How to ground a 35kV busbar

Neutral resistor grounding is the preferred method for 35kV busbars, limiting overvoltages and enabling fast, accurate fault detection.Neutral Resistor GroundingFor 35kV distribution systems, neutral resistor grounding (NRG) is commonly used. Each busbar is connected to the system neutral through a resistor, which serves to:Limit ground fault current to a safe level, preventing equipment damage and reducing arc flash hazards.Control overvoltages, including transient and intermittent arc-ground overvoltages.Enable accurate fault line selection, allowing rapid identification and isolation of the faulted line . The resistor value is selected based on the system's capacitive current. For example, in a cable-based 35kV system with three buses, each with a capacitive current of 50 A, the total system capacitive current is considered (e.g., 150 A) and adjusted for future load growth (e.g., 180 A) to determine the appropriate resistor rating .Fault Detection and ProtectionWhen a single-phase-to-ground fault occurs:The voltage of the faulted phase drops, while the other two phase-to-ground voltages rise.Arc suppression coils carry the compensation current corresponding to their tap settings.SCADA systems or substation alarms indicate “35kV busbar grounding” and may trigger arc suppression coil activation . Operators should inspect the substation and line equipment promptly, isolate the faulted line, and prevent escalation to phase-to-phase faults. Faulted equipment should generally be isolated within 2 hours to avoid overheating and damage to the arc suppression coil .Advantages of Neutral Resistor GroundingLimits all types of overvoltages, including resonant and intermittent arc-ground overvoltages.Facilitates fast and accurate fault line isolation, improving system reliability.Suitable for cable-dominated networks and industrial or auxiliary systems such as airports, steel plants, and power plants .Implementation ConsiderationsEnsure the grounding path is low-impedance and direct to safely dissipate fault currents .Proper sizing of the resistor is critical to balance fault current limitation and effective fault detection.Coordination with protective relays and SCADA systems is necessary for automatic or remote fault isolation. In summary, 35kV busbars are typically grounded via neutral resistor grounding, which provides controlled fault currents, limits overvoltages, and enables rapid fault detection and isolation, ensuring both personnel safety and equipment protection.