Investigation on Unexplained Faults in Transmission Lines: A Comprehensive Study on Pollution-Induced Outdoor Insulation Problems on Ethiopian Transmission System, and GIS-based Pollution Severity Mapping
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Date
2025-01
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Addis Ababa University
Abstract
Excessive unexplained outages on transmission lines significantly impact Ethiopian power system and,
consequently, the national economy. Resolving these issues requires accurately identifying the root
causes of outages and adopting appropriate mitigation strategies as a proactive approach. Such an
approach, incorporating improved design and maintenance practices, is more cost-effective in the long
term and ensures that critical issues are prioritized. Therefore, in line with addressing the challenges
resulting from excessive unexplained outages on transmission lines, this dissertation presents the
investigation of pollution-induced outdoor insulation problems in Ethiopian transmission system and
develops a GIS-based pollution severity map for the whole country, including the estimation of site
pollution severity parameters on carefully selected locations.
Statistical analysis of the unexplained faults on power transmission lines operating at 132 kV, 230 kV,
and 400 kV was the first focus area of this research. Long-term fault records, from 2015 to 2022, were
analyzed for identifying the main probable root causes of these outages by combining fault time stamp
data with known fault characteristics as well as with information on local climatic and environmental
conditions. Out of the total number of 8,891 registered fault records, 4,231 (47%) were unexplained.
Among these unexplained outages the analysis attributed 19% of them to lightning, 27% to pollution
events, 11% to fires, and 43% to external interferences.
Furthermore, this research places a particular emphasis on pollution-induced flashover of insulators, a
major factor contributing to unexplained outages in the Ethiopian power transmission network. A
detailed and refined methodology was developed to identify faults caused by insulation pollution
flashover, that associated fault characteristics with local meteorological and environmental conditions.
Results reveal that 24.7% of the previously unexplained faults were likely caused by pollution-induced
flashovers. The analysis showed that porcelain insulators exhibit the highest pollution-induced
flashover intensity. Silicone rubber insulators also have performed unsatisfactorily in Ethiopian
conditions, indicating the need for improved insulator selection and sizing practices that consider the
local climatic and environmental conditions.
The analysis allowed us to assess the outdoor insulation design practices. It highlights the lack of
systematic use of service experience, site pollution measurements, and laboratory tests in the practices
used for insulator selection. Recommendations to the Ethiopian Electric Power (EEP) are formulated
that aim at improving this process and request paying more attention when addressing the pollution
related challenges.
The study further evaluated the site pollution severity of selected sites in Ethiopia and developed a
GIS-based pollution severity map for the country. It was conducted at 364 selected sites along existing overhead transmission lines and substations, and other key locations for future grid expansion. Two
site pollution severity evaluation methods were used: analysis of climatic and environmental
conditions, and analysis of operational service experiences of existing transmission lines alongside of
local meteorological parameters. The map incorporates local pollution sources and requires validation
through ground-based measurements. As part of estimating the severity of environmental pollution,
the study focused on assessing the ambient particulate matter (PM2.5) levels. It analyzed annual mean
satellite-based PM2.5 density for Ethiopia from 1998 to 2022 using ArcGIS for spatial data processing
and Inverse Distance Weighted (IDW) interpolation to create a concentration surface map. The
analysis revealed an increasing trend in Ethiopia's average annual mean PM2.5 density. The North-
East grid region had the highest annual mean PM2.5 density (34.13 μg/m³), while the Southeast and
South regions had the lowest. A strong correlation was found between high PM2.5 density areas and
frequent pollution-induced flashovers. This is the first standardized pollution severity map for the
Ethiopian power grid, serving as a baseline for future updates.
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Keywords
Ethiopian power transmission system, Power transmission reliability, Root cause analysis, Unexplained faults, Pollution flashover, Outdoor insulators, Silicone rubber polymeric insulators, Site pollution severity, GIS-based pollution severity map, Particulate matter, Climatic conditions of Ethiopia