Study On The NMR Detection Method And Sensor For Assessing The Aging Status Of The Sheds Of Composite Insulator

Composite insulators have been widely used in high voltage transmission lines fortheir light weight, high mechanical strength, and excellent hydrophobicity. However,with the increase of the installed number and service time, the aging problem ofcomposite insulators has been noted by electric utility. The study on assessing thedeterioration of composite insulators with age, which can discover the defect withintransmission lines to avoid line accident, is of great significance to the safety andreliability of the power supply.There are many existed methods which have been used to assess the aging status ofcomposite insulators, but some of them are neither accurate, nor destructive. In thispaper, we introduced a low-field nuclear magnetic resonance (NMR) technology tonondestructively assess the aging status of the sheds of composite insulators. For thispurpose, we carried out the preliminary research on the aging properties of compositeinsulators based on low-field NMR principle. The main work in this paper is composedof four parts as follows:â‘ The aging detection method for the sheds of composite insulators based onlow-field NMR is proposed and the detection principle is also analyzed.â‘¡According to the structure characteristics of composite insulators, we designedand constructed a C-shape portable NMR sensor. The sensor consists of a C-shapestructure, magnet structure, RF coil and tuning&matching circuit. Once connected tothe NMR spectrometer, the portable NMR sensor can be used to detect the sheds ofcomposite insulators nondestructively.â‘¢The inverse Laplace transform of NMR echo decay data has been studied.Based on the inversion method analysis of NMR echo decay data, A NMR echoanalysis software is developed. The software has data processing function includingsingle or double exponential fit and inverse Laplace transformation.â‘£The portable NMR measurement experiments are performed on compositeinsulators with different service times in the same transmission line, using NMR echoanalysis software for processing. We select transverse relaxation time T2long meanobtained from inverse Laplace transformation to characterize the aging degree of thesheds of composite insulator. The results have demonstrated that an increase in the aging level of the insulatorclearly results in a decrease of T2long mean. This indicates that the T2long meanrelaxationtime obtained from our portable NMR sensor can reliably be used as an index to reflectthe aging status of silicone rubber insulator.This thesis establishes a new method for assessing the aging characteristics ofcomposite insulators based on low-field NMR principle, and has great practicalsignificance for scientifically evaluating the service life of composite insulator.