How to suppress interference in the power FTU feeder switch drive?

The main sources of interference in the feeder switch drive are the relay coil and power devices. Suppression measures include: a 1N4007W freewheeling diode and a 470Ω/2W resistor connected in parallel across the relay coil; an RC snubber (22Ω + 1nF) power MOSFET with a 10Ω resistor in series at the gate; an isolated DC-DC module WRB2405S-3W for the drive power supply; shielded twisted-pair cable used for the drive signal lines, with the shield grounded; and PCB layout with the drive circuit placed close to the switch to minimize loop area. The drive section inside the chassis is partially shielded. This solution reduces drive interference by 35dB, and the impact of switch operation on the sampling circuit is less than 0.5%, meeting the IEC 61000-4-4 EFT 4kV test requirements.