EGSA Prime Mover and Governors 5 — Questions and Answers
Question 1: What is the effect of increasing the integral gain (I-term) in a PID electronic governor?
- It makes the governor ignore small sustained speed errors
- It eliminates steady-state speed error more aggressively but can cause instability if too high (Correct answer)
- It reduces the speed of governor response to sudden load changes
- It increases the droop percentage
Correct answer: It eliminates steady-state speed error more aggressively but can cause instability if too high
Higher integral gain causes the governor to eliminate sustained speed errors more quickly but excessive integral gain can cause oscillation and instability.
Question 2: Which factor most influences the 'acceleration time' of a diesel prime mover when picking up a block load?
- Alternator winding resistance
- Engine displacement and turbocharger lag time (Correct answer)
- Governor droop percentage setting
- Battery charger output current
Correct answer: Engine displacement and turbocharger lag time
Engine displacement determines available torque reserve, and turbocharger lag (turbo lag) delays full boost pressure, both critically affecting how quickly the engine accelerates to meet sudden load demand.
Question 3: What is 'speed regulation' (also called 'steady-state frequency regulation') of a governor?
- The maximum speed the governor allows the engine to reach
- The difference between no-load and full-load speed expressed as a percentage of rated speed (Correct answer)
- The time required for the governor to restore rated speed after a transient
- The voltage change per unit load change
Correct answer: The difference between no-load and full-load speed expressed as a percentage of rated speed
Speed regulation is calculated as (no-load speed − full-load speed) / rated speed × 100%, and it is numerically equal to the droop percentage for droop governors.
Question 4: On a generator set with a mechanical governor, what must be done to synchronize it with the bus before paralleling?
- Adjust the AVR voltage setpoint only
- Manually adjust the governor speed control to match the bus frequency before closing the breaker (Correct answer)
- Connect the generators and let them automatically synchronize
- Reduce the load on the existing generator first
Correct answer: Manually adjust the governor speed control to match the bus frequency before closing the breaker
Before paralleling, the incoming generator's governor speed control must be adjusted so its frequency closely matches the bus frequency to enable synchronization.
Question 5: What is the primary purpose of a 'load sensor' or 'load sharing line' connection between paralleled generator governor controls?
- To equalize reactive power (kVAR) between generators
- To allow each governor to sense total system load and proportionally share real power (kW) (Correct answer)
- To provide backup frequency sensing if the MPU fails
- To transfer AVR reference signals between units
Correct answer: To allow each governor to sense total system load and proportionally share real power (kW)
The load sharing line allows isochronous governors to communicate current load levels so each unit proportionally shares real kW load without needing droop.
Question 6: Which prime mover characteristic is described by the 'heat rate' (BTU/kWh)?
- The cooling system capacity required per kilowatt of output
- The thermal efficiency of the prime mover — how much fuel energy is converted to electrical energy (Correct answer)
- The rate of heat rejected to the atmosphere through the exhaust
- The amount of heat generated by the alternator windings per hour
Correct answer: The thermal efficiency of the prime mover — how much fuel energy is converted to electrical energy
Heat rate (BTU/kWh) measures how much fuel energy (in BTUs) is required to produce one kilowatt-hour of electrical output; a lower heat rate indicates higher efficiency.
Question 7: A governor's 'stability' adjustment (derivative or dashpot setting) is used to:
- Set the maximum permissible speed setpoint
- Dampen governor response to prevent hunting and overshoot after load changes (Correct answer)
- Increase the speed of initial response to load transients
- Calibrate the magnetic pickup air gap
Correct answer: Dampen governor response to prevent hunting and overshoot after load changes
The stability (derivative) adjustment adds damping to the governor response, preventing it from overcorrecting and oscillating (hunting) after a load disturbance.
EGSA Prime Mover and Governors 5
What is the effect of increasing the integral gain (I-term) in a PID electronic governor?