Research Article

Evaluation of Overloading Effects on Distribution Transformers: A Case Study of Transformer Substations on 11kv Ile-Oluji Feeder

Abstract: This study evaluates the effects of overloading on the operational performance, efficiency, and lifespan of 11 kV distribution transformers using ten transformer substations in Ile-Oluji, Ondo State, Nigeria, as case study. Field measurements of load currents, voltages, and apparent power were obtained during peak demand periods and compared with transformer rated capacities to determine overload levels and associated thermal stresses. The analysis focused on insulation aging, loss characteristics, voltage regulation, and reliability implications under sustained overload conditions. Results indicate that a significant proportion of the transformers operated beyond recommended loading limits, leading to excessive copper losses, overheating, increased insulation degradation, and increased risk of premature failure. The findings further reveal that overloading contributes to voltage drops and reduced supply quality within the distribution network. The study underscores the necessity for continuous load monitoring, strategic load redistribution, and timely transformer capacity upgrades to mitigate overload impacts. These results provide practical insights for improving asset management, system reliability, and service quality in 11 kV distribution networks, particularly in rapidly growing urban and semi-urban environments.