Discussion on the Status Quo of Modern Expressway Communication Electromechanical System and Building Construction

The communication, monitoring, charging and ventilation lighting system of the expressway is a powerful electrical and electronic system, referred to as the highway electromechanical system. Due to the wide area, long distance and complex terrain, the expressway is extremely vulnerable to lightning interference. Fujian is a region with frequent lightning and lightning. Every year, many lightning strikes occur in the highway electromechanical system. For example, the highway tolls in Xiamen was hit by a lightning strike on June 30, 2002, resulting in almost a toll system and 8 types of damaged equipment, with a cumulative amount of more than 200,000 yuan. During the construction, maintenance and repair of the highway electromechanical system, we were deeply affected by the disaster caused by lightning and deeply felt the importance of highway lightning protection. This paper puts forward some key points in the design, construction, supervision, operation and maintenance of lightning protection engineering of expressway electromechanical system from the existing problems of lightning protection engineering of expressway electromechanical system. Put forward the main points of technical standardization;

First, the highway bidding stage is generally not paying enough attention to lightning protection, the indicators are not clear

The highway system is very extensive and is a very complicated system engineering. It has road engineering such as roadbed, road surface and tunnel, as well as a large number of housing construction projects such as control center and service area. The electromechanical system includes monitoring system and toll collection system. Communication systems, power and lighting systems, and tunnel ventilation systems. The housing construction, roadbed pavement, and electromechanical systems usually adopt sub-project bidding methods. The proportion of lightning protection projects in highway systems is often small, and sometimes it is difficult to separate them from each system. Due to the late start of China's expressway construction, the state has not yet formulated relevant lightning protection regulations for the construction of expressways. In the construction of expressway projects, although most bidding documents have put forward lightning protection requirements for building and communication, monitoring, charging and other electromechanical projects, but the requirements are usually not clear, and there are no specific technical indicators, so the bid unit response Incomplete, lightning protection design is generally independent, protective measures are generally imperfect, and lack of systemicity. Sometimes there are more than ten different manufacturers' products in a toll station or machine room, only lightning protection devices, lightning protection comprehensive and systematic The requirements are poor. In addition, there are no clear requirements for lightning protection measures such as grounding system, machine room and metal pipeline shielding, equipotential bonding, etc. In particular, various metal pipelines are usually laid for housing construction projects, and are generally not electrically connected throughout the line, at least grounded at both ends. The technical requirements require construction, and once the building is completed and the road is completed, these basic lightning protection measures are difficult to achieve. In addition, many design and construction units have a strong understanding of lightning protection in the lightning strikes of buildings and the protection of high-voltage equipment. There is not enough understanding of the damage caused by lightning electromagnetic pulses to weak current systems. There are many misunderstandings, especially for highways. There are still many weak links in the lightning protection of electromechanical projects.

Second, the highway building and electrical and mechanical systems lightning protection lacks unified planning and comprehensive design

At present, in the expressway system, the strong and weak electricity systems such as housing construction, roadbed pavement, lighting, monitoring, communication, and tolling are completed by many design and construction units. The lightning protection of building construction and the lightning protection of electromechanical systems are generally out of touch in design requirements. Phenomenon, lack of unified planning and design, scientific and rational comprehensive design.

Expressway lightning protection is a complex comprehensive protection project, which includes direct lightning protection for buildings (structures), comprehensive lightning protection for high-voltage systems and various weak current systems, ie equipotential bonding measures, shielding measures, standardized integrated wiring measures, Design and installation of SPD, perfect and reasonable common grounding system and other six parts. Therefore, as a system engineering, lightning protection can only achieve the protective effect by combining the overall planning of the expressway, design and construction at the same time.

Taking the grounding system as an example, no matter what kind of lightning protection measures are used, it is necessary to discharge the lightning current energy into the ground. Therefore, grounding has always been the focus and difficulty of lightning protection. In order to prevent ground potential counterattack, the potential difference of each point in the grounding network is reduced. To achieve the equalization potential of the grounding grid, the grounding device not only needs the grounding electrical yang value as small as possible, so as to improve the bleed capacity of the lightning current, and needs a good shape structure. The shape and structure size of the grounding device tends to be larger than the grounding resistance. The value is more important. For example, the grounding system of the highway toll station should use all the basic steel bars of the office building, power distribution room and toll island as the natural grounding system and form an organic whole, which is convenient for the lightning current to enter the ground and evenly spread in the ground network to balance the ground potential and avoid Ground potential counterattacks and reduces potential differences at ground points. A grounding system with excellent performance must be designed and synchronized with the construction of the building and the roadbed. Otherwise, once the building and road construction is completed, it will be difficult to implement. It is impossible to do so. One of the reasons why the mechanical and electrical equipment of highway toll stations is damaged by lightning is that the grounding system is unreasonable, and it is still difficult to rectify.

