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

9523128 Lesiutre新型俘获传感器可以测量介质中的电导率和介电常数分布。每个传感器都有一组交错的电极，这些电极在时间频率f和空间波长上施加一个空间周期性的电压源。在空间周期激励下，场在垂直方向衰减，穿透深度等于空间波长。用变频交流电压驱动一组电极，并对交替的一组浮动电极上的感应电压进行高阻抗测量。浮动电压的大小和相位取决于与传感器相邻的介质的介电常数和电导率。根据不同波长传感器的增益/相位随频率变化的测量结果，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依赖于其他物理变量，如水分、温度、可燃气体浓度、痕量杂质浓度等，因此不可能测量这些物理量随时间的空间分布。最近EPRI资助的研究已经完成了湿度和温度对电导率和介电常数的初步校准，从而使传感器可以用于监测浸油变压器绝缘纸板中水分的时间和空间动态。建议的研究是开发高效的计算机算法，可以提取变压器中绝缘纸板水分随时间和空间的函数，以便这个由EPRI和几家电力公用事业公司发起的趋势分析和高级诊断的监测系统。其他研究任务建议扩展介电测量传感器的能力，以包括研究特殊的封装涂层，这些涂层选择性地吸收或反应可燃气体S和变压器中其他微量杂质，如抗氧化剂、建议的抗静电添加剂，如苯并三唑(BZA)，以及其他因老化和腐蚀而产生的杂质。***

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. ***