Grounding design of electronic workshop

With the development of electronic technology, electronic products are increasingly used in various fields of production and life. Correspondingly, the construction of electronic production plants is increasing day by day. The grounding technology is more diverse than conventional building grounding, and involves a wide range of areas.　　 This article takes the design of an electronic storage product production plant as an example to discuss the grounding of the electronic plant. Many of the production equipment in the plant are microelectronic equipment. These equipment are characterized by low working signal voltage (usually only about 10 volts), poor anti-interference ability, and high requirements for anti-static. There is an IT information center and network in the workshop. Production management, so grounding plays an important role in this project. The grounding system can be divided into power system grounding, electrical protective grounding, anti-static grounding, information system grounding, electronic equipment grounding, and lightning protection grounding according to the specific purpose. 1. Grounding of the power supply system: The project consists of two three-story main factory buildings, office buildings, canteens and other auxiliary buildings. Although the building area is tens of thousands of square meters, the building group is relatively concentrated, so TN-S is given priority in the design system. The neutral point of the transformer is grounded, and the protection line of the system is completely separated from the neutral line. This method is very beneficial to power supply, protection, and economic rationality. The selection principle is the same as that of conventional buildings, so I won't repeat it here. For sporadic buildings that are far away from the main building at the same distance as the communication room, use a five-core power cable with PE wire for power supply. Buildings with a distance of more than 50 meters must be grounded repeatedly in accordance with the requirements of the code.　　 2. When the TN-S system is used for the electrical protection grounding, the uncharged metal exposed part of the electrical equipment is directly electrically connected to the grounding point of the power grid. When the live phase wire touches the equipment casing due to insulation damage, the equipment casing constitutes a single-phase short circuit of the fault with respect to the ground wire. Utilize a large short-circuit current to make the protective devices on the line (such as fuse, low-voltage circuit breaker, etc.) act quickly to cut off the circuit, thereby eliminating the risk of personal electric shock. In the electronics production plant, the production line is densely equipped, and most of them are electrical equipment with metal casings. If the protective grounding is not in place or does not meet the requirements, in the event of a ground fault, it is easy to cause electric shock hazards for workers. Therefore, the problem of protective grounding cannot be ignored. Whether in the design process or the construction process, the protective grounding should be put in place. The objects that should be protected and grounded mainly include: metal frames or enclosures of transformers, high-voltage switch cabinets, power distribution cabinets, control panels, etc.; metal enclosures of fixed, portable and mobile electrical appliances; metal protective pipes or power lines Cable tray, junction box shell, armored cable sheath, etc. The protective ground connection wire can be flat steel or copper wire, which requires a reliable electrical path. Equipotential bonding is an indispensable work in the electrical design of various buildings. Equipotential bonding has two types: total equipotential bonding and local equipotential bonding. The so-called total equipotential connection is to connect the PE trunk line, grounding dry connection, main water pipe, main gas pipe, heating and air conditioning riser, etc., at the power entrance of the building, so that the above parts are at the same potential. The total equipotential connection is a building or electrical device that must be set up in a building or electrical device that uses measures to cut off the faulty circuit to prevent personal shock. The so-called local equipotential connection is to make the same connection of the above-mentioned pipeline components again within a certain local range, which is used as a supplement to the total equipotential connection to further improve the safety level of electricity. In the electronic workshop, the potentials of all parts are equal, which can ensure that no counter voltage is generated in the building, and at the same time can reduce the interference caused by the lightning electromagnetic pulse.　　 3. Anti-static grounding:> Static electricity is mainly generated by the friction of different substances. In the production process of electronic workshops, the harm caused by static electricity is manifold. First of all, many equipment and instruments in this project are sensitive to electrostatic voltage, and static electricity will affect their normal operation and even make mistakes. Secondly, the high voltage generated by static electricity will cause personal electric shock. In addition, when the static electricity is serious, it may cause spark discharge. Serious fire accidents will result.　　 In order to eliminate the harm caused by static electricity, measures must be taken. There are many ways to eliminate static electricity, but the simplest and most effective way is to take grounding measures. In this electronic production plant, all equipment that generates static electricity should be reliably grounded. In order to prevent the static charge accumulated on the equipment and people from reaching dangerous potential, an anti-static floor is used in the main production occasions. The protective materials of this kind of floor are distributed with a network of copper wires. These metal networks form an electrical path with each other for the conduction of static electricity on the anti-static floor. As an electrical design coordination, appropriate grounding terminals should be reserved on the building column in the space where the anti-static floor is located. After the floor is laid, connect the metal wire in the anti-static floor to the ground terminal. In addition, the grounding terminal must be connected to the grounding electrode through the main rib in the column, so that static electricity flows to the grounding electrode along the main rib in the column through the grounding terminal. 4. Grounding of the information system. This project is equipped with a comprehensive wiring system and an IT information center in the office building. And there are IT management rooms in the auxiliary rooms of each plant, and information points are all over the workshops and offices for future production monitoring and management. In addition, this project is equipped with an automatic fire alarm system. This involves the grounding of the information system.　　 