Analysis of voltage drop causes at SMK Ponpes Manbaul Ulum Cirebon

This study aimed to identify the causes, evaluate, and quantify the magnitude of voltage drop at SMK Ponpes Manba'ul’Ulum Cirebon. A descriptive quantitative approach using a single case study strategy was applied. Data were collected from PT PLN ULP Sumber, Cirebon, and through direct field measurements using a Digital Earth Tester, Digital Insulation Tester, and monitoring of a three-phase kWh meter. The findings revealed that the main cause of voltage drop was transformer overload at Distribution Substation CKPB, with a loading level of 91.20%, exceeding the 80% limit specified by the Indonesian Electricity Supply Standard (SPLN). Additional contributing factors included a 710-meter conductor length with a 70 mm² cross-sectional area, inter-phase load imbalance (I₁ = 105 A, I₂ = 149 A, I₃ = 141 A), and insulation resistance anomalies detected at several test points (0 MΩ at N-T, T-G, and N-G). Before transformer uprating, the voltage drop reached 28.49 V (14.92%), exceeding the SPLN 72:1987 tolerance range of 5–10%. After uprating the transformer capacity from 100 kVA to 160 kVA combined with load splitting, the voltage drop decreased to 13.57 V (6.33%) and transformer loading declined to 57.10%.