A 35 kV busbar system typically uses single, double, or sectionalized bus configurations with copper conductors, insulated for medium-voltage operation, designed to handle rated currents and short-circuit conditions according to IEEE and IEC standards.

Common Busbar Configurations

For 35 kV substations, the most common busbar arrangements include:

• Single Bus: One main bus energized at all times; simplest but lowest reliability. A fault on the bus or breaker failure results in total outage .
• Double Bus, Single Breaker: Two buses with a single breaker per circuit; allows maintenance on one bus without interrupting supply .
• Double Bus, Double Breaker: Each circuit has two breakers connecting to two buses; provides high reliability and flexibility .
• Ring Bus or Breaker-and-a-Half: Offers redundancy and allows isolation of faults without affecting other circuits . The choice depends on reliability requirements, space, and cost.

Busbar Design Considerations

• Material: Copper is standard for 35 kV busbars due to high conductivity; joints are silver-plated for low contact resistance .
• Insulation: Flame-retardant, non-hygroscopic materials rated for continuous operation at 120°C; under-oil or fluid insulation may be used for switchgear .
• Current Rating: Busbars must carry the continuous rated current without exceeding permissible temperature rise; IEC 61439 and ANSI C37.23 provide sizing guidelines .
• Short-Circuit Withstand: Busbars and joints must withstand fault currents; bolted connections are torqued to maintain uniform pressure and prevent overheating .
• Mechanical Support: Supports must resist electromagnetic forces during faults and allow for thermal expansion/contraction .
• Grounding: Ground return conductors should match the size of voltage conductors; interleaved grounds can improve shielding and reduce noise .

Switchgear Integration

35 kV busbars are often integrated into underground or pad-mounted switchgear, using sectionalizing switches and drawout fuses for protection . The busbar layout must accommodate:

• Source and tap connections
• Loadbreak switches
• Adequate spacing for creepage and clearances
• Accessibility for maintenance

Sizing and Thermal Management

• Cross-Sectional Area: Determined by current-carrying requirements; a traditional basis is ~400 circular mils per ampere for single conductors, adjusted for laminated or multiple conductors .
• Temperature Rise: Maximum hotspot rise should not exceed 55°C above 50°C ambient; forced cooling is generally avoided unless approved .
• Airflow and Heat Dissipation: Low-profile busbar arrangements can improve natural convection; busbars may also act as heat sinks .

Summary

A standard 35 kV busbar system balances electrical reliability, mechanical strength, and thermal performance. Typical designs use copper conductors with flame-retardant insulation, bolted joints, and configurations such as single, double, or sectionalized buses. Compliance with IEEE C37.23, C37.74, and IEC 61439 ensures safe operation under continuous and fault conditions, while proper mechanical support and grounding maintain system integrity and minimize operational risks .