About "Lightning Protection Grounding System" "Lightning Protection Grounding System" is a system that must be set up in any engineering design. It can also be called the basic protection system of an engineering project. The relevant technical theory and practice have been relatively mature, and the relevant national regulations and standards should be strictly implemented during design. It is believed that the following two points should be noted in the specific design:
.1 For the "external lightning protection grounding system", the environmental conditions of the area in which the "design object" is located should be inquired and implemented before design, especially the "year thunderstorm day" statistics in meteorological conditions (most of the lightning days exceed 50 days) Distributed in China's low latitudes, high altitude areas - can be found in the relevant standard "accessories"), hydrogeology and environmental atmospheric corrosion conditions, components of the relevant devices of the lightning protection grounding system, metal components selection and grounding The technical conditions and quality of the body should be strictly controlled to ensure the safe, reliable and long-term effective operation of the system.
.2 For the "internal lightning protection grounding system", special attention should be paid to collecting the expected atmospheric overvoltage (current) parameters during the lightning occurrence in the area where the design object is located, and reasonable and strict selection at the correct position of the system. Reliable overvoltage (including "operating overvoltage") protection device. Attention should also be paid to the setting parameters of the upper and lower protection components. It should also be noted that when the overvoltage of the electrical system is operated with "surge protection components", the parameters between the protection devices and the above protection devices are used to avoid the failure of the system. The accident that should be.
The design of "main and local grounding system of electrical system" should be based on the design of lightning protection grounding system, and the over-voltage (flow) protection technical measures of conventional, safe, reliable, mature, long-life and adjustable control should be preferred. And equipment, such as overvoltage (flow), lightning arresters and other protection devices and grounding systems. When the low-voltage power distribution system does need to be equipped with a certain number of "surge protectors", it should be selectively configured in the main circuit power supply terminal that matches the main power distribution system or the power distribution system circuit of the large-scale power equipment. Special attention should be paid to the protection and cooperation of the upper and lower levels, the selection of qualified products with reliable quality, stable technical parameters and long service life. This is because the protection characteristics of the "surge protector" shaped products are generally non-adjustable and uncontrollable. There is still some uncertainty and difficulty in matching with the normal changes of the operating parameters of different electrical systems.
About the "common grounding system" The system grounding generation and application background is under the realistic conditions of the rapid development of modern technology, all kinds of new electronic information technology equipments are emerging and increasingly mature to the market, and the application range is wider and wider. How traditional protection grounding systems meet the safety grounding requirements of different voltage levels and different types (strong and weak) equipment and systems have encountered some new problems. In particular, the overvoltage (current) protection of low-voltage and low-voltage system special low-voltage electrical equipment is more stringent to the grounding system, and new requirements are also imposed on the electromagnetic shielding of the system equipment, the shielding protection of the radiation interference, and the system wiring. Obviously, the traditional lightning protection and its grounding system are difficult to adapt and cover the above protection requirements. Therefore, after continuous exploration, testing, testing, and practice, people put forward the theory of "common grounding system" and put it into practice.
I believe that there is no objection to this concept and system application, but there are several problems in actual engineering design that should be noted:
.1 Direct Strike Non-Protection Zone (LPZOA) Due to the absence of electromagnetic field attenuation, all types of objects may be subjected to direct lightning strikes, which are completely exposed and unprotected. Other building (structures) below the non-protection zone, overvoltage protection of different voltage grade electrical equipment systems and their grounding systems are in the LPZOB zone. In the LPZOB, although the electromagnetic field is not attenuated, due to the lightning strike protection device (including lightning rod, belt, net, down conductor and grounding device) at the LPZOA and the two-zone interface, there are few objects in the LPZOB area. Suffering from direct lightning strikes, it is a fully exposed direct lightning protection zone.
.2 Several issues to be aware of when using the "common grounding system".
The designer should make necessary environmental conditions and characteristics analysis for the engineering design object, for example, the geographical location of the project (latitude, altitude, address and landform, etc.), meteorological conditions (zoning of light, medium and heavy lightning disasters), engineering category (work, agriculture, business; towns, villages, etc.), the system configuration of electrical equipment and the level of automation equipment, especially for the lightning protection grounding protection in the LPzl-zn protection zone of buildings, it should be considered that the project is Factors such as the status and influence of the state and the national economy.
It has excellent environmental conditions and simple operating conditions (such as high latitude, light and lightning damage zone, flat area, simple internal equipment system and low level of automation), or independent construction of weak electrical system equipment. Buildings (such as independent communication stations, computer rooms, etc.) can use "common grounding system".
For the harsh environmental conditions and complex operating conditions (such as the location of low latitude, moderate damage and above, multiple mountainous areas, the construction of strong and weak internal equipment, the level of automation is high), the construction (structure should be carefully adopted) Grounding system", it is better to separate the grounding of the direct lightning protection system from other lightning protection grounding systems to prevent damage to electrical (especially weak) equipment systems caused by conductive waves, induced electric fields, strong electromagnetic radiation, etc. when lightning strikes occur. Accident. If a "common grounding system" is to be used, a capacity-compatible, reliable "gradient coupling" component must be installed between the direct lightning protection grounding device and other grounding devices. However, the coupling safety of this component is affected by many environments. The influence of the factors (such as parameter matching and selection, stability, aging degree, etc.) is quite difficult. In particular, the grounding system against direct lightning strikes is connected with the grounding common network of other systems, and potential hazards may be given full attention. The connection method of the equipotential bonding network of different voltage levels (especially weak current) and the "common grounding system" is directly connected. It is also necessary to install an adaptive "gradient-coupled" SPD component or to use a "suspended" (not directly grounded) scheme to ensure the safety of the system of the equipotential bonding network of the local weak current system. It should be carefully analyzed and selected. "Common grounding system", the connection conductor between each system grounding grid is difficult to install and materials, engineering quantity, and economic investment. Under the premise of meeting the technical requirements, the size of economic investment, how to make the design economical and Reasonable is an important factor that designers must consider. In short, designers should not use the "common grounding system" as a perfect "under the ground" when the geographical and meteorological environment of the design object is not fully investigated and analyzed. "The program looks at and chooses.
In engineering design, under the premise of ensuring the safe and reliable operation of the electrical system, it is necessary to establish a strong sense of technical and economic comparison, and it is necessary to establish a strong sense of technical and economic comparison, and neither adopt the "takenism" that should be applied at random or do it. The specific analysis is lightly carried out for engineering design. Can not forget, but should deeply understand the designer's responsibility for the design of the "lifelong responsibility system" and professional ethics.
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