Abstract: This paper elucidates the concept of comprehensive lightning protection for program-controlled exchanges (PCEs), provides some key lightning protection measures and details of their implementation, and offers useful suggestions for comprehensive lightning protection of communication equipment in power systems. Keywords: Power system , PCE, Lightning protection measures I. Introduction Power communication (dedicated power communication network) is an indispensable and important component of modern power systems and one of the three pillars for the safe and stable operation of modern power grids. PCEs are an important part of the Shaanxi power communication network. Once a fault occurs, the losses are not only economic, but more seriously, they pose a potential threat to power grid security. Therefore, strengthening the security protection of PCEs is particularly important. The most important component of a PCE is the integrated circuit (IC). ICs have relatively low anti-interference capabilities; even lightning electromagnetic pulses (LEMPs) induced from the line can break down IC components. Therefore, PCEs are prone to lightning strikes. The following section will analyze and discuss this issue in depth. II. Classification and Prevention Principles of Lightning Disasters Lightning strikes can produce different forms of damage (see Figure 1). The International Electrotechnical Commission (IEC) has called lightning disasters "a major public hazard of the electronic age." Lightning strikes, induced lightning strikes, and instantaneous overvoltages such as power spikes have become the main culprits in damaging electronic equipment. Analysis of numerous cases of lightning strikes on communication equipment has led experts to believe that lightning electromagnetic pulses (LEMPs) caused by lightning induction and lightning surges are the primary cause of damage to communication equipment. Therefore, our prevention principle is "overall defense, comprehensive management, and multiple protections," striving to minimize the damage caused. III. Main Lightning Protection Measures 3.1 A Sound Grounding System Grounding is the most basic and effective measure in a lightning protection system. 3.1.1 According to the different functions of "grounding," we can divide "ground" into "working ground," "protective ground," and "lightning protection ground," etc. For critical communication equipment systems, a "working ground" is essential. It provides a standard reference potential for the entire system, allowing it to function properly. If the system is also powered by a high-voltage power source, the equipment casing must be connected to a "protective ground" to ensure personal safety. If the system is connected to outdoor overhead metal equipment or cables, a "lightning protection ground" must be installed in a suitable location to prevent high-voltage lightning strikes from entering the system. 3.1.2 If the "working ground," "protective ground," and "lightning protection ground" of a communication system are installed separately and not connected, forming independent systems, we call it a "separate grounding system." If the three are combined into a unified grounding system, we call it a "combined grounding system." Currently, the Shaanxi Provincial Dispatch and Communication Building uses a combined grounding system. A combined grounding system eliminates potential differences between different grounding points and can effectively suppress discharge phenomena between different grounding points during lightning strikes. 3.1.3 The grounding of the program-controlled exchange and the grounding of the entire building are very important. According to the standards of the Ministry of Information Industry, the impulse grounding resistance of lightning protection grounding in telecommunications buildings should not exceed 10 ohms (YD5003-94 "Design Code for Telecommunications Dedicated Buildings"), and the grounding resistance of important telecommunications buildings should be below 1 ohm (YDJ20-88 "Provisional Technical Regulations for Installation Design of Program-Controlled Telephone Exchange Equipment"). If the grounding does not meet the requirements, serious damage to the equipment may occur when the exchange is subjected to strong power interference or lightning strikes. The grounding of program-controlled exchanges under the jurisdiction of Shaanxi Provincial Power Company adopts a combined grounding method, and the grounding resistance of the grounding body is <1Ω (measured 0.7Ω). 3.1.4 In the actual wiring process, a wiring method similar to "distributed grounding" is adopted, that is, both the working ground wire and the protective ground wire are led out from the grounding busbar, and the two types of ground wires are not directly connected nearby, as shown in Figure 2. Its advantage is that when lightning current flows through the grounding grid, the lightning current only flows longitudinally, and even if there are poor contact points, it will not cause lateral interference. 3.1.5 Grounding treatment of the exchange: a 135mm2 multi-strand copper core wire is used to connect it separately to the grounding busbar. Unlike the system, (1) it is not directly connected to the positive terminal of the switch, nor is the cabinet randomly connected to cables or wires with positive terminals. (2) The contact parts between the cabinet and the raised floor and base are insulated, which is equivalent to adopting the "floating grounding" method to prevent static electricity and stray currents from the adjacent surface layer from entering the cabinet and interfering with communication. 