Since the reform and opening up, with the rapid development of urban construction, some overhead lines in urban areas have been gradually replaced by power cable lines. Some 10kV, 35kV and even 110kV and 220kV overhead lines in some economically developed cities have all or part of the cables replaced Line, and some projects in the early stages of construction, just because of the path problem, the direct use of cable lines. As an engineering designer, talk about your own experience in the power line into the place.
In recent years, the rapid urban load growth, residents of the power supply reliability requirements; the other hand, the beauty of urban planning and construction more and more attention. As urban high-voltage overhead lines by the line corridor and the same pole number of loops, many of the street capacity can not keep up with the development of social electricity; overhead line failure, the operation mode is not flexible, often resulting in large-scale power outages, seriously affecting residents' normal life ; Overhead lines are generally located on one side of the street, limiting the growth height of green belt trees; the private pull of overhead lines across the street and other lines on the power pole seriously affect the urban beauty; affected by the live lines and all aspects of society Interference, the construction of overhead lines in urban areas more difficult and prone to endanger the safety of people off the wire, leakage and other accidents. With the rapid development of our country's urban areas, the overhead lines have revealed many contradictions with the uncoordinated development of cities.
Although the investment in cable lines is several times higher than that of overhead lines, the laying of cables in the ground does not occupy the space above the ground, which is good for the beautiful appearance of the city. The same underground cable channel can accommodate multiple lines and has strong adaptability of transmission capacity. It is less affected by the natural conditions and the surrounding environment, and has high reliability of power supply. The cable is hidden in the ground and is safer for human beings. The operation and maintenance cost of the cable line is relatively small, and the construction difficulty is small. , Can be multi-line contact to form a power supply network, the operation mode is extremely flexible, can greatly reduce the number of blackouts and power outages, easy to achieve distribution automation. Therefore, with the development of urban economy, the superiority of cable lines in unmanned overhead lines will result in more and more alternative overhead lines being used in urban distribution networks.
The construction cost of the cable route is generally relatively large. The laying way directly affects the civil cost of the project construction. Therefore, to rationally plan and select the cable laying way is the most important link of the cable entry work. Cable laying mode depends on engineering conditions, environmental characteristics and cable type, quantity and other factors, and according to meet the requirements of reliable operation, easy maintenance and technical and economic and reasonable principles to choose. The main use of a direct buried laying, laying pipe laying, laying of cable ditch, tunnel laying and so on.
Buried laying way: generally easier to implement, with the significant advantages of investment in the province, but vulnerable to external damage, aging and accidental replacement is not easy to overhaul after laying the limitations should not be used in the city trunk can be used for cables Branch or subscriber line. Cable trench laying is more common, but after a long run, the trench cover is prone to fracture and damage incomplete, surface water overflow into the trench, the greater impact on the aesthetics of the ground.
Pipe laying method: If we determine the use of pipe laying, the pipe selection is an important task. Cable protection tube must be smooth and burr-free inner wall, which should meet the mechanical strength and durability required by the conditions of use. At present, there are many types of cable protection tubes at home and abroad, including steel protection tubes, ceramic tubes, polyethylene bellows, vinylon Cement pipe, PVC pipe, FRP protection tube. Steel protective tube, ceramic pipe prices are high, the joints are not good to deal with; Polyethylene bellows deflection, should not be used in the parallel laying of lots; ordinary cement pipe wall roughness, cable laying difficult, easy to damage the cable. According to the actual use of the project, considering the cost and construction of many factors, it is recommended to use relatively low price, high strength and low flexibility of low-friction high-strength vinylon cable or buried power cable with chlorinated polyvinyl chloride (CPVC) Protective sleeve.
The tunnel laying method is a kind of laying method adopted when multiple power lines are in the same path and there is no overhead corridor, generally adopting brick-concrete structure, the sidewalls are made of 370mm thick brick walls, the bottom of the tunnels and the roof are made of cast-in-place reinforced concrete . Of course, this method is also the highest cost, but it is the highest building standards, maintenance and construction workers can pass in the tunnel, at the same time cable tunnel fire and ventilation requirements must also strictly enforce the relevant design rules and requirements. Install the cable support on the two side walls in the cable tunnel. The distance between the top bracket and the top of the cable is 300mm, the bottom bracket is 200mm from the bottom plate, and the vertical distance between the supports is 250mm. Cable brackets along the tunnel every 800mm set 1 pay, brick wall masonry, embedded screws fixed. Cable specifications for the main frame and each bracket depend on the number of cables carried. Cable shelf and main shelf are welded.
As a power-dedicated tunnel, it is generally necessary to set a long galvanized flat iron as a grounding for the cable tunnel, and it should be reliably connected with the cable support. A special grounding device is provided at the joint, the equipment well and the working well. At the same time, the drainage slope should be left in the tunnel to ensure the drainage is unobstructed and a water collection well is set up in a suitable place.
Of these types of cable laying, the economic conditions permit and ensure the smooth construction of the premise recommended cable tunnel laying. However, through concrete engineering practice, we often encounter some practical problems, that is, construction operations are subject to many limitations. Due to the relatively large operating area and long construction period, enormous pressure will be exerted on the urban traffic during the construction of urban areas. Cross-border issues with other municipal pipelines, especially in the old urban area, are densely covered and tunnel construction can easily bring about pressure to coordinate with multiple parties. Therefore, the power tunnel project is also a hot potato.
At this stage of our country's urban construction should learn from foreign years of mature urban construction experience, vigorously promote the tunnel underground underground pipe network construction. The tunnel-type underground pipe network is usually located below the urban traffic road. The cross-section resembles a multiplied cable tunnel. The pipelines can be installed and reserved on both sides of the tunnel. The middle road can be accessed through a large maintenance vehicle.
This is a systematic project. From the very beginning of urban planning, all needs must be considered clearly. It is an infrastructure that includes multiple departments and units and shares resources collectively. It is also an integrated underground facility that integrates functions of drainage, communications, electricity, heating and gas. The advantages of tunnel-type underground pipe network is obvious, the resources have been effectively integrated in a large tunnel space, to achieve a number of parallel functions.
Electricity As a beneficiary of the tunnel-type underground pipe network, the tunnel-type underground pipe network provides more extensive maintenance and repair access, and even maintenance vehicles can run smoothly, providing great convenience for overhauling and maintaining power facilities and shortening the length of conventional cables Laying the form of fault location, troubleshooting time, but also for the expansion of power engineering left a wide space, looking forward to the construction of tunnel-type underground pipe network can be increasingly tension for the contradiction between the route and urban congestion provide a perfect solution Program, but also open up a new world for the cable into the earth.
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