Mixed-Method Analysis of Reliability-Centered Design Practices in Medium and Low-Voltage Electrical Distribution Systems

Abstract

This study addresses the persistent reliability challenges in medium- and low-voltage electrical distribution systems, where interruptions, delayed restoration, weak fault isolation, and uneven design quality continue to undermine service continuity and operational efficiency. Its purpose was to examine how reliability-centered design practices influence reliability performance, operational efficiency, and system dependability across selected case-based electrical distribution environments. Using a quantitative, cross-sectional, case-based design, the study collected primary data from 120 usable respondents out of 150 distributed questionnaires, yielding an 80.0% usable response rate. The sample comprised electrical engineers, maintenance engineers, distribution planners, operations officers, and technical supervisors/managers working across medium-voltage systems, low-voltage systems, and both system classes. The key independent variables were protective coordination, redundancy planning, fault isolation capability, switching and restoration readiness, and equipment standardization, while the dependent variables were reliability performance, operational efficiency, and system dependability. Data were analyzed using descriptive statistics, a Reliability-Centered Design Practice Index, correlation, t-test, and multiple regression in SPSS. The findings showed a high overall level of design-practice adoption with an RCDPI mean of 3.87, while reliability performance, operational efficiency, and system dependability recorded means of 3.91, 3.83, and 3.88 respectively. Protective coordination had the highest mean score at 4.02, followed by fault isolation capability at 3.94. Reliability-centered design practices were strongly and positively associated with reliability performance (r = 0.71, p < 0.001) and operational efficiency (r = 0.66, p < 0.001), while the strongest relationship was observed with system dependability (r = 0.74, p < 0.001). Medium-voltage systems outperformed low-voltage systems, with RCDPI scores of 3.95 and 3.78 respectively, and the difference was statistically significant (t = 2.41, p = 0.017). Regression results further showed that design variables explained 58.4% of the variance in reliability performance and 61.7% of the variance in system dependability, confirming that reliability-centered design is a critical engineering and planning mechanism for improving distribution-system outcomes.