Electrical trees are one of the main mechanisms of degradation in solid polymeric insulation leading to the failure of high voltage equipment. They are interconnected networks of hollow tubules typically characterized from two-dimensional (2D) projections of their physical manifestation. It is shown that complete characterization requires a three-dimensional (3D) imaging technique such as X-ray computed tomography (XCT). We present a comprehensive set of parameters, quantitatively characterizing two types of tree topology, conventionally known as bush- and branchtype. Fractal dimensions are determined from 3D models and from 2D projections, and a simple quantitative relationship is established between the two for all but dense bush trees. Parameters such as number of nodes, segment length, tortuosity and branch angle are determined from tree skeletons. The parameters most strongly indicative of the differences in the structure are the number of branches, individual channel size, channel tortuosity, nodes per unit length and fractal dimension. Studying two stages of a bush tree's development showed that channels grew in width, while macroscopic parameters such as the fractal dimension and tortuosity were unchanged. These parameters provide a basis for tree growth models, and can shed light on growth mechanisms.

Partial discharges (PDs) are one of the most important classes of ageing processes that occur within electrical insulation. PD detection is a standardized technique to qualify the state of the insulation in electric assets such as machines and power cables. Generally, the classical phase-resolved partial discharge (PRPD) patterns are used to perform the identification of the type of PD source when they are related to a specific degradation process and when the electrical noise level is low compared to the magnitudes of the PD signals. However, in practical applications such as measurements carried out in the field or in industrial environments, several PD sources and large noise signals are usually present simultaneously. In this study, three different inductive sensors have been used to evaluate and compare their performance in the detection and separation of multiple PD sources by applying the chromatic technique to each of the measured signals.

This paper presents a recent characterization review of three cloud-to-ground lightning parameters [lightning peak current, ground flash density, and keraunic level (KL)] used in engineering applications based on available data from studies conducted in some tropical countries of Central and South America (Brazil, Colombia, Costa Rica, and Venezuela), considering seasonal and spatial variation aspects. There are some differences between the behaviors of the analyzed parameters in tropical areas in comparison with those published in the literature for temperate ones. The most significant conclusion is that historical data suggest that the highest ground flash density are located between latitude of 8° and 10° north. This value is much higher than the highest values reported for countries located in temperate regions. It is seen from the KL analysis that this parameter varies depending on the latitude with values up to 200 thunderstorm days (TDs).

The influence of pollution and atmospheric altitude on the dielectric performance of a glass insulator was studied by means of finite element analysis simulations. Contamination levels were represented by thin layers with different values of conductivities and thicknesses. Altitudes differences were simulated by equivalent voltages using correction factors. The results showed that by increasing the conductivity and altitude values, there was a considerable increase in the concentration of the electric field and leakage currents, changing from capacitive to resistive regime of electrical potential distribution along the insulator surface. The proposed levels of contamination and altitudes were analyzed by increasing the dimensions of the insulator according to IEC standards. In the case of the capacitive regime (conductivities lower than 10-4 S/m) there was a decrease in the electric field intensity up to 21% compared to an insulator at sea level. In resistive regime, a decrease up to 34.5% was obtained for leakage currents considering conductivities calculated according to the site pollution severity shown in the IEC standard. Despite the decrease of the leakage current after the increase of the insulator dimensions based on the standards, it did not mitigate all theoretical leakage current calculated along the insulator surface. Future work will focus on experimental research to validate this theoretical results.

This work presents the spatial distribution and temporal variability of lightning activity over the continental territory of Chile by means of Thunderstorms days (Td), on the basis of 7 years (2012–2018) of lightning measurement from World Wide Lightning Location Network (WWLLN). Td are obtained separately for the 15 geopolitical regions of Chile, reporting the higher lightning activity in the northeastern region of the country with 85 thunderstorms days per year. These values are mainly located in the mountains between 2,000 and 5,000 m.a.s.l. where extensive mining activity is located and there are electrical facilities of great importance for Chile. The Td values obtained in this study update the information presented by the World Meteorological Organization (WMO) in 1953, so far the only one available for the entire Chilean territory. From the diurnal cycle analysis, there is a marked mono‐modal behavior of lightning activity in the afternoon for latitudes between S and S (regions XV, I, and II) and a different behavior of lightning activity over the region between S and S (regions X, XI, and XII) known as Chilean Patagonia, due to special weather conditions in that area. Further more, the seasonal analysis showed that the highest lightning activity occurs in January and February and the lowest activity takes place between June and August. Once again, the Chilean Patagonia showed a different behavior because the highest activity is presented in May and August, and the lowest in September. The analysis and results presented here contribute to the knowledge of lightning activity in the region that has not been characterized before and can serve as a basis for future research to determine the behavior of this natural phenomenon.