Optical Heterodyne Interferometric Sensor for Ultrasonic Detection of Partial Discharge Based on Dual-Phase Detectors

The optical fiber sensors (OFSs) have been demonstrated to exhibit intrinsic safety and resistance to electromagnetic interference (EMI) that make them highly effective in partial discharge (PD) detection. In order to resolve the issue of output instability in traditional interferometric OFS and to reduce the sampling rate for real-time detection, the heterodyne interferometric PD detection method based on the dual-phase detectors (DPDs) scheme has been proposed. By introducing high-frequency shifting in the reference arm and combining it with analog phase detection, real-time stable demodulation of ultrasonic signals is achieved. The DPD scheme reduces the system’s sampling rate to 1/2000 of the algorithm’s demodulation rate and effectively resolves the signal distortion issues occurring in the nonlinear region. For the detection of PD signals in the typical model in the lab, amplitude detected by OFS is significantly higher than that of the piezoelectric transducer (PZT), with the signal-to-noise ratio (SNR) improvement of 3.6 dB. Regarding the PD detection of oil-immersed transformers in the field, the developed OFS based on DPD has achieved a 3.5-dB improvement in sensitivity for PD detection. The results demonstrate that the heterodyne interferometric method based on DPD holds profound potential in the field of PD detection in electrical equipment.