EXPERIMENTAL QUANTIFICATION AND TECHNO-ECONOMIC IMPACT OF LOAD UNBALANCE ON LOW-VOLTAGE DISTRIBUTION TRANSFORMERS: A CASE STUDY OF MBANZA-NGUNGU, DEMOCRATIC REPUBLIC OF THE CONGO

Abstract

Load unbalance in low-voltage (LV) distribution networks is a major cause of transformer degradation and technical losses, yet it remains under-documented in Sub-Saharan Africa. This study presents an experimental quantification of load unbalance on three 630 kVA distribution transformers (Yukula, Offitra, and Hôpital) in Mbanza-Ngungu, Democratic Republic of the Congo (DRC). A mixed-method approach combined stratified surveys of 367 subscribers (Cronbach's α = 0.785) with in-situ current measurements conducted from 2024 to 2026. Results show Current Unbalance Rates (IUR) ranging from 65% to 71%, with neutral currents reaching 145–240 A during peak hours. Joule losses exceeded 100 kW on the most critical feeder, and hot-spot temperatures reached 109.4°C, accelerating thermal aging (V_age = 2.85–4.68). A phase permutation strategy reduced IUR below 5%, neutral current by 85–92%, and Joule losses by 44–49%. The economic analysis yields a payback period of approximately 2 months, demonstrating that low-cost static rebalancing is a highly profitable asset management strategy for the national utility (SNEL).