For **lightning protection**, achieving effective results requires careful attention to the "placement of appropriate lightning protection devices in suitable locations." The selection of **lightning protection devices** is a critical step in ensuring system safety and performance.
1. When it comes to the distribution of lightning currents among different systems entering a building, approximately 50% of the current is dissipated through external lightning protection systems, while the remaining 50% flows through the metal components of the entire system. This model helps estimate the current capacity required for SPDs (Surge Protective Devices) and the specifications of metal conductors used for equipotential bonding at the boundaries between LPZ0A, LPZ0B, and LPZ1 zones. At this point, the lightning current waveform is typically 10/35 μs. The distribution of current among various metal structures depends on the impedance and inductive reactance of each path. These paths may include power lines, signal lines, water pipes, and other metallic conduits. In cases where precise values are unknown, it's reasonable to assume equal resistance among connections, leading to an even current distribution across the metal circuits.
2. If overhead power lines are susceptible to direct lightning strikes, the amount of current entering the protected area within the building depends on the impedance of the external path, the lightning arrester's discharge branch, and the internal wiring. If both ends have similar impedance, the power line will carry about half of the total lightning current. Therefore, a properly rated lightning arrester must be installed to protect the system effectively.
3. Subsequent evaluation models help assess the distribution of lightning currents at the boundary of the LPZ1 zone. Due to the high insulation impedance on the user side compared to the low impedance of the lightning arrester's discharge path and external lead wires, the current entering the next protection zone is significantly reduced. As a result, detailed numerical estimation is usually unnecessary. It is generally sufficient for the lightning protection device in the subsequent zone to have a current rating of 20 kA (8/20 μs) or less, without requiring a high-capacity device.
4. The choice of surge arresters in later zones should consider energy distribution and voltage coordination between levels. When multiple factors are hard to determine, using a series-parallel configuration of lightning protection devices can be a smart option. This approach combines multi-level surge protection with filtering technology, enabling better energy matching and voltage control. Series-parallel designs are widely applicable, especially in complex or hard-to-distinguish protected areas. They help manage transient overvoltage by introducing partial pressure and delay, improving energy coordination. These devices also reduce the rate of rise of transients, resulting in lower residual voltages, longer life, and faster response times.
5. Other parameters of the lightning protection device depend on the specific lightning protection zone where the equipment is located. The operating voltage of the device should be based on the rated voltage of all components in the circuit. Additionally, the rated current of serial and parallel lightning protectors should be considered carefully.
6. Several factors influence the distribution of lightning current in electronic wiring. A lower grounding resistance of the transformer increases the current flowing through the electronic lines. Longer power supply cables tend to reduce the current in the power line, allowing more balanced current distribution among multiple wires. However, short cables and very low neutral impedance can cause current imbalance, leading to differential mode interference. When multiple users are connected to the same power line, the effective impedance decreases, increasing the current distribution. During thunderstorms, most of the lightning current tends to flow into the power lines, which is why the majority of lightning-related damage occurs there.
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