EGSA Prime Mover and Governors 4 — Questions and Answers
Question 1: A natural gas engine prime mover uses which type of ignition system, unlike a diesel engine?
- Compression ignition
- Glow plug ignition
- Spark ignition (Correct answer)
- Catalytic ignition
Correct answer: Spark ignition
Natural gas engines use spark ignition because natural gas has a higher octane rating and will not self-ignite under diesel compression ratios.
Question 2: What is 'transient frequency dip' in generator performance and what primarily determines its magnitude?
- A steady-state frequency offset; determined by governor droop
- A momentary frequency drop upon sudden load application; determined by engine/governor response time and rotating inertia (Correct answer)
- An AC frequency shift caused by AVR hunting; determined by excitation levels
- A harmonic distortion spike; determined by load power factor
Correct answer: A momentary frequency drop upon sudden load application; determined by engine/governor response time and rotating inertia
Transient frequency dip is the momentary drop in frequency when a large block load is suddenly applied, and its depth depends on how quickly the governor and engine respond plus the system's rotational inertia (H constant).
Question 3: In a diesel prime mover governor system, what is the purpose of the 'speed bias' input signal often provided from a paralleling panel?
- To synchronize the alternator field current
- To remotely trim engine speed setpoint for load sharing or synchronization (Correct answer)
- To provide overspeed protection backup
- To initiate fuel shutoff during shutdown
Correct answer: To remotely trim engine speed setpoint for load sharing or synchronization
The speed bias signal allows a paralleling control panel to raise or lower the governor speed setpoint remotely, enabling automatic load sharing and synchronization.
Question 4: What is the typical overspeed shutdown setpoint for a diesel generator set as a percentage of rated speed?
- 105%
- 110% (Correct answer)
- 115%
- 120%
Correct answer: 110%
Most diesel generator sets are configured to shut down on overspeed at approximately 110% of rated speed to protect mechanical components.
Question 5: Which governor type provides the best frequency regulation for critical loads such as hospital or data center applications?
- Mechanical centrifugal governor with 5% droop
- Pneumatic governor
- Electronic isochronous governor (Correct answer)
- Hydraulic governor with fixed droop
Correct answer: Electronic isochronous governor
Electronic isochronous governors maintain virtually constant frequency under varying loads, making them ideal for critical applications sensitive to frequency variation.
Question 6: A Woodward governor is an example of which governor category?
- Purely mechanical centrifugal governor
- Hydro-mechanical or electronic governor widely used in industrial generator sets (Correct answer)
- Simple on/off relay-based speed controller
- A generator excitation regulator only
Correct answer: Hydro-mechanical or electronic governor widely used in industrial generator sets
Woodward governors are hydro-mechanical or electronic governors that are the industry standard for precision speed control in industrial generator sets.
Question 7: During a load rejection event (sudden loss of connected load), what immediate action does the governor take?
- Increases fuel delivery to maintain frequency
- Reduces fuel delivery to prevent engine overspeed (Correct answer)
- Opens the main circuit breaker to isolate the generator
- Increases field excitation to absorb excess energy
Correct answer: Reduces fuel delivery to prevent engine overspeed
When load is suddenly lost, the engine would overspeed without intervention, so the governor immediately reduces fuel delivery to bring speed back to rated.
EGSA Prime Mover and Governors 4
A natural gas engine prime mover uses which type of ignition system, unlike a diesel engine?