Power transformer insulation systems are subjected to many stresses during normal operation due to lightning and switching.If the spectrum of incoming surge voltage matches the winding one,the corresponding resonance ...Power transformer insulation systems are subjected to many stresses during normal operation due to lightning and switching.If the spectrum of incoming surge voltage matches the winding one,the corresponding resonance will be excited.Therefore external transients occurring in power systems might trigger internal overvoltages with large maximum value in transformer windings.Overvoltages having such characteristic have been the root cause of many power transformer failures.The paper presents an approach to the identification of sensitive zones in the transformer windings based on the measurements of overvoltages inside windings and frequency dependences of admittance of the power transformer.The frequency characteristic of the transformer winding may determine those regions in the frequency spectrum.The presented approach might be used both for design optimization and diagnostics of distribution and power transformers.展开更多
调制传递函数(modulation transfer function,MTF)是目前公认的最为客观、有效的光学镜头检测方法。针对ISO12233刃边法检测数据时存在误差,且抗噪性差的问题,提出了一种系统优化算法流程,通过基于最大类间方差法(Otsu)的Canny算子来提...调制传递函数(modulation transfer function,MTF)是目前公认的最为客观、有效的光学镜头检测方法。针对ISO12233刃边法检测数据时存在误差,且抗噪性差的问题,提出了一种系统优化算法流程,通过基于最大类间方差法(Otsu)的Canny算子来提高边缘检测的准确性和噪声抑制能力;将Bisquare方法代替最小二乘法以减小刃边拟合误差;采用三次Fermi函数求解边缘扩散函数(ESF),解决噪声引起的数据震荡以及离散数据后续处理中的误差问题。实验结果表明,与ISO12233算法相比,优化后的算法更准确,测试精度符合标准,完全满足实际工业生产中镜头检测任务的需求。展开更多
U型中深层地埋管换热器(U-bend Deep Borehole Heat Exchanger,UDBHE)具有广阔的应用前景。文章基于无限柱热源(Infinite Cylindrical Source,ICS)和无限线热源(Infinite Line Source,ILS)模型的G函数,建立了4种UDBHE传热模型,采用ICS或...U型中深层地埋管换热器(U-bend Deep Borehole Heat Exchanger,UDBHE)具有广阔的应用前景。文章基于无限柱热源(Infinite Cylindrical Source,ICS)和无限线热源(Infinite Line Source,ILS)模型的G函数,建立了4种UDBHE传热模型,采用ICS或ILS模型的G函数,考虑或忽略钻孔壁热流随时间变化,分别简称为ICS-q,ILS-q,ICS-c,ILS-c模型。通过与较为准确的二维数值模型及实验数据在2种边界条件下的对比,分析了这4种模型的准确性。结果表明:ILS-q模型在整体上最为准确,而ICS-q模型在分析UDBHE长期性能时最为准确;4种模型在前期均存在较大误差,但在足够长时间后,除了ILS-c和ICS-c模型在入口温度边界下仍有较大误差外,其他模型的误差均较小。研究结果可为UDBHE传热模型研究提供参考。展开更多
文摘Power transformer insulation systems are subjected to many stresses during normal operation due to lightning and switching.If the spectrum of incoming surge voltage matches the winding one,the corresponding resonance will be excited.Therefore external transients occurring in power systems might trigger internal overvoltages with large maximum value in transformer windings.Overvoltages having such characteristic have been the root cause of many power transformer failures.The paper presents an approach to the identification of sensitive zones in the transformer windings based on the measurements of overvoltages inside windings and frequency dependences of admittance of the power transformer.The frequency characteristic of the transformer winding may determine those regions in the frequency spectrum.The presented approach might be used both for design optimization and diagnostics of distribution and power transformers.
文摘调制传递函数(modulation transfer function,MTF)是目前公认的最为客观、有效的光学镜头检测方法。针对ISO12233刃边法检测数据时存在误差,且抗噪性差的问题,提出了一种系统优化算法流程,通过基于最大类间方差法(Otsu)的Canny算子来提高边缘检测的准确性和噪声抑制能力;将Bisquare方法代替最小二乘法以减小刃边拟合误差;采用三次Fermi函数求解边缘扩散函数(ESF),解决噪声引起的数据震荡以及离散数据后续处理中的误差问题。实验结果表明,与ISO12233算法相比,优化后的算法更准确,测试精度符合标准,完全满足实际工业生产中镜头检测任务的需求。
文摘U型中深层地埋管换热器(U-bend Deep Borehole Heat Exchanger,UDBHE)具有广阔的应用前景。文章基于无限柱热源(Infinite Cylindrical Source,ICS)和无限线热源(Infinite Line Source,ILS)模型的G函数,建立了4种UDBHE传热模型,采用ICS或ILS模型的G函数,考虑或忽略钻孔壁热流随时间变化,分别简称为ICS-q,ILS-q,ICS-c,ILS-c模型。通过与较为准确的二维数值模型及实验数据在2种边界条件下的对比,分析了这4种模型的准确性。结果表明:ILS-q模型在整体上最为准确,而ICS-q模型在分析UDBHE长期性能时最为准确;4种模型在前期均存在较大误差,但在足够长时间后,除了ILS-c和ICS-c模型在入口温度边界下仍有较大误差外,其他模型的误差均较小。研究结果可为UDBHE传热模型研究提供参考。
