There is complex electromagnetic interference in the substation. In order to improve detection accuracy, a digital lock-in amplifier is used in the detection of the grounding grid. This paper introduces the principle of non-destructive testing of grounding grid based on electromagnetic method. Firstly, the distribution characteristics of surface magnetic induction intensity at different frequencies are obtained by CDEGS simulation. At the same time, it describes the principle and structure of an orthogonal vector type digital lock-in amplifier in detail. In order to realize the high-precision grounding grid detection system, the hardware circuit of the digital lock-in amplifier is designed by FPGA and analog-to-digital converter. The digital lock-in amplifier algorithm is implemented in the FPGA. Finally, the digital lock-in amplifier is tested. The test results show that when the signal-to-noise ratio of the signal to be tested is -20 db, the signal amplitude measurement error is less than 3%. The designed digital lock-in amplifier is applied to the actual grounding grid detection, and the topology and corrosion of the grounding network can be detected. Therefore, the digital lock-in amplifier can be effectively applied to non-destructive testing of grounding grid.
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