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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Section 2. Sewerage of electricity Cable lines up to 220 kV. Cable selection
Encyclopedia of radio electronics and electrical engineering / Rules for the installation of electrical installations (PUE) 2.3.35. For cable lines laid along routes passing in various soils and environmental conditions, the choice of cable designs and sections should be made for the section with the most severe conditions, if the length of the sections with lighter conditions does not exceed the construction length of the cable. With a significant length of individual sections of the route with different laying conditions, appropriate designs and cable sections should be selected for each of them. 2.3.36. For cable lines laid along routes with different cooling conditions, the cable sections should be selected along the section of the route with the worst cooling conditions, if its length is more than 10 m. It is allowed for cable lines up to 10 kV, with the exception of submarine ones, the use of cables of different sections, but not more than three, provided that the length of the smallest segment is not less than 20 m (see also 2.3.70). 2.3.37. For cable lines laid in the ground or water, armored cables should be used predominantly. The metal sheaths of these cables must have an outer jacket to protect them from chemical attack. Cables with other designs of external protective coatings (unarmoured) must have the necessary resistance to mechanical stress when laying in all types of soil, when pulled in blocks and pipes, as well as resistance to thermal and mechanical stress during maintenance and repair work. 2.3.38. Pipelines of high-pressure oil-filled cable lines laid in earth or water must be protected against corrosion in accordance with the design. 2.3.39. In cable structures and industrial premises, if there is no danger of mechanical damage in operation, it is recommended to lay unarmored cables, and if there is a danger of mechanical damage in operation, armored cables or their protection from mechanical damage should be used. Outside cable structures, it is allowed to lay unarmored cables at an inaccessible height (at least 2 m); at a lower height, the laying of unarmored cables is allowed provided that they are protected from mechanical damage (boxes, angle steel, pipes, etc.). For mixed laying (ground - cable structure or industrial premises), it is recommended to use the same brands of cables as for laying in the ground (see 2.3.37), but without combustible outer protective covers. 2.3.40. When laying cable lines in cable structures, as well as in industrial premises, armored cables should not have protective covers made of combustible materials over the armor, and unarmored cables over metal sheaths. For open laying, it is not allowed to use power and control cables with combustible polyethylene insulation. Metal sheaths of cables and metal surfaces on which they are laid must be protected with a non-combustible anti-corrosion coating. When laying in rooms with an aggressive environment, cables resistant to this environment must be used. 2.3.41. For cable lines of power plants, switchgears and substations specified in 2.3.76, it is recommended to use cables armored with steel tape protected by a non-combustible coating. At power plants, the use of cables with combustible polyethylene insulation is not allowed. 2.3.42. For cable lines laid in cable blocks and pipes, as a rule, unarmoured cables in a lead reinforced sheath should be used. In sections of blocks and pipes, as well as branches from them up to 50 m long, it is allowed to lay armored cables in a lead or aluminum sheath without an outer cover of cable yarn. For cable lines laid in pipes, it is allowed to use cables in a plastic or rubber sheath. 2.3.43. For laying in soils containing substances that are destructive to cable sheaths (salt marshes, swamps, bulk soil with slag and building material, etc.), as well as in areas hazardous due to electrical corrosion, cables with lead sheaths should be used and reinforced protective covers of types Bl, B2l or cables with aluminum sheaths and especially reinforced protective covers of types Bv, Bp (in a continuous moisture-resistant plastic hose). 2.3.44. In places where cable lines cross swamps, cables should be selected taking into account geological conditions, as well as chemical and mechanical influences. 2.3.45. For laying in soils subject to displacement, cables with wire armor should be used or measures should be taken to eliminate the forces acting on the cable during soil displacement (reinforcement of the soil with sheet piles or pile rows, etc.). 2.3.46. In places where cable lines cross streams, their floodplains and ditches, the same cables should be used as for laying in the ground (see also 2.3.99). 2.3.47. For cable lines laid on railway bridges, as well as on other bridges with heavy traffic, it is recommended to use armored cables in an aluminum sheath. 2.3.48. For cable lines of mobile mechanisms, flexible cables with rubber or other similar insulation that can withstand multiple bends should be used (see also 1.7.11). 2.3.49. For submarine cable lines, cables with round wire armor should be used, if possible of the same construction length. For this purpose, the use of single-core cables is permitted. In places where cable lines cross from the shore to the sea in the presence of strong sea surf, when laying the cable in sections of rivers with strong currents and eroded banks, as well as at great depths (up to 40-60 m), a cable with double metal armor should be used. Cables with rubber insulation in a PVC sheath, as well as cables in an aluminum sheath without special waterproof coatings for laying in water are not allowed. When laying cable lines through small non-navigable and non-alloyable rivers with a width (together with a floodplain) of no more than 100 m, with a stable channel and bottom, it is allowed to use cables with tape armor. 2.3.50. For oil-filled cable lines with a voltage of 110-220 kV, the type and design of the cables are determined by the project. 2.3.51. When laying cable lines up to 35 kV on vertical and inclined sections of the route with a level difference exceeding the allowable according to GOST for cables with viscous impregnation, cables with non-draining impregnating mass, cables with depleted impregnated paper insulation and cables with rubber or plastic insulation should be used. For the specified conditions, cables with viscous impregnation can only be used with locking sleeves located along the route, in accordance with the permissible level differences for these cables in accordance with GOST. The difference in vertical marks between the stop sleeves of low-pressure oil-filled cable lines is determined by the relevant technical conditions for the cable and the calculation of make-up at extreme thermal conditions. 2.3.52. Four-wire networks must use four-wire cables. Laying of zero conductors separately from phase conductors is not allowed. It is allowed to use three-core power cables in an aluminum sheath with a voltage of up to 1 kV using their sheath as a neutral wire (fourth core) in four-wire AC networks (lighting, power and mixed) with a solidly grounded neutral, with the exception of installations with an explosive environment and installations in which, under normal operating conditions, the current in the neutral wire is more than 75% of the permissible continuous current of the phase wire. The use of lead sheaths of three-core power cables for this purpose is allowed only in reconstructed urban electrical networks 220/127 and 380/220 V. 2.3.53. For cable lines up to 35 kV, it is allowed to use single-core cables if this leads to significant savings in copper or aluminum in comparison with three-core ones, or if it is not possible to use a cable of the required construction length. The cross section of these cables must be selected taking into account their additional heating by currents induced in the sheaths. Measures must also be taken to ensure equal distribution of current between cables connected in parallel and safe contact with their sheaths, to exclude heating of metal parts located in the immediate vicinity and to securely fasten the cables in insulating clamps.
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