Marine Electrical, Automation and Control Systems
Core concepts
Understand three-phase AC generation, voltage and frequency control, paralleling and load sharing, protection (overcurrent, reverse power, earth fault), and distribution including essential and emergency switchboards. Know automation layers: sensors, transmitters, controllers (P, PI, PID), actuators, and alarm and monitoring systems. Familiarity with programmable logic controllers, remote control of pumps and valves, and auto-start of emergency generator is expected.
Traps in questions
- Confusing reverse power protection (generator motoring) with overcurrent protection.
- Assuming an earth fault on an insulated system trips the breaker; it usually only alarms.
- Mixing up PID terms: proportional responds to present error, integral to accumulated error, derivative to rate of change.
- Forgetting the emergency generator must start and take load automatically within a specified time.
Rule of thumb and worked example
For a three-phase load, P = √3 × V × I × power factor. A 440 V generator delivering 600 A at 0.8 pf gives P = 1.732 × 440 × 600 × 0.8 = 365,800 W ≈ 366 kW, so a 400 kW machine is near full load. For paralleled generators, kW load sharing is set by governor speed droop while reactive (kVAr) sharing is set by excitation. This is a common exam distinction.
Study focus
Revise insulation resistance testing, battery maintenance, safe isolation and lockout, and the meaning of IP ratings. Know alarm priorities and the difference between alarm, trip and shutdown. Understand fail-safe design and the purpose of dead-band and alarm delay.