Switchgear Panel

Overview

A switchgear panel controls, protects, and isolates a section of a medium-voltage power network. This metal-clad, draw-out cubicle is rated 12 kV, 1250 A, with a 25 kA short-circuit capacity, and forms one feeder of a substation lineup. "Metal-clad" means each functional part, breaker, busbars, cables, and instruments, sits in its own earthed metal compartment, so a fault in one is contained and the draw-out breaker can be withdrawn safely for maintenance.

Construction

The structure is the Cubicle Enclosure, a sheet-steel metal-clad enclosure partitioned into separate compartments with shutters that automatically cover live contacts when the breaker is withdrawn. Power passes horizontally along the Busbar System, insulated copper busbars and droppers that link this panel to the rest of the lineup.

The switching element is the Vacuum Circuit Breaker, a draw-out vacuum circuit breaker that interrupts current, including fault current, by separating contacts inside a vacuum bottle, where the arc extinguishes at the first current zero. The breaker truck racks in and out on rails for isolation and testing.

Measurement and protection rely on the Instrument Transformers: current transformers and voltage transformers that scale the high primary values down to safe signals. These feed the Numerical Protection Relay, a numerical relay that detects overcurrent, earth fault, and other conditions and trips the breaker within cycles.

Safety and conditioning hardware complete the panel. The Earthing Switch grounds the feeder before maintenance, the Surge Arrester set (one per phase) clamps lightning and switching overvoltages, and the Cable Termination terminates the incoming HV cable on each phase. Control wiring, metering, and the relay sit in the segregated LV Control Compartment compartment.