cable network, and the number of cable terminals is large. Therefore, it is one of the important measures to ensure the safe and reliable operation of the cable to close the leakage of the cable terminal and the intermediate joint.

4. Grounding of medium and low voltage power cables

In the public medium and low voltage power cable network, the three-phase load is not equal. Therefore, if the cable with metal sheath is adopted, the grounding of metal sheath must be considered and the normal induction voltage at any point of metal sheath which is not grounded shall not be greater than 100V. In the medium and low voltage cable network, grounding electrodes (NETs) shall be set at all cable joints, and the metal sheath shall be reliably grounded.


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