EGSA Power Generation Equipment 2 — Questions and Answers
Question 1: What is the primary function of an automatic voltage regulator (AVR) in a generator set?
- Regulate engine speed
- Maintain constant output voltage under varying loads (Correct answer)
- Control fuel injection timing
- Monitor coolant temperature
Correct answer: Maintain constant output voltage under varying loads
An AVR senses output voltage and adjusts excitation current to keep generator terminal voltage stable as load changes.
Question 2: In a diesel generator, what does the term 'wet stacking' describe?
- Water contamination in the fuel tank
- Unburned fuel and oil accumulating in the exhaust system (Correct answer)
- Coolant leaking into the exhaust manifold
- Condensation inside the air intake
Correct answer: Unburned fuel and oil accumulating in the exhaust system
Wet stacking occurs when a diesel engine runs at light load for extended periods, causing unburned fuel and carbon deposits to accumulate in the exhaust stack.
Question 3: Which generator winding configuration provides both 120V and 240V single-phase output from the same alternator?
- Delta winding
- Wye (star) winding
- Center-tapped single-phase winding (Correct answer)
- Scott-T transformer configuration
Correct answer: Center-tapped single-phase winding
A center-tapped single-phase winding allows both 120V (line-to-neutral) and 240V (line-to-line) to be derived from the same winding.
Question 4: What is the purpose of a droop governor setting on a generator operating in parallel?
- Prevent the engine from overspeeding
- Allow proportional load sharing between paralleled generators (Correct answer)
- Regulate fuel consumption at full load
- Set the minimum no-load speed
Correct answer: Allow proportional load sharing between paralleled generators
Droop governor settings cause engine speed to decrease slightly as load increases, enabling stable proportional load sharing when multiple generators run in parallel.
Question 5: What is the typical standby power rating for a generator set?
- Continuous 24/7 base load capacity
- Prime power rating minus 10%
- Maximum power available for up to 200 hours per year with varying load (Correct answer)
- Rated power at 0.8 power factor for utility backup only
Correct answer: Maximum power available for up to 200 hours per year with varying load
Standby rating represents maximum power for emergency use, typically not exceeding 200 hours per year at varying load with no average load factor limit.
Question 6: In a brushless generator, the exciter stator receives DC from the AVR to produce AC in which component?
- Main stator field winding
- Exciter rotor winding (Correct answer)
- Permanent magnet generator (PMG)
- Main rotor field winding
Correct answer: Exciter rotor winding
The AVR supplies DC to the exciter stator, inducing AC current in the rotating exciter rotor, which is then rectified and fed to the main rotor field.
Question 7: What NFPA standard governs the installation of emergency and standby power systems?
- NFPA 70
- NFPA 99
- NFPA 110 (Correct answer)
- NFPA 101
Correct answer: NFPA 110
NFPA 110 is the Standard for Emergency and Standby Power Systems, covering installation, testing, and maintenance requirements.
EGSA Power Generation Equipment 2
What is the primary function of an automatic voltage regulator (AVR) in a generator set?