35kV bus voltage abnormality

Abnormal 35 kV bus voltage can result from single-phase grounding, fuse blowouts, or resonance, and requires careful diagnosis and timely corrective action to maintain system reliability. Common Causes of 35 kV Bus Voltage AnomaliesHigh-Voltage Fuse Blowouts: When a single-phase, two-phase, or three-phase high-voltage fuse blows, the voltage of the affected phase drops significantly. If the fuse is partially blown, a bus grounding signal may not be triggered, making detection more challenging.

Single-

Phase Grounding Faults: A grounded phase voltage drops close to zero, while the other two phases rise to line voltage levels. This often triggers a “busbar grounding” alarm. Indicators include dimming of the faulted phase VT light and brightening of the healthy phases.

Resonance (Ferroresonance): All three-phase voltages rise abnormally but remain balanced. The bus voltage transformer may emit a buzzing sound, and overvoltage can reach 1. 5–3.

5 times the normal phase voltage. No bus grounding signal is typically issued.

Low-

Voltage Fuse Blowouts: Secondary voltage drops significantly without triggering a busbar grounding signal.

Identification and Diagnosis

Voltage Transformer (VT) Observations: Check VT indicator lights; the faulted phase dims while others brighten. Measure 3V₀ output to detect neutral displacement voltage.

SCAD

A and Alarm Signals: Look for “35 kV busbar grounding” or arc suppression coil activation signals. These provide early warning without tripping the system. Physical Inspection: For faults within the substation, visible arcing, smoke, or unusual noises can help locate the fault.

Corrective Actions

Immediate Notification: Alert central control and dispatch line operation teams to inspect equipment and protection status. Trial Switching or Remote Tripping: After confirming the fault, perform trial switching of lines or remote tripping via SCADA, ensuring critical loads are managed. Load Transfer: Prioritize transferring load from the faulty line before isolating it to prevent cascading outages.

Equipment Isolation: Faulted equipment should be isolated promptly, typically within 2 hours, to prevent overheating and damage to arc suppression coils. Monitoring and Maintenance: Continuously monitor bus voltage, VT readings, and arc suppression coil currents to prevent recurrence.

Operational Considerations

Abnormal bus voltage can indicate system reactive power imbalance and may affect overall network reliability. Timely detection and handling prevent voltage collapse, phase-to-phase short circuits, and potential large-area blackouts. Maintaining proper grounding, fuse integrity, and monitoring of arc suppression coils is critical for safe operation.

By systematically diagnosing the type of anomaly and following structured corrective procedures, operators can maintain 35 kV bus stability and ensure safe, reliable power system operation.