The span of a 10kV copper busbar is determined by its cross-sectional area, current rating, mechanical support spacing, and short-circuit withstand, following IEC standards.

Electrical Sizing

For a copper busbar, the cross-sectional area (A) is calculated using the rated current (I) and the recommended current density (J): A = I / J

• For medium-voltage copper busbars, IEC 61439-1 recommends a current density of 1.5–2.5 A/mm² depending on cooling conditions .
• Example: For a 2000 A busbar at 2 A/mm², A = 2000 / 2 = 1000 mm². Multiple bars can be used in parallel to achieve the required area and provide margin for heating . Temperature rise must be checked to ensure it does not exceed 65 K for insulated or 105°C for bare busbars under normal operation .

Short-Circuit Withstand

Busbars must withstand short-circuit conditions both thermally and electrodynamically:

• Thermal withstand ensures the busbar does not exceed 250°C during a fault. The required area can be estimated using: A ≥ I × √t / k where I is the short-circuit current, t is the fault duration, and k = 143 for copper per IEC 60865-1 .
• Electrodynamic withstand ensures the busbar and supports can resist peak electromagnetic forces: F = 0.2 × ip² / d where ip is the peak short-circuit current and d is the center-to-center spacing between phases in meters . Support spacing must limit deflection and stress below the yield strength of copper and insulators.

Mechanical Span Considerations

The span between supports depends on:

• Busbar thickness and width
• Material properties (copper yield strength)
• Electrodynamic forces during short-circuit
• Allowable deflection limits Typical practice is to use insulator supports spaced to maintain deflection within safe limits, often calculated using beam bending formulas for a simply supported bar under uniform load, including its own weight and electromagnetic forces .

Practical Design Steps

1. Determine rated current and select current density to calculate cross-sectional area.
2. Check temperature rise under normal operation.
3. Calculate short-circuit thermal and electrodynamic forces.
4. Determine support spacing to limit deflection and stress.
5. Verify phase-to-phase and phase-to-ground clearances per IEC 62271-1.
6. Adjust busbar dimensions or add parallel bars if necessary to meet both electrical and mechanical requirements . Using these steps ensures the 10kV copper busbar is electrically safe, mechanically stable, and compliant with IEC standards. Online busbar calculators can simplify these calculations by providing recommended width, thickness, and support spacing based on input parameters .