With the gradual increasing of the transmission voltage level, the situation of interference on secondary side equipment in smart substations is becoming more serious. The authors tested the interference waveforms caused by the circuit breaker’s operation at the smart substation, which showed the severity of the electromagnetic (EM) environment. This paper takes the electronic current transformer acquisition card as an example. The influence of EM interference sources on the reliability of the acquisition card is analyzed. Then, standardized electromagnetic compatibility (EMC) immunity tests of the international electrotechnical commission (IEC) for different interferences are implemented. Typical output characteristics of acquisition cards for different tests are analyzed. Innovatively, this paper proposes a quantitative evaluation method of output waveform disturbance to evaluate the acquisition card’s performance. This disturbance distortion is of great significance to the EM environment estimation of the acquisition card.

Sandwiched winding is widely used in transformer design due to its low AC resistance and small leakage inductance. However, the expansion of winding coupling area causes the increasing of common mode (CM) electromagnetic interference (EMI). Shielding method is the most effective way to reduce coupling inside the isolated transformer. Yet the foil shielding design of sandwiched winding transformer has rarely been involved, for purpose of suppressing the CM EMI in flyback converter. In this work, we propose a method to determine the optimal width of a double-layer foil shielding in the primary-secondary-primary sandwiched winding transformer, for minimizing the conducted CM EMI of flyback converters. The equipotential distribution and the structural capacitance are analyzed, and the model of equivalent CM capacitance is established to calculate the minimum CM current flowing through the sandwiched winding transformer. The proposed method is validated through comparison of calculated and measured results.

The electronic current transformer (ECT) acquisition card is widely used in smart grids with many advantages. However, with the continuous improvement of the power grid and localized intelligent electronic devices, the electromagnetic environment under the operating conditions of gas insulated switchgear (GIS) substations is becoming more complicated. The reliability and safety of the ECT acquisition card will be endangered due to the complicated electromagnetic environment. In order to solve these problems, this paper investigates the electromagnetic disturbed mechanism of the ECT acquisition card. The effects of different grounding methods on the electromagnetic interference of the ECT acquisition card were studied. A platform based on IEC 61000-4-4 was built, and the electromagnetic interference (EMI) of the ECT acquisition card with different grounding methods was measured. The results show that the lower grounding impedance of the ECT acquisition system increased the internal EMI. Further, the high frequency electrical fast transient/burst coupling mechanism was analyzed. The parasitic parameters of the acquisition card were extracted based on the critical circuit by using the finite element method. Then, the high-frequency EMI coupling model of the ECT acquisition card was established.