一种用于变压器局部放电在线监测的光纤声发射传感器实验研究

提出了一种光纤声发射传感器并构建传感系统实现变压器局部放电在线监测，利用传感光栅体积小，重量轻，灵敏度高和抗电磁干扰的特点，将传感器置于变压器内部实现局部放电声发射信号的测量。研究了传感光栅实现声发射应力波测量的机理，声发射信号引起传感光栅反射光谱发生漂移，导致特定频点处反射光强发生变化，通过反射光强的变化实现声发射信号的测量。构建声发射传感系统实验模型并提出了一种系统性能优化策略，使系统工作在传感光栅反射光谱上升或下降沿的半峰值频点处，从而保障传感系统具有良好的线性输出特性；研究传感系统工作点稳定技术，设计信号反馈回路自动跟踪反射光谱的漂移，保证系统稳定工作在传感光栅半峰值频点处，消除温度变化对传感系统测量精度的影响。将封装好的传感器用于变压器局部放电现场检测，结果表明，光纤光栅声发射传感器与压电传感器相比具有灵敏度高、动态范围宽等优点，可以实现变压器局部放电在线监测。

Study of Fiber-Optic Acoustic Emission Sensor for Partial Discharges Detection in Power Transformer

A fiber-optic sensor and its corresponding system are presented and evaluated for on-line detection of acoustic emission stress waves generated by partial discharges in high-voltage power transformer .The fiber-optic sensors are placed inside the transformer for acoustic emission stress waves detection according to its properties of small size ,light weight ,high sensitivity and anti-electromagnetic interference .The sensor employs a distinct Fiber Bragg Grating as sensitive unite and covers it with ep-oxy for the detection of acoustic emission stress waves .The sensing principle of acoustic emission stress wave detection with fi-ber-optic sensor is studied in detail .The reflected spectrum of the sensing grating is shifted because of the influence of acoustic emission stress waves ,which leads to the reflected light intensity changes at a special frequency point ,and thus the detection of the acoustic emission signals can be achieved by the measuring of the changes of reflected light intensity .The experimental model of the acoustic emission sensing system is constructed and a sensing system performance optimizing strategy is presented ,by which the sensing system is enable to operate at the half-peak frequency point of the rising or falling edge ,and thus the good lin-ear output of the system is obtained .Moreover ,the operating point stabilizing technology of the sensing system is studied ,and a signal feedback loop is established for automatic tracking of the sensor wavelength drifting ,by which the fiber-optic sensor is ensured to operate at half-peak frequency point stably .The performance evaluation on partial discharges detection of transformer is launched and the results have demonstrated that the fiber-optic acoustic emission sensors are capable of detecting acoustic emis-sion signals by partial discharges with high sensitivity and wide bandwidth compared with conventional piezoelectric transducers .