[Abstract] Based on the mechanism of lightning damage to the information system of power enterprises, this paper proposes the overall lightning protection requirements of external lightning protection and internal lightning protection, introduces the measures and approaches for lightning protection of information systems, and elaborates on the technical principles and practical measures that should be adopted for lightning protection of information systems of power enterprises. [Keywords] Power enterprise; Information system; Lightning protection; Equipotential bonding Computer systems are composed of electronic devices with low withstand voltage. In China, especially in South China where lightning is frequent, lightning interference and damage accidents to the computer systems of power enterprises are prone to occur, resulting in damage to various electronic devices. The indirect losses caused by the inability of computer systems to operate safely and reliably may far exceed the value of the equipment itself. If the system is interrupted or paralyzed, the losses are even more difficult to estimate. The Guangzhou Power Industry Bureau Transmission Management Office (hereinafter referred to as "Guangzhou Transmission Office") fully recognizes the hazards of lightning and the importance of computer system security, and carried out effective lightning protection for computer systems in 2001. 1 Overall Lightning Protection Technology 1.1 Three Lines of Lightning Protection The main way lightning damages buildings or structures is by directly striking them. The huge energy is concentrated at the point of impact, directly damaging the building structure. External lightning protection measures utilize metallic lightning rods to intercept lightning strikes and use down conductors to guide the current to the ground, thereby protecting the building's safety. Therefore, external lightning protection is the first line of defense in overall lightning protection. The main way lightning strikes damage computer systems is through the electromagnetic pulse (secondary effect of lightning) induced on power or communication lines. Since the surge overvoltages reaching millions of volts and the instantaneous currents of hundreds of kiloamperes generated on these lines are difficult for ordinary electronic equipment to withstand, blocking the overvoltage waves introduced along power or communication lines that could damage equipment (internal lightning protection) and limiting the surge overvoltage amplitude on the protected equipment (overvoltage protection) become the second and third lines of defense in lightning protection. 1.2 Technical Measures for Lightning Protection Based on extensive experiments and research on lightning phenomena, the IEC's Lightning Protection Technical Group (TC/81) proposed a theoretical system of graded protection and overall lightning protection, namely: overall lightning protection should be a unified system of external lightning protection, internal lightning overvoltage protection, and grounding technology. In terms of specific technical measures, these can be summarized as equalization-shunting-shielding-grounding technology, which are the four most important and effective elements in lightning protection. 2. Application of Overall Lightning Protection Technology A surge arrester is a discharge channel for lightning current and also an equipotential bonding device. It is installed in parallel to ground on the line and is normally in a high-impedance state. In the instant of a lightning strike, it rapidly conducts, discharging the lightning current into the ground, simultaneously bringing the ground, equipment, and lines to equipotential, thus protecting the equipment from damage caused by strong potential differences. Because the energy of a lightning strike or lightning-induced strike is considerable, it is difficult for a single surge arrester to conduct all the lightning current to the ground without damaging itself. Therefore, the IEC established a graded and zoned lightning protection theoretical system. Its core content is to use surge protection overvoltage protection devices with different functions in spaces with different electromagnetic field strengths. The coordinated operation of each device ensures both high current to ground and low residual voltage, while also extending the lifespan of the surge arrester. 2.1 Lightning Protection of Power Supply System Lightning protection of power supply system is to provide overvoltage protection for all levels of AC power distribution related to the power supply of computer system. It requires the installation of surge arresters at the power inlet where lightning surges may occur. The technical principles are as follows: (1) Lightning protection of power supply system is divided into several different protection levels. According to the different protection levels, select a power surge arrester with appropriate nominal discharge current (rated current capacity) and voltage protection level, and ensure that the surge arrester has sufficient lightning impulse resistance. (2) Residual voltage characteristic is the most important characteristic of power surge arrester. The lower the residual voltage, the better the protection effect. At the same time, it is also necessary to consider that the surge arrester has a sufficiently high maximum continuous operating voltage. Because if the maximum continuous rated operating voltage is too low, it will easily cause damage to the surge arrester. (3) Power surge arrester should have failure alarm indication and telemetry port to facilitate monitoring, management and maintenance. (4) Power surge arrester must have flame retardant function and will not catch fire when it fails or self-destructs. (5) Power surge arrester must have failure separation device. When the surge arrester fails, it can automatically disconnect from the power system without