3.1.6 Grounding of the main distribution frame: Two 50mm2 multi-strand copper core wires are introduced separately from the busbar, one of which is connected to the base of the distribution frame, and the other is connected to the grounding copper busbar at the top of the distribution frame. The advantages of dual-wire grounding are: on the one hand, it can improve the reliability of security equipment and alarm signal circuits; on the other hand, when the communication line is struck by lightning and high voltage current enters the ground through the protector, the potential on the distribution frame can be quickly reduced. After adopting the combined grounding method, the grounding of the equipment and the floor is more reliable, effectively ensuring the safety of equipment and personnel. 3.2 Reasonable Comprehensive Cabling of Program-Controlled Switches Cabling for program-controlled switches is a highly specialized task. The cabling scheme should consider lightning safety during the design phase. Cabling work includes trunk lines, internal lines, power supply lines, and indoor grounding wires for the program-controlled switch. 3.2.1 Outdoor transmission networks of the switch utilize both overhead and underground methods. For overhead cables, telephone lines or cables should be buried before entering the building, with a burial length >2ρ (ρ is the resistivity of the grounding resistance, in Ω*m), and an actual length >50m. Buried cables generally use metal-armored cables directly buried, or non-metallic shielded cables buried directly in metal conduits. From a lightning protection perspective, underground cabling should be chosen for indoor cables where conditions permit. 3.2.2 Indoor transmission networks of program-controlled switches should be laid along dedicated signal cable trays, avoiding laying along building structural columns or close to exterior walls; strong and weak current cables should not be laid in the same tray to reduce interference. For example, in a dispatch center building in Shaanxi Province, there is no dedicated signal cable tray. Signal lines and power lines are laid in the same tray. When the power line is struck by lightning or an induced lightning pulse is generated, an electromagnetic pulse is also induced on the signal line and transmitted along the signal line to the switch, causing damage to the switch. 3.3 Determining Current Diversion and Voltage Limiting Measures 3.3.1 Program-controlled telephone lines and dedicated data lines entering the building should be equipped with surge arresters. When selecting surge arresters, the starting voltage should be 1.5 times the peak value of the protected line signal voltage, the lightning current flux should be greater than or equal to 0.2kA, the characteristic impedance should be 600 ohms, and the operating frequency should be 0-5MHz. 3.3.2 For outdoor receiving devices with signal lines connected to indoor equipment, a surge arrester of the appropriate model should be connected in series between the antenna receiving device's lead-in line and the equipment. 3.3.3 The signal surge arresters installed on the above lines and equipment should be grounded nearby, with a grounding resistance of less than 4 ohms (for some special grounding requirements, less than 1 ohm). Furthermore, its grounding wire should not be connected to the lightning rod or lightning strip, but should be connected to the grounding wire of a dedicated surge arrester and directly connected to the grounding grid. Install surge protectors (commonly known as lightning arresters) on power lines and signal lines to promptly divert lightning current to the ground during lightning electromagnetic pulse attacks, thus providing protection. When selecting surge protection devices, pay attention to their response time. Some surge protectors remain intact even when the protected device is damaged by lightning current, because their response time is too slow. Currently, line surge arresters using zinc oxide resistors (also known as varistors) as the core component are popular in the market, offering faster response speeds and better performance. 3.4 Other Effective Measures 3.4.1 Determine Equipotential Bonding for Communication Equipment Rooms: All metal devices, external conductive objects, power lines, communication lines, and other cables entering and exiting the equipment room should be properly equipotentially bonded to the main busbar. An equipotential bonding network should be installed in the equipment room and connected to the building's grounding system. Equipotential bonding should preferably adopt an M-shaped network, with the DC ground of each device connected to the equipotential bonding network along the shortest possible distance. 3.4.2 Shielding Principles for Switches: In addition to signal and power lines, the switch room itself should also be shielded (including spatial and line shielding). Specifically, metal doors, windows, ceiling joists, and anti-static flooring should be grounded. Uniform potential distribution at all points ensures good shielding protection for personnel and equipment inside. IV. Conclusion In modern communication systems, a well-designed lightning protection system is crucial for the safe operation of equipment, not just for program-controlled switches. Only by strictly adhering to the principles of comprehensive lightning protection and planning protection from all possible lightning strike paths can the safe operation of the entire communication network be guaranteed. References [1] Modern Lightning Protection Technology Fundamentals, edited by Yu Hao et al., Tsinghua University Press, December 1995 [2] Code for Lightning Protection Design of Buildings, edited by the Ministry of Construction of the People's Republic of China, Machinery Industry Press, April 1994 [3] Power Supply Engineer's Technical Handbook, edited by Liu Jiecai, Machinery Industry Press, April 2000 [4] Lightning Protection and Grounding Technology of Buildings, edited by Zhang Xiaoqing, China Electric Power Press, June 2003