WTT Hydraulic & Lubrication Systems 2 — Questions and Answers
Question 1: What is the primary purpose of a hydraulic accumulator in a wind turbine pitch system?
- To filter hydraulic fluid
- To store pressurized fluid for emergency pitch feathering (Correct answer)
- To cool the hydraulic pump
- To regulate oil viscosity
Correct answer: To store pressurized fluid for emergency pitch feathering
Hydraulic accumulators store pressurized fluid so the pitch system can feather blades even during a grid loss or pump failure.
Question 2: Which type of hydraulic pump is most commonly used in wind turbine pitch control systems due to its variable displacement capability?
- Gear pump
- Vane pump
- Axial piston pump (Correct answer)
- Centrifugal pump
Correct answer: Axial piston pump
Axial piston pumps support variable displacement, allowing precise flow control needed for pitch regulation.
Question 3: A technician notices the hydraulic system pressure drops rapidly when the pump is off. What is the most likely cause?
- Overcharged accumulator
- Internal leakage in a hydraulic cylinder or valve (Correct answer)
- High ambient temperature
- Incorrect oil viscosity grade
Correct answer: Internal leakage in a hydraulic cylinder or valve
Rapid pressure drop with the pump off indicates internal leakage past cylinder seals or valve seats allowing fluid to bypass.
Question 4: What is the correct procedure for checking the nitrogen pre-charge pressure in a hydraulic accumulator?
- Check with the system fully pressurized
- Isolate and depressurize the hydraulic side before checking gas charge (Correct answer)
- Check while the turbine is at rated power
- Add hydraulic oil until gauge reads correct
Correct answer: Isolate and depressurize the hydraulic side before checking gas charge
The hydraulic side must be depressurized before checking nitrogen pre-charge to get an accurate gas pressure reading.
Question 5: ISO VG 46 hydraulic oil is specified for a turbine. Which alternative viscosity grade is acceptable in an emergency if VG 46 is unavailable?
- ISO VG 10
- ISO VG 100
- ISO VG 32 or VG 68 within the OEM's approved range (Correct answer)
- Any SAE 10W-30 motor oil
Correct answer: ISO VG 32 or VG 68 within the OEM's approved range
Adjacent viscosity grades like VG 32 or VG 68 may be acceptable if approved by the OEM, but always verify the service manual.
Question 6: What does a high differential pressure reading across a hydraulic filter indicate?
- The filter is new and requires break-in
- The filter is bypassing due to a stuck bypass valve
- The filter element is loaded and requires replacement (Correct answer)
- System pressure is too low
Correct answer: The filter element is loaded and requires replacement
High differential pressure (delta-P) across a filter indicates the element is clogged and restricting flow, requiring replacement.
Question 7: Which seal material is most compatible with mineral-based hydraulic oils used in wind turbine systems?
- PTFE and nitrile (NBR) (Correct answer)
- Neoprene and silicone
- EPDM and natural rubber
- Viton and LDPE
Correct answer: PTFE and nitrile (NBR)
PTFE and nitrile (NBR) seals are standard for mineral oil hydraulic systems due to their excellent oil resistance and durability.
WTT Hydraulic & Lubrication Systems 2
What is the primary purpose of a hydraulic accumulator in a wind turbine pitch system?