Electrical, Electronic and Control Engineering; Automation and Instrumentation
What this domain tests
This domain tests whether you can operate and troubleshoot generation, distribution, control loops and alarms as a engineer rather than an electrician: paralleling machines, keeping protection selective, reading instruments and proving safety systems.
Generation and distribution
- Ship's distribution is normally an insulated-neutral system: a single earth fault does not trip the supply, but the earth fault alarm must be investigated because a second fault produces a short circuit.
- Synchronising: bring the incoming machine slightly fast, watch the synchroscope, and close the breaker just before the twelve o'clock position while the pointer rotates slowly clockwise.
- Load sharing: kW follows the governor and load-sharing line, kVAr follows excitation. Adjust speed to move kW and excitation to move kVAr.
- Reverse power, preferential trip and load shedding protect the alternator and switchboard; prove the trips rather than assuming they will work.
Control and instrumentation
- A 4–20 mA loop carries the measurement, with 4 mA as the live zero, so a broken wire reads below 4 mA rather than at zero pressure.
- Resistance thermometers and thermocouples need the correct extension or compensating cable; a wrong thermocouple type reads plausibly wrong.
- In PID control the proportional term responds to error, integral removes steady offset and derivative anticipates; oscillation about the set point usually means excessive gain or a failing sensor.
- Alarm and shutdown set points are maker's values recorded in the set-point list; they are not changed to silence nuisance alarms without a documented management-of-change.
Worked example
A pressure transmitter is ranged 0–10 bar over 4–20 mA. At 6 bar the output is 4 + 16 × (6 ÷ 10) = 13.6 mA. If the reading shows 4.5 mA while the local gauge says 6 bar, the loop or transmitter is faulty, not the process. The reasoning matters: the current is the measurement, so compare it with the local gauge and check the loop before touching the control valve, the controller tuning or the set point.
Traps that cost marks
Closing the breaker on a fast-rotating synchroscope; adjusting kVAr with the speed governor; shorting out an earth fault to clear the alarm; changing shutdown set points to stop nuisance trips; assuming 0 mA means zero pressure; paralleling without checking the reverse power trip.
Key points
- Insulated-neutral system: one earth fault is tolerated, two are a short circuit