Electrical, Electronic, and Control Engineering
Core concepts
Understand three-phase generation: prime mover, alternator, excitation, voltage and frequency control, and the conditions for paralleling generators (same voltage, frequency, phase sequence, and phase angle). Know load sharing, kW vs. kVAR division, and the role of the governor (frequency/active load) versus the AVR (voltage/reactive load). Be comfortable with switchboard protection-overcurrent, reverse power, preferential trips, and earth-fault indication-and with automation: sensors, transmitters (4–20 mA), PID control, and alarm/control systems.
Traps to expect
A classic trap is mixing up what the governor controls (frequency and kW sharing) with what the AVR controls (voltage and kVAR sharing). Another is confusing reverse power (a generator being motored) with overload. Questions on 4–20 mA loops test whether you know the live-zero principle: 4 mA is the zero reading, so a broken wire (0 mA) is distinguishable from a true zero. Earth-fault questions test that a single earth on an insulated system is an alarm, not an immediate trip.
Worked example / rule of thumb
Before closing the breaker to parallel a generator, match voltage and frequency and check synchroscope/lamps for phase. Rule of thumb: governor = kW/frequency; AVR = kVAR/voltage. For instrumentation, remember 4 mA = minimum, 20 mA = maximum, 0 mA = fault.
Control and safety
Understand PID: proportional responds to error, integral removes offset, derivative anticipates. Know that safety interlocks and trips should fail safe, and that bypassing a protection requires authorization and documentation.