Lightning protection projects often involve debates regarding the placement and selection of power surge arresters. Drawing from years of practical experience and theoretical knowledge in lightning protection, I’d like to share some personal insights on this topic:
Class B Surge Arrester (installed in LPZ0A area)
1. Installation Principle: Ideally, the first-level surge arrester (Class B) should be installed as close as possible to the main power inlet. If that's not feasible, it can be placed at the rear end. However, if there is a dual-power switching device at the front, the arrester must be installed before it. This is because modern dual-power switches are often mechanical or electronically controlled, and they may include 232/485 control interfaces or 24V fire power supplies. A lightning strike could easily damage these components. The key reason for installing the arrester ahead is that its response time is much faster than the circuit breaker. When a surge occurs, the arrester will activate first, diverting the overcurrent and protecting downstream equipment.
2. Selection Principle: It’s recommended to choose a voltage-switching type Class B arrester with high current capacity and low clamping voltage (UP). A circuit breaker should be connected in series with the arrester at the front end. The circuit breaker serves two purposes: it allows for easy replacement when the arrester fails, and it prevents ground faults caused by aging arrester components.
Class C Surge Arrester (installed in LPZ1 area)
1. Installation Principle: Class C arresters are typically voltage-limiting types and can be installed either at the front or rear end of the secondary power supply. A circuit breaker should also be connected in series with the arrester at the front end, serving the same purpose as mentioned above.
2. Selection Principle: Class C arresters should be voltage-limiting types, ensuring that the residual voltage after the Class B arrester activates remains below the equipment’s impulse insulation level. Since voltage-limiting components respond faster (about 25 ns) compared to discharge gaps (around 100 ns), it's crucial that the Class B arrester triggers before the Class C one. This requires a certain distance between the two levels. Theoretical analysis using traveling wave theory helps in calculating the spacing between SPDs for optimal performance.
Class D Surge Arrester
Class D arresters are typically used as a final protective layer, especially in sensitive equipment areas. They help further reduce the residual voltage to ensure the safety of critical devices.
Class B arresters are mainly responsible for discharging large currents, while Classes C and D focus on limiting the residual voltage from Class B to a safe level for the downstream equipment. To maximize protection, Class C and D arresters should be installed as close as possible to the protected devices.
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