How can the arc-extinguishing circuit of the power measurement switch (PMS) reduce EMI?

When a switch controlling a high-current inductive load (such as a contactor or motor) in a power supply system (PMS) is disconnected, it generates a strong electric arc, whose broadband electromagnetic noise is a serious source of EMI. The core of reducing EMI in arc-extinguishing circuits is to quickly extinguish the arc and absorb its energy. Commonly used arc-extinguishing circuits include: RC snubbers, MOV varistors, and combinations of diodes and Zener diodes. For DC loads, a freewheeling diode (such as a 1N4007) or a TVS diode (such as an SMCJ33CA) is connected in reverse parallel across the load to provide a freewheeling path for the inductive current. For AC loads, an RC snubber (such as a 0.1μF+100Ω) or a bidirectional MOV (such as a 7D390K) is connected in parallel across the switch contacts.

An even more effective solution is to use a solid-state relay (SSR) with built-in zero-crossing detection to turn off at the zero-crossing point of the current. Furthermore, the arc-extinguishing circuit should be enclosed in a metal shielded box, and the shielding box should be properly grounded. The leads of the arc-extinguishing circuit should be as short and thick as possible to reduce parasitic inductance. By optimizing arc extinguishing, the arc duration can be shortened from milliseconds to microseconds, the peak value of conducted interference voltage can be reduced by more than 60%, the intensity of radiated interference can be reduced by 20dB, and the switch contacts can be protected at the same time.