Assessing the aging status of the silicone rubber insulator using unilateral NMR technology

The aging of silicone rubber insulator threatens the safety of the power grid. An accurate estimation of the insulator aging status is necessary for taking precautions against insulation failure. In this study, we propose a novel unilateral nuclear magnetic resonance (NMR) method to quantify insulator degradation attributed to aging. The CPMG sequence was employed to record the 1H NMR transverse relaxation curves of the silicone rubber insulators with different service years. The decay curves were fitted to the bi-exponential functions. Further data processing of the decay curves was performed with the inverse Laplace transformation for one dimensional T2 distribution analysis, and the mean life time of the long T2 component (T2long mean) was obtained. The result demonstrates that an increase in the aging level of the insulator clearly results in a decrease of T2long mean. To compare with the results of NMR measurement, the relative permittivity of the insulator was measured. It shows a same changing trend as that of T2long mean. It indicates that T2long mean relaxation time obtained from our portable NMR sensor can be used as an index to reflect the aging status of the silicone rubber insulator.