Shipboard Electrical, Electronic and Control Systems: Generation, Distribution, Protection and Automation
This domain tests the ship service electrical plant and its control layer: alternators and excitation, parallel operation and load sharing, protection and discrimination, insulation and earthing, plus automation, alarms and shutdowns. Expect questions that ask what a symptom means or what the correct operating action is.
Core rules
- kW load sharing is set by the engine governor speed setting; kVAr sharing is set by excitation. Adjusting voltage never shifts kW.
- To take load on a generator, raise its speed setting slightly so it accepts more kW, then trim others back; frequency returns to normal as a group.
- Synchronising requires matched voltage, frequency and phase sequence, with the incoming machine slightly fast and the synchroscope rotating slowly in the fast direction.
- Protection typically includes overcurrent, earth fault, reverse-power trip, preferential tripping of non-essential loads, and generator over/under-voltage and frequency trips.
- Insulation resistance is measured with a DC insulation tester at the correct voltage, with the circuit isolated and earthed first; readings are temperature corrected.
- Automation uses 4-20 mA transmitters, setpoints and PID loops; safety systems (low lube-oil pressure, overspeed, high jacket-water temperature) act independently of the alarm system.
Worked example
A 1000 kVA, 440 V, three-phase generator at 0.8 power factor. Rated current = 1000000 / (1.732 x 440) = 1312 A. Rated kW = 1000 x 0.8 = 800 kW. If the machine is carrying 600 kW, it is at 75 percent of rating, so a further 200 kW can be added before another machine must be paralleled.
Traps
Closing the breaker with frequency or phase mismatch, which produces a damaging current surge; using the AVR to correct kW balance; and treating an alarm as a trip when the safety system is separate.