1 buried cable laying process
With the development of urban modernization, the overhead light lines of the street lamps have gradually turned into buried cable lines, and the technical requirements for the cable laying process have also been standardized. Generally, buried cable lines are divided into underground buried cables and cables are laid in pipes and trenches.
Regardless of the method of laying, the following technical requirements must be met.
1.1 Basic requirements for buried cables
The insulation resistance must be measured with a 500V megohmmeter before and after cable laying, generally not less than 10MΩ.
The cable core should be connected by a round sleeve. The bushing is generally divided into a copper bushing and an aluminum bushing. The copper core cable is crimped with a copper bushing. The copper bushing is made of a copper pipe containing more than 99.9% copper, the wall thickness is not less than 1 mm, and the length is the diameter of the casing. 8 ~ 10 times; aluminum core cable is crimped with aluminum sleeve, aluminum sleeve should be not less than 99.6%, wall thickness is not less than 1.2mm, length is also 8-10 times the diameter of the casing; if laying cable It is the connection of copper core and aluminum core cable. Copper-aluminum transition joint should be used, and the copper-aluminum transition joint needs to be annealed before crimping with the wire.
Hand hole wells or standard piles must be installed at the joints and corners of buried cable lines. For ease of maintenance and inspection, the spacing of hand hole wells should be less than 50m.
In cable trenches, hand-hole wells, and cables and intermediate connectors and terminal heads that enter the control box and power distribution cabinet, cable indicators that record cable specifications, model numbers, line names, or circuit numbers should be provided.
The middle or terminal end of the cable connection must be sealed and waterproof. Cutting the cable is not to damage the cable core insulation. The original record of the construction shall be provided for each cable line construction, including: cable type, specification, length, installation date, intermediate joint and terminal head number.
The advantage of this is that it can prevent the change and modification of the cable line, and facilitate the investigation and maintenance of the buried cable line.
Every time the buried cable line changes, the corresponding technical data and cable signs should be corrected in time to ensure the correctness of the line information.
1.2 Requirements for underground direct buried cable lines
The underground direct buried cable line shall be a braided cable. The buried depth of the cable shall be not less than 0.7 m from the ground to the cable sheath; the ground of the cable sheath to the underground building shall be 0.6 m, not less than 0.3 m; the distance between the cables shall be: the minimum is 0.1 m when the level is close, and the distance between the cables of different departments is 0.5. m; the minimum clearance is 0.5m when the cables cross each other; the net distance when the cable is close to the heat pipe, gas and oil pipeline is 2m, the clearance is 0.5m when crossing each other; the distance between the cable and the trunk of the tree is not less than 0.7m.
There shall be no other hard objects such as stones in the buried cable trench. Otherwise, 100mm thick soft soil or sand layer shall be laid. After the cable is laid, 100mm thick soft soil or sand layer shall be laid on the top, and then covered with concrete protection board. Or brick, the width of the cover should exceed 50mm on each side of the cable.
Straight buried cables shall be worn in the protective pipe when entering the hand hole, manhole, control box and power distribution room, and the pipe mouth shall be waterproof plug. When crossing urban roads, bridges, etc., the protection pipe shall be added. The depth from the top of the protection pipe to the road surface shall not be less than 0.7m, and the extension of the two ends of the protection pipe shall be not less than 0.5m. When the cable is led out from the ground, a section shall be added to the ground. For the protection pipe of 2.5m, the root of the pipe should extend into the ground 0.2m, and the protection pipe must be fixed firmly.
1.3 Requirements for laying cable lines in pipes and trenches
The masonry of the cable trench should be considered for segmental drainage. The bottom of the trench should have a good water-slope gradient. The cover of the trench is generally covered with a reinforced concrete cover. The cable trench that is often required to be opened indoors is generally covered with a steel cover. The entire cable trench should be equipped with a continuous grounding wire. The two ends of the grounding wire are connected to the grounding pole. The metal cable bracket must be connected to the grounding wire. The grounding wire can be made of 40×4 flat steel (minimum section is not less than 80mm2), and all metal components in the groove should be hot dip galvanized. When the cable is laid horizontally on the bracket, the terminal, the turn and both sides of the cable joint must be fixed. The horizontal spacing of the cable bracket is 0.8m and the vertical spacing is 1m.
