Nuclear magnetic resonance detection method for aging state of composite insulators

Aging of the composite insulator threatens the safety of power grid. A portable nuclear magnetic resonance (NMR) sensor with an adjustable ‘clamp’ structure is constructed for the noninvasive measurement of the aging status of the composite insulator. Two cylindrical permanent magnets are used to establish static magnetic field B0. Magnets can be adjusted to adapt to different thickness of sheds. An “8-shaped” plane radio frequency (RF) coil is used. Composite insulator samples of different service time are measured. Their nuclear magnetic resonance (NMR) echo decay signal was collected, and the decay signal was fitted with an exponential function. After this processing the transverse relaxation time (T2) was obtained. For comparison, the relative permittivity of the samples is measured by an Agilent 4294A. The result in demonstrates that an increase in the aging level of composite insulator results in a decrease of T2. The trend of transverse relaxation time T2 is the same as that of the relative permittivity. The field test results show that NMR sensor can be used to detect the aging status of composite insulator shed. The T2 obtained by our portable NMR sensor can reliably be used as an index to reflect the aging status of composite insulator.