Size of 35kV busbar

The size of a 35 kV busbar depends on its current-carrying capacity, material, and installation conditions, typically designed using cross-sectional areas ranging from 100 mm² to 630 mm² for copper or larger for aluminum.

Overview

A 35 kV busbar is a critical node in medium-voltage power systems, used to collect and distribute electrical energy between generators, transformers, and outgoing feeders . Its design ensures safe current conduction, minimal voltage drop, and mechanical stability under short-circuit conditions . Busbars can be solid, tubular, or laminated, with copper or aluminum as the primary conductor material .

Material and Cross-Section

• Copper busbars are preferred for high current applications due to their high conductivity (58 MS/m), allowing more compact dimensions .
• Aluminum busbars are lighter and cheaper but require larger cross-sectional areas due to lower conductivity (35 MS/m), .
• The cross-sectional area is calculated based on the expected load current, a safety factor (typically 1.25), and allowable temperature rise . Standard cross-sectional areas for medium-voltage busbars range from 100 mm² to 630 mm² for copper, with corresponding width and thickness dimensions adjusted to meet IEC 61439 and NEC 366 standards .

Typical Dimensions and Layout

• A 35 kV busbar is often mounted on steel frame structures with strain insulator strings to support the conductors and reduce floor space .
• Width and thickness are determined by the cross-sectional area and current density. For example, a copper busbar carrying several hundred amperes may have a width of 100–200 mm and thickness of 6–20 mm, depending on ventilation and temperature rise limits .
• Tubular busbars are sometimes used in substations to simplify installation and reduce misalignment issues .

Design Considerations

• Current-carrying capacity: Must accommodate normal load plus a safety margin for temporary overloads .
• Voltage drop: Should not exceed 3% for feeders .
• Temperature rise: Typically limited to 50°C above ambient .
• Mechanical strength: Must withstand short-circuit forces .
• Arc flash protection: Medium-voltage busbars often include arc flash devices to rapidly clear faults . In practice, the exact size of a 35 kV busbar is determined using busbar sizing calculators or manufacturer tables, which consider current, material, installation type, and environmental conditions . This ensures compliance with international standards and safe operation in substations or switchgear assemblies.