The operating mechanism is the electromechanical system that opens and closes circuit breakers or switches in switchgear. So it plays an vital role in switchgear. It can opens contacts in 15–100 milliseconds to interrupt faults, ensures operation after years of inactivity (vital for protection), prevents re-closing on persistent faults, and allows immediate opening even during closing command.
It also provides the kinetic energy required to: close contacts against spring pressure & electromagnetic forces, and trip (open) contacts rapidly during faults or manual operation.
Some Key Components inside operating mechaniam:
- Springs (Most Common): Pre-charged (stored energy) for fast operation.
- Solenoids: Electromagnetic coils for direct tripping/closing.
- Pneumatic/Hydraulic: Pressurized gas/fluid (common in HV systems).
- Manual Handles: For small LV breakers or backup.
- Trip Unit Interface: Receives signals from protective relays (e.g., overcurrent, differential) or manual controls.
- Linkage System: Transfers energy to moving contacts via rods, levers, or gears.
- Latching/Unlatching Assembly: Holds contacts closed until a trip signal releases stored energy.
Here are some types being classified by applications:
- Spring-Operated operating mechanism, mostly used in Most MV/LV breakers (VCB, ACB, MCCB).
- Solenoid-Operated operating mechanism, used in older LV breakers, some trip coils.
- Pneumatic operating mechanism, used in HV breakers, GIS.
- Hydraulic operating mechanism, used in EHV systems (345kV+).
The normal state is current flows normally when contacts are closed. When fault occurs, the trip unit senses the abnormal condition. The mechanism releases the stored energy, when triggering.The contacts open, breaking the circuit. Internal arc-quenching system extinguishes the electric arc. After resolving the fault, the mechanism is manually or automatically reset to resume operation.
Why it matters, a failed mechanism can cause catastrophic arc flashes or system blackouts, which will cause major safety accidents, threatening life safety and property losses.
