The full arrival of the digital age has placed new demands on relay protection, and even led to a complete reform and advancement of traditional usage methods. For example, higher requirements have been placed on the electromagnetic compatibility (EMC) and protection level (IP) of relay protection devices. The function and application of relay protection have also evolved from single distributed protection to integrated automation. In some places, it is even necessary to build unattended integrated automated substations. Direct integration of relay protection into local high and low voltage switchgear has also become a common usage method. All of these have presented new challenges and higher requirements for structural design. On the other hand, the advancement of industrial technology has also provided structural designers with a large number of new materials, new processes, and new methods, enabling them to exert more initiative and creativity in their fields. The following is a preliminary discussion based on my years of experience in relay protection structural design. I. Requirements and Characteristics of Relay Protection Structural Design in the Digital Age (I) Functional Requirements With the advancement of science and technology, relay protection products have evolved from rectifier-type products through several generations to entirely new digital products. The integrated functions of single protection devices are becoming increasingly powerful, with higher reliability and accuracy. Human-machine interfaces are required to be simple and clear, and communication and testing functions must be convenient, easy to use, and reliable. Structural design must meet and guarantee the functional requirements of the product; this is paramount. Simultaneously, the external design of the structure must fully reflect the product's high technology, high reliability, and high precision. The structure should be upright, with smooth lines and a fine surface, displaying exquisite design art and craftsmanship, giving people a direct sense of the product's high-end and precision. (II) Requirements for Usage Methods and Environments The application of protection products is gradually developing towards integrated automation. Low-voltage protection may even need to adapt to the requirements of unattended substations, and some low-voltage protection devices need to be directly installed on the switchgear. These requirements necessitate that protection devices develop towards high reliability and intelligence, and adapt to various different usage environments. As is well known, the usage environment of switchgear is much harsher than that of the protection control room. First, the temperature varies greatly, reaching as high as 40-50℃ in summer and dropping to -40 to -50℃ in winter, particularly in northern my country. Second, humidity also varies greatly, with higher humidity in coastal and southern regions, and coastal areas also experiencing salt spray corrosion. Currently, the sealing performance of domestic switchgear is poor, and there is a lot of dust. The operation of the switchgear itself has a significant impact on relay protection devices. The opening and closing of various switches and the operation of various relays in the switchgear generate a lot of electromagnetic interference and a strong electrostatic field, as well as a certain amount of vibration and impact. Such an environment requires protection devices to have the ability to withstand high and low temperatures, high protection level of the enclosure design, good sealing performance, and the entire enclosure to meet the requirements of three protections (proof, dustproof, and shockproof). The device must have strong resistance to vibration and impact, and have good electromagnetic compatibility and antistatic capabilities. (III) Electromagnetic Compatibility (EMC) Requirements Electromagnetic compatibility (EMC) is simply the ability of a product to be neither affected by external interference nor to emit interfering electromagnetic waves in an electromagnetic environment. It includes two aspects: anti-interference (the ability of the equipment to resist electromagnetic interference) and electromagnetic emission control (the control of the electromagnetic energy emitted by the equipment itself). With the rapid development of electronic technology, there are more and more sources of electromagnetic interference, making EMC an important factor restricting the performance of products and systems, and has also attracted widespread attention from all parties. The International Electrotechnical Commission (IEC) has published four standards related to EMC for relay protection products: IEC 255-22-1 1 MHz Pulse Interference Test, IEC 255-22-2 Electrostatic Discharge Interference Test, IEC 255-22-3 Radiated Electromagnetic Field Interference Test, and IEC 255-22-4 Fast Transient Interference Test. To meet these standards, electromagnetic compatibility (EMC) design is indispensable. EMC design involves resisting interference and controlling emissions. In terms of structural design, this is essentially electromagnetic shielding design. Structural shielding design generally includes three aspects: selection of shielding materials, structural form, and grounding. 1. Electromagnetic shielding mainly utilizes the reflection from the metal surface and the absorption within the metal layer to suppress electromagnetic radiation interference. Shielding bodies are usually made of good conductors, such as steel, copper, and aluminum. 2. The metal body should be as enclosed as possible, with labyrinthine connections at joints, and dedicated shielding gaskets and shielding contact springs added when necessary. Heat dissipation holes should use small round or square holes; narrow, long holes and long gaps result in serious leakage. 3. In electronic devices, grounding is an important method of electromagnetic shielding. Correct and reasonable grounding can greatly improve shielding effectiveness and eliminate electrostatic induction, while also playing a role in electrostatic shielding. (IV) Opportunities brought by the development of science and technology. The rapid progress of science and technology, especially electronic technology, has brought new opportunities to the design of protection devices and their structures. For example, the miniaturization of electronic circuits, the high efficiency of power supply, and the low power consumption of functions have opened up new avenues for the powerful functions, compact structure, and aesthetics of devices. In addition, the progress of machining technology and the application of new processes and materials have also brought a wide range of operational space to structural design. The reasonable selection of new devices and materials and the active application of new processes are not only a powerful means to enrich the shape and color expression and reflect the sense of the times of the product, but also an important means to improve the reliability and user-friendliness of the whole machine. (V) Guidance and application of industrial design. Industrial design plays a guiding role in the structural design of relay protection products from the aspects of human-machine engineering, shape principles, and color matching. For example, the panel design of protection devices should consider the user-friendliness of the human-machine