When it comes to lightning protection systems, there are often debates about where to install surge protectors and how to choose the right ones. Drawing from years of practical experience and theoretical knowledge in lightning protection, I'd like to share some of my insights on this topic.
Class B Surge Arrester (installed in LPZ0A area)
1. Installation Principle: Ideally, the first-level 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 of the incoming line, the Class B arrester must be installed before this device. This is because many dual power switches are mechanical or electronically controlled and may include 232, 485 control interfaces and 24V fire power supplies. A lightning strike could easily damage these components. The arrester acts much faster than the circuit breaker, so it will discharge the overvoltage before the breaker trips, protecting the downstream equipment effectively.
2. Selection Principle: It's recommended to use a voltage-switching type arrester for Class B. These have a high current capacity and a low clamping voltage (UP). A circuit breaker with appropriate rating should be connected in series before the arrester. This serves two purposes: it allows for easy replacement when the arrester fails, and it prevents ground faults caused by aging arresters.
Class C Surge Arrester (installed in LPZ1 area)
1. Installation Principle: Class C arresters are typically voltage-limiting types and can be installed either on the front or rear end of the secondary power supply. Again, a corresponding circuit breaker should be placed in series before the arrester for the same reasons as with Class B.
2. Selection Principle: Class C arresters should also be voltage-limiting types. They need to ensure that the residual voltage after the Class B arrester triggers is below the equipment's impulse insulation level. Since voltage-limiting components respond faster (about 25 ns) compared to discharge gaps (around 100 ns), the Class B arrester must activate before the Class C one. This requires a certain distance between the two levels. According to traveling wave theory, proper spacing helps prevent voltage reflection and ensures effective protection.
Class D Surge Arrester
Class D arresters are usually used as a final stage of protection. Their main function is to further reduce the residual voltage from the previous stages to a level that the protected equipment can safely withstand. In general, they should be installed as close as possible to the equipment they are protecting.
In summary, the primary role of Class B arresters is to handle large currents from lightning strikes, while Classes C and D focus on limiting the residual voltage to protect sensitive electronics. Proper placement and coordination between different classes of arresters are essential for an effective lightning protection system.
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