EGSA System Troubleshooting and Maintenance 3 — Questions and Answers
Question 1: When troubleshooting a paralleling failure between two generators, which parameter mismatch will most commonly cause a large circulating current between units?
- Mismatched oil pressure readings
- Voltage or frequency difference between the two sources (Correct answer)
- Unequal coolant temperatures
- Different battery charger voltages
Correct answer: Voltage or frequency difference between the two sources
Voltage or frequency mismatch between two paralleled generators creates a potential difference that drives circulating currents through the windings.
Question 2: A governor hunting symptom (oscillating engine speed) on a mechanical governor system is most commonly caused by:
- Worn injector tips
- Improper governor speed droop adjustment or linkage wear (Correct answer)
- Low battery voltage
- Clogged fuel return line
Correct answer: Improper governor speed droop adjustment or linkage wear
Improper droop adjustment or worn governor linkage causes the system to over-correct repeatedly, producing speed oscillation.
Question 3: Which maintenance interval task specifically addresses the degradation of diesel fuel quality in long-term storage applications?
- Replacing air filters every 500 hours
- Fuel polishing and microbial contamination testing (Correct answer)
- Adjusting valve clearances annually
- Torquing cylinder head bolts
Correct answer: Fuel polishing and microbial contamination testing
Fuel polishing removes water, sediment, and microbial growth that degrade stored diesel fuel quality over time.
Question 4: A generator starts and runs normally but produces output voltage 15% below the nominal setting. After confirming AVR input power is present, what is the most likely fault?
- Stuck open exhaust valve
- Failed or misadjusted voltage sensing resistor in the AVR trim circuit (Correct answer)
- Clogged fuel injector on cylinder 3
- Excessive crankcase pressure
Correct answer: Failed or misadjusted voltage sensing resistor in the AVR trim circuit
A failed or incorrectly trimmed voltage sensing circuit prevents the AVR from raising excitation to the correct level.
Question 5: During a transfer switch maintenance inspection, what test verifies that the switch will correctly detect a utility outage and command generator start?
- Insulation resistance test of switch contacts
- Simulated utility voltage dropout test with ATS in auto mode (Correct answer)
- Load bank connection test
- Battery capacity discharge test
Correct answer: Simulated utility voltage dropout test with ATS in auto mode
A simulated utility dropout test confirms the ATS sensing circuit and time delays operate correctly before commanding generator start.
Question 6: What does a high crankcase pressure reading (blowby) during engine diagnostics indicate?
- Coolant thermostat failure
- Worn piston rings or cylinder liner damage allowing combustion gases to bypass (Correct answer)
- Low fuel pressure
- Defective oil pressure relief valve
Correct answer: Worn piston rings or cylinder liner damage allowing combustion gases to bypass
Excessive blowby indicates combustion gases are bypassing worn piston rings or damaged cylinder liners into the crankcase.
Question 7: When replacing a generator set's air cleaner element, which condition in the old element would indicate an air restriction problem likely contributed to black exhaust smoke?
- Element is slightly dusty on the outside
- Element is heavily clogged, restricting airflow below manufacturer specifications (Correct answer)
- Element has minor surface cracks
- Element is within the recommended service interval
Correct answer: Element is heavily clogged, restricting airflow below manufacturer specifications
A heavily clogged air cleaner restricts the combustion air supply, causing a rich fuel-to-air mixture that produces black smoke.
EGSA System Troubleshooting and Maintenance 3
When troubleshooting a paralleling failure between two generators, which parameter mismatch will most commonly cause a large circulating current between units?