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.

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.

A magnetic field sensing system with a single primary sensor and multiple reference sensors deployed locally and orthogonally, was proposed for downlink signal reception and interference cancelling for Through-theEarth Communication (TEC). This paper mathematically analyzes a design optimization process for a search coil magnetometer (SCM), and applies that process to minimize the bandwidth of the primary SCM for TEC signal reception and the volume of reference SCMs for multiple distributions. The primary SCM achieves a 3-dB bandwidth of 7 Hz, a sensitivity threshold of 120 fT/√Hz, and a volume of 2.32 × 10 −4 m 3 . The entire sensing system volume is as small as 10 −2 m 3. Experiments with interference from industrial frequency harmonics demonstrated an average of 36 dB and 18 dB improvements in signal-to-interference ratio and signal-tointerference plus noise ratio, respectively, using multichannel recursive-least-squares algorithm. Thus, the proposed sensing system can reduce the interference effectively and allows reliable downlink signal reception.

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This paper presents a fully differential switched capacitor amplifier with programmable gain design and offset cancellation technique used in digital DC-DC converter. To trade off the effective resolution for dynamic range of the error ADC, the gain of the switched capacitor amplifier is designed programmable that can be configured 1X, 2X, 4X or 8X. To improve system offset performance, the first stage is utilized full-differential switch-capacitor architecture conducive to common mode noise rejection and differential offset cancellation caused by charge injection. In addition, to cancel the offset brought by amplifier input stage, offset cancellation techniques are also implemented. The offset voltage is stored in calibration capacitor in sampling phase and cancels the input offset in amplification phase. This proposed circuit is simulated in 180nm 4P6M CMOS technology. From the simulation result, the offset voltage is fully cancelled. In addition, programmable gain design is also verified that dynamic adjustment accuracy in DC-DC feedback loop in X8 is superior than X1.