DFB-FL Applied in the Liquid-Solid Composite Dielectric for Ultra-High Sensitive Partial Discharge Acoustic Emission Detection

The traditional fiber optic acoustic emission (AE) sensor, used to detect the partial discharge (PD) in the liquid-solid composite dielectric such as oil-immersed transformers, is not satisfactory in engineering applications due to the limitation of sensitivity and sensor size. This work proposes that the distributed feedback fiber laser (DFB-FL), benefiting from its tiny size and ultra-high sensitivity, is a better choice for PD AE detection. We build the PD AE detection system using erbium-ytterbium co-doped (Er-Yb-co-doped) DFB-FL, with suitable photoelectric components to design the demodulation system and intensity noise of DFB-FL as an index. Noise analysis shows that the average noise amplitude of the system is reduced by 91.67% after digital filtering technology and pump laser power regulation technology. We also use an 80 kVA oil-immersed transformer winding structure to construct a liquid-solid composite dielectric PD AE detection platform. Moreover, experiment results in different pump power show that the DFB-FL PD AE detection system can effectively detect the PD AE signal in the environment with sizeable acoustic impedance. The peak-to-peak value of its response is 31.36 times larger than the background noise and 637% higher than piezoelectric transducer sensors (PZT).