I. Introduction As human society enters the information age, the widespread use of various advanced electronic devices has greatly increased the probability of them being damaged by lightning. Electronic equipment in substations, in particular, which relies on primary equipment within the protection range of lightning rods, is even more susceptible to lightning strikes. Furthermore, traditional lightning protection measures are often inadequate and should be taken seriously. II. Several Modes of Lightning Hazards 2.1 Direct and Circumferential Lightning A single thundercloud floats above the ground, its charge dragging the opposite charge on the ground like a shadow carried by the wind. If it passes by a lightning rod in a substation or other protruding objects on the ground, the ground charge will cause the electric field distortion at the tip of the protruding object to concentrate. Before the lightning strike begins, the initial leader at the base of the thundercloud develops towards the ground in an intermittent, graded leap. When it reaches 50-100m above the ground, a vertically upward-facing leader is generated from the area where the electric field distortion is concentrated, such as a lightning rod or other surface protrusion. When the two connect, the main discharge stage, either a direct strike or a circumferential strike, begins. When the height of a protrusion on the ground is h, and the average electric field strength directly below the thundercloud is greater than or equal to 580h-0.7kV/m, the protrusion will be easily struck by direct lightning. The reason is that a lightning rod with a height of h can affect the radius of the downward development direction of the leader of the thundercloud, which can be expressed by the formula: R=16.3h0.61m. This formula also shows that after an independent lightning rod is installed on the ground, a large number of scattered strikes will occur in its vicinity, and even the lightning rod will be directly struck, and objects within the protection range of the lightning rod will be struck around it. [1] The main discharge of a single lightning strike is generally tens of thousands to hundreds of thousands of amperes. The instantaneous high heat and electrodynamic force will cause the concrete pole to crack, the small section of metal to melt, causing fires and explosions, the metal conductor connection to break and break, the building to collapse, and the electrical equipment to be damaged. 2.2 Lightning backlash The direct lightning current enters the ground through the resistance of the protrusion on the ground. If the ground resistance is 10Ω, a 30kA lightning current will raise the ground grid potential to 300kV. If the transmission line of the lightning-struck substation comes from a substation with a different ground grid, the rising ground potential will create a huge difference with the potential on the transmission line, leading to damage to the electrical equipment connected to the transmission line. Not only transmission lines and power cables, but all metal pipelines entering the substation can be affected by lightning backflash. Another type of lightning backflash also poses a significant threat to the electronic equipment in the substation. The lightning current dissipates along the substation's grounding grid, and the lightning current on the branch lines and the potential differences at various points are large. Electronic equipment connected to different equipotential grounding grids will be damaged if there is an electrical signal connection between them, as the ground potential difference exceeding their allowable tolerance will cause equipment damage. 2.3 Induced Lightning Direct Strike The energy of a lightning discharge radiates to the surroundings through electromagnetic induction and electrostatic induction, causing overvoltage discharge in equipment; this is called induced lightning. Obviously, induced lightning has a large-area hazard and is a nemesis of electronic equipment. Calculations show that when a lightning strike with a 30kA oblique wave, a thundercloud height of 3 km, and a conductor height of 10 m, strikes the ground 100 m from the midpoint of a 500m long overhead line, the induced voltage on the line is an oscillating wave with an amplitude of 150kV. This wave is the result of the combined effects of electromagnetic induction and electrostatic induction. Further calculations show that when a 10-story building (60m × 30m × 100m, 10m high per floor) with an I-beam frame and metal sections connected to form a Faraday cage is struck on its roof by a -2.6/40µs, 100kA lightning strike, the vertical component of the induced electric field at a height of 1 m on each floor reaches several kV/m. The intensity of the induced electric field tends to become more uniform as the floor decreases, but the overall intensity does not decrease significantly. In fact, in production practice, the destructive power of electrostatic induction from lightning strikes is several times greater than that of electromagnetic induction. Electrostatic induction can also be explained using the theory of the secondary effects of lightning strikes. Charged thunderclouds float above the Earth's surface, carrying an equal amount of charge opposite to that of the thunderclouds. After a lightning strike, the ground at the point of impact becomes a relative void of charge. Charges on conductors in the surrounding high-charge area that are insulated from the ground potential will surge towards the point of impact like a sudden wave of water, causing equipment to spark, insulation damage, and electronic equipment failure. Particular attention should be paid to high-impedance input circuits and signal circuits of electronic equipment, where leads are long and directly connected to large metal volumes. Even with electromagnetic shielding (using shielded cables with grounded shielding at both ends), these areas can still be affected. 