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What aspects should be paid attention to when installing medium-voltage switch cabinets during the initial stage of subway operation?

Felix Spark
Field: Failure and maintenance
China
1. Statistics on Common Faults of Medium-Voltage Switchgear in the Early Operation Stage
As project participants, we found during the early operation of a new metro line: 21 sets of power supply equipment were put into use, with a total of 266 accident phenomena in the first year. Among them, 77 faults occurred in medium-voltage switchgear, accounting for 28.9%—significantly higher than faults in other equipment. Statistical analysis shows that major fault types include: protection device signal anomalies, air chamber pressure sensor false alarms, live indication failures on the feeder cable side of switches, and loose voltage busbars between cabinets. These issues directly affect the operational safety and quality of medium-voltage switchgear.
2. Fault Causes and Rectification Measures
We conducted a 3-month tracking statistics on fault data, comprehensively investigated causes, and formulated rectification plans. After six months of rectification, the fault frequency significantly decreased, and operational stability improved. The specific analysis is as follows:
2.1 Signal Faults
  • Cause: Internal board failures of live line indicators were the main reason for frequent signal false alarms in the early stage.
  • Rectification: After inspecting equipment across the line, all damaged live line indicators were replaced to ensure accurate signal transmission.

2.2 Switch Air Chamber Pressure Faults

  • Cause: Loose plug-in connectors of air chamber pressure sensors in 35kV switchgear led to poor contact and signal mistransmission.
  • Rectification: All air chamber pressure sensor plugs were replaced, and circuit connections were reinforced to eliminate contact hidden dangers.

2.3 Communication Faults

  • Cause: Hardware board defects or software operation anomalies in protection devices triggered abnormal monitoring conditions.
  • Rectification: Faulty hardware boards were replaced, and software was upgraded to optimize communication stability.

2.4 Voltage Phase Loss Faults

  • Cause: The voltage busbar in the cabinet top circuit loosened due to external forces, preventing the protection module from normal signal acquisition.
  • Rectification: A bridge was installed at the top of the cabinet to fix the voltage busbar, standardize wiring processes, and eliminate phase loss faults caused by loose terminals.
3. Follow-up Maintenance Planning
From equipment operation and maintenance experience, the early operation stage is a high-risk period for faults, where design defects, installation craftsmanship, and operational environment issues tend to emerge intensively. Incomplete initial defect inspection directly threatens traffic safety. From a cost perspective, defect handling during the warranty period can obtain free technical support from manufacturers, while maintenance costs will increase significantly after the warranty expires. Therefore, we have formulated the following strategies:
  • Maintenance Process Optimization: Include voltage busbar terminal inspections in the annual maintenance plan, and simultaneously verify switch position status.
  • Reliability Enhancement: Adopt scientific maintenance strategies to extend equipment service life and reduce life-cycle costs through regular inspections and condition monitoring.

4. Conclusion
Incorporating medium-voltage switchgear in the early operation stage into key maintenance scopes helps accurately statistical analyze equipment faults. We must use fault data as a basis to formulate maintenance outlines, dynamically adjust maintenance plans, and improve equipment reliability through standardized operations to ensure metro safety.
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About experts
Felix Spark
China
Expertise area
Failure and maintenance
Professional article
107
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