The number of composite insulators used in power transmission lines increases year by year. To detect and assess the aging status accurately concerns the security and stability of the power system. In order to achieve nondestructive testing of the sheds of composite insulators, a unilateral mini Nuclear Magnetic Resonance (NMR) sensor is proposed in this paper. The design of the magnet body and the optimization of the RF coil are presented. The Carr-Purcell-Meiboom-Gill (CPMG) sequence was employed to record the 1H relaxation curves of the sheds of three composite insulators from 110 kv lines with different service years. The curves were fitted to both single exponential function and inverse Laplace transformation functions. The results demonstrate that an increase of service year of the insulator results in a decrease of the effective transverse relaxation time (T2eff). It is indicated that the sensor has a potential to assess the aging status of the composite insulators.
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