WTT Mechanical Systems & Drivetrain 3 — Questions and Answers
Question 1: Which main bearing configuration uses two rows of rollers arranged in a tapered pattern to handle both radial and axial loads on a wind turbine rotor?
- Cylindrical roller bearing
- Double-row tapered roller bearing (Correct answer)
- Deep groove ball bearing
- Spherical plain bearing
Correct answer: Double-row tapered roller bearing
Double-row tapered roller bearings can carry combined radial and bidirectional axial (thrust) loads, making them suitable for wind turbine main shafts.
Question 2: What does 'preload' mean in the context of wind turbine main shaft bearings?
- The weight of the rotor applied before turbine assembly
- A deliberately applied axial force that removes internal clearance from the bearing (Correct answer)
- The maximum rated load capacity of the bearing
- The initial grease fill quantity at installation
Correct answer: A deliberately applied axial force that removes internal clearance from the bearing
Bearing preload is an intentional compressive force that eliminates internal clearance, improving stiffness, reducing vibration, and extending fatigue life.
Question 3: A wind turbine technician notices metallic particles in the gearbox oil sample that are silvery flakes larger than 50 µm. What does this most likely indicate?
- Normal wear-in during initial operation
- Fatigue spalling of gear tooth surfaces or bearing raceways (Correct answer)
- Contamination from the oil fill port
- Corrosion from moisture ingress
Correct answer: Fatigue spalling of gear tooth surfaces or bearing raceways
Large silvery flakes are characteristic of fatigue spalling, where surface material breaks away from gear teeth or bearing raceways under cyclic stress.
Question 4: What is the purpose of an oil cooler in a wind turbine gearbox lubrication system?
- Filter abrasive particles from circulating oil
- Maintain oil within its optimal viscosity and temperature operating range (Correct answer)
- Pressurize oil delivery to splash-lubricated stages
- Purge water contamination from the sump
Correct answer: Maintain oil within its optimal viscosity and temperature operating range
An oil cooler dissipates heat generated by gear meshing and bearing friction, keeping oil temperature within the range where viscosity provides adequate film thickness.
Question 5: Which component transfers rotor torque from the low-speed shaft to the gearbox in a direct-drive or semi-direct-drive wind turbine that uses a torque tube?
- Flexible jaw coupling
- Splined torque tube bolted to the rotor hub flange
- Keyway main shaft
- Shrink disc locking assembly (Correct answer)
Correct answer: Shrink disc locking assembly
A shrink disc (also called a locking disc) creates a high-friction interference fit between the main shaft and the gearbox input shaft without requiring keyways.
Question 6: During a gearbox oil change, a technician finds the oil appears milky white. What is the most probable cause?
- Gear additive package breakdown from overheating
- Water contamination causing an oil-water emulsion (Correct answer)
- Mixing of two incompatible oil grades
- Excessive foam from overfilling the gearbox
Correct answer: Water contamination causing an oil-water emulsion
Milky white oil is the classic visual sign of water emulsification, typically caused by condensation, rain ingress, or a failed cooling-circuit seal.
Question 7: What is the function of the yaw drive gearbox in a wind turbine?
- Adjust blade pitch during variable wind conditions
- Rotate the nacelle to align the rotor with incoming wind direction (Correct answer)
- Drive the hydraulic pump for blade pitch actuation
- Control main shaft speed during grid connection
Correct answer: Rotate the nacelle to align the rotor with incoming wind direction
The yaw drive gearbox transmits motor torque to a ring gear mounted on the tower top, rotating the nacelle to track the wind direction.
WTT Mechanical Systems & Drivetrain 3
Which main bearing configuration uses two rows of rollers arranged in a tapered pattern to handle both radial and axial loads on a wind turbine rotor?