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35kV bus voltage is abnormal

35kV bus voltage is abnormal

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35kV bus voltage is abnormal - BENNIE OPTICAL [PDF]

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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 Anomalies

  1. High-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 .
  2. 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 .
  3. 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 .
  4. 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 .
  • SCADA 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

  1. Immediate Notification: Alert central control and dispatch line operation teams to inspect equipment and protection status .
  2. Trial Switching or Remote Tripping: After confirming the fault, perform trial switching of lines or remote tripping via SCADA, ensuring critical loads are managed .
  3. Load Transfer: Prioritize transferring load from the faulty line before isolating it to prevent cascading outages .
  4. Equipment Isolation: Faulted equipment should be isolated promptly, typically within 2 hours, to prevent overheating and damage to arc suppression coils .
  5. 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.
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