Abstract
Access to reliable electricity remains a critical challenge in secondary cities of Sub-Saharan Africa, where distribution networks suffer from aging infrastructure, chronic underinvestment, and deficient maintenance. This study presents a comprehensive reliability assessment and criticality analysis of the medium-voltage (MT) and low-voltage (LV) distribution network of Mbanza-Ngungu, Democratic Republic of the Congo (DRC). A mixed-method approach combined quantitative analysis of 12 months of outage records (January–December 2025) with stratified surveys of 367 subscribers and exhaustive interviews of 30 SNEL technical staff. Reliability was evaluated using IEEE Std 1366 indices (SAIFI, SAIDI, CAIDI, ASAI, ENS) and probabilistic reliability theory (MTBF, MTTR, λ, R(t), A). Criticality was assessed using an AMDEC (FMEA) matrix combining frequency, severity, and non-detectability. Results reveal a critically degraded network: SAIFI = 31.5 interruptions/subscriber/year, SAIDI = 90.6 h/subscriber/year, CAIDI = 2.88 h, ASAI = 98.97%, and ENS = 1,450 MWh/year. The network MTBF is 1.95 h with a global availability of 42.2%. Transformer failure is the most critical mode (IC = 25), followed by network overload (IC = 20) and equipment aging (IC = 20). Economic analysis estimates the annual cost of non-reliability at 2.83 million USD, while a targeted investment of 1.6 million USD would be recovered in 14 months, generating net savings of 11.35 million USD over 5 years. The proposed framework provides SNEL and local decision-makers with an operational tool for prioritizing maintenance and renewal investments.