Tubular busbars typically have continuous current ratings of 1250 A or 2000 A for aluminum tubes, with copper extensions matching existing systems, depending on size and installation standards.

Overview

Tubular busbars are metallic conductors used to interconnect equipment in substations and switchgear, designed to carry high currents efficiently while minimizing voltage drop and heating. They are commonly made from aluminum or copper tubes, with aluminum preferred for new installations due to its lighter weight and cost-effectiveness, while copper is used for extensions to existing systems .

Continuous Current Ratings

For aluminum tubular busbars, standard continuous current ratings are:

• 1250 A
• 2000 A These ratings are based on the tube's cross-sectional area, material conductivity, and cooling conditions, as specified in ENA TS 41-11 . Copper tubular busbars are sized to match existing installations and have similar or slightly higher current-carrying capacity due to copper's higher conductivity.

Factors Affecting Current Capacity

1. Material: Copper has higher conductivity than aluminum, allowing smaller cross-sections for the same current .
2. Cross-sectional Area: Larger width and thickness increase current capacity. The busbar current can be estimated using the formula:
   • Copper: I = 1.2 × width (mm) × thickness (mm)
   • Aluminum: I = 0.8 × width (mm) × thickness (mm) This provides the approximate continuous current in amperes .
3. Cooling Conditions: Open-air or enclosed installations affect heat dissipation, influencing allowable current density. Typical current density for enclosed copper busbars is 1.5–2.5 A/mm² .
4. Short-Circuit Withstand: Busbars must withstand short-circuit currents without exceeding material temperature limits, calculated using adiabatic equations .
5. Mechanical Forces: Electromagnetic forces between parallel busbars during faults must be considered to prevent deformation .

Standards and Guidelines

• BS EN 61936-1: Power installations exceeding 1 kV AC
• ENA TS 41-11: Aluminum tubular busbar systems
• ENA TS 41-16: Copper tubular busbar systems
• IEC 61439-1: Low-voltage switchgear assemblies, including current density and temperature rise limits

Practical Considerations

• Ensure busbar dimensions match the required current rating to avoid overheating or voltage drop.
• Use compatible fittings and clamps to prevent mechanical or electrochemical issues at connections.
• Extensions to existing systems should match the original material and type to maintain system integrity . By following these guidelines, tubular busbars can safely carry high currents in substations and switchgear while maintaining reliability and compliance with international standards.