WTT Mechanical Systems & Drivetrain 2 — Questions and Answers
Question 1: What is the primary function of a wind turbine's pitch system in the drivetrain context?
- Adjust blade angle to control rotor speed and power output (Correct answer)
- Lubricate the main shaft bearings
- Connect the rotor to the gearbox input shaft
- Regulate generator cooling airflow
Correct answer: Adjust blade angle to control rotor speed and power output
The pitch system rotates each blade around its longitudinal axis to regulate aerodynamic forces, controlling rotor speed and power capture.
Question 2: Which type of coupling is most commonly used between the gearbox output shaft and the generator input shaft in a wind turbine?
- Rigid flange coupling
- Flexible disc coupling (Correct answer)
- Chain coupling
- Jaw coupling
Correct answer: Flexible disc coupling
Flexible disc couplings accommodate misalignment and dampen torsional vibrations between the gearbox and generator shafts.
Question 3: What does the term 'gear ratio' mean in a wind turbine gearbox?
- The ratio of lubricant volume to gear mass
- The ratio of output shaft speed to input shaft speed (Correct answer)
- The ratio of gearbox weight to torque capacity
- The ratio of gear teeth width to pitch diameter
Correct answer: The ratio of output shaft speed to input shaft speed
Gear ratio is the output shaft speed divided by input shaft speed, typically stepping up from ~15–25 RPM at the rotor to ~1,500–1,800 RPM at the generator.
Question 4: Which seal type is typically used on a wind turbine main shaft to prevent lubricant leakage while allowing rotation?
- Compression fitting
- Labyrinth seal with radial lip seal (Correct answer)
- O-ring face seal only
- Mechanical face seal used in pumps
Correct answer: Labyrinth seal with radial lip seal
A labyrinth seal combined with a radial lip seal prevents grease or oil from escaping along the rotating main shaft without creating excessive friction.
Question 5: What is the likely cause if a wind turbine gearbox produces a high-pitched whine at rated speed but operates normally at low speed?
- Excessive main shaft end-float
- Gear tooth wear or misalignment at high-speed stage (Correct answer)
- Low oil viscosity at cold startup
- Brake disc glazing
Correct answer: Gear tooth wear or misalignment at high-speed stage
High-pitched whine at rated speed typically indicates tooth wear, pitting, or misalignment in the high-speed gearbox stage where frequencies are highest.
Question 6: In a three-stage wind turbine gearbox, what is the correct description of stage arrangement from rotor to generator?
- Planetary → helical → helical (Correct answer)
- Helical → helical → planetary
- Planetary → planetary → planetary
- Bevel → helical → planetary
Correct answer: Planetary → helical → helical
Most three-stage gearboxes use a planetary stage for the high-torque low-speed input, followed by two helical stages for higher-speed lower-torque output.
Question 7: What is the purpose of an elastomeric torque arm in a wind turbine gearbox mounting system?
- Prevent gearbox from rotating under reaction torque while absorbing vibration (Correct answer)
- Align the gearbox input shaft with the main bearing
- Measure torque transmitted to the generator
- Provide emergency braking in case of overspeed
Correct answer: Prevent gearbox from rotating under reaction torque while absorbing vibration
The elastomeric torque arm restrains the gearbox body from rotating under reaction torque while its rubber elements absorb vibration and shock loads.
WTT Mechanical Systems & Drivetrain 2
What is the primary function of a wind turbine's pitch system in the drivetrain context?