Marine Electrical, Control and Automation Systems
What this domain tests
Power generation and distribution, protection and selectivity, the emergency source, automation and alarm philosophy, and cyber resilience. Expect both a calculation and a question about redundancy.
Power system basics
IEC 60092 governs marine electrical installations. Typical generation is 450 V, 60 Hz, three-phase, with 230 V distribution and 24 V DC for control and emergency lighting. Many ships run an insulated neutral system with earth-fault detection, so a single earth fault does not trip the circuit but must be found and cleared.
- Protection must be selective: the breaker nearest the fault clears it without tripping upstream devices.
- Cable sizing considers current-carrying capacity, voltage drop and short-circuit withstand.
- Harmonic distortion from variable-frequency drives is limited by filter design and checked at the main busbar.
Emergency power
SOLAS II-1 requires an emergency source, usually a generator, that starts automatically and is connected to the emergency switchboard within 45 seconds. The emergency switchboard supplies steering, emergency lighting, navigation lights, radio, fire detection and other essential services for the required duration, and is separated from the main switchboard by fire-resistant boundaries.
Automation and cyber
Integrated automation systems monitor and alarm; periodically unattended machinery spaces require specific alarms, safety systems and fire detection. Control systems should fail safe. Cyber resilience is addressed by IMO guidance and by IACS UR E26 and E27 for newbuildings contracted on or after 1 July 2024.
Worked example
A ship has a service load of 1,200 kW at 450 V and power factor 0.8. Current = 1,200,000 / (1.732 x 450 x 0.8) = 1,925 A. Two 1,000 kVA generators at 0.8 pf give 800 kW each, so the load is 75% of each machine, which is acceptable. If one generator fails, the remaining 800 kW cannot carry 1,200 kW, so the automation must start a standby set or shed non-essential load before the breaker trips.
Traps
Assuming the 45-second start requirement is optional; forgetting that selectivity is a coordination study, not a rating check; neglecting the earth-fault detection on an insulated system; treating automation as a substitute for a hard-wired safety trip; ignoring cyber requirements on newbuildings.