affecting the normal power supply of the power system. (6) Installation requirements for power surge arresters: ① The connection lead between the surge arrester and the power system should be as short as possible, and flame-retardant multi-strand copper wire with a cross-sectional area of ​​not less than 25 mm2 should be used, and it should be laid out compactly side by side or bundled. ② The grounding wire of the surge arrester should use flame-retardant multi-strand copper wire of 25-35 mm2, and should be buried in the ground as close as possible, or directly connected to the AC protective grounding busbar or grounding grid as close as possible. Based on the above principles, the power supply system lightning protection of the Guangzhou Power Transmission Station's computer system implements three levels of lightning and overvoltage protection at the low-voltage distribution cabinet, the output terminal of the main power switch in the computer room, and the equipment switch sockets: Level 1 uses a DEHNventi1VGA280/4 surge arrester (maximum current carrying capacity 100 kA, test waveform 8/20, residual voltage less than 2.5 kV), installed in parallel at the output terminal of the main power switch in the low-voltage distribution room; Level 2 uses a DEHNguard385/3+1 surge arrester (maximum current carrying capacity 40 kA, test waveform 8/20, residual voltage less than 1.5 kV), installed in parallel at the output terminal of the AC distribution panel in the computer room; Level 3 uses ASP brand domestically assembled socket-type surge protectors (maximum current carrying capacity 15 kA, test waveform 8/20, residual voltage less than 600 V), installed at the front end of communication cabinets, servers, and other central equipment in the computer room, with parallel connection. 2.2 Lightning Protection of Communication Systems The technical principles of lightning overvoltage protection for communication systems are as follows: (1) Interface surge arresters are usually connected in series in the data lines. Their selection and application must be based on the premise of not affecting data transmission. (2) According to the interface rate, a surge arrester with suitable working bandwidth and physical interface should be selected for data interface protection. The connection with the data equipment interface should use as few adapters as possible to avoid increasing insertion loss and affecting signal transmission. (3) For data equipment interfaces with high speed, a data surge arrester with the smallest possible inter-electrode capacitance, leakage current, insertion loss, VSWR, and response time should be selected. (4) According to the different signal working voltages, a data interface protection surge arrester with suitable operating voltage and limiting voltage should be selected. (5) According to the lightning protection requirements of the equipment interface, a data surge arrester with sufficient lightning impulse resistance should be selected. (6) The data surge arrester must have a reliable grounding connection. The grounding wire should be reliably connected to the ground wire of the protected data equipment nearby. The cross-sectional area of ​​the grounding wire should not be less than 25 mm2. Based on the above principles, the communication system uses two DEHNUGKF/RJ45 surge arresters (maximum current carrying capacity 5 kV, test waveform 8/20, residual voltage less than 35 V) connected in series at the server's RJ45 signal interface and the dedicated MODEM input RJ45 interface in the communication cabinet, respectively. 2.3 Grounding Modification of the Computer Room In the lightning protection and overvoltage protection technology of computer systems, the grounding system plays a crucial role. Grounding technology includes lightning protection grounding, protective grounding, functional grounding, signal grounding, and anti-static grounding. These types of grounding have different meanings, functions, and requirements. A common practice is to set up separate independent grounding bodies, but in the event of a lightning strike, the potential difference between the lightning protection grounding system and other grounding systems can easily cause backflashover accidents, damaging electronic equipment. From the perspective of overall lightning protection technology, all grounding systems should be equipotentially connected. The grounding system of the computer room has specific and strict construction process requirements in its implementation. The Guangzhou Power Transmission Station constructed a new equipment grounding busbar and an equipotential bonding strip in its computer room to maintain equal potential across all locations. The grounding busbar was installed on the ground near the mainframe cabinet and connected to the equipotential bonding strip using 95 mm² bare copper cable. A 95 mm² copper cable was used as the down conductor, reliably connected to the grounding grid of the dedicated transformer room on the first floor via crimped lugs. The grounding wiring utilized existing cable trays or racks in the office building as much as possible, or used independent galvanized iron cable trays, with both ends connected to the grounding system using 25 mm² copper cable. In power enterprise management, computer system security should receive increasing attention. Since lightning strikes are low-probability events, achieving absolute safety (100% lightning protection) is economically unreasonable. It is crucial to emphasize tailored lightning protection for computer systems based on local conditions, correctly implement lightning protection technical standards, and ensure the reliability of lightning protection projects. The overall lightning protection project for the Guangzhou Power Transmission Station's computer system involved a relatively small investment, implemented basic lightning overvoltage protection, and achieved the expected goals.