Abstract : This article introduces the basic principles and protective measures for lightning electromagnetic pulse protection, the performance and characteristics of commonly used surge protectors (SPDs), and briefly introduces some commonly used SPD products. Keywords : Equipotential bonding, overvoltage protection, SPD. In recent years, with the rapid advancement of microelectronics technology, the use of personal PCs, various medium, large, and super-large computers, and large program-controlled exchanges has become increasingly widespread. Because these electronic devices contain a large number of large-scale or very large-scale integrated circuits that are highly sensitive to overvoltage, the losses caused by overvoltage are becoming increasingly significant. In response to this situation, Chapter 6—Lightning Electromagnetic Pulse Protection—was added to the "Code for Design of Lightning Protection of Buildings" GB50057-94 (2000 edition). Based on this requirement, some manufacturers have also launched corresponding overvoltage protection products, which are now commonly referred to as surge protectors (SPDs). To protect electrical and electronic systems, it is crucial to install a complete equipotential bonding system, including all active conductors, within the electromagnetic compatibility protection zone. No. Different types of overvoltage protection devices have both advantages and disadvantages in the physical characteristics of discharge components in practical applications. Therefore, protection circuits using combinations of multiple components are more widely used. However, product series that can meet all the technical requirements of modern technology, including lightning current dischargers capable of conducting 10/350μs pulse currents, pluggable surge protectors for secondary power distribution, electrical power supply protection devices, and even power filters, are extremely rare. Such product series should also include applications for all circuits, including not only power supplies but also circuits for measurement, control, and regulation, electronic data processing and transmission, as well as dischargers suitable for wireless and wired communications, for customer use. This article will provide a brief introduction to several commonly used surge protection products and a brief analysis of their characteristics and applicable scenarios. 1. Equipotential Bonding System The basic principle of overvoltage protection is that at the instant of a transient overvoltage (microseconds or nanoseconds), an equipotential bond should be achieved between all metal components within the protected area. "Equipotential bonding is the connection of lightning protection devices, building metal frames, metal installations, external conductors, electrical and telecommunications equipment, etc., within a space requiring lightning protection using connecting wires or overvoltage protectors." (Explanation of Clauses in the Code for Design of Lightning Protection of Buildings) (GB50057-94). "The purpose of equipotential bonding is to reduce the potential difference between various metal components and systems within a space requiring lightning protection" (IEC1312 3.4). The Code for Design of Lightning Protection of Buildings (GB50057-94) stipulates: "Article 3.1.2 For buildings equipped with lightning protection devices, where the lightning protection devices cannot be isolated from other facilities and personnel within the building, equipotential bonding shall be adopted." When establishing this equipotential bonding network, care should be taken to ensure that the connecting wires between electrical and electronic equipment that must exchange information with each other are kept at the shortest possible distance from the equipotential bonding strip. According to the inductance theorem, the larger the inductance, the higher the voltage generated by the transient current in the circuit; (U=L·di/dt). The magnitude of inductance is mainly related to the length of the wire and has little to do with the cross-sectional area of ​​the wire. Therefore, the grounding conductor should be as short as possible. Parallel connection of multiple conductors can significantly reduce the inductance of the potential compensation system. To put these two points into practice, theoretically, all circuits and equipment that should be connected to the equipotential bonding device can be connected to the same metal plate. Based on the metal plate concept, linear, star, or mesh structures can be used when supplementing the equipotential bonding system. In principle, only mesh equipotential bonding systems should be used when designing new equipment. 2. Connecting power lines to the equipotential bonding system Transient voltage or transient current means that its existence time is only microseconds or nanoseconds. The basic principle of surge protection is: during the extremely short time of a transient overvoltage, an equipotential is established between all conductive components in the protected area. These conductive components also include power lines in the circuit. Components with response times faster than microseconds are needed, and even faster than nanoseconds for electrostatic discharge. Such components can conduct very powerful currents, up to several times tens of kiloamperes, within extremely short time intervals. Under anticipated lightning strike conditions, calculated using a 10/350μs pulse, the current can reach as high as 50kA. With a complete equipotential bonding device, an equipotential island can be formed in a very short time, and this island can withstand potential differences of hundreds of thousands of volts over distant locations. Importantly, within the protected area, all conductive components can be considered to have nearly equal or absolutely equal potentials, without significant potential differences. 3. Installation and Function of Surge Protectors Surge protection electrical components can be categorized as hard or soft in terms of response characteristics. Hard-response discharge elements include gas discharge tubes and discharge gap type dischargers, which are either angle-type spark gaps based on arc-chopping technology or coaxial discharge spark gaps. Soft-response discharge elements include varistors and suppression diodes. The differences between all these components lie in their discharge capacity, response characteristics, and residual voltage. Because these components each have their advantages and disadvantages, they are combined into special protection circuits to maximize their strengths and minimize their weaknesses. In civil engineering, surge protectors commonly used are mainly discharge gap type and varistor type. Lightning current and its aftercurrent require surge protectors with extremely high discharge performance. To guide lightning current through the equipotential bonding system to the grounding device, it is recommended to use a lightning current discharger with an angled spark gap based on arc-chopping technology. Only this type can conduct 10/350μs pulse currents greater than 50kA and can also achieve