弧形核磁共振传感器设计及其在复合绝缘子老化状态检测中的应用

摘要

Silicone rubber composite insulators are widely used in the power system because of advantages such as excellent hydrophobicity, high mechanical strength and light weight. Currently the methods for accuracy and effective analysis of the aging status of the composite insulators are still lacking. Although previous studies have investigated the degradation of composite insulator shied, none of them focused on composite insulator rod sheath. To measure the aging status of rod sheath, a nuclear magnetic resonance (NMR) sensor was designed, which could be applied to arc-shaped samples. The magnet structure was optimized to have a main magnetic field distribution matching up with the curvature of the rod sheath. A flexional helical radio frequency transmission coil was designed and optimized. The sensor was applied to three kinds of rod sheath with different ages. A CPMG pulse sequence was used to acquireT2 relaxation curves of the samples, which were then subjected to an inverse Laplace transformation to obtainT2 spectrum. The result showed that the T2 of the rod sheath decreased with increasing operation time. It is concluded that the parameterT2, long mean calculated from theT2 spectrum can be used for measuring the aging status of rod sheath.%硅橡胶复合绝缘子具有憎水性、强度高和重量轻等优势,被广泛应用于电力系统,然而,目前尚没有准确有效的方法来检测硅橡胶复合绝缘子的老化状态.许多学者对复合绝缘子伞裙的老化状态开展了相关研究,但目前尚未有对复合绝缘子芯棒护套老化状态的研究报道.针对这一问题,该文设计了一种能够测量弧形表面样品的核磁共振(NMR)传感器,并应用于芯棒护套老化状态的检测.首先,对产生主磁场(B0)的磁体结构进行了设计及优化,使得主磁场的分布具有和芯棒护套一样的曲率.其次,设计并优化了一种可弯曲的螺线线圈作为射频线圈.最后,用该传感器测量了3种在220 kV输电线路上挂网运行了不同年限的复合绝缘子的芯棒护套.采用CPMG脉冲序列激励样品,并得到横向弛豫衰减曲线,然后对横向弛豫衰减曲线做拉普拉斯逆变换获得横向弛豫时间(T2)谱.T2谱显示,随着运行年限的增长,复合绝缘子芯棒护套的T2会减小.因此,从T2谱中提取的T2,long mean可以作为一个衡量复合绝缘子芯棒护套老化状态的参数.