At present, the construction of expressways in China is developing rapidly. In order to make highways unobstructed, to ensure the normal operation of expressway communication, monitoring, and toll systems, and to reduce lightning disasters to a lower limit, lightning protection engineers and technicians should conduct comprehensive planning, comprehensive management, Develop a comprehensive design for comprehensive lightning protection.
System lightning protection is a comprehensive project, which mainly includes two aspects: external lightning protection and internal lightning protection:
External lightning protection includes: lightning rods, lightning rods, down conductors, ground electrodes, etc. Its main function is to ensure that the building body is protected from direct lightning strikes. Lightning that may hit the building is passed through the lightning rod, lightning rod, Lead down the line, etc., and drain it into the ground.
The internal lightning protection system is provided to protect the equipment and personnel inside the building. The main measures are space shielding, equipotential bonding, reduction of close coupling, and over-voltage protection. By installing appropriate lightning arresters, that is, over-voltage protection, at the front end of the equipment to be protected, the equipment, lines, and ground form a conditional equipotential body. The possible incoming lightning current is blocked, and the lightning current induced by the internal facilities can be safely discharged into the ground due to the lightning strike.
Expressways, which are located in relatively open areas or mountain areas, are prone to lightning strikes and cause equipment to fail to operate properly. The importance is self-evident.
(1) IEC61024 "Lightning Protection for Buildings"
(2) IEC61312 "Protection against lightning electromagnetic pulses"
(3) ITU K25 "Lightning Protection for Optical Cables"
(4) ITU K27 "Connection structure and grounding in telecommunication buildings"
(5) GB50057-94 "Code for Lightning Protection Design of Buildings"
(6) GB50174-93 "Code for Design of Computer Room"
(7) GB50200-94 "Technical Specifications for Cable TV System Engineering"
(8) GB50198-94 "Engineering Technical Specifications for Civilian Closed Circuit Surveillance Television System"
(9) GB / T50311-2000 "Engineering Design Code for Integrated Wiring System of Buildings and Building Groups"
(10) YD5078-98 "Technical Specifications for Lightning Protection of Communication Engineering Power System"
The highway collection and management station and toll station are located in an open area or mountainous area and belong to the minefield area. As far as its buildings are concerned, whether it is a collection office or a toll station, the floor area is not small. According to the lightning protection regulations and the importance of the highway information command center, the buildings are classified as second-class lightning protection buildings. Design this project.
The highway collection and management office is a frame building. The command center computer room is located on the second floor. The roof is flat. There are no lightning protection facilities such as lightning protection belts. There is camera equipment on the roof. Although the toll station is a metal truss ceiling, the metal frame columns supported by it are not grounded. From the above, it can be seen that the external lightning protection facilities are incomplete, and there is a hidden danger that cannot be ignored for the safety of the building itself and the equipment. For the imperfect external lightning protection of the above buildings, the following rectifications are recommended:
On the top of the second floor of the office building, a hot-dip galvanized round steel with a diameter of 10 mm is laid around the daughter wall, and it is fixed to the daughter wall with support clips every 1 m. The support clip is L-shaped, using hot-dip galvanized round steel with a diameter of 10cm and a length of 21cm, which is embedded with 砼 5cm, exposed on the daughter's wall 10cm high, and the length of the welding with the lightning protection strip is not less than 6cm (using double-sided welding).
In addition, when the lightning protection belt is laid around the daughter wall, at the position of each frame column around the building (around the ellipse), a hot-dip galvanized round steel with a diameter of 10mm is used to weld it to the main reinforcement in the column of the building structure. The average distance between welds does not exceed 18 meters. That is, the number of down wires is not less than six. Four 1-meter lightning rods are installed at the four corners of the top of the building and connected to the lightning protection belt.
Because the toll station is a metal frame structure, the building itself is a lightning arrester, but it is not properly grounded. The method is to excavate a 50cm * 50cm opening on the surface of the four tolled stainless steel pillars of the toll station, weld one end of the hot-dip galvanized flat steel with a cross section of 50 * 5 to the metal frame column of the toll station, and the other end toll along the trench in the toll station The ground flat steel in the ditch inside the kiosk (whose ground resistance value was detected to be 1.5 ohms) was welded.
According to the division of lightning protection zones in the IEC1312 lightning protection and overvoltage specifications, lightning protection for important systems should be divided into three zones and considered separately. Doing only single-level lightning protection may result in damage to the equipment caused by excessive residual voltage after discharge due to excessive lightning current or damage to the equipment. The multi-level protection of the power system can prevent the over-voltage attack from various levels from direct lightning strikes to industrial surges.
According to the relevant national regulations on low-voltage lightning protection, external metal lines must be buried through metal pipe trenches at a distance of more than 15 meters before entering the building, and low-voltage lightning arresters must be installed at the line entry end of the building. It is necessary to install a low-voltage total power lightning arrester at the input end of the power supply to direct the high voltage of lightning strikes that may be introduced from external lines to the ground to release the ground to ensure the safety of the connected equipment.
As the main-level lightning arrester at the input end of the system power supply, it should have a flow capacity of at least 60-100KA in lightning-prone zones, which can limit the overvoltage of lightning strikes of tens of thousands or even hundreds of thousands of volts to thousands of volts. Installed in parallel in the main power distribution cabinet of the office building or at the low-voltage output end of the distribution room.
A set of Class B power supply lightning protection box is installed in parallel at the low-voltage output end of the power distribution room of the highway collection and management station, which is used for the primary protection of the first-level lightning protection of the power supply of the overall equipment of the collection and management station. Or use TECHWIN power lightning protection module, installed in parallel in the low-voltage output end of the power distribution room.
A set of power lightning protection modules is installed in parallel at the three-phase power main incoming end of the toll station of the expressway, which is used to protect the power supply of all electrical equipment in the toll plaza from lightning protection.
The power lightning arrester of the distribution cabinet further discharges the lightning energy passed through the primary lightning arrester of the power supply, which can further limit the overvoltage of several thousand volts to one to several thousand volts. The lightning-prone zone needs to have a current of 40KA Capacity, lightning arresters can be installed in parallel at the distribution cabinet.
At the main power line of the monitoring center office on the second floor of the highway collection and management office, a set of secondary lightning protection box for the power supply is installed in parallel for the second-level lightning protection of the power supply of the important office equipment on the second floor of the collection and management office. Or use a power lightning protection module.
A single-level power supply lightning protection box is installed in parallel at the single-phase power supply incoming end of each toll station on the expressway, which is used for the secondary lightning protection of the power supply of all electrical equipment in the toll plaza. Or use a power lightning protection module.