Portable Unilateral NMR Measuring System for Assessing the Aging Status of Silicon Rubber Insulators

Silicon rubber insulators (SRIs) are widely used in power transmission lines as line support and as insulation between the line and the tower. Given that the aging of SRIs threatens the safety and stability of power grids, the accurate assessment of the aging status of SRIs is crucial. In this study, a portable unilateral magnetic resonance (UMR) measuring system for the nondestructive testing of the aging status of SRIs was proposed. The proposed NMR measurement system includes a mini UMR sensor and a measurement circuit. Details of the mini UMR sensor structure and low-cost circuit design were discussed. The Carr–Purcell–Meiboom–Gill sequence was used to record the ¹H transverse relaxation curves of SRI sheds. Inverse Laplace transformation was employed to obtain the T₂ distribution, and two peaks in the T₂ distribution curve were observed. The long T₂ component was selected to quantify the aging degree because of its stability compared with the short T₂ component. To eliminate the inaccuracy of measurement introduced by the different chemical structures of SRIs produced by different companies, the aging status of the SRIs was represented by the changes in T₂ between the surface and internal materials of the SRI.