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Highway lightning protection solution


I. Overview: 

       At present, the construction of expressways in China is developing rapidly. In order to make the expressway unimpeded, the highway communication, monitoring and toll collection systems are guaranteed to operate normally, and lightning disasters are reduced to a minimum. Lightning protection technicians should comprehensively plan, comprehensively manage and formulate the system. Complete integrated lightning protection design.

       System lightning protection is a comprehensive project, which mainly includes external lightning protection and internal lightning protection:

       External lightning protection includes: lightning rods, lightning protection belts, down conductors, grounding poles, etc. Its main function is to ensure that the building body is protected from direct lightning strikes, and lightning that may hit the building passes through lightning rods and lightning protection belts. Lead down the line, etc., and vent it to the ground.

       The internal lightning protection system is designed to protect the equipment inside the building as well as the safety of personnel. Mainly with space shielding, equipotential bonding, reducing proximity coupling, over-voltage protection and other measures, by installing a suitable lightning arrester at the front end of the protection equipment, that is, over-voltage protection, the equipment, the line and the ground form a conditional equipotential body. Blocking the possible lightning current, the lightning current induced by the internal facilities will be safely discharged into the ground due to lightning strikes.

       Highways, located in relatively open areas or mountainous areas, are prone to lightning strikes, resulting in equipment that cannot operate properly, and its importance is self-evident.

Second, the design basis:

    (1) IEC61024 "Building Lightning Protection"

    (2) IEC61312 "Protection of Lightning Electromagnetic Pulses"

    (3) ITU K25 "Lightning Protection for Optical Cables"

    (4) ITU K27 "Connection Structure and Grounding in Telecommunications Buildings"

    (5) GB50057-94 "Code for lightning protection design of buildings"

    (6) GB50174-93 "Design Specification for Electronic Computer Room"

    (7) GB50200-94 "Technical Specifications for Cable TV System Engineering"

    (8) GB50198-94 "Technical Specifications for Civil Closed Circuit Surveillance Television System"

    (9) GB/T50311-2000 "Code for Design of Integrated Wiring System for Buildings and Buildings"

    (10) YD5078-98 "Technical Specifications for Lightning Protection of Communication Engineering Power System"

Third, the design plan:

    1. External lightning protection:

       The expressway collection and toll station is located in an open area or mountainous area, belonging to the multi-mine area. As far as the building itself is concerned, whether it is a collection or toll station, its footprint is not small. According to the provisions of lightning protection regulations, combined with the importance of the highway information command center, according to the second type of lightning protection buildings. Design this project.

       The expressway collection and management office is a frame building. The command center engine room is located on the second floor. The top of the building is a flat roof. There is no lightning protection facilities such as lightning protection belts, and there are camera equipment on the roof. Although the toll station is a metal truss roof, the metal frame column supported by it is not grounded.

It can be seen from the above that the external lightning protection facilities are imperfect, and there are hidden dangers to the safety of the building itself and the equipment. For the external lightning protection imperfections of the above buildings, it is recommended to rectify as follows:

       a) External lightning protection and rectification measures for the office building of the expressway collection and management office:

On the second floor of the office building, a hot-dip galvanized round steel with a diameter of 10 mm is placed around the parapet wall, and is fixed to the daughter's wall with a support clip every 1 m. The support clip is L-shaped, with a diameter of 10cm hot-dip galvanized round steel, the length is 21cm, which is embedded in 砼 5cm, exposed on the daughter wall 10cm high, and the lightning-proof belt welding length is not less than 6cm (double-sided welding).

       In addition, when the lightning protection belt is laid along the parapet wall, hot-dip galvanized round steel with a diameter of 10mm is applied to each frame column position around the building (around the elliptical shape), and it is welded to the main ribs in the column of the building structure, each The average distance of the weld is no more than 18 meters. That is, the number of down conductors is not less than six. Four 1 meter long lightning rods are placed at the top corner of the building and connected to the lightning protection belt.

       b) External lightning protection measures for highway toll stations:

Since the toll booth is a metal frame structure, the building itself is a lightning receptor, but it is not grounded. The method is to excavate a 50cm*50cm hole in the surface of four outsourcing stainless steel pillars of the toll station, and weld one end of the hot-dip galvanized flat steel with a section of 50*5 to the metal frame column of the toll station, and the other end along the inner trench of the toll station and charge. The grounded flat steel in the pavilion (the grounding resistance value is detected as 1.5 ohms) is welded.

       2, internal lightning protection:

      ( 3-2-1 ) Power system lightning protection

According to the division of lightning protection and overvoltage specifications in IEC1312, the lightning protection for important systems should be divided into three zones and considered separately. Only one-level lightning protection may bring damage to the equipment caused by excessive residual voltage caused by excessive lightning current and damage to the equipment or insufficient protection capability. The multi-level protection of the power system protects against overvoltages at all levels from direct lightning strikes to industrial surges.

       The first level of power supply lightning protection:

       According to the relevant national regulations on low-voltage lightning protection, external metal lines must be buried in the metal pipe groove to enter the building more than 15 meters before entering the building, and a low-voltage arrester should be installed at the entrance end of the building. The main power supply lightning arrester at the low-voltage end must be installed at the inlet end of the power supply, and the high voltage of the lightning strike that may be introduced by the external circuit is led to the earth to ensure the safety of the subsequent equipment.

As the main-stage lightning protection device at the incoming end of the system power supply, there should be at least 60-100KA flow capacity in the lightning strike zone, which can limit the lightning strike voltage of tens of thousands or even hundreds of thousands of volts to several thousand volts. Parallel installation in the main power distribution cabinet of the office building or the low-voltage output of the distribution room.

specific measure: 

       并联 Install the B-level power supply lightning protection box in parallel at the low-voltage output end of the power distribution room of the expressway collection and control station, which is used for the first-level lightning protection primary protection of the power supply of the whole equipment. Or use TECHWIN power lightning protection module, installed in parallel in the low-voltage output of the power distribution room.

       ◇ At the total incoming line end of the three-way power supply at the toll station of the expressway, the power supply lightning protection module is installed in parallel for the lightning protection of the power supply of all electrical equipment in the toll plaza.

       Second-level power supply lightning protection:

       The power supply lightning arrester of the distribution cabinet further bleeds the lightning energy through the primary lightning arrester of the power supply, and can further limit the overvoltage of several kilovolts to one kilo kV, and the lightning-prone zone needs to have a flow of 40 kA. Capacity, lightning arresters can be installed in parallel at the distribution cabinet.

       specific measure: 

       ◇ In the power supply main line of the monitoring center office on the second floor of the expressway collection and control office, parallel installation of the power supply secondary lightning protection box for the second-level lightning protection of the equipment in the important office on the second floor of the collection and management office. Or use a power lightning protection module.

       ◇ At the single-phase power input end of each station of the expressway toll, parallel installation of the power supply secondary lightning protection box for the secondary lightning protection of all electrical equipment in the toll plaza. Or use a power lightning protection module.

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