35kV bus voltage too low

A low 35kV bus voltage typically indicates a fault, load imbalance, or equipment issue, requiring immediate inspection and corrective action.

Common Causes of Low 35kV Bus Voltage

1. Grounding or Phase Faults: Single-phase-to-ground faults, phase loss, or blown voltage transformer fuses can cause one or more phase voltages to drop significantly, while other phases may rise due to neutral displacement . In solid ground faults, the faulted phase voltage can drop to zero, triggering busbar grounding alarms.
2. Load Imbalance or Overload: Excessive load downstream of the bus can reduce voltage levels. Sudden load changes or improper load distribution may cause the bus voltage to fall below nominal.
3. Equipment Malfunction: Faulty voltage transformers (VTs), switchgear issues, or arc suppression coil problems can result in incorrect voltage readings or actual voltage drops .
4. SCADA or Protection System Signals: Alarms from SCADA or relay systems may indicate low bus voltage due to detected neutral displacement or abnormal phase voltages .

Diagnostic Steps

• Check SCADA and Relay Alarms: Identify if the busbar grounding or low-voltage alarms are active. Review 3V₀ voltage, arc suppression coil current, and small-current fault line selector status .
• Inspect Physical Equipment: Look for visible arcing, smoke, or unusual noises in the substation. Confirm the integrity of VTs, breakers, and bus connections .
• Measure Phase Voltages: Verify each phase-to-ground and line-to-line voltage to detect phase drops or imbalances. Compare with upstream and downstream voltages.
• Check Load Conditions: Ensure that downstream loads are within rated capacity and that no sudden load changes are causing voltage dips.

Corrective Actions

• Isolate Faulted Equipment: If a specific line or piece of equipment is identified as faulty, transfer its load and isolate it to prevent further voltage drop or damage .
• Trial Switching or Remote Tripping: Perform controlled switching to identify and clear faults, ensuring critical loads are notified before operation .
• Inspect and Maintain Switchgear: Confirm that 35kV switchgear insulation, breakers, and protection relays are functioning correctly and rated for the system's fault duty .
• Monitor and Adjust Load: Redistribute loads if necessary to balance the bus voltage and prevent recurrence of low-voltage conditions.

Safety Considerations

• Always notify central control and downstream users before switching operations.
• Ensure arc suppression coils and busbars are not overloaded to prevent overheating.
• Follow standard operating procedures for high-voltage equipment and maintain proper clearances and insulation ratings .

By systematically diagnosing faults, inspecting equipment, and managing loads, low 35kV bus voltage can be safely corrected while minimizing the risk of outages or equipment damage.