Wiring method of 35kV busbar

35kV busbars can be wired using single bus, double bus, sectionalized, or F busbar systems, with protection schemes tailored to the configuration and load requirements.

Common Busbar Configurations

1. Single Bus: A single main bus energized at all times, connecting all circuits. It is simple but has low reliability; a fault or breaker failure can result in total substation outage .
2. Double Bus: Two main buses allow flexibility; feeders can be connected to either bus, improving reliability and maintenance options .
3. Sectionalized Single Bus: The bus is divided into sections with sectionalizing breakers, allowing parts of the bus to be isolated during faults without affecting the entire system .
4. F Busbar System: Specifically designed for 35kV GIS switchgear, this system uses fully insulated, sealed, and screened busbars with bolt-crimping connections. It supports currents of 1250A, 2000A, and 2500A, and is resistant to weather, contamination, and partial discharge .

Wiring and Installation Considerations

• Conductor Size: Cross-sectional area depends on current rating; for 35kV systems, typical conductor sizes range from 50–630 mm² .
• Insulation: Busbars are often fully insulated using materials like epoxy-glass, Nomex®, or Mylar/Tedlar laminates to reduce inductance and prevent short circuits .
• Spacing: Minimum center distance between busbars is generally 500 mm to ensure safe clearance .
• Connection Method: Bolt-crimping is commonly used for F busbar systems, providing secure mechanical and electrical connections .

Protection Methods

• Overcurrent-Based Interlocking: Simple and cost-effective, suitable for distribution busbars with lower fault currents .
• Differential Protection: High-speed fault clearing for critical busbars; includes high-impedance or percentage differential schemes to handle CT saturation and complex bus arrangements .
• Dynamic Bus Replica: Numerical relays like B90 can create dynamic bus replicas for flexible protection zones, especially in multi-section or double-bus systems .

Practical Tips

• Coordinate with equipment manufacturers to ensure busbar dimensions, insulation, and connection methods match the switchgear and transformers.
• Consider future expansion; sectionalized or double-bus systems provide better scalability.
• Ensure proper grounding and stress control to minimize partial discharge and maintain reliability under adverse weather conditions . By selecting the appropriate bus configuration, conductor sizing, insulation, and protection scheme, a 35kV busbar system can achieve high reliability, safety, and operational flexibility.