Abstract: This paper analyzes the data flickering and sampling failure of electronic transformer acquisition cards during high-voltage disconnector operation in smart substations. A hybrid electromagnetic interference mechanism involving fast transient overvoltage and damped oscillatory magnetic field is studied, and an ADC coupling model is established. A synchronized test platform based on FPGA timing control is built according to IEC 61000-4-4 and IEC 61000-4-10. Test results show that hybrid interference causes nonlinear degradation of acquisition accuracy. A protection method combining ground-plane partitioning and permalloy composite shielding is proposed and verified to improve data acquisition integrity.