35kV Hard Busbar Spacing

Busbar support spacing for 35kV systems depends on dielectric clearance, mechanical strength, and short-circuit withstand, typically ranging from 1. 2 to 1. 5 meters for straight runs, but exact spacing must be verified against manufacturer and ANSI standards.

Key Considerations

Dielectric Clearance: The spacing between busbars and supports must ensure sufficient air and surface creepage distances to prevent flashover. For 35kV systems, phase-to-phase and phase-to-ground clearances are critical, and the design must pass power frequency and impulse withstand tests as per ANSI standards. Clearance values vary depending on whether conductors are insulated or bare.

Mechanical Support: Bus supports must withstand the rated short-circuit forces and thermal expansion. Supports are typically made from flame-retardant, non-hygroscopic materials and should be positioned to prevent sagging or vibration. The spacing is influenced by busbar cross-section, material (copper or aluminum), and current rating.

Typical Spacing Guidelines: While ANSI standards do not prescribe exact distances, practical engineering experience suggests: Straight busbar runs: 1. 2–1. 5 meters between supports for 35kV, depending on busbar size and weight.

Near joints or bends: Supports should be closer, often 0. 5–0. 8 meters, to maintain mechanical stability and prevent excessive deflection.

Insulated busbars: Can allow slightly longer spans due to reduced risk of flashover, but must still meet dielectric tests. Environmental and Installation Factors: Outdoor installations, vibration-prone areas, or high-humidity environments may require closer support spacing. Supports should also accommodate thermal expansion and allow for inspection and maintenance.

Summary: The exact support spacing for a 35kV busbar is not fixed by ANSI standards but is determined by a combination of electrical clearance, mechanical strength, and short-circuit withstand requirements. Engineers typically use 1. 2–1.

5 meters for straight runs, with closer spacing near bends or joints, and always verify against manufacturer guidelines and dielectric testing requirements.