EGSA Electrical Systems Troubleshooting 2 — Questions and Answers
Question 1: A generator shows high AC voltage output but the frequency is correct. What is the most likely cause?
- Faulty AVR (Correct answer)
- Incorrect governor setting
- Open phase winding
- Worn brushes
Correct answer: Faulty AVR
The Automatic Voltage Regulator (AVR) controls output voltage; a faulty AVR can cause voltage to rise above set point while frequency remains governed correctly.
Question 2: When troubleshooting a generator that trips on overcurrent, which test should be performed first?
- Megohmmeter test on windings (Correct answer)
- Fuel system pressure check
- Governor actuator test
- Battery load test
Correct answer: Megohmmeter test on windings
A megohmmeter test identifies insulation breakdown in windings, which is a common cause of sustained overcurrent trips.
Question 3: A transfer switch fails to transfer to the emergency source after generator start. The most likely cause is:
- Faulty sensing relay in the transfer switch (Correct answer)
- Low coolant level
- Incorrect fuel octane rating
- Loose alternator belt
Correct answer: Faulty sensing relay in the transfer switch
The transfer switch sensing relay monitors utility voltage loss and initiates the transfer; a faulty relay prevents the switching sequence from completing.
Question 4: What does a high resistance measurement across a closed circuit breaker indicate?
- Damaged or pitted contacts (Correct answer)
- Correct contact seating
- Overloaded circuit
- Correct torque on connections
Correct answer: Damaged or pitted contacts
High resistance across a closed breaker indicates damaged, burned, or pitted contacts that increase contact resistance and cause voltage drop.
Question 5: A three-phase generator produces balanced voltage but one phase has no load current. What is the most likely fault?
- Open circuit on the load side of that phase (Correct answer)
- Faulty AVR potentiometer
- Unbalanced rotor field
- High ambient temperature
Correct answer: Open circuit on the load side of that phase
Balanced voltage with zero current on one phase points to an open circuit on the load distribution side for that phase, not within the generator itself.
Question 6: Which instrument is used to measure insulation resistance in generator windings?
- Megohmmeter (Correct answer)
- Clamp-on ammeter
- Power factor meter
- Frequency counter
Correct answer: Megohmmeter
A megohmmeter applies high DC voltage to measure insulation resistance, identifying degradation before it causes catastrophic failure.
Question 7: A diesel generator hunts (surges) at no-load but stabilizes under load. The most likely cause is:
- Worn or sticking governor linkage (Correct answer)
- Faulty AVR
- Low fuel level
- Incorrect oil viscosity
Correct answer: Worn or sticking governor linkage
Governor hunting at no-load with stabilization under load typically indicates a mechanical issue such as worn or sticking governor linkage affecting fuel control sensitivity.
EGSA Electrical Systems Troubleshooting 2
A generator shows high AC voltage output but the frequency is correct.
What is the most likely cause?