2.4 Lightning Intrusion Waves: Lightning strikes from afar, entering substations through direct impact or electromagnetic and electrostatic induction via high-voltage transmission lines, distribution lines, low-voltage power lines, communication lines, cables, and metal pipes. Due to the relatively long length of these pipelines and the presence of distributed inductance and capacitance, the propagation speed of lightning is slowed. This phenomenon, explained by wave propagation theory, is called a lightning wave. When lightning waves travel through connecting segments or line endpoints with different parameters, changes in wave impedance can cause reflection and refraction, leading to a significant voltage increase at the point of impedance abrupt change, thus increasing the damage to equipment. 3.1 Lightning Rods: To prevent damage from direct lightning strikes, substations generally have independent lightning rods and frame lightning rods. Some substations in canyon areas use lightning wire protection. Their structures all consist of a lightning rod, down conductor, and grounding electrode, and the lightning protection principle is the same. To prevent backflashover, the distance between the lightning rod and the protected equipment in the air must be no less than 5m, and the distance in the ground must be no less than 3m. Frame lightning rods are generally used for 110kV and above, and are connected to the main grounding grid after being equipped with a centralized grounding device. The protection range of an independent lightning rod is 1.5h (rod height) above the ground. For spaces exceeding half the rod height, the protection range can only be checked within a 45° angle. Currently, the internationally popular rolling sphere method is relatively accurate in checking the protection range of independent lightning rods. The rolling sphere theory posits that direct and indirect lightning strikes are related to the charge of the thundercloud; lower-energy lightning is more prone to indirect strikes. This can be visualized as a sphere with a radius proportional to the thundercloud's charge, centered on the thundercloud leader, rolling across the ground until it hits the tip of a lightning rod. If the arc from the point of contact with the ground to the rod tip does not reach the protected object, then the protected object is within the protection zone. For example, for a medium-intensity thundercloud (U0=50MV), using the lightning leader's strike distance formula rs=1.63U01.75, the radius of the sphere is 133m. The protection radius obtained in this case is slightly larger than that specified in relevant design codes. According to lightning protection specifications, a medium-sized 110kV substation typically uses 3-5 lightning rods, and a 35kV substation uses 1-4 rods approximately 30m long, to cover the entire protected area. Microwave towers are also a type of independent lightning rod. For substations with microwave towers, regulations stipulate that the towers must be connected to the grounding network of the communication room. The grounding network of the communication room and the main control room is integrated, and the lightning current is discharged through the grounding network of the main control room. According to the previous analysis, if the protection, monitoring, metering, RTU and other equipment in the high-voltage distribution room, the main control room and the communication room are connected to the grounding network that is far apart, and there is an electrical connection between them, the probability of backflashover to the electronic equipment in the station is greater. The annual number of lightning strikes to the lightning rod can be calculated according to the empirical formula N= 0.015 ·n·k(l+5h)(b+5h)10-6[4]. Where n is the number of thunderstorm days in a year, K is the correction coefficient, and 2 is taken for metal structures. l, b and h are the length, width and height of the building, respectively. According to this formula, in an area with 40 thunderstorm days in a year, a 35kV outdoor terminal substation with a busbar frame of 5.5m high has a lightning strike probability of 0.000454 times per year, while after adding a 30m high lightning rod, it will be struck by lightning 0.027 times per year. If a substation has four lightning rods, each 50m apart, the probability of a lightning strike is 0.048 times per year. Lightning rods significantly increase the probability of lightning strikes, greatly increasing the likelihood of lightning damage to the microelectronic equipment (protection, monitoring, automation, and communication systems) that are currently being upgraded and attached to primary equipment. The damage can occur in various ways, leading to significant losses in power production. 