The width and height of a 35kV busbar bridge depend on current rating, material, and insulation requirements, typically ranging from 100–300 mm in width and 150–400 mm in height for standard medium-voltage applications.

Busbar Sizing Principles

The dimensions of a busbar bridge are determined primarily by:

• Current-carrying capacity: Higher currents require larger cross-sectional areas to limit temperature rise. For copper, IEC 61439 recommends a current density of 1.2–1.6 A/mm² for air-cooled busbars, while aluminum uses 0.8–1.2 A/mm² .
• Voltage level and insulation: At 35kV, sufficient spacing and insulation thickness are required to prevent flashover. Typical phase-to-phase clearances for 35kV are 150–200 mm, influencing the overall height of the busbar bridge.
• Short-circuit withstand: Busbars must resist thermal and electrodynamic forces during faults. The cross-section and spacing are calculated using IEC 60865-1 formulas .
• Mechanical support: Height and width must accommodate support insulators and maintain structural integrity under electrodynamic forces.

Typical Dimensions

While exact dimensions vary by manufacturer and current rating, medium-voltage busbar bridges for 35kV systems generally follow these ranges:

• Width: 100–300 mm, depending on the number of phases and busbar thickness.
• Height: 150–400 mm, including insulation and phase spacing.
• Busbar thickness: 10–25 mm for copper, adjusted for current rating.
• Phase spacing: 150–200 mm for 35kV air-insulated systems. For example, a 630A 4-pole busbar bridge for low-voltage switchboards has dimensions of 470 × 235 × 115 mm (width × height × depth), which illustrates how width and height scale with current and insulation requirements . For 35kV, the dimensions are larger due to higher insulation and clearance requirements.

Design Recommendations

1. Calculate required cross-sectional area using the formula: A = I / J, where I is the rated current and J is the allowable current density for the material .
2. Determine phase spacing based on voltage and insulation standards (IEC 62271-200 for medium voltage).
3. Include mechanical and thermal margins for short-circuit withstand and temperature rise.
4. Verify dimensions with busbar sizing calculators or manufacturer datasheets to ensure compliance with IEC 61439-1 and IEC 60865-1 . In summary, a 35kV busbar bridge typically requires wider and taller dimensions than low-voltage equivalents, with width around 100–300 mm and height 150–400 mm, depending on current, insulation, and mechanical design considerations. Always confirm with manufacturer specifications and IEC standards for precise sizing.