35kV busbar power supply requirements

A 35kV busbar system requires proper sizing, insulation, short-circuit withstand, temperature control, grounding, and protection coordination to ensure safe and reliable operation.

Electrical Requirements

Voltage Rating and Insulation: The busbar must be rated for continuous operation at 35kV, with insulation materials capable of withstanding the system voltage and environmental conditions. Flame-retardant, non-hygroscopic insulation rated for continuous operation at 120°C is recommended for high-voltage busbars to prevent corona and insulation failure . Current Rating and Sizing: The busbar cross-section must be sized to carry the expected load current without exceeding permissible temperature rise. IEC 61439 and IEC 60287 provide guidelines for calculating current-carrying capacity, considering ambient temperature, enclosure type, and material (copper or aluminum). Copper is preferred for higher conductivity, while aluminum requires a larger cross-section for the same current . Short-Circuit Withstand: The busbar must withstand fault currents for a specified duration (typically 1–3 seconds) without mechanical or thermal damage. Supports and joints should be designed to handle electromagnetic forces generated during short-circuit events . Temperature Rise: The allowable temperature rise for copper busbars is typically 70°C above ambient, while aluminum is limited to 55°C. Busbar joints should not exceed a 5°C rise above the busbar itself .

Mechanical and Installation Requirements

Enclosure and Supports: Indoor busbars should use NEMA 12 enclosures, while outdoor installations require NEMA 4X enclosures with sloped tops to prevent water accumulation. Supports must be flame-retardant, track-resistant, and capable of handling thermal expansion and short-circuit forces . Expansion and Contraction: The design must accommodate thermal expansion and contraction to prevent mechanical stress and maintain electrical continuity. Flexible joints or expansion sections are recommended . Grounding: Proper bonding of the busbar enclosure to the system ground is essential to ensure low-impedance fault paths and personnel safety .

Protection Requirements

Bus Protection Schemes: High-voltage busbars require fast and secure protection to minimize equipment damage and maintain system stability. Common methods include overcurrent-based interlocking, differential protection, high-impedance differential, or percentage differential protection. The choice depends on fault current levels, speed requirements, and cost considerations . Coordination with Circuit Breakers: Busbar protection must coordinate with upstream and downstream breakers to isolate faults quickly while maintaining supply continuity to unaffected feeders .

Additional Considerations

• Phase Spacing and Clearance: Adequate spacing between phases and to ground is critical to prevent flashover and ensure insulation coordination .
• Tap-Off Points: Locations for connecting transformers, feeders, or switchgear must be planned to minimize voltage drop and allow maintenance access .
• Environmental Factors: Temperature, humidity, and exposure to dust or corrosive elements must be considered in material selection and enclosure design . By adhering to these requirements, a 35kV busbar system can operate safely, efficiently, and reliably under normal and fault conditions, ensuring long-term performance and protection of connected equipment.