Surge Arrester (Lightning Protection) System Solution: Integrated External and Internal Protection Scheme

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​1. Solution Background and Objectives​

Lightning activity is a significant factor threatening the safety of buildings, personnel, and internal equipment. Lightning strikes generate high-intensity direct currents and transient overvoltages. These can not only cause building damage and physical destruction of equipment but also penetrate via metallic lines such as power supply lines and signal lines, leading to electronic equipment malfunctions, data loss, and even secondary disasters like fires. This solution aims to establish a comprehensive protection system composed of an External Lightning Protection System (ELPS) and Surge Protective Devices (SPDs), effectively intercepting, guiding, discharging, and limiting lightning energy to maximize the structural safety of the building and ensure the continuity and stability of internal equipment and system operations.

​2. Overview of Lightning Protection System (LPS) Components​

An effective integrated Lightning Protection System (LPS) comprises two indispensable and mutually reinforcing core components:

• ​External Lightning Protection System (ELPS):​​ Primarily designed to defend against direct lightning strikes.
• ​Internal Lightning Protection System (Surge Protection, SPD System):​​ Primarily designed to defend against transient overvoltages (surges) caused by Lightning Electromagnetic Pulse (LEMP) entering equipment via lines.

​3. External Surge Arrester Installation Scheme (Protection Against Direct Strikes)​​

• ​Core Function:​​ To intercept direct lightning strikes and safely conduct the massive lightning current into the ground, preventing the physical damage (such as penetration, fire, structural damage) that a direct strike can inflict on the building structure itself.
• ​Key Components:​​
• ​Air Termination System (Lightning rods/strips/meshes):​​ Installed on the building rooftop or highest points to attract and receive lightning strikes. Select the appropriate type (e.g., rod, mesh, strip) and layout according to the building shape and area, ensuring protection coverage meets the requirements of the "rolling sphere method" principle.
• ​Down Conductors:​​ Used to conduct the lightning current from the air termination system to the earth termination system. Should be routed via the shortest and straightest paths, with sufficient quantity and uniform distribution (spacing compliant with regulations). Materials are typically galvanized flat steel or round steel. Avoid installation near common personnel paths or apply insulation protection measures.
• ​Earth Termination System:​​ Discharges the lightning current into the ground. This is the core and foundation of the protection system; its quality (earth resistance value) is crucial. Typically consists of earth electrodes (vertical rods, horizontal conductors) and connecting conductors. Use corrosion-resistant materials (e.g., galvanized steel, copper), ensure sufficient burial depth, and form an effective equipotential bonding ring (foundation earthing) around the building. Earth resistance should be minimized (generally required ≤10Ω, specific requirements according to relevant standards).
• ​Installation Locations:​​
• Highest points of the building roof and locations vulnerable to strikes (corners, eaves, parapets, vents, chimneys, etc.).
• Special structures (e.g., towers, antennas, solar panel supports) require individual or integrated consideration.
• ​Scheme Key Points:​​
• ​Compliance with Standards:​​ Strictly adhere to national and industry lightning protection design standards (e.g., GB 50057 "Design Code for Lightning Protection of Buildings", equivalent to IEC 62305 series).
• ​Material Quality:​​ Use high-quality, corrosion-resistant materials meeting standards.
• ​Equipotential Bonding:​​ All metallic components (e.g., pipes, equipment enclosures, metal roofs, steel structures) must be reliably bonded to the nearest down conductor or earth termination system to prevent side flashes.
• ​Safety Separation Distances:​​ Ensure adequate safety separation distances exist between air terminations and the structure, and between down conductors and services/pipelines.
• ​Reliable Connections:​​ All connection points must be robust (welding or approved clamps) to ensure good electrical continuity.

