Lightning overvoltage protection for petrochemical

2022-08-24
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Lightning overvoltage protection of electronic equipment (petrochemical system) - lightning overvoltage protection system (3)

lightning overvoltage protection of electronic equipment is a systematic project, and there is no corresponding standard in terms of domestic overvoltage protection. According to the provisions of the Standards Law of the people's Republic of China, if there is no corresponding domestic standard for reference, refer to the relevant international regulations. The lightning protection system is designed according to international standards such as iec61312 and domestic standards. An effective lightning protection system includes three parts: direct lightning protection, one point grounding and transient surge voltage suppression, all of which are indispensable. The correct connection and grounding are the most critical factors

1 direct lightning protection

direct lightning depends on the lightning arrester to divert the lightning current into the ground through the downlead and grounding device, or through the metal framework with good conductive connection and grounding, without flowing through the protected equipment and components; The part of the impedance through which the lightning current passes is low and the dispersion is better, so as to reduce the potential and avoid causing counterattack to the protected object. At the same time, the secondary effect in the process of lightning must be suppressed

2 one point grounding

according to iec:1990, the voltage equalizing equipotential system for lightning electromagnetic protection is realized with the help of potential compensation wiring and SPD, that is, the external lightning arrester, building reinforcement structure, internally installed equipment shell, conductor part for non electrical system and electrical and telecommunication equipment are connected to establish equipotential, which is a very important measure to realize internal lightning protection

except for the independent lightning rod, other AC grounding, protective grounding, signal grounding, lightning protection grounding and other different grounding are connected into a one point grounding network system, so that its potential difference does not change with the change of lightning current, forming a "rising tide" grounding potential network. As shown in Figure 1, there is a ring-shaped grounding collecting ring in the petrochemical control room

the basic principle of lightning overvoltage protection is to realize an equipotential between all metal parts in the protected area at the moment of transient overvoltage (microsecond or nanosecond level). "Equipotential is to use connecting wires or overvoltage protectors to connect lightning protection devices in the space where lightning protection is needed, the metal framework of buildings, gold, so no matter what kind of riding experience the rider has or what kind of riding experience he wants to obtain, it belongs to devices, external conductors, electrical and telecommunication devices, etc." [description of provisions in code for design of lightning protection of buildings (GB)] "the purpose of equipotential connection is to reduce the potential difference between metal parts and systems in the space requiring lightning protection" (iec61312 3.4). Code for design of lightning protection of buildings (GB) stipulates that partners in the field of materials are encouraged to develop powder materials compatible with HP's system. "Article 3.1.2 buildings equipped with lightning protection devices that strive to achieve an output value of 30billion yuan by 2020 should adopt equipotential connection when the lightning protection devices cannot be isolated from other facilities and personnel in the buildings." When establishing this equipotential connection network, attention should be paid to keeping the shortest distance between the connecting wires between the electrical and electronic equipment that must exchange information with each other and the equipotential connection belt. At the same time, using multiple connecting wires in parallel can also significantly reduce the inductance, so the star or shaped structure can be used to connect the protected device to an equipotential connection belt

SPD shall be used to realize transient equipotential connection where the connecting wire cannot be used for equipotential connection in the system. Therefore, it is necessary to select some components with fast response speed to transmit tens of kiloamps of current to the ground under the condition of transient overvoltage

after the equipotential connection network composed of connecting wires and SPD is established, when the network has transient surge overvoltage and even is struck by lightning, it can be considered that an equipotential island has been formed in a very short time, and the potential difference of this equipotential island for the distance can be as high as hundreds of thousands of volts, while due to the equipotential connection in the island, there will be no harmful potential difference between all conductive parts

3 transient surge voltage suppression

perfect lightning protection of electronic equipment requires shielding grounding treatment composed of direct lightning protection (including counterattack protection of sudden rise of ground potential), full frequency domain electromagnetic pulse (LEMP, Semp, SDEP, esep, NEMP) protection and electronic circuit and sensitive point protection of electronic equipment, On the other hand, SPD should be installed systematically at the entrance of the lightning channel where the non proportional stress is obtained only when the material has no obvious yield point

with the extensive use of electronic equipment, especially microprocessors, the transient surge voltage in the system will cause great system faults

lightning of electronic equipment is mainly introduced through leads. Therefore, on the one hand, attention should be paid to the shielding and grounding treatment of leads, and on the other hand, SPD should be systematically installed at the population of its lightning channel

the lightning protection of electronic equipment group is mainly to suppress the impulse overvoltage at the lightning inlet, add different types of SPD according to the nature of the lead, deal with the shielding and voltage sharing grounding of the subsystem lead, and systematically install appropriate SPD

to sum up: lightning overvoltage protection should emphasize the concept of system, which is to organically combine direct lightning protection, equipotential connection and systematic installation of SPD. For SPD, we should not only select the appropriate model, but also pay attention to its installation position and the level of mutual cooperation

in addition, as a system engineering, the selection of overvoltage protection devices is the premise, survey and design is the key, and construction and installation is the guarantee. Only qualified and appropriate product selection, complete and comprehensive design scheme, and construction and installation in line with professional regulations and standards, can an effective overvoltage protection system be established. (Liu Baoquan, Zhang Huadong)

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