Selection of 35kV Indoor Busbar

Selecting a 35kV indoor busbar requires careful consideration of current rating, material, insulation, mechanical design, and compliance with IEC standards to ensure safe and efficient operation.

Key Considerations for 35kV Indoor Busbars

1. Material Selection Busbars are typically made of copper or aluminum. Copper offers higher conductivity and better thermal performance but is more expensive, while aluminum is lighter and cost-effective but requires a larger cross-sectional area to carry the same current . For a 35kV indoor system, copper is often preferred for high-current applications due to its superior conductivity and lower voltage drop. 2. Current Rating and Cross-Sectional Area The continuous current (Ir) and short-circuit current (Isc) ratings are critical. The busbar must carry the rated current without exceeding permissible temperature rise and withstand fault currents for a specified duration (typically 1–3 seconds), . The cross-sectional area is calculated based on conductor width and thickness, with a traditional design guideline of approximately 400 circular mils per ampere, adjusted for laminated busbars and multiple layers . AC frequency effects, such as the skin effect, should also be considered for high-current applications. 3. Insulation and Safety Indoor 35kV busbars require high-quality insulation to prevent phase-to-phase faults and ensure operator safety. Common insulation materials include Nomex®, Tedlar®, Mylar®, Kapton®, epoxy-glass, and heat-shrink tubing . The insulation thickness must comply with voltage withstand requirements and environmental conditions, including humidity and potential contamination. 4. Mechanical Design Mechanical considerations include rigidity, mounting holes, tabs, and connections. The width of the conductor should be at least three times its thickness to avoid hot spots, and the maximum current for each termination must be evaluated . Supports and clamps are necessary to counteract electromagnetic forces during short-circuit events, and flexible joints may be used to accommodate thermal expansion . 5. Configuration and Layout Busbars can be arranged in single, double, or sectionalized bus systems depending on redundancy and maintenance requirements . Laminated busbars reduce inductance and improve efficiency, while hollow or tubular designs may be used for weight reduction and better cooling. 6. Compliance with Standards IEC 61439 provides guidelines for busbar sizing, including temperature rise limits, ambient temperature corrections, and installation orientation . For indoor 35kV systems, the standard ensures safe operation under normal and fault conditions, and software tools like Ecodial, Simaris, or ETAP can optimize busbar dimensions and layout. 7. Environmental and Operational Factors Indoor busbars must consider ventilation, enclosure type, and IP rating. For example, IP65 protection ensures dust and water resistance, while hermetically sealed enclosures protect against condensation and small animals . Optional aseismic design may be required in earthquake-prone areas.

Summary

To select a 35kV indoor busbar:

• Choose copper or aluminum based on current and cost.
• Calculate cross-sectional area for continuous and fault currents, considering AC effects.
• Apply adequate insulation for voltage and environmental conditions.
• Ensure mechanical robustness with proper supports and thermal expansion allowances.
• Follow IEC 61439 standards for sizing, temperature rise, and installation.
• Optimize layout for redundancy, efficiency, and maintenance. Early involvement of experienced engineers and use of design software can significantly improve safety, efficiency, and cost-effectiveness .