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In our work, we must all have encountered situations where, during thunderstorm weather, the PLC restarts while operating normally, causing the production equipment to stop working and resulting in losses. I now want to improve the situation by using UPS and surge protectors; I’m not sure what the results will be, so let’s discuss it. Attached: A Brief Overview of the Principles and Applications of Surge Protectors. Abstract: This article introduces the basic principles of protecting against lightning-induced electromagnetic pulses and the protective measures taken for this purpose. It also covers the performance and characteristics of commonly used surge protectors, and provides a brief introduction to some of the most common SPD products. Keywords equipotential bonding, overvoltage protection, SPD. In recent years, with the rapid progress of microelectronics technology, the use of personal PCs, various medium-sized, large-sized, and super-large computers, as well as large-scale program-controlled switches has become increasingly widespread. Due to the large number of large-scale or very large-scale integrated circuits inside such electronic devices, which are highly sensitive to overvoltage, the losses caused by overvoltage become increasingly severe. In response to this situation, Chapter 6 on electromagnetic pulses resulting from lightning strikes was added to the \"Code for Design of Lightning Protection of Buildings\" GB50057-94 (2000 edition). In response to this requirement, some manufacturers have also introduced corresponding overvoltage protection products, which are what we now commonly refer to as surge protective devices (Surge Protective Devices, SPDs). To protect electrical and electronic systems, it is important to establish a complete equipotential bonding system that includes all active conductors within the electromagnetic compatibility protection area. The physical properties of discharge components in different types of overvoltage protection devices present both advantages and disadvantages in practical applications; therefore, protection circuits that utilize a combination of various components are more widely used. However, product lines that can meet the technical requirements of contemporary standards – such as devices capable of conducting pulse currents of 10/350 μs, plug-in surge protectors for secondary power distribution, electrical power protection devices, and even power filters – are extremely rare. Similarly, this product series should include components suitable for all types of circuits; that is, in addition to power supplies, it should also contain components for measurement, control, and regulation, as well as circuitry for electronic data processing and transmission, along with discharge devices for wireless and wired communication, to be used by customers. This article will provide a brief introduction to several commonly used surge protection products today, and offer a concise analysis of their characteristics and applicable scenarios. 1 Equipotential bonding system The basic principle of overvoltage protection is to achieve equipotentiality among all metal components within the protected area at the moment a transient overvoltage occurs (on the order of microseconds or nanoseconds). “Equipotentialization is achieved by connecting lightning protection devices located in areas that need protection from lightning, the metal framework of buildings, metal fixtures, external conductive objects, electrical and telecommunications equipment, etc., using connection wires or overvoltage protectors. ”(Explanations to 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 the space that needs to be protected against lightning” (IEC 1312 3.4). The Code for Design of Lightning Protection of Buildings (GB50057–94) stipulates: “Article 3.1.2 For buildings equipped with lightning protection systems, where it is not possible to isolate such systems from other facilities and the people inside the buildings, equipotential bonding shall be implemented.” ”When establishing this equipotential bonding network, care should be taken to keep the connection wires between the electrical and electronic devices that need to exchange information with each other and the equipotential bonding strips as short as possible. According to the law of induction, the greater the inductance, the higher the voltage generated by the transient current in the circuit ； (U = L·di/dt) The value of inductance is primarily related to the length of the wire, with little relation to the cross-sectional area of the wire. Therefore, the grounding wire should be as short as possible. The parallel connection of multiple wires can significantly reduce the inductance of the potential compensation system. To put these two ideas into practice, in theory, all the circuits and devices 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-shaped, or mesh structures can be employed when installing equipotential bonding systems. In principle, only a mesh equipotential bonding system should be used when designing new equipment. 