3.2 Surge Arresters To protect against induced lightning and lightning surge waves from transmission lines, substations use surge arresters. Previously installed surge arresters were mostly tubular surge arresters installed at the line ends and valve-type surge arresters installed at busbars and equipment; these have now been replaced by higher-performance metal oxide surge arresters. Since lightning surge waves are most harmful to systems below 35kV, substations focus on protecting against surge waves from 35kV and 10kV lines. For 35kV overhead incoming lines, a 1-2km section of overhead lightning protection wire with tubular surge arresters at both ends is generally used for protection. For 10kV lines, each incoming line is protected by a set of valve-type or zinc oxide surge arresters. For 3-10kV distribution transformers, generally only valve-type surge arresters are specified for protection on the high-voltage side. For Y/Y0 connected transformers supplying power to areas prone to lightning strikes, only surge arresters are specified to prevent lightning surges and low-voltage side lightning intrusion waves from breaking down the high-voltage side insulation of the transformer. The above protection measures do not consider overvoltage in the low-voltage section, nor do they consider the threat to electronic equipment posed by lightning intrusion waves or dangerous potentials introduced through the metal pipelines entering the substation. 3.3 Lightning Protection Measures in Buildings Outdoor substation buildings generally include a high-voltage room, main control room, communication room, and some auxiliary residential and office buildings. According to the classification of building lightning protection levels, substation production buildings are generally classified as Class III industrial buildings. Because these buildings are generally designed to be within the protection range of substation lightning rods, except for the communication room which has undergone lightning protection treatment according to relevant standards, other parts do not have rooftop lightning rods or lightning protection strips. Therefore, measures such as equipotential bonding strips, using building steel reinforcement as shunt lines, and forming Faraday cage shielding nets are not adopted. For protection against lightning surge intrusion, cables entering the building are generally introduced through cable trench supports and cable shaft supports integrated with the grounding grid, and some cables have shielded grounding treatment at both ends. Because previous building lightning protection did not consider the protection of a large number of electronic devices, many existing and under-construction buildings have serious inherent defects in lightning protection. The protection of electronic equipment against induced lightning relies mainly on the casing and internal measures, which reduces its reliability. 3.4 Grounding Grid and Metal Part Treatment of Buildings Because substation buildings do not consider direct lightning strike discharge paths, their grounding grid treatment is generally connected to the main grounding grid within the substation. Although many regulations distinguish between lightning protection ground, AC ground, DC ground, protective ground, and data ground, implementation is difficult due to two main reasons: firstly, stringent conditions and limited space; secondly, the equipment used is often small-scale, making such precise distinctions unnecessary, thus creating a de facto combined grounding network. Modern research suggests that this combined grounding network is economical and effective, and can resolve potential differences caused by internal and external overvoltages, preventing backlashes to electronic equipment with low withstand levels. However, the safety of equipment in a combined grounding network must be addressed through proper grounding wire placement, equipotential bonding techniques, and electromagnetic compatibility protection of the equipment itself. Currently, the combined grounding network in substations extends from the main control room to the high-voltage room and to outdoor high-voltage distribution equipment. Due to the long distances, large areas, and complex connections between various electronic devices, potential differences at various points in the grounding network can easily cause equipment malfunctions and damage. The most affected components include high-frequency cables, long-distance guide cables, control cables, and network cables between locally located electronic equipment and the main control room. Metal doors and windows, glass curtain walls, ceiling frames, lighting wiring, and pipelines within buildings are often neglected and not grounded. Furthermore, the DC batteries used in the secondary circuits operate at floating point (especially the older, bulky batteries), which contribute to the secondary effects of lightning strikes and are potential killers of electronic equipment. Strengthening Lightning Protection Measures in Substations Traditional lightning protection measures in substations are effective for protecting high-voltage electrical equipment, but inadequate for protecting electronic equipment. To adapt to the development requirements of intelligent substations, further protection measures must be implemented beyond the existing ones. The principles for these measures are zoned protection, three-level overvoltage protection, multiple shielding, equal potential, and floating potential control. Based on the new concept of lightning protection zones proposed in IEC/TC81 at the 1992 International Conference on Lightning Protection of Buildings, lightning protection for substations is divided into three zones for graded protection. Strengthening shielding according to the sensitivity and importance of the equipment can achieve twice the result with half the effort. 