The cable laid on the bridge should be padded with elastic material. The cable ends should be left at the ends of the bridge and the expansion joint to prevent the cable from being damaged due to structural expansion and contraction.
When the length of the cable protection tube is less than 30m, the inner diameter of the straight-line protection tube is not less than 1.5 times the outer diameter of the cable; there is not less than 2 times when there is one bend; and not less than 2.5 times when there are two bends. When the length of the cable protection tube is more than 30m, the inner diameter of the straight-line protection tube is not less than 2.5 times the outer diameter of the cable. When the cable is too long, a hand hole or a manhole should be provided.
The bending angle of the steel pipe laying is generally not less than 90°, and the bending radius is not less than 6 times the diameter of the steel pipe. When the condition permits, the diameter of the steel pipe can be 10 times, and when the pipe is laid only one bend, it can be 4 times. When the steel pipe is connected by the bundle, it must be firmly coated with anti-corrosion grease, and the steel pipe at both ends of the bundle must have a reliable electrical connection. The nozzle must be smooth, free of burrs, and clean inside the tube without impurities. When pre-buried, various types of protective pipe nozzles use corks to block the nozzles to prevent debris from entering the tubes. Wires are not allowed to have joints or scratches in the pipe. After the wires are passed through the pipe, they are wrapped with insulating cloth or plastic sleeves. It is strictly forbidden to wear wires of two different specifications in the same pipe.
1.4 Cable overhead laying requirements
Cable overhead laying is a different method than conventional cable laying. It is because of the special reasons such as other underground pipelines or municipal public facilities in the city. If the cable cannot be laid underground or the general overhead line is used, the cable can be laid overhead.
The section of the steel strand used for cable overhead shall be selected according to the span, load and mechanical strength of the cable line. The minimum section shall not be less than 10 mm2, and the strand and cable fixture shall be hot-dip galvanized. The distance between the fixed points of the cable on the steel strand shall be less than 0.75m; the spacing of the fixed points of the control cable shall be less than 0.6m.
When the cable line is laid overhead, the clear distance from the heat pipe should be greater than 1m; when the net distance is less than or equal to 1m, the insulation should be used. The clearance between the cable and the non-heat pipe shall be greater than 0.5m. When the clearance is less than or equal to 0.5m, it shall be taken on the cable segment that is close to the pipe or extends outward from the two ends of the segment not less than 0.5m. The cable is subject to mechanical damage.
When the overhead cable is led down from the pole into the ground, a 2.5m long protective pipe is applied to the ground and fixed firmly. The root of the protective pipe should extend into the ground 0.2m.
2 choose the ideal anti-theft device
With the increasing scope of urban lighting, the management of urban lighting facilities has become more and more prominent. What is more serious is the frequent theft or damage of lighting equipment and lighting cables, which can not brighten the street lights. This not only affects the city's landscape and traffic, but also provides a favorable environment for criminals to commit crimes and brings a series of law and order to the society. problem.
2.1 The ideal cable anti-theft alarm scheme should meet the following conditions
The ideal cable anti-theft alarm scheme should be required at the end of the anti-theft alarm scheme during the light-off period without any form of power supply; the anti-theft alarm scheme during the light-on period should be independent of the line status (ie line length, lamp type); The alarm scheme should be independent of the power supply status (ie transformer power supply mode or public power supply mode); the end equipment and the front box equipment of the control box should have various protection measures such as surge protection; the anti-theft alarm system should have multiple redundant means to prevent virtual The alarm occurs; as far as possible, the front-end multi-channel alarm mode of the control box is used, that is, multiple lines are connected by a main control device to the central control room through a radio or other communication equipment, which is a low input cost method.
2.2 ideal anti-theft device
In view of the serious phenomenon of street lamp being stolen. The author suggests to use the WJ1090 series street lamp cable anti-theft alarm device developed by Suzhou Urban Lighting Management Office and the 50th Research Institute of China Electronics Technology Group Corporation. The device can realize real-time remote monitoring through the street lamp wireless monitoring system, and can find the cable disconnection situation at the first time and perform corresponding processing.
WJ1090 series street lamp cable anti-theft alarm device is mainly divided into two parts. The line detection centralized unit is installed in the street lamp meter control box, and the signal sending unit is installed in the terminal light pole. In this way, the 24-hour disconnection alarm function can be realized from the street lamp control box to the entire end of the cable.
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