This work aimed to study the influence of contamination profiles and humidity on flashover electrical characteristics of polluted insulators. Firstly, the flashover tests on cap and pin glass insulators under four pollution levels represented by salinity were conducted. Eight artificial contamination profiles based on the solid layer method have been modeled for the selected insulators. The numerical analysis has been used to determine the insulator electrical characteristics such as potential, electric field, and power dissipation under proposed contamination profiles using finite element methods (FEM). Next, the power dissipation has been simulated with consideration of thermal stress propagation in locations with high power. Finally, flashover voltage gradient tests have been conducted under various humidity and contamination profiles. The values of the flashover voltage gradient due to pollution were determined as the percentage of the value of the flashover voltage gradient in the clean condition which was identified as the reference point. The numerical model indicated that the initiation of arc generally occurs at area in which the electric field and power dissipation is maximum. It was also observed from experimental results that the flashover voltage gradient under different contamination profiles has different values depends on the location and dimension of the pollution region.

Due to the increasing demand on developing good insulation, several researchers have performed experimental studies to prove the effectiveness and capabilities of transformer oil. This is done by suspending nanosized solid particles in the oil (nanofluid) for transformer applications. In brief, this paper presents a compilation of research studies which is divided into three parts. Part I discuss the preparation of the nanofluid which involves different types of nanomaterials, the optimal amount of concentrations, and applicable synthesisation methods for producing stably suspended nanofluids. In Part II, the nanofluid’s performances including the electrical breakdown voltages, impulse tests, and thermal and dielectric behaviour are reviewed in depth and compared. Part III emphasizes the limitation of nanofluids. Most researchers have agreed that appropriate concentrations of nanomaterials and the preparation method for nanofluids mainly affect the performance of nanofluids especially in terms of electrical properties. Meanwhile, types of nanomaterials and base oil also play a vital role in producing nanofluids as a better alternative transformer oil. However, among a few researchers, there are concerns regarding the issue of agglomeration and inconsistencies of findings that need to be resolved. Therefore, a few aspects must be taken into consideration to produce the next generation of high heat dissipation insulation.

Over the past decades, extensive experimental-based research works have been carried out to investigate the flashover phenomenon on the performance of polluted transmission line insulators. The critical focus has been on developing methods that can determine the safety, reliability, and sustainability of the overall power transmission network based on experimental results obtained from polluted insulators’ flashover voltage tests. In this paper, a systematic review of available scientific works, published as early as the 1990s, for the analysis of pollution flashover voltage, is undertaken. The review mainly focuses on factors influencing the efficiency of transmission line insulators under polluted conditions. Specifically, publication databases utilizing various synonyms and keywords associated with the terms “contaminated insulators” and “flashover voltage test” have been scrutinized. The search has resulted in 1364 articles, from which 97 articles have satisfied the review requirements and have been subsequently analyzed to determine the parameters associated with polluted insulators. Major factors that affect the performance of insulators, including electrical and environmental impacts, are discussed. Variations in factors affecting flashover test development and insulator efficiency are also considered. Overall, the current analysis provides an important insight toward successful evaluations of the health of transmission line insulators and research advancements of electric power transmission line insulators.

Based on experiments and numerical analysis techniques, this paper aims to investigate the influence of the four different coating damage profiles on the performance of coated 33 kV porcelain insulator strings under polluted and clean surface conditions. The performance of the insulators coated with room temperature vulcanizing (RTV) under partial coating damage and undamaged coating was evaluated. The influence of humidity on pollution flashover was taken into consideration. The ring-shaped, fan-shaped, and random-shaped coating was applied following coating damage. The results showed that the flashover characteristic of the RTV-coated insulators had a significant difference as compared to the normal insulators. Electrical characteristics such as the flashover voltage, critical current, and surface resistance were significantly affected by coating damage distribution and humidity level on the insulators’ surface. The electric field and potential difference were analyzed as well using the finite element method (FEM). The initiation of the arc was observed to appear at the area of insulators where the electric field was the highest. It was also observed that different coating distributions of pollution and humidity levels resulted in a change in the surface pollution layer resistance and an uneven distribution of the electric field. This indicates that the coated insulators’ parameters are directly related to the coating damage distribution on the insulator surface, particularly in the presence of humidity.

The monitoring of leakage current (LC) and voltage characteristics in transmission line insulators is regarded as a good technique for anticipating the physical state of in-service insulators. In the current work, the temporal and frequency characteristics of LC and voltage under various situations were derived for assessing the health condition of porcelain, glass, and silicone rubber insulators. The contamination severity indicated by soluble deposit density, wetting level (Wt), non-soluble deposit density, and uneven pollution distribution (P_u/P_L) were chosen as the environmental factors that impact the insulators. Six criteria were utilized to evaluate the physical state of the insulators, with four of those derived from the LC signal in the time domain, namely, the LC signal peak (C₁), the phase shift between applied voltage and LC (C₂), the LC signal slope between two consecutive peaks (C₃), and the crest factor (C₄). The remaining two indices, namely, the total harmonics distribution (C₅) and the harmonics ratio indicator (C₆), were obtained from the frequency domain of the LC signal. In addition, the flashover voltage index (C₇) was also employed. The LC indicators were then classified based on the laboratory test results to reflect the physical state of the insulators. The findings revealed that the proposed indicators had an important impact in determining the physical state of the insulators. Furthermore, a confusion matrix was created for the test and prediction data using the suggested indicators to determine the effectiveness of each indicator.

Alternative transformer oil has been investigated universally in the past years. Different types of vegetable oil have been proposed and evaluated as replacements for conventional transformer oil (mineral oil) due to increasing exploitation and depleting petroleum reserves. In response to growing concern about global environmental and sustainable issues, this article discusses the suitability of palm oil (PO) and palm oil-based nanofluids (PO-N) as alternative transformer oils. A brief discussion of environmental concerns is provided in this paper, and the detailed properties of PO are thoroughly addressed. The electrical performance (alternating current breakdown voltage and lightning impulse breakdown voltage), physical behaviour (viscosity, flash point, and fire point), tan delta, and relative permittivity of PO and PO-N are also discussed in this paper. Based on reliable data and research, it has been proven that refined, bleached, deodorised palm oil (RBDPO) has been determined to be the most promising type of PO when compared to others. Furthermore, when CuO nanoparticles are added to RBDPO with the use of CTAB surfactant, the AC breakdown voltage increases by 173.42 % compared to RBDPO without CuO. However, there is still scope for further improvement in nanofluid stability. In addition to these studies, future research should focus on other aspects such as ageing studies, partial discharge breakdown voltage, etc. PO has interesting properties that make the industry and scientific community take notice.