Analysis of Load Imbalance in 20 kV/400 V Distribution Transformers at PT PLN (Persero) Siantar Kota ULP Operational Area Robinson Sinaga, Siti Anisah, Dian Yulis Wulandari

Abstract

Load unbalance in distribution transformers causes increased power losses and degraded voltage quality. This study analyzes the load unbalance level of 623 distribution transformers (20 kV/400 V) in the service area of PT PLN (Persero) ULP Siantar Kota, distributed across twenty-one feeders with seven transformer codes (A, K, L, M, P, S, and T). The Current Unbalance Factor (CUF) method was applied using phase current measurement data under Off-Peak Load (LBP) and Peak Load (BP) conditions in February 2026. Results show that the overall average CUF reached 33.81% (LBP) and 32.32% (BP), far exceeding PLN’s 20% tolerance limit. A total of 410 transformers (65.8%) under LBP and 399 transformers (64.0%) under BP fall into the severe unbalance category (CUF ≥ 20%). Substation codes K recorded the highest average CUF of 37.15% (LBP) and 37.76% (BP). Immediate load balancing through the redistribution of customer connections across phases is strongly recommended.