Fatigue fracture of composite insulator sheds utilized in strong wind areas

Abstract

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 lowperformance 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.

Study on material and mechanical characteristics of silicone rubber shed of field-aged 110 kV composite insulators

“…Many studies employ static contact angle test method to analyze the aging characteristics of SIR samples [8][9][10][11] . The relationship between hardening, cracking and aging degree of composite insulator sheds has also been studied [12][13][14] . The sheds of composite insulator samples from different regions are collected and tested by Chen.…”

A Proposal for the Evaluation of HTV Silicone Rubber Composite Insulators

“…This is probably due to the different material blends and manufacturing processes used by each manufacturer. According to previous research works, as high as possible tear strength of the housing material is required, as this prevents damage from careless handling, strong wind and bird pecking when the insulators are going to be installed or are already installed in the electrical network [29][30][31]. Tear strength test was conducted to all test pieces obtained from all available insulators and the average values of tear strength (columns), and the corresponding standard deviations (error bars), for each pack of five test pieces, are presented in Figure 10.…”

“…This is probably due to the different material blends and manufacturing processes used by each manufacturer. According to previous research works, as high as possible tear strength of the housing material is required, as this prevents damage from careless handling, strong wind and bird pecking when the insulators are going to be installed or are already installed in the electrical network [29][30][31].…”

Experimental Study and Mechanism Analysis of Composite Insulator Chalking in Extra-High Voltage (EHV) Transmission Line

“…However, since the sheds and sheath of the composite insulators are made of organic silicone rubber, the aging and deterioration of which would be more serious under the influence of harsh environment during operation. Some of the specific manifestations include the loss of hydrophobicity, the cracks on the sheath, the hardening of the sheds, and a less common but equally detrimental form of aging, the chalking [5][6][7].…”