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What should be paid attention to during the construction and laying of cables?

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  • Time of issue:2020-03-29 20:54
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(Summary description)There are several types of cable laying methods: direct buried laying, pipe laying, shallow trench laying, cable trench laying, cable tunnel laying, and overhead laying. Several methods have advantages and disadvantages.Generally, city development planning and existing buildings should be considered.

What should be paid attention to during the construction and laying of cables?

(Summary description)There are several types of cable laying methods: direct buried laying, pipe laying, shallow trench laying, cable trench laying, cable tunnel laying, and overhead laying. Several methods have advantages and disadvantages.Generally, city development planning and existing buildings should be considered.

  • Categories:company news
  • Author:
  • Origin:
  • Time of issue:2020-03-29 20:54
  • Views:
Information

1. Cable laying method
There are several types of cable laying methods: direct buried laying, pipe laying, shallow trench laying, cable trench laying, cable tunnel laying, and overhead laying. Several methods have advantages and disadvantages.Generally, city development planning and existing buildings should be considered. The length of the density cable line laying and the impact of its surrounding environment. From a technical comparison point of view, cable tunneling and cable trench laying methods are convenient for cable construction, maintenance, and overhaul. In some developed cities, public tunnels have been considered in urban planning and construction. Practice has proved that public tunnels operate well, greatly reducing the number of repeated investment and repeated excavation of the road surface, but the initial investment is huge, and the construction materials consume money. In China, due to various factors, this type of laying is very rare. . In comparison, direct buried laying and shallow trench laying are economical laying methods. Directly buried cables are the most economical and widely used electrical laying method, which is used in suburban areas and places where vehicles do not pass frequently. But it is not conducive to the maintenance and repair of the cable. Once a cable fault is encountered, even if the fault point is detected using a tester, it is extremely inconvenient to dig the cable trench again. Therefore, the choice of cable laying method should be determined according to the actual conditions, according to factors such as engineering conditions, environmental characteristics, cable type and quantity, and with a development perspective, in accordance with the requirements of meeting operational reliability, easy maintenance, and technical, economic and reasonable principles.

2. Selection of cable
Commonly used power cables include oil-immersed cables, polyvinyl chloride insulated cables, cross-linked polyethylene cables, etc., which can be extended to different types of special cables according to the use occasions. At present, with the continuous improvement of production technology and production technology, cross-linked polyethylene cable has become the most widely used cable product.When selecting the cable, it should be selected according to the different environments and conditions of use and combined with the specific circumstances to minimize Pass through various pipe-side railways, highways and communication cables; if directly buried and shallow trench laying is used, steel-clad cables should be considered.

3. Selection of cable cross-sectional area   
Choose the cross-sectional area of ​​the cable, related to how much investment, line loss and voltage quality, cable life, etc. If the cross-sectional area is too small, the voltage quality will be reduced and the line loss will be too large, which will make the initial investment too high. Therefore, according to the load prediction results, development planning, select the appropriate cross-sectional area, so that the power cable meets the requirements of the core temperature and voltage drop under the maximum operating current, and the thermal stability requirements under the maximum short-circuit current. Due to the high difficulty and low accuracy of load forecasting, when selecting the cable cross-sectional area, it is necessary to meet the requirements of "Technical Guidelines for Urban Medium and Low Voltage Distribution Network Transformation" and "Guidelines for Urban Power Network Planning".
When selecting power cables for the three-phase four-wire low-voltage power grid, the choice of zero-line cross-sectional area must also be considered.In the public low-voltage network, due to the greater influence of user factors, the three-phase load balance is difficult to control. For line loss, the cross-sectional area of ​​the zero line should be the same as the cross-sectional area of ​​the phase line.   

4. Problems that should be paid attention to in the construction of power cables      
1) It is the eddy current problem caused by high-current power cable   
In the construction of power cables, some use steel brackets, some use steel protection tubes, and some use cable clamps and overhead laying. Anyone that forms a steel (iron) closed loop around the power cable may form eddy currents. Especially in large current power cable systems, the eddy current is greater. During the construction of power cables, measures must be taken to prevent steel (iron) closed loops from forming around the cables to prevent eddy currents caused by the cables.
2) It is the mechanical damage caused by the turning of the power cable
Due to the large outer diameter of the power cable, it is difficult to transport and lay, and the power cable has strict requirements on the turning radius. In the construction of power cables, if the turning angle is too large, the conductor may be mechanically damaged, and the mechanical damage is reduced by the insulation strength of the cable until a failure occurs.A cable head failure is found during construction.When the cable head is made, three cables The length of the head is the same. When connected to the equipment, due to the limitation of the terrain, the middle-phase cable head becomes long and arched, and the root of the cable head is damaged and discharged. After taking measures, in the connection of the equipment, the connection length of the middle-phase cable head is appropriately shortened, so that the three-phase cable head is not subject to external force, and practice has proved that the operation effect is good. It can be seen that in the process of cable construction, the torsion force of the cable should be reduced as much as possible. When the cable is turned and the cable is left, the cable is naturally bent to prevent internal mechanical damage.
3), is the moisture proof problem of power cable
Operation experience shows that most of the failures of medium and low voltage power cables are the failure of the middle connector and the terminal of the cable, and the failure of the middle connector and the terminal is mostly due to poor sealing and moisture intrusion, which causes the insulation strength to decrease. Most of the network adopts dendritic power supply, 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 seal and seal the cable terminal and the intermediate joint.
4), is the grounding problem of medium and low voltage power cables
In the public medium and low voltage power cable network, because the three-phase load is not equal, if you use a cable with a metal sheath, you must consider the grounding problem of the metal sheath and ensure that it is not grounded at any point of the metal sheath The normal induced voltage should not be greater than 100V. We believe that in the medium and low voltage cable networks, all cable joints should be equipped with grounding poles (nets), and the metal sheath should be reliably grounded.

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