Improving SNR and Sensing Distance of COTDR for Distributed Partial Discharge Detection in Power Cable Joints

Distributed detection of partial discharge (PD) in joints of long power cables is both a necessity and a challenge. In order to improve the distance and sensitivity of PD detection, an improved coherent optical time-domain reflectometer (COTDR) system is proposed in this article. A two-stage optical amplification scheme was established, and the pump currents of erbium-doped fiber amplifiers (EDFAs) were optimized to improve the signal-to-noise ratio (SNR) of the beat signal. The dual-frequency probe pulses were introduced to suppress fading noises in the distance domain and prevent false positives in PD detection. The test results based on real cable joints indicated that the system enabled distributed detection and accurate waveform retrieval of PD events. Based on the above improvements, the proposed system enhanced the PD sensing performance from the existing 1-km sensing distance and nC-level detection limit to 20 km and 127 pC, respectively. This performance indicated that the COTDR system possessed practicality in the distributed detection of cable joints PDs.