Highly Sensitive Partial Discharge Ultrasonic Multipoint Detection Using Single Channel Distributed Feedback Fiber Lasers

To realize the highly sensitive multiple-point detection of partial discharge (PD) acoustic emission (AE) in power transformers, an ultrasonic sensing system based on a distributed feedback fiber laser (DFB-FL) array was proposed. Four DFB-FLs were connected on a single optical fiber as sensing elements to synchronously detect PD AE signals. The heterodyne coherent detection structure was formed by introducing an acousto-optic modulator (AOM) into the unbalanced Mach-Zehnder interferometer (MZI) to realize the rapid and highly sensitive demodulation of ultrasonic signals. The influence of noises and arm length difference on the lower limit of detection (LLOD) were theoretically discussed and experimentally verified. By adopting a 70-meter-long delay fiber, the proposed system performed a 9.54 dB lower average detection limit than that of PZT. Finally, based on the proposed system, a partial discharge source was accurately located in a 1000 mm×1000 mm×1100 mm oil tank, and the localization error was 24.6 mm. The proposed method exhibited promising application prospects in sensitivity, installation convenience, anti-interference and reliability.