This article presents a new selective method for identifying a faulty feeder in 6–35 kV electrical distribution networks with the isolated neutral configuration during single-phase ground faults (SPGFs) with transient resistance. The method is based on simultaneous comparison of the zero-sequence current (ZSC) angle and magnitude across all outgoing feeders and substation buses. Unlike conventional protection approaches relying solely on current magnitude or direction, the proposed algorithm enhances sensitivity and selectivity by detecting the 180° phase opposition between the faulted feeder's ZSC and the unfaulted feeders’ capacitive ZSC. To implement this strategy, a Centralized Ground Fault Protection Unit (CGFPU) was developed, capable of real-time feeder status monitoring, fault localization, and differentiated alarm or trip signal generation. Extensive modeling of SPGF processes was conducted in Matlab Simulink, considering transient resistance values ranging from 1 Ω to 10,000 Ω. Results demonstrated the nonlinear behavior of ground fault and capacitive currents relative to the transient resistance, with a notable shift in phasor angles approaching 180° for faulty feeders and near 0° for unfaulted feeders during bus faults. The CGFPU algorithm was tested under various scenarios, including feeder and busbar faults with different resistance levels, validating its capability to issue an alarm at high- resistance faults and trip signals for low-resistance bolted faults. The proposed method effectively ensures stable operation over a wide range of transient resistance values, maintains protection sensitivity even under high-impedance fault conditions, and resists nuisance tripping caused by charging or inrush currents. Integration of advanced concepts such as dynamic threshold setting, angle-magnitude multi-criteria decision-making, and principles of transient fault analysis further enhances the system's robustness. The protection system design is adaptable for future smart grid and microgrid applications requiring precise ground fault detection. The article also provides functional diagrams, operation algorithms, and a thorough theoretical analysis supported by simulation results.

Single-phase ground faults (SPGFs) in isolated neutral medium-voltage networks are difficult to detect, especially under high transient resistance. This paper proposes a centralized ground fault protection unit (CGFPU) that combines zero-sequence current (ZSC) magnitude and phase-angle analysis to enhance selectivity. Simulation results show that as transient resistance increases from 1 Ohm to 10 kOhm, fault currents decrease significantly, yet the CGFPU reliably identifies the faulty feeder by exploiting the characteristic 180° phase shift of ZSC phasors. The method remains selective with angular deviations up to ±20° and distinguishes between feeder and busbar faults. Compared with conventional amplitude- or model-based techniques, the proposed approach achieves faster detection, lower computational complexity, and robustness against unbalanced and charging currents. Furthermore, the CGFPU operates adaptively in alarm or trip mode depending on fault severity, thus preserving continuity for high-resistance faults and ensuring rapid isolation of bolted faults. These contributions establish a practical, scalable, and future-ready solution for SPGF protection in medium-voltage isolated neutral networks.

This article presents a new selective method for identifying a faulty feeder in 6–35 kV electrical distribution networks with isolated neutral configuration during single-phase ground faults (SPGFs) with transient resistance. The method is based on simultaneous comparison of the zero-sequence current (ZSC) angle and magnitude across all outgoing feeders and substation buses. Unlike conventional protection approaches relying solely on current amplitude or direction, the proposed algorithm enhances sensitivity and selectivity by detecting the 180° phase opposition between the faulted feeder's ZSC and the unfaulted feeders’ capacitive ZSC. To implement this strategy, a centralized ground fault protection unit (CGFPU) was developed, capable of real-time feeder status monitoring, fault localization, and differentiated alarm or trip signal generation. Extensive modeling of SPGF processes was conducted in Matlab Simulink, considering transient resistance values ranging from 1 Ω to 10,000 Ω. Results demonstrated the nonlinear behavior of ground fault and capacitive currents relative to the transient resistance, with a notable shift in phasor angles approaching 180° for faulty feeders and near 0° for healthy feeders during bus faults. The CGFPU algorithm was tested under various scenarios, including feeder and busbar faults with different resistance levels, validating its capability to issue an alarm at high-resistance faults and trip signals for low-resistance bolted faults. The proposed method effectively ensures stable operation over a wide range of transient resistance values, maintains protection sensitivity even under high-impedance fault conditions, and resists nuisance tripping caused by charging or inrush currents. Integration of advanced concepts such as dynamic threshold setting, angle-magnitude multi-criteria decision-making, and principles of transient fault analysis further enhances the system's robustness. The protection system design is adaptable for future smart grid and microgrid applications requiring precise ground fault detection. The article also provides functional diagrams, operation algorithms, and a thorough theoretical analysis supported by simulation results.

Today, the electric power industry occupies a key position in the country's economy. In the age of digitalization, it is impossible to imagine any working system without electricity. Due to the growing dependence of all spheres of human activity on electricity, the requirements for quality and reliability of electrical energy are also growing. Today, the problem associated with ground faults (GF) in 6-35 kV distribution electrical networks remains unresolved. In Kazakhstan, they are the most common networks, in terms of line length, they account for about 70% of the entire existing line, i.e. about 341.3 thousand km. These networks are implemented with an isolated neutral configuration and resistive grounding (with high or low impedance grounding) and with compensated or combined neutral grounding. Analysis of operational data on electrical installation faults in 6-35 kV networks showed that most of these events occurred due to damage to phase insulation and because of ground faults, whose share is about 70-80% of the total number of faults. The ground faults are accompanied by possible damage to electrical equipment due to the overvoltages. During the operation of the 6-35 kV network, it is important to detect ground faults, since this mode occurs at low currents, commensurate with the operating current or even less, but with overvoltages. Overvoltages can lead to the phase insulation damage of other normal phases and to two phase-to-ground faults. Under short-circuit conditions, the protection relay operates and several lines are isolated, which reduces the reliability of power supply to consumers and overall efficiency of the distribution electric network. Existing methods for identifying ground fault locations do not provide the required selectivity. Low sensitivity of overvoltage protection is possible if GF occurs through the transient resistance. In combination, the existing methods reduce the efficiency of the electric network during ground faults. The paper proposes detection method for ground faults that is highly selective and sensitive to low currents due to the transient resistance. The proposed protection operates and isolates only the faulty line, due to its selective operation and eliminates the long-term impact of high over voltages on electrical installations, which is important during operation of an electrical network with the isolated neutral.