Small busbar of 10kV switchgear

Small busbars in a 10kV switchgear are secondary or auxiliary conductors that distribute power from the main busbars to individual circuit breakers or functional units.

Function of Small Busbars

In medium-voltage switchgear, the main busbars carry the full system current, while small busbars (sometimes called sub-busbars or feeder busbars) branch off from the main bus to supply individual breakers, relays, or auxiliary circuits. They act as intermediate conductors, ensuring that power is distributed efficiently and safely to each section of the switchgear without overloading the main busbar system .

Design Considerations

Small busbars are typically made of copper or aluminum, like main busbars, but are smaller in cross-section because they carry lower currents than the main bus . Their design must account for:

• Current-carrying capacity: Sized to handle the rated current of the connected breaker or feeder without excessive heating .
• Short-circuit withstand: Must tolerate short-duration fault currents without mechanical deformation or insulation failure .
• Insulation and spacing: Proper clearance and insulation prevent flashovers and ensure safety within the switchgear compartment .
• Mechanical support: Often mounted on finger-type insulators or brackets to resist electrodynamic forces during faults .

Types and Shapes

Small busbars can be flat, laminated, or tubular, depending on space constraints, cooling requirements, and mechanical strength needs. Flat busbars are common because they dissipate heat efficiently and are easy to connect to breakers, while laminated busbars reduce eddy currents and skin effect losses in AC systems .

Summary

In essence, small busbars inside a 10kV switchgear serve as the distribution network from the main busbars to individual functional units, ensuring reliable power delivery, thermal stability, and mechanical safety. Their size, material, and configuration are carefully engineered to match the current requirements and operational conditions of the switchgear .