# Failure Trends of High-Voltage Porcelain Insulators Depending on the Constituents of the Porcelain
## 1 Introduction
Many researchers have performed research on the lifetime assessment of porcelain insulators before. Most of the articles predicted the useful life of insulators to be more than 40 years. However, some also reported active lives below 30 years [14]. This study investigated the dependency of the mechanical and electrical characteristics of porcelain insulators on the porcelain constituents. Further, the relation between the probability of failure of porcelain insulators with varying weight percentages of SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), and Fe\({}_{2}\)O\({}_{3}\) was found. Influence of the Material Contents of Porcelain Body on the Electrical and Mechanical Properties of Porcelain Insulators  
Porcelain insulator samples that were manufactured in different years with a mass of 36,000 lbs and operated at 154 kV were collected from various power transmission lines in South Korea. These were discarded from utility systems to assess the condition of similar samples. Table 1 shows the essential specifications of the insulators required for the evaluation of the aging state. The M&E and T&M loading tests were performed on insulators to evaluate their mechanical and electrical strengths. Load tests were performed as per the Acronym for the American National Standards Institute ANSI. Instron(tm) hydraulic press with a maximum capacity of 135,000 lbs has been used. The mechanical load was raised up to load of 50% of the M&E rating and fixed at this value for 1 min. Consequently, a thermal chamber was maintained with 24-h cycles with two temperature levels, \(-\)30 \({}^{\circ}\)C and 40 \({}^{\circ}\)C, and the insulator had to withstand for 4 h. Figure 1 shows the condition of the insulator samples that failed the load tests. During the load tests, these failed samples showed different issues like cap separation, pulling out of pins, breaking of the porcelain body, etc. Table 1 shows specifications of the insulators collected from different places in South Korea. Remarks represent location of porcelain insulator at which failure occur. The collected samples were categorized into three sections according to the constituents of the porcelain body and the manufacturing year. Tables 1 and 2 show that the average load at which failure occurred increased approximately 14.7% in samples manufactured in 2005 compared to those manufactured in 1975. The quality factor (K), which evaluates any insulator mechanically and electrically, was calculated. For a passing load test, K should be greater than 3 [8]. It was observed that there was an increase of 90.95% in K in the case of samples manufactured in 2005 compared to those manufactured in 1975. \[\text{K}=\frac{Q_{M}-Q_{A}}{Y_{U}} \tag{1}\]  
where \(Q_{M}\) is the initial quality index, \(Q_{A}\) is the current quality index, and \(Y_{u}\) is the remaining lifetime. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Insulator I**} & \multicolumn{5}{c}{**Failure Load (lbs)**} \\ \cline{2-6}  & **Sample A (1975)** & **Remarks** & **Sample B (1995)** & **Remarks** & **Sample C (2005)** & **Remarks** \\ \hline
1 & 20,980 & Neck & 22,960 & Pin & 22,760 & Pin \\
2 & 20,560 & Neck & 22,400 & Pin & 22,240 & Pin \\
3 & 22,160 & Pin & 23,100 & Pin & 23,460 & Pin \\
4 & 21,820 & Pin & 22,710 & Pin & 22,710 & Pin \\
5 & 22,180 & Pin & 21,450 & Neck & 23,140 & Pin \\
6 & 13,680 & Neck & 22,690 & Pin & 23,270 & Pin \\
7 & 14,940 & Neck & 22,750 & Pin & 22,790 & Pin \\
8 & 22,160 & Pin & 22,480 & Pin & 21,940 & Pin \\
9 & 18,030 & Neck & 21,960 & Pin & 23,270 & Pin \\
10 & 22,410 & Pin & 23,300 & Pin & 23,410 & Pin \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Details of mechanical load tests with electrical voltage (M&E) test results. Figure 1: Mechanical and electrical failure of insulators that failed the load tests: (**a**) separated cap, (**b**) broken insulator, (**c**) cap separated, (**d**) broken insulator, (**e**) pin pulled out and mechanical failure, and (**f**) break due to electrical failure.