Dielectrometry Sensors and Algorithms to Monitor Moisture Dynamics and Other Impurities in Transformers

9523128 Lesieutre新型捕获式传感器可以测量电介质中电导率和介电常数的分布。每个传感器具有一组交错电极，该电极在时间频率f和空间波长施加空间周期性电压源。在空间周期性激发下，场沿垂直方向衰减，穿透深度等于空间波长。其中一组电极由变频交流电压驱动，对另一组浮动电极的感应电压进行高阻抗测量。浮电压的大小和相位取决于传感器附近介质的介电常数和电导率。从增益/相位测量作为不同波长传感器频率的函数，计算机算法可以计算出介电常数和电导率的空间分布。由于介电常数和电导率的校准依赖于其他物理变量，如湿度、温度、可燃气体浓度、微量杂质浓度等，因此不可能测量这些物理量作为时间函数的空间分布。最近EPRI资助的研究已经完成了水分和温度与电导率和介电常数之间的初步校准，以便传感器可以用于监测油浸变压器压板中水分的时间和空间动态。该研究旨在开发有效的计算机算法，以提取变压器中压板湿度作为时间和空间的函数，从而实现由EPRI和几家电力公司赞助的趋势分析和高级诊断监测系统。其他研究任务建议扩展介电测量传感器的能力，包括研究特殊的封装涂层，这些涂层可以选择性地吸收可燃气体和变压器中的其他微量杂质，如抗氧化剂，拟议的抗静电添加剂，如苯并三唑（BZA），以及其他由老化和腐蚀产生的杂质。＊＊＊

9523128 Lesieutre New captive sensors can measure distributions of conductivity and permittivity in dielectrics. Each sensor has a set of interdigitated electrodes which impose a spatially periodic source of voltage at temporal frequency f and spatial wavelength. With an excitation that is periodic in space, the fields decay in the perpendicular direction with a penetration depth equal to the spatial wavelength. One set of electrodes are driven with a variable frequency AC voltage, and a high impedance measurement is made of the induced voltage on the alternate set of floating electrodes. The magnitude and phase of the floating voltage depends on the dielectric permittivity and electrical conductivity of the medium adjacent to the sensor. From such gain/phase measurements as a function of frequency for different wavelength sensors, computer algorithms can calculate spatial profiles of the permittivity and conductivity. With calibration of permittivity and conductivity dependence on other physical variables such as moisture, temperature, concentration of combustible gas, concentration of trace impurities, etc., it is impossible to measure spatial distributions of such physical quantities as a function of time. Recent EPRI funded research has performed the preliminary calibration between moisture and temperature to conductivity and permittivity so that the sensors can be used to monitor the time and space dynamics of moisture in oil impregnated transformer pressboard. The proposed research is to develop efficient computer algorithms that can extract the pressboard moisture as a function of time and space in transformers so that this monitoring system of trend analysis and advanced diagnostics sponsored by EPRI and several electric utilities. Other research tasks propose to extend the capability of the dielectrometry sensor to include the investigation of special encapsulating coatings that are selectively absorbing or reactive to combustible ga s and other trace impurities in transformers such as anti-oxidants, proposed anti-static additives such as benzontriazole (BZA), and other impurities resulting from aging and corrosion. ***