A 35kV common enclosed busbar must comply with international standards for current rating, short-circuit withstand, insulation, material, temperature rise, and structural support.

Standards and Compliance

For 35kV busbars, compliance with ANSI C37.23, IEC 61439, and ENA TS 41-11 is essential. These standards define the design, testing, and operational limits for medium-voltage busbars, including continuous current ratings, short-circuit withstand, and environmental considerations .

Material and Construction

• Conductor Material: Copper or aluminum. Copper offers higher conductivity but is heavier and more expensive, while aluminum is lighter and requires a larger cross-section to carry the same current .
• Busbar Type: Common enclosed tubular or insulated tubular busbars are preferred for 35kV applications, providing mechanical protection and electrical insulation .
• Insulation: Tubular busbars are fully insulated to prevent phase-to-phase or phase-to-ground faults. Insulation must withstand the rated voltage and environmental conditions.

Electrical Ratings

• Continuous Current Rating: Determined by cross-sectional area, material, ambient temperature, and enclosure type. Typical ratings for 35kV tubular busbars range from 1250A to 8000A depending on design .
• Short-Circuit Withstand: Busbars must withstand short-circuit currents for a specified duration (usually 1–2 seconds). ANSI C37.23 provides peak and RMS asymmetrical current ratings for 35kV systems .
• Temperature Rise: Maximum allowable temperature rise is typically 65–70°C above ambient for continuous operation, ensuring insulation integrity and minimal power loss .

Mechanical and Structural Requirements

• Support Insulators: Must comply with post insulator specifications (e.g., NPS/003/015) to handle electrical and mechanical loads .
• Support Structures: Should meet substation structural standards (e.g., NPS/003/033) to resist wind, seismic, and short-circuit forces .
• Fittings and Connectors: Joints, clamps, and terminal fittings must prevent deformation and ensure reliable current transfer. Copper-to-aluminum connections require anti-corrosion measures .

Installation and Environmental Considerations

• Enclosure: Fully enclosed, non-ventilated construction is standard to protect against dust, moisture, and accidental contact .
• Ambient Conditions: Design must account for site temperature, solar radiation, and potential forced cooling if required .
• Seismic Qualification: Busbar systems should be evaluated for seismic loads according to local regulations .

Documentation and Testing

• Design Verification: Busbars must be tested for current-carrying capacity, short-circuit withstand, and insulation integrity according to IEC or ANSI standards .
• Traceability: All components, fittings, and materials should be documented for compliance and maintenance purposes . In summary, a 35kV common enclosed busbar requires careful consideration of material, insulation, current rating, short-circuit capacity, temperature rise, mechanical support, and compliance with IEC, ANSI, and ENA standards to ensure safe and reliable operation in medium-voltage substations.