How to reduce EMI during the reclosing operation of a power FTU?

Strong electromagnetic interference is generated during reclosing operations due to the motor drive and contactor opening and closing. The solution employs motor drive filtering and contactor protection. The motor drive circuit uses a three-phase filter, with each phase connected in series with a CMZ3225A-101T common-mode inductor (100μH) and two 0.1μF/630V capacitors in parallel. A 1N4007W freewheeling diode and a 470Ω/2W resistor are connected in parallel across the contactor coil to absorb back electromotive force. A PBZ3216E120Z0T ferrite bead (120Ω@100MHz) is installed at the power input. On the PCB, the motor drive lines are routed perpendicularly to the signal lines with a spacing greater than 25mm. A 0.8mm thick local shielding cover is added to the motor section inside the chassis. This solution reduces conducted interference by 30dB and radiated interference by 20dB during reclosing operations, ensuring the FTU does not malfunction during reclosing and meeting the IEC 61000-4-4 EFT 4kV test requirements.