For **lightning protection** systems, achieving effective results requires careful attention to the **placement of appropriate lightning protection devices** in strategic locations. The selection of **lightning protection devices** is a critical factor that directly influences the system's performance and safety.
1. When it comes to how lightning currents are distributed among different facilities entering a building, approximately 50% of the current is dissipated into the ground through external lightning protection devices, while the remaining 50% flows through the metal components of the entire system. This model helps estimate the current capacity of SPDs (Surge Protective Devices) and the specifications for equipotential bonding at the boundaries between LPAOA, LPZOB, and LPZ1 zones. At this point, the lightning current typically follows a 10/35μs waveform. The distribution of current among various metallic elements depends on the impedance and inductive reactance of each path. These paths include power lines, signal lines, metal pipes, and other grounded structures. In cases where precise values are uncertain, it’s reasonable to assume equal resistance across connections, meaning the current is evenly distributed among the metal circuits.
2. If a power line is introduced overhead and is susceptible to a direct lightning strike, the amount of current entering the protected area within the building depends on the impedance and inductive reactance 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 direct lightning current. Therefore, a properly rated lightning arrester must be installed to manage this load effectively.
3. Subsequent evaluation models help estimate the distribution of lightning current at the boundary of the LPZ1 zone. Since the insulation impedance on the user side is much higher than the impedance of the lightning arrester’s discharge path and the external lead-in, the current entering the next protection zone is significantly reduced. As a result, detailed numerical calculations are usually unnecessary. It is generally sufficient to ensure that the lightning protection device in this zone has a current capacity of 20 kA (8/20 μs) or less. High-capacity devices are not required here.
4. The selection of surge arresters in subsequent protection zones should consider energy distribution and voltage coordination between different levels. When multiple factors are difficult to determine, using a series-parallel configuration of lightning protection devices can be an effective solution. This approach combines multi-level surge protectors with filter technology, optimizing energy matching and voltage distribution. Series-parallel lightning protection offers wide applicability, especially in areas where protection zones are hard to distinguish. It also helps reduce transient overvoltage by inducing partial pressure and delay, improving energy coordination and reducing the rate of rise of interference. This leads to lower residual voltage, longer lifespan, and faster response times.
5. The choice of other parameters for lightning protection devices depends on the specific lightning protection zone where the equipment is located. The operating voltage of the device should match the rated voltage of all components in the circuit. For series and parallel lightning protectors, the rated current is also an important consideration.
6. Additional factors that influence the distribution of lightning current in electronic wiring include the grounding resistance of the transformer, which, when reduced, increases the current flowing through the wiring. Longer power supply cables tend to reduce current distribution in the power lines, allowing for more balanced current flow among multiple wires. However, short cable lengths and low neutral impedance can cause current imbalance, leading to differential mode interference. Multiple users connected to the same power line can lower the effective impedance, increasing the current distribution. During thunderstorms, most of the lightning-induced current tends to flow through the power lines, which is why most lightning damage occurs in these circuits.
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