EGSA Prime Mover and Governors 3 — Questions and Answers
Question 1: When two diesel generators are operated in parallel with droop governors, how is real load (kW) shared between them?
- Equally regardless of governor settings
- Proportional to each unit's kVAR rating
- Determined by the relative droop characteristics and speed settings of each governor (Correct answer)
- Controlled entirely by the AVR
Correct answer: Determined by the relative droop characteristics and speed settings of each governor
Real load sharing in parallel droop operation depends on each governor's droop percentage and speed setpoint; units with less droop will pick up more load.
Question 2: What is the typical steady-state frequency regulation band required for generator sets used in standby power applications per NFPA 110?
- ±0.5 Hz
- ±2 Hz (Correct answer)
- ±5 Hz
- ±10% of rated frequency
Correct answer: ±2 Hz
NFPA 110 requires standby generator sets to regulate frequency within ±2 Hz (±3.3% of 60 Hz) under steady-state conditions.
Question 3: Which prime mover type uses combustion gases to drive a turbine wheel directly rather than a piston?
- Reciprocating diesel engine
- Gas turbine engine (Correct answer)
- Spark-ignited natural gas engine
- Stirling cycle engine
Correct answer: Gas turbine engine
A gas turbine directs high-velocity combustion gases through turbine blades, converting thermal energy to shaft rotation without pistons.
Question 4: In a gas turbine generator, the governor controls speed primarily by adjusting which variable?
- Compressor inlet guide vane angle only
- Fuel flow rate to the combustion chamber (Correct answer)
- Turbine exhaust backpressure
- Generator field excitation current
Correct answer: Fuel flow rate to the combustion chamber
The gas turbine governor regulates speed by modulating fuel flow to the combustion chamber, controlling the energy input to the turbine.
Question 5: What governor parameter determines how quickly the governor corrects speed deviation after a load change?
- Droop percentage
- Speed bias
- Gain (proportional gain) (Correct answer)
- Offset voltage
Correct answer: Gain (proportional gain)
Governor gain (proportional gain) determines the magnitude of the corrective fuel response per unit of speed error; too high a gain causes instability.
Question 6: Which condition is most likely to cause a diesel engine prime mover to 'hunt' (oscillate in speed)?
- Governor gain set too low
- Governor gain set too high or stability adjustments incorrect (Correct answer)
- Excessive droop percentage
- Low engine oil temperature
Correct answer: Governor gain set too high or stability adjustments incorrect
Hunting occurs when governor gain is too high or stability (derivative) is improperly set, causing the governor to overcorrect and create oscillations.
Question 7: What is the role of the 'speed droop' trim control on an electronic governor?
- Sets the maximum RPM limit
- Adjusts the amount of speed decrease per unit of load increase (Correct answer)
- Controls the rate of fuel delivery during startup
- Modifies the excitation voltage of the alternator
Correct answer: Adjusts the amount of speed decrease per unit of load increase
The speed droop trim control adjusts what percentage the engine speed decreases as the generator load increases from no-load to full load.
EGSA Prime Mover and Governors 3
When two diesel generators are operated in parallel with droop governors, how is real load (kW) shared between them?