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35kV tubular busbar spacing

35kV tubular busbar spacing

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35kV tubular busbar spacing - BENNIE OPTICAL [PDF]

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For 35 kV tubular busbars, typical phase-to-phase and phase-to-ground spacing ranges from approximately 300 mm to 400 mm, depending on insulation, environmental conditions, and manufacturer specifications.

Recommended Clearance

For medium-voltage tubular busbars rated at 35 kV:

  • Phase-to-phase spacing: Generally around 300–400 mm for bare aluminium or copper tubular busbars in outdoor substations, following IEC 60664-1 guidelines and ENA TS 41-11 specifications .
  • Phase-to-ground spacing: Similar to phase-to-phase, typically 300–400 mm, ensuring safe dielectric clearance under normal and fault conditions .
  • Insulated busbars: If the busbars are coated with epoxy or heat-shrink insulation, the spacing can be reduced, as the insulation provides additional dielectric protection .

Factors Affecting Spacing

  1. Pollution Degree: In areas with high pollution (degree 3), larger clearances or additional insulation barriers are recommended to prevent flashover .
  2. Altitude: At elevations above 2000 meters, air dielectric strength decreases, requiring an increase in spacing by approximately 25% at 3000 meters .
  3. Mechanical Support: Busbar supports must prevent sagging or vibration, which could reduce the effective clearance between phases .
  4. Thermal Expansion: Metal expansion due to temperature rise can reduce spacing over time, so designers must account for this in the layout .

Practical Installation Notes

  • Support Insulators: Use glass-reinforced polymer or equivalent insulating supports, spaced according to busbar orientation (e.g., horizontal supports up to 36 inches center-to-center, vertical supports up to 18 inches) to maintain mechanical stability .
  • Fittings and Clamps: Ensure all joints and clamps are designed to avoid deformation of the tubular conductor and maintain consistent spacing .
  • Switchgear Integration: When integrating with 35 kV switchgear, follow manufacturer-specific bushing spacing guidelines, which may specify 8-inch (≈203 mm) minimum between bushings for certain configurations .

Summary

For 35 kV tubular busbars, maintaining 300–400 mm spacing between phases and to ground is a practical and safe range, with adjustments based on insulation, environmental conditions, altitude, and mechanical support. Always verify against IEC 60664-1, ENA TS 41-11, and manufacturer-specific specifications to ensure compliance and long-term reliability.

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