Lightning protection device selection - Solutions - Huaqiang Electronic Network

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Proper installation of the right lightning protection device in the correct location is crucial for effective lightning protection. Choosing the appropriate surge protector is essential, as it directly impacts the safety and reliability of electrical systems. 1. When lightning strikes, the current is distributed between different facilities entering a building. Approximately 50% of the current is discharged through the external lightning protection system, while the other 50% flows through the metal components of the entire system. This distribution method helps estimate the current capacity of the surge protector and the required cross-sectional area of the bonding conductor at the boundaries of different lightning protection zones (LPZ0A, LPZ1, etc.). The lightning current at these points typically follows a 10/35μs waveform. The actual distribution of current across each metal component depends on the impedance and inductive reactance of the path, such as power lines, signal cables, and metal pipes. Grounding systems like water pipes or structural frames are usually estimated based on their grounding resistance. In uncertain cases, it’s reasonable to assume equal resistance, meaning the current is evenly distributed among the conductors. 2. If overhead power lines are exposed and could be struck by lightning, the amount of current entering the protected area depends on the impedance of the external lead-in line, the surge arrester branch, and the internal wiring. If the impedance at both ends is similar, the lightning current will split evenly, with half flowing into the building. In this case, a surge arrester designed for direct lightning strikes is necessary to protect the system. 3. The second stage of evaluation focuses on the current distribution within the LPZ1 zone. Since the insulation resistance on the user side is much higher than that of the surge arrester and external lines, the current entering the next protection zone is significantly reduced. Therefore, detailed calculations are not always required. It is generally recommended that surge arresters used in subsequent zones have a current capacity of less than 20 kA (8/20μs), without the need for high-capacity devices. When selecting surge protectors for later zones, it's important to consider energy distribution and voltage coordination between stages. In complex situations where many variables are hard to determine, using a series-connected surge arrester is a practical choice. This approach, widely applied in modern lightning protection, involves differentiating protection levels compared to traditional parallel systems. The core idea is combining multi-stage surge arresters with filtering technology through proper energy matching and voltage distribution. Series-type surge arresters offer several advantages: they are versatile, suitable for areas where protection zones are unclear, and help manage transient overvoltage by introducing partial pressure and delay. They also reduce the rate of rise of disturbances, leading to lower residual voltages, longer lifespan, and fast response times. 4. Other parameters of the surge arrester depend on the specific lightning protection zone where the equipment is located. The operating voltage should be based on the rated voltage of all components in the circuit. For series-type arresters, attention should also be given to their rated current. 5. Several factors influence the distribution of lightning current on electronic lines. Reducing the grounding resistance at the transformer terminal increases the current flowing through the electronic lines. Increasing the length of the power cable can decrease the current in the power line and balance the distribution among multiple conductors. However, short cable lengths and low neutral impedance may cause current imbalance, leading to differential mode interference. When a power cable serves multiple users, the effective impedance decreases, increasing the current distribution. In continuous power supply conditions, most of the lightning current tends to flow into the power line, which is why most lightning-related damage occurs there.