Application Of Quasi-distributed FBG To Brittle Fracture Monitoring Of GFRP Rods In Composite Insulators

A new method,the fiber Bragg grating(FBG)online monitoring method,was used to monitor composite insulator brittle fracture in this paper.Based on this method,the 10 k V and110 k V optical fiber composite insulators are designed and manufactured,and the temperature and tension calibration test system and the stress corrosion test system were established.The influence factors of FBG temperature and tension coefficient were found in the calibration test.The mechanical model of FBG wavelength shift identification for axial section crack is proposed.The warning threshold for evaluating the composite insulator’s brittle fracture process is found,which realizes the online monitoring of the complete brittle fracture process of the composite insulator.Firstly,the temperature and stress detection principle of FBG was described.The 10 k V and 110 k V optic fiber composite insulators without sheath were designed.Four optical fibers were pasted on the 10 k V composite insulator rod’s surface,one of which was cascaded with two temperature FBG,and the other three were cascaded with three or five FBG.Four optical fibers were pasted on the rod of the 110 k V composite insulator,one of which was cascaded with two temperature FBG,and the other three were cascaded with nine FBG.Because of the changes in the temperature and tension coefficient of the FBG after it was posted on the rod’s surface,a temperature and tension calibration test system were proposed.Then establish an optical fiber monitoring system for the brittle fracture process of the rod.Secondly,by using the established temperature and tension calibration test system,many experiments are carried out to obtain the temperature and tension coefficient accurately.FBG temperature calibration tests were carried out before and after pasting,under the different adhesive thickness and different curing temperatures of adhesive.The influence of adhesive pasting process difference on temperature coefficient is studied.Then,the tension calibration tests are carried out with or without installing an acid container,different thickness of adhesive,different temperature and different distribution positions,and the effects of the adhesive bonding process,ambient temperature,and position difference on the tension coefficient are studied.The tension calibration test of the FBG temperature compensation sensor was carried out,and the bonding mode of the FBG temperature compensation sensor is studied.At the same time,it was verified that the FBG temperature compensation sensor insulates the influence of stress.Finally,the stress corrosion tests of composite insulators with different nitric acid concentrations,tension,and rod material were carried out on the optical fiber monitoring system.FBGs monitored the temperature and stress of composite insulator rods during brittle fracture.Combined with the morphology of brittle fracture and the wavelength shift of FBGs,the critical stage of brittle fracture is analyzed.Based on the analysis of the relationship between the stress distribution and the wavelength shift of FBG in the crack development process,the mechanical model of wavelength shift identification for axial section crack is proposed,the warning threshold for monitoring the brittle fracture stage is summarized.The system and method of FBG monitoring the crack severity in the brittle fracture process of composite insulators are studied.