For an A.C. generator circuit breaker, describe its arc control, explain short-circuit opening sequence and checks, and give a safe procedure if it fails to open under fault?

flowchart TD
    A[Overcurrent Relay] --> B[Trip Coil Energised]
    B --> C[Contacts Part]
    C --> D[Arc Drawn]
    D --> E[Arc Chute]
    E --> F[De-ionizing Grids]
    F --> G[Current Zero]
    G --> H[Breaker Open]

• Breaker type: Circuit breaker between A.C. generator and switchboard
• Arc control: Arc drawn upward into chute with de-ionizing grids and magnetic blowout
• Short-circuit sequence: Overcurrent relay → trip coil → contacts part → arc controlled → current zero → breaker opens
• Checks after trip: Contact condition, arc chute damage, insulation resistance, trip settings, relay calibration
• Failed-to-open procedure: Stop prime mover, isolate upstream, prove dead, lock off, investigate, clear fault, test before reset
• ETO scope: Maintenance, testing, safe isolation per STCW A-III/6
• Regulatory: Rec. 182 §3.6.1 (trips and alarms), UR E17 §4 (short-circuit current sufficiency), UK Code of Safe Working Practices §20.7.1 and §20.12.3 (isolation and notices)