EGSA Power Generation Equipment 4 — Questions and Answers
Question 1: What causes harmonic distortion in a generator's output voltage waveform?
- Excessive cooling airflow through the alternator
- Non-linear loads such as variable frequency drives and switch-mode power supplies (Correct answer)
- Under-excitation of the rotor field winding
- Misalignment between engine and alternator coupling
Correct answer: Non-linear loads such as variable frequency drives and switch-mode power supplies
Non-linear loads draw current in pulses rather than sinusoidally, injecting harmonic currents that distort the generator's output voltage waveform.
Question 2: When two generators are being synchronized for parallel operation, which parameter must be matched last to avoid circulating currents?
- Frequency
- Voltage magnitude
- Phase sequence
- Phase angle (Correct answer)
Correct answer: Phase angle
Phase angle is matched last (at closing) using a synchroscope or sync check relay to ensure the breaker closes at the exact moment the phase angles align.
Question 3: What is the purpose of the anti-condensation heater installed in a generator alternator?
- Maintain optimal combustion chamber temperature
- Prevent moisture condensation on alternator windings during shutdown periods (Correct answer)
- Warm the fuel in cold weather
- Pre-heat the engine coolant before starting
Correct answer: Prevent moisture condensation on alternator windings during shutdown periods
Anti-condensation heaters keep alternator windings slightly above ambient temperature during standby to prevent moisture from condensing and degrading insulation resistance.
Question 4: Which factor primarily determines the synchronous speed of an AC generator?
- Load current magnitude
- Number of magnetic poles and operating frequency (Correct answer)
- Rotor field winding resistance
- Coolant temperature
Correct answer: Number of magnetic poles and operating frequency
Synchronous speed (RPM) = (120 × frequency) / number of poles; a 4-pole generator must spin at 1800 RPM to produce 60 Hz output.
Question 5: What is the primary hazard of operating a generator with a single-phase load heavily unbalanced across phases?
- Increased fuel consumption with no electrical risk
- Overheating of the most heavily loaded phase winding and neutral conductor (Correct answer)
- Automatic derating of the kVA rating
- Increased parasitic drag on the engine
Correct answer: Overheating of the most heavily loaded phase winding and neutral conductor
Severe phase unbalance causes one phase winding and the neutral conductor to carry excess current, leading to overheating and potential insulation failure.
Question 6: In a diesel generator fuel system, what is the purpose of the day tank?
- Store emergency coolant near the engine
- Provide a local fuel supply close to the engine to ensure reliable fuel delivery and gravity feed (Correct answer)
- Filter fuel before it reaches the main tank
- Monitor fuel contamination levels
Correct answer: Provide a local fuel supply close to the engine to ensure reliable fuel delivery and gravity feed
The day tank is a small local reservoir that gravity-feeds fuel to the engine, providing reliable delivery independent of the main bulk storage tank pump.
Question 7: What type of circuit breaker trip unit is required to coordinate with generator subtransient fault currents?
- Thermal-magnetic trip unit with high instantaneous pickup
- Electronic trip unit with adjustable long-time, short-time, and instantaneous settings (Correct answer)
- Fuse with time-current characteristics only
- Shunt trip coil activated by an external relay
Correct answer: Electronic trip unit with adjustable long-time, short-time, and instantaneous settings
Electronic trip units with adjustable settings allow coordination with the generator's subtransient, transient, and synchronous fault current levels across multiple time bands.
EGSA Power Generation Equipment 4
What causes harmonic distortion in a generator's output voltage waveform?