Research on Fiber Bragg Grating Sensor for Salt Density Detection on Insulator Surface
Online monitoring of the pollution level of insulators in operation can detect hidden dangers early and reduce pollution flashover accidents. The existing online monitoring systems for external insulation pollution of transmission lines have disadvantages such as poor measurement accuracy, low reliability, susceptibility to electromagnetic interference, need for on-site power supply, and high cost. To solve these problems, this paper proposes the use of Fiber Bragg Grating (FBG) for online monitoring of salt density on insulator surfaces. This study found that sodium chloride has a significant effect on the moisture sensitivity of polyimide-coated fiber Bragg gratings. On this basis, the influence mechanism was analyzed, and a polyimide film-coated fiber Bragg grating (PI-FBG) was proposed for salt density detection on insulator surfaces. Experiments show that the better the humidity sensitivity of PI-FBG, the more obvious the inhibitory effect of sodium chloride on it. In response to the problems of multiple peaks, uneven film formation, and bending of the grating area in traditional methods of multi-layer polyimide coating, this study improved the polyimide coating process and prepared a PI-FBG sensor with high humidity sensitivity. The main components of natural pollution on insulator surfaces are soluble salt sodium chloride, insoluble calcium sulfate, and insoluble silicon dioxide. Experiments show that calcium sulfate and silicon dioxide have almost no inhibitory effect on the wavelength increase of PI-FBG sensors under high humidity environments, while sodium chloride has a significant inhibitory effect, thereby eliminating the influence of insoluble calcium sulfate and insoluble silicon dioxide on salt density measurement results. The relationship between salt density on insulator surfaces and the wavelength suppression of PI-FBG sensors under relative humidity conditions of 98%RH, 90%RH, and 80%RH was quantitatively analyzed, and the minimum salt density identification value of PI-FBG sensors under the above relative humidity conditions was determined. Based on the sensor development, this paper constructed an all-optical network online monitoring system for salt density on insulator surfaces based on PI-FBG sensors. This system has the advantages of strong anti-electromagnetic interference capability, high reliability, and remote passive quasi-distributed measurement. A fiber Bragg grating wavelength demodulator based on FBGA demodulation module was developed, and the upper computer software development based on virtual instruments was completed.
