How to eliminate strong electrical coupling interference in a power measurement switch (PMS)?

In a Power Management System (PMS), the high-voltage main circuit (e.g., 400VAC/630A) coexists with the low-voltage measurement/control circuit. The strong magnetic field generated by the high current and the electric field coupling caused by the high voltage through parasitic capacitance are the main sources of interference leading to malfunctions in the low-voltage system. Eliminating this coupling requires the comprehensive application of shielding, isolation, and filtering techniques. Structurally, high-voltage and low-voltage modules should be arranged in separate compartments, separated by a metal partition. The partition should have a low-impedance contact with the chassis (contact resistance <2.5mΩ). All signal or power lines passing through the partition should use metal through-hole capacitors or filtered connectors, such as using a D-Sub connector with filtering function, internally integrating a CML3225A-510T common-mode inductor.

At the PCB level, low-voltage circuits should be kept away from high-voltage traces. If parallel routing is unavoidable, the spacing should be greater than 10mm, and a grounding guard trace should be installed in the middle. For current transformers (CTs) used for sampling, their secondary output lines should use twisted-pair shielded cables, with the shield grounded at the PMS terminal. Meanwhile, a secondary filter is added to the low-voltage power supply, such as using a PBZ2012E600Z0T ferrite bead in conjunction with a TVS diode SMBJ24CA. After optimization, the low-voltage system can maintain fault-free operation in the IEC 61000-4-3 radiated immunity test (10V/m) when the high-voltage system is operating at full load.