automatic arc extinguishing; the rated voltage of this product can reach 400V. Furthermore, when the short-circuit current reaches 4kA, this type of discharger will not cause a 125A rated current fuse to blow. Due to its excellent performance, the uninterrupted operation characteristics of instruments and equipment installed within the protected area are greatly improved. It is particularly important to note that this depends not only on the ability to handle very high amplitude currents, but more importantly, on the pulse form of the current. Both must be considered simultaneously. Therefore, although angled spark gaps can also conduct currents up to 100kA, their pulse form is shorter (8/80μs). This pulse is an impulse current pulse, which served as the design basis for developing lightning current dischargers before October 1992. Although lightning current dischargers have excellent discharge capabilities, they also have drawbacks: their residual voltage can reach as high as 2.5–3.5 kV. Therefore, when installing lightning current dischargers as a whole, they must be used in combination with other dischargers. These products mainly include ABB's Limit MB, Limit NB-B, Limit GB, and Limit GN-B; DEHN's coaxial spark gaps: DEHNportMaxi (10/350μs, 50kA/phase) and DEHNport255 (10/350μs, 75kA/phase); PHOENIX's angle spark gaps: FLT60-400 (10/350μs, 60kA/phase) and FLT25-400 (10/350μs, 25kA/phase); Schneider's PRF1 surge protector; and MOELLER's VBF series products. A varistor functions similarly to many bidirectional suppressor diodes connected in series and parallel, operating on a voltage-dependent principle. When the voltage exceeds a specified value, the varistor conducts; when the voltage is below the specified value, the varistor does not conduct. In this way, the varistor can play a very good role in voltage limiting. Varistors operate extremely quickly, with response times in the nanosecond range. Commonly used varistors in power supplies can conduct up to 40kA of current in an 8/20μs pulse, making them very suitable as a second-stage discharger in power supplies. However, they are unsuitable as lightning current dischargers. The International Electron Technology Committee (IEC) document 1024-1 states that to handle a 10/350μs pulse, the charge is equivalent to 20 times the charge in an 8/20μs pulse. Q(10/350)μs = 20 × Q(8/20)μs. From this formula, it can be seen that not only the amplitude of the discharge current but also the pulse form must be carefully considered; this is crucial. The disadvantages of varistors are their susceptibility to aging and high capacitance. Aging refers to the breakdown of the diode components within the varistor. Because PN junctions often short-circuit under overload, depending on the frequency of the load, varistors begin to attract leakage current. This leakage current can cause measurement errors in sensitive test circuits and, especially in circuits with high rated voltage, can generate significant heat. The high capacitance of varistors also precludes their use in signal transmission lines in many cases. The capacitance and wire inductance form a low-pass circuit, causing significant signal attenuation. However, attenuation below approximately 30kHz is negligible. These products mainly include ABB's Limit V, Limit VTS, Limit VE, Limit VETS, and Limit GE-S; Schneider's PRD series of replaceable surge protectors; MOELLER's VR7- and VS7- series products; DEHN's DEHNguard385 (8/20μs, 40kA/phase) and DEHNguard275 (8/20μs, 40kA/phase); PHOENIX's VAL-MS400ST (8/20μs, 40kA/phase) and VAL-ME400ST/FM (8/20μs, 40kA/phase); and Wanmashen's DB30-4A/B (8/20μs, 30kA/phase) and DB40-4A/B (8/20μs, 40kA/phase). 4. Install Surge Protectors According to Overvoltage Protection Schemes A surge protector is an assembly containing a single protective element or a combined protective circuit, integrated according to installation technical conditions (DIN rail mounted, power socket type, adapter type). In almost all cases, overvoltage protection should be divided into at least two levels. For example, in power supplies, individual surge protectors containing only one level of protection can be installed in different locations, and the same surge protector may also contain multiple levels of protection. To achieve effective overvoltage protection, the area requiring protection is divided into different electromagnetic compatibility (EMC) zones. This protection range includes lightning protection zone 0, overvoltage protection zones 1 to 3, and so on, up to interference voltage protection zones with higher numbers. EMC protection zones 0 to 3 are set up to avoid equipment damage due to high-energy coupling. Higher-numbered EMC protection zones are set up to prevent information distortion and loss. The higher the protection zone number, the lower the expected interference energy and interference voltage level. The electrical and electronic equipment requiring protection is installed within a highly effective protective enclosure. This enclosure can be for a single electronic device, a space containing multiple electronic devices, or even an entire building. All wires passing through this enclosure, which is typically spatially shielded, are connected to a surge protector upon reaching the peripheral equipment within the enclosure. The selection of the surge protector depends on the specific circuit and parameters. The operating voltage of the surge protector is based on the rated voltage of all components installed in the circuit, while the residual voltage to be achieved is determined by the withstand voltage of all components installed in the circuit. The withstand voltage is tested using a 1.2/50μs pulse. When connected in parallel, i.e., between the active conductor and ground, the rated current of the surge protector is not a concern, as the rated current does not pass through the surge protector. When a circuit has surge protectors in series, their rated current must be considered. In circuits with high data transmission rates, the surge protector's attenuation plays a crucial role. As for surge protectors specifically designed for data transmission circuits, the manufacturers have already taken into account the transmission rate. To achieve the optimal overvoltage protection solution, users need to communicate promptly with electrical and electronic equipment planners and building designers. Paying attention to the basic principles of electromagnetic compatibility during the design and planning phase can significantly reduce costs and most effectively achieve the goal of overvoltage protection. During the design phase, the setup of the mesh potential compensation system should be determined, laying the foundation for spatial shielding and the layout of electrical and electronic equipment wiring. Surge protectors selected based on circuit parameters will then easily have their suitable installation locations determined. It is particularly important to note that only installations that comply with professional regulations and standards can successfully implement an excellent and easy-to-use overvoltage protection solution.