2 Connect the power supply lines to the equipotential bonding system. Transient voltages or currents refer to those that exist for only microseconds or nanoseconds. The basic principle of surge protection is to establish an equipotential state among all conductive components within the protected area during the very short period in which transient overvoltages exist. Such conductive components also include the power supply wires in a circuit. People need components with response speeds faster than microseconds, and even faster than nanoseconds for electrostatic discharge. Such a component is capable of delivering extremely high currents, up to several times ten kiloamperes, within an extremely short time interval. Based on calculations for the expected lightning strikes using 10/350 μs pulses, the current can reach as high as 50 kA. Through a complete equipotential bonding system, an equipotential island can be formed in an extremely short time; this equipotential island can have potential differences of hundreds of thousands of volts even with respect to more distant areas. But it is important that, within the area that needs to be protected, all conductive components can be considered to have a nearly equal or absolutely equal potential, with no significant voltage difference. 3 Installation of surge protectors and their functions In terms of response characteristics, surge protection components can be divided into soft and hard types. Discharge elements with hard-response characteristics include gas discharge tubes and discharge-gap type discharge devices, which are either angular spark gaps based on arc-chopping technology or coaxial discharge spark gaps. Discharge components with soft response characteristics include varistors and suppression diodes. The differences among all these components lie in their discharge capacity, response characteristics, and residual voltage. Due to the advantages and disadvantages of each of these components, they are combined into special protection circuits to leverage their strengths and mitigate their weaknesses. The surge protectors commonly used in the field of civil buildings are mainly discharge-gap type discharge devices and varistor type discharge devices. Lightning current and subsequent lightning currents require discharge devices with extremely high discharge capabilities. To direct lightning current into the grounding device through the equipotential bonding system, it is recommended to use a lightning current arrester with angled spark gaps based on arc-breaking technology. Only with it can pulse currents of over 50 kA at a 10/350 μs duration be conducted, and automatic arc extinction can also be achieved; the rated voltage for such products can reach 400 V. Furthermore, when the short-circuit current reaches 4 kA, this discharge device does not cause a fuse with a rated current of 125 A to blow. Thanks to its excellent performance, it **improves** the uninterrupted operation of the instruments and equipment installed in the protected area. It is particularly important to note that it depends not only on the ability to handle currents with very high amplitudes, but more importantly, the pulsed nature of the current plays a decisive role. Both must be considered simultaneously. Therefore, although corner-type spark gaps can also conduct currents of up to 100 kA, their pulse shape is shorter (8/80 μs). This pulse is a surge current pulse, which served as the design basis for developing lightning current discharge devices prior to October 1992. Although lightning current discharge devices have good discharge capabilities, they still have their drawbacks: their residual voltage is as high as 2.5–3.5 kV. Therefore, when installing a lightning current arrester as a whole, it also needs to be used in combination with other arresters. Such products mainly include ABB’s Limitor M-B, Limitor NB-B, Limitor G-B, and Limitor GN-B ； German DEHN coaxial spark gaps: DEHNportMaxi (10/350μs, 50kA per phase), DEHNport255 (10/350μs, 75kA per phase) ； German PHOENIX angular spark gaps: FLT60-400 (10/350μs, 60kA per phase), FLT25-400 (10/350μs, 25kA per phase) ； Schneider’s PRF1 surge protector ； MOELLER’s VBF-series products. A varistor functions similarly to many bidirectional suppression diodes connected in series and parallel, and its operating principle is that of a voltage-dependent resistor. When the voltage exceeds the specified level, the varistor can conduct electricity ； When the voltage is below the specified level, the varistor does not conduct electricity. In this way, the varistor can serve as an effective voltage limiter. Varistors operate extremely quickly, with a response time in the low nanosecond range. The varistors commonly used in power supplies can conduct currents up to 40 kA for 8/20 μs pulses, making them very suitable as discharge devices in the second stage of power supplies. But it is not suitable as a lightning current discharge device. According to IEC 1024-1 standards, to handle a charge amount corresponding to a pulse width of 10/350 μs is equivalent to 20 times the charge amount in the case of a pulse with a width of 8/20 μs. 