​4. Internal Surge Arrester (SPD) Installation Scheme (Protection Against Lightning Surges)​​

• ​Core Function:​​ To limit lightning-induced transient overvoltages (surges) entering via power lines, signal lines, communication lines, etc., clamping them to a safe level that the equipment can withstand, preventing damage from overvoltage/overcurrent.
• ​Key Components: Surge Protective Device (SPD),​​ also known as a surge suppressor or lightning arrester:
• ​Transient Voltage Suppressor (TVS):​​ Often used for fine equipment protection or signal lines.
• ​Overvoltage Protector:​​ General term encompassing various technologies (e.g., Metal Oxide Varistor MOV, Gas Discharge Tube GDT, solid-state protectors).
• ​Power SPD:​​ Installed at various levels of the power distribution system (main distribution, sub-distribution, ahead of terminal equipment).
• ​Signal/Data SPD:​​ Installed at entry ports for telephone lines, network lines (e.g., RJ45), coaxial cables (e.g., CCTV video, satellite signals), control lines, etc.
• ​Earth Connection:​​ SPDs must be well earthed via a low-impedance path to effectively discharge surge currents. Earthing conductors should be as ​short, straight, and thick​ as possible ("Short-Straight-Thick" Principle).
• ​Installation Locations and Levels (Staged Protection - Coordination):​​
• ​First-Level Protection (Class I / Type 1 SPD):​​
• ​Location:​​ Building Main Distribution Panel/Mains Incomer (typically at the LPZ 0A/0B → LPZ 1 boundary).
• ​Function:​​ Discharges the vast majority of the massive energy (10/350μs waveform) from direct strikes or nearby strikes, limiting the residual voltage to a lower level. Typically uses high-discharge capacity spark-gap type SPDs. Requires highly reliable earthing.
• ​Second-Level Protection (Class II / Type 2 SPD):​​
• ​Location:​​ Floor Distribution Boards, Area Distribution Panels, Main Switchboard within Equipment Rooms (at the LPZ 1 → LPZ 2 boundary).
• ​Function:​​ Further limits residual surge voltages passed by the first level and overvoltages caused by internal switching operations (8/20μs waveform), providing zonal equipment protection. Typically uses voltage-limiting type SPDs (e.g., MOV based).
• ​Third-Level Protection (Class III / Type 3 SPD / Point-of-Use Protection):​​
• ​Location:​​ Immediately in front of equipment, within socket outlets/plug strips, or equipment internal circuitry (at the LPZ 2 → LPZ 3 boundary).
• ​Function:​​ Clamps the residual overvoltage (combination wave) at equipment ports, providing final-stage fine protection. Critically important for sensitive electronic equipment (e.g., servers, workstations, PLCs, medical devices, communication equipment). Also used at signal line entries.
• ​Scheme Key Points:​​
• ​Coordination:​​ SPDs at different levels must achieve energy and voltage coordination (using coupling/isolation elements between stages or the inherent decoupling characteristics of the SPDs), ensuring energy is discharged progressively and voltage is reduced step-wise. This prevents lower level SPDs from failing due to excessive energy.
• ​Earthing Quality:​​ Effective earthing of SPDs is critical to the entire scheme's effectiveness. Earthing conductors should ideally be shorter than 0.5 meters, with a sufficient cross-sectional area (as per SPD class and location, typically ≥6-25mm² stranded copper).
• ​Installation Compliance:​​ Install according to the SPD product instructions and relevant standards, ensuring correct phase and earth connections.
• ​Equipotential Bonding:​​ Bond metal cabinets, racks, cable trays, etc., to establish a "Faraday cage" effect, minimizing internal potential differences.
• ​Regular Maintenance:​​ SPDs are often "sacrificial" devices requiring regular inspection (visual status indicator, remote alarm monitoring) and testing. Failed SPDs must be replaced promptly.

​5. Comprehensive Solution Benefits and Implementation Value​

• ​All-Round Protection:​​ External system protects against direct strikes; internal system protects against induced surges (LEMP), forming a complete protection chain.
• ​Maximized Safety:​​ Protects building structure, human life, and valuable electrical/electronic equipment assets from damage.
• ​Ensures Operational Continuity:​​ Reduces the risk of equipment failure, system downtime, and data loss caused by lightning, enhancing system reliability and business continuity.
• ​Reduces Total Cost of Ownership:​​ Preventive investment is significantly cost-effective compared to the direct costs of lightning strike damage (equipment replacement) and indirect costs (production stoppage, data loss, reputational impact).
• ​Regulatory Compliance:​​ Meets national building safety, electrical safety, and lightning protection regulatory requirements and standards.