Marine Electrical, Electronic and Control Engineering
This domain examines the ship's power system, protection philosophy, automation and instrumentation - the knowledge needed to operate, isolate and troubleshoot without creating a second fault.
Distribution
Typically 440 V three-phase for power, 220 V for lighting and small consumers, and 24 V DC for control and alarms. Insulation resistance is monitored by an earth-fault relay that alarms but does not trip: a single earth fault must be traced and cleared before a second one produces a short circuit.
Generators and protection
Synchronous generators with an AVR control voltage and reactive load; governor speed droop (usually 3-5%) shares active load between parallel sets. Protection includes overload, reverse power, under/over voltage, over/under frequency, and preferential tripping of non-essential loads before the main breaker opens.
Control and automation
PID loops on temperature, pressure and level; the alarm and monitoring system supporting UMS operation; fail-safe versus fail-to-danger design; the telegraph and bridge control interface.
Worked example
A 440 V three-phase load draws 100 A at 0.8 power factor. Apparent power S = 1.732 x 440 x 100 = 76.2 kVA. Active power P = 76.2 x 0.8 = 61 kW. The reasoning: kW = 1.732 x line voltage x line current x power factor, the 1.732 coming from the balanced three-phase relationship.
Traps
Treating an earth fault as a trip; confusing kVA with kW; assuming the generator with the smaller droop takes less load - it takes more; adjusting the AVR to change frequency, which is the governor's job.