Xilin Wang

Micro characterization and degradation mechanism of liquid silicone rubber used for external insulation

In recent years, some hollow core composite insulators, of which housings were made of liquid silicone rubber (LSR) of current and voltage transformers used in China Southern Power Grid have showed different levels of degradation and cracking phenomena. Based on SEM, FTIR, XPS and XRD methods, analyses have been conducted from several aspects such as organic functional groups concentration, microscopic appearance, element valence etc. It is found that organic groups (mainly Si-(CH3)2) on the side-chains of LSR are much more vulnerable than the backbone during the degradation process, thus Si-O/Si-C absorption peak ratio could be applied to characterize the degradation level of LSR. For severely aged LSR samples, the ratio is around 1.787-2.436. The valences of Si element and Si-O, Si-C functional group relative concentration of the aged LSR surface have changed and crystal structure is formed. Macro properties tests show that the surface of aged LSR is almost hydrophilic and tracking and erosion resistance is deteriorated remarkably. It is concluded that the crystallization caused by thermal/optical oxidation over crosslinking reaction is the main reason why degradation occurred.

Polymer light-emitting electrochemical cells with the block copolymers containing PEO segments

Abstract Polymer light-emitting electrochemical cells (LECs) were fabricated and characterized with three block copolymers containing PEO segments as the luminescent polymers. The block copolymers are composed of PPV segments with three phenylene vinylene units and PEO segments with three ethylene oxide units. Blue–green light-emission of the LECs was demonstrated with the onset voltage lower than 3 V and EL efficiency of 0.74 cd/A at 2.8 V. The response time of the LECs is approximately 5 s. The transient response and a.c. impedance data indicate that the operating mechanism of the LECs is an electrochemical doping model.

Analysis of causes of outdoor insulators damages on HV and UHV transmission lines in China

In this paper the statistical analysis for the causes of outdoor insulation accidents of AC and DC high-voltage transmission lines in China were described. This paper focuses on lightning strike, pollution flashover, icing, birds-caused damage, and other factors which may damage the safe operation of power transmission lines. This paper also analyzes the service situation of insulators, the reasons of damages as well as the development tendency of insulators with different types in transmission lines.

Fatigue fracture of composite insulator sheds utilized in strong wind areas

This paper presents the fracture failure mechanism of composite insulators that have been deployed for only one year on 750 kV transmission lines in strong wind areas. Investigations indicate that the flexible shed structure was vulnerable to flow-induced oscillation, which further brought cracking to the shed root. The interactive process of fatigue and fracture was reviewed by inspecting the failed samples to gain insight into the cracking mechanism. The fatigue theory of silicone rubber was introduced to illustrate the fatigue resistance of the material. Simulations of wind load and stress distribution were performed to demonstrate the load condition and stress concentration at the root area on sheds. Wind tunnel tests show the oscillation of two types of 750 kV insulators under strong winds of up to 60 m/s. Four samples of silicone rubber from major insulator manufacturers were tested to investigate the fatigue resistance property, and withstand limit of high- and low-performance silicone rubbers. Results indicate that, composite insulators without specific design and wind tunnel tests were risky to apply on transmission lines in strong wind areas, which is common type of climate in northwestern China.

Elemental analysis of RTV and HTV silicone rubber with laser-induced breakdown spectroscopy

Silicone rubber composite materials, such as the room temperature vulcanized silicone rubber (RTV) and the high temperature vulcanized silicone rubber (HTV) have been widely used in the field of high voltage insulation for their good surface hydrophobicity and hydrophobicity transfer. To get a comprehensive understanding of the mechanism of their hydrophobicity, it is necessary to analyze their chemical composition with suitable methods, which is better should be easily used on site in transmission lines. With laser-induced breakdown spectroscopy (LIBS), this paper analysed the elemental composition of HTV sample and studied the effect of change in laser energy per single shot on the spectra and the electron number density. The spectra showed that carbon (C), oxygen (O), aluminum (Al), silicon (Si) and zinc (Zn) were contained in the sample, which was proved with the EDS result. And it is noted that with the increase of the laser energy per single shot, intensities of the spectral lines increased.

A new method to measure RTV coatings thickness with laser-induced breakdown spectroscopy (LIBS) technique

Room temperature vulcanized silicone rubber (RTV) coatings have been widely used in the world to prevent the pollution flashover in transmission lines. Thickness of the RTV coatings which was hard to measure with regular methods, was one of the most important properties and required by State Grid Company. As a fast and online analysis method, laser-induced breakdown spectroscopy (LIBS) has been applied in different fields. With LIBS, this paper studied the depth of the laser-ablated craters and the emission spectra of RTV coatings. Using a laser, focusing on the coating surface, together with a spectrometer and the scanning electron microscope (SEM) for observation, the linear relationship between the crater depth and the number of laser pulses was observed and the emission spectra were observed. The result showed that the depth of laser-ablated craters on RTV had a linear relationship with the number of laser pulses, which could be further applied to the measurement of the RTV thickness of coatings.