EGSA Load Bank Testing 4 — Questions and Answers
Question 1: What effect does high ambient temperature have on a diesel generator's output during a load bank test?
- It increases the generator's kW capacity
- It reduces the generator's output capacity due to derating (Correct answer)
- It has no measurable effect on output
- It improves combustion efficiency
Correct answer: It reduces the generator's output capacity due to derating
High ambient temperatures reduce air density, causing the engine to derate (produce less power) due to reduced oxygen intake.
Question 2: Which type of load bank is required to test a generator's response to a load with a 0.8 lagging power factor?
- Resistive only
- Capacitive only
- Resistive/reactive (inductive) combination (Correct answer)
- DC load bank
Correct answer: Resistive/reactive (inductive) combination
A combined resistive/reactive load bank is needed to produce a lagging power factor load that simulates real inductive equipment.
Question 3: During load bank testing, oil pressure falls below the low-oil-pressure shutdown setpoint. The correct response is to:
- Reduce the load bank to 50% and continue monitoring
- Allow the engine to shut itself down automatically (Correct answer)
- Increase fuel flow to compensate
- Bypass the oil pressure sender and continue the test
Correct answer: Allow the engine to shut itself down automatically
Low oil pressure is a critical fault; the engine's automatic shutdown protects it from catastrophic bearing and internal damage.
Question 4: What does the term 'transient response' refer to in generator load bank testing?
- The time it takes the generator to start from cold
- The generator's voltage and frequency behavior during sudden load changes (Correct answer)
- The delay before the transfer switch closes
- The total test duration from start to finish
Correct answer: The generator's voltage and frequency behavior during sudden load changes
Transient response describes how quickly and accurately the generator recovers voltage and frequency after a sudden load step change.
Question 5: Per NFPA 110, what is the required full-load test duration for a Level 1 emergency generator under load?
- 30 minutes
- 1 hour
- 2 hours (Correct answer)
- 4 hours
Correct answer: 2 hours
NFPA 110 requires Level 1 emergency generators to be exercised under load for a minimum of 2 hours at least monthly.
Question 6: A generator produces 480V at no load but 455V at full load. The voltage regulation percentage is approximately:
- 5.2% (Correct answer)
- 6.5%
- 10.0%
- 2.5%
Correct answer: 5.2%
Voltage regulation = (480-455)/480 × 100 = 5.2%, which falls within acceptable limits for most standby generators.
Question 7: Which condition would cause a generator to fail a load bank acceptance test even if it runs at full load without shutting down?
- Coolant temperature at 180°F
- Voltage regulation exceeding manufacturer's specification (Correct answer)
- Fuel consumption within 5% of rated value
- Oil pressure within normal operating range
Correct answer: Voltage regulation exceeding manufacturer's specification
Voltage regulation outside manufacturer specifications indicates AVR or alternator problems that make the unit unacceptable for service.
EGSA Load Bank Testing 4
What effect does high ambient temperature have on a diesel generator's output during a load bank test?