Connection method of small busbar in high voltage switchgear

Small busbars in high-voltage switchgear are connected to the main bus system using insulated or bare conductors, with careful attention to current rating, mechanical support, and electrical clearances.

Purpose and Role

Small busbars in high-voltage switchgear serve as branch connections between the main bus and individual circuit breakers or outgoing feeders. They act as distribution points, ensuring that power is delivered safely and efficiently to each connected circuit while maintaining system stability and minimizing voltage drops .

Connection Principles

1. Material Selection: Small busbars are typically made of copper or aluminum. Copper is preferred for high-reliability applications due to its superior conductivity and mechanical strength, while aluminum may be used where cost or weight is a concern .
2. Insulation and Safety: Depending on the design, small busbars can be bare or insulated. Insulated busbars allow for closer spacing and reduce the risk of short circuits, which is critical in high-voltage switchgear .
3. Mechanical Support: Proper bracing and support insulators are essential to withstand electromechanical forces during short-circuit events. These forces can be significant, and inadequate support may lead to displacement or damage .
4. Thermal Considerations: The busbar must handle the full-load current without exceeding permissible temperature rise limits. Adequate spacing, ventilation, and plating (e.g., tin or silver) improve heat dissipation and prevent overheating .
5. Short-Circuit Withstand: Connections must be designed to endure high fault currents for short durations. This includes ensuring that the busbar cross-section and connection hardware can withstand both thermal and electrodynamic stresses .

Connection Methods

• Direct Bolted Connections: Small busbars are often bolted to the main bus or to breaker terminals using copper or aluminum connectors. This provides a low-resistance, mechanically stable connection .
• Flexible Braided Connectors: In areas subject to vibration or movement, flexible copper braids may be used to connect small busbars to the main bus, allowing for slight movement without stressing the busbar .
• Parallel Busbars: For high-current branches, multiple small busbars may be connected in parallel to increase current capacity and reduce heating .

Layout and Spacing

• Maintain adequate creepage and clearance distances between live conductors and to earth to prevent arcing or insulation failure .
• Ensure that the small busbar layout allows for easy maintenance and future expansion, often guided by the switchgear's single-line diagram .

Summary

The connection of small busbars in high-voltage switchgear requires careful consideration of electrical, thermal, and mechanical factors. Proper material selection, insulation, support, and connection methods ensure safe, reliable operation while allowing flexibility for maintenance and system expansion .