Cause of 35kV busbar grounding

A 35kV busbar can ground due to single-phase-to-ground faults, insulation failures, equipment malfunctions, or operational disturbances in the substation.

Common Causes

1. Single-Phase-to-Ground Faults: A primary cause of busbar grounding is a single-phase-to-ground fault, where one phase of the busbar unintentionally contacts the ground. This can occur due to insulation breakdown, moisture ingress, or physical damage to conductors or bus supports. During such faults, the voltage of the faulted phase drops, while the other two phase-to-ground voltages rise, and the substation may trigger a “busbar grounding” alarm . 2. Equipment Failures: Failures in voltage transformers (VTs), circuit breakers, or disconnectors can lead to busbar grounding. For example, blown fuses in VTs or malfunctioning switchgear can create conditions where the busbar becomes grounded. Internal arcs or arc-flash incidents in switchgear assemblies can also cause a phase to contact the ground . 3. Ferroresonance and Phase Loss: Operational disturbances such as ferroresonance or the loss of a phase can mimic grounding conditions. These phenomena alter the neutral point voltage, causing current to flow through arc suppression coils and triggering busbar grounding alarms even if a direct metallic fault is not present . 4. Insulation Degradation: Over time, insulation on busbars, connectors, or supporting structures can degrade due to thermal stress, contamination, or aging. This increases the likelihood of a phase-to-ground fault, especially in high-voltage systems like 35kV distribution networks . 5. External Factors: Environmental conditions such as lightning strikes, tree contact, or foreign objects bridging the busbar to ground can also cause grounding events. These external faults often require line patrols and inspection to locate the faulted section .

Detection and Protection

Busbar grounding is typically detected using relay protection systems, arc suppression coils, and small-current fault line selectors. In a solid ground fault, the faulted phase voltage drops to zero, the other two phase-to-ground voltages increase by √3 times, and the 3V₀ output of the VT rises, triggering alarms . High-speed differential protection or overcurrent-based schemes are used to isolate the fault quickly, preventing equipment damage and maintaining system stability .

Preventive Measures

• Regular inspection and maintenance of insulation and switchgear.
• Monitoring of VT and arc suppression coil currents.
• Implementation of high-speed busbar protection schemes to quickly clear faults.
• Environmental management to reduce external fault risks, such as tree trimming and lightning protection . In summary, a 35kV busbar grounds primarily due to single-phase-to-ground faults, equipment failures, insulation breakdown, or operational disturbances, and effective detection and protection systems are essential to minimize damage and maintain system reliability.