How to design surge protection for frequency converters in stages?

surge protection hierarchy design for frequency converters aims to build a reliable protection system at a reasonable cost, typically employing two or three levels of protection. The first level (coarse protection) is installed at the input port to discharge most of the surge current. Common components are gas discharge tubes or varistors, such as the 20D series varistors used at the AC input. The second level (fine protection) is installed at the power board input inside the frequency converter to clamp residual voltage to a safe level. Common components are TVS diodes or varistors, such as the SMDJ series TVS diodes. Decoupling components, such as inductors, resistors, or fuses, are needed in series between the two levels to achieve energy matching and ensure the first level activates first.

For signal ports, such as Ethernet and RS485, dedicated surge protection modules can be used. The hierarchical design must consider the current-carrying capacity, response time, and clamping voltage matching of each component to ensure that subsequent components are protected. The ground wires of all protection devices must be very short and thick, connected to a separate "dirty ground" or chassis ground. The effectiveness of the protection scheme is verified through simulation and testing. Eintech offers a complete range of surge protection devices, from GDTs and varistors to TVSs, supporting graded protection designs.