Effect of voltage at the small busbar of the high-voltage switchgear

The voltage of a small busbar in high-voltage switchgear typically corresponds to the system voltage of the switchgear, commonly ranging from 11 kV to 36 kV in medium to high-voltage installations.

Overview

In high-voltage switchgear, a busbar is a metallic conductor used to distribute electrical power to multiple circuits in parallel, housed inside switchgear panels or substations . The term "small busbar" usually refers to a busbar with lower current-carrying capacity or a bypass/auxiliary bus used for sectionalizing or maintenance purposes . Despite its smaller size, the voltage rating of the busbar matches the system voltage to ensure proper insulation and safe operation.

Typical Voltage Levels

• High-voltage switchgear: Busbars are designed for system voltages typically between 11 kV and 36 kV, though some installations may go up to 72.5 kV or higher depending on the substation design .
• Medium-voltage switchgear: Busbars often operate at 3.3 kV, 6.6 kV, or 11 kV.
• The "small" designation usually refers to current capacity, not voltage; the busbar may carry less current but must withstand the same system voltage.

Design Considerations

• Insulation and clearance: Even small busbars must maintain adequate creepage and clearance distances to prevent arcing at the rated voltage .
• Current rating: Smaller busbars are sized for lower currents, often used in bypass or auxiliary circuits, but the voltage withstand requirement remains the same as the main busbar .
• Operational flexibility: Small busbars are often part of double bus or bypass bus configurations, allowing maintenance without interrupting supply .

Summary

The small busbar in high-voltage switchgear carries the same voltage as the main system, typically in the range of 11–36 kV for standard high-voltage installations. Its "small" designation refers to current capacity or physical size, not voltage. Proper insulation, spacing, and design ensure safe operation at the system voltage while providing operational flexibility for maintenance and sectionalizing .