Analysis of the coupling optical fiber ultrasonic sensor for partial discharges detection

The responses of ultrasonic sensor with different structure parameters to acoustic emission of partial discharge have been investigated numerically and experimentally. By taking into account both the elasto-optic effect and the geometric effect, a comprehensive analysis of the ultrasonic sensing mechanism is presented. It is found that a direct deformation of the sensor induced by acoustic emission signals which is closely related to the sensor sensitivity is the critical factor in the sensing mechanism. Then, numerical simulations were carried out to analyze the relationships between structure parameters of the sensor and the corresponding deformation. Related simulation results show that the sensor deformation grows with the deepening of the fusion degree, and the rise of the coupling length leads to the exponential enhancement of the sensor deformation. According to theoretical analyses, sensors based on the directional coupler were fabricated and acoustic emissions of PD detection experiments were carried out. Experiments results are consistent with the theoretical analysis results. Moreover, experiment results show that the bandwidth of the sensor is in the range of 10 kHz up to 5MHz. And the frequency response of the optical sensor ranged from tens of kHz to hundreds of kHz. These analysis results could provide a useful guide to optimization design of the sensors used in practical acoustic emission detection from partial discharges.