Third, lightning protection engineering design, construction and supervision personnel lack professional lightning protection knowledge and experience

Due to the large amount of highway construction projects, the construction period is tight and the construction is difficult. Most of the electromechanical system design and construction units have no professional lightning protection engineering design and construction qualification. The design, construction and supervision personnel generally lack the necessary lightning protection knowledge and design and construction experience. The division and function of the lightning protection zone, the joint grounding system and the equipotential bonding There is a lack of systematic understanding of various shielding measures, characteristics and functions of various types of surge protectors, installation locations and installation methods. As a result, lightning protection projects, whether it is lightning protection design, construction plans and construction requirements, generally do not meet the corresponding technical requirements. There are mainly the following problems:

â—†The grounding system setting does not meet the specification requirements.

In the past few years, there have been many grounding systems for highways to prevent lightning strikes, grounding, signal grounding, and safety grounding. Due to the large number of various metal pipelines laid on the highway electromechanical system, it is difficult to achieve a safe distance between the ground grids. In fact, some ground grids are only a few centimeters apart. Some ground grids are separated, but the grounding trunks are close together in the same trench or cable well, which can easily cause ground potential counterattack.

â—† Outdoor laying of metal cables without shielding measures

Some outdoor laying (sometimes up to several hundred meters) power supply lines, signal lines and control lines are laid underground without metal pipes, or are not grounded at the entrance of the building and at both ends of the metal pipe.

â—†The setting of surge protector is not scientific or comprehensive

There are many kinds of power supply lines and communication control signal lines for expressway electromechanical systems. The surge protector should select the corresponding surge protector according to the signal characteristics and physical location. However, the surge protector in the electromechanical system of the expressway is unreasonable or Mismatch, lack of overall concept, sometimes a toll station, monitoring room installed with more than ten different types of surge protectors (SPD). Even some signal surge protectors have been installed to affect the normal operation of the system.

â—† Surge protector assembly problem

The installation of surge protectors is generally the case where the connecting wires at both ends are too long, too thin and entangled. When subjected to lightning strikes, the inductance of the wire itself cannot be ignored. This inductance prevents large current, high-frequency lightning current from entering the ground, and causes overvoltage, and the inductance of the wire and its material, wire diameter, length, Regarding the degree of curvature, etc., in the case of the same material and bending degree, the smaller the length diameter, the smaller the inductance. Therefore, the surge protector connection wire should be straight and should not exceed 50cm.

â—† equipment grounding, equipotential problems, especially the problem of toll stations

Most of the lane weighing machine control cabinets, fee display, lane camera poles and guard rails are not grounded. The power lines, signal lines, and control lines laid in the toll islands are not metal piped or grounded or equipotentially treated.

â—†The highway lightning protection device lacks regular inspection and inspection and disaster investigation and analysis system.

In order to ensure the normal operation of the lightning protection device and prevent personal injury and equipment damage accidents caused by the failure of the lightning protection device, the relevant regulations and regulations clearly stipulate that the lightning protection device should perform regular safety inspection and system maintenance, and check and check the general items once a year. The key system or part should be inspected after each lightning strike and rectified in time. At present, some highways have not yet established a regular inspection and inspection system, and the lightning protection hazards found in the inspections cannot be rectified in time, causing repeated lightning disasters.

Conclusion

In short, highway lightning protection project is a very complicated system engineering, in addition to the above aspects should be noted, in the actual engineering design and construction process, optimization of lightning protection structure, determination of technical parameters, lightning protection product selection Type, construction material selection, construction technology, lightning arrester installation skills, etc. are worthy of our in-depth research and discussion, but also should be adapted to local conditions, combined with the actual situation, meticulous design of the corresponding lightning protection program, and strive to obtain prevention Lei Engineering has low investment, comprehensive protection, reasonable configuration, excellent performance and convenient maintenance. The entire highway electromechanical system is stable and reliable.