The ordering length of cables should meet the following requirements: 1. For long distance cable lines, the calculated length should be taken as the ordering length. For single core cables above 35kV, it shall be calculated by phase; When the lines are connected in sections such as cross interconnection, they shall be listed by sections.
When two pairs of 35kV and below cables are used for non long distance, it is advisable to take into account the factor that the remaining section of the whole cable can not be used after interception, and include 5%~10% allowance according to the calculated length as the ordering length of cables of the same model and specification.
3 The length of each reel of underwater cable shall not be less than the laying length of underwater section. In case of difficulties, factory made flexible joints can be included.
Selection of laying method
Selection of cable laying mode, such as New energy cable The laying shall be selected according to engineering conditions, environmental characteristics, cable type, quantity and other factors, as well as the principle of reliable operation, easy maintenance and reasonable technology and economy.
The selection of directly buried cable laying mode shall meet the following requirements:
1 35kV and below with less than 6 pieces of the same channel power cable Direct burial should be adopted in areas where frequent excavation is not easy, such as the plant area leading to remote auxiliary facilities or suburban areas; Direct burial can also be used when it is easy to repair under the urban sidewalk or at the edge of the road.
2 In the plant area where there are many underground pipe networks, where molten metal and high-temperature liquid may overflow, and where there is frequent excavation to be developed, direct burial is not suitable.
3 Direct burial is not allowed in the soil area where chemical corrosion or stray current corrosion occurs.
The selection of cable threading and laying method shall meet the following requirements:
1 Cables laid in open places with explosion hazards, cables exposed to the ground that need to be protected, and underground cables crossing roads and railways shall be threaded.
2 For the sections where underground cables pass through houses and squares, as well as the sections where cables will be laid as roads in the planning, pipes should be used.
3 When there are many cables in the factory area with dense underground pipe network, narrow urban roads and passages with heavy traffic or difficult road excavation, pipe threading can be used.
Shallow trench laying should be adopted in the following places:
1 Where the groundwater level is high.
2. The number of power cables in the channel is small, and in places such as outdoor power distribution devices where there are few trucks passing.
The selection of cable trench laying method shall comply with the following provisions:
1 Cable trenches shall not be used in places where chemical corrosive liquids or high-temperature molten metals overflow, or where heavy vehicles frequently pass by.
2 Cable trench shall not be used in the plant where industrial water often overflows and combustible dust is diffused.
3. There are many underground cables in the plant area and buildings, but no tunnel is needed. It is inconvenient to excavate the sidewalk in cities and towns, and the cables need to be laid by stages. At the same time, when the above situations do not exist, cable trenches should be used.
4 For exposed cables with explosion-proof and fireproof requirements, buried sand cable trench shall be used.
The selection of cable tunnel laying mode shall meet the following requirements:
1 If there are many underground cables in the same channel and the cable trench is insufficient to accommodate them, tunnels should be used.
2 If there are many underground cables in the same channel, and they are located in places with corrosive liquids or frequent overflow of ground water, or contain high-voltage cables above 35kV, and cross roads, railways and other sections, tunnels should be used.
3 Under roads with limited urban underground passage conditions or large traffic flow, when there are non high-temperature water, gas and communication cable pipelines along the same path with many cables, cables can be laid in public tunnels.
Cables in vertical direction should be laid along walls and columns; When there are many or more high-voltage cables above 35kV, the shaft shall be used. Cable interlayer should be set at the lower part of control room, relay protection room, etc., where there are many cables. When the number of cables is small, the cable layer with movable cover plate can also be used. In places with high groundwater level and chemical corrosion liquid overflow, supporting overhead laying shall be adopted in the plant. When it is not suitable to lay power cables underground in buildings or plant areas, overhead laying can be adopted.