interface, conform to human physiological characteristics, and not cause operator fatigue or misoperation during long-term observation and operation. On the other hand, the emotional impact of product design on viewers is a combination of the three elements of shape, color, and texture. The handling of shape, color, and texture in relay protection products should fully reflect the modern feel and high reliability of high-tech products in the digital age. (VI) Sealing and Heat Dissipation Sealing and heat dissipation are contradictory, but with the development of science and technology, the power consumption of components is decreasing and power efficiency is continuously improving. The contradiction of heat dissipation in relay protection is no longer very prominent, while the requirements for sealing (protection level) are becoming increasingly higher. This should be given sufficient attention in structural design. Heat dissipation can generally be addressed with several design solutions: 1. Cold plate heat pipe design; 2. Cabinet-built air conditioning; 3. Ventilation duct design. Regarding the technical requirements for sealing, the International Electrotechnical Commission and my country's national standards have established corresponding standards—Protection Level (IP). Relay protection devices in developed countries can achieve IP54 or even IP65 protection levels, meaning they can be dustproof, splashproof, and even dust-tight and water-sprayproof. Digital relay protection devices must also achieve high protection levels to meet the high reliability requirements of relay protection. II. Relay Protection Structure Design Practice Based on the functional requirements of relay protection, as well as different usage methods and environmental requirements, the structure of relay protection devices can be roughly divided into two different types: one is for high-voltage line protection, generator-transformer group protection, large transformer protection, and other high-power main equipment protection. This type of protection has high comprehensive performance requirements, the protected objects are very important, and the reliability requirements are high. We call this a high-level protection structure. The other is for low-voltage line protection, motor protection, capacitor protection, and some relay protection that directly enters the local switchgear. We call these low-level protection structures. Because the performance requirements, usage occasions, and usage methods of these two types of protection are not entirely the same, the structural forms and design ideas are different. (I) High-level protection structure design The structure of the protection device generally selects a 482.6 mm (19″) standard socket conforming to IEC 297 and GB 3047 standards. There are roughly four types of insertion boxes: sheet metal structure insertion boxes; aluminum profile structure insertion boxes; wood-plastic composite structure insertion boxes; and all-plastic structure insertion boxes. The first two types are generally suitable for protective structures. The device panel can be a split panel or a modular insertion type; it can also be a single panel with independent insertion cages inside the insertion box. In human-machine interface design and device EMC design, the single panel type has shown increasing advantages. Another structural type: the front of the device is a single panel, and the individual insertion boxes are inserted from the back of the insertion box, i.e., a rear-insertion type. This structural type is compact. The wiring is convenient, and strong and weak current wires are easily separated. AC and DC leads can be connected to the device through a filter, and EMC requirements are well guaranteed. Imported plug-in terminals are used for the outgoing lines, ensuring neat wiring and easy testing. The entire panel features a menu-driven human-machine interface with an LCD display, which is simple, clear, and user-friendly. Combined with a comfortable rubber keyboard, operation is simple, straightforward, and error-free. The panel surface uses a brushed aluminum alloy finish, giving it a refined appearance and suggesting superior performance. The overall EMC design of the entire device is also quite reasonable. Special EMC springs are added to the side panels and upper and lower cover plates of the insertion box, the connection points between the aluminum profiles and the upper and lower cover plates, and the gaps between the panel and the insertion box. EMC films are also added to the gaps in the LCD panel. The connection between the upper and lower cover plates and the front and rear profiles adopts a labyrinthine structure (as shown in Figure 1), thus making the entire device almost free of electromagnetic gaps. The device using this structure successfully passed the relevant EMC tests. Figure 1 Labyrinthine structure (II) Low-level protection structure design Low-level protection structures are generally smaller, and can use insertion boxes with a width of 1/2, 1/3, or even 1/4 of 482.6 mm (19″). The panel cabinet can be arranged as shown in Figures 2 and 3, or it can be separately installed in the switch room of the local switch cabinet. Because the size of the switch room is limited, the installation depth is generally <250 mm. Using the same structural type for a 482.6 mm (19″) width insert box would be unreasonable and difficult to meet its usage requirements. Generally, the following two types are adopted. Figure 2: 1/2 width insert box panel layout; Figure 3: 1/3 width insert box panel layout. (I) Sheet metal wrapping type: The main body of this structure—the cylinder—is a sheet metal wrapping, forming a seamless unit. A front cover is added to seal the cylinder, resulting in a very compact and simple structure that meets EMC requirements and achieves a high protection level (as shown in Figure 4). Figure 4: Sheet metal structure. (II) Aluminum profile box type: The structural type is similar to the above, except the cylinder is directly drawn into an aluminum profile, which can also meet various requirements (as shown in Figure 5). Figure 5: Aluminum profile structure. III. Conclusion my country's relay protection industry is not lagging behind any developed country in terms of principles and design; in some aspects, it is even at the forefront of international advanced technology. However, compared with the relay protection devices produced by major companies in developed countries, there is a significant gap. In other words, while our protection principles and technologies are more advanced, the resulting protection assemblies are not top-notch. One of the important reasons for this is the relatively backward structure and manufacturing process. As we all know, the external structures of our consumer products, such as color TVs, refrigerators, air conditioners, and washing machines, have made rapid progress in recent years and are now fully comparable to similar products from developed countries. However, our relay protection structure design and manufacturing technology still lag behind significantly. To catch up, those engaged in relay protection structure work need to continuously strive and learn. It is also hoped that the entire industry will pay attention to and support this weak link of structure and process, and strive to improve the overall quality of relay protection products.