According to the relevant provisions of the "Building Lightning Protection Design Code", in the design of the information system grounding of this project, an S-type equipotential connection network is adopted. Set a ground reference point in the places where information equipment is more concentrated, such as the central computer room, weak current shaft, etc. This reference point is connected to the common grounding system of the building, and all metal components of the information system, such as various boxes, shells, and racks Connect with the reference point through the equipotential connecting line. When all lines and cables between the equipment are unshielded, they should radiate parallel to the equipotential connecting lines in a star structure to avoid induction loops.　　 5. Grounding of electronic equipment 　　 There are some industrial electronic equipment used for testing in the production plant. The grounding of electronic equipment is not mainly for personal safety, but for the accuracy of equipment work. Because high-frequency voltage is not harmful to the human body, and even if the shell of the electronic device is not grounded and insulated from the ground, the device shell forms a capacitance with the ground. As the frequency increases, the reactance value of the capacitor will decrease. When the frequency reaches a certain level When it is a value, it is equal to grounding. However, in order to reduce the influence of stray current on the meter reading, it is best to use a short and thick wire to connect to the ground. Generally, a copper wire of 6 square millimeters is used to connect to a special grounding busbar set near the equipment, and then to the ground. The main grounding trunk is connected. The grounding resistance must not exceed 10 ohms. For individual equipment, if the product manual has special requirements for grounding resistance, ground it according to the requirements.　　 6. Lightning protection grounding 　　 For general buildings, after lightning protection measures are taken, the probability of lightning damage caused by direct lightning and lightning wave intrusion can be greatly reduced. For general electrical equipment, the allowable lightning pulse is relatively high, so it is extremely effective to take measures such as lightning rods and lightning protection nets to prevent direct lightning strikes. However, microelectronic equipment is very sensitive and has a low withstand voltage level, generally only about 10V. It is extremely sensitive to lightning electromagnetic pulses and is susceptible to electromagnetic interference and damage. Lightning electromagnetic pulses are generated by electromagnetic induction, and can be introduced into microelectronic equipment through the coupling of power lines, antennas, and signal lines. This is the main cause of damage to microelectronic equipment. If the lightning protection design is only carried out in accordance with the general building, the damage rate of the building electronic equipment by lightning is very high, so corresponding measures should be taken for the lightning protection grounding design of the electronic production plant.　　 When choosing an air-termination device, the form of lightning protection net should be preferred. This is because the lightning rod protects the object from direct lightning strikes by guiding the lightning to itself. This lightning-induced mechanism increases the probability of lightning strikes for the lightning protection system. Of course, lightning rods are not completely unusable. Now some lightning rod manufacturers have introduced new optimized lightning rods, which have the functions of preventing direct lightning and suppressing secondary induced lightning. It is a relatively advanced product in the lightning protection market.　　 When laying down the down conductor, it should be arranged around the building and avoid using the inner main reinforcement of the middle column as the down conductor. This is because when the electronic information system is grounded, a single-point grounding system is usually used. The ground reference point is led to the grounding plate at the bottom of the building at the center of the building. The interference of strong magnetic field generated by offline.　　 Regarding the installation of grounding devices, lightning protection grounding, power system grounding, electrical protection grounding, and anti-static grounding can simultaneously use the foundation steel bars of the building as the grounding electrode. There were disagreements on the grounding of information systems for a long time. In the past, it was generally believed that the grounding system of the information system should be installed separately and insulated from the building. It is called an insulated grounding method abroad. However, in practical applications, it is found that two independent grounding systems are not conducive to overvoltage protection. This is because when the building is exposed to lightning current, the voltage of the building is very high, and the "signal ground" of the information equipment is connected to the building. Connected to the ground 20 meters away, its potential is much lower than that of the lightning protection grounding device. The voltage of the equipment is maintained at the "signal ground" potential level during a lightning strike. The potential difference between the two is coupled through the capacitive coupling to make the voltage withstand capability very high. Low electronic components are damaged.　　 In recent years, many domestic and foreign standards do not advocate the use of independent grounding devices for information equipment, and a shared grounding system is recommended. For example, the 2000 edition of GB50057-94 "Code for Design of Lightning Protection for Buildings" clearly stated: "Each building itself should adopt a common grounding system." That is, all kinds of grounding in the building are connected to the foundation of the building or Outdoor grounding device. When the building is struck by lightning, the voltage of the power system and the working grounding voltage of the electronic equipment rise at the same time, keeping the working voltage of the equipment unchanged, so that the microelectronic equipment can work normally during the lightning strike. The common grounding system usually uses the foundation of the building as the grounding electrode, and its grounding resistance is generally below 1 ohm. If there are equipment that requires lower grounding resistance, the minimum value should be used.　　 The above are some of my learning experience in the grounding design process of the electronic factory. I would like to discuss with you all the omissions and shortcomings. In the future development and application of electronic technology, various advanced grounding technologies and products are constantly emerging. The grounding design technology of electronic workshops will surely have new progress. We look forward to the design work that can provide more for social production. Scientifically beneficial technical support and guarantee