【作者】 李敏；

【导师】 赵洪；

【作者基本信息】 哈尔滨理工大学 ， 电气工程， 2009， 博士

【摘要】 声发射探测技术是监测由局部放电引起的液—固复合绝缘电力设备的突发性故障的有效方法。与压电式超声传感器相比,光纤传感器可埋入液体介质中直接测量局部放电声发射信号,信号的传输及传感过程均不受电磁干扰。光纤非本征法珀型传感器是由声波与光波耦合元件——膜片、光纤端面及中间的腔体构成,体积小、结构灵活、无需保偏装置,用于液体介质中的局部放电探测有潜在的竞争力。本文就传感器的结构参数设计、元件及传感器的制备、特性的描述、仿真分析和试验测试、环境影响因素及消除方法等开展了研究工作。提出用于液体介质局部放电监测的光纤非本征法珀型传感器的结构设计方法,用仿真和超声激励法对膜的结构尺寸与传感器灵敏度、一阶固有频率的关系进行理论分析和测试;研制应用石英膜和基于MEMS工艺制备的硅膜分别与尾纤端面构成的法珀传感器,研究利用传感器构成元件的结构参数与性能的改变提高灵敏度的方法;分析了传感器光谱特性产生附加调制的原因并提出解决的方案。利用超声激励法对传感器偏离工作点产生的信号传递增益下降、波形畸变等问题进行分析。利用理论估算和实验测试随温度造成传感器结构热膨胀改变法珀腔长而改变传感器特性曲线上工作点的规律。研究传感器对声波信号的不同调制方法及解调方法,并重点研究工作点在强度调制中的意义。提出应用中心波长可改变的分布式光源照明传感器的方法,自动跟踪由温度和静液压改变腔长而改变的工作点。针对环境温度和液体静压力的变化使得传感器的工作点漂移导致传递特性劣化的问题,根据法珀传感器的基本理论,通过改变光源的中心波长改变传感器的特性曲线,使测试保证在理想工作点状态下进行。构建这种光源和实验系统,检验工作点调节效果。对局部放电进行测试确定传感器的结构参数。利用实验室制备的不同材料、结构参数和不同端面反射率的传感器及工作点调节系统,在实验室建立的局部放电测试系统下进行测试。通过对不同放电电压下的局部放电声发射信号进行测量,分析的影响局部放电声信号测试的因素,如传感器的膜的厚度和有效面积、端面反射率、固有频率等。端面反射率90%的尾纤和4mm×4mm×60μm的镀金硅膜构成的传感器放置在距针板放电源20cm处,在实验室建立的装置下测试的可测放电量为0.3～130kpC。更多还原

【Abstract】 Acoustic emission detection technology is an effective way to monitor sudden failure caused by partial discharge (PD) in liquid-solid composite insulation of electrical equipment. Compared to piezoelectric acoustic sensors, fiber optic sensor buried in the liquid medium can detect PD-induced acoustic directly. The signal transmission and sensing process are not subject to electromagnetic interference from the environment. Extrinsic fiber Fabry-Perot (FP) sensor is made of a diaphragm as coupling components to acoustic and light, end face of optical fiber and a cavity composed. The sensor has compact and flexible structure without polarization component, which has potential prospect for PD detection in liquid. Research in the paper was carried out about structure design of FP sensor and preparation, characteristic description, simulation and experiment to the sensor and its component. The effect of environmental factors and elimination methods were studied.Structure design method of extrinsic fiber FP sensor is set up for monitoring PD in liquid medium. The relationship was obtained by simulation and ultrasonic excitation between the sensitivity and first-order natural frequency of the sensor and structure parameters of the diaphragm. FP sensors were made of pigtail and silicon diaphragm by MEMS or quartz diaphragm respectively. The structural parameters and performance changes of components of the sensor were studied to improve the sensitivity. Reason about the additional modulation in spectral characteristics of FP sensor were analysed and the solutions were put forward.Drift of operating point of the sensor resulted in decreased gain and distorted waveform by acoustic excitation. The laws of change of the operating point on the sensor characteristic curves was obtained by theoretical estimates and experimental tests with the change of cavity length caused by thermal expansion of the sensor structure. Modulation and demodulation methods of FP sensors on the acoustic signal were investigated, which focused on the significance of operating point in the intensity modulation.A distribution source with tunable center wavelength was put forward to launch the sensor in order to track automatically operating point with changes of FP cavity length caused by temperature and hydrostatic pressure. Drift of the operating point of the sensor by changes of ambient temperature and hydrostatic pressure result in degradation of transmission characteristics. According to interference principle FP sensor, characteristic curve of FP sensor can be changed by the source with tunable center wavelength. This technology can be able to ensure the ideal point, and the source and the experimental system were built up to test the effect of adjusting operating point.The structure parameters of the sensor were determined to detect PD-induced acoustic emission. Seven types of sensors with different materials, structural parameters and different end-reflectance were prepared to detect PD-induced acoustic signals in the system set up in the lab. The test was achieved in the operating point-adjusting systems with the source of tunable center wavelength. PD-induced acoustic signals were test under different discharge voltage. The effects on PD-induced acoustic detecting of the structure parameters and frequency characteristics of the sensor, such as thickness and effective area of the diaghragm, face reflectivity, and natural frequencies were analyzed. FP sensors with 90% end reflectivity of the pigtail and 4mm×4mm×60μm silicon diaphragm with gold coating film were able to detect 0.3～130kpC of discharge level at 2cm from discharge source in the laboratory test.更多还原