How to filter out power line spike interference in a power measurement switch (PMS)?

Industrial power grids connected to PMS often experience transient high-voltage spikes (up to several kilovolts) caused by inductive load switching, lightning strikes, or switching of nearby equipment. These transient interferences can damage port devices or cause program crashes. Filtering out spikes requires a combination of multi-stage protection and filtering.

The first stage of coarse protection can use a gas discharge tube, for example, a 2R600L-8×6 GDT (DC breakdown voltage 600V) connected in parallel between the L/N lines to dissipate amplified surge energy. The second stage of clamping uses a TVS diode, such as an SMCJ33CA (bidirectional, Vrwm=33V), to limit the voltage to a safe range. The third stage of filtering uses a combination of common-mode inductors and capacitors, using a CML4532A-101T (100μH) to suppress common-mode noise, and two capacitors (0.47μF) connected in parallel to filter out differential-mode components. For extremely sensitive metering chip power supplies, a PBZ1608E600Z0T ferrite bead can be added in series along with a Zener diode.

This collaborative protection scheme can withstand the 1.2/50μs-8/20μs combined wave lightning strike test (common mode 2kV, differential mode 1kV) specified in the IEC 61000-4-5 standard, and attenuates the peak voltage amplitude entering the board level by more than 40dB, ensuring the stable operation of the core circuit.