4.1 The first-level protection zone covers the high-voltage equipment and the incoming section of high-voltage lines throughout the entire substation. The main measures include independent lightning rods, frame lightning rods, overhead lightning conductors, high-voltage surge arresters, equipment down conductors, main grounding grids, and microwave towers and their grounding. Its main tasks are lightning attraction, current discharge, amplitude limiting, and voltage equalization, completing basic lightning protection functions. The use of lightning rods increases the probability of lightning strikes, thus increasing the likelihood of induced lightning damage to electronic equipment. To mitigate induced lightning radiation, some projects have adopted shielded down conductors, while others have used multiple down conductors for current distribution; these measures can all play a role. Additionally, some substations have previously selected various types of passive lightning arresters, such as conductor lightning arresters, semiconductor lightning arresters, and short-needle lightning arresters. Their evaluations are mixed, but one undeniable fact remains: the protection range of a lightning arrester is at least the same as that of a lightning rod of the same height. Regarding the operation of lightning arresters, as long as their grounding meets the requirements of lightning protection specifications, and the spatial and ground safety distances and protection range meet the regulations, they should continue to be used with proper observation and recording. If lightning can be eliminated or partially eliminated, it will benefit electronic equipment. 4.2 The second-level protection zone includes pipelines entering and exiting the substation, secondary cables, terminal boxes, the power system used by the substation, and microwave antenna feeders. Its main tasks are to prevent the transmission of induced lightning overvoltage and surge surge overvoltage, as well as to transmit dangerous potentials internally and externally. 4.2.1 Handling of Pipelines Entering and Exiting the Substation Pipelines entering and exiting the substation include water pipes, gas pipes, heating pipes, power lines, longitudinal protection guide lines, information transmission lines, etc. All metal pipes entering the substation should be directly buried and connected to the grounding network in several locations. They should preferably be isolated by insulated pipes before entering the substation. The power supply used is generally not transmitted externally. If it is introduced internally, it should be introduced through an isolation transformer and directly buried for 15m before entering the substation. If longitudinal protection guide lines are still used, the guide lines should be introduced through an isolation transformer according to the departmental countermeasures, and the part entering the substation should be directly buried in conduit. Information transmission cables entering and exiting the substation should be directly buried in conduit and introduced into the computer room after passing through the security unit or the corresponding data surge arrester. Optical cables with metal wires should be directly buried in conduit and introduced into the computer room only after passing through the grounding busbar. Grounded waveguides themselves have good lightning protection and do not require additional surge arresters. Grounding along the route according to regulations is sufficient. For coaxial cable antenna feeders, appropriate high-frequency surge arresters should be installed, and the ground wire of the surge arrester should be connected to the grounding busbar of the computer room as close as possible. 4.2.2 Control signal cables, current, and voltage circuit cables directly connected to electronic equipment cabinets and devices via secondary cables and terminal boxes should all be shielded cables, and the shielding metal protective layer and spare core should be grounded at both ends. Terminal boxes, circuit breaker mechanism boxes, and control cabinets, regardless of whether they contain electronic equipment, should be grounded away from the main current-diffusing wires of surge arresters or lightning rods. 4.2.3 Most lightning damage accidents involving electronic equipment in the power supply system are related to the power source. This indicates both insufficient protection and the sufficiently large energy of lightning waves entering from the power supply, which still possesses strong destructive power even after several levels of high-voltage discharge. According to the national standard (GB50057-94) "Code for Design of Lightning Protection of Buildings," three levels of overvoltage protection should be adopted for the power supply and distribution system of microelectronic equipment. The three levels are the low-voltage outlet of the substation, the branch outlets of the substation power distribution cabinet, and the UPS power outlets of each piece of equipment. Surge arresters in low-voltage power distribution systems are generally MOV (metal oxide variable resistors). MOVs have a relatively high failure rate. Although improved MOVs have increased current-carrying capacity, and some products use fuses and temperature-disconnect devices for protection, damage still occurs. Therefore, three-level redundancy is necessary to enhance reliability. 