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 needs to be taken into account, but also the pulse shape – this is crucial. The disadvantages of varistors are their tendency to age and their high capacitance; aging refers to the breakdown of the diode elements within the varistor. Since, in most cases, an overload of the P-N junction results in a short circuit, the varistor begins to draw leakage current depending on the frequency of such loading. This leakage current can cause errors in the measurement data in sensitive test circuits; moreover, it can lead to significant heating, especially in circuits with high rated voltages. The high capacitance of varistors prevents them from being used in signal transmission lines in many cases. The capacitance and the inductance of the wire form a low-pass circuit that causes the signal to attenuate significantly. However, the attenuation at frequencies below about 30 kHz can be ignored. Such products mainly include ABB’s Limitor V, Limitor VTS, Limitor VE, Limitor VETS, and Limitor GE-S ； Schneider’s PRD series of replaceable surge protectors ； MOELLER’s VR7–VS7–series products ； German DEHN’s DEHNguard385 (8/20μs, 40kA/phase), DEHNguard275 (8/20μs, 40kA/phase) ； German PHOENIX VAL-MS400ST (8/20μs, 40kA/phase), VAL-ME400ST/FM (8/20μs, 40kA/phase) ； Domestically produced Wanma Shen’s DB30-4A/B (8/20μs, 30kA per phase) and DB40-4A/B (8/20μs, 40kA per phase). 4. Install surge protectors in accordance with the overvoltage protection scheme. These consist of a single protective element or a combined protection circuit; assemblies that are integrated based on installation requirements (rail-mounted, power socket-mounted, adapters) are referred to as discharge devices. Overvoltage protection in almost all cases should be divided into at least two stages. For example, power supplies and individual discharge devices that have only one level of protection can be installed in different locations; a single discharge device may also include multiple levels of protection. To achieve effective overvoltage protection, it is necessary to divide the area that needs to be protected into different electromagnetic compatibility zones. These protection zones include the lightning protection zone 0, the overvoltage protection zones 1 to 3, and so on, with zones for interference voltages having even higher numbers. Setting the electromagnetic compatibility protection zones from 0 to 3 is intended to prevent equipment damage caused by high-energy coupling. The electromagnetic compatibility protections with higher sequence numbers are designed to prevent information distortion and loss. The higher the number of the protection zone, the lower the expected interference energy and interference voltage levels. Electrical and electronic devices that need protection are installed within a highly effective protective enclosure. Such an enclosure can be designed for a single electronic device, or it can cover a space containing multiple electronic devices, or even an entire building. All wires that pass through this protective enclosure, which usually has spatial shielding, are equipped with voltage protection discharge devices as they connect to the devices located at the periphery of the enclosure. The selection of surge protectors depends on various circuits and parameters. The operating voltage of the surge protector is determined by the rated voltage of all components installed in this circuit, while the residual voltage to be achieved is determined based on the voltage tolerance of all components installed in this circuit. The voltage withstanding strength is tested using 1.2/50 μs pulses. In parallel operation, that is, when a discharge device is connected between the active wire and ground, there is no need to pay attention to the rated current of the discharge device, as this current does not flow through it. When a circuit is equipped with a series-connected surge protector, attention must be paid to its rated current; in circuits with high data transfer rates, the attenuation of the surge protector plays a decisive role. As for the discharge devices designed specifically for data transmission circuits, manufacturers have taken their transmission speed into account. To achieve an optimized overvoltage protection scheme, users need to communicate promptly with the planners of electrical and electronic equipment, as well as building designers. It is during the design and planning phase that it becomes apparent that the basic principles of electromagnetic compatibility can **reduce costs and achieve overvoltage protection most effectively**. During the design phase, the setup of the mesh potential compensation system is determined, laying the foundation for spatial shielding and the layout of electrical and electronic equipment circuits. With a surge protector selected based on circuit parameters, it is easy to determine its appropriate installation location. It is important to note that only an installation that meets professional regulations and standards can enable an excellent and practical overvoltage protection solution to be successfully implemented.