Data-Driven Condition Assessment and Remaining Life Prediction of Low-Voltage Distribution Transformers Using Insulation Resistance Measurements: A Case Study of Ajayi Crowther University Distribution Network

Abstract

This paper presents a comprehensive insulation resistance (IR) assessment of low voltage distribution transformers at Ajayi Crowther University (ACU), Oyo, Nigeria. The study evaluates the safety, reliability, and operational efficiency of four distribution transformers (three 500 kVA units and one 750 kVA unit) through systematic IR testing using a Megger MIT1025 insulation tester. Testing was conducted in three configurations: Line-to-Earth (L-E), Neutral-to-Earth (N-E), and Line-to-Neutral (L-N), with results corrected to a standard temperature of 20°C and benchmarked against IEEE standards. Statistical analysis revealed an overall mean corrected IR of 137.5 MΩ with a standard deviation of 21.46 MΩ. Three transformers (T1, T3, and T4) demonstrated healthy insulation with corrected IR values ranging from 100 to 160 MΩ. However, transformer T2 exhibited localized insulation degradation, failing the L-N test with a corrected IR of 90 MΩ, below the IEEE minimum threshold of 100 MΩ. The findings indicate that while the university's electrical distribution system is largely in satisfactory condition, immediate corrective maintenance is required for T2.