Rotor imbalance on wind turbines
The rotor is the first point of energy conversion. Imbalances on the rotor have an economic impact on profitability and a technical impact on the entire structure.
Deviations in the blade angles lead to yield losses as the aerodynamics are disturbed. In our experience, around 1/4 of wind turbines are operated with blades that are not optimally adjusted. The yield losses are usually in the order of 1 to 2 per cent.
Unbalances generate unnecessary loads in the system and lead to premature wear. The following diagram shows the axial tower movements before and after the correction. Correcting the unbalance reduced the tower vibrations by a factor of 5.
Detection of rotor imbalances
Our range of services includes mobile measurements. With the measuring systems developed by us, aerodynamic and mass-excited imbalances can be detected very accurately and easily during normal operation of the system.
Characteristics of our measurement methods:
- no downtime
- Measurements under real operating conditions in mains operation
The measurement results are available on site and can be used immediately for corrective measures.
We have various measuring systems at our disposal for detecting rotor imbalances. Depending on the requirements, laser-based, acoustic or a combination of both measurement methods are used.
Measuring principle
The rotor generates a geometric and an acoustic profile during operation. The measuring principle is to record the profiles over several revolutions.
The profile contours and sound emissions change depending on the angle of attack.
- We record the geometric profile with a reflectorless laser distance sensor.
- We record the acoustic profile with a directional microphone.
Geometric profile
In laser measurement, the information from the distance measurement is used to record the profile contours and the tower movements.
A mass imbalance is characterised by the fact that the centre of gravity of the rotor is not in the axis of rotation. Following the earth's gravitational field, the rotor is thus accelerated and decelerated in its rotation. By counting the measured values between the blades, speed changes can be recorded with high precision.
- Determination of the relative blade angle differences
- Detection of mass-excited imbalances
Acoustic profile
The acoustic method was developed in particular for determining blade angles on offshore turbines, but can also be used onshore.
During the acoustic measurement, the recorded time signals are broken down into their frequency components and analysed.
- Determination of the relative blade angle differences
- Comparison of identical systems for the detection of deviations in the absolute blade angle.
Overview of measuring methods
Laser
Onshore
Acoustic
Offshore
Laser-Acoustic
Onshore
Relative blade angle deviations
Misalignment of individual blades
yes
yes
yes
Absolute blade angle deviations
Misalignment of all blades
no
no
yes
Mass imbalance
Detection of mass-excited imbalances
yes
no
yes
