Shipboard Electrical, Electronic and Control Engineering
Core concepts
Expect questions spanning generation, distribution and automation. Understand three-phase generation: excitation, automatic voltage regulator, droop and isochronous load sharing, and parallel operation including synchronising checks (voltage, frequency, phase angle, phase sequence). Know protection: overcurrent, earth fault, reverse power, preferential tripping and the purpose of the emergency generator and emergency switchboard. Insulation resistance testing and the megohmmeter, class rules on minimum values, and the significance of an IT (unearthed) distribution system are standard. Automation content includes programmable logic controllers, sensors and transmitters (4-20 mA loops), PID control tuning concepts, alarm and trip settings, and the difference between fail-safe and fail-to-danger design. Unattended machinery space notation requires understanding of the safety systems that justify it.
Traps
A common error is confusing reverse power protection (prevents a generator motoring) with reverse current in a parallel DC system. Another is treating an earth fault on an unearthed system as an immediate trip; the first fault usually alarms only, and a second fault on another phase creates a short circuit. Do not assume a higher PID proportional band gives faster response; it gives a smaller proportional action. Questions on synchronising often test phase-angle versus frequency mismatch consequences.
Worked rule of thumb
For insulation resistance, a rough minimum for a 440 V machine is 1 megohm at 500 V DC test, but always cite the class rule or manufacturer figure. When paralleling, adjust incoming frequency slightly above busbar frequency so the synchroscope rotates slowly clockwise, then close at the twelve o'clock position.