# Failure Trends of High-Voltage Porcelain Insulators Depending on the Constituents of the Porcelain
## 1 Introduction  
Power industries are highly cautious regarding the aging assessment of transmission systems. The consistency and durability of insulators are extremely necessary for the efficient performance of power utilities. Despite insulators being only 5% of the capital cost, they require 70% of the maintenance costs of transmission lines [1; 2; 3]. Many works have been reported regarding the failure of porcelain insulators due to impulsive stresses caused by electrical, mechanical, thermal, and various environmental stresses. These stresses lead to the failure of the insulator, either mechanically or electrically. The failure probability is highly dependent on the mechanical and electrical characteristics of insulators, as mechanical and electrical properties are responsible for the strength of the insulator. It has been reported in many articles that the composition constituents of the porcelain body has a large impact on the mechanical and electrical characteristics of insulators [4; 5; 6; 7]. This article focused on studying the relation between the failure probability of insulators and the weight percentage of porcelain contents, such as SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), and Fe\({}_{2}\)O\({}_{3}\), for the lifetime assessment of a porcelain insulator. Many articles have been reported on the contribution of SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), and Fe\({}_{2}\)O\({}_{3}\) in porcelaininsulators. [PERSON] et al. reported that whenever porcelain insulators having SiO\({}_{2}\) as the major component have been subjected for firing at higher temperatures, the corners of the quartz (SiO\({}_{2}\)) particles are dissolved into feldspar. Thus, this decreases the solid quartz (SiO\({}_{2}\)) content, leading to a degradation of mechanical strength [8; 9; 10; 11]. Therefore, the firing temperature has to be performed attentively in the case of porcelain insulators that have quartz (SiO\({}_{2}\)) as a major portion. However, another considerable issue with insulators having SiO\({}_{2}\) as a major portion is the difference in the thermal coefficient of the quartz grain and matrix around it. This condition leads to tensile stress in the quartz grains, and the surrounding matrix undergoes compressive stress. Thus, micro cracks are generated, which reduces the bulk density of the porcelain body of the insulators. However, in the case where SiO\({}_{2}\) has been altered with Al\({}_{2}\)O\({}_{3}\) in the porcelain body, the density of the fired porcelain body improves. At the same time, [PERSON] reported on the replacement of SiO\({}_{2}\) with Al\({}_{2}\)O\({}_{3}\) to enhance the bending strength of electrical porcelain bodies. This improves the mechanical and electrical strength of the insulator [9]. Furthermore, [PERSON] reported that Fe\({}_{2}\)O\({}_{3}\) enhances the dielectric constant and loss tangent, which tends to result in an increase in heating through dielectric losses [1; 12; 13]. Porcelain insulator samples were collected from various power transmission lines throughout South Korea, which were 36,000 lbs and operated at 154 kV. These insulators were discarded from utility systems to assess the condition of similar samples. The samples collected were categorized into three sections according to the year of installation. Mechanical load tests with electrical voltage (M&E), thermal and mechanical load tests (T&M), and hardness tests (HRB) were performed on all three categories of insulators to evaluate their mechanical and electrical characteristics. X-ray fluorescence (XRF) and scanning electron microscopy (SEM) characterization techniques were adapted to study the detailed change in weight percentage of the SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), and Fe\({}_{2}\)O\({}_{3}\) and its impact on the microstructure of the porcelain of porcelain insulators. Finally, statistical distributions were implemented to analyze the trends of the probability of failure of collected samples depending on the constituents of the porcelain body.