4.3 The third-level protection zone includes the substation main control room, remote communication equipment room, and all electronic equipment. Its main tasks are multiple shielding, power overvoltage clamping, signal amplitude limiting and filtering, ground potential equalization, and floating-point potential restraint. 4.3.1 Multiple Shielding: Microelectronic equipment operates at low voltages and has low breakdown power; single shielding is insufficient to achieve the desired effect, necessitating multiple shielding. This involves using a Faraday cage composed of building steel reinforcement mesh, as well as the metal casings of equipment cabinets and devices for tiered shielding. Early substation buildings had many inherent deficiencies in lightning protection. Newly built substations must comply with national standards (GB50057-94) "Code for Design of Lightning Protection for Buildings," the Ministry of Posts and Telecommunications (YD2011-93) "Code for Design of Lightning Protection and Grounding of Microwave Stations," and the Ministry of Electric Power (DL548-94) "Regulations for Operation and Management of Lightning Protection for Communication Stations in Power Systems," etc., utilizing the building's parapet walls, rooftop lightning protection networks, and a network welded together with structural and foundation steel bars, as well as metal curtain walls with special equipment requirements, to form the first level of shielding. When ordering equipment cabinets and devices, the electromagnetic compatibility protection level and operating environment must be specified. 4.3.2 Ground Potential Equalization: The author agrees with using a combined grounding grid indoors, with a ring ground busbar and grounding convergence line. The ground busbar and grounding grid are symmetrically connected by multiple down conductors. For functional grounds such as digital ground and analog ground that truly need to be separated from protective ground, ground electrode surge protectors can be used for connection. For sections where electrical connections between electronic devices span large distances, crossing several protection zones, uneven ground potential often causes malfunctions or damage. The National Power Dispatch and Communication Center has issued a document outlining countermeasures, including laying a copper grounding grid of at least 100mm² in the cable layer of the substation's main control room, extending to the 220kV coupling capacitor and filter connection. This measure has proven effective. This problem isn't limited to high-frequency protection; currently, if communication between locally deployed electronic equipment and sub-control rooms or main control rooms uses electrical connections, the same issue arises. Ground potential balancing measures can be implemented on-site based on specific circumstances. 4.3.3 Floating-Point Potential Constraints: Metal doors and windows, glass curtain walls, ceiling joists, and lighting fixtures within buildings can be damaged by secondary lightning strikes and should be grounded at multiple points nearby to prevent unforeseen damage. Substation secondary circuit DC batteries operate at floating point for extended periods. To prevent lightning damage, DC surge arresters and gas discharge tubes should be installed in the insulation monitoring device. V. Conclusion The hazards of lightning strikes to substation electronic equipment mainly manifest as induced overvoltage, surge overvoltage, ground potential backflashover, and secondary lightning effects. Lightning protection for substation electronic equipment should be implemented in a zoned and tiered manner, combining lightning attraction, current shunting, current dissipation, shielding, voltage equalization, isolation, amplitude limiting, clamping, and filtering. It should fully utilize advanced technologies and select low-voltage surge arresters, such as high-frequency surge arresters, data surge arresters, discharge tubes, silicon transient diodes, transient overvoltage protectors, and combined surge arresters, based on the operating characteristics of the electronic equipment, to minimize lightning damage and interference. References: 1. Xue Donghua. "Conductor Lightning Suppressors". Wuhan High Voltage Research Institute, Ministry of Energy, Electric Power Technology Development Company. 1992.9 2. Wuhan Institute of Water Resources. He Ping, Wen Xishan, et al. "Calculation Problems of Induced Overvoltage in Overhead Lines". High Voltage Engineering. 1999.2 3. Shanghai Jiaotong University. Feng Lei, Zhou Peibai. "Calculation of Induced Electric Field in High-Rise Buildings When Struck by Lightning". High Voltage Engineering. 2001.1 4. "Code for Design of Lightning Protection of Buildings" (GBJ57-83). 5. Notice No. 112 of 1998, "Notice on Issuing Improvement Measures for High-Frequency Channel Work of Relay Protection".