Improving Reliability of a 20 kV HRG Distribution Feeder Using Directional Ground and VROC Relays

Abstract

A 20 kV distribution feeder with high-resistance grounding (HRG) at PLN ULP Sutojayan was investigated to address recurrent maloperation of conventional overcurrent and ground-fault protection under low ground-fault current conditions. The feeder neutral is grounded through a 500Ω resistor, which limits single line-to-ground fault current to approximately 25 A and makes fault discrimination more difficult. This study evaluates an analytical and field-validated PT-assisted DGR-VROC coordination framework for a 20 kV high-resistance grounded feeder. The proposed framework combines residual-current and residual-voltage based directional ground fault discrimination, voltage-restrained overcurrent sensitivity adjustment, and coordination-time assessment. Field disturbance records, MATLAB/Simulink time-domain relay modeling, ETAP reliability assessment, and Failure Mode and Effect Analysis (FMEA) are integrated to evaluate both the protection performance and reliability improvement. Field data over two one-year operating periods showed that recloser disturbance events decreased from 70 to 17 after implementation. The reliability indices also improved significantly, with SAIFI decreasing from 3.20 to 0.90 int./ customer.year, SAIDI from 9.60 to 2.30 h/customer.year, and ENS from 2.40 to $\mathbf{0. 6 5 ~ M W h} /$ year. ETAP simulations reproduced the same trend, while FMEA results showed substantial reductions in Risk Priority Number for critical failure modes such as reverse-fault mal-trip and nuisance trip during open-phase conditions. These results demonstrate that the proposed PT-assisted DGR and VROC scheme improves protection selectivity and significantly enhances the reliability of the 20 kV HRG distribution feeder.