Reliability Assessment and Improvement Planning for 33kV Feeders in Onitsha, Anambra State

This study conducts a quantitative reliability assessment of 33kV distribution feeders serving Onitsha, Anambra State, South East Nigeria, and develops an evidence-based improvement investment plan. Onitsha hosts one of West Africa's largest commercial markets and a significant industrial base, making reliable electricity supply an economic imperative, yet the city experiences chronic and prolonged outages that impose severe losses on traders and manufacturers. Outage records for 24 feeders were obtained from the Enugu Electricity Distribution Company for a three-year period and analysed to compute System Average Interruption Frequency Index, System Average Interruption Duration Index, and Customer Average Interruption Duration Index for each feeder. Results show that SAIFI values range from 18 to 147 interruptions per year across the assessed feeders, with most feeders significantly exceeding the acceptable thresholds in NERC's minimum service standards. The primary causes of high SAIFI feeders include ageing wooden poles, vegetation encroachment on 33kV lines, and overloaded distribution transformers that trip their overcurrent protection frequently. SAIDI analysis identifies outage restoration time as a significant reliability driver, attributable to insufficient maintenance crew staffing and vehicle availability. A prioritised network improvement plan is developed, ranking feeders by commercial customer density and potential reliability improvement per naira of investment. Targeted interventions include pole replacement, right-of-way clearing contracts, transformer upsizing, and auto-recloser installation on the five highest-priority feeders. Keywords: reliability assessment, SAIDI, SAIFI, distribution feeder, Onitsha.