Permissible Current for Tubular Busbars

Tubular busbars typically have continuous current ratings of 1250 A or 2000 A for aluminum systems, with copper extensions matching existing installations.

Continuous Current Ratings

For aluminum tubular busbars used in outdoor primary substations up to 132 kV, the standard continuous current ratings are 1250 A and 2000 A according to Northern Powergrid specifications. When extending existing copper busbar systems, the new copper tubes should match the existing type, ensuring compatibility and maintaining the current-carrying capacity. The current rating depends on material, cross-sectional area, and cooling conditions.

For copper busbars, typical engineering practice and IEC 61439-1 recommend a current density of 1. 5–2. 5 A/mm² for enclosed busbars, depending on ventilation and temperature rise limits.

The cross-sectional area A can be calculated using A=I/J, where I is the rated current and J is the current density. For example, a 2000 A copper busbar at 2. 0 A/mm² requires a cross-sectional area of 1000 mm².

Thermal and Short-

Circuit Considerations

Busbars must be designed to limit temperature rise during continuous operation.

IE

C 61439-1 specifies a maximum temperature rise of 65 K above ambient for bare copper busbars. Short-circuit withstand is also critical: tubular busbars must handle thermal and electrodynamic forces without exceeding material limits, typically 250°C for copper during fault conditions.

Installation and Fittings

Tubular busbars use current-carrying half clamps for all terminal fittings, with at least two complete clamps on fixed fittings to ensure mechanical stability and proper current transfer. When connecting copper to aluminum, precautions must be taken to prevent electrochemical corrosion at the interface.

Summary

Aluminum tubular busbars: 1250 A or 2000 A continuous current rating Copper extensions: match existing busbar type, maintain current rating Design factors: material, cross-section, cooling, temperature rise, short-circuit withstand Fittings: half clamps, minimum two per fixed fitting, compatible materials These ratings ensure safe operation under normal and fault conditions while complying with IEC 61439 and ENA TS 41-11 standards.